Patent Publication Number: US-10314954-B2

Title: Controlled negative pressure apparatus and alarm mechanism

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 14/267,786, filed May 1, 2014, which is a continuation of U.S. application Ser. No. 13/207,360, filed Aug. 10, 2011, which a) claims benefit from U.S. Provisional Application Ser. No. 61/372,837, filed Aug. 11, 2010, and b) is a continuation-in-part of U.S. application Ser. No. 13/175,744, filed Jul. 1, 2011, which claims benefit from U.S. Provisional Application Ser. No. 61/372,419, filed Aug. 10, 2010, U.S. Provisional Application Ser. No. 61/372,843, filed Aug. 11, 2010, and U.S. Provisional Application Ser. No. 61/470,423, filed Mar. 31, 2011, each of which is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     Research has shown that applying reduced pressure to a tissue wound may provide several beneficial effects. For example, applying sub-atmospheric pressure to a wound may lead to retraction of the damaged tissue edges and thus may expedite healing by facilitating wound contraction. Reduced pressure wound therapy may also provide mechanical stimulation to the damaged tissue, which may release growth factors to the wound bed to promote healing. In some cases, applying suction to a wound may remove necrotic tissue from the wound bed and may help to reduce bacterial load. 
     In the delivery of reduced pressure wound therapy, an airtight dressing is applied to a part of the body having a wound and a certain negative pressure is introduced to the wound area. It is desirable to maintain a substantially constant level of reduced pressure to the wound site. In such therapy, factors such as air leaks and fluid ingress contribute to the overall decrease in the magnitude of the reduced pressure; thus the reduced pressure tends to move towards atmospheric pressure. Except with the use of vacuum bottles, the source of the substantially constant reduced pressure may include some mechanism to compensate for the leaks or fluid ingress in order to maintain the pre-set negative pressure of the system. Examples of negative pressure sources that accomplish this are regulated by an electrically-powered pump, a pressure sensing means and a controller means to adjust the output of the pump. However, these systems require an electrical source, are bulky, noisy, and limit patient mobility. 
     In light of these and other benefits of reduced pressure tissue therapy, methods and devices that ensure a reliable application of reduced pressure to a wound may be desirable. 
     BRIEF SUMMARY 
     In one example, a reduced pressure therapy system is provided, comprising a suction device comprising a suction chamber and a slidable seal therein, a magnet coupled to the slidable seal, and an alarm device configured to retain the suction device, wherein the alarm device comprises a sensor configured to detect the location of the magnet within the suction chamber, and a notification mechanism configured to generate an alert according to the location of the magnet. The alarm device may be configured to be electrically activated when retaining the suction device. The suction device may further comprise a conductive element along an outer surface and the alarm device comprises two or more connectors, wherein the conductive element is configured to provide an electrical conduit between the two or more connectors to electrically activate the alarm device. The alarm device may further comprise a tactile power switch configured to be pressed when the alarm device retains the suction device. The suction device may further comprise a fluid absorption material retained by a carrier within the suction chamber. The fluid absorption material may be bonded to an outer surface of the carrier. The carrier may comprise a pouch configured to releasably retain the fluid absorption material. The suction device may further comprise a screen configured to sequester the expandable fluid absorbent material in a selected region of the suction chamber. The expandable fluid absorbent material may be sequestered in the selected region of the suction chamber that is independent of suction device orientation. The suction device may further comprise a screen located between the carrier and the distal portion of the suction chamber. The screen may be adhesively attached to the suction chamber, and/or to the carrier. The suction device may have a charged configuration and a depleted configuration, wherein in the charged configuration, the magnet is not detectable by the sensor and in the depleted configuration, the magnet is detectable by the sensor. The alarm device may be configured to detect the configuration of the suction device regardless of the orientation of the suction device as it is retained within the alarm device. The sensor may comprise a first reed switch at a first location and a second reed switch at a second location separate from the first location, and where the alarm device retains the suction device such that in the charged configuration, the magnet may be located between the first and second locations and not detectable by either reed switch, and in the depleted configuration, the magnet is detectable by at least one reed switch. The first and second locations may define a first line with a first midpoint, wherein the travel path of the magnet from charged to depleted configurations define a second line with a second midpoint, and wherein the first and second midpoints are offset from each other. The distance of the magnet to the nearest reed switch may be less in the depleted configuration than in the charged configuration. The suction device may be retained within the alarm device in two orientations, or in four orientations. The second orientation may the first orientation rotated 180 degrees around a transverse axis of the suction device, or rotated 180 degrees around a longitudinal axis of the suction device. The reduced pressure therapy system may further comprise a reed switch at a proximal location of the alarm device, where the alarm device retains the suction device such that in the charged configuration, the magnet is not detectable by the reed switch, and in the depleted configuration, the magnet is detectable by the reed switch. 
     In another example, a reduced pressure therapy system is provided, comprising a suction device comprising a suction chamber with an inlet opening and a slidable seal therein, a expandable fluid absorbent material located within the suction chamber, and a screen configured to block displacement of the expandable fluid absorbent material out of the suction device. The screen may be located within the suction chamber. The expandable fluid absorbent material, prior to any fluid absorption, may have a fixed location in the suction chamber that is independent of suction device orientation. The expandable fluid absorbent material may be retained by a carrier structure, and may be bonded to a surface of the carrier structure, but may be releasably contained within the carrier structure. The carrier structure may comprise a permeable pouch. The red permeable pouch comprises two permeable layers sealed together. 
     In one example, a device for reduced pressure therapy, comprising a suction chamber with a longitudinal axis and a radial axis perpendicular to the longitudinal axis, a seal assembly located within the suction chamber, the seal assembly comprising a seal coupled to a seal mount, wherein the seal and seal mount are movable with respect to each other, and wherein the seal assembly is configured to slide along the longitudinal axis of the suction chamber. The seal may comprise a distal flange and a proximal flange, wherein the distal and proximal flanges are deflectable. The seal may further comprise a lumen with a proximal aperture, and a distal ledge, and wherein the seal mount comprises a protruding edge configured to engage the ledge. The seal and the seal mount may be coupled such that a portion of an inner wall of the lumen and the seal mount are separated by a gap. The protruding edge of the seal mount may not contact the lumen ledge when the seal assembly slides distally and wherein the protruding edge contacts the lumen ledge when the seal assembly slides proximally. The proximal flange of the seal is capable of greater radial compression than the distal flange. The side walls of the seal may be radially compressible, and/or may be configured to radially deflect when the proximal flanges are deflected. The device may further comprise a lubricant located along the inner walls of the suction chamber, which may be flowable. The lubricant may be characterized by a viscosity of greater than 1,000,000 cP, or 1,500,000 cP. The lubricant may comprise at least one silicone, and/or may comprise at least one member from the group consisting of fluorosilicone, dimethylsilicone, perfluoropolyether, mineral spirits, synthetic oils, and polyxylene. At least a portion of the seal assembly may be made of dimethylsilicone and lubricant comprises fluorosilicone and dimethylsilicone, in an amount wherein the viscosity of the lubricant is at least 1,500,000 cP. The lubricant may comprise 20 Mol % fluorosilicone fluid and 80 Mol % dimethylsilicone fluid. The lubricant may be substantially non-reactive with at least the surfaces the lubricant is in contact with, wherein the surfaces comprise at least the inner walls of the chamber and at least a portion of the seal assembly. The lubricant may be in simultaneous contact with at least a portion of the seal assembly and the inner surface of the suction chamber. 
     In another example, a method of treating a patient is disclosed, comprising providing negative pressure to a treatment site using a suction device comprising a suction chamber having a distal and proximal portion, a sliding seal assembly within the suction chamber, and a constant force spring attached to the sliding seal assembly and configured to move the sliding seal assembly across the suction chamber, wherein the distal portion of the chamber has a first cross-sectional area and the proximal portion of the chamber has a second cross-sectional area that is greater than the first cross-sectional area. The sliding seal assembly may comprise a seal coupled to a seal mount, wherein the seal and seal mount are movable with respect to each other as the sliding seal assembly moves between the distal and proximal portions. The suction device may further comprise a lubricant that is simultaneously in contact with at least a portion of the sliding seal assembly and an inner wall of the suction chamber. 
     In still another example, a method of treating a patient is disclosed, comprising providing suction to a treatment site using a suction device, and absorbing fluid from a treatment site using a fluid absorbent material, wherein the fluid absorbent, prior to fluid absorption, has a fixed location within the suction device. The method may further comprise blocking expulsion of the fluid absorbent material using a screen located within the suction device. The suction device may comprise a suction-generating chamber with a sliding seal, and wherein the fluid absorbent material and the screen are located within the suction-generating chamber. 
     Various embodiments herein disclose a suction device that can maintain a substantially constant pressure within a certain tolerance for pressure variations over a particular leakage or infusion rate. In particular, the suction device maintains the substantially constant pressure even during fluid or air ingress into the reduced pressure system. Furthermore, the suction device may achieve this by reducing the friction between the seal and the chamber wall. The disclosure describes suction devices that achieve narrow pressure tolerances by employing certain lubricants, spring assembly configurations, or seal designs. In addition, some embodiments are configured to provide containment of exudates from the wound that may enter the suction chamber. 
     In one embodiment, a suction device is configured to generate and substantially maintain a set reduced pressure for use in treating tissue of a subject, comprising a suction chamber, a ribbon spring, and a lubricant; wherein when a volume of at least air or exudate is introduced into the reduced pressure system, a plot of the reduced pressure of the system against the volume introduced into the system results in a substantially oscillating wave pattern, wherein the magnitude of the typical peak-to-peak amplitude, if any, is no greater than 20 mmHg. In some embodiments, the magnitude of the typical peak-to-peak amplitude is no greater than 10 mmHg. In some of the foregoing embodiments, the magnitude of the typical peak-to-peak amplitude is no greater than 5 mmHg. In some of the foregoing embodiments, the oscillating wave pattern is substantially a saw tooth wave or substantially flat over test conditions involving continuous constant rate infusion or leakage. 
     In some of the foregoing embodiments, the negative pressure generated by the suction device is reduced by less than 15 mmHg over a period of 10 hours from the time the set negative pressure is reached. In some of the foregoing embodiments, the negative pressure generated by the suction device is reduced by less than 20 mmHg over a period of at least 80 hours from the time the set negative pressure is reached. 
     These changes may be evaluated, for example, under test conditions involving a constant infusion or leakage rate of a liquid or gas, up to a certain volume. In one instance, the maximum variations occur during an infusion rate of up to 1 cc/hr, 2 cc/hr, 3 cc/hr, 4 cc/hr, 5 cc/hr, 6 cc/hr, 7 cc/hr, 8 cc/hr, 9 cc/hr 10 cc/hr, or 15 cc/hr or 20 cc/hr, up to a volume of 10 cc, 20 cc, 30 cc, 40 cc, 50 cc, 60 cc, 70 cc, 80 cc, 90 cc, 100 cc, 150 cc, 200 cc, 250 cc or 300 cc, for example. In some of the foregoing embodiments, a volume of at least a gas or liquid introduced into the suction chamber at a rate of 3 cc/hour for at least a duration of 16 hours. In a further embodiment, the average pressure in the suction chamber over the duration of time is 80±5 mmHg. In some of the foregoing embodiments, the temperature of the suction device varies by no more than 5° C. during test conditions. 
     In some of the foregoing embodiments, the reduced pressure generating assembly comprises a.) a suction chamber, wherein the suction chamber has a longitudinal axis and an inner surface; b.) a seal assembly comprising a sliding seal coupled to a seal mount, wherein the seal assembly is configured to slide in the suction chamber along the longitudinal axis; and c.) a lubricant, wherein the lubricant is in simultaneous contact with at least a portion of the sliding seal and the inner surface of the suction chamber. In some embodiments, the lubricant is characterized by a viscosity of greater than 1,000,000 cP. 
     In some of the foregoing embodiments, the lubricant comprises at least one silicone. In specific embodiments, the lubricant comprises at least one member from the group consisting of fluorosilicone, dimethylsilicone, perfluoropolyether, mineral spirits, synthetic oils, and polyxylene. In some of the foregoing embodiments, the lubricant comprises fluorosilicone and dimethyl silicone, in an amount wherein the viscosity of the lubricant is at least 1,500,000 cP. 
     In some of the foregoing embodiments, the lubricant is non-reactive with at least the surfaces the lubricant is in contact with, wherein the surfaces comprise at least the inner surface of the chamber and at least a section of the sliding seal assembly surface. In other embodiments, the lubricant composition and the seal material are selected to substantial reduce seal degradation that results in seal leaks for a minimum pre-specified period of time, which may be at least 6 months, 9 months, 12 months, 15 months, 18 months, 24 months, 30 months or 36 months or more. 
     In some of the foregoing embodiments, at least a portion of the sliding seal and at least a portion of the seal mount is separated by a gap. In some of the foregoing embodiments, the gap is configured to provide a space for the sliding seal to occupy when it is compressed by the inner surface of the suction chamber. The portion of the sliding seal may be a radially inward facing surface and the portion of the seal mount may be a radially outwardly facing surface, and the radially inward facing surface of the sliding seal may be configured to resiliently deflect inward toward, and even contact, the radially outward facing surface of the seal mount. The radially inward facing surface of the sliding seal may also be a radially inward facing surface with the smallest radial location compared to other radially inward facing surfaces of the sliding seal. The radially outward facing surface of the seal mount may also have the smallest radial location compared to other radially outward facing surfaces of the seal mount. 
     In some of the foregoing embodiments, at least a portion of the sliding seal has an inner and outer surface, wherein at least a portion of the outer surface of the sliding seal is in contact with at least the inner surface of the suction chamber and the inner surface of the sliding seal does not contact with a solid surface when the sliding seal travels along the longitudinal axis of the chamber. In some of the foregoing embodiments, the sliding seal is comprises a material selected from an elastomer compatible with the lubricant. 
     In another embodiment herein discloses a suction device for use in treating tissue of a subject, wherein the device is configured to generate and substantially maintain a set negative pressure of at least 50 mmHg, comprising at least two ribbon springs coupled to the sliding seal assembly, wherein the ribbon springs are configured to unwind in opposite direction relative to each other, and the springs are of different lengths relative to each other. 
     Various embodiments herein disclose a suction device for use in treating tissue of a subject, wherein the device is configured to generate and substantially maintain a set negative pressure of at least 50 mmHg, comprising a.) at least one ribbon spring comprising an interior end, and an exterior end; and b.) a sliding seal assembly coupled to the exterior end of the ribbon spring, wherein the sliding seal assembly comprises a seal, wherein the uncoiling of the spring permits a travel distance of the seal along the longitudinal axis of the interior of the suction chamber, and the spring has a diameter such that travel distance of the seal can be covered in less than one rotation of the spring; wherein the spring is configured such that during the coiling of the ribbon spring, the interior end of the ribbon spring does not transition from non load-bearing to load-bearing at any point. 
     Various embodiments herein disclose a suction device for use in treating tissue of a subject, wherein the device is configured to generate and substantially maintain a set negative pressure of at least 50 mmHg, comprising a.) at least one ribbon spring comprising an interior end and a top surface; and b.) a bushing, wherein the exterior surface of the bushing is configured with an indentation; wherein the interior end of the ribbon spring is mounted on the bushing to form a spring-bushing assembly, and the interior spring end is positioned in the indentation of the bushing, such that the top surface of the spring end is approximately flush with the exterior surface of the bushing adjacent to the indentation. In a particular embodiment, the depth of the indentation in the bushing is approximately the thickness of the spring end. In a more specific embodiment, the depth of the indentation is 6/1000 to 7/1000 of an inch. 
     Various embodiments herein disclose a suction device for use in treating tissue of a subject, wherein the device is configured to generate and substantially maintain a set negative pressure of at least 50 mmHg, comprising a suction chamber configured with a bio-hazard containment assembly, wherein the bio-hazard containment assembly comprises a superabsorbent material. In some embodiments, the bio-hazard containment assembly has a total volume of less than 4 cc prior to contact with a liquid. In some of the foregoing embodiments, the superabsorbent material absorbs an amount of liquid at least 10 times its weight. In some of the foregoing embodiments, the superabsorbent material is selected from at least a natural, synthetic, or modified natural polymers. In some of the foregoing embodiments, the superabsorbent material is selected from a silica gel or cross-linked polymers. In some of the foregoing embodiments, the amount of superabsorbent material is less than 2.5 g. In some of the foregoing embodiments, the superabsorbent material is contained in a liquid permeable layer. In some of the foregoing embodiments, the liquid permeable layer is selected from at least one of the members of the group consisting of polypropylene, nylon, rayon, and cellulose. 
     Various embodiments herein disclose a dressing for a wound bed, comprising a pressure sensor and a communication channel having a first and second end, wherein the first end is connected to the pressure sensor and the second end is positioned on or near the wound bed, wherein the dressing is configured such that the pressure sensor is in fluid communication with the wound bed. In some of the foregoing embodiments, the channel is a flexible catheter. In specific embodiments, the second end of the catheter comprises perforations. In some of the foregoing embodiments, the pressure sensor comprises a bellow. In some of the foregoing embodiments, the pressure sensor comprises a microelectronic pressure sensing device. 
     Disclosed herein is a reduced pressure therapy device that may comprise a suction device with a suction chamber and a slidable seal within the suction chamber, a magnet coupled to the slidable seal, and an alarm device comprising a sensor that is configured to detect the location of a magnet within the suction chamber. The alarm device may be configured to retain the suction device, and may also comprise a notification mechanism that is configured to generate an alert based on the location of the magnet. In some variations, the alarm device is configured to be electrically activated when retaining the suction device. The alarm device may comprise a conductive element along an outer surface and the alarm device comprises two or more connectors. The conductive element may be configured to provide an electrical conduit between the two or more connectors to electrically activate the alarm device. In some variations, the alarm device may comprise a tactile power switch configured to be pressed when the alarm device retains the suction device. 
     Optionally, a suction device may comprise a fluid absorption material retained by a carrier within the suction chamber. In some variations, the fluid absorption material may be bonded to an outer surface of the carrier. Alternatively or additionally, the carrier may comprise a pouch configured to releasably retain the fluid absorption material. A suction device may also comprise a screen located between the carrier and the distal portion of the suction chamber. In some variations, the screen may be adhesively attached to the suction chamber or may be adhesively attached to the carrier. 
     Disclosed herein is a reduced pressure therapy system that may comprise a suction device comprising a suction chamber with an inlet opening and a slidable seal within the suction chamber. The reduced pressure therapy system may also comprise an expandable fluid absorbent material located within the suction chamber and a screen configured to block displacement of the expandable fluid absorbent material out of the suction device. The screen may also be configured to sequester the expandable fluid absorbent material in a selected region of the suction chamber. The screen may be located within the suction chamber. In some variations, the expandable fluid absorbent material, prior to any fluid absorption, may have a fixed location in the suction chamber that is independent of suction device orientation. In some variations, the expandable fluid absorbent material may be retained by a carrier structure. The carrier structure may be retained at a selected region in the suction chamber. For example, the expandable fluid absorbent material may be bonded to the carrier structure, and in some cases, may be bonded on a surface of the carrier structure. Additionally or alternatively, the expandable fluid absorbent material may be releasably contained within the carrier structure. The expandable fluid absorbent material may be woven into the carrier structure. In some variations, the carrier structure comprises a permeable pouch. One variation of a permeable pouch may comprise two permeable layers sealed together. Optionally, the expandable fluid absorbent material may comprise one or more disinfecting agents. 
     In some variations of a suction device fluid retention assembly, the carrier structure may comprise an aperture therethrough, and may be located within the suction chamber such that the aperture is aligned with the inlet opening of the suction chamber. The screen of the fluid retention assembly may be interposed between the inlet opening and the carrier structure. 
     In some variations of a suction device fluid retention assembly, the carrier structure may comprise a permeable pouch. The permeable pouch may comprise two permeable layers sealed together, and may optionally be sealed together along the perimeter of each of the layers. The permeable pouch may be attached to the screen of the fluid retention assembly. In some variations, the expandable fluid absorbent material may be releasably contained within the carrier structure. 
     Methods of treating a patient using reduced pressure therapy are also described herein. One variation of a method for treating a patient may comprise providing suction to a treatment site using a suction device and absorbing fluid from a treatment site using a fluid absorbent material. Prior to fluid absorption, the fluid absorbent material may have a fixed location within the suction device. Some methods may further comprise blocking expulsion of the fluid absorbent material using a screen located within the suction device. In some variations, the method may use a suction device comprising a suction-generating chamber with a sliding seal, where the fluid absorbent material and the screen are located within the suction-generating chamber. 
     One variation of a method for treating a patient may comprise providing suction to a treatment site using a suction device comprising a suction-generating chamber, absorbing fluid from a treatment site using a fluid absorbent material, and blocking expulsion of the fluid absorbent material using a screen located within the suction-generating chamber. In some variations, the fluid absorbent material may have a fixed location within the suction-generating chamber. 
     Provided herein is a reduced pressure therapy system comprising a suction device comprising a suction chamber, a expandable fluid absorbent material located within the suction chamber; and a screen configured to sequester the expandable fluid absorbent material in a selected region of the suction chamber. The suction chamber may comprise an inlet opening at a distal portion of the chamber and a slidable seal therein. In some variations, the expandable fluid absorbent material may be sequestered in the selected region of the suction chamber that is independent of suction device orientation. For example, the screen may sequester the expandable fluid absorbent material at the distal portion of the suction chamber. Alternatively or additionally, the expandable fluid absorbent material may be retained by a carrier structure, wherein the carrier structure is retained at the selected region in the suction chamber. In some variations, the expandable fluid absorbent material may be bonded to the carrier structure, such as to a surface of the carrier structure. The expandable fluid absorbent material may alternatively or additionally be woven into the carrier structure. Optionally, the expandable fluid absorbent material may comprise one or more disinfecting agents. 
     In some variations, the carrier structure may comprise an aperture therethrough, and the aperture may be aligned with the inlet opening of the suction chamber. The screen may be interposed between the inlet opening and the carrier structure. In some variations, the expandable fluid absorbent material may be releasably contained within the carrier structure. The carrier structure may comprise a permeable pouch, and in some variations, the permeable pouch may be attached to the screen. The permeable pouch may comprise two permeable layers sealed together. The two permeable layers may be sealed together along the perimeter of each of the layers. 
     Another variation of a reduced pressure therapy system may comprise a chamber with a movable magnet and a magnet sensitive mechanism configured to detect a magnetic field of the movable magnet. The chamber may be a vacuum-generating chamber configured with a fixed wall and a movable wall. In some variations, the movable wall may comprise a slidable seal, while in other variations, the vacuum-generating chamber may comprise a bellows mechanism, where the magnet is located on the movable wall of the bellows. The chamber may also be a fluid trap chamber, and in some variations, may comprise a float, where the float is coupled to the movable magnet. In some variations of a reduced pressure therapy system, the magnet sensitive mechanism may comprise one or more reed switch, where the reed switch may normally have an open state. A plurality of reed switches may be provided along a movement axis of the movable magnet. Alternatively, the reduced pressure therapy system may comprise a Hall effect sensor. The magnet sensitive mechanism may be coupled to a clip configured to attach to the vacuum system. In certain variations, the reduced pressure therapy system may further comprise an indicator mechanism connected to the magnet sensitive mechanism and configured to provide at least one signal indicated of a position of the movable magnet. The at least one signal may be a visual, auditory, or tactile signal. 
     Another variation of a reduced pressure therapy system may comprise a non-electrically powered vacuum-generating chamber configured with a position element located on a movable region of the vacuum-generating chamber, and a circuit comprising a first state when the position element is at a first location and a second state when the position element is at a second location. The circuit may be configured to be detachably attachable to the vacuum-generating chamber. The circuit may also comprise an electrical power source and a signaling mechanism, where the signaling mechanism is configured to generate at least one signal that is an audio, visual, and/or tactile signal. In some variations, the signaling mechanism may be configured to generate a wireless signal, or may be configured to transmit an alarm signal to a remote monitoring display. 
     The position element of a reduced pressure therapy system may comprise an electrical pathway having a first end located about a first surface of the chamber and a second end located about a second surface of the chamber, and the first state of the circuit is an open circuit and the second state of the circuit is a closed circuit state. In some variations, the first surface of the chamber may be an outer surface of the chamber, and in some cases, the chamber may be a bellows chamber. In other variations, the first surface of the chamber may be an inner surface of the chamber, and in some cases, the movable region of the vacuum-generating chamber may be a slidable sealing wall. The position element of a reduced pressure therapy system may be a magnet. In some variations, the circuit may be a Hall effect sensor circuit and/or a reed switch circuit. 
     Also described below are methods for treating a patient using a reduced pressure therapy system. One example of a method for treating a patient may comprise treating a patient with a reduced pressure therapy system comprising a non-electrically powered vacuum mechanism and an electrically powered alarm system, wherein the electrically powered alarm system comprises a magnetic sensitive mechanism, and using a magnetic sensitive mechanism to indicate a state of the vacuum mechanism. The magnetic sensitive mechanism may comprise a reed switch, where the reed switch has a sensitivity of about 10 to about 60 Ampere-Turns. The reed switch may be in a normally open state. The method may also comprise detaching the vacuum mechanism from the alarm system and attaching a new vacuum mechanism to the same alarm system. The method may also comprise activating the new vacuum mechanism. 
     Another variation of a reduced pressure therapy device may comprise a suction device with a suction chamber and a slidable seal within the suction chamber, where the slidable seal is oriented transversely to the longitudinal axis of the suction chamber, a magnet coupled to the slidable seal transversely to the longitudinal axis of the suction chamber, and an alarm device comprising one or more sensors that may be configured to detect the location of a magnet within the suction chamber. The alarm device may be configured to retain the suction device along the longitudinal axis. The alarm device may comprise a first sensor at a distal portion of the alarm device, and a second sensor at a proximal portion of the alarm device, where the first and second sensors are configured to detect the location of the magnet. Additionally, the alarm device may comprise a notification mechanism configured to generate an alert when the magnet is aligned with the second sensor. 
     Another variation of a reduced pressure therapy device with an alarm system using a magnetic sensor mechanism may comprise a suction device, the suction device comprising a suction chamber, a slidable seal within the suction chamber, and a central shaft coupled to the slidable seal, a magnet coupled along the longitudinal axis of the central shaft, and an alarm device configured to retain the suction device. The alarm device may comprise a sensor configured to detect the position of the magnet within the suction chamber, and a notification mechanism configured to generate an alert according to the position of the magnet. 
     Some variations of a reduced pressure therapy device with an alarm system may comprise a suction device comprising a suction chamber with a longitudinal axis from a proximal portion to a distal portion, a slidable seal disposed within the suction chamber transverse to the longitudinal axis, and a shaft fixedly attached to the slidable seal, wherein the shaft is oriented along the longitudinal axis, a magnet coupled to the shaft along the longitudinal axis, and an alarm device configured to retain the suction device. The alarm device may comprise a sensor configured to detect the position of the magnet within the suction chamber, and a notification mechanism configured to generate an alert according to the position of the magnet. 
     Certain variations of reduced pressure therapy devices with an alarm system may use an electrical switch mechanism. For example, a reduced pressure therapy device may comprise a suction device comprising a suction chamber and a slidable seal within the suction chamber, an electrical switch coupled to the slidable seal, and an alarm device configured to retain the suction device. The attachment feature may comprise a notification mechanism configured to generate an alert when aligned with the electrical switch. 
     Another variation of a reduced pressure therapy device may comprise a suction device comprising a suction chamber and a slidable seal transversely disposed within the suction chamber, an electrical current conduit coupled to the slidable seal, wherein the conduit extends across the entire transverse width of the slidable seal, and an alarm device configured to retain the suction device. The alarm device may comprise a notification mechanism with a first electrical contact and a second electrical contact opposite the first electrical contact, wherein the notification mechanism is configured to generate an alert when the first and second electrical contacts are connected by the current conduit. 
     Certain variations of reduced pressure therapy devices may comprise a suction device comprising a suction chamber and a slidable seal within the suction chamber, a magnet coupled to the slidable seal, and an alarm device configured to retain the suction device. The alarm device may comprise a magnetic field sensitive switch configured to activate a notification mechanism to generate an alert according to the location of the magnet. In some variations, the magnetic field sensitive switch may be a reed switch. Alternatively or additionally, the magnetic field sensitive switch may comprise a sensor to detect the location of the magnet within the suction chamber. 
     Other variations of reduced pressure therapy devices may comprise a suction device comprising a suction chamber and a slidable seal transversely disposed within the suction chamber, a magnet coupled to the slidable seal, and an attachment feature configured to retain the suction device along the longitudinal axis. The slidable seal may be oriented transversely to the longitudinal axis of the suction chamber. The attachment feature may comprise a reed switch at a proximal portion, where the reed switch is configured to be closed when the magnet is at or near the proximal portion. The attachment feature may also comprise a notification mechanism configured to generate an alert when the reed switch is closed. 
