Patent Publication Number: US-8986267-B2

Title: Reduced pressure indicator for a reduced pressure source

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 12/434,579, filed May 1, 2009, which claims the benefit of U.S. Provisional Application No. 61/050,107, filed May 2, 2008, and which is a continuation-in-part application of U.S. patent application Ser. No. 11/974,534, filed Oct. 15, 2007, which claims the benefit U.S. Provisional Application No. 60/851,494, filed Oct. 13, 2006; this application is a continuation-in-part application of U.S. patent application Ser. No. 12/069,262, filed Feb. 8, 2008, which claims the benefit U.S. Provisional Application No. 60/900,555, filed Feb. 9, 2007. All of the above-referenced applications are hereby incorporated by reference. 
    
    
     BACKGROUND 
     1. Field of the Invention 
     The present invention relates generally to the field of tissue treatment, and more specifically to a system and method for applying reduced pressure at a tissue site. 
     2. Description of Related Art 
     Clinical studies and practice have shown that providing a reduced pressure in proximity to a tissue site augments and accelerates the growth of new tissue at the tissue site. The applications of this phenomenon are numerous, but one particular application of reduced pressure has involved treating wounds. This treatment (frequently referred to in the medical community as “negative pressure wound therapy,” “reduced pressure therapy,” or “vacuum therapy”) provides a number of benefits, including migration of epithelial and subcutaneous tissues, improved blood flow, and micro-deformation of tissue at the wound site. Together these benefits result in increased development of granulation tissue and faster healing times. Typically, reduced pressure is applied to tissue through a porous pad or other manifold device. The porous pad contains cells or pores that are capable of distributing reduced pressure to the tissue and channeling fluids that are drawn from the tissue. The porous pad may be incorporated into a dressing having other components that facilitate treatment. 
     SUMMARY 
     The problems presented by existing reduced pressure systems are solved by the systems and methods of the illustrative embodiments described herein. In one illustrative embodiment, a reduced pressure apparatus includes a first casing portion and a second casing portion, the second casing portion being slidably coupled to the first casing portion such that the first casing portion is compressible into a plurality of positions relative to the second casing portion. The plurality of positions includes a fully compressed position and a fully uncompressed position. An indicator is disposed on at least one of the first casing portion and the second casing portion, the indicator being exposed when the first casing portion is in the fully uncompressed position. 
     In another embodiment, a reduced pressure therapy system for administering reduced pressure treatment to a tissue site includes a manifold adapted to be positioned at the tissue site, a reduced pressure source in fluid communication with the manifold to deliver a reduced pressure to the manifold, and a sealing member adapted to cover the tissue site to form a sealed space between the sealing member and the tissue site, the sealed space being in fluid communication with the reduced pressure source. The reduced pressure source includes a top casing portion and a bottom casing portion, the bottom casing portion being slidably coupled to the top casing portion such that the top casing portion is positionable in a plurality of positions relative to the bottom casing portion. The plurality of positions includes a fully compressed position, a fully uncompressed position, and a plurality of intermediate positions between the fully compressed position and the fully uncompressed position. The reduced pressure source is operable to deliver the reduced pressure when the top casing portion is in the fully compressed position. The reduced pressure source further includes an indicator disposed on at least one of the top casing portion and the bottom casing portion. The indicator is exposed when the top casing portion is in at least one of the plurality of intermediate positions. 
     In yet another embodiment, a reduced pressure apparatus includes a substantially cylindrical top casing portion and a substantially cylindrical bottom casing portion. The substantially cylindrical bottom casing portion has a larger diameter than the substantially cylindrical top casing portion. The substantially cylindrical top casing portion is slidably received by the substantially cylindrical bottom casing portion such that the substantially cylindrical top casing portion is positionable in a plurality of positions relative to the substantially cylindrical bottom casing portion. The plurality of positions includes a fully compressed position, a fully uncompressed position, and a plurality of intermediate positions between the fully compressed position and the fully uncompressed position. The reduced pressure apparatus is operable to deliver a reduced pressure as the substantially cylindrical top casing portion moves from the fully compressed position to the fully uncompressed position. The reduced pressure apparatus further includes a color strip disposed on the substantially cylindrical top casing portion such that the color strip is exposed when the substantially cylindrical top casing portion is in the fully uncompressed position and is obscured when the substantially cylindrical top casing portion is in the fully compressed position. 
     Other objects, features, and advantages of the illustrative embodiments will become apparent with reference to the drawings and detailed description that follow. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a block diagram of an apparatus for applying reduced pressure at a tissue site in accordance with an illustrative embodiment; 
         FIG. 2  illustrates a cross-sectional view of an apparatus for applying reduced pressure at a tissue site in accordance with an illustrative embodiment; 
         FIG. 3  illustrates a perspective view of a compressible pump in an apparatus for applying reduced pressure at a tissue site in accordance with an illustrative embodiment; 
         FIG. 4  illustrates a cross-sectional view of a filter housing in an apparatus for applying reduced pressure at a tissue site in accordance with an illustrative embodiment; 
         FIG. 5  illustrates a cross-sectional view of an interlocking seal in an apparatus for applying reduced pressure at a tissue site in accordance with an illustrative embodiment; 
         FIG. 6  illustrates a cross-sectional view of an interlocking seal in an apparatus for applying reduced pressure at a tissue site in accordance with an illustrative embodiment; 
         FIG. 7  illustrates a cross-sectional view of an outlet valve in an apparatus for applying reduced pressure at a tissue site in accordance with an illustrative embodiment; 
         FIG. 8  illustrates a cross-sectional view of a connection joint in an apparatus for applying reduced pressure at a tissue site in accordance with an illustrative embodiment; 
         FIG. 9  illustrates a perspective view of outlet valves on a compressible pump in an apparatus for applying reduced pressure at a tissue site in accordance with an illustrative embodiment; 
         FIG. 10  illustrates a cross-sectional view of an outlet valve in an apparatus for applying reduced pressure at a tissue site in accordance with an illustrative embodiment; 
         FIG. 11  illustrates a cross-sectional view of an outlet valve in an apparatus for applying reduced pressure at a tissue site in accordance with an illustrative embodiment; 
         FIG. 12  illustrates a cross-sectional view of an outlet valve in an apparatus for applying reduced pressure at a tissue site in accordance with an illustrative embodiment; 
         FIG. 13  illustrates a perspective view of an outlet valve in an apparatus for applying reduced pressure at a tissue site in accordance with an illustrative embodiment; 
         FIG. 14  illustrates a perspective view of an apparatus for applying reduced pressure at a tissue site in accordance with an illustrative embodiment; 
         FIG. 15  illustrates a perspective view of two compressible pumps in an apparatus for applying reduced pressure at a tissue site in accordance with an illustrative embodiment; 
         FIG. 16  illustrates a perspective view of an apparatus for applying reduced pressure at a tissue site in accordance with an illustrative embodiment; 
         FIG. 17   a  illustrates a perspective view of an apparatus for determining a reduced pressure associated with a reduced pressure source in accordance with an illustrative embodiment; 
         FIG. 17   b  shows a side view of the apparatus of  FIG. 17   a  in the compressed position; 
         FIG. 17   c  shows a reduced pressure therapy system that utilizes the apparatus shown in  FIG. 17   a;    
         FIG. 18  illustrates a perspective view of an apparatus for determining a reduced pressure associated with a reduced pressure source in accordance with an illustrative embodiment; and 
         FIG. 19  illustrates a flowchart illustrating a process for applying reduced pressure at a tissue site in accordance with an illustrative embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS 
     In the following detailed description of the illustrative embodiments, reference is made to the accompanying drawings that form a part hereof. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is understood that other embodiments may be utilized and that logical structural, mechanical, electrical, and chemical changes may be made without departing from the spirit or scope of the invention. To avoid detail not necessary to enable those skilled in the art to practice the embodiments described herein, the description may omit certain information known to those skilled in the art. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims. 
