Abstract:
A portable NPWT system includes a dressing assembly for positioning over a wound to apply a negative pressure to the wound and a canister assembly. The canister assembly includes a control unit having a vacuum source and a controller and a collection canister in communication with the dressing assembly operable to receive fluid from the wound. The collection canister has ports to introduce a vacuum from the vacuum source into the collection canister. A ball float is provided to substantially close the suction port in response to one of collection of a predetermined volume of exudate in the collection canister, tilting of the collection canister beyond a predetermined angle of orientation or inversion of the collection canister.

Description:
CROSS-REFERENCE TO RELATED DOCUMENTS 
       [0001]    The present invention claims the benefit of and priority to U.S. provisional patent Application Ser. No. 61/078,838, filed on Jul. 8, 2008, disclosure of which may be referred to herein by reference. 
     
    
     BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    The present disclosure relates generally to treating a wound by applying negative pressure to the wound, and, more specifically, to a portable negative pressure wound therapy system for treating a wound. 
         [0004]    2. Description of Related Art 
         [0005]    Wound closure involves the migration of epithelial and subcutaneous tissue adjacent the wound towards the center and away from the base of the wound until the wound closes. Unfortunately, closure is difficult with large wounds, chronic wounds or wounds that have become infected. In such wounds, a zone of stasis (i.e. an area in which localized swelling of tissue restricts the flow of blood to the tissues) forms near the surface of the wound. Without sufficient blood flow, the epithelial and subcutaneous tissues surrounding the wound not only receive diminished oxygen and nutrients, but, are also less able to successfully fight microbial infection and, thus, are less able to close the wound naturally. Such wounds have presented difficulties to medical personnel for many years. 
         [0006]    Negative pressure wound therapy (NPWT), also known as suction or vacuum therapy, has been used in treating and healing wounds. Application of negative pressure, e.g. reduced or sub-atmospheric pressure, to a localized reservoir over a wound has been found to assist in closing the wound by promoting blood flow to the area, stimulating the formation of granulation tissue, and encouraging the migration of healthy tissue over the wound. Negative pressure may also inhibit bacterial growth by drawing fluids from the wound such as exudates, which may tend to harbor bacteria. This technique has proven particularly effective for chronic or healing-resistant wounds, and is also used for other purposes such as post-operative wound care. 
         [0007]    Generally, negative pressure therapy provides for a wound covering to be positioned over the wound to facilitate suction at the wound area. A conduit is introduced through the wound covering to provide fluid communication to an external vacuum source. Atmospheric gas, wound exudates, or other fluids may thus be drawn from the reservoir through the fluid conduit to stimulate healing of the wound. Exudates drawn from the reservoir may be deposited in a collection canister. 
         [0008]    Often, a portable NPWT device is worn by the patient so that the patient may remain ambulatory instead of being confined to a stationary position. While a patient is ambulatory, the portable NPWT device tends to tip or tilt in a multitude of directions. If there are enough exudates in the collection canister, the exudates may cover a suction port leading from the vacuum source to the collection canister because fluid 
         [0009]    In addition, portable NPWT devices have a control unit attached to the canister. The control unit generally contains the suction pump and sensitive electronics such as a pressure transducers, microprocessors, or the like. When the NPWT device tips, exudate may aspirate from the canister into the control unit thereby damaging the suction pump and/or electronic components. 
       SUMMARY 
       [0010]    The present disclosure relates to a portable NPWT system including a dressing assembly for positioning over a wound to apply a negative pressure to the wound and a canister assembly. The canister assembly includes a control unit having a vacuum source and a controller and a collection canister in communication with the dressing assembly operable to receive fluid from the wound. The collection canister has ports to introduce a vacuum from the vacuum source into the collection canister. A ball float is provided to substantially close the suction port in response to one of collection of a predetermined volume of exudate in the collection canister, tilting of the collection canister beyond a predetermined angle of orientation or inversion of the collection canister. 