     Disclosed herein is another variation of a reduced pressure therapy device that may comprise a suction device with a suction chamber and a slidable seal within the suction chamber, a magnet coupled to the slidable seal, and an alarm device comprising a sensor that is configured to detect the location of a magnet within the suction chamber. The alarm device may be configured to retain the suction device, and may also comprise a notification mechanism that is configured to generate an alert based on the location of the magnet. The alarm device may optionally comprise a tactile power switch configured to be pressed with the alarm device retains a suction device therein. The suction device may have a charged configuration and a depleted configuration. In the charged configuration, the magnet may not be detectable by the sensor, while in the depleted configuration, the magnet may be detectable by the sensor. In some variations, the alarm device is configured to detect the configuration of the suction device regardless of the orientation of the suction device within the alarm device. In some variations, the sensor may comprise a first reed switch at a first location and a second reed switch at a second location separate from the first location. The alarm device may retain the suction device such that in the charged configuration, the magnet is located between the first and second locations and not detectable by either reed switch, and in the depleted configuration, the magnet is detectable by at least one reed switch. Optionally, the first and second locations may define a first line with a first midpoint, wherein the travel path of the magnet from charged to depleted configurations define a second line with a second midpoint. The first and second midpoints are offset from each other. In some variations, the distance of the magnet to the nearest reed switch is less in the depleted configuration than in the charged configuration. The suction device may be retained in the alarm device in two or more orientations, e.g., four orientations. In one embodiment, the suction device may be retained within the alarm device in a first orientation and a second orientation, where the second orientation is the first orientation rotated 180 degrees around a transverse and/or longitudinal axis of the suction device. In another variation of a reduced pressure therapy device, the alarm device may comprise a reed switch at a proximal location of the alarm device, where the alarm device retains the suction device such that in the charged configuration, the magnet is not detectable by the reed switch, and in the depleted configuration, the magnet is detectable by the reed switch. 
     Disclosed herein is another variation of a reduced pressure therapy device that may comprise a suction chamber with a slidable seal therein, a magnetic element or magnet coupled to the slidable seal, a first alignment protrusion at a distal portion, and a second alignment protrusion at a proximal portion. The suction device may have a charged configuration and a depleted configuration, wherein the distance of the magnet to the first alignment protrusion in the charged configuration is greater than the distance of the magnet to the second alignment protrusion in the depleted configuration. In another variation of a reduced pressure therapy device, the distance of the magnet to the distal end of the suction chamber in the charged configuration is greater than the distance of the magnet to the proximal end of the suction chamber in the depleted configuration. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A better understanding of various features and advantages of the embodiments described herein may be obtained by reference to the following detailed description that sets forth illustrative examples and the accompanying drawings of which: 
         FIGS. 1A and 1B  are perspective views of a variation of a reduced pressure therapy device in a mechanically uncharged and charged configuration, respectively;  FIGS. 1C and 1D  are superior and side elevational views of the device in  FIGS. 1A and 1B  in an activated and partially depleted state.  FIGS. 1E and 1F  are posterior and anterior perspective component views of the embodiment from  FIG. 1A . 
         FIG. 2A  is a perspective view of another variation of a suction device for reduced pressure therapy comprising a magnetic alarm system and an alarm device;  FIGS. 2B and 2C  are superior component views of the suction device and alarm device, in charged and depleted states, respectively. 
         FIG. 3A  is a superior component view of another variation of a suction device in a mechanically charged configuration, comprising an alarm system with a magnetic sensor mechanism;  FIG. 3B  is a superior component of another variation of a suction device in a mechanically charged configuration with a magnetic sensor mechanism. 
         FIG. 4A  depicts one variation of a suction device for reduced pressure therapy comprising an alarm system with an electric switch mechanism in a mechanically charged configuration;  FIG. 4B  is a depiction of the suction device of  FIG. 4A  in a depleted configuration;  FIG. 4C  is an anterior perspective component view of the suction device and an alarm device of  FIG. 4A ;  FIG. 4D  is a posterior perspective view of the suction device and alarm device of  FIG. 4A  with an alarm device;  FIG. 4E  is a side elevational view of the alarm device of  FIG. 4C . 
         FIG. 5  depicts one example of a notification circuit that may be used an alarm system for reduced pressure therapy devices. 
         FIG. 6A  is a schematic representation of a spring assembly in an extended configuration with a rotary sensor that may be used in a suction device;  FIG. 6B  depicts the spring assembly of  FIG. 6A  in a retracted configuration. 
         FIGS. 7A and 7B  are schematic depictions of a reed sensor in an open and a closed configuration, respectively. 
         FIG. 8  depicts another variation of a suction device for reduced pressure therapy comprising an alarm system with one or more reed sensors, where the slidable seal of the suction device comprises one or more magnets. 
         FIG. 9  is a block diagram of one variation of an alarm system that may be used with reduced pressure therapy devices. 
         FIG. 10A  depicts a block diagram representation of another variation of an alarm system that may be used with reduced pressure therapy devices.  FIGS. 10B to 10D  depict examples of circuits that may be implemented in the alarm system of  FIG. 10A .  FIG. 10B  depicts one variation of an orientation circuit;  FIG. 10C  depicts one variation of a sensor circuit;  FIG. 10D  depicts one variation of an amplifier circuit. 
         FIG. 11  is a schematic of exemplary alarm system components as arranged on a printed circuit board. 
         FIG. 12A  is a perspective view of one variation of an alarm device.  FIG. 12B  is a perspective view of a suction device coupled to the alarm device of  FIG. 12A . 
         FIG. 13  is state machine diagram that depicts one variation of a state machine that may be programmed into a microcontroller of an alarm system that may be used with reduced pressure therapy devices. 
         FIG. 14A  is a schematic representation of a suction device with a conductive element;  FIG. 14B  depicts a first orientation of the suction device of  FIG. 14A ;  FIG. 14C  depicts a second orientation of the suction device of  FIG. 14A ;  FIG. 14D  is a perspective view of a variation of a suction device with a conductive element;  FIG. 14E  is a perspective view of an alarm device with one or more connectors. 
         FIGS. 15A and 15B  are perspective views of a variation of an alarm device that may be used with a suction device;  FIG. 15C  is a perspective view of one variation of a suction device that may be retained within the alarm device of  FIGS. 15A and 15B ;  FIG. 15D  is a superior view of the back of the attachment and suction devices of  FIGS. 15A-15C . 
         FIG. 16A  is an elevational component view of one variation of a suction device for reduced pressure wound therapy;  FIG. 16B  is a superior view of one variation of a fluid retention assembly comprising a pouch that may be used with the suction device of  FIG. 16A . 
         FIG. 17A  is a perspective view of another variation of a fluid retention assembly comprising an absorbent pad and filter;  FIG. 17B  is a side view of the fluid retention assembly of  FIG. 17A ;  FIG. 17C  is a perspective view of the absorbent pad of the fluid retention assembly of  FIG. 17A ;  FIG. 17C  is top view of the filter of the fluid retention assembly of  FIG. 17A ;  FIG. 17D  is a top view of a mesh of the fluid retention assembly of  FIG. 17A . 
         FIG. 18A  is a schematic depiction of a suction device with a fluid retention assembly comprising a pouch;  FIG. 18B  is a schematic depiction of a suction device with a fluid retention assembly comprising a mesh;  FIG. 18C  is a schematic depiction of a suction device with a fluid retention assembly comprising an absorbent pad;  FIG. 18D  is a schematic depiction of a suction device with a fluid retention assembly comprising a pouch and a mesh;  FIG. 18E  is a schematic depiction of a suction device with a fluid retention assembly comprising an absorbent pad and a mesh. 
         FIG. 19A  is a schematic depiction of one orientation in which a suction device may be retained in an alarm device;  FIGS. 19B and 19C  are schematic depictions of the relative positioning between a suction device and an alarm device;  FIG. 19D  is a example of an alternate orientation in which a suction device may be retained in an alarm device. 
         FIG. 20  is a schematic depiction of another variation of an alarm device comprising a single sensor and a suction device. 
         FIG. 21  is a plot of the measured pressure generated by the suction device over a period of 18 hours, wherein the device employs a non-optimized lubricant. 
         FIG. 22  is a plot of the measured pressure generated by the suction device over a period of 18 hours, wherein the device employs a high viscosity lubricant of 1,500.00 cP. 
         FIG. 23  is an image of a cross-section of a part of the suction device showing a section of the outer surface of the seal in contact with the inner surface of the suction chamber, and a gap between a section of the inner surface of the seal and the rigid piston. 
         FIG. 24A  is a plot of the pressure exerted by a suction device with a simulated leak of 9 mL/hr over a period of 3 hours.  FIG. 24B  is a perspective drawing of a bushing comprising an axial indentation in the outer surface of the bushing, and  FIG. 24C  is a cross-sectional view of the bushing-spring assembly. 
         FIG. 25A  is a superior elevational view of the suction chamber;  FIG. 25B  is a cross-sectional view of the distal end of the suction chamber. 
         FIG. 26A  is a component view of a fitting assembly;  FIG. 26B  is a cross-sectional view of the fitting of the fitting assembly from  FIG. 26A . 
         FIG. 27A  is a schematic cut-away view of one embodiment of a connecting mechanism between a fitting and a suction chamber connector;  FIGS. 27B and 27C  are cross-sectional views of the connecting mechanism from  FIG. 27A . 
         FIGS. 28A and 28B  are posterior and anterior component views of one embodiment of a spring assembly, respectively. 
         FIGS. 29A and 29B  are posterior and anterior perspective component views, respectively, of one embodiment of a sliding seal assembly and spring assembly.  FIG. 29C  is a front elevational view of the sliding seal assembly. 
         FIG. 30  is a cross sectional view of one embodiment of a sliding seal assembly coupled to a spring assembly. 
         FIGS. 31A to 31C  are schematic perspective views depicting one example of a priming procedure using a activation or priming tool. 
         FIG. 32  is a plot comparing pressure exerted by low and high viscosity lubricated devices over a time period of 4 days. 
         FIGS. 33A and 33B  are schematic front and back elevational views of a liquid permeable pouch containing superabsorbent materials. 
         FIG. 34A  is a schematic illustration of a first layer of material with an opening cut out of the layer, wherein the opening is smaller than the profile of the pouch;  FIG. 34B  schematically depicts the front-side of the liquid-permeable pouch secured over the opening of the first layer; and  FIG. 34C  schematically depicts a second layer covering the pouch and the first layer, wherein the first and second layers are sealed around the perimeter. 
         FIG. 35  shows an image of the pouch sandwiched between two layers that are sealed together around the perimeter of the bag. 
         FIGS. 36A-36B  are schematic illustrations of two embodiments comprising a sensor is in communication with a wound bed. 
         FIG. 37  depicts one variation of a tissue cover comprising a dressing that may be used with any of the suction devices described herein. 
     
    
    
     DETAILED DESCRIPTION 
     While embodiments have been described and presented herein, those embodiments are provided by way of example only. Variations, changes and substitutions may be made without departing from the invention. It should be noted that various alternatives to the exemplary embodiments described herein may be employed in practicing the invention. For all of the embodiments described herein, the steps of the methods need not to be performed sequentially. 
     Various types of reduced pressure therapy systems may be used depending on the severity of the tissue wound and the activity level of the patient. In some cases, reduced pressure tissue therapy systems may extract tissue exudates, e.g., wound exudates and interstitial fluids, while providing reduced pressure therapy. Some reduced pressure tissue therapy systems comprise a suction device with an open pressure supply, e.g., continuous electric pump. These systems typically are noisy, and their bulkiness and weight often restricts the mobility of a patient. Patients that desire greater mobility may use a reduced pressure tissue therapy system comprising a wearable suction device that does not rely on power from an electrical source, e.g., non-electrically powered. 
       FIG. 1A  is a perspective view of one example of a wearable suction device  2200  that may be used in reduced pressure tissue therapy. As depicted there, the suction device  2200  may comprise a suction chamber  2210 , a suction generating mechanism (not shown), and a sliding seal assembly  2260  that is movably retained in the suction chamber  2210 . One variation of a suction generating mechanism of the suction device  2200  is depicted in  FIGS. 1C and 1D , and may comprise one or more springs  2950 , and the proximal side of the sliding seal assembly  2260  may be coupled to one or more springs  2950 . The springs  2950  may be constant force springs, or any other type of springs that may be used to apply a force on the sliding seal assembly  2260  in a proximal direction. The suction device  2200  may also comprise a housing  2202  that may retain the suction chamber  2210 . The housing  2202  may comprise a proximal cap  2230  with proximal opening  2232  and a distal cap  2220  with a distal port  2242 . In some variations, the distal cap  2220  may comprise a fitting housing  2240  configured for interfacing with a tube (e.g., a tube connected to a dressing) such that the tube is in fluid connection with the suction chamber. In some variations, the fitting housing  2240  may be detachable from the distal cap  2220 . Negative pressure generated in the suction chamber  2210  may be conveyed to a tissue site through a distal aperture in the suction chamber leading to the distal port  2242  of the fitting housing  2240 . Tubing connected to the distal port  2242  may allow the negative pressure to be directed to the tissue site and/or dressing. The suction device may also comprise an activation tool  2290  that may be inserted through the proximal opening  2232 , where the activation tool  2290  is configured to mechanically charge the suction device  2200 , for example, by urging the sliding seal assembly to certain positions in the suction chamber. In some variations, the activation tool  2290  may be releasably snap-locked in the proximal opening  2232 , which may help secure the sliding sealing assembly  2260  in a certain position within the suction chamber  2210 . For example, the activation tool  2290  may comprise release buttons  3150  with  3140  latches such that when the release buttons  3150  are released, the  3140  latches may be engaged in one or more grooves in the proximal cap  2230  at or near the proximal opening  2232 , thereby retaining the activation tool in the suction chamber. When the release buttons  3150  are pressed (e.g., squeezed), the  3140  latches may disengage from the grooves and allow the activation tool  2290  to be withdrawn from the proximal opening  2232 .  FIG. 1A  depicts the configuration of the suction device  2200  before it is activated, where the sliding seal assembly  2260  is located at a proximal portion  2214  of the suction chamber, and where the activation tool  2290  is inserted into the proximal opening  2232  of the proximal cap  2230  but has not yet displaced the sliding seal assembly  2260 . The suction chamber  2210  may comprise a translucent or optically clear material, or an opaque material with or without a translucent or optically clear window. 
       FIG. 1B  depicts the suction device  2200  in a mechanically charged configuration. To mechanically charge the suction device  2200 , the activation tool  2290  may be pushed through the proximal opening  2232  to extend or distally displace the sliding seal assembly  2260  from the proximal portion  2214  of the suction chamber  2210  to a distal portion  106  of the suction chamber  2210 . Depending upon the particular configuration, the activation tool  2290  may be pushed until the sliding seal assembly  2260  contacts a wall of the distal cap  2220 , until it is adjacent the distal end wall of the suction chamber  2210 , until the springs  2950  are maximally extended, and/or until mechanical interference between the activation tool  2290  and the proximal cap  2230  resist further insertion. Urging the sliding seal assembly  2260  to the distal position  106  as depicted in  FIG. 1B  may in turn extend the springs  2950  that are attached to the proximal side of the sliding seal assembly. This may generate potential energy within the springs  2950 . Other variations of wearable suction devices that may be used in a reduced pressure tissue therapy system, as well as methods of using the systems and devices, are described in U.S. patent application Ser. No. 12/372,661, filed on Feb. 17, 2009, which is hereby incorporated by reference in its entirety. 
     Upon removal of the activation tool  2290 , the springs  2950  are able to exert a proximally directed force onto the sliding seal assembly  2260 , which is capable of generating reduced pressure in the suction chamber  2210  and transmitting the reduced pressure to a sealed wound enclosure coupled to the device  2200 . The reduced pressure is generated by expanding the volume of air initially located in a sealed enclosure or chamber of the device from a smaller volume of the chamber to a larger volume. Upon expansion of the air within the sealed enclosure, the density of the air molecules is decreased and the pressure within the sealed chamber is reduced to a sub-atmospheric level. As exudates and/or gaseous leakage occurs, the springs  2950  will retract the sliding seal assembly  2260 , thereby maintaining the reduced pressure level within the collection chamber. In some variations, there may be a lubricant provided between the sliding seal assembly  2260  and the internal walls of the suction chamber  2210 , which may help the sliding seal assembly to move smoothly and consistently across the suction chamber to generate negative pressure. As the sliding seal assembly  2260  returns to its maximum retracted state, the level of reduced pressure level will begin to decrease and may be replaced or recharged. 
       FIGS. 1C and 1D  are superior and side elevational views of the device from  FIG. 1A  in an activated state and with the springs  2950  having partially expended the potential energy from the fully charged configuration. As can be seen when the sliding seal assembly  2260  is in a partially expended position, the suction chamber  2210  may be subdivided by the sliding seal assembly  2260  into a collection chamber  2262  and a working chamber  2264 , where the collection chamber  2262  is the space between the sliding seal assembly  2260  and the distal end wall  2212  of the suction chamber  2210 , and the working chamber  2264  is the space between the proximal end  2214  of the suction chamber  2210  and the sliding seal assembly  2260  which contain the springs  2950 . When the suction device is in the charged configuration, the volume of the collection chamber may be about zero, or sometimes less than about 5 cc. In some instances, upon activation of the mechanically charged device, the collection chamber may increase in volume up to about 3%, sometimes about 5% and other times about 10% or even about 20% until the force exerted by the springs  2950  is counterbalanced by the force generated by the reduced pressure in the collection chamber  2262 . In some variations, a suction device may be configured to apply a pre-determined amount of negative pressure. For example, the volume of the suction chamber and/or the spring constant of constant force springs may be selected in order to provide a pre-determined amount of pressure. Pre-determined pressure levels may range from −50 mmHg to −150 mmHg, e.g., −75 mmHg, −100 mmHg, −125 mmHg, etc. 
       FIGS. 1E and 1F  depict posterior and anterior component views of the suction device  2200 . The distal cap  2220  and the proximal cap  2230  may be configured to be detachably secured to the distal end  2212  and the proximal end  2214  of the suction chamber  2210 , respectively. The proximal end  2212  and/or the distal end  2214  of the suction chamber  2210  may also comprise notches  2360  and  2370 , respectively, which may be configured to facilitate coupling to the proximal cap  2230  and/or distal cap  2220  of the device  2200 , respectively. Notches  2372  or apertures may also be provided for attaching the spring assembly  2270  to the suction chamber  2210 . A fitting housing  2240  may be coupled to the distal cap  2220 , enclosing a distal port  2242  that may be configured to connect the suction chamber  2210  with another component of the therapy system (e.g., an extension tube or an attachment port on a sealant layer). The suction chamber may be fabricated from a rigid polymer adapted to maintain the external shape of the suction chamber shape under reduced pressure. In some embodiments, the entire body of the suction chamber may be transparent, thereby permitting visual inspection the quantity and quality of wound exudates contained therein. In other embodiments, the suction chamber may comprise a non-transparent body but with an inspection window. 
     As mentioned above, the fitting housing  2240  may be configured to removably detach from to the distal cap  2220 , while in other examples, the fitting housing may be integrally formed with the distal cap  2220  or otherwise configured not to be detached once joined. A sliding seal assembly may be movably located within the suction chamber  2210 . The sliding seal assembly  2260  may be coupled to a spring assembly secured to the proximal cap  2230  of the suction device  2200 . In other embodiments, the spring assembly  2270  may also be secured about the proximal opening  2216  of the suction chamber  2210 . An opening  2232  may be provided in the proximal cap  2230  to permit insertion of a priming or activation tool  2290  which is configured to prime the suction device  2200 . Once the suction device  2200  is primed and activated, the activation tool  2290  may be removed, and the opening  2232  on the proximal cap  2230  may be closed by a proximal cap seal  2280 . The proximal cap seal  2280  may be any type of seal that may prevent entry of undesired contaminants or other environmental agents (e.g. water during showering) into the suction chamber  2210 . In other examples, the proximal cap seal may be attached to the proximal cap by a tether. In still other examples, the proximal cap seal may be configured with a passageway or slit and comprises a deformable material that permits insertion and/or removal of the activation tool and reseals upon removal of the activation tool. In the latter embodiments, the proximal cap seal need not be removed before priming or inserted back into the opening after removal of the activation tool. 
     In some embodiments, the reduced pressure therapy device comprises a non-circular suction chamber design which may provide the therapy device with a low or reduced profile. In some examples, the low profile permits placement of the reduced pressure system on the body near the wound, with or without the use of extension tubing. This ergonomic chamber design coupled with the integrated system configuration may permit discrete wearing of the devices to enhance life quality. In one particular example, the suction device comprises a variable volume chamber with an oval cross-sectional geometry that provides a substantial exudate handling capacity while also providing a low profile. In other examples, the cross-sectional shape (i.e. transverse shape to the longitudinal axis of the device) of the suction chamber may have any of a variety of other types of geometric configurations (e.g., circular, rectangular, triangular, octagonal (or other polygonal shapes), etc.). This permits improved mobility, discretion, flexibility, and/or comfort during treatment. The low-profile geometry may also streamline the workflow of using the reduced pressure therapy system by locating the suction device at or adjacent to the treatment site, rather than a remote site, and may also eliminate the use of extension tubing to maintain fluid communication between a treatment site and a separate suction device. 
     In some embodiments of the tissue therapy system the suction device is fabricated from a rigid polymer adapted to maintain the external shape of the suction chamber shape under reduced pressure. The suction chamber can be made of any suitable polymer such as, but not limited to polycarbonate, co-polyester, polyethylene, polypropylene, acrylic, ABS, glass, medical-grade polymers, or a combination thereof. 
     A suction device may be configured to provide negative pressure to a tissue region via a conduit (e.g., tubing) that is in communication with an enclosure that provides an airtight environment around the tissue region. For example, a tube may connect a suction device to a tissue cover structure or dressing comprising an occlusive cover sheet with an adhesive layer is applied over the tissue region (e.g., wound). The dressing may be able to enhance the functionality and/or usability of delivery of reduced pressure to body surfaces. In some examples, the tissue cover and/or dressing may be filled with a contact material such as gauze, foam or other porous materials, to provide cushioning and distribute the reduced pressure throughout the tissue region (e.g., wound bed). The adhesive sheet may serve as a dressing and create a substantially airtight enclosure which encompasses the tissue region. This enclosure is in fluid communication with a reduced pressure source. The reduced pressure source may comprise an electric vacuum pump, in-wall suction, or any of the suction devices described herein. The fluid communication between the vacuum source and the occlusive sheet is provided by a conduit which communicates with an opening in the occlusive sheet, or which passes through the tissue cover (e.g., through the dressing). 
     In one configuration of the device the tissue cover may comprise a dressing that is made of a hydrocolloid dressing having some or all of the properties mentioned above, and/or one or more breathability, moisture absorbent abilities, skin protective properties, and wound healing characteristics. This dressing may also provide for a moist wound healing environment and is an appropriate dressing for satellite wound lesions. In one embodiment, the adhesive dressing may be formulated such that it flows on application of body heat and/or pressure to the dressing surface to eliminate potential leak channels that may form during application. In other embodiments, the application of light energy may also initiate a softening phenomenon to allow the adhesive to flow more readily and fill gaps. 
     One example of a tissue cover comprising a dressing that may be used with any of the suction devices described herein as part of a reduced pressure therapy system is depicted in  FIG. 37 . A tissue cover  3700  may be attached to a suction device or vacuum source (not shown). The tissue cover  3700  may comprise a flexible, adhesive sheet which may be placed over a body surface. The tissue cover  3700  may further comprise release liners, carrier films or other features known in the art to facilitate application of the dressing  3700  to a treatment site. The tissue cover  3700  may also comprise a port member  3701  with an elastomeric membrane pressure indicator  3702  attached to a dressing  3705  of the tissue cover. In this example, the tubing attachment portion or connector  3703  of the port member  3701  is surrounded by a radial section  3704  of elastomeric membrane which deforms under pressure. Optionally, the tissue cover  3700  may comprise a port which allows passage of the fluid communication conduit from one side of the dressing  3705  to the other. The dressing  3705  may comprise at least one adhesive side which in practice may be adhered to a body surface to create a substantially airtight seal. The dressing and dressing adhesive may comprised polyurethane, hydrocolloid, hydrogel, silicone, acrylic, any other material or any combination thereof known in the art. Other variations of tissue covers and dressings that may be used in a reduced pressure tissue therapy system, are further described in U.S. patent application Ser. No. 12/626,426, filed on Nov. 25, 2009, and in U.S. patent application Ser. No. 12/683,987, filed on Jan. 7, 2010, which are hereby incorporated by reference in their entirety. 
     In some embodiments, a one-way flow mechanism may be interposed along the length of the fluid communication pathway between a dressing of a tissue cover and the vacuum source. In some mechanisms, the one way flow mechanism is located in or integrated into the body of the port member, while in some embodiments, the one-way flow mechanism may be integrated into the dressing or port-dressing interface. In still other embodiments, the one way flow mechanism may be located in or integrated into the tubing. In some embodiments, the one way flow mechanism may prevent or reduce the degree or risk of backflow of wound drainage (e.g., wound aspirate or exudates) collected by the reduced pressure source back to the wound. The one way flow mechanism may also permit detachment of the vacuum source without backflow of gas back into the treatment site. Multiple one way flow mechanisms may be provided along a flow pathway. In other embodiments, one way flow mechanism may be incorporated into port, or the vacuum source attached to the one way flow mechanism. In some embodiments, the one way flow mechanism may be a one way valve, such as a duckbill valve, a slit valve, a spring valve, an umbrella valve or any other suitable one way valve known in the art. In some embodiments, a plurality of one way flow mechanisms may be interspersed throughout the fluid communication conduit. In further embodiments, the one way flow mechanisms may have non-uniform opening or cracking pressures to account for fluid pressure differentials from pressure head or flow rate. 
     In order to produce substantially constant levels of reduced pressure within a certain tolerance range, there are several potential challenges. For instance, the sliding friction between the seal and the wall of the chamber, defects in the seal, variations in the force profile of the constant force springs, and the variability in the dimensions of the device components all contribute to fluctuations or perturbation in the reduced pressure level of the system. 
     For example, in a suction device comprising a constant force spring/sliding seal mechanism configured to deliver a substantially constant reduced pressure, there may be two main opposing forces acting on the sliding seal: the force exerted by the springs and the force created by the negative pressure in the suction chamber. Another force that contributes to the system may be frictional resistance. This force relates to the resistance of the relative motion between seal of the suction device and the wall of the chamber. In one way, this frictional force contributes to the variation in the reduced pressure of the system when, for example, a leak is introduced into the system. 
     A change in the pressure level may result from an air leak through the occlusive dressing, or by generation of exudate at the wound site, for example. Exudates are typically body fluids or mixed fluids and other cellular matter. When the magnitude of the reduced pressure within the system is lowered by a leak or by exudate generation, the force that the reduced pressure exerts on the sliding seal may decrease relative to the force exerted by the oppositional constant force springs. In a truly frictionless system, the constant force spring mechanism would immediately compensate for the imbalance of forces, pulling the seal and expanding the volume of the suction chamber, thus increasing the magnitude of the reduced pressure until the pull force from the reduced pressure equals the pull force of the constant force springs. 
     However, taking frictional forces into account, the friction from the contact of the sliding seal-chamber wall may add to the resistance of the reduced pressure and provides additional resistance for the oppositional springs. Thus, the magnitude of the reduced pressure may decrease until the force of the reduced pressure and frictional resistance is less than the opposing force of the constant spring. At this point, the constant force spring system engages and pulls the seal such that an increased volume is created in the suction chamber, thereby increasing the pull of the reduced pressure until a balance is restored between the opposing forces. This cycle repeats until the device is discharged, the seal travels the course of the device or the maximum volume of the suction chamber is reached. 
     If the pressure of the suction chamber is measured as a function of the volume of air introduced into the system by the leak, the resulting signal may be characterized by an oscillating pattern. The oscillating pattern may be described as a substantially regular, repetitive wave pattern with a peak and trough. In some embodiments, the peak-to-peak amplitude refers to the difference between the high and low values of adjacent peaks (peak and trough) in an oscillating wave. In some embodiments, the average peak-to-peak amplitude may be calculated over the course of the discharge of the suction device. Occasionally, there may be one or more variations in the signal where a substantially greater amplitude than the average amplitude is observed as a spike in the trace. The term “typical peak-to-peak” amplitude does not refer to these anomalies. 