     The term “reduced pressure” as used herein generally refers to a pressure less than the ambient pressure at a tissue site that is being subjected to treatment. In most cases, this reduced pressure will be less than the atmospheric pressure at which the patient is located. Alternatively, the reduced pressure may be less than a hydrostatic pressure associated with tissue at the tissue site. Although the terms “vacuum” and “negative pressure” may be used to describe the pressure applied to the tissue site, the actual pressure reduction applied to the tissue site may be significantly less than the pressure reduction normally associated with a complete vacuum. Reduced pressure may initially generate fluid flow in the area of the tissue site. As the hydrostatic pressure around the tissue site approaches the desired reduced pressure, the flow may subside, and the reduced pressure is then maintained. Unless otherwise indicated, values of pressure stated herein are gauge pressures. Similarly, references to increases in reduced pressure typically refer to a decrease in absolute pressure, while decreases in reduced pressure typically refer to an increase in absolute pressure. 
     The term “tissue site” as used herein refers to a wound or defect located on or within any tissue, including but not limited to, bone tissue, adipose tissue, muscle tissue, neural tissue, dermal tissue, vascular tissue, connective tissue, cartilage, tendons, or ligaments. The term “tissue site” may further refer to areas of any tissue that are not necessarily wounded or defective, but are instead areas in which it is desired to add or promote the growth of, additional tissue. For example, reduced pressure tissue treatment may be used in certain tissue areas to grow additional tissue that may be harvested and transplanted to another tissue location. 
     Reduced pressure treatment systems are often applied to large, highly exudating wounds present on patients undergoing acute or chronic care, as well as other severe wounds that are not readily susceptible to healing without application of reduced pressure. Low-severity wounds that are smaller in volume and produce less exudate have generally been treated using advanced dressings instead of reduced pressure treatment. 
     Currently, the use of reduced pressure treatment is not considered a viable or affordable option for low-severity wounds due to the manpower required to monitor and change system components, the requirement for trained medical personnel overseeing treatment, and the high cost of treatment. For example, the complexity of current reduced pressure treatment systems precludes a person with little or no specialized knowledge from administering such treatment to oneself or others. The size and power consumption characteristics of current reduced pressure treatment systems also limit the mobility of both the treatment system and the person to whom the treatment is being applied. Also, the high cost of current reduced pressure treatment systems can preclude the accessibility of such treatment systems to some users. Current reduced pressure treatment systems are also typically non-disposable after each treatment. In addition, users with little or no specialized knowledge have no easy and convenient way to determine whether a manually actuated reduced pressure source requires attention to maintain a desired reduced pressure level at a tissue site. 
     Referring to  FIG. 1 , a reduced pressure treatment system  100  according to an illustrative embodiment applies reduced pressure to a tissue site  105  to promote the drainage of exudate and other liquids from tissue site  105 , as well as stimulate the growth of additional tissue. Reduced pressure treatment system  100  includes a pump  102 . Pump  102  includes a variable volume chamber  110  and a fixed volume chamber  115 , which are coupled to one another via filter housing  120 . Variable volume chamber  110  has a variable volume that is affected by the compression of compressible pump along an axis  122 . Variable volume chamber  110  may also be compressed along other axes. 
     Variable volume chamber  110  may be manually-actuated. That is, the compression of variable volume chamber  110  may be performed by any living organism. For example, variable volume chamber  110  may be manually pushed, squeezed, or otherwise compressed by a human hand, finger, or other limb. Variable volume chamber  110  may be any type of manually-actuated chamber. For example, variable volume chamber  110  may be a compressible bellows having corrugated side walls. 
     In one embodiment, variable volume chamber  110  is compressible into, a plurality of positions, each of which may be representative of a different volume for variable volume chamber  110 . For example, variable volume chamber  110  has the greatest volume when the variable volume chamber  110  is in a fully uncompressed position. In a fully compressed position, variable volume chamber  110  has the smallest volume. Variable volume chamber  110  may also have a plurality of intermediate positions between the fully uncompressed position and the fully compressed position, including partially compressed or partially uncompressed positions. 
     Variable volume chamber  110  includes an outlet valve  124 . Outlet valve  124  permits the passage of gas, such as air, out of variable volume chamber  110 . Outlet valve  124  also prevents gas from entering variable volume chamber  110 . Thus, when the volume of variable volume chamber  110  is reduced due to the compression of compressible pump from an uncompressed position to a compressed position, gas is forced out of variable volume chamber  110 . Outlet valve  124  may be any type of valve capable of permitting the passage of gas out of variable volume chamber  110  while preventing the passage of gas into variable volume chamber  110 . A non-limiting example of outlet valve  124  is an umbrella valve, duckbill valve, ball valve, diaphragm valve, and any type of one-way valve. 
     Although  FIG. 1  shows variable volume chamber  110  as having a single outlet valve  124 , variable volume chamber  110  may have any number of outlet valves. Also, although  FIG. 1  shows outlet valve  124  at the end portion of variable volume chamber  110 , outlet valve  124  may be located on any portion of variable volume chamber  110 , such as the side walls of variable volume chamber  110 . In one embodiment, outlet valve  124  is located at an end of variable volume chamber  110  that is opposite of the end at which filter housing  120  is located. Additional details regarding outlet valve  124  will be provided in  FIGS. 2 ,  7 , and  9 - 13  below. 
     Fixed volume chamber  115  is capable of containing any fluid, such as gases and liquids, as well as fluids that contain solids. For example, fixed volume chamber  115  may contain exudates from tissue site  105 . In one example, fixed volume chamber  115  has a substantially fixed volume. Fixed volume chamber  115  may be made of any material capable of providing fixed volume chamber  115  with a substantially fixed volume, including metal, plastic, or hardened rubber. 
     Fixed volume chamber  115  includes side walls  125  and  127 , which are coupled to an end wall  130 . Side walls  125  and  127  may be contiguously formed with an end wall  130  such that no joint exists between side walls  125  and  127  and end wall  130 . In addition, side walls  125  and  127  may be welded, screwed, glued, bolted, air-lock sealed, or snapped onto end wall  130 . 