         [0011]    The present disclosure also relates to a portable NPWT system including a dressing assembly for positioning over a wound to apply a negative pressure to the wound and a canister assembly. The canister assembly includes a control unit having a vacuum source and a controller and a collection canister in communication with the dressing assembly operable to receive fluid from the wound. The collection canister has ports to introduce a vacuum from the vacuum source into the collection canister. A closure valve mounted adjacent to the suction port is provided and is adapted to move from an open position where the negative pressure source is capable of drawing a vacuum in the collection canister through the suction port and a closed position where the suction port is substantially closed in response to one of collection of a predetermined volume of exudate in the collection canister, tilting of the collection canister beyond a predetermined angle of orientation or inversion of the collection canister. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    Various embodiments of the wound dressing system of the present disclosure are described herein with reference to the drawings wherein: 
           [0013]      FIG. 1  is a diagram of an embodiment of a NPWT system in accordance with the present disclosure; 
           [0014]      FIG. 2  is a diagram of an embodiment of a NPWT system in accordance with the present disclosure; 
           [0015]      FIG. 3  is a system diagram of a control system for a NPWT system in accordance with the present disclosure; 
           [0016]      FIG. 4A  is a diagram of a canister assembly for a NPWT system in accordance with the present disclosure; 
           [0017]      FIG. 4B  is a diagram of a canister assembly for a NPWT system in accordance with the present disclosure; 
           [0018]      FIG. 5  is a diagram of a control unit for a NPWT system in accordance with the present disclosure; 
           [0019]      FIG. 6  is a diagram of a collection canister for a NPWT system in accordance with the present disclosure; 
           [0020]      FIG. 7A  is a diagram of a collection canister for a NPWT system in accordance with the present disclosure; 
           [0021]      FIGS. 7B-7F  are a diagrams of a ball floats for a NPWT system in accordance with the present disclosure 
           [0022]      FIG. 8  is a diagram of a canister assembly for a NPWT system in accordance with the present disclosure; 
           [0023]      FIG. 8  is a top view of a collection canister for a NPWT system in accordance with the present disclosure; 
           [0024]      FIG. 10  is a diagram of a canister assembly for a NPWT system in accordance with the present disclosure. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0025]    Various embodiments of the present disclosure provide NPWT systems (or apparatus) including a collection canister having a chamber to collect wound fluids. Embodiments of the presently disclosed NPWT systems are generally suitable for use in applying negative pressure to a wound to facilitate healing of the wound in accordance with various treatment modalities. Embodiments of the presently disclosed NPWT systems are entirely portable and may be worn or carried by the user such that the user may be completely ambulatory during the therapy period. Embodiments of the presently disclosed NPWT apparatus and components thereof may be entirely reusable or may be entirely disposable after a predetermined period of use or may be individually disposable whereby some of the components are reused for a subsequent therapy application. 
         [0026]    Hereinafter, embodiments of the presently disclosed NPWT systems and embodiments of the presently disclosed sensors for use in NPWT systems will be described with reference to the accompanying drawings. Like reference numerals may refer to similar or identical elements throughout the description of the figures. As used herein, “wound exudate”, or, simply, “exudate”, generally refers to any fluid output from a wound, e.g., blood, serum, and/or pus, etc. As used herein, “fluid” generally refers to a liquid, a gas or both. 
         [0027]    Referring to  FIG. 1 , a NPWT apparatus according to an embodiment of the present disclosure is depicted generally as  10  for use on a wound bed “w” surrounded by healthy skin “s”. NPWT apparatus  10  includes a wound dressing  12  positioned relative to the wound bed “w” to define a vacuum chamber  14  about the wound bed “w” to maintain negative pressure at the wound area. Wound dressing  12  includes a contact layer  18 , a wound filler  20  and a wound cover  24 . 
         [0028]    Contact layer  18  is intended for placement within the wound bed “w” and may be relatively non-supportive or flexible to substantially conform to the topography of the wound bed “w”. A variety of materials may be used for the contact layer  18 . Contact layer  18  selection may depend on various factors such as the patient&#39;s condition, the condition of the periwound skin, the amount of exudate and/or the condition of the wound bed “w”. Contact layer  18  may be formed from perforated film material. The porous characteristic of the contact layer  18  permits exudate to pass from the wound bed “w” through the contact layer  18 . Passage of wound exudate through the contact layer  18  may be substantially unidirectional such that exudate does not tend to flow back into the wound bed “w”. Unidirectional flow may be encouraged by directional apertures, e.g., apertures positioned at peaks of undulations or cone-shaped formations protruding from the contact layer  18 . Unidirectional flow may also be encouraged by laminating the contact layer  18  with materials having absorption properties differing from those of the contact layer  18 , or by selection of materials that promote directional flow. A non-adherent material may be selected for forming the contact layer  18  such that the contact layer  18  does not tend to cling to the wound bed “w” or surrounding tissue when it is removed. One example of a material that may be suitable for use as a contact layer  18  is commercially available under the trademark XEROFLOW® offered by Tyco Healthcare Group LP (d/b/a Covidien). Another example of a material that may be suitable for use as the contact layer  18  is the commercially available CURITY® non-adherent dressing offered by Tyco Healthcare Group LP (d/b/a Covidien). 