     A non-limiting example of an oscillating pattern is a saw tooth wave. For instance,  FIG. 21  shows a pressure signal having a saw tooth pattern. The portion of the wave that decreases from the peak to the trough corresponds to the decrease in the magnitude of the pressure as the leak progresses and the negative pressure is reduced. The pressure continues to decrease to a certain point, which point is determined, in part, by the amount of frictional resistance between the seal and the chamber wall, until the force exerted by the springs is greater than the sum of the frictional resistance and the force exerted by the reduced pressure. At this point, an inflection point in the signal may be followed by an increase in negative pressure and the signal begins the upward climb from the trough to the next peak. This increase corresponds to the sliding seal being pulled back by the springs, increasing the volume of the suction chamber and increasing the magnitude of the reduced pressure until the resistance of the springs is counterbalanced by the force of the reduced pressure and the frictional resistance. This is known as the slip/stick effect. In a frictionless system, a constant leak may result in the seal traveling at a constant rate to adjust from the decrease in negative pressure. In contrast, the frictional resistance of the sealing surfaces results in the periodic “sticking” of the sliding seal. In addition, the frictional resistance experienced by a seal at rest is higher than when the seal is in motion. Thus, the force required to move the seal at rest must overcome static frictional resistance which can be higher than the kinetic frictional resistance when the seal is in motion. 
     In order to reduce the oscillating pressure signal that results from this phenomenon, this disclosure provides a suction device that reduces the frictional resistance resulting from the contact of the sliding seal and the chamber wall. Various embodiments herein disclose a suction device configured to generate and substantially maintain a set negative pressure for use in treating tissue of a subject, comprising a suction chamber, a ribbon spring, and a lubricant; wherein when a volume of at least air or exudate is introduced into the reduced pressure system, a plot of the negative pressure of the system against the volume introduced into the system results in a substantially oscillating wave pattern, wherein the magnitude of the typical peak-to-peak amplitude is no greater than 20 mmHg. In some embodiments, the magnitude of the typical peak-to-peak amplitude is no greater than 10 mmHg. In some embodiments, the magnitude of the typical peak-to-peak amplitude is no greater than 5 mmHg. In some embodiments, the magnitude of the typical peak-to-peak amplitude is no greater than 1 mmHg. In some of the foregoing embodiments the volume introduced into the system is at least 50 cc. In some of the foregoing embodiments the volume introduced into the system is at least 25 cc. In some of the foregoing embodiments the volume introduced into the system is at least 10 cc. The magnitude of variation may also be characterized in relative terms as a percentage of variation from the nominal relative pressure reduction level. In some examples, the percentage of variation may be less than 25%, less than 20%, less than 15%, less than 10%, less than 8%, less than 6%, less than 5%. The maximum variation may be measured in a number of ways, e.g., under test conditions involving a constant infusion or leakage rate of a liquid or gas, up to a certain volume. In some instances, the maximum variations occur during an infusion rate of up to 1 cc/hr, 2 cc/hr, 3 cc/hr, 4 cc/hr, 5 cc/hr, 6 cc/hr, 7 cc/hr, 8 cc/hr, 9 cc/hr 10 cc/hr, or 15 cc/hr or 20 cc/hr, up to a volume of 10 cc, 20 cc, 30 cc, 40 cc, 50 cc, 60 cc, 70 cc, 80 cc, 90 cc, 100 cc, 150 cc, 200 cc, 250 cc or 300 cc, for example. In some of the foregoing embodiments, depicted in  FIG. 21 , a volume of at least a gas or liquid introduced into the suction chamber at a rate of 3 cc/hour for at least a duration of 16 hours for suction chamber nominally configured to generated a relative reduction in pressure level of 80±5 mmHg. 
     As mentioned previously, leaks in the system may involve the interfaces between the device, tubing, dressing and treatment site, or any non-continuous junction that forms the substantially closed system of the reduced pressure system. In some of the foregoing embodiments, the source of the leak originates from imperfections in the seal formed by the sliding seal and the chamber wall. In some of the foregoing embodiments, the source of the leak originates from where the sealing layer attaches to the body of the subject. In some of the foregoing embodiments, the source of the leak originates from any of the connection points between the suction device and the wound. 
     Some variations of suction devices may comprise lubricants that may be used to resist leaks in the interface between the seal and the suction chamber wall, and/or may an interface material to reduce static and/or dynamic friction effect such that the seal may move with respect to the chamber wall without sudden fluctuations in movement or direction. Lubricants may help the seal to slide with a gradual and/or constant speed along the suction chamber, thereby maintaining a substantially constant level of pressure within the chamber. Optionally, a lubricant may also be capable of flowing across the surfaces of the seal and/or chamber wall so that the lubricant is not displaced from the interface as the seal moves across the chamber. Lubricants may also help to decrease the frictional resistance between the seal and the chamber walls, which may help to mitigate the oscillating pattern pressure changes of the system. For example, lubricants may reduce the coefficient of friction between the seal and the suction chamber wall while still maintaining and airtight seal. In some variations, lubricants may be able to provide an interaction between the seal and the suction chamber such that the static coefficient of friction is substantially equal to, or similar to, the kinetic coefficient of friction. Optionally, lubricants may be non-reactive with the material of the seal and/or seal mount such that the lubricant is not absorbed into the seal or seal mount, and/or does not cause any deterioration of the seal or seal mount. Some variations of suction devices may not have any lubricants contacting the seal and/or suction chamber. 
     In some variations, the use of lubricants between the sliding seal assembly and the suction chamber wall may still result in an oscillating pattern of pressure changes as shown in the saw tooth wave of  FIG. 21 , where a fluorosilicone lubricant was used. While not bound by theory, it is believed that the force exerted by the seal against the chamber wall may displace the lubricant from the critical contact area or interface between the seal and the suction chamber wall, thus reducing the benefits of a lubricant. This behavior is similar to a “squeegee” effect. Lubricants may be selected with certain properties (e.g., viscosity, hydrophobicity, adhesion, cohesion, etc.) that enable it to remain substantially between the surface of the seal and suction wall. For example, the lubricant may be characterized by a high viscosity, however the viscosity of the lubricant should allow for the lubricant to flow across the surfaces of the sliding seal assembly and/or suction chamber wall and may have the ability to resist the “squeegee” effect of the sliding seal lips pushing the lubricant away from the sealing contact surfaces. For example, a lubricant with very high viscosity may help reduce the tendency of the lubricant to be pushed aside by the compression of the sliding seal lips. 
     A sufficiently viscous lubricant may also be able to fill in defects in the sealing surface. This may help provide a low-friction interface between the seal and the suction chamber walls, and may also help maintain an airtight interaction between the seal and the suction chamber wall. A viscous lubricant may have cohesive properties that may help ensure an even coating across the surfaces of the seal and/or suction chamber. For example, the molecules of the lubricant may mutually attract each other so that the lubricant maintains a continuous fluid coating across the chamber walls and/or seal. Alternatively or additionally, the lubricant may exert a weak adhesive and/or cohesive to the surface of the chamber walls and/or seal, which may allow the lubricant to fill in any micro-cracks or surface irregularities while allowing relative motion between the chamber walls and seal to occur. Such cohesive properties of a viscous fluid may also help the lubricant remain substantially localized to the contact area between the seal and the chamber walls, while still retaining a certain degree of flowability. 
     A lubricant&#39;s viscosity can be measured by techniques known in the art. In some of the embodiments, the lubricant is characterized by a viscosity of at least 1,000,000 cP. In some of the embodiments, the lubricant is characterized by a viscosity of at least 500,000 cP. In some of the embodiments, the lubricant is characterized by a viscosity of at least 1,500,000 cP. In some of the embodiments, the lubricant is characterized by a viscosity of between 750,000 and 1,750,000 cP, or between about 1,400.00 cP and about 1,600,000 cP. In some of the embodiments, the lubricant is characterized by a viscosity of between 500,000 and 1,500,000 cP. In some of the embodiments, the lubricant is characterized by a viscosity of between 1,000,000 and 2,500,000 cP. In some of the embodiments, the lubricant is characterized by a viscosity of between 1,000,000 and 2,000,000 cP. 
     In some of the foregoing embodiments the viscosity of the lubricant is not less than 100,000 cP. In some of the foregoing embodiments the viscosity of the lubricant is not less than 10,000 cP. 
     In some of the foregoing embodiments, the lubricant is a silicone. In some of the foregoing embodiments, the lubricant is at least one of the members of the group consisting of fluorosilicone and dimethylsilicone. In some of the foregoing embodiments, the lubricant comprises a 20% fluorosilicone and 80% dimethylsilicone by weight. In some of the foregoing embodiments, the lubricant is a silicone lubricant with a viscosity between 1,000,000 and 2,000,000. 
     Dry lubricants can be chemically cross-linked or otherwise bonded to the chamber wall or seal prevents the lubricant being displaced by the compressive force from the sliding seal lips. However, the use of a flowable lubricant has the advantage of sealing small physical defects or imperfections in the sliding seal or suction chamber, and reduces air leaks. 
     Since the overall friction experienced by the seal should be reduced or minimized, in some embodiments it is advantageous to design the sliding seal and the chamber such that there is a reduced amount of compression needed to create an airtight seal. Where a reduced amount of compression is used to create a seal, minor imperfections in the sealing surfaces have a greater chance of permitting air leaks. Thus, the ability of a flowable lubricant to fill in and correct these defects presents an advantage not available with dry lubricants. 
     Factors that influence the selection of an appropriate lubricant and material for the sliding seal material include the non-reactivity and compatibility between the two materials. For instance the sliding seal should have limited swelling from being in contact with the lubricant. More generally, the material of the sliding seal assembly and the lubricant material may be selected to limit undesirable interactions between these components (e.g., absorption of the lubricant into the seal, degradation of the seal by the lubricant, etc.). In one embodiment, fluorosilicone is combined with dimethylsilicone to form a lubricant that reduces swelling of the dimethylsilicone elastomer seal. In some of the foregoing embodiments, the sliding seal is an elastomer. In some of the foregoing embodiments, the sliding seal is dimethylsilicone elastomer. 
     In some variations, the static coefficient of friction between the sliding seal and the suction chamber wall is less than about 0.3, 0.2, 0.15, 0.12, 0.1, 0.08, 0.06 or 0.05. In some variations, the difference between the static coefficient of friction and the dynamic coefficient of friction between the sliding seal and the wall of the suction chamber may be less than 0.1, 0.08, 0.06, 0.05, 0.04, 0.03, 0.02 or 0.01, for example. 
     In some embodiments, the components of the system, such as the chamber, may be manufactured by thermoplastic injection techniques. This method may permit scalability of the component, reduces cost, and increases the dimensional consistency of the components. The chamber of the device has a long bore and to produce this part via injection molding, in some embodiments, requires the introduction of a slight draft to allow the injection mold tool to release the part. The draft causes the cross sectional area near the closed end of the chamber (i.e., the distal end, which may have a distal conduit or extension structure to which tubing may be attached) to be slightly smaller than the cross sectional area near the open end of the chamber (i.e., the proximal end). The cross-sectional area will typically increase linearly from the closed to the open side. In some embodiments, the draft across the longitudinal length of the chamber should be less than ½ of 1 degree per side, and in other embodiments, may be less than ¼ of 1 degree. In some variations, the draft may be such that the distal end may be smaller than the proximal end by about 0.014 inch. A chamber may have an elliptical cross sectional area with a major and minor axis, and the draft may vary differently along the major and minor axes. For example, the length of the minor axis may vary by about 0.01 inch across the longitudinal length of the chamber, and the length of the major axis may vary by about 0.0075 inch across the longitudinal length of the chamber. 
     The differences in cross-sectional area introduced by the draft may introduce variability in the amount of radial compression of the sliding seal. For instance, the smaller cross-section near the closed end of the chamber compresses sliding seal more than the larger cross-sectional area near the open end of the chamber. Greater radial compressive stress on the sliding seal may increase the amount of frictional resistance between the sealing surfaces. In one embodiment, the seal design reduces radial compressive stress of the sliding seal, especially when the sliding seal moves from an area of broader inner chamber dimensions to an area of narrower inner chamber dimensions. By reducing the compressive stress on the seal, the difference in the effective sliding friction between a less-compressed and a more compressed state may be reduced. 
     In some of the foregoing embodiments, the device comprises a sliding seal coupled to a seal mount, wherein the sliding seal has an inner surface and an outer surface and the seal mount has an outer surface. In some of the foregoing embodiments, at least a portion of the outer surface of the seal mount and at least a portion of the inner surface of the sliding seal is separated by a gap. In specific embodiments, the sliding seal undergoes radial compression as the seal slides to narrower portions of the chamber, wherein the compression of the sliding seal results in seal being displaced by a certain amount, wherein the gap is an amount equal to or greater than the amount of displacement of the sliding seal. In some of the foregoing embodiments, the sliding seal is free-floating. 
     In other embodiments of the reduced pressure system, the sliding seal may be fabricated from a material adapted to create an airtight separation between the portion of the suction device below it and the remainder of the suction device. The material may be elastomeric or non-elastomeric. The sliding seal can be made of materials such as: silicone, dimethylsilicone, fluorosilicone, nitrile, natural rubber, thermoplastic elastomer, thermoplastic urethane, butyl, polyolefin, polyurethane, styrene, polytetrafluoroethylene, any other suitable material, or a combination thereof. 
     Sliding seals may be made of a compressible material such that the sliding seal may be able to reversibly transition from a compressed state to an expanded state while still maintaining an airtight seal against the inner walls of the suction chamber. Examples of suitable materials for a sliding seal may include silicone, dimethylsilicone, fluorosilicone, nitrile, natural rubber, thermoplastic elastomer, thermoplastic urethane, butyl, polyolefin, polyurethane, styrene, polytetrafluoroethylene, any other suitable material, or a combination thereof. In some variations, a sliding seal may comprise one or more protruding edges (e.g., flanges) that may be capable of both radial compression and longitudinal deflection. For example,  FIG. 23  depicts a sliding seal  3400  that may comprise a distal flange  3402  and a proximal flange  3404  which may be configured to longitudinally deflect as the sliding seal moves along the longitudinal axis of the suction chamber  3410  and/or in the presence of negative pressure within the chamber. The flanges  3402 ,  3404  may have a low deflection force, which may help the sliding seal to accommodate a draft in the chamber. The deflectable flanges  3402 ,  3404  may also help prevent angular deviations or displacement of the sliding seal  3400  within the chamber  3410 . The distal flange  3402  and the proximal flange  3404  may have similar or different deflection forces. For example, the proximal flange  3404  may have a lower deflection force than the distal flange  3402 . 
     Additionally or alternatively, a sliding seal may be coupled to a seal mount such that the sliding seal may yield under radial compression against the walls of the suction chamber. The interface between the sliding seal and the seal mount may allow additional radial compression of the seal, which may limit and/or reduce the frictional force on the seal as it moves longitudinally along the suction chamber (e.g., from a broader region to a narrower region of the suction chamber or vice versa). For example, the sliding seal  3400  may comprise a lumen  3406  with a proximal aperture  3405  and a distal ledge  3407 . The distal ledge  3407  may be located proximally from the distal side  3401  of the sliding seal. A seal mount  3420  may comprise a protruding edge  3422  at a distal-most side that is configured to contact and/or engage the ledge  3407  of the sliding seal. The width W 1  of the seal mount  3420  may be less than the width W 2  of the lumen aperture  3406 , such that there is a radial gap  3424  between the lumen walls of the sliding seal and the surface of the seal mount. Optionally, the lengths of the seal mount  3420  and sliding seal lumen  3406  may be such that there may be a longitudinal gap  3426  between the lumen walls of the sliding seal and the surface of the seal mount. The radial gap  3424  may provide additional space for the seal mount  3420  to yield to compressive forces, for example, by allowing the proximal flange  3404  to radially compress into the gap  3424 . Compression of the proximal flange  3404  may also cause the side walls  3408  of the sliding seal to radially deflect as permitted by the radial gap  3424 . The size of the radial gap  3424  may be at least partially determined by the draft of the suction chamber  3410 . For example, the radial gap  3424  may be such that the sliding seal can accommodate the draft of the chamber without excessively increasing the frictional force experienced by the sliding seal (e.g., as the sliding seal moves from a broader to a narrower portion of the chamber). The longitudinal gap  3426  may provide some space for longitudinal expansion of the sliding seal  3400  as its side walls  3408  deflect into the radial gap  3424 . In some variations, the size of the radial gap  3424  may be from about 0.005″ to about 0.015″, and the size of the longitudinal gap  3426  may be from about 0.005″ to about 0.015″. In some variations, there may not be a longitudinal gap between the sliding seal and seal mount, and the distal portion of the mount may abut with the distal wall of the lumen. 
     As the seal mount  3420  is moved by an activation tool or force-generating mechanism (e.g., constant force springs), the mount may move with respect to the seal because of the radial and longitudinal gaps. The contact between the seal mount  3424  and the sliding seal  3400  may vary. For example, when the seal mount  3420  is urged distally (e.g., towards the distal portion  3403  of the suction chamber as the suction device is being charged by an activation tool), the distal-most side of the seal mount  3420  may be contacting the distal wall  3412  of the lumen  3406 . In some cases, the protruding edge  3422  may contact the distal-most portion of the lumen  3406 , and may not be in contact with the distal edge  3407  when the seal mount is urged distally. When the seal mount  3420  is urged proximally (e.g., towards a proximal portion of the suction chamber by constant force springs during the generation of negative pressure), the protruding edge  3422  may contact the distal ledge  3407  and not the distal wall  3412  of the lumen. As the mount is urged proximally, the engagement between the protruding edge  3422  and the ledge  3407  may act to pull the sliding seal  3400  along with the seal mount. While the seal mount  3422  being urged either distally or proximally, the protruding edge  3422  of the seal mount  3420  may be pressed against either the distal wall  3412  and/or the distal ledge  3407  with sufficient force such that the seal and the mount may not move radially with respect to each other. This may help stabilize the sliding seal within the suction chamber and help reduce angular deviations. However, in cases, the seal mount  3422  may be urged distally with sufficient force so that the protruding edge  3422  is not contacting the distal ledge  3407 , but is not yet contacting the distal wall  3412 . Optionally, the seal and the mount may not be in contact at all. In this state, because of the radial gap  3424  and in the absence of frictional force between the seal mount and the sliding seal, the seal mount  3420  may move radially with respect to the sliding seal  3400 . 
     The deflection force of the proximal and distal flanges  3402 ,  3404  may be different due to the differing distance between the flanges to the lumen  3406 . For example, the proximal flange  3404  is in closer proximity to the lumen  3406  than the distal flange  3402 , and this may allow the proximal flange to deflect and/or compress more readily than the distal flange. In other variations, the proximal and distal flanges  3402 ,  3404  may have substantially similar deflection forces, as may be desirable. The thickness T 1  of the sliding seal  3400  at the distal side  3401  may be greater in the middle of the seal than towards the side of the seal. A thickened middle portion of a sliding seal may provide the necessary rigidity for generating and maintaining negative pressure in the distal portion  3403  of the chamber  3410 , while thinner side portions may allow the flanges  3402 ,  3404  to deflect and/or compress as the seal moves along the chamber. In some variations, the thickness T 1  of the sliding seal at the distal side  3401  may be in the range of about 0.2″ to about 0.01″, sometimes about 0.15″ to about 0.05″, other times about 0.125″ to about 0.075″. In one example, the thickness T 1  of the sliding at the distal side  3401  may be 0.125″ in the thickened middle portion, and may be 0.075″ in the thinner side portions. 
     Various embodiments herein may comprise a reduced pressure wound treatment system that features the ability to contain and store exudates released into the system. Sources of the exudate generally originate from the tissue or wound of the patient to which the system is attached. Exudates are typically body fluids and contain bio-hazardous products. Exudates that enter into the reduced pressure system may collect in the suction chamber. A used suction device may contain biohazardous materials such as exudates from the wound bed and create a challenge in safely disposing of the spent device. 
     Various embodiments herein disclose a device wherein exudates which enter the suction chamber may be contained within the chamber without the ability to leak out of the suction device. In one embodiment, the device reduces the risk of contamination anyone in contact with the suction device and permits the suction device to be disposed of in solid waste disposal sites. The reduced pressure chamber of the suction device contains a fluid retention assembly (e.g., a biohazard containment assembly) comprising a superabsorbent material, wherein when the exudate comes into contact with superabsorbent material, it is absorbed by the material and unable to exit the suction device chamber. The liquid is stored in the superabsorbent material. The ideal superabsorbent material is able to absorb and contain an amount of liquid that is many times its own weight and has a high absorbance capacity. In addition, in some of the foregoing embodiments, a fluid retention assembly (e.g., a biohazard containment assembly) comprises anti-bacterial agents which can further reduce the risk of contamination and improve safety in handling the suction device. 
     Methods and devices for treatment of damaged tissue are disclosed, including treatment of wounds by employing non-electrically powered reduced pressure therapy devices. Maintenance and control of the sub-atmospheric pressure generated may be provided by such devices while reducing usage discomfort to the user. In some embodiments, a reduced pressure therapy system may comprise a suction device, and a tissue cover structure that comprises a sealant layer, a contact matrix and optional extension tubing. The suction device may be a non-electrically powered device, which may be configured to be silent and/or wearable. In some embodiments, the suction device may have a low-profile so that it may be worn inconspicuously under clothing. The sealant layer may create a substantially airtight enclosure over the damaged tissue to provide fluid communication between the suction device and the enclosure containing the damaged tissue. Fluid communication may be provided by a direct connection between the suction device and the sealant layer, or may be provided through extension tubing connecting the suction device and the attachment port. In some embodiments, the sealant layer may be flexible, but in other embodiments the sealant layer may be semi-rigid or rigid. In some examples, a semi-rigid or rigid sealant layer may facilitate handling or application of the sealant layer to a treatment site while reducing or eliminating the risk that the sealant layer may fold and adhere on itself. The extension tubing may be coupled to the sealant layer and/or suction device using a connector or fitting. The connector may optionally comprise a releasable locking mechanism to facilitate attachment and detachment of the extension tubing, and/or to prevent accidental disconnection. For example, the releasable locking mechanism may comprise a release button or other actuator which serves as a locking mechanism which may be manipulated during attachment and/or detachment of the tubing. In other embodiments, the suction device may be connected directly to the sealant layer attachment port, and may comprise a connector with the same or similar connector as the extension tubing, to permit both direct attachment of the suction device and remote attachment using the tubing. 
     In one embodiment, a system for reduced pressure therapy may comprise a tissue cover structure that comprises a contact layer matrix that is placed into or over the wound bed or other tissue defect. In some embodiments, the contact layer matrix may be used to distribute the reduced pressure more evenly through the wound bed, and may also provide a scaffold or contact surface which promotes healing. In another embodiment, the damaged tissue cavity, packed with the contact layer matrix, is then placed under a sealant layer to produce a sealed enclosure containing the contact layer and the wound bed. Fluid communication to the interior of enclosure is provided by an attachment port of the sealant layer. 
     In some embodiments of the device, the tissue cover structure may comprise a sealant layer made of a hydrocolloid material or any other material known to those skilled in the art. The hydrocolloid sealant layer may be semi-porous and breathable to absorb moisture from the wound while protecting the skin. In addition, the hydrocolloid sealant layer is typically thicker than other materials such as acrylic adhesives to allow for easier placement with less folding and wrinkling and to seal potential fluid leak paths. 
     In one embodiment of the device disclosed herein, the attachment port is directly mounted to a distal portion of the suction device. In other embodiments the attachment port is connected to the suction device via an extension tube. In some embodiments, the extension tube may be adapted to mitigate entanglement. The suction device and the extension tubing may have similar fittings and release buttons to resist accidental disconnection. In embodiments in which extension tubing is used, the proximal end of the extension tubing may be connectable to the distal end of the suction device with a complementary fitting that is similar to the fitting on the attachment port. Likewise, the distal end of the extension tubing may be connectable to the suction port with a complementary fitting that is similar to the fitting at the distal end of the suction device. 
     Various embodiments herein also disclose a device and method to detect a blocked base layer. During the application of negative pressure, it is possible for the path from the wound bed to the suction source to become blocked. Blockage of the path can occur for a variety of reasons, such as development of a clot, thick exudate ingression, crust, or other solid material from exudates. Kinks or compression of the extension tube or other portion of the reduced pressure pathway, for instance, may cause blockage. Such blockage can result in a difference in pressures below and above the blockage, such as at the wound bed level and at the suction device, respectively. Thus, although the suction device appears to maintain a desired negative pressure, the pressure at wound bed level may be closer to atmospheric pressure and any benefit of reduced pressure therapy would be lost. The ability to detect a loss of reduced pressure specifically at the wound bed level would give clinicians an opportunity to address potential blockages. 
     There are some existing solutions for detecting a loss of suction for powered pumps such as the disclosure of U.S. Pat. No. 7,438,705. However, detecting a loss of reduced pressure at the wound bed in a non-electrically powered device has yet to be seen. 
     Various embodiments herein disclose a dressing for a wound bed capable of indicating decreased negative pressure at the wound bed, wherein the dressing comprises a sensor and a communication channel between the dressing and the wound bed. The sensor detects and indicates a reduction or lack of negative pressure at the wound bed site. Some embodiments of the device disclosed herein comprise a pressure gauge integrated into the attachment port or another component. The mounting of the pressure gauge into the attachment port enables accurate measurement of pressure level within the enclosure adjacent to the wound and formed by the sealant layer. The pressure gauge described herein may less susceptible to incorrect pressure readings that are typically caused by clots in the tubing connecting the reduced pressure source to the wound. Examples of a pressure sensor include a collapsible bellow or an electronic pressure sensor. Examples of these embodiments are illustrated in  FIGS. 36A and 36B . However, other embodiments may not have a pressure gauge or sensor. 
     In  FIG. 36A , a portion of a wound dressing  3600  placed over a wound bed  3602  and comprising an optional base layer or contact layer  3604  (e.g. gauze or foam) placed in the wound bed  3602 . The dressing  3600  comprises a port  3606  that is attached (or integrally formed) with tubing  3608  used for attachment to a vacuum source  3610 , and a pressure-sensitive structure  3612  that is in communication with the wound bed  3602  via an opening in the dressing, or an optional communication tube  3614 . In  FIG. 36A , the communication tube  3614  is depicted with its distal end  3616  located below the contact layer  3604 , but in other examples, the distal end may be located within or above the contact layer  3604 . In still further examples, the communication tube may be fenestrated along its length or may comprise multiple tubes. In the example in  FIG. 36A , the pressure-sensitive structure  3612  comprises a bellows structure that is normally expanded at atmospheric pressure but collapses at certain relative reduced pressure levels that are used with negative pressure wound therapy (e.g. −50 mm Hg, −75 mm Hg, −100 mm Hg, −125 mm Hg, or −150 mm Hg, or greater). 
     In sensors or indicators utilizing a bellow design, the bellow is collapsed under negative pressure, and upon loss of negative pressure, the bellow expands. Thus, expansion of the bellow provides the clinician an indication that reduced pressure at the site of the wound bed is lost. The bellow is in fluid communication with the wound bed site. The bellow shape or conformation should change in response to the reduction of negative pressure at the wound bed site. For instance, if the wound bed site has adequate negative pressure, the bellow appears collapsed. As the negative pressure at the wound bed level is reduced, the bellow changes from a collapsed to an expanded state. In some embodiments, the fully expanded bellow indicates that the wound bed is at atmospheric pressure. In some embodiments, the bellow volume is at least 0.5 cc. In some embodiments, the bellow volume is at least 1 cc. In some embodiments, the bellow volume is at least 2 cc. In some embodiments, the bellow volume is at least 3 cc. In some embodiments, the bellow volume is between 1-5 cc. In some embodiments, the bellow volume is between 1-3 cc. In some embodiments, the bellow volume is less than 10 cc. 
     The bellow material is flexible and permits the bellow to change shape in response to changes in pressure. In some embodiments the material may stretch. In other embodiments the material has a low stretch characteristic. The bellow material may comprise, for example, silicone or polyurethane. In some embodiments the bellow has “accordion” shaped folds to accommodate the collapsed and expanded states. In other embodiments, the bellow is smooth without folds. Moreover, the bellow is designed to change appearance to indicate to a person having ordinary skill in the art if there is a change in negative pressure. In some embodiments, the sensor does not rely on any electronic circuitry or electrical impulse to indicate a change in negative pressure. 
     In alternative embodiments, the sensor comprises an electrical component, such as MEMS technology to communicate the information of a change in negative pressure to the clinician. Microsystem Technology or MEMS Technology is the integration of miniaturized components of sensor applications using newly developed miniaturization techniques. Microsystems combine microelectronic components (Integrated Circuits) with micromechanical or micro-optical components. The microelectronic element employs standard semiconductor technology to analyze and manage the output data of the micromechanical or optical element. One of the first microsystem applications, the pressure sensor, uses the combination of mechanical sensing elements and electronic circuitry. The micromechanical components are produced on silicon wafers, a material well known in chip manufacturing. 