     Fixed volume chamber  115  is coupled to variable volume chamber  110  by a filter housing  120 . Fixed volume chamber  115  and variable volume chamber  110  may be coupled to filter housing  120  in a variety of ways. For example, fixed volume chamber  115  or variable volume chamber  110  may be welded, screwed, glued, bolted, air-lock sealed, or snapped onto filter housing  120 . Fixed volume chamber  115  or variable volume chamber  110  may also be part of the same material as filter housing  120 , thereby eliminating the need for joints or seals between fixed volume chamber  115  and filter housing  120 . In another example, variable volume chamber  110  may be sealed to filter housing  120  using an interlocking seal. Additional details regarding the coupling of filter housing  120  with fixed volume chamber  115  or variable volume chamber  110  are described below in  FIGS. 2 ,  5 ,  6 ,  10 - 13 , and  14 . 
     Filter housing  120  is capable of including one or more filters. In one embodiment, filter housing  120  includes a hydrophobic filter that prevents liquid from entering variable volume chamber  110  from fixed volume chamber  115 . However, as described below, the hydrophobic filter permits the passage of air such that reduced pressure may be transferred from variable volume chamber  110  to fixed volume chamber  115 . Filter housing  120  may also include an odor filter that restrains or prevents the transmission of odor from fixed volume chamber  115  to variable volume chamber  110 . Additional details regarding the hydrophobic filter and odor filter will be provided in  FIGS. 2 ,  4 , and  14  below. 
     Fixed volume chamber  115  is coupled to a delivery tube  135  via an inlet valve  140 . Inlet valve  140  is located at an inlet point  143 . Inlet valve  140  permits the passage of fluid, such as exudate, into fixed volume chamber  115  at inlet point  143 . Inlet valve  140  also restrains the passage of fluid out of fixed volume chamber  115  at inlet point  143 . Inlet valve  140  may be any type of valve, such as an umbrella valve, duck bill valve, or a combination thereof. 
     Inlet valve  140  may be located at the center of end wall  130 . Although  FIG. 1  shows fixed volume chamber  115  as having a single inlet valve  140 , fixed volume chamber  115  may have any number of inlet valves. Also, although  FIG. 1  shows inlet valve  140  at end wall  130  of fixed volume chamber  115 , inlet valve  140  may be located on any portion of fixed volume chamber  115 , such as side walls  125  and  127  of fixed volume chamber  115 . Additional details regarding inlet valve  140  will be provided in  FIGS. 2 and 17  below. 
     Delivery tube  135  is any tube through which a fluid may flow. Delivery tube  135  may be made from any material, and may include one or more paths or lumens through which fluid may flow. For example, delivery tube  135  may include two lumens. In this example, one lumen may be used for the passage of exudate from tissue site  105  to fixed volume chamber  115 . The other lumen may be used to deliver fluids, such as air, antibacterial agents, antiviral agents, cell-growth promotion agents, irrigation fluids, or other chemically active agents, to tissue site  105 . The fluid source from which these deliverable fluids originate is not shown in  FIG. 1 . 
     Delivery tube  135  may be fixedly attached to fixed volume chamber  115  at inlet point  143 . Also, delivery tube  135  may be detachable from fixed volume chamber  115  at inlet point  143 . For example, delivery tube  135  may be snapped onto fixed volume chamber  115 . Additional details regarding the coupling the delivery tube  135  to fixed volume chamber  115  will be provided in FIGS.  2  and  16 - 18  below. 
     The opposite end of delivery tube  135  is coupled to a manifold  145 . Manifold  145  may be a biocompatible, porous material that is capable of being placed in contact with tissue site  105  and distributing reduced pressure to the tissue site  105 . Manifold  145  may be made from foam, gauze, felted mat, or any other material suited to a particular biological application. Manifold  145  may include a plurality of flow channels or pathways to facilitate distribution of reduced pressure or fluids to or, from the tissue site. 
     Manifold  145  may be secured to tissue site  105  using a sealing member  150 . Sealing member  150  may be a cover that is used to secure manifold  145  at tissue site  105 . While sealing member  150  may be impermeable or semi-permeable, in one example sealing member  150  is capable of maintaining a reduced pressure at tissue site  105  after installation of the sealing member  150  over manifold  145 . Sealing member  150  may be a flexible drape or film made from a silicone based compound, acrylic, hydrogel or hydrogel-forming material, or any other biocompatible material that includes the impermeability or permeability characteristics desired for tissue site  105 . 
     In one embodiment, sealing member  150  is configured to provide a sealed connection with the tissue surrounding manifold  145  and tissue site  105 . The sealed connection may be provided by an adhesive positioned along a perimeter of sealing member  150  or on any portion of sealing member  150  to secure sealing member  150  to manifold  145  or the tissue surrounding tissue site  105 . The adhesive may be pre-positioned on sealing member  150  or may be sprayed or otherwise applied to sealing member  150  immediately prior to installing sealing member  150 . 
     In one embodiment, delivery tube  135  is coupled to manifold  145  via a connection member  155 . Connection member  155  permits the passage of fluid from manifold  145  to delivery tube  135 , and vice versa. For example, exudates collected from tissue site  105  using manifold  145  may enter delivery tube  135  via connection member  155 . In another embodiment, reduced pressure treatment system  100  does not include connection member  155 . In this embodiment, delivery tube  135  may be inserted directly into sealing member  150  such that an end of delivery tube  135  is adjacent to manifold  145 . 
     Reduced pressure treatment system  100  may also include a pressure feedback system  160 . Pressure feedback system  160  may be operably associated with the other components of reduced pressure treatment system  100  to provide information to a user of reduced pressure treatment system  100  that indicates a relative or absolute amount of pressure that is being delivered to tissue site  105 . Pressure feedback system  160  allows a user to accurately track the amount of reduced pressure that is being generated by reduced pressure treatment system  100 . Non-limiting examples of pressure feedback systems include pop valves that activate when the reduced pressure rises above a selected value, low power electronic indicators powered by miniature cells, dial indicators that indicate specific pressure values that are being applied to the tissue site, deflection pop valves, polymers with various deflection characteristics, and films that move relative to one another to produce visual identifiers indicating the relative or absolute pressure values being generated by reduced pressure treatment system  100 . An example of a film-based system may include a yellow film anchored to a first part of pump  102  that is capable of movement relative to a blue film anchored to a second part. When the first and second parts are moved relative to one another to apply a reduced pressure, the yellow and blue films overlap to create a green indicator. As the pressure increases and the films move away from one another, the loss of the green color indicates that the pressure has increased (i.e., more reduced pressure needs to be applied). 
     Also, although pressure feedback system  160  is shown as separate from the other components of reduced pressure treatment system  100 , pressure feedback system  160  may form an integral part of any of the components of reduced pressure treatment system  100 . Additional details regarding pressure feedback system  160  will be described in  FIGS. 14 and 16  below. In addition to the above-mentioned components and systems, reduced pressure treatment system  100  may include valves, regulators, switches, and other electrical, mechanical, and fluid components to facilitate administration of reduced pressure treatment to tissue site  105 . 