         [0029]    Wound filler  20  is positioned in the wound bed “w” over the contact layer  18  and is intended to transfer wound exudate. Wound filler  20  is conformable to assume the shape of any wound bed “w” and may be packed up to any level, e.g., up to the level of healthy skin “s” or to overfill the wound such that wound filler  20  protrudes over healthy skin “s”. Wound filler  20  may be treated with agents such as polyhexamethylene biguanide (PHMB) to decrease the incidence of infection and/or other medicaments to promote wound healing. A variety of materials may be used for the wound filler  20 . An example of a material that may be suitable for use as the wound filler  20  is the antimicrobial dressing commercially available under the trademark KERLIX™ AMD offered by Tyco Healthcare Group LP (d/b/a Covidien). 
         [0030]    Cover layer  24  may be formed of a flexible membrane, e.g., a polymeric or elastomeric film, which may include a biocompatible adhesive on at least a portion of the cover layer  24 , e.g., at the periphery  26  of the cover layer  24 . Alternately, the cover layer  24  may be a substantially rigid member. Cover layer  24  may be positioned over the wound bed “w” such that a substantially continuous band of a biocompatible adhesive at the periphery  26  of the cover layer  24  forms a substantially fluid-tight seal with the surrounding skin “s”. An example of a material that may be suitable for use as the cover layer  24  is commercially available under the trademark CURAFORM ISLAND® offered by Tyco Healthcare Group LP (d/b/a Covidien). 
         [0031]    Cover layer  24  may act as both a microbial barrier and a fluid barrier to prevent contaminants from entering the wound bed “w” and to help maintain the integrity thereof. 
         [0032]    In one embodiment, the cover layer  24  is formed from a moisture vapor permeable membrane, e.g., to promote the exchange of oxygen and moisture between the wound bed “w” and the atmosphere. An example of a membrane that may provide a suitable moisture vapor transmission rate (MVTR) is a transparent membrane commercially available under the trade name POLYSKIN®II offered by Tyco Healthcare Group LP (d/b/a Covidien). A transparent membrane may help to permit a visual assessment of wound conditions to be made without requiring removal of the cover layer  24 . 
         [0033]    Wound dressing  12  may include a vacuum port  30  having a flange  34  to facilitate connection of the vacuum chamber  14  to a vacuum system. Vacuum port  30  may be configured as a rigid or flexible, low-profile component and may be adapted to receive a conduit  36  in a releasable and fluid-tight manner. An adhesive on at least a portion of the underside of the flange  34  may be used to provide a mechanism for affixing the vacuum port  30  to the cover layer  24 . The relative positions, size and/or shape of the vacuum port  30  and the flange  34  may be varied from an embodiment depicted in  FIG. 1 . For example, the flange  34  may be positioned within the vacuum chamber  14  such that an adhesive on at least a portion of an upper side surface of the flange  34  affixes the vacuum port  30  to the cover layer  24 . A hollow interior portion of the vacuum port  30  provides fluid communication between the conduit  36  and the vacuum chamber  14 . Conduit  36  extends from the vacuum port  30  to provide fluid communication between the vacuum chamber  14  and the vacuum source  40 . Alternately, the vacuum port  30  may not be included in the dressing  12  if other provisions are made for providing fluid communication with the conduit  36 . 
         [0034]    Any suitable conduit may be used for the conduit  36 , including conduit fabricated from flexible elastomeric or polymeric materials. In the NPWT apparatus  10  illustrated in  FIG. 1 , the conduit  36  includes a first conduit section  36 A, a second conduit section  36 B, a third conduit section  36 C and a fourth conduit section  36 D. The first conduit section  36 A extends from the vacuum port  30  and is coupled via a fluid line coupling  100  to the second conduit section  36 B, which extends to the collection canister  38 . The third conduit section  36 C extends from the collection canister  38  and is coupled via another fluid line coupling  100  to the fourth conduit section  36 D, which extends to the vacuum source  40 . The shape, size and/or number of conduit sections of the conduit  36  may be varied from the first, second, third and fourth conduit sections  36 A,  36 B,  36 C and  36 D depicted in  FIG. 1 . 
         [0035]    The first, second, third and fourth conduit sections  36 A,  36 B,  36 C and  36 D of the conduit  36  may be connected to components of the apparatus  10  by conventional air-tight means, such as, for example, friction fit, bayonet coupling, or barbed connectors. The connections may be made permanent. Alternately, a quick-disconnect or other releasable connection means may be used to provide some adjustment flexibility to the apparatus  10 . 