     In  FIG. 36B , the wound bed  3602  may also be treated with an optional base layer or contact layer  3604  (e.g. gauze or foam). The dressing  3620  likewise may also comprise a port  3622  that is attached (or integrally formed) with tubing  3624  used for attachment to a vacuum source  3610 , but an electronic sensor  3626  may attached to the dressing  3620  or otherwise in communication with an opening in the dressing to measure the pressure in the wound bed  3602 . An optional communication tube  3628  may also be provided for the electronic sensor to isolate and sample pressure at locations remote from the electronic sensor. In other variations, the electronic sensor  3626  may comprise an elongate sensor lead with a sensor mechanism at its tip. This sensor lead may be located in the communication tube  3628 , which may protect the sensor lead from damage or interference from wound bend exudates. The electronic sensor may be configured with any of a variety of functions, including indicators of battery power, and/or adequate levels of pressure reduction. The indicator may be a light  3630 , and the sensor may also include a on/off mechanism  3632 . 
     The sensor, including the responder coil and the pressure sensitive capacitor may be enclosed and/or encapsulated suitable for attachment to or embedding in the wound dressing. The enclosure and encapsulation materials are biocompatible. To facilitate the functioning of the present invention, the dressing comprises a connection between the pressure sensitive capacitor and the wound bed. 
     Examples of pressure sensors include, for instance, the disclosure U.S. Pat. No. 6,840,111 entitled “Micromechanical Component And Pressure Sensor Having A Component Of This Type.” This patent discloses a micromechanical component for mounting on a carrier as well as a pressure sensor. 
     The dressing and wound bed is in communication via a channel. An example of a communication channel is a flexible catheter tube, comprising a first and second end, wherein the first end is connected to the dressing and the second end is located at the wound bed, below the base layer. Moreover, any type of flexible tubing that permits the sensor to indicate the pressure level at the wound layer is appropriate. In specific embodiments, the first end of the communication channel is in communication with the sensor. The tubing should be flexible to allow for positioning to the wound bed, yet the tubing should be able to have the mechanical strength to maintain fluid communication between the sensor and the wound bed and avoid collapsing or kinking. 
     The sealant layer may also comprise an attachment port to facilitate attachment and/or detachment of the suction device or extension tubing to the sealant layer. In some examples, the attachment port may have a variety of relative configurations and/or relative positions with respect to the sealant layer and the suction device. In some instances, the attachment port may be articulated and/or flexible. For example, an attachment port may be configured with a swivel base, which may permit the attachment port to rotate. An articulated and/or flexible attachment port may also reduce the transmission of torsion or other forces that may be transmitted between the suction device and the sealant layer. The attachment port may be integrally formed with sealant layer at the point of manufacture, or may be provided separately and attached to the sealant layer at the point of use. The latter embodiments may permit clinician flexibility or customization of the relative location of the attachment port with respect to the sealant layer. The attachment port configuration may also provide improved patient comfort as the attachment port design reduces communication of torsion forces to the wound bed, which may be caused by the suction device movements, while allowing quick integration. Furthermore, ability to bend and/or rotate allows independent placement of the sealant layer with respect to the attachment port orientation. The flexibility of the attachment port may also reduce the risk of pressure point induced injury. The attachment port may allow for simple snap-in attachment of the vacuum source. The connection of the attachment port nozzle to the dressing interface may have a small footprint and/or a low profile to reduce the possibility of pressure point injury. In some embodiments, the swivel base of the attachment port may have a thin elastomeric base which is integrated into the sealant layer. The swivel base is configured to allow maximal sealant layer moldability while maintaining integration with the more rigid system elements to form a seal around body surfaces. In some embodiments, a reduced pressure therapy device with an attachment port may reduce or eliminate one or more steps that are used to attach the reduced pressure source to the sealant layer and to create fluid communication between the wound and reduced pressure source. Unlike existing reduced pressure therapy systems, the attachment port may be configured to attach the vacuum source without adhesives and/or without cutting the sealant layer. 
     In some embodiments, the reduced pressure therapy device may be configured with one or more actuators to facilitate activation of the suction device and/or release of the suction device from the skin or tissue. For example, the suction device may comprise an activation mechanism. In some embodiments, the suction device contains a button or other actuator which initiates the application of reduced pressure at the treatment site. The activation mechanism may be provide with indicia, such as the word “ACTIVATE” or a color green, or any other word or coding with similar meaning, is provided thereon or nearby. Pressing the said button may open a valve and allow fluid communication between the enclosure formed adjacent to the wound bed and the suction chamber, or may unlock a sliding seal to permit movement. More specifically, the activation may cause constant force springs to retract in order to expand the combined volume of the space below the sliding seal and within the wound enclosure. The reduced pressure created therein may exert a force on the sliding seal substantially equal to that of the springs. 
     In some embodiments, the reduced pressure therapy device may further comprise an additional button or actuator which is configured to close the valve and/or decouple the suction device from the extension tubing or sealant layer enclosing the wound. Pressing the additional button may allow detachment of the suction device from the attachment port or the extension tubing and activate a one way valve which traps the exudates within the suction chamber or otherwise closes any pathway out of the suction chamber. The tubing to the dressing may have a one way valve such that air and/or exudates may move in one direction (e.g., away from the wound bed) and not the other (e.g., towards the wound bed). 
     In some embodiments, the therapy device may be primed or charged prior to applying the reduced pressure. In some configurations of the device, the charging and activating method may be performed in a single continuous step. While in other configurations, the charging and the activating method may be performed in distinctly separate steps. In one example, the sliding seal within the suction device may be primed by being positioned at the distal end of the suction device. The positioning of the sliding seal may be performed by any of a variety of priming mechanisms, such as a slider or push rod, for example. In some embodiments, the sliding seal may automatically begin to slide back to generate a pressure differential in the reduced pressure chamber after priming. In other embodiments, the suction device may comprise an activating mechanism which is actuated separately from a priming mechanism to initiate the generation of the pressure differential. In some configurations, the activating mechanism may directly block or restrict movement of the sliding seal, while in other configurations, the activating mechanism may restrict or limit flow of fluid and/or materials into the chamber of the suction device. In one example, the release mechanism may comprise a separate button or lever that is configured to alter communication or flow through a valve coupled to the reduced pressure chamber. The valve may be a blade valve or rotatable valve, for example. Pressing the activation button may lift a blade valve or turn the lever of a rotatable valve to permit fluid flow into the reduced pressure chamber. 
     In certain embodiments, the priming mechanism comprises a priming key or activation tool configured extend the force mechanism or displace the sliding seal into its primed position. In some examples, the activation tool comprises an elongate rigid member that is configured to be positioned in an opening in the body of the suction device and may be used as a lever or push rod to prime the reduced pressure generation mechanism. In some embodiments, the activation tool can be used to mechanically press the sliding seal towards the distal end of the suction device until a latch, embedded within the shaft of the activation tool, locks into place. In some embodiments the activation tool is integrated into the body of the suction device and may also serve as a cap to close the suction device. In some embodiments, the activation tool may be configured to hold and maintain the suction device in a non-charged state. For example, the activation tool may be releasably locked to the body of the suction device to provide safe storage of noncharged suction device, with the locked activation tool preventing or limiting a non-charged spring mechanism from retracting during storage and/or handling. In some instances, without the activation tool in place, retraction from storage and/or handling may occur, due to micro-leaks out of the suction chamber that may cause the springs to lose the energy stored in them, for example. In other embodiments, the activation tool enables re-charging of the spring or other force mechanism that has been depleted or otherwise lost some charge. For example, recharging may be performed when accidental discharge or an undetected leak causes the springs to lose the energy stored in them, or after emptying the collection chamber. 
     In another embodiment, a method for treating a patient is provided where the method comprises steps of (a) detaching a non-electrically powered and non-circular reduced pressure generating device from a wound covering, (b) charging the reduced pressure generating device with potential energy without generating a reduced pressure, (c) attaching the recharged reduced pressure generating device to the wound cover, and (d) activating the recharged reduced pressure generating device to generate reduced pressure in an enclosure underneath the wound covering. 
     Further provided herein is a method for treating a patient, where the method comprises steps of (a) sealing a wound cover to a body site, and (b) reducing the pressure level at the body site using a vacuum generating device that has an elongate length and a non-circular cross-sectional shape transverse to the elongate length. In some embodiments, the vacuum generating device may be configured to maintain substantially constant reduced pressure level at the wound site without changing its external dimensions and independent of its orientation with respect to the body site. In such an embodiment, the method may further comprise a step of sliding a non-circular seal along a movement axis in a non-circular reduced pressure chamber, wherein the seal and the suction chamber have non-circular configurations transverse to the movement axis. 
     In one embodiment of the reduced pressure system, the suction chamber comprises an ellipsoidal cylinder having a sliding seal concentrically disposed therein. The chamber has a variable effective volume defined by the distance between the distal end of the chamber, which is located adjacent to the opening connected to the sliding blade valve and a current position of the sliding seal. In the primed state, the seal is closest to the distal end of the suction device, and the effective volume of the chamber is zero or nearly zero. The sliding seal may be connected to one or a series of springs which may be used to bias the seal towards an activated state where the effective volume of the chamber is the maximum. The springs may have any of a variety of configurations, including ribbon springs. The ribbon spring may be a substantially constant force spring or a variable force spring. In some examples, a combination of spring types may be used. In still other examples, a single ribbon may be configured with a coil at each end and attached to a slidable seal at a middle region of the single ribbon. In one embodiment of the device, the spring(s) may exert a force of less than 0.5 pounds. In other embodiments of the present invention the constant force spring(s) may exert a force of less than 1 pound. In some embodiments of the reduced pressure system the constant force spring(s) may exert a force of less than 5 pounds. In other embodiments of the device disclosed herein the substantially constant force spring(s) may exert a force of less than 20 pounds. In other examples, the force per square inch exerted across the collection volume of the device may be in the range of 0.1 psi to 15 psi, in some examples 0.5 to 10 psi, and in other examples 1 psi to 5 psi, or 0.5 psi to 2.5 psi, or 1.5 psi to 2.5 psi. This pressure may be exerted by a single force member or may be the aggregate pressure from two or more force members. The force or pressure may be selected based on the type, size, location, or another suitable characteristic of the wound being treated. 
     In some embodiments, the suction device may be configured to generate a reduced pressure which may be generally characterized by the absolute pressure level and/or by a pressure level reduction relative to the atmospheric pressure. In some embodiments, the device is configured to generate a level of reduced pressure between 0 and 760 mmHg. In some embodiments, the generated amount of reduced pressure in the enclosure formed by the sealant layer and treatment site is more than 10 mmHg, 20 mmHg, 50 mmHg, 80 mmHg, 100 mmHg, 150 mmHg, 200 mmHg, 500 mmHg, 700 mmHg, or even 750 mmHg or more. The device may generate an absolute reduced pressure underneath the sealant layer where the reduced pressure is anywhere between 0 and 760 mmHg. In some embodiments, the generated level of reduced pressure in the enclosure formed by the sealant layer is less than 700 mmHg, sometimes less than 600 mmHg, other times less than 400 mmHg, or even less than 250 mmHg, 125 mmHg, 75 mmHg, 50 mmHg, less than 25 mmHg, or less than 10 mmHg. In some embodiments, the sealant layer generally follows the perimeter of the area of tissue being treated. The tissue therapy devices may have different collection chamber sizes which allow for treatment of larger, more exudative wounds while maintaining the smallest configuration possible for enhanced usage comfort. This may be particularly advantageous for small wounds or treatment sites, as a smaller reduced pressure source can be partially or fully integrated into the dressing or sealant layer. In some embodiments, the cavity of the suction device is 50 cc or less in volume, while in other embodiments, the cavity may be 100 cc in volume. In other embodiments, the collection chamber is less than 150 cc in volume. In some embodiments, the collection chamber is less than 200 cc in volume. In other embodiments, the collection chamber is smaller than 300 cc in volume. In some embodiments, the collection chamber is less than 500 cc in volume. In other embodiments, the collection chamber is less than 1000 cc in volume. In other embodiments, the cavity of the suction device may be at least 50 cc, 100 cc, 150 cc, 200 cc, 300 cc, 500 cc or 1000 cc or more. 
     To convey negative pressure to a desired tissue region, a suction device may comprise a distal port with a conduit lumen. For example,  FIG. 25A  provides a detailed superior view of the suction chamber  2210  and  FIG. 25B  provides a cross-sectional view of the distal portion of the suction chamber  2210  from  FIG. 25A . The distal end wall  2213  of the suction chamber  2210  may further comprise a distal opening to permit communication with the suction chamber. The distal end wall  2213  of the suction chamber  2210  may further comprise a conduit  2330  or other extension structure. The conduit  2330  comprises a conduit lumen  2340  with a conduit opening  2342  which are in fluid communication with the collection chamber  2310  of the suction chamber via the distal opening  2215  of the distal end wall  2213 . The conduit  2330  may comprise any of a variety of notches  2350 , grooves or flanges, which may facilitate attachment of the conduit  2330  to one or more components associated with the fitting housing  2240 . 
     Although a user-controlled valve may be provided in some embodiments to open or close fluid communication with the suction chamber, in some examples, the fluid communication may be controlled automatically by the coupling and/or decoupling of the device components. For example, the conduit  2330  of the device  2200  may also comprise an inner conduit  2380  located in the main conduit lumen  2340 , the inner conduit  2380  comprising an inner conduit lumen  2382  and an inner conduit opening  2384 . Referring to  FIG. 25B , a chamber slit seal  2390  may be located about the inner conduit opening  2384 . In its base configuration, the chamber slit seal  2390  may be configured with a normally closed configuration to block fluid communication through the conduit  2330 . In some examples, a chamber slit seal  2390  may be opened by inserting a structure through the seal to deform it and maintain the patency of the opening formed in the seal. As will be explained in greater detail below, in other examples, such as the slit seal  2390  in  FIG. 25B , the slit seal  2390  may be configured to be pushed over, around, and/or down toward the base of the inner conduit  2380  when a complementary structure is inserted into the main conduit lumen  2340 . 
       FIG. 26A  is a top component view of a fitting assembly  2600 , comprising the fitting housing  2240 , a distal port  2242  and a fitting slit seal  2602 . As mentioned previously, the fitting housing  2240  may be configured to permanently or detachably couple to the distal cap  2220  of the device  2200 , or may be integrally formed with the distal cap. In the embodiment shown in  FIG. 26A , fitting  2610  comprises a connector section  2604  that is accessible through an opening  2606  in the fitting housing  2240  and permits a complementary fit with the connector of another component. For example, connector section  2604  may be coupled to a connector of an extension tube or the attachment port of a sealing layer with a snap fit or an interference fit. In the specific example in  FIG. 26A , the connector section  2604  comprises multiple flanges  2608  which may be used to provide a resistance fit with tubing, but may also be used with a complementary connector to form a complementary interfit. 
     Referring to  FIGS. 26A and 26B , the distal port  2242  may also comprise a chamber connector  2610  with a fitting slit seal  2602 . When the device is assembles, the chamber connector  2610  may be located within the distal cap  2220  of the device  2200 , but the particular location may vary with the particular embodiment. The fitting slit seal  2602  may comprise a distal ring  2612  with an inner profile configured to engage a groove  2614  on the chamber connector  2610  of the distal port  2242 . The outer profile of the seal  2602  and/or the distal ring  2612  may be configured to seal against the inner surface main conduit lumen  2340 . The fitting slit seal  2602  may also comprise a slit that provides a deformable passageway through the seal  2602 . Thus, in some embodiments, the fitting slit seal  2602  may be configured to both form an airtight seal between the chamber connector  2610  and the conduit lumen  2340  of the suction chamber  2210  and also to control fluid communication through the fitting assembly  2600 .  FIG. 26B  illustrates a side cross sectional view of fitting  2610  coupled to the fitting slit seal  2612  at the fitting&#39;s proximal end. 
     Referring back to  FIG. 26A , fitting assembly  2600  may also comprise an interlocking structure that comprises at least one resilient tab  2616  that is disposed on and project outwardly from a base member  2618  coupled or integrally formed with the distal port  2242 . When the fitting assembly  2600  is coupled to the suction chamber  2210 , the tabs  2616  are configured to engage complementary recesses ( 2350  in  FIGS. 25A and 25B ) on the conduit  2330  of the suction chamber  2210 . An interlocking mechanism may resist or prevents inadvertent decoupling of the distal port  2242  from the suction chamber  2210 . The fitting housing  2240  may further comprise one or more release structures or buttons  2622  that are coupled to or interface with the levers  2624  of the projecting tabs  2618 . Depressing the buttons  2622  will release the interlocking mechanism by displacing the tabs  2616  from the notches  2350  on the suction chamber  2210  and permit decoupling of the distal port  2242  and fitting housing  2240  from the distal cap  2220  and the suction chamber conduit  2330 . The release buttons  2622  may comprise one or more textured gripping surfaces  2626  that may facilitate manual connection or disconnection of the distal port  2242 . 
       FIG. 27A  is a schematic superior cut-away view of the suction chamber  2210  and the distal port  2242  of the fitting assembly  2600  when the distal port  2242  is fully inserted into the conduit  2330 . As illustrated, the tabs  2616  projecting from the base member  2618  of the distal port  2242  form an interfit with the notches  2350  on the surface of the suction chamber conduit  2330 .  FIGS. 27B and 27C  are side cross sectional views of a portion of the suction chamber  2210  and the distal port  2242 , before and after the distal port  2242  has been fully seated into the conduit  2330 .  FIGS. 27B and 27C  further illustrate the connecting mechanism between chamber slit seal  2390  on the inner conduit  2380  and fitting slit seal  2602  of the distal port  2242 . In  FIG. 27B , when distal port  2242  is inserted into the conduit  2330 , the fitting slit seal  2602  initially contacts chamber slit seal  2390 , which is mounted on a seal base  2392 . As illustrated in  FIG. 27C , further insertion causes the edge  2628  of the chamber connector  2610  to exert a force along the perimeter  2660  of the chamber slit seal  2390 . An inner gap  2632  and/or an outer gap  2634  about the chamber slit seal  2390  provide space for the chamber slit seal  2390  to deform or compress away from the edge  2628  of the chamber connector  2610 . This results in the enlargement of the opening or slit  2636  of the chamber slit seal  2390  as it is pushed proximally away from the inner conduit opening  2384 . In some examples, the inner and outer gaps  2632   2634  may also reduce the frictional resistance of the chamber slit seal  2390  against the inner conduit  2380  or the surface of the conduit lumen  2340 , respectively. As the distal port  2242  is further inserted into the conduit lumen  2340 , the exposed inner conduit  2380  penetrates through the slit  2603  of the fitting slit seal  2602 , thereby opening fluid communication from the suction chamber  2210 , through the distal opening  2215  of the suction chamber  2210 , through the inner conduit  2380  and through the distal port  2242 . In the embodiment depicted in  FIGS. 27A to 27C , the tabs  2616  and the notches  2350  of the locking mechanism may be used to provide rotational alignment of the between the fitting slit seal  2602  and the chamber slit seal  2390 , if needed. This may be useful where the slits of the seals  2602  and  2390  are single linear slits. In other configurations where the slits are multiple radial slits, rotational alignment may or may not affect the patency of the fluid communication. 
     When distal port  2242  is decoupled from the suction chamber conduit  2330 , of the withdrawal of the inner conduit  2380  from the fitting slit seal  2602  results in closure of the fluid passageways to the sealed wound and may limit air entry into the wound during decoupling. As the distal port  2242  is further separated, the edge  2628  of the chamber connector  2610  is withdrawn and the chamber slit seal  2380  is able to elastically revert back to a closed position to seal the suction chamber  2210 . In some embodiments, chamber slit seal  2380  is able to elastically revert back to a closed position with the aid of a coaxially mounted coil spring. Although both seals  2602  and  2390  are closed, the outer surface of the fitting slit seal  2602  continues to form a seal with the conduit lumen  2340  until further separation occurs. As may be seen in  FIGS. 27B and 27C , the conduit lumen  2340  of suction chamber  2210  has a non-uniform diameter along it longitudinal length, and may comprise a proximal segment  2638  having a reduced diameter relative to the distal segment  2640 . The transition in diameter between the proximal and distal segments  2638  and  2640  may be gradual or stepped. The conduit lumen  2340 , for example, comprises at least one step transition region  2642  between the segments  2638  and  2640 . In some examples, step transition region may provide different tactile feedback compared to gradual transitions. 
     The slit seal may be fluid impervious and may be fabricated from any of suitable resilient materials, such as, but not limited to, synthetic elastomer, silicone rubber, or natural rubber. The seal material may be compatible with wound exudates that may be collected by the suction chamber during a reduced pressure treatment. The seal material may be sterilized by treatment of radiation, steam, ethylene oxide or other suitable techniques known to those skilled in the art. 
     Turning to  FIGS. 28A and 28B  now, the spring assembly  2270 , which is mounted at the proximal end of the suction chamber and covered by the chamber proximal cap, comprises a spring carrier  2820  and a U-shaped spring retainer  2810  containing two bushings  2830  mounted on the two vertical rails  2812  of the spring retainer  2810 . Two substantially constant force springs (not shown in this figure) may each comprise a coiled body coupled to and wrapped around bushing  2830  and a free end distally extended and attached to the sliding seal assembly. The springs may or may not be constant force springs. The spring attachment mechanism will be discussed in greater detail below. The spring carrier  2820  comprises a central opening  2824  and two side openings  2826 . The central opening  2824  is configured to permit passage of the activation tool to access and displace the sliding seal assembly. The side openings  2826  are configured to house the bushings  2830  and the springs when the spring retainer  2810  is coupled to the spring carrier  2820 . As shown in this figure, multiple ridges  2821  may be located adjacent the side openings  2826  to limit the movement of the bushings  2830  and springs coiled around bushings  2830 , thereby reducing deflections or deformations of the springs during operation of the suction device. The spring carrier  2820  may also comprise resilient tabs  2822  that may slidably engage one or more grooves on the activation tool shaft, which may reduce angular deviations of the activation tool with respect to the longitudinal movement axis of the seal. The spring carrier  2820  may also comprises two interlocking structures  2823  configured to releasably lock the activation tool in place after the suction device is primed. The interlocking mechanism will be described in detail later. Fixation structures  2828  may be provided to form a snapfit or other type of interfit with complementary structures on the suction chamber. 
       FIGS. 29A and 29B  are component views of the sliding seal assembly  2260  that comprises a piston seal  2910  and a piston  2920 . The sliding seal assembly  2260  may be configured to traverse between the distal end and the proximal end of the suction chamber while maintaining a substantially airtight seal. As mentioned previously, the sliding seal assembly  2260  provides an airtight separation the suction chamber between a collection chamber and a working chamber. In the depicted embodiment, the piston seal  2910  has a non-circular, elliptical cross-sectional shape with respect to its movement axis in the suction chamber, but in other embodiments, other shapes as described herein may be used. The piston seal  2910  may comprise a side wall  2911  and a distal end wall  2912 . The side wall  2911  of the piston seal  2910  further comprises a distal perimeter ridge  2914  and a proximal perimeter ridge  2916 , the dimensions of which may be larger than that of the side wall  2911  of piston seal  2910 . The ridges  2914  and  2916  may be configured to be in a sliding contact with the interior surface of the suction chamber. They may provide a sealed contact while limiting sliding friction. The exterior surfaces of the piston seal and/or the interior surfaces of the suction chamber may comprise a friction-reducing lubricant or a lubricious coating material. 
     The piston seal  2910  may be detachably coupled to the piston  2920  or in some embodiments, the piston seal  2910  and the piston  2910  may be integrally formed. In the depicted embodiment, the piston  2920  may comprise an elliptical frame with a side wall  2924 . The distal portion of side wall  2924  may comprise a recess  2926  and a raised edge or flange  2928  configured form a complementary interfit with the piston seal  2910 . The proximal perimeter edge  2930  of side wall  2924  may have a complementary shape to the distal edge  2829  of the spring carrier  2820 . In the depicted embodiment, both the proximal edge  2930  of the piston side wall  2924  and the distal perimeter edge  2829  of the spring carrier have a curved, non-planar configuration. As mentioned previously, the seal and/or seal mount (e.g. piston  2920 ) may have a variable longitudinal length along its perimeter. In some instances, an increased longitudinal dimension may provide additional stability to the seal along a dimension of the seal. In some examples, the side length along a section of the perimeter of the piston  2920  may be related to the transverse dimension intersecting a) that side length of the perimeter and b) the central movement axis of the seal and/or piston. In the example in  FIG. 29A , the lateral longitudinal surface of the piston  2920  may have a longitudinal length  2932 , based upon the increased width  2934  of the piston  2920  relative to the height  2936  of the suction chamber  2210  (corresponding to the increased width and reduced height of the suction chamber  2210 ). In comparison, the superior longitudinal surface of the piston  2920  may have a longitudinal length  2938  that is smaller than the longitudinal length  2932  of the lateral longitudinal surface from the reduced height  2936  of the piston  2920 . 
     Referring to  FIGS. 29A, 29B and 30 , the piston  2920  may also comprise a central opening  2940  which may be aligned with the central opening  2824  of spring carrier  2820 . The piston central opening  2940  may be configured to provide passage of the distal ends of the constant force springs.  FIG. 29C  provides a frontal elevational view of the piston  2920 . The distal regions  2952  of the constant force springs  2950  (depicted only in  FIG. 30 ) may extend through the central opening  2940  and are coupled to a pair of spring retaining structures  2942  disposed on the front surface of piston  2920 . In this particular embodiment, the retaining structures  2942  are configured to be inserted into apertures provided on the springs and may or may not maintain their coupling using residual spring force that may be present in the springs in the retracted configuration. The retaining structure and the springs may have any of a variety of other coupling configurations, however (e.g. the retaining structures may comprise posts which block displacement of T-shaped spring ends). Between the central opening  2940  and the retaining structures  2942  are curved support surfaces  2944  which are configured to push against the springs. In some examples, the length of the curved support surfaces  2944  between the central opening  2940  and the retaining structures  2930  may be at least one or one and a half times the width of the springs, while in other examples may be two or three times or four times the width of the springs. In some examples, the curved support surfaces  2944  provide a substantial surface area to distribute the pushing forces and may reduce the risk of damage to the springs. Referring back to  FIG. 29A , the piston  2920  may further comprise convex supports  2946  adjacent to the central opening  2940 , which may also support the springs as the springs converge into the central opening  2940 . The convex supports  2946  may have a curved length of at least about the width of the springs, but in other examples may be at least two or three times the width of the springs. Referring to  FIGS. 29A and 30 , the convex supports  2926  may also comprise a concave region  2948 , which may accommodate the coils of the spring and the spring carriers  2830  when the sliding seal assembly  2260  is in a retracted configuration. Although the sliding seal assembly  2260  and the spring assembly  2270  depicted in  FIGS. 28A to 29B  utilized two springs, in other examples, one spring, three springs, four springs, or five or more springs may be used. The number of springs, the type of springs, and the width and length of the springs may be varied, and in other examples, non-spring bias members may be used (e.g. sealed pneumatic shocks). 
       FIGS. 31A to 31C  schematically illustrate one example of a priming procedure of the suction device  2200  with a activation tool  2290  from  FIGS. 23A and 23B , where the springs have not been shown to better illustrate the interactions between the sliding seal assembly  2260 , spring assembly  2270  and the activation tool  2290 . The activation tool  2290  comprises a tool shaft  3100  with a distal recess  3110  and a proximal recess  3120  on each side of the shaft  3100 . Located between the recesses  3110  and  3120  is a non-recessed portion  3112  of the shaft  3100 . The distal end  3130  of the activation tool  2290  is has a cross sectional shape and size that is able to pass through the central opening  2824  of the spring assembly  2270  to contact the piston  2920  of the sliding seal assembly  2260 . During the priming procedure, the activation tool  2290  may be pushed against the piston  2920  but is not configured to couple or attach to the piston  2920 . In other embodiments, however, the distal end  3130  of the activation tool  2290  and the piston  2920  may be configured to form a complementary interlocking fit or interference fit. Before priming, the springs will pull and maintain the sliding seal assembly  2260  into a proximal or retracted position against the spring assembly  2270 . As the activation tool  2290  is inserted into the suction device, the resilient tabs  2822  on the spring assembly  2270  will slidably engage the distal recess  3110  on the tool shaft  3100 . As the activation tool  2290  is further inserted, the user may receive tactile feedback of increased resistance as the tabs  2822  are resiliently displaced out of the distal recesses  3110 . Further insertion may provide additional tactile feedback from increased frictional resistance by the tabs  2822  against the non-recessed portion  3112  of the shaft  3100 . As the activation tool  2290  is further inserted, the sliding seal assembly  2260  is separated from the spring assembly  2270  and the constant force springs or bias members attaching the assemblies  2260  and  2270  will elongate and generate potential energy. As sliding seal assembly  2260  is further displaced distally, the tabs  2822  will then engage the proximal recess  3120  on the prime tool shaft  3100 . The position and length of the of the non-recessed portion  3112  and the recesses  3110  and  3120  of the shaft  3100  may be configured to provide the user with tactile feedback indication, or may be provided to resist ejection of the activation tool  2290  out of the suction device. For example, if the wound or fluid communication to the wound is incompletely sealed, or if there is an excessive volume of air or exudates the wound, upon activation of the suction device, the sliding seal assembly  2260  may retract suddenly. The non-recessed portion  3112  of the activation tool  2290  may provide at least partial retention of the tool  2290  so that the user can reprime the suction device. The recesses  3110  and  3120  may be configured with ramped proximal and distal surfaces movement of the tabs  2822  in and out of the recesses  3110  and  3120 . 