     A desiccant or absorptive material may be disposed within fixed volume chamber  115  to trap or control fluid once the fluid has been collected. In the absence of fixed volume chamber  115 , a method for controlling exudate and other fluids may be employed in which the fluids, especially those that are water soluble, are allowed to evaporate from manifold  145 . 
     In one embodiment, variable volume chamber  110  is moved from an uncompressed position to a compressed position, thereby decreasing the volume of variable volume chamber  110 . As a result, gas is expelled from variable volume chamber  110  through outlet valve  124 . Because gas cannot enter variable volume chamber  110  via outlet valve  124 , gas cannot enter variable volume chamber  110  from a surrounding space  165 . Thus, as variable volume chamber  110  expands from the compressed position to the uncompressed position, gas is transferred from fixed volume chamber  115  to variable volume chamber  110 . The movement of variable volume chamber  110  from a compressed position to an uncompressed position may be caused by any expansion force. In an illustrative example in which the side walls of variable volume chamber  110  are corrugated side walls, the expansion force may be caused by the tendency of the corrugations in the corrugated side walls to move away from one another and thereby return variable volume chamber  110  to the uncompressed position. The expansion force may also be caused by an independent biasing member, such as a spring or foam component, that is located within or outside of variable volume chamber  110 . In another example, the resiliency of non-corrugated side walls of variable volume chamber  110  may be used to move variable volume chamber  110  to an uncompressed position. 
     Liquid, such as exudate, is prevented from being transferred from fixed volume chamber  115  to variable volume chamber  110  by a filter, such as a hydrophobic filter, in filter housing  120 . Because fixed volume chamber  115  is sealed from surrounding space  165 , a reduced pressure is generated in fixed volume chamber  115  as variable volume chamber  110  expands from the compressed position to the uncompressed position. This reduced pressure is than transferred to tissue site  105  via delivery tube  135  and manifold  145 . This reduced pressure may be maintained at tissue site  105  using sealing member  150 . 
     This process of moving variable volume chamber  110  from an uncompressed to a compressed position, and vice versa, in order to achieve a reduced pressure at tissue site  105  may be repeated. In particular, variable volume chamber  110  may undergo multiple compression/expansion cycles until fixed volume chamber  115  is filled with liquid, such as exudate, from tissue site  105 . The multi-chamber configuration of pump  102 , which includes variable volume chamber  110  and fixed volume chamber  115 , permits compressible pump to be compressed regardless of the amount of liquid in fixed volume chamber  115 . As a result, the desired pressure may be achieved during the compression/expansion cycles regardless of the amount of liquid in fixed volume chamber  115 . 
     Referring to  FIG. 2 , pump  200 , which is a non-limiting example of pump  102  in  FIG. 1 , is shown in accordance with an illustrative embodiment. Pump  200  may be used as a substitute for pump  102  in  FIG. 1 . 
     Pump  200  includes a compressible bellows  210 . Compressible bellows  210  is a non-limiting example of variable volume chamber  110  in  FIG. 1 . Compressible bellows  210  may be moved into a plurality of positions, such as an uncompressed position and a compressed position. Compressible bellows  210  is formed from corrugated side walls with corrugations  212 . Corrugations  212  may move toward and away from one another, resulting in a compression and expansion of compressible bellows  210 . For example, compressible bellows  210  may move from a compressed position to an uncompressed position due to the expansion force provided by a decrease in the linear density of corrugations  212 . This expansion force may be provided by the tendency of corrugations  212  to move away from one another. 
     In addition, compressible bellows  210  may be composed of any material that allows the compression and expansion of compressible bellows  210 . The expansion force provided by the corrugated side walls may depend on the material from which compressible bellows  210  is composed. Thus, the amount of pressure provided by compressible bellows  210  to a tissue site, such as tissue site  105  in  FIG. 1 , may also depend on the material from which compressible bellows  210  is composed. Factors that may affect the amount of pressure provided by compressible bellows  210  include material hardness, elasticity, thickness, resiliency, and permeability. A material may also be selected based on the degree of pressure decay experienced by pump  200  as compressible bellows  210  moves from a compressed position to an uncompressed position. The expansion force provided by the corrugated side walls may also depend on the design of compressible bellows  210 . The variance in cross-section of compressible bellows  210  affects the amount of obtainable reduced pressure as well as the input input pressure required to initiate compressible bellows  210 . 
     In one non-limiting example, compressible bellows  210  is composed of Shore 65 A. Shore 65 A may be capable of providing between 125 and 150 mm Hg of pressure. These levels of pressure may also be capable of being maintained for at least six hours. For higher pressures, harder materials, such as Shore 85 A, may be used. By varying the material from which compressible bellows  210  is composed, pressures of 250 mm Hg, as well as pressures above 400 mm Hg, may by achieved using compressible bellows  210 . 
     Although compressible bellows  210  is shown to have a circular cross-sectional shape, compressible bellows  210  may have any cross-sectional shape. For example, the cross sectional shape of compressible bellows  210  may be an oval or polygon, such as a pentagon, hexagon, or octagon. 
     Compressible bellows  210  includes outlet valve  224 . Outlet valve  224  is a non-limiting example of outlet valve  124  in  FIG. 1 . Gas exits compressible bellows  210  via outlet valve  224  in response to a movement of compressible bellows  210  from an uncompressed position to a compressed position. Outlet valve  224  may be located anywhere on compressible bellows  210 . For example, outlet valve  224  may be located on an end of compressible bellows  210  that is opposite of the end at which filter housing  220  is located. Outlet valve  224  may also be centrally disposed on an end wall of compressible bellows  210 . The directional flow of the gas from compressible bellows  210  is indicated by arrows  226 . Outlet valve  224  prevents gas from entering compressible bellows  210 . In  FIG. 2 , outlet valve  224  is an umbrella valve, although outlet valve  224  may be any type of valve. Additional details regarding outlet valve  224  are described in  FIG. 7  below. 
     As indicated by dotted lines  228 , compressible bellows  210  is coupled to filter housing  220 . Compressible bellows  210  may be welded, screwed, glued, bolted, air-lock sealed, or snapped onto filter housing  220 . Additional details regarding the coupling between compressible bellows  210  and filter housing  220  are described in  FIGS. 5 and 6  below. 
     Filter housing  220  is a non-limiting example of filter housing  120  in  FIG. 1 . Filter housing may be composed of any material, such as plastic, metal, rubber, or any other material capable of holding one or more filters. Filter housing  220  contains an odor filter  231 , which is attached to filter housing  220  as indicated by dotted lines  236 . Odor filter  231  may be screwed, glued, bolted, air-lock sealed, snapped onto, or otherwise placed adjacent to filter housing  220 . Also, filter housing  220  may include a groove into which odor filter  231  is placed. 