         [0036]    Collection canister  38  may be formed of any type of container that is suitable for containing wound fluids. For example, a semi-rigid plastic bottle may be used for the collection canister  38 . A flexible polymeric pouch or other hollow container body may be used for the collection canister  38 . Collection canister  38  may contain an absorbent material to consolidate or contain the wound fluids or debris. For example, 
         [0037]    The collection canister  38  is in fluid communication with the wound dressing  12  via the first and second conduit sections  36 A,  36 B. The third and fourth conduit sections  36 C,  36 D connect the collection canister  38  to the vacuum source  40  that generates or otherwise provides a negative pressure to the collection canister  38 . Vacuum source  40  may include a peristaltic pump, a diaphragmatic pump, continuous pump or other suitable mechanism. Vacuum source  40  may be a miniature pump or micropump that may be biocompatible and adapted to maintain or draw adequate and therapeutic vacuum levels. The vacuum level of subatmospheric pressure achieved may be in the range of about 20 mmHg to about 500 mmHg. In embodiments, the vacuum level may be about 75 mmHg to about 125 mmHg, or about 40 mmHg to about 80 mmHg. One example of a peristaltic pump that may be used as the vacuum source  40  is the commercially available Kangaroo PET Eternal Feeding Pump offered by Tyco Healthcare Group LP (d/b/a Covidien). Vacuum source  40  may be actuated by an actuator (not shown) which may be any means known by those skilled in the art, including, for example, alternating current (AC) motors, direct current (DC) motors, 
         [0038]    In embodiments, the NPWT apparatus  10  includes one or more fluid line couplings  100  that allow for selectable coupling and decoupling of conduit sections. For example, a fluid line coupling  100  may be used to maintain fluid communication between the first and second conduit sections  36 A,  36 B when engaged, and may interrupt fluid flow between the first and second conduit sections  36 A,  36 B when disengaged. Thus, fluid line coupling  100  may facilitate the connection, disconnection or maintenance of components of the NPWT apparatus  10 , including the replacement of the collection canister  38 . Additional or alternate placement of one or more fluid line couplings  100  at any location in line with the conduit  36  may facilitate other procedures. For example, the placement of a fluid line coupling  100  between the third and fourth conduit sections  36 C,  36 D, as depicted in  FIG. 1 , may facilitate servicing of the vacuum source  40 . 
         [0039]    Referring to  FIG. 2 , the NPWT system shown generally as  200  can be worn by a patient or user and includes a dressing assembly  210 , a wound port assembly  220 , an extension assembly  230  and a canister assembly  240 . Dressing assembly  210  is positioned relative to the wound area to define a vacuum chamber about the wound area to maintain negative pressure at the wound area. Dressing assembly  210  may be substantially sealed from extraneous air leakage, e.g., using adhesive coverings. Wound port assembly  220  is mounted to the dressing assembly  210 . For example, wound port assembly  220  may include a substantially continuous band of adhesive at its periphery for affixing the wound port assembly  220  to the dressing assembly  210 . Extension assembly  230  is coupled between the wound port assembly  220  and the canister assembly  240  and defines a fluid flow path between the wound port assembly  220  and the canister assembly  240 . A hollow interior of the wound port assembly  220  provides fluid communication between the extension assembly  230  and the interior of the dressing assembly  210 . Dressing assembly  210  and the wound port assembly  220  shown in  FIG. 2  are similar to components of the wound dressing  12  of  FIG. 1  and further description thereof is omitted in the interests of brevity. 
         [0040]    Canister assembly  240  includes a control unit  246  and a collection canister  242  disposed below the control unit  246 . Control unit  246  may be reusable and collection canister  242  may be disposable. Control unit  246  and the collection canister  242  may be releasably coupled. Mechanisms for selective coupling and decoupling of the control unit  246  and the collection canister  242  include fasteners, latches, clips, straps, bayonet mounts, magnetic couplings, and other devices. Collection canister  242  may consist of any container suitable for containing wound fluids. 
         [0041]    In one embodiment, the NPWT system  200  is capable of operating in a continuous mode or an alternating mode. In the continuous mode, the control unit  246  controls a pump to continuously supply a selected vacuum level at the collection canister  242  to create a reduced pressure state within the dressing assembly  210 . In the alternating mode, the control unit  246  controls the pump to alternating supply a first negative pressure, e.g., about 80 mmHg, at the collection canister  242  for a preset fixed amount of time and a second negative pressure, e.g., about 50 mmHg, at the collection canister  242  for a different preset fixed amount of time. 
         [0042]    In general, the output of the pump is directly related to the degree of air leakage in the NPWT system  200  and the open volume in the collection canister  242 . If there is sufficient air leakage in the system  200 , e.g., at the dressing assembly  210 , the pump can remain on continuously and the control unit  246  can control negative pressure at the collection canister  242  by adjusting the pump speed. Alternatively, if there is not sufficient air leakage in the system  200  to permit the pump to remain on continuously, the control unit  246  can control negative pressure at the collection canister  242  by turning the pump on and off, e.g., for non-equal on/off periods of time. 