     Upon full priming of the suction device, latches  3140  located on the prime tool shaft  3100  may engage the interlocking structures  2823  on the spring assembly  2270  to locks the activation tool  2290  into place, as depicted in  FIG. 31C . The activation tool  2290  may be left in the locked configuration in the suction device, and may even be stored and/or distributed in a primed position. The locking mechanism also permits the suction device to be primed without requiring that the suction device be already coupled to the sealant layer. Thus, the user need not be concerned about uncoupling the suction device or unsealing the sealant layer during the priming procedure, and may handle or orient the suction device in any manner, e.g. abutting the connector surface of the suction device against a table or wall to provide leverage when pushing the priming tool. 
     To activate the primed suction device, the user may depress the release buttons  3150  located at the proximal end of the prime tool  2290 . Pressing the release buttons  3150  disengage the latches disengages latches  3140  from the interlocking structures  2823 , thereby permitting the removal of the activation tool  2290  out of the suction chamber. The release buttons  3150  may also comprise one or more textured gripping structures or materials to facilitate latch release. Although the embodiment depicts in  FIGS. 31A to 31C  comprises a activation tool  2290  with two latches  3140  and two release buttons  3150 , in other embodiments, a different number latches and/or buttons may be provided, or a different configuration of a locking mechanism may be provided (e.g. a locking pin that may be inserted and removed by the user). 
     As described previously, once the activation tool  2290  is proximally withdrawn, the sliding seal assembly will be retracted by the charged constant force springs. Such movement will expand the combined volume of the space below the sliding seal assembly and the sealed wound enclosure, and reduce the pressure level therein. Where there has been an inadvertent leak in the system or excessive air or exudates in the wound, the activation tool  2290  may be used to reprime the device. In these embodiments, the method for using the suction device may further comprise resealing the wound and/or reseating one or more connectors of the reduced pressure therapy device, and repositioning the slidable seal or sliding seal assembly to the extended or primed position and reactivating the device. 
     In some embodiments, the method of treating an area of damaged tissue may comprise affixing a sealant layer around an area of tissue to be treated; creating a sealed enclosure around the area of the tissue with the sealant layer, inserting a collection chamber into a housing chamber and priming the collection chamber; creating a fluid communication between the collection chamber and the sealed wound enclosure; activating the collection chamber to create a reduced pressure level within the sealed wound enclosure; if the collection chamber is filled up with wound exudates, terminating the fluid communication between the collection chamber and the wound seal and releasing the collection chamber from the wound site; withdrawing the collection chamber from the housing chamber and replacing it with a new collection chamber; and repeating the steps as appropriate to continue a reduced pressure treatment. 
     Example 1 
     Reduced Variation in Pressure with High Viscosity Lubricant 
     In this example, the use of a high-viscosity liquid lubricant is shown to reduce pressure fluctuations in the suction device with a simulated leak. 
     Cartridge A: A suction device (SNaP suction device), wherein a non-optimized lubricant (fluorosilicone; 100,000 cP) was used to reduce friction between the seal and inner surface of the suction chamber was primed. A simulated air leak of 3 cc/hour was introduced into the apparatus. A total of 50 cc of air was allowed into the suction chamber over a period of about 16.7 hours. The pressure was measured over the duration of the experiment. 
     Cartridge B: The same conditions described above were applied to a different suction device, wherein a lubricant of a higher viscosity (20:80 fluorosilicone/dimethylsilicone, 1,500,000 cP) was employed. 
       FIGS. 21 and 22  show the plots of the pressure over time for each of the apparatuses, respectively. 
     The pressure variation of cartridge A results in a saw tooth wave. The magnitude of peak-to-peak amplitude appears to range from about 15 to over 25 mmHg, with the majority of peak-to-peak difference of over 20 mmHg. In contrast, the peak-to-peak amplitude is significantly reduced in cartridge B at the observed resolution, resulting in a smoother line. Although there is overall variations in pressure, the peak-to-peak amplitude appears to be less than or close to 1 mmHg. Thus, the higher viscosity lubricant in cartridge B was more effective in reducing the frictional resistance of the sealing surfaces (the surface of the seal lips in contact with the chamber wall surfaces), resulting in a reduced pressure that is characterized by a tighter, narrower tolerance. 
     Example 2 
     Seal to Seal Mount Configuration 
     This example provides a description of a free-floating sliding seal that can accommodate radial compression from narrowing of the inner diameter of the chamber.  FIG. 23  is a cross-sectional view of a seal assembly positioned within the suction chamber. The elastomer seal is supported by a seal mount. A gap exists between the portion of the seal closer to the chamber wall and structures of the seal mount. As the inner dimensions of the chamber narrows, the walls of the chamber applies a force to the contact areas of the sliding seal, which in turn are displaced into the small gap. The gap, therefore, absorbs deformation of the sliding seal and any increase in frictional resistance between the seal lips and the chamber wall is reduced. If instead the design incorporated a line-to-line fit between the sliding seal inner surface and seal mount, upon narrowing of the chamber, the seal lips would exert a force against the chamber wall and the frictional force would increase. 
     Example 3 
     Modified Bushing-Spring Assembly 
     This example describes a modified bushing design which reduces rotational resistance variations in the spring. 
     Another factor which hinders the ability to deliver constant pressure throughout the length of the seal travel relates to the construction of the springs. Ribbon springs are constructed from thin strips of metal, such as 301 Stainless steel, which are coiled tightly. The springs extend by unwinding, and as they are unwound, their coiled state provides resistance. Because the local geometry at the point of unwinding remains relatively unchanged regardless of the length of spring that has been unwound, the resistance, and therefore force, remains constant. If, on the other hand, the local geometry was disturbed, the resistance of the spring and subsequently the force it exerts changes. 
     Because of the coiled construction of the ribbon spring, there will always be one end of the spring which will be present on the inside diameter of the coil. The unwinding, and therefore extension of the springs causes rotational motion of the coil, which can be modulated by a radial bushing or bearing surface. The load of the spring is born by the upper half of the bearing surface, regardless of the rotational position of the spring coil. As the spring coil rotates, at some point the interior end of the ribbon spring will transition from the non load-bearing area to the load-bearing area. Because of the additional thickness of the spring end, subsequent layers of spring on top of the spring end are slightly deformed. Thus, the local geometry in that region is different from the other points around the circumference of the coiled spring. The slight deformation results in additional resistance to rotation at the transition point, resulting in a drop in the force exerted and a reduction of negative pressure in the system. The drop in negative pressure corresponds to a trough observed in  FIG. 22  as well as in  FIG. 24A  around 300 minutes. 
     The additional resistance of rotation when the interior spring end transitions from non-load bearing to the load-bearing area can be mitigated by reducing or eliminating the thickness introduced by the interior spring end. The exterior diameter of a bushing is configured with an indentation which accepts the interior end of the springs. This indentation can be a notch, cut-out or other depression which accommodates the thickness of the spring end. As the interior end of the springs reaches the transition point from non-load bearing area to load-bearing area, no additional thickness is introduced because the spring end surface is flush with the bushing surface, and the force trough is mitigated. 
       FIG. 24B  and is a perspective drawing of a bushing  2400 . The indentation  2402  has a depth corresponding to approximately the thickness of the spring.  FIG. 24C  shows a cross sectional view of the bushing  2400  mounted on the vertical rails  2812  of the spring retainer  2810  in  FIG. 28A , for example. The section of the bushing  2400  shown has an indentation  2402 , the depth of the indentation  2402  corresponds to the thickness of the spring ribbon  2404 , which is the darkened area, such that the top surface  2406  of the ribbon  2404  is approximately flush with the adjacent outer surface  2408  of the bushing  2400 . 
     Example 4 
     Comparison of Lubricant Performance in Suction Device 
     This example compares the difference in pressure performance of different viscosity lubricants in a suction device with and without introduced leaks. 
       FIG. 32  is a graph which shows the plots the pressure exerted by the suction device against a time period of over 4 days without any leaks into the system. The top two traces represent units that are lubricated with a 20/80% fluorosilicone/dimethyl silicone mixture having a viscosity of 1,500,000 cP (e.g., a 20 Mol. % fluorosilicone fluid from Nusil Technologies, Carpinteria, CSM-420-7). The bottom traces, shows the unit employing a lubricant having a viscosity of 100,000 cP. 
     A constant pressure of about 100 mmHg is maintained in the apparatuses employing the higher viscosity lubricant. The effect of the lower viscosity lubricant results in over a 10 mmHg reduction in the average pressure. 
     Example 5 
     Biohazard Containment Assembly 
     This example describes a biohazard containment assembly capable of retaining exudates that enter the suction chamber. In one embodiment, the assembly is positioned in the distal region of the interior of the suction chamber.  FIGS. 33A and 33B  are schematic illustrations of a sealed liquid permeable pouch  3300  containing superabsorbent materials with front-side and rear-side views shown respectively. The pouch  3300  may manufactured using a single layer of material that is folded over itself and sealed at its side seams  3302  and  3304  and end seam  3306 . Of course, the pouch may also be manufactured using multiple layers or materials sealed together, and in some variations, different materials may be used and/or materials of different shapes may be fused to together. Also, multi-laminate materials may be used in one or regions of the pouch or container. The seals of the pouch, and/or the walls of the pouch, may be configured to rupture, tear or separate as the pouch contents expand with liquid contact. To resist contamination or issues relating to dispersal of the pouch contents into the suction device, the pouch may be placed in a containment bag of sufficient size to accept the expanded superabsorbent pouch material.  FIG. 34A  is an illustration of a layer  3402  of a bag with an opening  3404  cut out or otherwise formed in the layer  3402 , wherein the area of the opening  3404  is smaller than the profile of the pouch.  FIG. 34B  is an illustration of front-side of the liquid-permeable pouch  3300  placed over the opening of the layer  3402  of the bag and secured in place (e.g. using an adhesive, head melting, stitching, or combinations thereof).  FIG. 34C  is an illustration of a second layer  3406  of the bag  3400  positioned over the first layer  3402  and the pouch  3300 . The first and second layers  3402  and  3406  are sealed to each other around the perimeter  3408  of the bag  3400 . In  FIG. 34C , the second layer  3406  is schematically depicted as slightly smaller than the first layer  3402 , but in other examples the second layer may have the same size and/or shape as the first layer, or may be larger and/or have a different shape than the first layer. The containment bag may also be prefabricated with an opening cut out and one or more sides sealed prior to assembly of the superabsorbent pouch into the containment bag.  FIG. 35  is a superior elevational photograph of the liquid-permeable pouch sandwiched between two layers that are sealed together around the perimeter of the bag. The back surface of the pouch is oriented superiorly, while the front surface of the pouch is exposed to the opening bag layer, which is oriented inferiorly. 
     Some variations of a reduced pressure therapy system may be configured to remove and store exudates located at the treatment site. Exudates are typically body fluids or mixed fluids and other cellular matter. In some variations, the device may be configured with a fluid retention mechanism to resist or prevent leakage of the exudates that have been suctioned into the suction chamber. For example, some fluid retention mechanisms may be configured to sequester exudates within a certain portion of the suction device, regardless of the orientation of the suction device. This may help to reduce the risk of contamination to users or healthcare personnel and their surroundings during use and/or disposal. In some variations, the fluid retention mechanism may be configured to prevent exudates that have been drawn into the suction device from flowing out of the suction device. For example, a fluid retention mechanism may be configured to allow exudates to flow in one direction (e.g., into the suction device), but not in the opposite direction (e.g., out of the suction device). In some variations, a suction device may have a fluid retention assembly in its suction chamber, where the fluid retention assembly may comprise an absorbent material so that when the exudates come into contact with the absorbent material, it is absorbed by the material and retained and/or sequestered within the suction chamber. Optionally, the fluid retention assembly may also comprise a screen or mesh that may be used to sequester the absorbent material in a certain portion of the suction chamber. The screen or mesh may also help to prevent the absorbent material from moving around and/or exiting the suction chamber, and in some variations, may also help to prevent exudates collected in the suction chamber from exiting the chamber through the distal port or inlet. While some suction devices may have one or more fluid retention assemblies, some suction devices may not. 
     Absorbent materials that may be used in a fluid retention assembly may be selected according to the expected viscosity (or other liquid characteristic) and/or quantity of the exudates. Certain absorbent materials may also be selected based on the desired absorption capacity. The absorption capacity of the material may be maintained under negative and/or positive pressure conditions. Some variations of an absorption material may hygroscopic, and may be able to absorb vapor. The fluid absorption material may be permeable to air, such that the negative pressure generated by the suction device may be conveyed to the wound without substantial hindrance. Suitable absorbent materials may be selected from natural, synthetic, and modified natural polymers and materials. Absorbent materials may be inorganic or organic materials, such as sodium acrylic-based polymers, silica gels, cross-linked polymers, etc. Other examples of absorbent materials may include gauze, pulp, sponges, foams, desiccated hydrogels, and cross-linked polyprotic resins. Suitable absorbent materials may be available from various commercial vendors, such as Dow Chemical Company located in Midland, Mich., U.S.A., and Stockhausen GmbH &amp; Co. KG, D-47805 Krefeld, Federal Republic of Germany. Other examples of absorbent materials may include starch-acrylonitrile co-polymers, carboxy methyl cellulose (CMC), acrylic acid, polyvinyl alcohol (PVA) and isobutylene maleic anhydride (IMA), as well as various foams, including XTRASORB™. Some variations of a fluid retention assembly may use a superabsorbent material, which may be capable of retaining an amount of water equal to at least 100% of its dry weight (e.g., as measured by the test of Intrinsic Absorbent Capacity). As used herein, “absorbent capacity” refers to the total mass of water that a specified quantity of absorbent material can hold, and is simply the Intrinsic Absorbent Capacity multiplied by the dry mass of the absorbent material. Thus 10 g of material having an Intrinsic Absorbent Capacity of 5 has an absorbent capacity of 50 g (or 50 ml of fluid). For example, a superabsorbent material may have an Intrinsic Absorbent Capacity of at 1 or greater. The ability for a material to absorb a relatively large amount of liquid compared to its own weight permits a larger capacity of liquid to be contained in the suction chamber than the same amount of material having a lower absorbance capacity. In some of the foregoing embodiments, the superabsorbent material may be Isolyser™ by Microtek Medical. Other examples of absorbent materials that may be used with a fluid retention assembly for a suction device may include sodium polyacrylate with sodium dichloro-S-triazinetrione dihydrate, cellulose based substrates, AQUA KEEP® polymer products, etc. More generally, the absorbent materials used in the absorbent members of the present disclosure may have an Intrinsic Absorbent Capacity of 2 or greater. In some embodiments the intrinsic absorbent capacity is 4 or greater. In some embodiments the intrinsic absorbent capacity is 7 or greater. In some embodiments the intrinsic absorbent capacity is 10 or greater. In some embodiments the intrinsic absorbent capacity is 3 to 30. In some embodiments the intrinsic absorbent capacity is 4 to 25. In some embodiments the intrinsic absorbent capacity is 12 to 40. 
     In some variations, the fluid absorbent material may have a first non-hydrated state and a second hydrated state, where in the non-hydrated state the absorbent material may occupy a smaller volume than when in the hydrated state. For example, the absorbent material may expand as it absorbs fluids and transitions from the non-hydrated to hydrated configuration. In some variations, the absorbent material in the non-hydrated state may be powder-like, and in the hydrated state, the absorbent material may be gel-like, or may be a solid or a semi-solid. In other variations, the absorbent material may be a planar sheet or pad that thickens or expands as it absorbs fluid. The fluid absorbent material may be a porous material (e.g. a sponge, foam, textile, etc), and may be a planar or three dimensional porous matrix. An absorbent material that is a planar pad may have a first thickness in the non-hydrated state, and a second thickness in the hydrated state, where the second thickness is greater than the first thickness. Alternatively or additionally, the absorbent material may comprise loose components such as pellets, spheres, granules, clusters, powder, and the like. The particle sizes may range from about 20 μm to about 500 μm, for example, about 20 μm to 30 μm, or about 200 μm to 300 μm, or about 350 μm to 390 μm in the non-hydrated state. The absorbent material may also take the form of a collapsed woven material, such as a textile, or compressed polymer or sponge or porous matrix in its non-hydrated state. In the expanded hydrated state, the absorbent material may expand, and may be enlarged pellets or clusters, an expanded textile or sponge or porous matrix. In some cases, the absorbent material in the hydrated state may be a solid, a semi-solid, or a gel. Some variations of absorbent materials may decompose as it absorbs fluids. In some examples, the fluid absorbent material may be a volume neutral material, wherein the total volume of the separate fluid and separate absorbent material is approximately the same volume of the fluid and absorbent material when intermixed. For example, the separated total volumes and the intermixed volume may be equal, or at least within 5% or 10% of each other. In other examples, the fluid absorbent material may be a volume increasing material, wherein the intermixed volume is at least 15% or 25% or more than the total separated volumes. 
     The amount of absorbent material that is provided in the suction chamber may be limited by the dimensions of the collection chamber of a charged suction device. Thus, when the seal is moved to the distal end of the chamber, it reduces the volume of space available in the suction chamber. In some embodiments, the absorbent material may occupy a volume of less than about 10 cc, about 5 cc or about 4 cc. In some embodiments, the biohazard containment assembly occupies a volume of less than 5 cc. In some embodiments, the biohazard containment assembly occupies a volume of less than 4 cc. In other embodiments, the volume of the absorbent material may be characterized by the maximum volume of the chamber in which it resides. For example, the absorbent material may less than about 25%, about 20%, about 15%, or about 10% of the chamber volume. In some embodiments, the amount of absorbent material may be between 0.5 g to 4 g. In some embodiments, the amount of absorbent material may be between 0.5 g to 2.5 g. In some embodiments, the amount of absorbent material may be between 0.5 g to 1.75 g. In some embodiments, the amount of absorbent material may be about 1.5 g. In some embodiments, the amount of absorbent material may be at least 1 g. In some embodiments, the amount of absorbent material may be at most 2 g. In some embodiments, the amount of absorbent material may be at most 3 g. In some embodiments, the amount of absorbent material may be at most 4 g. 
     Optionally, some variations of a fluid retention assembly may comprise a disinfectant, which may help to sanitize exudates that enter the collection chamber. For example, the disinfectant may be attached to, bonded to, embedded in, cross-linked with and/or otherwise incorporated with the absorbent material. In other examples, the disinfectant may be freely disposed within the collection chamber, or may be attached to other structures, such as the slidable seal assembly. The disinfectant may be anti-bacterial (e.g. bacteriostatic or bacteriocidal), anti-viral, anti-fungal, and/or anti-parasitic. Some examples of disinfectant compounds that may be used in a fluid retention system may include chlorhexidine, sodium hypochlorite, sodium dichloro-s-triazinetrione dehydrate (or other chlorine-based disinfectant), a sulfonamide, silver sulfadiazine, polyhexanide. In some variations, the absorbent material itself may also act as a disinfectant. For example, a fluid retention assembly may use a liquid medical waste solidifier, such as Isolyser LTS-Plus® Solidifier or Isosorb® Solidifier by Microtek Medical. Optionally, the fluid retention assembly may also comprise a deodorizer, such as zeolite, activated charcoal, silica gel, or hydrogen peroxide. In some variations, the disinfectant treat the collected exudates such that the expended device may be disposed as regular trash, rather than as biohazardous waste. 
     A fluid retention assembly may be installed in the suction chamber of a suction device in a variety of configurations. Fluid retention assemblies may comprise an absorbent material that may be sequestered in a portion of the suction chamber, temporarily or permanently. For example, a fluid retention assembly may comprise an absorbent pad or sheet that may be attached to the walls of the suction chamber so that it does not move within the suction chamber as the suction device changes orientation. Alternatively or additionally, a fluid retention assembly may comprise a screen (e.g., a mesh, filter, etc.) that may be attached at a distal portion of the suction chamber. For example, the screen may be attached within the distal portion of the suction chamber, just proximal to a distal portion leading to the distal port of the suction device. In some fluid retention assemblies, the absorbent material may be retained by a carrier structure, e.g. bonded to a surface of a supporting sheet or other structure, or enclosed in a pouch or other container. The pouch may freely move within the suction chamber, or may be attached to any desired region of suction chamber such that it remains at the desired region despite any changes in the orientation of the suction device. A fluid retention assembly may comprise a combination of one or more of the above described components, as may be desirable. For example, a fluid retention assembly may comprise absorbent materials enclosed in a pouch, where the pouch is sequestered to a portion of the suction chamber by one or more screens. A fluid retention assembly may comprise an absorbent pad or sheet that may be temporarily or permanently secured within the suction chamber using adhesives and/or one or more screens. Various examples of fluid retention assemblies are described below. 
     In some variations, the absorbent material of a fluid retention assembly may be retained by a carrier structure, such as a pouch. In some variations, the absorbent material may be enclosed in an internal pouch made of a semi-permeable membrane. This internal pouch may help to prevent the fluid absorption material from obstructing or clogging the various valve and/or conduits of the suction device. A pouch  1804  may be temporarily or permanently attached to any portion of the suction device, for example, in a distal portion of a suction chamber  1800  (toward the distal port  1802 ), as depicted in  FIG. 18A . In some variations, the pouch may be located adjacent to the internal opening of the distal port  1802 . The absorbent material may be surrounded by and enclosed in a liquid permeable membrane to form an absorbent bag. The membrane may be a mesh, filter, screen, molecular sieve, and the like. Non-limiting examples of suitable materials for the liquid permeable membrane may include woven and nonwoven polyester, polypropylene, nylon, rayon or the like, particularly in the form of formed or apertured thermoplastic films, including those described in U.S. Pat. No. 4,324,246 issued to Mullane and Smith on Apr. 13, 1982 and U.S. Pat. No. 4,342,314 issued to Radel and Thompson on Aug. 3, 1982. Other known semi-permeable membrane materials can be employed, including those made from textured cellulosic basesheets with hydrophobic matter added to selected portions of the basesheet, particularly the most elevated portions of the basesheet, as described in commonly owned copending U.S. application, “Dual-zoned Absorbent Webs”, Ser. No. 08/997,287, filed Dec. 22, 1997. In some of the foregoing embodiments, an outer surface of the liquid permeable membrane may be treated with a surfactant to improve liquid penetration, and may have gradients in wettability created having different chemical treatments on the two surfaces of the topsheet, such that fluid is preferentially absorbed in targeted intake regions and repelled by other regions. In some of the foregoing embodiments, the liquid permeable membrane may comprise at least one seam wherein at least two sections of the membrane are joined together. In some embodiments, the expansion of the absorbent material within the liquid permeable membrane may result in the rupture of the liquid-permeable membrane. In certain embodiments, the absorbent material may be expelled upon rupture of at least one seam of the liquid-permeable membrane. 
     In some of the foregoing embodiments, at least a portion of the liquid permeable layer is enclosed in a secondary enclosure, such as a plastic bag. In some of the foregoing embodiments, expansion of the superabsorbent material ruptures the liquid-permeable layer and is expelled into the secondary enclosure. The secondary enclosure prevents the superabsorbent material from contacting the interior surfaces of the suction chamber. The secondary enclosure is designed to permit liquid to enter the liquid permeable layer. 
     In some of the foregoing embodiments, a semi-permeable membrane of a fluid retention assembly may contain the absorbent material and help to isolate the material from contacting the suction device. The semi-permeable membrane may allow fluids to cross the membrane in one direction, but not in the other direction. For example, a semi-permeable membrane pouch containing absorbent material inside may allow exudates to be drawn by the absorbent material into the pouch, while the semi-permeable membrane prevents the exudates from flowing out of the pouch. The membrane may be permeable to air, as may be desirable. In some variations, a fluid retention assembly may comprise a pouch made of a fluid impermeable material that is directly connected to the distal portion of the suction device. Negative pressure may be generated in the pouch and conveyed to the tissue site. Any exudates collected by the pouch during reduced pressure therapy may be retained such that exudates do not contact the walls of the suction chamber. When the suction device is depleted, the pouch may be removed from the suction device and discarded. 
     Optionally, some variations of a fluid retention assembly may comprise a screen or mesh positioned near the distal end of the suction chamber to retain the absorption material within a certain region of the suction device. The screen or mesh may prevent or resist the extrusion or release of the absorbent material from the suction chamber, which may occur during patient movement and/or recharging of the device. For example, a screen or mesh may be semi-permeable, which may allow exudates to be collected in a suction chamber, but may prevent the exudates from exiting the distal port of the suction chamber. In some variations, the screen or mesh may be air and fluid permeable, but not fluid absorbent.  FIG. 18B  schematically depicts a suction chamber  1800  with a distal port  1802 , and a screen  1806  proximal to the distal port  1802 . In some variations, a fluid retention assembly may comprise a plurality of screens or meshes, arranged such that the absorbent material is constrained between two screens. In some variations, the screen or mesh may block movement of particles of a certain size and/or liquid or semi-solid of a certain viscosity, while allowing smaller particles and liquids to pass therethrough. The screen or mesh may be provided over the distal portion of the suction chamber, for example, the screen may be attached over a distal valve of the suction device leading to the tissue treatment area. Suction devices that use an absorbent material that has discrete components in its non-hydrated state, such as powder, pellets, loosely associated particles, may have such a screen or mesh to help prevent the material from exiting the suction chamber. 
     The screen or mesh may have a sieve size large enough to permit the fluid exchange of liquid and air through the mesh, but small enough to not allow solids or semi-solids to pass through. The mesh may have two sides, a proximal and a distal side. The proximal side faces the sliding seal assembly while the distal side faces the distal end of the chamber. In some embodiments, the sieve size of the mesh may be less than 5 mm. In some embodiments, the sieve size of the mesh may be less than 2 mm. In some embodiments, the sieve size of the mesh may be less than 1 mm. In some embodiments, the sieve size of the mesh may be less than 0.5 mm. In some embodiments, the sieve size of the mesh may be less than 10 mm. The mesh may comprise any of a variety of materials, including a metal (e.g. steel, copper), a ceramic, or a plastic (e.g. polypropylene, polyethylene, polyester, polyamide or other thermoplastic. 
     Some fluid retention assemblies may use a screen or mesh made of a woven or a fibrous material. For example, the screen may be made from random-laid fibers (e.g., from wood pulp) using water or air to transfer the fibers. After the fibers have been air or liquid laid, synthetic resin bonding agents may be applied to the pulp web using a spray process. Meshes that may be used in a fluid retention assembly may be made of Airtex® airlaid fabrics, which may be obtained from Georgia-Pacific (Neenah, Wis.). 
     Other variations of fluid retention assemblies may comprise an absorbent material that has a self-contained form (e.g., a porous matrix, sponge, gauze, pad, foam, etc.). The absorbent material may be permeable to air, as may be desirable. In some examples, the absorbent material may be woven or non-woven sponges or gauze, and/or may be made of a porous material. In some variations, the absorbent material may be permeable to air, as may be desirable. The absorbent material may be made of any of the materials previously described. In some variations, the absorbent material may be retained by a carrier structure. For example, the absorbent material may be immobilized in a substrate (e.g., impregnated or woven into a matrix, adsorbed to a porous matrix, etc.). In some variations, the absorbent material may be bonded to the carrier structure and/or integrated with the substrate matrix. The absorbent material may or may not be sterile. Fluid retention assemblies comprising such absorbent materials may or may not include a screen or mesh to prevent movement of the absorbent material as the suction device changes orientation. An absorbent material, e.g., an absorbent pad  1808 , may be temporarily or permanently attached at any desirable portion of the suction device, for example, at a distal portion of the suction chamber  1800 , as depicted in  FIG. 18C . The self-contained absorbent material may be retained in the suction chamber by adhesion, friction fit, and the like, and/or may conform to the cross-sectional geometry of the suction chamber (e.g., form fit). 