     Odor filter  231  restrains or prevents the transmission of odor from fixed volume chamber  215  to compressible bellows  210 . Such odor may be the result of exudate or other liquid contained in fixed volume chamber  215 . In one embodiment, odor filter  231  is a carbon odor filter. In this embodiment, the carbon odor filter may include charcoal. Although  FIG. 2  depicts odor filter  231  as a having a flattened shape, odor filter  231  may have any shape capable of restraining or preventing the transmission of odor from fixed volume chamber  215  to compressible bellows  210 . For example, odor filter  231  may have circular, ovular, or polygonal disk shape. 
     Filter housing  220  also includes a hydrophobic filter  234 , which is attached to filter housing  220  as indicated by dotted lines  238 . Hydrophobic filter  234  may be screwed, glued, bolted, air-lock sealed, snapped onto, ultrasonically welded, or otherwise placed adjacent to filter housing  220 . In one example, odor filter  231  is sandwiched between filter housing  220  and hydrophobic filter  234 . In the example in which hydrophobic filter  234  is secured to filter housing  220 , odor filter  231  may be secured as a result of being sandwiched between filter housing  220  and hydrophobic filter  234 . Odor filter  231  and hydrophobic filter  234  may be coupled to a side of filter housing  220  that is nearer to fixed volume chamber  215 , as shown in  FIG. 2 . 
     Hydrophobic filter  234  prevents liquid, such as exudate, from entering compressible bellows  210 . However, hydrophobic filter  234  allows the passage of gas, such as air, such that reduced pressure may be transferred from compressible bellows  210  and fixed volume chamber  215 . Hydrophobic filter  234  may be composed from any of a variety of materials, such as expanded polytetrafluoroethene. 
     Pump  200  includes fixed volume chamber  215 . Fixed volume chamber  215  is a non-limiting example of fixed volume chamber  115  in  FIG. 1 . Fixed volume chamber  215  has a fixed volume and may contain any liquid, such as exudate from a tissue site, such as tissue site  105  in  FIG. 1 . Fixed volume chamber  215  may be welded, screwed, glued, bolted, air-lock sealed, or snapped onto filter housing  220 . 
     Fixed volume chamber  215  includes inlet valve  240 . Inlet valve  240  is a non-limiting example of inlet valve  140  in  FIG. 1 . As shown in  FIG. 2 , inlet valve  240  is centrally located at an end wall of fixed volume chamber  215 . Also, inlet valve  240  and outlet valve  224  are each located along a central longitudinal axis  290 , which traverses the center of pump  200 . 
     Any liquid, such as exudate, may flow from a manifold, such as manifold  145  in  FIG. 1 , into fixed volume chamber  215  via inlet valve  240 . The flow of liquid into fixed volume chamber  215  via inlet valve  240  is indicated by an arrow  242 . Inlet valve  240  also restrains or prevents the passage of liquid out of fixed volume chamber  215  at the point at which inlet valve  240  is located. 
     Any of a variety of valves may be used to achieve the functionality of inlet valve  240 . In one embodiment, top portion  246  of inlet valve  240  is a duck bill valve. Inlet valve  240  may also be an umbrella valve, duckbill valve, ball valve, diaphragm valve, and any type of one-way valve. 
     Liquid flow into fixed volume chamber  215  is caused by the reduced pressure in fixed volume chamber  215 . The reduced pressure in fixed volume chamber  215  is caused by the reduced pressure transferred from compressible bellows  210  to fixed volume chamber  215 . As compressible bellows  210  is moved from a compressed position to an uncompressed position, gas is transferred from fixed volume chamber  215  to compressible bellows  210 . As a result, reduced pressure is transferred to fixed volume chamber  215  from compressible bellows  210  in response to a movement of compressible bellows  210  from a compressed position to an uncompressed position. As compressible bellows  210  is moved from an uncompressed position to a compressed position, gas moves out of compressible bellows  210  via outlet valve  224 . Such compression/expansion cycles may be repeated to apply a desired amount of reduced pressure to a tissue site, such as tissue site  105  in  FIG. 1 . 
     Referring to  FIG. 3 , compressible bellows  300 , which is a non-limiting example of bellows pump  200  in  FIG. 2 , is shown in accordance with an illustrative embodiment. In  FIG. 3 , compressible bellows  300  is shown in two different positions in the range of positions that may be achieved by compressible bellows  300 . In particular, compressible bellows  300  is shown in an uncompressed position  305  and a compressed position  310 . Compressible bellows  300  has a greater volume in uncompressed position  305  than in compressed position  310 . 
     As compressible bellows  300  is compressed from uncompressed position  305  to compressed position  310 , the gas in compressible bellows  300  is expelled through outlet valve  324 , which is a non-limiting example of outlet valve  224  in  FIG. 2 . The volume of compressible bellows  300  decreases as the compressible bellows  300  is compressed. 
     As compressible bellows  300  expands from compressed position  310  to uncompressed position  305 , gas does not enter compressible bellows  300  via outlet valve  324  because outlet valve  324  allows air only to exit compressible bellows  300 . Instead, gas enters bellows pump from a fixed volume chamber, such as fixed volume chamber  215  in  FIG. 2 , to which compressible bellows  300  is coupled. The volume of compressible bellows  300  increases as compressible bellows  300  expands from compressed position  310  to uncompressed position  305 . 
     The expansion force necessary to expand compressible bellows  300  is provided by an expansion or biasing force. The material from which compressible bellows  300  is composed is elastically deformed when compressible bellows  300  is in compressed position  310 . Elastic properties of the material from which compressible bellows  300  is composed biases the corrugations included on compressible bellows  300  to move away from one another such that compressible bellows  300  expands to uncompressed position  305 . As compressible bellows  300  expands, the sealed nature of the variable volume chamber results in a reduced pressure being created within the variable volume chamber. The reduced pressure may then be transmitted through a hydrophobic filter to a fixed volume chamber, which, in turn, transmits the reduced pressure to a tissue site. 
     Referring to  FIG. 4 , a portion of filter housing  420 , which is a non-limiting example of filter housing  220  in  FIG. 2 , is shown in accordance with an illustrative embodiment. Odor filter  431 , which is a non-limiting example of odor filter  231  in  FIG. 2 , fits onto filter housing  420  at a groove  432 . Hydrophobic filter  434 , which is a non-limiting example of hydrophobic filter  234  in  FIG. 2 , is ultrasonically welded to filter housing  420  at a protrusion  439 . However, as described above, hydrophobic filter  234  may be coupled to filter housing  420  in a variety of ways. Odor filter  431  is sandwiched in between filter housing  420  and hydrophobic filter  434  at groove  432 , and may or may not be independently attached to filter housing  420 . 
     As indicated by arrows  443 , gas, such as air, is permitted to flow though hydrophobic filter  434  and odor filter  431 , via a gap  445 . However, hydrophobic filter  434  prevents liquid, such as exudate, from passing through gap  445 . Also, odor filter  431  prevents odor from passing through gap  445 . 