         [0043]    Canister assembly  240  may be constructed from a variety of materials such as Lucite™ polycarbonate, metals, metal alloys, plastics, or other durable materials capable of withstanding forces applied during normal use, and may have some capability of withstanding possibly excessive forces resulting from misuse. Collection canister  242  may include a window with fluid level markings or for promoting visual assessment of the amount of exudate contained within the collection canister  242 . A transparent or partially transparent collection canister  242  may thus assist in determining the remaining capacity of the collection canister  242  and/or when the collection canister  242  should be replaced. 
         [0044]    Referring to  FIG. 3 , the NPWT device has a control system generally shown as  300 . Control system  300  may include a controller  310  that controls the operation of the NPWT device. Controller  310  may include at least one processor  312  and at least one memory module  314 . The memory module  314  may be a volatile memory (e.g. DRAM, SRAM, or the like) or a non-volatile memory (e.g., ROM, PROM, EPROM, EEPROM, a semiconductor flash memory, or the like). The memory module  314  stores instructions that are executed by the processor  312  for controlling the NPWT device. 
         [0045]    Controller  310  controls a vacuum source  320  based on the mode of therapy selected as well as inputs received from pressure transducer  330  and pressure transducer  330 . Vacuum source  320  may be a miniature pump or micropump that may be biocompatible and adapted to maintain or draw adequate and therapeutic vacuum levels. The vacuum level of subatmospheric pressure achieved may be in the range of about 20 mmHg to about 500 mmHg. In embodiments, the vacuum level may be about 75 mmHg and about 125 mmHg, or between about 30 mmHg and 80 mmHg. Vacuum source  320  is actuated by an actuator which may be any means known by those skilled in the art, including, for example, AC motors, DC motors, voice coil actuators, solenoids, etc. 
         [0046]    Controller  310  maintains a selected vacuum level at the canister  242  by monitoring the pressure in the canister  242  using pressure transducer  330 . If the vacuum level in the canister  242  exceeds a threshold as measured by pressure transducer  340 , the controller  310  turns the vacuum source  320  off or reduces the output of the vacuum source  320  to reduce the vacuum level in the canister  242 . If the vacuum level in the canister  242  falls below a threshold as measured by pressure transducer  340 , the controller  310  turns the vacuum source  320  on or increases the output of the vacuum source  320  to increase the vacuum level in the canister  242 . 
         [0047]    Controller  310  also controls operation of the vacuum source  320  based on the output of pressure transducer  340 . Pressure transducer  340 , which could be a pressure switch, monitors the pressure at the inlet of the vacuum source  320  to determine a pressure spike indicative of the replace canister condition which will be described in more detail below. Alternately, if a pressure switch is used, once a threshold of negative pressure is reached, it will actuate thereby signaling the controller  310  to turn the vacuum source  320  off. 
         [0048]    Control system  300  may include a speaker  350  to produce an audible indication to notify the user of a condition, e.g., leak, canister assembly tip, failed pressure sensor, failed pump, excessive vacuum, or low battery conditions. The control system  300  may also include a display  360  to notify a user of an alarm condition, a state of the NPWT device, or other information related to the treatment of a wound by the NPWT device. Display  360  may be a liquid crystal display (LCD), a light emitting diode (LED) display, or any number of LEDs, neon lamps, incandescent bulbs, or the like. 
         [0049]    Control system  300  responds to various sensed events by signaling alarms. Various types of conditions may be signaled by alarms. In embodiments, control system  300  is capable of signaling alarms for failed pressure sensor condition, use odometer expired condition, watchdog reset condition, failed pump condition, leak condition, replace canister condition, excessive vacuum condition, failed LEDs condition, low battery condition, very low battery condition, and failed battery condition. Priority levels may be associated with alarms. In embodiments, the priority levels of alarms are low priority alarm, medium priority alarm, and system alarm (highest priority). Low priority alarms, when triggered, may be continuously indicated. Medium priority alarms and system alarms, when triggered, may have a flashing indication. 
         [0050]    Control system  300  may stop operation of the in response to an alarm, e.g., depending on alarm type and/or priority level. In embodiments, the control system  300  stops operation of the pump in response to system alarms, e.g., failed pressure sensor system alarm, use odometer expired system alarm, watchdog reset system alarm, failed pump system alarm, excessive vacuum system alarm, and/or failed LEDs system alarm. 
         [0051]    If an air leak develops in the NPWT system  200 , e.g., at the dressing assembly  210 , for which the control unit  246  cannot compensate by increasing the pump speed, the control system  300  may indicate an alarm. For example, the control system  300  may indicate a leak alarm after two consecutive minutes of operation in which the vacuum level is below the current set point (or below the minimum level of a set point range). 