     Fluid retention assemblies may comprise any combination of the features described above. For example, a fluid retention assembly may comprise a screen  1812  attached at a distal portion of the suction chamber  1800  (e.g., covering the distal port  1802 ) and a pouch  1810  comprising an absorbent material enclosed in a semi-permeable membrane, as depicted in  FIG. 18D . The screen  1812  may have a smaller cross-sectional area than that of the suction chamber  1800 . In other variations, a fluid retention assembly may comprise a screen  1816  attached at a distal portion of the suction chamber  1800  just proximal to the distal port  1802  and a porous matrix  1814  attached to the walls of the suction chamber  1800 , just proximal to the screen, as illustrated in  FIG. 18E . The screen  1816  may have a similarly sized cross-sectional area as compared to the suction chamber  1800 . In still other variations, a fluid retention assembly may comprise a porous matrix attached to the side walls of the suction chamber at a distal portion of the chamber, and a pouch comprising an absorbent material enclosed in a semi-permeable membrane proximal to the porous matrix. Alternatively, the porous matrix may be located proximal to the absorbent pouch. The components of the fluid retention assemblies described here may be arranged in any order, as may be suitable (e.g., the pouch or porous matrix may be distal to the screen). While retention assemblies comprising a single screen or filter have been described here, in some variations, there may be more than one screen. Additional screens may be helpful for sequestering the absorbent material in one or more selected regions of the suction chamber, and may provide for additional filtration of exudates, as may be desired. 
     One example of a suction device with a fluid retention assembly is depicted in  FIGS. 16A and 16B . Suction device  1600  may have a fluid retention assembly comprising a pouch  1602  configured to retain a fluid absorbent material, an air and liquid-permeable screen or mesh  1604  between the pouch  1602  and a distal port  1607 , and optionally one or more adhesive tabs  1606  to attach the pouch  1602  to the mesh, and/or to attach the mesh  1604  to the distal portion of the suction chamber  1605 . The pouch  1602  may comprise a semi-permeable membrane (e.g., an air and liquid permeable membrane) so that the absorbent material in the pouch may draw exudates into the pouch. In some variations, the semi-permeable membrane may be configured to help reduce leakage of exudates out of the pouch. The absorbent material in the pouch may be any of the materials previously described. The pouch and mesh may or may not have a shape that corresponds to the cross-sectional shape of the suction device (e.g., the cross-section of the suction chamber).  FIG. 16B  depicts an enlarged view of the pouch  1602 , which has an elliptical shape corresponding to the elliptical shape of the suction chamber  1605 . The pouch  1602  may comprise a sealed opening, or a perimeter seal  1603  between two layers of the pouch, which may help to retain the fluid absorbent material in the pouch prior to use. In some variations, upon absorption of a sufficient amount of fluid into the pouch, the sealed opening or the perimeter seal  1603  may be configured to open or separate, permitting expansion and/or release of the fluid absorption material into the rest of the suction chamber. In some other variations, the sealed opening or the perimeter seal  1603  may also be used to help temporarily or permanently secure the pouch  1602  to a location in the suction chamber, e.g., the proximal or distal side, so that the pouch  1602  does not move within the suction device chamber. Optionally, the fluid retention assembly may comprise additional meshes, which may be used to secure the pouch and/or to filter exudates. For example, an additional mesh may be provided on other proximal side of pouch  1602 , across from the mesh  1604 , where the two meshes may act to retain the pouch  1602  between them. Additional descriptions of suction devices and fluid absorption materials that may be used within a suction device are provided in U.S. Pat. Appl. No. 61/372,837, filed on Aug. 11, 2010, which is hereby incorporated by reference in its entirety. In some of the foregoing embodiments the pouch may be placed in the suction chamber in contact with the proximal side of the mesh in a way that permits air and liquid to fluidly exchange from one side of the mesh to the other. 
     Another example of a fluid retention assembly  1700  is depicted in  FIGS. 17A-17C . The fluid retention assembly  1700  may comprise an absorbent pad  1702  at a proximal location, a first adhesive layer  1704 , a mesh or screen  1706 , and a second adhesive layer  1708  at a distal location. The absorbent pad may be made of any of the absorbent materials described previously. The fluid retention assembly  1700  may be located towards a distal portion of the suction device, such that the absorbent pad  1702  faces the suction chamber, and the second adhesive layer faces the distal-most portion of the suction device. For example, the fluid retention assembly  1700  may be placed at a distal portion of the suction chamber, over the internal aperture of the distal port of the suction device. The first and second adhesive layers  1704 ,  1708  may be made of any suitable adhesive, such as pressure sensitive adhesives, and may have adhesive properties on both sides. The first adhesive layer  1704  may be used to attach the absorbent pad  1702  to the screen  1706 . The second adhesive layer  1706  may be used to attach the screen  1706  to a distal surface of the suction device. As depicted in the side view of  FIG. 17B , the second adhesive layer  1708  may optionally have an additional release liner layer  1707 , which may allow the fluid retention assembly  1700  to be manufactured separately from the suction device, and then subsequently attached to the device prior to use. The screen  1706  may be made from any air or liquid permeable material, such as the screen materials described above. 
     The second adhesive layer  1708  may have an aperture  1709  (and the first adhesive layer  1704  may have a corresponding aperture which is not shown). In some variations, the aperture  1709  may facilitate the flow of suction through the fluid retention assembly  1700 . In other variations, one or more adhesive structures or regions may be provided that need not attach the entire distal surface or entire perimeter of the fluid retention assembly to the suction chamber. The one or more adhesive structures may or may not be located over an opening of the suction chamber. As depicted in  FIG. 17C , the absorbent pad  1702  may also have an aperture  1710  that is aligned with the adhesive layer aperture  1709 . As shown in  FIG. 17D , the screen  1706  may not have an aperture, and therefore, the screen  1706  spans across the adhesive and absorbent pad apertures  1709 ,  1710 . However, since the screen may be made of an air and liquid permeable material, the negative pressure generated in the suction chamber may be conveyed to a distal wound bed. The mesh size of the screen  1706  may be selected such that particles larger than the mesh size may not pass between the wound and the suction chamber. For example, wound exudates with blood material that is substantially liquid may pass from the wound to the suction chamber, but after the blood has clotted in the suction chamber, it cannot pass from the chamber back to the wound bed. Optionally, one or more additional screens may be provided to provide additional filtration of exudates and/or to secure the absorbent pad  1702 , as may be desirable. For example, an additional screen may be provided on a proximal side of the absorbent pad  1702 , thereby retaining the absorbent between the additional screen and the screen  1706 . Other variations of a fluid retention assembly may not have any screens, which may allow for the exchange of materials between the wound bed and the suction chamber. 
     While some suction devices described herein may have fluid retention assemblies (e.g., biohazard containment assemblies), it should be understood that other variations of suction device may not have a fluid retention assembly. 
     Some variations of suction devices may comprise one or more indicators to inform a patient and/or practitioner when the device needs to be replaced (e.g., when the suction device is in a depleted state and no longer able to generate negative pressure). Visual indicators may be provided to indicate the state of the suction device, i.e., fully charged, at least partially charged or depleted, or fully depleted. Visual indicators may allow the position of the sliding seal assembly within the suction chamber to be readily identified. For example, the suction device may display a certain color to indicate that it is fully charged or at least partially charged or partially depleted, and a different color to indicate that it is fully depleted. In one variation, the sliding seal assembly may have a first portion that is colored green, and a second portion that is colored red. The suction chamber may comprise opaque and transparent portions that reveal certain portions of the sliding seal assembly as the suction device generates negative pressure. In some variations, the suction chamber may comprise an opaque material with one or more translucent or optically clear windows that may be used to view the location and/or colors of the sliding seal assembly within the suction chamber. For example, when the suction device is fully or partially charged, the green portion of the sliding seal assembly may be visible in an optically clear window, while the red portion is obscured by the opaque portion of the suction chamber. The green portion of the sliding seal assembly may allow a patient and/or practitioner to readily determine the depletion state of the suction device based on the location of the sliding seal assembly in the suction chamber. When the suction device is depleted and no longer able to generate any negative pressure, the red portion of the sliding seal assembly may become visible while the green portion may be obscured. In other variations, the sliding seal assembly may have additional colors to indicate intermediate levels of depletion. For example, the sliding seal assembly may have a first green portion, a second red portion, and a third yellow portion. The suction chamber may comprise opaque and transparent portions that reveal only the green portion of the sliding seal when the suction device is fully charged, only the yellow portion when the suction device is partially charged or partially depleted, and only the red portion when the suction device is fully depleted. Alternatively, the sliding seal assembly may have a single color or pattern that is readily visible through the suction chamber (e.g., having bright intensity, high contrast, highly noticeable visual attributes including contrasting edges, patterns, stripes, etc.). In some variations, the sliding seal assembly may have arrows or other symbols that may be used in combination with indicia on the suction chamber to indicate capacity of the device to generate negative pressure. Examples of suction devices with such visual indicators are described below. 
     Additionally or alternatively, certain variations of a suction device may comprise an alarm system to inform a patient and/or practitioner when the device needs to be recharged or replaced. For example, an alarm system may generate an alert to inform a patient and/or practitioner that a suction device is exhausted or nearly exhausted of its ability to provide negative pressure to a wound, and may prompt the patient to recharge the device, empty or replace the collection chamber, and/or replace the suction device. Once the suction device has been recharged, emptied, or replaced, the alert generated by the alarm system may be deactivated and/or reset. An alarm system may also provide confirmation to the patient and/or practitioner that the suction device has been properly initialized or charged. 
     In some examples, the alarm systems for use with a suction device may comprise a sensor mechanism and a notification mechanism. The sensor mechanism may directly or indirectly detect the capability of a suction device to continue to provide negative pressure, and may signal the notification mechanism to generate an alarm. For example, an alarm system may directly measure the pressure that is applied to the wound, while other sensor mechanisms detect indirect device configurations that are related to the pressure that is applied to the wound. Examples of sensor mechanisms that directly measure the pressure applied to the wound, and/or directly measure the capability of the suction device to provide negative pressure may include pressure transducers or gauges. Examples of sensor mechanisms that indirectly measure the pressure applied to the wound may include position detectors, proximity detectors, or mechanisms that are otherwise sensitive or responsive to the location of a slidable seal of the suction device. These may include, for example, linear encoders, rotary encoders, liquid sensors, volume sensors, and movement sensors, and the like. Some variations of sensor mechanisms may be configured to detect the configuration of the suction generating mechanism. For example, sensors may be used to measure the tension and/or coil state of the constant force springs of a suction mechanism. In some variations, sensor mechanisms may provide a binary output, i.e., indicating that the suction device is either charged or depleted, while in other variations, sensor mechanisms may provide a graded output, i.e., indicating that the suction device is 100%, 80%, 50%, 30%, 10%, 0%, charged or depleted. Examples of binary type sensor mechanisms may include a variety of switches, such as electrical or magnetic switches. Examples of graded type sensor mechanisms may include various encoders, such as linear or rotary encoders. 
     One or more types of notification mechanisms may be used in an alarm system for use with a suction device. Notification mechanisms may comprise visual alerts, audio alerts, electronic alerts, and/or tactile alerts. Examples of notification mechanisms may include LED activation, buzzers, tones, e-mail messages, text messages, vibratory mechanisms, etc. An alarm system may comprise a plurality of sensors, which may each drive one or more notification mechanisms. For example, an alarm system may comprise a first sensor to detect that the suction device is properly charged, where the first sensor is configured to trigger a first notification mechanism, e.g., LED activation. The alarm system may comprise a second sensor to detect that the suction device is depleted (or depleted beyond a pre-determined threshold), where the second sensor is configured to trigger a second notification mechanism, e.g., a buzzer. An alarm system may comprise any number of sensor mechanisms and/or notification mechanism as may be desirable to inform a patient and/or practitioner of the use and configuration of the suction device. 
     The components of an alarm system may be located on one or more components of a suction device, e.g. on the suction device, and/or may be located on a strap, clip or housing of an attachment device that may be used to attach the suction device to the patient. The location(s) of the alarm system components on the suction device and/or attachment device may be selected such that the components work in combination when the suction device is coupled to the attachment device. The alarm system may be integrated with the suction device and attachment device, or may be detachably coupled to the suction and attachment devices. In some cases, the location of the alarm system components may be determined in part by the location of the alarm system power source, as well as by the frequency with which the suction device or the attachment clip are replaced. For example, if the suction device is replaced more frequently than the attachment device, then it may be desirable for the reusable components of the alarm system (e.g., notification mechanism, sensor mechanism, battery pack, etc.) to be located on the attachment device. An alarm device may comprise an attachment device with an alarm system. Any alarm system components that may come in contact with body fluids may also be separated from the other components to prevent contamination of the other components. For example, portions of the sensor mechanism may contact exudates collected in the suction chamber, and may be segregated and/or detachable from the notification mechanism. In some variations, portions of both the sensor and the notification mechanisms may be located on the suction device and the attachment device. For example, alert component(s) of the notification mechanism may be located on the attachment device while a trigger component of the notification mechanism may be located on the suction device, where the trigger component activates the alert component when the suction device attains a certain configuration. In some variations, the sensor and/or notification mechanisms of an alarm system may be detachably coupled to the suction device and/or attachment device. This may allow the alarm system to be removed after the suction device is depleted. The alarm system may then be used with a new suction device (e.g., a charged suction device). The configuration of the alarm system and its arrangement with respect to the suction device and/or attachment device may be varied according to the needs of the patient and/or the practitioner. 
     Examples of alarm system mechanisms that may be used with a suction device for reduced pressure wound therapy are described below. While the components of the alarm system may be described in certain locations and configurations, it should be understood that the components may be in alternate locations and configurations as desired. 
     Some variations of alarm systems may comprise a magnetic sensor that is able to detect the position and/or location of a magnetic component. A magnetic component may itself generate a magnetic field, and/or may be any material that is capable of causing a detectable flux in a magnetic field (e.g., a wire carrying a changing an electric current), and/or may be any material that responds to the presence of a magnetic field (e.g., a ferromagnetic material). The movement and/or location of a magnetic component may activate a sensor by causing a potential difference in the sensor, which is known as the Hall effect. Magnetic sensors may comprise Hall effect detection elements that measure the potential difference caused by a moving magnet to determine the position of the magnet. The potential difference may indicate the precise location of the magnet with respect to the location of the magnetic sensor. One or more components of a suction device may comprise a magnetic component, and the position and/or location of the magnetic component may be detected by a magnetic sensor on the suction device or an alarm device. For example, a sliding seal assembly of a suction device may comprise a magnetic component, and a magnetic sensor on the alarm device may determine the location of the sliding seal assembly by detecting the location of the magnetic component. Alternatively, an alarm device may comprise one or more magnetic components at certain locations and the suction device may comprise a magnetic sensor. For example, an alarm device may comprise a magnetic component (e.g., along or embedded in an attachment clip or side wall), and a sliding seal assembly of a suction device may comprise a magnetic sensor. As the sliding seal assembly moves along the suction device, the sensor detects the location of the sliding seal assembly with respect to the magnetic components in alarm device. The position of the magnetic component relative to the sensor may be determined based on the magnetic characteristics of the magnetic component and a measured potential difference in a sensor caused by the movement of that magnetic component. The sensor voltage may be amplified and activate a notification mechanism on the alarm device to generate an alarm that informs the patient and/or practitioner of the status of the suction device. In some variations, the notification mechanism may comprise a thresholding function that converts an output from a graded type sensor into a binary alert, e.g., generating an alert only when the device is depleted past a certain threshold. 
     One variation of a suction device  200  with an alarm system using a magnetic sensor mechanism is depicted in  FIGS. 2A-2C . The suction device  200  is configured to be retained by an alarm device comprising a clip  210  and a strap (not shown). As depicted in  FIG. 2B , the sliding seal  202  of the suction device  200  may comprise a magnetic material  204 . One or more magnetic sensors  206  and  208  may be provided to detect the location of the sliding seal  202  using the magnetic material  204 . The location of the magnetic sensors  206  and  208  may be configured to facilitate detection of one or more states. For example, as illustrated in  FIG. 2B , the first magnetic sensor  206  may be located at a proximal portion  207  of the clip  210  to detect when the sliding seal  202  is in a retracted position, which is indicative of the exhaustion or near exhaustion of the suction device  200 . Another sensor  208  may be located in a distal portion  205  of the clip  210 , for example, to detect that the sliding seal  202  has been adequately displaced by the activation tool, e.g., during the mechanical charging process. The magnetic sensors  206 ,  208  may be configured to detect the presence of absence of the magnetic material  204 , and may be configured to provide a binary output to indicate the position of the magnetic material. Alternatively, the magnetic sensors  206 ,  208  may be configured to detect the proximity of the magnetic material  204 , and may be configured to provide a graded output to indicate the position and proximity of the magnetic material to the sensors. The power source for the magnetic sensors  206 ,  208  may be a battery embedded within the clip  210 . 
     Optionally, the suction device  200  may comprise a visual indicator such that a patient and/or practitioner can determine the depletion state of the suction device by visual inspection. For example, the sliding seal  202  may have a first region that is colored green and a second portion that is colored red. As illustrated in  FIG. 2A , the suction chamber  220  of the suction device  200  may comprise an opaque portion  222 , a first transparent portion  224 , and a second transparent portion  226 . The first transparent portion  224  may extend longitudinally from a distal portion to a proximal portion along the suction chamber  220 . The width of the first transparent portion  224  may be such that the green region of the sliding seal  202  is exposed, while the red region of the sliding seal is obscured by the opaque portion  222 . As the sliding seal  202  moves from a distal portion to a proximal portion of the suction chamber  220  (i.e., as the suction device transitions from a fully charged or partially charged state to a depleted state), the location of the green region as seen along the first transparent portion  224  may indicate the degree to which the suction device is depleted. When the suction device  200  is fully depleted, the sliding seal  202  may be co-localized with the second transparent portion  226 , such that the red region of the sliding seal is visible in the second transparent portion  226  while the green region of the sliding seal is obscured. As depicted in  FIG. 2A , the first transparent portion  224  may be longitudinally disposed with an oblong geometry and the second transparent portion  226  may be transversely disposed with a curved elongated geometry. However, it should be understood that the transparent portions may be located anywhere on the suction device and may have any size or shape as suitable for cooperating with the markings on the sliding seal to provide a visual indicator of the state of the suction device. Such a visual indicator mechanism may be used alone or in combination with any of the alarm systems described herein. 
     The output of an indicator or sensor mechanism may be used to generate an alert. In some variations, the output voltage of a magnetic sensor may be amplified in order to drive notification mechanisms and/or circuits. For example, the magnetic sensor may comprise a Hall effect sensing mechanism whose output voltage or current may be amplified to drive one or more notification mechanisms. Each magnetic sensor may activate independent notification mechanisms, and/or may signal a shared notification mechanism. As an example, the first magnetic sensor  206  may activate a first notification mechanism when the magnetic component  204  of the sliding seal  202  is located at or near the proximal portion  207  of the clip, and the second magnetic sensor  208  may activate a second notification mechanism that is distinct from the first notification mechanism when the sliding seal  202  is located at or near the proximal portion  207  of the clip. In some variations, the voltage outputs of the first and second magnetic sensors  206  and  208  may be inputs to a logic circuit that computes the location of the sliding seal  202  when it is between the distal portion  205  and the proximal portion  207  of the clip. The result of this logic circuit may be used to activate a third notification mechanism. For example, when a fully charged suction device  200  is attached to the clip  210 , the first notification mechanism may be activated by the first magnetic sensor  206 , and issue a first visual and/or audio alert. As the suction device  200  is used to apply negative pressure to a tissue region, the third notification mechanism may be activated by the first and second magnetic sensors  206  and  208 , and issue a second visual and/or audio alert when the sliding seal  202  is halfway between the distal portion  205  and the proximal portion  207  of the clip  210 . When the suction device  200  is exhausted or depleted, the second notification mechanism may be activated by the second magnetic sensor  208 , and issue a third visual and/or audio alert. Some magnetic sensors may provide a binary output that indicates whether or not the sliding seal is at the location of the sensor or not, while other magnetic sensors may provide a graded output that indicates how far away the sliding seal is from the sensor. In some alarm systems, a plurality of binary type sensors may approximate the functional output of a graded type sensor. For example, while clip  210  is shown to have two magnetic sensors, it should be understood that other variations of alarm devices may have any number of magnetic sensors, e.g., there may be 1, 3, 4, 5, 6, 10, 12 or more magnetic sensors to detect the position of the sliding seal. 
     One example of a binary type sensor is a magnetic field sensitive switch, which may be configured to activate a notification mechanism in the presence of a magnetic field. Such binary type magnetic field sensitive switches change between an open and closed configuration according to the proximity of magnet. One example of a magnetic field sensitive switch is a reed switch, which is schematically depicted in  FIGS. 7A and 7B . A reed switch  700  comprises a first electrical contact  702  on a first ferrous metal reed  706 , and a second electrical contact  708  on a second ferrous metal reed  710 . In the absence of a magnetic field, e.g., when a magnet  712  is some distance away from a central region  701  of the reed switch  700 , the ferrous metal reeds  706 ,  710  and the associated electrical contacts  702 ,  708  may be in an open configuration such that the electrical contacts  702 ,  708  are separated by a distance, i.e., not touching or contacting each other. In the presence of a magnetic field, e.g., when the magnet  712  is in proximity of or within the central region  701  of the reed switch  700 , the ferrous metal reeds  706 ,  710  may move according to the field and cause the electrical contacts  702 ,  708  to touch, thus closing the reed switch  700 . In other variations, reed switches may be in a closed configuration in the absence of a magnetic field, and transition to an open configuration in the presence of a magnetic field. While a reed switch is described here, other examples of binary magnetic field sensitive switches may include proximity switches, speed switches, and the like. Any type of binary type magnetic field sensitive switches, as well as graded type magnetic field sensitive detectors, may be used to detect the presence of a magnet, as appropriate. 
     One example of a suction device  230  with an alarm system using a magnetic field sensitive switch is depicted in  FIG. 8 , which illustrates the suction device  230  in a depleted configuration, e.g., just prior to charging with a key. As depicted there, the sliding seal  232  of the suction device comprises a magnet  234 . The magnet  234  may be located on one side of the sliding seal  232  (e.g., the right side  253 ), but may also be located in the center of the sliding seal, or may extend along the entire length of the sliding seal, for example, similar to the magnetic component  204  depicted in  FIGS. 2A to 2C . The magnet may be located on the superior portion  250  of the sliding seal (as depicted in  FIG. 8 ), on the inferior portion  251 , and/or the left side  252  and/or right side  253  (e.g., the left or right edge) of the sliding seal. In some variations, the magnet may be embedded within the sliding seal. Alarm device  242  may comprise one or more clips  240  for retaining suction device  230  and a strap coupled to the one or more clips (not shown). A first reed switch  236  may be provided at any location on the alarm device  242 , for example, at a location that is close to the position of the sliding seal  232  when the suction device  230  is depleted, e.g., at a proximal portion  237  of the clip  240 . When the magnet  234  is sufficiently close to the proximal portion  237 , the magnetic field from the magnet  234  may affect the first reed switch  236  such that it transitions from an open configuration to a closed configuration. Closing the first reed switch  236  may activate any of the notification mechanisms described below to generate an alert to indicate that the suction device is depleted. Optionally, a second reed switch  238  may be provided at a distal portion  235  of the clip  240  which may be configured to activate the same or different notification mechanism as the first reed switch  236 . For example, the second reed switch  238  may be transitioned from an open configuration to a closed configuration when the sliding seal  232  is a distal portion of the suction device  230 , which may activate a notification mechanism to indicate that the device has been successfully charged. In some variations, as discussed in further detail below, a second reed switch may be provided to permit the coupling of the suction device to the alarm device in either orientation. Any number of locations on the alarm device may have one or more reed switches according to where the practitioner and/or patient desires to be informed of the location of the sliding seal  232 . The sensitivity of the reed switch may be configured depending upon the particular configuration of the suction device and magnetic shielding provided, if any, to protect other surrounding electronic devices. In some variations, greater magnetic shielding may be provided for use in the intensive care unit or hospital setting, or with patients with implantable devices such as a defibrillator or pacemaker. In some examples, non-magnetic MRI-compatible units may be provided in addition to magnetic variants of the device, and the clip may be configured with two or more detector mechanisms to accommodate multiple types of devices. 
     In some variations, the sliding seal  232  may comprise a second magnet  233  that is located on the left side  252  of the sliding seal  232 . The additional magnet may allow the suction device  230  to be retained in the alarm device  242  in an alternate orientation. For example, the suction device  230  may be retained in the alarm device in an orientation that is rotated 180° around the longitudinal axis from the orientation depicted in  FIG. 8  (e.g., such that the relative position of the superior portion  250  of the suction device is interchanged with the inferior portion  251 , and the left side  252  is interchanged with the right side). Suction and alarm devices with alarm systems that are configured to accommodate a plurality of retention orientations will be described in detail below. 
     One variation of a suction device  330  with an alarm system using a graded type magnetic sensor mechanism is depicted in  FIG. 3A . Suction device  330  is configured to be retained within alarm device  344 , which may comprise a clip with a magnetic linear encoder  342  at a proximal portion  346  of the alarm device  344 . Optionally, the alarm device  344  may comprise a strap that may be coupled to the clip to attach it to a patient. The power source for the linear encoder  342  may be a battery embedded within the alarm device  344 . Suction device  330  comprises a multi-pole flexible magnetic strip  332  that spans along a longitudinal length of the device, from a proximal portion  334  to a distal portion  336  of the device, and aligned over the magnetic linear encoder  342 . The distal end of the flexible magnetic strip  332  may be fixedly attached to the base of a sliding seal  338  of the suction device  330 , and rotatably attached to the proximal portion  334  of the suction device. The relative motion due to the longitudinal shortening of the magnetic strip during the application of negative pressure may be detected by the magnetic linear encoder  342 . In some variations, the magnetic strip  332  may be coupled to a portion of the springs  340 . In the charged configuration, the magnetic strip  332  is extended, as depicted in  FIG. 3A . As the springs  340  recoil and shorten during the course of negative pressure therapy, the magnetic strip may recoil and shorten similarly (as the magnetic strip  332  may be at least partially coiled at the proximal portion  334 ). In other variations, as depicted in  FIG. 3A , the magnetic strip  332  may be coupled to a non-central region of the sliding seal  338 , and as the suction device  330  is used to apply negative pressure, the magnetic strip  332  shorten and form a coil around a rotatable pin that is separate from the coil of the springs  340 . Alternatively or additionally, the magnetic strip  332  may be wrapped around a first rotatable pin at the proximal portion  334 , and coupled to a second slidable and/or rotatable pin that retains the magnetic strip within the housing of the suction device  330 . For example, the second pin may be slidable on a side slit in the housing of the suction device  330 , and may be coupled to the sliding seal  338  such that its movement across the suction device corresponds to the movement of the sliding seal. The rotation of the pin and/or the movement of the magnetic strip  332  across the magnetic linear encoder  342  may be detected and used to trigger an alarm when the suction device  330  is exhausted or depleted. The second pin may be made of a magnetically detectable material (e.g., a magnet or ferromagnetic metal, etc.), which may allow its location along the suction device to be detected by any suitable proximity detector (e.g., any of the sensors described above). 
     In other variations, a multi-pole magnetic strip may be located along a longitudinal length of the clip, and the magnetic linear encoder may be embedded in the slidable seal of the suction device, in alignment with the magnetic strip. As the slidable seal with the linear encoder moves across the magnetic strip, the linear encoder detects the relative movement between the seal and the magnetic strip, which may be used to compute the location of the slidable seal within the suction device. In this variation, a power source such as a battery may be provided on the suction device, where the power source may be mechanically or electrically recharged and/or may be replaced when depleted. 
     Another variation of a suction device  300  with an alarm system using a graded type magnetic sensor mechanism with an alarm device  310  is illustrated in  FIG. 3B . The suction device  300  comprises a shaft  302  that is fixedly attached to a sliding seal  306 . The shaft  302  may comprise an elongate magnetic component  304  that may be embedded along a substantial length of the shaft. The alarm device  310  may comprise a clip having one or more magnetic linear encoders  308  to detect the movement of the elongate magnetic component  304  embedded in the shaft  302 . A magnetic linear encoder located at the proximal portion  307  of the clip  310  may detect when the suction device  300  is depleted and trigger a notification mechanism to generate an alert. 