     Referring to  FIG. 5 , an interlocking seal between compressible bellows  510 , which is a non-limiting example of compressible bellows  210  in  FIG. 2 , and filter housing  520 , which is a non-limiting example of filter housing  220  in  FIG. 2 , is shown in accordance with an illustrative embodiment. The interlocking seal shown in  FIG. 5  allows compressible bellows  510  to be snapped onto filter housing  520 , while maintaining an air-tight seal for the proper operation of the reduced pressure treatment system. Compressible bellows  510  includes a snap protrusion  530 . Filter housing  520  includes an undercut  540  into which snap protrusion  530  may be inserted. The large area of contact between compressible bellows  510  and filter housing  520 , as indicated by a span  550 , assists in maintaining a proper seal between compressible bellows  510  and filter housing  520 . 
     Referring to  FIG. 6 , an interlocking seal between compressible bellows  610 , which is a non-limiting example of compressible bellows  210  in  FIG. 2 , and filter housing  620 , which is a non-limiting example of filter housing  220  in  FIG. 2 , is shown in accordance with an illustrative embodiment. Similar to the interlocking seal in  FIG. 5 , filter housing  620  includes undercut  640  into which snap protrusion  630  of compressible bellows  610  may be inserted. However, in contrast to  FIG. 5 , the illustrative embodiment of the interlocking seal in  FIG. 6  shows that compressible bellows  610  includes ribs  655 . Filter housing  620  also includes indentations  660 , into which ribs  655  may be inserted. The use of interlocking ribs  655  and indentations  660  may help create a tighter seal between compressible bellows  610  and filter housing  620 . 
     Referring to  FIG. 7 , outlet valve  724 , which is a non-limiting example of outlet valve  224  in  FIG. 2 , is shown in accordance with an illustrative embodiment. Outlet valve  724  is coupled to an end wall  730  of compressible bellows  710 , which is a non-limiting example of compressible bellows  210  in  FIG. 2 . End wall  730  may be made of metal, plastic, rubber, or any other material. In  FIG. 7 , end wall  730  may be welded onto compressible bellows  710  at the spans indicated by spans  735 . However, end wall  730  may also be screwed, glued, bolted, air-lock sealed, or snapped onto compressible bellows  710 . 
     Gas, such as air, flows out of compressible bellows  710  as indicated by arrows  740 . In particular, gas flows out of compressible bellows  710  through gaps  741  and then passes through the space between outlet valve flaps  742  and  743  and end wall  730 . However, because outlet valve flaps  742  and  743  are only opened by the flow of gas out of compressible bellows  710 , gas cannot enter compressible bellows  710  through outlet valve  724 . In  FIG. 7 , outlet valve  724  is an umbrella valve. However, outlet valve  724  may be any valve capable of allowing gas to pass out of compressible bellows  710  while restraining or preventing gas from passing out of compressible bellows  710 . 
     Referring to  FIG. 8 , a connection between end wall  830 , which is a non-limiting example of end wall  730  in  FIG. 7 , and compressible bellows  810 , which is a non-limiting example of compressible bellows  710  in  FIG. 7 , is shown in accordance with an illustrative embodiment. In contrast to  FIG. 7 , the illustrative embodiment of  FIG. 8  shows a protrusion  840  included on compressible bellows  810 . End wall  830  also includes an indentation  850  into which protrusion  840  may be inserted. The use of protrusion  840  and indentation  850  may help create a tighter seal between compressible bellows  810  and end wall  830 , as well as help reduce the amount of welding necessary to couple compressible bellows  810  to end wall  830 . 
     Referring to  FIG. 9 , compressible bellows  910 , which is a non-limiting example of compressible bellows  210  in  FIG. 2 , is shown in accordance with an illustrative embodiment. Compressible bellows  910  is coupled to filter housing  920 , which is a non-limiting example of filter housing  220  in  FIG. 2 . In  FIG. 9 , end wall  930  of compressible bellows  910  does not include an outlet valve. Instead, compressible bellows  910  includes outlet valves at the portions of compressible bellows  910  indicated by brackets  940  and  945 . In addition, compressible bellows  910  may include one or more outlet valves around the perimeter of compressible bellows  910  indicated by brackets  940  and  945 . Additional details regarding the outlet valves at the portion of compressible bellows  910  indicated by brackets  940  and  945  is described in  FIGS. 10-13  below. 
     Turning now to  FIG. 10 , an umbrella outlet valve that is part of compressible bellows  1010 , which is a non-limiting example of compressible bellows  910  in  FIG. 9 , is shown in accordance with an illustrative embodiment. The outlet valve includes a flap  1025 . Filter housing  1020 , which is a non-limiting example of filter housing  920  in  FIG. 9 , includes a gap  1027 . Upon moving compressible bellows  1010  from an uncompressed position to a compressed position, gas flows out of compressible bellows through gap  1027  as indicated by arrow  1029 . The flow of gas lifts flap  1025  into open position  1035 , as indicated by an arrow  1037 , thereby allowing the passage of gas out of compressible bellows  1010 . When air is not flowing out of compressible bellows  1010 , such as when compressible bellows  1010  is moving from a compressed position to an uncompressed position, flap  1025  is in contact with filter housing  1020  such that gas may not flow into compressible bellows  1010 . 
     In this embodiment, compressible bellows  1010  may also have protrusion  1040 , which fits into indentation  1045  of filter housing  1020 . The fitting of protrusion  1040  into indentation  1045  helps to maintain a snap fit between compressible bellows  1010  and filter housing  1020 . 
     Referring to  FIG. 11 , an outlet valve located on compressible bellows  1110  at the general portion of compressible bellows  1110  that contacts filter housing  1120  is shown in accordance with an illustrative embodiment. Compressible bellows  1110  is a non-limiting example of compressible bellows  910  in  FIG. 9 , and filter housing  1120  is anon-limiting example of filter housing  920  in  FIG. 9 . 
     Upon compression of compressible bellows  1110  from an uncompressed position to a compressed position, gas attempts to flow out of compressible bellows  1110  through gap  1127  as indicated by arrow  1129 . The gas encounters flap  1125 , which includes a rib  1135 . The strength of rib  1135 , which may depend on the thickness or material of rib  1135 , determines the amount of force that must be exerted by the gas in order to bend flap  1125  such that air can escape compressible bellows  1110 . Thus, the strength of rib  1135  also determines the amount of pressure that is created by compressible bellows  1110 , and which is ultimately transferred to a tissue site, such as tissue site  105  in  FIG. 1 . 
     Referring to  FIG. 12 , the outlet valve of  FIG. 11  in an open position is shown in accordance with an illustrative embodiment. The flow of gas, which is indicated by arrow  1229 , has exerted sufficient force upon flap  1225  of compressible bellows  1210  such that flap  1225  has been bent to allow for the release of gas from compressible bellows  1210 . In particular, the force exerted by the flow of gas is sufficient to overcome the strengthening force of rib  1235 . 