         [0052]    In embodiments, the control system  300  includes a user interface (not shown) which may be incorporated into the display  360  or may be a set of user actuated switches or buttons. The user turns ON the canister assembly  240  by pressing a power button (not shown). When the power button is pressed, the control system  300  performs a series of internal checks during power up. In one embodiment, after successfully completing the power-up tasks, the control system  300  turns on the pump  320  using the stored settings. At initial activation of the canister assembly  240 , the stored settings are the default settings. In one embodiment, the default settings for controlling the pump  320  are 80 mmHg and continuous mode. In one embodiment, the currently stored vacuum level setting can be altered by the user, e.g., to 50 mmHg. In one embodiment, the currently stored mode setting can be altered by the user, e.g., to an alternating mode. 
         [0053]    Referring to  FIGS. 4A and 4B , the two cross-sectional views of a canister assembly  240  illustrate the electronic, electrical and pneumatic components of a NPWT device in accordance with an embodiment of the present disclosure. At the top portion of the control unit  246 , immediately below a user interface (not shown), is a printed circuit board (PCB)  402 . Pressure transducer  330  is attached to the PCB  402 . The controller  310  includes circuits that power the pressure transducer  330  and receive its pressure signals (i.e., electrical signals indicative of the negative pressure being measured). The PCB  402  includes signal processing circuits that condition the signals, including filtering to reject electrical noise and provide a clean signal to the controller  310 . 
         [0054]    Pressure transducer  330  has a hydrophobic filter at area  404 , which protects the pressure transducer  330  if exudate fluid entered a pressure transducer tube (not shown). The pressure transducer is attached to the hydrophobic filter at area  404  and the opposite end of the pressure transducer tube attaches to a transducer port  503  (shown in  FIG. 5 ), at the bottom of the control unit  246 . The tube is fit by friction. The transducer port  503  at the bottom of the control unit  246  pneumatically communicates with the canister  242  through the canister transducer port  604  (shown in  FIG. 6 ), when the canister  242  is attached to the control unit  246 . The pressure transducer  330  directly monitors the vacuum level at the canister transducer port  604 . 
         [0055]    A pressure transducer  340  (shown in  FIG. 4B ), which could be a pressure switch, may also be attached to the PCB  402 . The pressure transducer  340  has its own set of signal conditioning circuits in controller  310  as may be required. A pressure transducer tube  340 T is attached to the neck of the pressure transducer  340 . The other end of the pressure transducer tube  340 T is attached to the pump inlet tube  408  (shown in  FIG. 4A ). The pressure transducer  340  monitors the pressure at the pump inlet  412  to determine a pressure spike indicative of the replace canister condition which will be described below. 
         [0056]    A direct current (DC) motor-driven pump  410  is contained within the control unit  246 . A vibration damping tape, e.g., visco-elastic damping tape, may be applied to the outer surface of the pump  410  to reduce vibration and its associated noise. The pump  410  may be contained within its own sub-housing  414  which may be hollow or formed entirely of open cell molded foam, e.g., used as a silencer to provide sound mitigation by reducing the sound energy of the expelled air during operation. As part of the sound mitigation arrangement, a tube may be fitted to the pump sub-housing  414 . 
         [0057]    A pump inlet tube  408  is attached on one end to the inlet port  412  of the pump  410  on one end. The other end of the pump inlet tube  408  attaches to the filter assembly  416 . The filter assembly  416  has an orifice  418 . A suction chamber is located directly below the filter assembly  416  that receives the canister suction port  601  (shown in  FIGS. 6 &amp; 7 ) when the canister  242  is attached to the control unit.  246 . 
         [0058]      FIG. 5  is a view of the bottom portion of the control unit  246  and illustrates a control unit suction port  504  and a control unit transducer port  503 . Control unit suction port  504  is connected internally to the pump  510 . The control unit transducer port  503  is connected internally to the pressure transducer  330 . Associated with the control unit transducer port  503  is a protrusion  505  which interfaces with the canister transducer port  604 , which pushes open a silicone valve  420  (shown in  FIG. 4B ). 
         [0059]      FIG. 6  illustrates the canister top  600  which encloses the open volume of the canister  242 . In  FIG. 6 , the canister top  600  is depicted in the assembled condition with respect to the canister  242 . The canister top  600  includes a canister suction port  601  and a canister transducer port  604 . The canister suction port  601  and the canister transducer port  604  include respective o-rings  602 ,  605  which are received within the respective control unit suction port  504  and the control unit transducer port  503  of the control unit ( FIG. 5 ) in fluid tight relation when the control unit  246  is mounted to the canister top  600 . The canister top  600  further includes a wound exudate port  607  extending into the open volume portion  608  of the canister  242  in fluid communication with extension assembly  230  to receive exudate from the wound. 