     The elongate magnetic component  304  may be embedded over 30% to about 100% of the total length of the shaft  302 . The shaft  302  may have a length such that it does not protrude from the body of the suction device  300 . For example, the shaft length may be is less than or equal to the distance between the sliding seal  306  and the proximal portion  313  of the suction device  300  in the depleted configuration. For example, the distance between the sliding seal  306  and the proximal portion  313  of the suction device in the depleted configuration may be from about 30 millimeters (mm) to about 200 mm, e.g., 90 mm. Accordingly, the length of the shaft  302  may be from about 10 mm to about 60 mm, e.g., 30 mm. Alternatively, certain suction devices may have a shaft with an elongate magnetic component that has a length that may protrude from the body of the suction device in the depleted configuration. Optionally, the shaft  302  may have a lumen therethrough configured to retain a key to mechanically charge the device. 
     In some variations, the elongate magnetic component  304  may be a multi-pole magnetic strip, where the pole length may be about 1.00 millimeter (mm). The location of the sliding seal  306  may be determined by the location of the elongate magnetic component  304  embedded within the shaft  302 . The location of the elongate magnetic component may be detected by one or more magnetic linear encoders located on an alarm device  310 . In some variations, the magnetic linear encoders may comprise an array of magnetic sensors, e.g., an array of Hall effect sensors. 
     Referring again to  FIG. 3B , the alarm device  310  may have a first device retaining structure  314  and a second device retaining structure  316  that is directly opposite the first device retaining structure. The alarm device  310  also comprises a back panel  318  that is attached to the first and second retaining structures  314  and  316  on either side. When the suction device  300  is retained by the alarm device  310 , the shaft  302  may move longitudinally across the length of the back panel  318 . The one or more magnetic linear encoders  308  may be located anywhere on the alarm device  310  such that the longitudinal axis  312  of the shaft  302  passes over the linear encoder as the shaft moves. For example, in the alarm device  310  depicted in  FIG. 3B , magnetic linear encoders  308  are located at a distal portion  305  and proximal portion  307  of the back panel  318  that overlaps with the longitudinal axis  312 . In other variations of alarm devices, the magnetic linear encoder may be located anywhere on the alarm device that overlaps with the longitudinal axis of the suction device shaft, e.g. any location between the proximal  307  and distal portion  305  along the longitudinal axis of the shaft. 
     Additionally, the location of magnetic linear encoder  308  with respect to the elongate magnetic component  304  may be determined by the specification of the particular magnetic linear encoder selected. For example, the alignment of the elongate magnetic component over the magnetic linear encoder, the distance between the elongate magnetic component and the magnetic linear encoder, and other such positional details may be described in the specification of the magnetic linear encoder selected. Examples of elongate magnetic components and magnetic linear encoders that may be used here may include the MS10-10 magnetic multipole strip (pole length 1.0 mm, 10 poles) and the AS5311 high resolution magnetic linear encoder (AustriaMicrosystems AG). Other suitable types of magnetic components and magnetic sensors and encoders may also be used with the suction and alarm devices described above. 
     While the magnetic components described above may be embedded or fixedly coupled to the sliding seal or shaft of the suction device, in other variations, the sliding seal or shaft may be itself magnetic, i.e., made of magnetic materials. The sliding seal and/or shaft may comprise an integral magnetic component, or may comprise a plurality of magnetic components throughout its length. Examples of magnetic materials that may be used in an alarm system comprising magnetic sensors include but are not limited to neodymium, iron, boron, samarium cobalt, alnico, ceramic, ferrite, various alloys (such as an alloy of neodymium, iron and boron) and the like. Alternatively or additionally, the magnetic components may be electromagnetic. The magnetic components may have any size or shape as may be suitable for attaching to the suction device and/or alarm device. For example, the magnetic components may be magnetic sheets or strips. Magnetic components may also be shaped as a disc, rectangular block, cylinder, etc. 
     The output of the magnetic linear encoder  308  may activate a notification mechanism that informs the patient and/or practitioner about the status of the suction device  300 . The notification mechanism may be configured or programmed to issue certain indicators or alerts depending on the positional output of the magnetic linear encoder  308 . For example, the magnetic linear encoder  308  may activate the notification mechanism to issue a first alert when the suction device  300  is fully charged and installed in the alarm device  310  as depicted in  FIG. 3B . When the shaft  302  has moved to a position where the suction device  300  is partly depleted (e.g., about 30% depleted) the magnetic linear encoder  308  may activate the notification mechanism to issue a second alert. Any desired number of alerts may be issued according to the position of the shaft  302  as detected by the magnetic linear encoder  308 . When the shaft  302  has moved to a position where the suction device  300  is nearly or fully depleted, the magnetic linear encoder  308  may activate the notification mechanism to issue another alert. More generally, the magnetic linear encoder and the notification mechanism may be configured or programmed to provide alerts at any frequency as desired by the patient and/or practitioner. While an encoder that detects longitudinal or linear movement is described above, other types of graded sensors will be described below. 
     In addition to a magnetic field sensitive reed switch described above, electrical switches that are triggered by certain configurations of the suction device may be used to activate (e.g. by closing or opening) a circuit of a notification circuit to generate an alert. Such electrical binary type switches may be triggered to particular configurations of the suction device, and may be used to activate a notification mechanism. One variation of a suction device  400  using a binary type electrical switch mechanism is depicted in  FIGS. 4A-4E . The suction device  400  may comprise a slidable seal  420 , where the slidable seal is attached or coupled to one or more springs  422  or a shaft  428  of a activation tool  426 , as previously described. Suction device  400  also comprises a circuit conduit  410  embedded in the slidable seal  420 . A notification mechanism as described below may be activated when the slidable seal  420  and the circuit conduit  410  are at a certain location in the suction device. For example, when the slidable seal  420  seal is in the location depicted in  FIG. 4A , the notification mechanism may not be activated, but when the slidable seal  420  is in the location depicted in  FIG. 4B , the notification mechanism may be activated. 
       FIGS. 4C-4E  illustrate one variation of a notification mechanism that may be activated closing a switch when the suction device attains a certain configuration. For example, a notification mechanism may be configured to generate an alert when the position sensor mechanism detects that the slidable seal is in a proximal position, i.e., the suction device  400  is depleted or exhausted. The notification mechanism may comprise a first activation contact  402  on one side of a proximal portion of the suction device housing  424 , and a second activation contact  403  that may be directly across from the first activation contact. The activation contacts may extend through the entire thickness of the housing  424 . The first activation contact  402  may be electrically coupled to the second activation contact  403  via an activation element in the sliding seal  420 , e.g., the circuit conduit  410 . When the circuit conduit  410  is not aligned with both the activation contacts  402  and  403 , i.e., the suction device  400  is in the configuration depicted in  FIG. 4A , the activation contacts are electrically isolated. When the circuit conduit  410  is aligned with both the activation contacts  402  and  403 , i.e., the suction device  400  is in the configuration depicted in  FIG. 4B , the activation contacts are electrically coupled, and current may flow between the activation contacts. There may be several pairs of activation contacts along the length of the suction device  400 , which may sense various locations of the slidable seal  420  as desired. For example, the activation contacts  402  and  403  are located so that they may be aligned with the circuit conduit  410  of the slidable seal  420  when the suction device is depleted or exhausted. When the suction device  400  is in the depleted configuration shown in  FIG. 4B , the activation contact  402 , the circuit conduit  410 , and the activation contact  403  may be aligned to form an electrical pathway therebetween. 
     The notification mechanism may comprise a circuit configured to generate an alert. For example, the notification mechanism may comprise a notification circuit  408 , where the notification circuit  408  may comprise an open circuit which may be activated when the circuit is closed. The notification circuit  408  may be located on an alarm device  404  that is configured to retain the suction device  400 , as illustrated in  FIGS. 4C and 4D . The alarm device may comprise a clip, sheath, case, etc. that may have one or more grooves, protrusions, high-friction surfaces, etc. that are arranged to reliably retain and align the suction device within the alarm device. The alarm device may also have one or more bands, clips, belts, straps, etc. that may couple the suction device to a patient, e.g., an arm or wrist band, leg strap or brace, waist belt, and the like. 
     The notification circuit  408  may be attached to a back panel  428  of the alarm device  404 , which is illustrated in  FIG. 4E . The notification circuit  408  may comprise a first alarm contact  406  on one side of the alarm device, a second alarm contact  407  that may be opposite the first alarm contact  406 , and a battery (not shown). The alarm contacts  406  and  407  may be the terminal nodes of an open circuit of the notification mechanism. In the open circuit configuration depicted in  FIG. 4E , the notification circuit is in an inactivated state. Activation of the notification circuit  408  may require an electrical conduit between the alarm contacts  406  and  407 . The alarm contacts  406  and  407  may be located such that when the suction device  400  is retained within the alarm device  404 , the activation contacts  402  and  403  are aligned and touch each other. The connection between the alarm and activation contacts may be sufficiently intimate such that an electrical current may pass between them. Optionally, the engagement between the alarm and activation contacts may help to retain the suction device  400  within the alarm device  404 . In some variations, the alarm contacts and the activation contacts may be complementary structures, such that they engage or mate when the suction device  400  is retained by the alarm device  404 . For example, the alarm contacts and the activation contacts may be engaged by snap-fit, friction-fit, mechanical interfit, magnetic attraction, and the like. 
     As described above, a notification mechanism may comprise an electrical circuit with an open circuit where the termination nodes correspond to two or more alarm contacts. A notification circuit may be held in an inactivated state by the open circuit, and activated when the open circuit is closed, i.e., when one or more conductive pathways are provided between the alarm contacts. The alarm contacts may be electrical switch contacts and/or reed switch contacts that respond when a magnetic field is present. 
     In the variation of the suction device  400  described above, the alarm system is configured to alert the practitioner when the suction device is depleted of its ability to provide reduced pressure to a tissue.  FIG. 4B  depicts the location of the slidable seal  420  when the suction device is nearly depleted, where the activation contacts  402  and  403  are connected via the circuit contact  410 . As described previously, when the suction device  400  is retained in the alarm device  404 , the activation contacts  402  and  403  engage and connect with the alarm contacts  406  and  407 . When the suction device  400  is in the configuration shown in  FIG. 4B , the open circuit  432  of the notification circuit  408  is closed, and the tone generator  434  is activated. While the open circuit  432  has been described as being closed by circuit conduit  410 , in other variations, the open circuit may be closed by other switch mechanisms. For example, the open circuit  432  may be closed by a spring-loaded button or knob that may be depressed when the slidable seal attains a certain position. In some variations, the slidable seal may have a protrusion that depresses the spring-loaded button to close the open circuit and activate the tone generator. As described previously, the alarm contacts of the notification circuit  408  may be closed by a reed switch. For example, when the magnet coupled to the slidable seal is in the vicinity of the reed switch, the reed switch may change to a closed configuration and activate the notification circuit. 
     The activation contacts, alarm contacts, and circuit conduit may be made of any electrically conductive material, such as copper, gold, silver, etc. Other types of electrically conductive materials may be used in to activate the notification circuit. 
     While some suction devices may comprise alarm systems with sensor and/or notification mechanisms that track the position of the sliding seal assembly in the suction chamber of the device, alternatively or additionally, other suction devices may comprise alarm systems that track other moving components, such the one or more components of the suction generating mechanism. As described previously, a suction device may use one or more constant force springs to provide reduced pressure to a tissue region. The constant force springs may be extended using a shaft and/or an activation tool to push the slidable seal distally. As the constant force springs retract (e.g., as the ability to provide reduced pressure decreases), they may form a coil in a proximal portion of the suction device. In some variations, the retraction of the constant force springs as the suction device is depleted may rotate an axle around which the springs are wound. When the springs retract as the suction device is depleted, it may form a coil with increasing diameter as the springs retract. An alarm system may comprise a sensor mechanism that is triggered by the coiling of the constant force springs.  FIGS. 6A and 6B  schematically depict one example of a sensor mechanism that detects the coil size of a suction device spring assembly, and may be used to trigger a notification mechanism based on the degree to which the springs are coiled.  FIG. 6A  depicts the configuration of a spring assembly of a suction device when the suction device is charged.  FIG. 6B  depicts the configuration of the spring assembly when the suction device is depleted, where a notification mechanism may be triggered to generate an alert. The spring assembly  600  comprises a first spring  602  wrapped around a first rotatable axle  604  to form a first coil  630 , and a second spring  606  wrapped around a second rotatable axle  608  to form a second coil  632 . The distal portions  610  of the springs are attached to a slidable seal  612 . During the use of the suction device, the springs retract to apply negative pressure to a tissue site, and rotate the first and second rotatable axles  604 ,  608 . A rotary encoder, which may provide either a binary or graded type output, may be used to measure the rotation of the axles  604 ,  608  as the spring is extended or retracted, as well as the size of the coils  630 ,  632 . Examples of how rotary encoders may be used are described below. 
     The rotary encoder (not shown) may measure the rotation of the axle  604  and map the measured rotation of the axle  604  to a particular sliding seal location. For example, the rotary encoder may maintain an internal count of the number of clockwise and counterclockwise rotations of the axles  604 ,  608 . The linear movement of the springs may be computed based on the number of rotations in both directions. The linear movement of the springs may be mapped to the location of the sliding seal  612 . According to the sliding seal location, the rotary encoder may generate a graded output that drives a notification mechanism, e.g., notification circuit  408 , to generate an alert to the patient and/or practitioner. 
     Additionally or alternatively, the location of the sliding seal  612  may be determined using sensors that are configured to detect the diameter of the coils  630 ,  632 , which may vary as the suction device is used. The constant force spring assembly  600  may also comprise a first sensor  626  and a second sensor  628 , where the first and second sensors are configured to general a signal to the notification mechanism when the coils  630  and  632  are sufficiently large. The first and second sensors  626 ,  628  may be located at a distance D 3  away from the respective axles  604 ,  608 , such that the sensors are not activated when the suction device is charged, and activated when the suction device is depleted. For example, when the suction device using the constant force spring assembly  600  is fully charged (e.g., the slidable seal is in a distal position), the springs are fully extended as depicted in  FIG. 6A , and a first coil  630  formed by the first spring  602 , and a second coil  632  formed by the second spring  606  may have a diameter D 1 , where 0.5(D 1 )&lt;D 3 , and may be from about 0 mm to about 16 mm, e.g. D 1  may be from about 0 mm to about 30 mm, or from about 14 mm to about 17 mm, or from about 15.7 mm to about 15.9 mm. When the suction device is fully depleted (e.g., the slidable seal is in a proximal portion), the springs may be fully coiled, as depicted in  FIG. 6B , and the first and second coils  630 ,  632  may have a diameter D 2 , where 0.5(D 2 )&gt;=D 3 , and D 2  may be from about 0.2 mm to about 35 mm, or from about 14.3 mm to about 17.3 mm, or from about 16.0 mm to about 16.2 mm. While the variation of the spring assembly described here may have two sensors, other variations of spring assemblies may have three or more sensors as desired, e.g., 3, 4, 5, 6, 8, 10 or more. Each of the sensors may drive individual notification mechanisms, or may drive two or more notification mechanisms. The sensors  626 ,  628  may also be used to detect when one or both the springs  602 ,  606  break, which may result in the sudden increase in coil diameter. 
     Additionally or alternatively, the springs  602 ,  606  may have a plurality of stripes oriented transversely to the length of the springs, where the spacing between the stripes may vary along the length of the springs (e.g., the spacing between stripes is directly related to the location of the stripes on the length of the spring). One or more optical sensors, e.g., a barcode scanner or laser backscatter sensor, may be provided to detect the stripe spacing of the springs at a reference location, which may map to slidable seal location. Optical sensors may be at a proximal location, e.g. longitudinally adjacent to the sensors  626 ,  628 , or may be located anywhere along the length of the springs. The rotary encoders described above may provide graded type outputs that not only indicate a charged or depleted configuration, but also provide outputs that indicate intermediate configurations, e.g., suction device is about 100%, about 80%, about 50%, about 30%, about 10%, about 0%, charged or depleted. The notification mechanism may be adapted and/or configured to generate an alarm based on one or more intermediate configurations as desired. 
     Alarm systems with optical sensor mechanisms may also be used to detect the position of the slidable seal. For example, an optical sensor may be located at a proximal location (i.e., in proximity to the location of the slidable seal when the suction device exhausted or nearly exhausted, or at any location along the length of the suction device) that is configured to detect a certain optical cue on the slidable seal. For example, the slidable seal may have markings with a certain color, pattern (e.g., striped, dotted, zig-zag, etc.), reflectance or absorbance property that may be detected by an optical sensor, which may drive a notification mechanism to indicate that the slidable seal is at the location of the optical sensor, i.e., the suction device is exhausted or depleted. Examples of optical sensors that may include infrared sensors, photodiodes, CCD devices, and the like. 
     Some optical sensors may be configured to detect an optical interference. For example, the housing of a suction device may be substantially transparent or translucent, while the slidable seal may be substantially opaque. An interference sensor located at a proximal portion of the clip, at the location where the slidable seal may be when the suction device is exhausted or depleted. The interference sensor may detect an occlusion or blockage of light that may result from the movement of the opaque slidable seal when the device is exhausted, and trigger the notification mechanism accordingly. An alarm system comprising an optical sensor may be detachably coupled to the suction device, such that they may be removed from a depleted suction device and attached to a different (e.g., newly charged) suction device. In this way, the alarm system may be reused for multiple sessions of reduced pressure therapy. 
     Certain variations of suction devices may comprise a pressure transducer that may directly measure the pressure in the suction chamber, and signal a notification mechanism according to the measured pressure. The pressure transducer may be located at a distal portion of the suction chamber. Optionally, there may be a display or monitor that indicates the exact pressure being applied to a tissue region. Notification mechanisms may be configured to generate alerts according to certain pressure levels, as desired. 
     Certain variations of suction devices may also comprise liquid sensors that detect the presence of any fluids within the suction chamber. An alarm device may comprise a liquid sensor interface that receives the signal from the suction device liquid sensor, and drives a notification mechanism to notify the patient and/or practitioner when there is liquid in the suction chamber. Some types of liquid sensor mechanisms may also provide data about the quantity of liquid in the suction chamber, which may trigger an alert for the patient and/or practitioner to empty or replace the suction device. For example, some liquid sensor mechanisms may sense the location of a float within the suction device chamber, where the float moves according to the quantity of air and/or fluids in the chamber. In some variations, the float may comprise one or more magnetic components that may be detected by any of the magnetic field sensitive mechanism described above. The detected location of the float may activate the notification mechanism to generate an alert. 
     Suction devices may be retained in an alarm device in a particular orientation. Various features on the housing of the suction device may correspond to and/or be aligned with features on the alarm device to help ensure a certain alignment and/or orientation when the suction device is coupled to the alarm device. For example, one or more surface structures of the suction device housing and the alarm device may be configured to help ensure precise positioning of the suction device with respect to the alarm device. The interface between the suction device housing and the alarm device may also comprise features that secure the suction device in a desired alignment with the alarm device. In some variations, the suction device and/or alarm device may be configured such that the suction device may be retained in the alarm device in a plurality of orientations, as described further below. Examples of surface structures that may retain the alignment and position between two surfaces may include interlocking flanges or hooks, interlocking slits or seals, hook and loop engagement, a protrusion and a recess coupled by friction-fit, snap-fit structures, and the like. Examples of suction and/or alarm devices with features for alignment are described below. 
     In some variations, the suction device housing may have one or more protrusions or grooves that are complementary to one or more grooves or protrusions on the alarm device, e.g., form a mechanical interfit. For example, as depicted in  FIG. 4D , the alarm device  404  may have one or more protrusions  440  that fit into recesses  441  on the housing of the suction device  400 . In some variations, the suction device housing may also have curved grooves along its surface to accommodate the portions of the alarm device that contact the suction device. Alternatively or additionally, the suction and alarm devices may have snap latches and snap grooves at corresponding locations. 
     Suction and alarm devices with different sensor mechanisms may have different surface structures. This may help to ensure that only suction and alarm devices with compatible sensor mechanisms may be coupled together. For example, attachment clips with magnetic sensors may have alignment features that form an interfit with the alignment features of suction devices with a magnetic component in the sliding seal, but do not interfit with the alignment features of suction devices without a magnetic sliding seal. For example, the alignment features of the suction device  200  may not be compatible with the alignment features of the alarm device  310 . 
     In other variations, suction and alarm devices may have electrical components that correspond to each other to help ensure that devices with compatible sensor mechanisms are coupled together. For example, the suction device may have a conductive element with a particular shape that corresponds to the location of one or more electrical pins on the alarm device. When the conductive element of the suction device is in alignment with the one or more pins on the alarm device, an electrical signal is provided to a microcontroller of the alarm system to indicate that the suction and alarm devices are compatible and/or are properly assembled together. In some variations, power is provided to the microcontroller only when certain pins on the alarm device are shorted together by the conductive element of the suction device. In some variations, the alarm device may comprise one or more electrical contacts configured to align with corresponding conductive elements on the suction device such that the alarm device is powered only when a suction device is placed within the alarm device such that the conductive elements are aligned with the one or more electrical contacts. Additionally or alternatively, the alarm device may comprise a power switch that is configured to be depressed by a suction device that is retained within the alarm device. Depressing the power switch may complete a circuit and connect a power source to an alarm system microcontroller that may be included with the alarm device. When the suction device is removed from the alarm device, the pressure on the switch may be released, thereby disconnecting the power source to the alarm system microcontroller. The power switch may be a tactile switch, or any suitable mechanical or electrical switch mechanism. For example, an alarm device may comprise a tactile switch located on the inside of the device (e.g., a back panel of the alarm device that is to receive a suction device). Insertion of a suction device into the alarm device may push on the tactile switch to power the alarm system on, and removal of the suction device from the alarm device may release the pressure on the switch to power the alarm system off. Such power switch mechanisms may be used to reduce power consumption of the reduced pressure therapy system by helping to ensure that the alarm device does not draw any power from the power source in the absence of a suction device. 
       FIGS. 14A-14C  schematically depicts one example of an electrical mechanism that may be used to ensure that suction and alarm devices are compatible. Such an electrical mechanism may also be used to indicate the orientation of the suction device with respect to the alarm device so that a microcontroller on the alarm device may activate the appropriate sensors for depletion detection. In some variations, this mechanism may also be used to power the alarm system only when the suction device is retained in the alarm device. A suction device  1400  may comprise a conductive element  1402  that is accessible to an alarm device. The conductive element  1402  may have any geometry that is suitable for alignment purposes. For example, the conductive element  1402  may have an elongate portion  1404  along a length of the suction device  1400 , and may also comprise an end portion  1406  that substantially extends from the elongate portion  1404 . The conductive element may be located along a central axis of the suction device, or may be offset from the center. The overall geometry of the conductive element  1402  may be asymmetric or symmetric, depending on the configuration of electrical pins or pads on the alarm device.  FIG. 14B  schematically illustrates the positioning of suction device  1400  with respect to a plurality of pins on an alarm device. In some cases, the pins may be electrically isolated until coupled by a conductive element on the suction device. The pins  1410 ,  1412  and  1414  are schematically depicted, but for the sake of simplicity, the alarm device is not shown.  FIG. 14B  depicts a first orientation  1420  of the suction device, where the conductive element  1402  on the suction device electrically couples a first pin  1410 , a second pin  1412 , and a third pin  1414  together. Shorting these three pins together may send a first electrical signal to an alarm system microcontroller to indicate that the suction device is in the first orientation  1420 .  FIG. 14C  depicts a second orientation  1422  that is a 180 degree rotation from the first orientation  1420 . In the second orientation  1422 , the first pin  1410  and the second pin  1412  are electrically coupled, however, the third pin  1414  is electrically isolated from the first and second pins. Shorting the first and second pins but not the third pin may send a second electrical signal to the microcontroller to indicate that the suction device is in the second orientation  1422 . In some variations, power may be supplied to the microcontroller only when the suction device  1400  is in the first orientation  1420  or second orientation  1422 , but not in the other orientation. While the conductive element  1402  on the suction device and the pins  1410 ,  1412 ,  1414  on the alarm device are configured to indicate two orientations, other suction devices may have one or more conductive elements with different geometries that correspond to three or more pins on the alarm device to indicate any number or orientations. 
       FIGS. 14D and 14E  depict one example of a suction device  1430  and an alarm device  1440  that have an electrical mechanism that may be used for orientation identification, and/or to ensure that suction and alarm devices are compatible. The electrical mechanism may also be used as a power switch such that alarm device  1440  is not powered on until the suction device  1430  is retained therein. The suction device  1430  may comprise a conductive element  1432 , and the alarm device  1440  may comprise a first pin connector  1442  and a second pin connector  1444  located such that the conductive element  1432  and the pin connectors contact each other when the suction device  1430  is placed within the alarm device  1440 . As illustrated in  FIG. 14D , the conductive element  1432  is located along a side portion of the housing  1434  of the suction device. The conductive element  1432  may have any suitable geometry, for example, it may have an elongate portion  1436  that extends along a longitudinal axis of the suction device, and an end portion  1438  that extends transversely to the elongate portion  1436 . Portions of the conductive region  1432  may have any number of tapered, curved, rounded, etc. regions, as may be desirable. The location of the first connector  1442  and the second connector  1444  of the alarm device  1440  may correspond to the location of the conductive element  1432  of the suction device when retained in the alarm device. As illustrated in  FIG. 14E , the first connector  1442  may comprise two pins  1443   a ,  1443   b , and the second connector  1333  may comprise three pins  1445   a ,  1445   b ,  1445   c , however, it should be understood that an alarm device may have any number of connectors, and each connector may have any number of pins. The connectors on the alarm device may correspond to the pin pads of an alarm system circuit, such as the alarm system circuit of  FIG. 11 , which will be described below. The number of pins on a connector may or may not match with the number of pins on the pin pad corresponding to that connector. The number of pins on each connector or pin pad may vary according to the alarm system circuitry. 
     While alarm devices may have connectors configured to be shorted by a conductive element on a suction device have been described above, alternatively or additionally, suction devices may have an alarm system with connectors, and the alarm device may have a conductive element configured to short the suction device connectors. For example, in variations where the suction device is electrically powered or has an alarm system that is electrically powered, the suction device may have electrical connectors that interface with a conductive element on the attachment feature. These electrical connectors may act as a power switch for the suction device, and/or an orientation and/or a compatibility interface between the suction device and alarm device, such that the suction device is not electrically activated until retained within the alarm device. 
     Various types of visual, audio, and tactile alerts generated by various notification mechanisms may be used with any of the sensor and/or detection mechanisms described above. In some examples, the alert may be an audio signal (e.g. a buzzer or ringing sound), a visual signal (e.g. flashing colored light) or a tactile signal (e.g. vibration from an asymmetric weight attached to a rotary motor), or a combination thereof. Other signals may include data signals that may be connected wirelessly or by wired connection to one or more displays and/or electronic healthcare/nursing record databases. These displays and/or electronic databases may be local (e.g. in the clip or a pocket-sized mobile device) to the user, or remote (e.g. the nursing station of the treatment facility, online electronic healthcare record database or the user&#39;s personal computer), and utilize any of a variety data transmission modalities (e.g. cellular networks and/or internet). 
     One example of a notification circuit  408  is depicted in  FIG. 5 . The notification circuit  408  may comprise an open circuit  432  with alarm contacts  406  and  407  as terminal nodes, and a tone generator  434  configured to drive speakers  430 . All the components may be powered by a battery  436 , which may provide a DC voltage that is appropriate for selected tone generator  434 , e.g., from about 1.5 V to about 4.5 V. The tone generator  432  may be activated depending on the connectivity of the open circuit  432 . Additional features may be included with the notification mechanism  408  to adjust the sound produced by the tone generator  434 , the volume of the sound, and the duration that the sound is produced, etc. Variations of notification mechanisms may be used to activate different notification circuits to generate an alarm (e.g., visual or tactile alarms, as well as wireless signal generators), and may be included as separate modes that may be activated by the practitioner and/or patient. Notification circuits may also comprise memory components that may be configured to retain information about past alarm events, pre-programmed instructions, snooze functions, and the like. Notification circuit  408  may be located on the alarm device or on the suction device, as desired. 
     Additionally or alternatively to visual and/or audio alerts, notification mechanisms may issue electronic messages, such as text messages, e-mails, pages, etc., to indicate the state of the suction device, and whether or not the device needs to be replaced or emptied. The alerts may be provided to local monitors, such as the patient and/or attending medical practitioner, and/or may be provided to remote monitors, such as a medial practitioner who may be at a removed location. In some variations, the remote monitor may send a command to the suction device alarm system to issue an alert to prompt the patient to check on the suction device. 