     Referring to  FIG. 13 , an outlet valve located on a side wall of bellow pump  1310 , which is a non-limiting example of compressible bellows  1110  and  1210  in  FIGS. 11 and 12 , respectively, is shown in accordance with an illustrative embodiment.  FIG. 13  shows flap  1325 , which is a non-limiting example of flaps  1125  and  1225  in  FIGS. 11 and 12 , respectively.  FIG. 13  also shows rib  1335 , which is a non-limiting example of ribs  1135  and  1235  in  FIGS. 11 and 12 , respectively. As described above, rib  1335  may be used to adjust the force required to open flap  1325 , thereby varying the amount of pressure that may be created by bellow pump  1310 . 
     Referring to  FIG. 14 , reduced pressure treatment system  1400 , which is encased by a casing having a top casing portion  1402  and a bottom casing portion  1404 , is shown in accordance with an illustrative embodiment. Reduced pressure treatment system  1400  compressible bellows  1410 , filter housing  1420 , odor filter  1431 , hydrophobic filter  1434 , an variable volume chamber  1415 . 
       FIG. 14  shows the orientation of the different components of reduced pressure treatment system  1400  relative to one another. Compressible bellows  1410 , which is a non-limiting example of compressible bellows  210  in  FIG. 2 , may be inserted into top casing portion  1402 . Top casing portion also includes a grip  1403 . Grip  1403  may be composed of rubber, plastic, or any other material capable of improving tactile grip on top casing portion  1402 . 
     The cross-sectional shape of compressible bellows  1410  is an oval. In particular, compressible bellows  1410  has an elongated middle portion  1412  and rounded end portions  1414 . The cross sectional shape of compressible bellows  1410  allows compressible bellows  1410  to fit into top casing portion  1402 . The cross sectional shape of compressible bellows  1410  may vary depending on the shape of the casing for the reduced pressure treatment system. 
     Compressible bellows  1410  couples to filter housing  1420 , which is a non-limiting example of filter housing  220  in  FIG. 2 . Filter housing  1420  includes a grid mesh  1425  through which gas may flow. 
     Odor filter  1431  and hydrophobic filter  1434 , which are non-limiting examples of odor filter  231  and hydrophobic filter  234  in  FIG. 2 , respectively, fit into filter housing  1420  as described in the previous Figures. Fixed volume chamber  1415 , which is anon-limiting example of fixed volume chamber  215  in  FIG. 2 , couples to filter housing  1420 . Fixed volume chamber  415  may be inserted into bottom casing portion  1404 . 
     Top casing portion  1402  and bottom casing portion  1404  may be composed of any material. For example, top casing portion  1402  and bottom casing portion  1404  may be composed of materials that are suitable to protect the inner components of reduced pressure treatment system  1400 . Non-limiting examples of the material from which top casing portion  1402  and bottom casing portion  1404  may be composed include plastic, metal, or rubber. 
     Referring to  FIG. 15 , compressible bellows  1510  and  1512 , each of which is a non-limiting example of compressible bellows  210  in  FIG. 2 , is shown in accordance with an illustrative embodiment. Compressible bellows  1510  and  1512  can replace the oval compressible bellows  1410  in  FIG. 14 . Thus, compressible bellows  1510  and  1512  may be configured to be inserted into atop casing portion, such as top casing portion  1402  in  FIG. 14 . Each of compressible bellows  1510  and  1512  are coupled to filter housing  1520 , which is a non-limiting example of filter housing  1420  in  FIG. 14 . 
     The use of two compressible bellows  1510  and  1512  allows the reduced pressure treatment system in which compressible bellows  1510  and  1512  are employed to continue functioning in the event that one of the compressible bellows leaks or otherwise fails. The use of compressible bellows  1510  and  1512  may also improve manufacturing efficiency in the construction of a reduced pressure treatment system. For example, the manufacture of compressible bellows  1510  and  1512  having a circular cross-section may be easier than the manufacture of a single compressible bellows having an elongated cross section that allows the single compressible bellows to fit inside top casing portion  1402 . 
     Referring to  FIG. 16 , reduced pressure treatment system  1600 , which is a non-limiting example of reduced pressure treatment system  1400  in  FIG. 14 , is shown in accordance with an illustrative embodiment. Reduced pressure treatment system  1600  shows reduced pressure treatment system  1400  when reduced pressure treatment system  1400  has been assembled. In reduced pressure treatment system  1600 , top and bottom casing portions  1602  and  1604  encase the various components of reduced pressure treatment system  1600 , such as a compressible bellows, filter housing, odor filter, hydrophobic filter, and fixed volume chamber. Top and bottom casing portions  1602  and  1604  are non-limiting examples of top and bottom casing portions  1402  and  1404  in  FIG. 14 , respectively. 
     Reduced pressure treatment system  1600  also includes visual indicators  1608 . Visual indicators  1608  indicate to a user an amount of reduced pressure to be delivered to a tissue site, such as tissue site  105  in  FIG. 1 . In particular, the lines of visual indicators  1608  indicate the degree to which top casing portion  1602  has been compressed relative to bottom casing portion  1604 , and therefore also indicates the degree to which the one or more compressible bellows inside top casing portion  1602  has been compressed. Using visual indicators  1608 , a user can consistently deliver a desired amount of reduced pressure to a tissue site. The visual indicators  1608  may be located on either or both of the top casing portion  1602  or the bottom casing portion  1604 . 
     Reduced pressure treatment system  1600  also includes an end cap  1612 . End cap  1612  fits onto bottom casing portion  1604  and may be coupled to delivery tube  1635 , which is a non-limiting example of delivery tube  135  in  FIG. 1 . Additional details regarding end cap  1612  will be described in  FIGS. 19 and 20  below. 
     Referring to  FIGS. 17   a ,  17   b , and  17   c , a reduced pressure apparatus  1700  includes a top casing portion  1702  and a bottom casing portion  1704 , each of which have a substantially cylindrical shape. The bottom casing portion  1704  has a larger diameter than the top casing portion  1702  such that the top casing portion  1702  can be slidingly received by the bottom casing portion  1704 . The top casing portion  1702  is compressible into a plurality of positions relative to the bottom casing portion  1704 , including the uncompressed position shown in  FIG. 17   a , the fully compressed position shown in  FIG. 17   b , and a plurality of intermediate positions (which are partially compressed) between the uncompressed position and the fully compressed position. The top casing portion  1702  may be slidable into the bottom casing portion  1704  along an axis substantially parallel to bidirectional arrow  1706 . 
     The top casing portion  1702  includes an indicator  1710 . The indicator  1710  is disposed on a region of the top casing portion  1702  that is adjacent the bottom casing portion  1704  when the reduced pressure apparatus  1700  is in the uncompressed position. The indicator  1710  is visible when the top casing portion  1702  is in the uncompressed position but is obscured, or not visible, when the top casing portion  1702  is in the fully compressed position. The indicator  1710  may also be visible in at least one of the intermediate positions between the compressed position and the uncompressed position. 