         [0060]      FIG. 7A  illustrates the bottom portion  700  of canister top  600 . The bottom portion  700  contains a suction port  601  with an o-ring  602  as discussed before. A silicone valve  703 , also known as a rolling sleeve valve, may be located at the bottom of the suction port  601 . Below the silicone valve  703 , is a splash guard  704 , which restricts contact of fluid with the silicone valve  703  if the canister  242  is tipped or shaken while not attached to the control unit  246 . A ball seat housing  705  is below the splash guard  704 , further protecting the silicone valve and also providing an attachment point to the ball cage  707 . Inside of the ball seat housing  705  is a recess that receives the ball seat  708 . An orifice  709  is centered in the ball seat  708  embedded in the ball seat housing. To prevent encrustation of bottom portion  700  and all associated parts by the drying exudate, a coating may be applied to the components, which inhibit this encrustation by affecting the formation and binding of proteins or may decrease wetability to allow liquid to shed. In conjunction with the splash guard  704  a second layer may be added to it on the exudate side facing the open volume canister that is permeable and does not allow exudate to encrust upon it. Encrustation of the membrane inhibits air flow through it. 
         [0061]    When the ball float  706  contacts the seat  708 , air flow to the pump  410  is blocked while the pump  410  continues to run, thereby producing the pressure spike mentioned, which indicates the replace canister condition. A fixed leak is incorporated either into the pump  410  or to the pump inlet tube  408 , which is meant to relieve the negative pressure at the pump inlet and at the floating ball seat  708 , so that the floating ball  706  can fall out of the sealing position. 
         [0062]      FIGS. 7B through 7F  depict examples of ball floats that may be used in the NPWT device according to an embodiment of the present disclosure. To prevent encrustation of the ball float by the drying exudate, a coating  712  may be applied to the ball float  710  (as shown in  FIG. 7B ), which inhibit this encrustation by affecting the formation and binding of proteins or may decrease wetability to allow liquid to shed. Coating  712  may be made from a hydrophobic material, latex or TEFLON®, or the like. 
         [0063]      FIG. 7C  depicts a ball float  720  having a groove or track  722  running along the center of the ball float  720 . Groove  722  could be a straight line or a wavy line.  FIG. 7D  depicts a ball float  730  having multiple grooves or tracks  732 . Grooves  732  may be arranged in concentric circles around to the ball float  730 . The distance between each concentric circle may be constant or may vary.  FIG. 7E  depicts a ball float  740  having a first groove or track  742  and a second groove or track  744 . Groove  742  and groove  744  intersect each other at two points on ball float  740 . The angle “α” between groove  742  and groove  744  can range from greater than 0° to less than 180°.  FIG. 7F  depicts a ball float  750  having multiple grooves  752 . Grooves  752  may be spaced evenly around the ball float or spaced at varying degrees. Grooves  752  intersect each other at an axis of the ball float  750  generally shown as  754 . 
         [0064]      FIGS. 8 and 9  illustrate a canister assembly  800  in accordance with an embodiment of the present disclosure. Canister assembly  800  includes housing  810 , control unit  812  disposed within the housing  810  and collection canister  814 . Housing  810  may be any suitable rigid member adapted for donning by the subject. Control unit  812  may incorporate vacuum source or pump  824 , actuator or motor  826  for activating the vacuum source  824  and power source  828 . Vacuum source  824  generates or otherwise provides negative pressure to the wound. 
         [0065]    Power source  828  may be disposed within housing  810  or separately mountable to the housing  810 . A suitable power source  828  includes alkaline batteries, wet cell batteries, dry cell batteries, nickel cadmium batteries, solar generated means, lithium batteries, NiMH batteries (nickel metal hydride) each of which may be of the disposable or rechargeable variety. 
         [0066]    Housing  810  further includes vent portal  830  configured to vent exhaust air from vacuum source  824  through exhaust port  832 . Vent portal  830  extends from housing  810  and may be directly connected to vacuum source  824 . It is also envisions that vent portal  830  may exhaust air from within housing  810  rather than directly from vacuum source  824 . Exhaust port  832  may include filter  834  extending across the exhaust port  832 . Filter  834  may be a bacterial filter to prevent emission of bacteria from housing  810 . 
         [0067]    Collection canister  814  collects exudates “e” removed from the wound bed “w’ during therapy through conduit, or tubing,  806 . Collection canister  814  is associated with housing  810  and may be incorporated within the housing  810  or releasably connected to the housing  810  by conventional means. Housing  810  and collection canister  814  of canister assembly  800  may be releasably coupled. Mechanisms for selective coupling and decoupling of housing  810  and collection canister  814  include fasteners, latches, clips, straps, bayonet mounts, magnetic couplings, and other devices. 