       FIG. 9  depicts a block diagram representation of one variation of an alarm system  900 . The alarm system  900  may comprise a microcontroller module  908  that has a microcontroller chip that may be programmed to accept sensor and/or user inputs and drive indicator outputs. For example, the microcontroller module  908  may receive input signals from a suction device orientation module  902 , a sensor module  904 , and a user input module  906 . The orientation module  902  may provide information to the microcontroller module  908  regarding the position and/or orientation of the suction device with respect to the alarm device. The sensor module  904  may have one or more sensor mechanisms as described above, and may have, for example, one or more reed switches. The user input module  906  may comprise switches (e.g., power switch, toggle switches, etc.), buttons, dials, keyboards, and the like which may provide patient-specific information to the microcontroller  908 , as well as to regulate the state of the alarm system  900 . In addition to these inputs, the microcontroller module  908  may drive any number of output modules. For example, the microcontroller module  908  may drive a light-emitting diode (LED) module  910  that may be used as optical notifications to the patient, and/or may be used to backlight a display, such as a monitor. Outputs from the microcontroller may also be used to drive an indicator module  912  comprising notification circuits such as the ones previously described. In some variations, the indicator module  912  may comprise amplifiers that may augment the notification signal, whether audio, optical, tactile, electronic or otherwise, to help ensure that the patient and/or practitioner is made aware of the status of the alarm system. For example, the microcontroller may provide a signal to an audio amplifier that may in turn drive a speaker to generate an audible alert. 
     The various modules depicted in  FIG. 9  may be located on either or both the suction device and alarm device. For example, the microcontroller module  908 , optical notification module  910 , user input module  906 , and indicator module  912 , may be located on the alarm device, while the sensor module  904  and the orientation module  902  may be located on the suction device. Alternatively, the components of both sensor module  904  and the orientation module  902  may be located on both the suction and alarm devices. The optical notification module  910  and the user input module  906  may also be on the suction device, as may be desirable. In other variations, all the modules depicted in  FIG. 9  may be located only on the alarm device or only on the suction device. In still other variations, the modules depicted in  FIG. 9  may be detachably coupled to the suction and alarm devices. 
     One variation of a system that comprises two reed sensors and generates an alarm based on signals from the reed sensors is depicted in  FIG. 10A . The alarm system  1000  may comprise a first reed switch module  1004  and a second reed switch module  1006  that detect the position of the sliding seal within a suction device, and provide electrical signals, e.g., voltage or current signals, that correlate with the position of the sliding seal to a microcontroller module  1012 . The microcontroller module  1012  may comprise a voltage sensor  1010 . In some cases, the microcontroller module may comprise a programmable microcontroller or microprocessor with an embedded voltage sensor, for example, a system-on-a-chip microcontroller unit (MCU), such as any MCU in the C8051F93x-C8051F92x MCU family (Silicon Labs Inc of Austin, Tex.), for example. Any microcontroller with the appropriate power consumption (i.e., low power consumption), size (i.e., small size), and programmability (i.e., flexible software programming interface, compatibility with a variety of electronic components) may be used. The microcontroller module  1012  may receive inputs from a suction device orientation module  1002  which may be used to interpret the inputs from other modules in the alarm system  1000 . The alarm system  1000  may also comprise a user switch module  1008  which may allow the patient to activate or deactivate the system, as well as to provide patient-specific data to the alarm system. The microcontroller module  1012  may drive a number of output modules, such as a LCD sense indicator module  1014 , a LCD battery indicator module  1016 , a LCD alarm indicator module  1018 , a LED backlight module  1020 , and an amplifier module  1022 . In some variations, the microcontroller module may drive the LCD sense indicator module  1014  or a LCD segment to indicate that a suction device/cartridge is properly installed in the alarm device and/or that the alarm system is powered. For example, the LCD sense indicator module  1014  may be turned on or activated to indicate that there is a valid and/or compatible suction device coupled to the alarm device, and may be turned off or deactivated to indicate that there is no valid and/or compatible suction device coupled to the alarm device. Additionally or alternatively, the microcontroller module  1012  may drive radiofrequency transmitters or other electronic messaging devices to provide an e-mail or a text to a patient and/or practitioner to alert them of the state of the suction device. 
     One example of an orientation circuit that may be used with an alarm device orientation module is depicted in  FIG. 10B . Orientation circuit  1031  may comprise a first pin pad  1033  and a second pin pad  1038 , where each pin pad may comprise one or more pins in any arrangement that corresponds to a conductive element in a suction device, as previously described. The first pin pad  1033  has a first pin  1034  and a second pin  1036 , where electrically shorting them together may indicate a first suction device orientation. The first pin pad  1033  may be connected as a switch to a battery  1030  that may be configured to supply power to the alarm system, e.g., via a connection to the microcontroller module at the first terminal  1040 . When the first pin  1034  and the second pin  1036  are electrically isolated, the first pin pad  1033  may be as an open circuit, and the battery  1030  may be disconnected from the electrical components of the alarm system. Shorting the first pin  1034  and second pin  1036  together may act to close the circuit such that the battery  1030  may provide power to the alarm system, e.g., by turning on the microcontroller module, etc. An optional LED diode  1046  connected to the first terminal  1040  may be activated when the first and second pins are shorted, which may provide a visual indication to the user that power is provided to the alarm system. The second pin pad  1038  may have a third pin  1039 , where electrically shorting all three pins  1034 ,  1036 , and  1039  may indicate a second suction device orientation. The connectivity of the second pin pad  1038  may be indicated to the microcontroller module via a second terminal  1042 . Other variations of orientation circuits may have different a different number of pin pads and pins in a variety of arrangements. The battery  1030  may store sufficient energy to power the one or more electronic components of the alarm system, and may be selected according to the desired shelf life, service life, size, voltage, compatibility with other alarm system components, and/or discharge capacity. Any suitable batteries may be used with the orientation circuit  1031 , for example, a battery with a shelf life of 10 years, service life of at least 8 weeks, such as the 3V CR2032 battery. Optionally, the orientation circuit  1031  may have a battery sensor  1032  that may provide an indication of how much energy is stored in the battery  1030 , and activate a LED that may prompt the patient and/or practitioner to replace the battery or the alarm system. In certain variations, the alarm system may be powered by plugging into a wall socket instead of, or in addition to, using a battery. 
     One example of a sensor circuit that may be used with an alarm device sensor module is depicted in  FIG. 10C . The sensor circuit  1050  may comprise any number and types of sensors and/or switches, as previously described, for example, a first reed switch  1052  and a second reed switch  1054 . When the slidable seal of a suction device is in proximity to the first reed switch  1052 , it will close the switch and communicate the proximity of the slidable seal to the microcontroller module via a connection through a first terminal  1053 . When the slidable seal of the suction device is in proximity to the second reed switch  1054 , it will close the switch and communicate the proximity of the slidable seal to the microcontroller module via a connection through a second terminal  1055 . Based on the data from the orientation module, the microcontroller module will make a determination as to the depletion state of the suction device. The sensor circuit  1050  may also comprise a user-activated switch  1056  that when closed, will activate the first and second reed switches. For example, the third terminal  1057  that is connected to a node of the user-activated switch  1056  may be connected to the microcontroller module, which may provide a certain voltage or current level that may only be conveyed to the first terminal  1053  and/or second terminal  1055  if the user-activated switch  1056  is closed and either or both the reed switches  1052 ,  1054  are closed. Other mechanisms for activating and/or deactivating the sensor circuit  1050 , e.g., ON-OFF switches, may be used as appropriate. 
     One example of an amplifier circuit that may be used with an alarm device orientation module is depicted in  FIG. 10D . The amplifier circuit  1060  may comprise an amplifier chip  1062 , which may receive signals from the microcontroller module via a first terminal  1066  and/or a second terminal  1068 , and drive a speaker  1064  according to the microcontroller signals. Any suitable amplifier chip may be used in the amplifier circuit  1060 , for example, the LM4675 amplifier. Amplifiers may be used with any desirable type(s) of indicators, including auditory, vibratory, visual, electronic, etc. to augment the activity of the indicators. 
     LED circuits that may be used with an alarm device alarm system may comprise a LED array with one or more LEDs driven by an input bus from the microcontroller module. Each LED in the LED array may represent the status of a component in the alarm system and/or the state of the microcontroller. For example, individual LEDs in the LED array may represent the status of the battery, activation of the microcontroller, orientation of the suction device with respect to the alarm device, the depletion or charging of the suction device, alarm mode, sleep or active mode, power mode, etc. The LED array may also be used as a LCD backlight, as appropriate. Optionally, the LED circuit may also comprise a zener diode array that may be used as a shunt voltage regulator to prevent sudden voltage surges. Alternatively, certain alarm systems may comprise an array of LCD segments or other electronic devices that may be used to represent the status of one or more components in the alarm system. 
     The components of any of the alarm systems described above may be mounted on a printed circuit board in accordance with their desired position on the alarm device. For example, the sensor mechanisms that are triggered to the location of the slidable seal of a suction device coupled to the alarm device may be positioned to correspond to the location of the seal in the charged and/or depleted configuration.  FIG. 11  depicts one example of an alarm system  1100  with its components mounted on a printed circuit board  1101 . The alarm system  1100  may comprise a microcontroller  1102  that receives signals from a first sensor mechanism  1104  located on a first side of the printed circuit board  1101  and a second sensor  1106  located on a second side of the board, where the second side is opposite the first side. The alarm system  1100  may also comprise a first pin pad  1108  and a second pin pad  1110  that may be used to determine the orientation of the suction device with respect to the alarm device. For example, the first connector  1442  depicted in  FIG. 14E  may correspond to the first pin pad  1108 , and the second connector  1444  of  FIG. 14E  may correspond to the second pin pad  1110 . The microcontroller  1102  may use the inputs from the first sensor mechanism  1104 , second sensor mechanism  1106 , first pin pad  1108 , and second pin pad  1110  to determine the depletion or charge state of the suction device. The state of the suction device as determined by the microcontroller  1102  may be used to drive an amplifier module  1112  to generate any of the indicators descried above. The microcontroller  1102  may also be used to drive a LCD-LED array  1114  that may provide information to a patient and/or practitioner, e.g., by providing backlighting to a monitor, binary encoding of the suction device state, etc. While the printed circuit board  1101  is an oblong elliptical shape, it should be understood that it may have any geometry as suitable for the alarm device or clip. 
     One example of an alarm device  1200  that may use the alarm systems described above is depicted in  FIG. 12A . The alarm device  1200  may have an alarm system  1202  embedded along a portion of the alarm device to detect the position of the slidable seal within a suction device. For example, the alarm system  1100  may be embedded along the longest dimension, e.g. its length, of the alarm device  1200 . The alarm system  1202  embedded within the alarm device  1200  may comprise an audio speaker  1204 , indicators  1206 , and a user-activated switch  1208 . The indicators  1206  may be configured to signal the state of the alarm system (e.g., active or inactive), the state of the suction device (e.g., depleted or charged, etc.), the state of the battery (e.g., charged or drained, etc.), and the state of any of the components in the alarm system. The user-activated switch  1208  may be a press-button or slide-button that may be used to activate backlight illumination for the indicators  1206  or to snooze an activated indicator or alert.  FIG. 12B  depicts an example of a suction device  1220  that may be retained within the alarm device  1200 . In this example, a first sensing mechanism of the alarm system (e.g., a first reed switch) may be located at a proximal portion  1222  of the alarm device  1200  while a second sensing mechanism (e.g., a second reed switch) may be located at a distal portion  1224 . The suction device  1220  may comprise a conductive element as previously described so that the alarm system microcontroller may determine the orientation of the suction device  1220  with respect to the alarm device  1200 . 
     Another example of an alarm device  1500  that may use the alarm systems described above is depicted in  FIG. 15A . The alarm device  1500  may have an alarm system  1502  embedded along a portion of the alarm device to detect the position of the slidable seal within a suction device. The alarm system  1502  embedded within the alarm device  1500  may comprise an audio speaker  1504 , a display  1506 , and a user-activated switch  1508 . The display  1506  may comprise, for example, light bulbs, or an LED, LCD, OLED or other type of optical display. The display  1506  may be configured to signal the state of the alarm system (e.g., active or inactive), the state of the suction device (e.g., depleted or charged, etc.), the state of the battery (e.g., charged or drained, etc.), and the state of any of the components in the alarm system. For example, display  1506  may present an indicator  1506   a  may be in the shape of a circle and used to indicate that the system is powered on and active, i.e. that the suction device has been properly inserted and seated, and that there is adequate battery power to perform its detection and alarm functions. In other examples, the indicator  1506   a  may be configured to identify the current suction capacity of a suction device retained within the alarm device. The indicator  1506   b  may be used to indicate the status of the battery. The battery status may indicate a binary state (powered/unpowered), or may be configured to indicate multiple battery states, with three or more levels of battery power. The indicator  1506   c  may be used to indicate the alarm mode (e.g., alarm frequency, pre-programmed modes, snooze mode, etc.). The user-activated switch  1508  may be a press-button or slide-button that may be used to activate backlight illumination for the indicators  1506  or to snooze an activated indicator or alert (e.g., by silencing an audible alarm for a pre-selected period of time). An alarm device may also comprise one or more side connectors and/or one or more panel connectors. As depicted in  FIG. 15B , the alarm device  1500  comprises a clip comprising one or more side connectors  1516  and a power supply button  1517 . These connectors may be used as described above, for example, as a power switch, and/or orientation and/or compatibility verification mechanism. The power supply button  1517   c  may be depressed when a suction device is retained in the alarm device, thereby closing an open circuit and supplying power to the alarm system. 
       FIG. 15C  depicts an example of a suction device  1520  that may be retained within the alarm device  1500 . The suction device  1520  may comprise measurement markings  1521  on a transparent portion of the suction chamber  1523  that may be used to quantify the position of a piston, and/or the quantity of a fluid, or volume of a solid or gel contained in the chamber. The suction device  1520  may also comprise one or more protrusions configured to engage with the alarm device, i.e., by snap-locking, such that an electrical connection may be made between a conductive element on the suction device and connectors on the alarm device. The protrusions may also help the alarm device retain the suction device with a certain alignment. For example, first and second protrusions  1526 ,  1528  may be located at a proximal portion  1522 , while third and fourth protrusions  1530 ,  1532  may be located at a distal portion  1524  to retain the position of the suction device  1520  within the alarm device. In other variations, a suction device may comprise one or more recesses that correspond to one or more protrusions on the alarm device. The protrusions may be symmetrically arranged on the suction device (e.g., along a longitudinal and/or transverse axis) or asymmetrically arranged, as may be suitable. The protrusions may help ensure that a suction device retained in the alarm device does not move or change configuration during reduced pressure therapy. The location and geometry of the protrusions of the suction device may be configured such that the suction device may be retained in the alarm device in a variety of orientations, as described further below. Additionally or alternatively, engagement mechanisms such as magnetic, adhesive, hook-and-loop, etc. may be used to couple the suction and alarm devices, as described previously. A back panel of the alarm device  1500  retaining the suction device  1520  is depicted in  FIG. 15D . The alarm device  1500  may optionally comprise a first loop portion  1510  and a second loop portion  1512 , which may be used for coupling the alarm device to a belt or strap. In some variations, the alarm device  1500  may be coupled to a belt or strap by hook-and-loop engagement, snap-lock, buttons, clasps, adhesives, and the like. The suction device  1520  may comprise a conductive element as previously described so that the alarm system microcontroller may determine the orientation of the suction device  1520  with respect to the alarm device  1500 . 
     In some variations, the suction device may be configured to be retained by the alarm device in a plurality of orientations, and the alarm device may be configured to detect the depletion state of the suction device (e.g., fully charged, partially charged/depleted, or fully depleted) regardless of the orientation in which the alarm device retains the suction device. For example, the suction device may be retained in the alarm device as shown in  FIG. 15C , where the superior portion  1542  is facing up and the left side  1545  is closest to the alarm system  1502 . The suction device  1520  may also be retained in an orientation where the inferior portion  1543  is facing up and the right side  1544  is closest to the alarm system  1502 . Optionally, the suction device  1520  may also be retained in an orientation where the relative position of the distal end  1546  and the proximal end  1547  are switched.  FIG. 19  schematically illustrates the various orientations that a suction device  1900  may be retained in an alarm device. For example, the suction device  1900  comprising a suction chamber  1902  and a sliding seal assembly  1904  may be configured to be retained such that the superior portion  1920  is facing up. The alarm device may also be configured to retain the suction device  1900  in an orientation that is rotated around longitudinal axis A 1  (e.g., 180°, such that the relative positions of the superior  1920  and inferior  1921  portions are switched, and the relative positions of the left  1922  and right  1923  sides are switched). The alarm device may also be configured to retain the suction device  1900  in an orientation that is rotated around transverse axis A 2  (e.g., 180°, such that the relative positions of the distal  1925  and proximal  1926  portions are switched, and the relative positions of the superior  1920  and inferior  1921  portions are switched). The alarm device may be configured to retain the suction device  1900  in an orientation that is rotated around both axes A 1  and A 2  (e.g., rotated 180° around axis A 1  and rotated 180° around axis A 2  such that the relative positions of the superior  1920  and inferior  1921  portions, distal  1925  and proximal  1926  portions, and left  1922  and right sides  1924  are interchanged with each other, etc.). Accordingly, the alarm device may be configured to detect when the suction device  1900  is in a fully depleted state (e.g., sliding seal assembly  1904  has moved to a proximal portion of the suction chamber) in some or all of these retention orientations. For example, some alarm devices may be configured to detect the depletion state of a suction device in two retention orientations (e.g., in a first orientation and in a second orientation, where the second orientation is a front-to-back rotation of the first orientation). Some alarm devices may be configured to operate with a device that may be retained in three or more orientations (e.g., in a first, a second, a third, and a fourth orientation, where the second orientation is the first orientation rotated 180° around axis A 1 , the third orientation is the first orientation rotated 180° around axis A 2 , and the fourth orientation is the first orientation rotated 180° around axis A 1  and rotated 180° around axis A 2 ). 
     Suction devices may also be configured to be retained in the alarm device in a plurality of orientations. For example, suction devices may comprise protrusions similar to those described and depicted in  FIGS. 15C-15D  that can accommodate a plurality of retention orientations. Suction device may also comprise a sliding seal assembly with two or more magnetic elements, so that the location of the sliding seal assembly may be detected by the alarm device regardless of the retention orientation. Alternatively, alignment protrusions on a suction device may constrain the retention orientation of the suction device, such that the suction device may be retained in the alarm device in one or two orientations. In some variations, the alarm device is configured to only detect the depleted state of the suction device. For example, a suction device  1900  may have a first magnetic element  1914  on the left side  1922  of the sliding seal assembly and a second magnetic element  1915  on the right side  1924  of the sliding seal assembly, as schematically depicted in  FIGS. 19B-19D . The alarm device may comprise a first reed switch  1906  at a first location and a second reed switch  1908  at a second location separate from the first location (e.g., the second reed switch  1908  may be proximal to the first reed switch). The suction device may be retained by the alarm device such that the location of the sliding seal assembly  1904  in the fully charged state is proximal to the location of the first reed switch  1906  of the alarm device, as depicted in  FIG. 19B . The suction device  1900  may comprise a tab, shoulder, or any suitable stop structure (e.g., a wall of a distal cap) that may prevent the sliding seal assembly  1904  from moving to the distal-most portion of the suction chamber. When the suction device is this fully charged state, the location of the magnetic elements  1914 ,  1915  is such that they are undetected by the first reed switch  1906 . When the suction device is fully depleted, the sliding seal assembly may be at the location  1905  depicted in  FIG. 19C , and at least one of the magnets  1914 ,  1915  may be close enough to be detected by the second reed sensor  1908 , thereby triggering an alert. The suction device  1900  may comprise a proximal tab, shoulder, or any suitable stop structure (e.g., a wall of a proximal cap) that may prevent the sliding seal assembly  1904  from moving further in the proximal direction. This particular arrangement of the alarm device with the suction device allows for the detection of the depleted state regardless of the orientation with which it is retained in the alarm device. For example, when the retention orientation of the suction device  1900  depicted in  FIG. 19B  is rotated 180° around axis A 2 , the device may be oriented as depicted in  FIG. 19D . In this retention orientation, the magnetic elements  1914 ,  1915  of the sliding seal assembly in the fully charged configuration may be undetectable by the second reed switch  1908 , but when the suction device is in the fully depleted configuration where the sliding seal assembly is at location  1905 , the magnets  1914 ,  1915  may be detected by the first reed switch  1906 . Such an arrangement of reed switches in the alarm device and magnets in the suction device may help to reduce patient confusion when installing the suction device in the alarm device, and may help to ensure that the alarm system is able to alert a patient when the suction device is depleted, regardless of the suction device orientation in the alarm device. 
     As described previously, the attachment protrusions of a suction device may help to ensure that the reed switches and magnetic elements are situated in a specific configuration with respect to each other (e.g., such that the alarm system may detect the depleted state of the suction device regardless of the retention orientation). For example, the location of the first and second reed switches  1906 ,  1908  may define a line segment L 1  with a midpoint  1912 . The position of the sliding seal assembly  1904  in the fully charged state and the position of the sliding seal assembly in the depleted state may define a travel path along a line segment L 2  with a midpoint  1910 , as depicted in  FIG. 19C . The travel path may extend along the entire length of the suction chamber, or may extend along a portion thereof (e.g., ½, ⅔, ¾, of the length of the suction chamber, centered or offset from the center of the suction chamber). The attachment protrusions may be positioned such that the midpoint  1910  of the sliding seal assembly travel path is offset proximally from the midpoint  1912 , for example, by an offset amount L 3 . Shifting the midpoint  1910  by offset L 3  from the midpoint  1912  may help to ensure that when the suction device  1900  is in the fully charged state, the magnetic elements  1914 ,  1915  are not detectable by either reed switch, and when the suction device  1900  is in the fully depleted state, the magnet elements  1914 ,  1915  are detectable by at least one reed switch, regardless of the retention orientation of the suction device. For example,  FIG. 19B  depicts the location of the sliding seal assembly  1904  when the suction device  1900  is in the fully charged state. In such a location, the sliding seal assembly  1904  is not detectable by reed switch  1906 . When the suction device  1900  transitions to the depleted configuration, the sliding seal assembly may be at location  1905 , as depicted in  FIG. 19C , and may be detectable by reed switch  1908 .  FIG. 19D  depicts the suction device  1900 , but retained in the alarm device after it has been rotated 180° around the axis A 2  from the configuration shown in  FIG. 19B . In the fully charged state and/or partially depleted intermediate states, the magnetic elements  1914 ,  1915  are not detectable by either reed switch  1908  or reed switch  1906 . However, in the depleted configuration, the sliding seal assembly may be at location  1905 , where it may be detectable by reed switch  1906 . 
     The suction device may be configured to be retained in the alarm device such that the distance of magnetic elements of the sliding seal assembly to the nearest reed switch is less in the fully depleted state than in the fully charged state. As such, the alarm device may detect when the suction device is in the fully depleted state and generate an alert, but may not detect when the suction device is in the fully charged state. In some embodiments, the travel of the sliding seal assembly within the suction device may be such that the distance of the magnetic elements to the distal protrusions (e.g., protrusions  1530 ,  1532  of  FIG. 15C ) in the fully charged state may be greater than the distance of the magnetic elements to the proximal protrusions (e.g., protrusions  1526 ,  1528 ). Variations of these arrangements may be contemplated to ensure that regardless of the orientation of the suction device in the alarm device, the alarm system is able to detect when the suction device is depleted and to generate a signal to the patient. 
     In other variations, the suction device may be configured to be retained in the alarm device such that the distance of magnetic elements of the sliding seal assembly to the nearest reed switch is greater in the fully depleted state than in the fully charged state. In this variation, the alarm device may detect when the suction device is in the fully charged state, but not when it is in the fully depleted state, which may help signal that the suction device is properly installed. 
     While alarm devices comprising two reed switches have been described and depicted herein, it should be understood that some variations may have only one reed switch. For example, one variation of a reduced pressure therapy system may comprise a suction device comprising a sliding seal assembly with two magnetic elements and an alarm device comprising only one reed switch, as depicted schematically in  FIG. 20 . The alarm device  2000  may be configured to detect the depleted state (and not the charged state) of the suction device  2010 . The alarm device  2000  may comprise a reed switch  2002  located at a proximal portion  2001 , and one or more alignment tabs  2004  (e.g., one located on the left  2003  and right  2005  side of the alarm device). The suction device  2010  may comprise a suction chamber  2011  with a sliding seal assembly  2014  in the suction chamber, and one or more alignment protrusions  2016  along the left  2013  and right  2015  sides. The alignment tabs  2004  may be located towards the proximal portion  2001 . The alignment protrusions  2016  may be located in positions that correspond to the location of the alignment tabs  2004 , and may interlock with each other (e.g., by snap lock, etc.). Placement of the alignment features in an offset position (e.g., towards the proximal or distal end of the devices) may help a patient and/or practitioner to install the suction device in a desired orientation with respect to the alarm device. The suction device  2010  may be retained in the alarm device  2000  such that the left  2013  and right  2015  sides of the suction device are aligned with the left  2003  and right  2005  sides of the alarm device. The suction device  2010  may also be retained in the alarm device  2000  such that the right  2015  and left  2013  sides of the suction device are aligned with the left  2003  and right  2005  sides of the alarm device (e.g., rotated 180° around the longitudinal axis). Optionally, the suction device  2010  may be retained by the alarm device  2000  in an orientation where the relative position of the distal portion  2018  and the proximal portion  2019  is interchanged (e.g., rotated 180° around a transverse axis from the orientation depicted in  FIG. 20 ). The alignment tabs  2004  may be configured to interlock with the alignment protrusions  2016  in this transversely-rotated orientation. In such an orientation, the alarm device  2000  may be able to detect the depleted state of the suction device  2010 . In some variations, suction devices may comprise a sliding seal assembly having only have one magnetic element, and may be retained in an alarm device in two or fewer orientations. 
     In alternative variations, the alarm device may comprise three or more reed switches, which may allow for the detection of additional suction device configurations and orientations. Optionally, suction devices may comprise sliding seal assemblies that have two or more magnetic elements in various locations. The number and locations of reed switches and magnetic elements on the suction device and alarm device may be varied in accordance with the desired retention orientation of the suction device, as well as the number of suction device configurations that are to be detected. 
     Once the suction device has been detected to be in the fully depleted state, the microcontroller of an alarm system may response according to pre-programmed algorithms. For example, certain microcontroller modules may additionally comprise a programming interface that may allow scripts and instruction sets to be downloaded into the microcontroller. In some variations, the microcontroller may be programmed to implement a state machine  1300 , as represented by the state machine diagram depicted in  FIG. 13 . The microcontroller may activate certain alarm system components (e.g., LEDs, LCD screen, amplifiers, speakers, etc.) in accordance to its current state as determined by sensor and/or user inputs.  FIG. 13  merely depicts an example of a state machine that may be programmed into a microcontroller for used with an alarm system for a suction device, and it should be understood that a variety of state machines (e.g., with more or less states) may be implemented as may be suitable. In some variations, the microcontroller may be programmed to be in a “sleep” or low-power mode for the majority of its operation, and “wake” or activate every second or minute to check signals from the alarm system sensors and/or switches. In some variations, signal filters may be programmed into the microcontroller to help reduce false positive signals. If an alarm condition is detected (e.g., low battery, suction device nearing or at depletion, etc.), the microcontroller may remain in the activated state to generate the necessary alerts and indicators to trigger an action on the part of the patient and/or practitioner. The microcontroller may be programmed to drive the alert or indicator module for a certain amount of time, e.g., 1 minute, 2 minutes, 5 minutes, etc., and may be dormant or snoozed for a certain amount of time, e.g., 1 minute, 10 minutes, 30 minutes, etc., before driving the alert or indicator module again. For example, the alert module may issue a sound for 5 minutes (either continuously or in bursts), remain silent for 30 minutes, and then sound for 5 minutes if the suction device is not replaced. Optionally, a visual alert may accompany the audio alert. A snooze function may be provided where the audio alert may be silenced for a period of time (e.g., 5 minutes, 15 minutes, 25 minutes, etc.). If after the period time has elapsed and the suction device has not been replaced, the audio alert may continue to sound. Other such functions and modes may be programmed into the microcontroller as desired. 
     While some reduced pressure therapy systems described herein may have an alarm system, it should be understood that other variations of suction device may not have an alarm system. For example, some reduced pressure therapy systems may comprise a suction device and a clip, where the suction device and clip do not have any kind of alarm sensors or alerts. In some variations, a reduced pressure therapy system may comprise a suction device with a visual indicator (e.g., color) and a clip, without any sensor-based alarm system. In still other variations, a reduced pressure therapy system may comprise a suction device and an attachment strap, where suction device and the strap do not have any kind of alarm sensors or alerts. 
     Although the embodiments herein have been described in relation to certain examples, various additional embodiments and alterations to the described examples are contemplated within the scope of the invention. Thus, no part of the foregoing description should be interpreted to limit the scope of the invention as set forth in the following claims. For all of the embodiments described above, the steps of the methods need not be performed sequentially. Accordingly, it is not intended that the invention be limited, except as by the appended claims.