         [0068]    Collection canister  814  may comprise any container suitable for containing wound fluids and is substantially rigid defining an internal chamber  836  in fluid communication with tubing  806 . Collection canister  814  may contain an absorbent material to consolidate or contain the wound drainage or debris. In embodiments, at least a portion of collection canister  814  may be transparent to assist in evaluating the color, quality, or quantity of wound exudates. A transparent canister may thus assist in determining the remaining capacity of the canister or when the canister should be replaced. In the alternative, collection canister  814  may be relatively flexible. 
         [0069]    Collection canister  814  includes fluid inlet  838  and suction port  840 . Fluid inlet  838  is configured to operably engage conduit  806 . Fluid inlet  838  may be connectable with conduit  806  by conventional air and fluid tight means, such as those described above. In embodiments, fluid inlet  838  may contain a luer lock or other connector within the purview of those skilled in the art to secure the end of conduit  806  with the fluid inlet  838 . It is envisioned that fluid inlet  838  is configured to receive a cap in order to prevent leakage of exudates and odor from internal chamber  836  of collection canister  814  when housing  810  is separated from the canister  814 . 
         [0070]    Suction port  840  is in fluid communication with vacuum source  824  and may be an opening defined in a wall of housing  810 . A filter  842 , such as a hydrophobic membrane or baffling to prevent exudates from being aspirated into pump  810  may be disposed adjacent or within suction port  840 . Filter  842  may also include charcoal or other odor absorbing materials and may prevent the passage of bacteria. Pump  824  creates a vacuum within internal chamber  836  of collection canister  832  by drawing air through suction port  840 . 
         [0071]    Collection canister  814  includes closure valve  844 . Closure valve  844  is pivotally mounted about hinge  846  which is connected to internal chamber surface of collection canister  814 . Closure valve  844  assumes the open position depicted in  FIG. 8  when collection canister  814  is upright and not filled with exudates “e”. Specifically, the gravitational weight of closure valve  844  will ensure that the closure valve is pivoted to the open condition in the presence of the aforedescribed conditions. As an alternative, closure valve  844  also may be resiliently biased to the open position depicted as in  FIG. 8 . Means for biasing closure valve  844  are envisioned including a torsion spring  848  mounted about hinge  846  and operatively engageable with the closure valve  844 . In the alternative, a leaf spring  850  may be connected to an interior surface of canister  814  and extend into engagement with closure valve  844  to normally bias the closure valve  844  to the open position. In embodiments, closure valve  844  is at a predetermined angle “A” when in the fully open position. Angle may range from about 10° to about 70° relative to the longitudinal axis “k” of collection canister  814 . Closure valve  844  is of sufficient weight or mass to remain in the open condition even in the presence of a vacuum draw generated during operation of pump  824 . 
         [0072]    Closure valve  844  prevents exudates from clogging and/or entering pump  824  or control unit  812  when collection canister  814  is in an inverted or a tilted position. For example, when collection canister  844  is tilted beyond a predetermined orientation, e.g., when on its side or inverted with suction port  840  facing in a general downward direction, closure valve  844  moves under its own weight, the weight of exudates, and/or gravity to a closed position. Moreover, when tilted or inverted, closure valve  844  defines a moment arm thereby causing the closure valve  844  to pivot about hinge  846  from the open position to the closed position ( FIG. 10 ). The moment arm defined by closure valve  844  may be altered by adjusting the length or weight of the closure valve  844 . 
         [0073]    In the closed position of  FIG. 10 , closure valve  844  seals suction port  840  thereby sealing the exudates “e” within canister  814  and/or preventing clogging of filter  842 . It is envisioned that closure valve  844  may define seat  852  which resides within suction port  844  in sealed engagement with the wall surfaces defining the suction port  840 . Seat  852  may include an elastomeric member to facilitate formation of a seal between the two components. In the closed position, a vacuum change (e.g., drop in vacuum) will alert the subject of the disoriented canister. The vacuum change may be identified or recognized by the user through increased noise or churning of the vacuum source  824 . In the alternative, a pressure transducer  856  may be in communication with internal chamber  836  to detect changes in pressure. Logic associated with transducer  856  and vacuum source  824  may reduce the speed of vacuum source  824  or stop operation of the vacuum source  824 . 
         [0074]    While the disclosure has been illustrated and described, it is not intended to be limited to the details shown, since various modifications and substitutions can be made without departing in any way from the spirit of the present disclosure. As such, further modifications and equivalents of the invention herein disclosed can occur to persons skilled in the art using no more than routine experimentation, and all such modifications and equivalents are believed to be within the spirit and scope of the disclosure as defined by the following claims.