     In another embodiment, the visual indicators described herein may be provided to indicate when the reduced pressure apparatus is in a fully compressed position prior to a first use of the reduced pressure apparatus. Such an indicator would assist in ensuring that the reduced pressure apparatus is fully charged or that the reduced pressure apparatus is not being reused on another patient. 
     The indicator  1710  may be any indicia or markings that is capable of indicating a position of the top casing portion  1702  relative to the bottom casing portion  1704 . In the embodiment illustrated in  FIG. 17 , the indicator  1710  is a color band or color strip that is a contrasting color to the color of adjacent portions of the top casing portion  1702 . The color of the indicator  1710  may be any color or multiple colors. Alternatively, the indicator  1710  may not be a solid color band, but instead may be an outline of a band or strip. Similarly, the indicator  1710  may be a region on the top casing portion  1702  that includes striping, letters, numbers, symbols, or other indicia. In  FIG. 17   a , the indicator  1710  is partially disposed around the circumference of the top casing portion  1702 , but the indicator  1710  may also be disposed around an entire circumference of the top casing portion  1702 . 
     In another embodiment, the indicator  1710  is a tactile indicator that has a texture that is different from the texture of the remainder of the top casing portion  1702 . In this embodiment, a visually-impaired user may touch the top casing portion  1702  to determine the position of the reduced pressure apparatus  1700 . When the reduced pressure apparatus  1700  is in the uncompressed position, the user will be able to feel the indicator  1710  and thereby be notified that the system  1710  is in the uncompressed position. 
     In operation, the reduced pressure apparatus  1700  is manually actuated to generate a reduced pressure at an outlet  1716 . Manual actuation of the reduced pressure apparatus  1700  is accomplished by a user manually compressing the top casing portion  1702  within the bottom casing portion  1704  such that the top casing portion  1702  is placed in the fully compressed position or at least one of the intermediate positions. The internal mechanism for generating reduced pressure may be any suitable mechanism including, without limitation, those mechanisms that have been described herein. In at least one embodiment, the mechanism by which reduced pressure is generated involves the reduction in volume of and expulsion of gas from a chamber (not shown), and then subsequently a sealing of the chamber and expansion in volume of the chamber. As the volume of the sealed chamber increases, the reduced pressure is generated within the chamber. The reduction in volume of the chamber may be accomplished by compressing the top casing portion  1702  within the bottom casing portion  1704 . 
       FIG. 17   c  shows the reduced pressure apparatus  1700  as part of a reduced pressure therapy system  1701 . The reduced pressure apparatus  1700  is fluidly coupled to a dressing  1720  via a conduit  1735  that delivers reduced pressure. A sealing member  1750  covers the tissue site  105  of a patient  1707 . The sealing member  1750  has an aperture in which the connection member  1755  is disposed. The conduit  1735  is in fluid communication with a sealed space  1751  that is covered by the sealing member  1750  via the connection member  1755 . The dressing  1720  may also include a manifold in the sealed space  1751 . Reduced pressure may be delivered to the sealed space  1751  by the reduced pressure apparatus  1700 . 
     When the top casing portion  1702  is placed in the fully compressed position, the indicator  1710  is no longer visible since the portion of the top casing portion  1702  on which the indicator  1710  lies is hidden from view within the bottom casing portion  1704 . When fully compressed, reduced pressure is delivered to an outlet  1716 , and this reduced pressure is available for delivery the tissue site  105 . As time passes, air leakage from the sealed space  1751 , as well as other factors that cause local increases in pressure at the tissue site  105 , results in a movement of the top casing portion  1702  toward the uncompressed position. As the top casing portion  1702  moves closer to the uncompressed position, the indicator  1710  begins to become exposed. Since movement toward the uncompressed position indicates a loss of reduced pressure, or a loss of remaining capacity to generate reduced pressure, the presence of the indicator  1710  communicates to a user that a partial discharge of the reduced pressure apparatus  1700  has occurred. The presence of the visual indicator  1710  further communicates to the user the approaching need to re-charge or re-compress the reduced pressure apparatus  1700  back into a compressed position in order to deliver or maintain a therapeutic reduced pressure at the tissue site  105 . If the rate of discharge of the reduced pressure apparatus  1700  is constant, the initial presence of the indicator  1710  at an intermediate position may be determinative of the amount of time remaining during which reduced pressure will be generated or applied. 
     The indicator  1710  includes a height, H, in a direction parallel to the direction of travel of the top casing portion  1702  indicated by bidirectional arrow  1706 . The height, H, is determinative of when the indicator  1710  will first be exposed during operation of the reduced pressure apparatus  1700 . As the reduced pressure apparatus  1700  discharges and the top casing portion moves from the fully compressed position to the uncompressed position, an indicator having a greater height will be visible earlier than an indicator having a lesser height. 
     As explained above, the indicator  1710  is capable of communicating the approaching cessation of reduced pressure generation or delivery, and in some cases, the amount of time left until such cessation. The indicator  1710  may also be capable of alerting a user that a particular amount of reduced pressure is being applied. In one example, the compression of the top casing portion  1702  into a compressed position decreases the volume of a variable volume chamber located in the bottom casing portion  1704 . The reduced pressure in the variable volume chamber in the bottom casing portion  1704  may decrease as the top casing portion  1702  moves toward an uncompressed position. As the top casing portion  1702  moves through the intermediate positions toward the uncompressed position, the indicator  1710  becomes more exposed. The relative positioning of the top casing portion  1702  and the bottom casing portion  1704  at the time the indicator  1710  is first exposed, and at times subsequent to the first exposure, may be indicative of a particular reduced pressure, which may be communicated to the user by the presence and positioning of the indicator  1710 . 
     Referring to  FIG. 18 , a reduced pressure treatment system  1800  is shown according to an illustrative embodiment. The reduced pressure treatment system  1800 , in contrast to the reduced pressure apparatus  1700 , includes indicia or markings  1810 . Although each of the markings  1810  are shown to be circles, each of the markings  1810  may have any shape, such as a square, a triangle, or other polygon. Alternatively, the markings  1810  may be lines, symbols, numbers, or letters, or some combination thereof. In the embodiment in which the markings  1810  are lines, the lines may be substantially perpendicular to the axis along which the top casing portion  1802  is compressible. Although the plurality of markings  1810  includes three markings, the plurality of markings  1810  may include any number of markings. When the top casing portion  1802  is compressed into the bottom casing portion  1804 , all or a portion of the plurality of markings  1810  are hidden from view. 
     As the top casing portion  1802  moves toward an uncompressed position, each of the plurality of markings  1810  may gradually become exposed. For example, as the top casing portion  1802  moves toward an uncompressed position from a fully compressed position, the marking  1812  may first become exposed. The marking  1814  may then become exposed as the top casing portion  1802  moves further toward the uncompressed position. Finally, the marking  1816  may then become exposed as the top casing portion  1802  moves into a fully uncompressed position. Each of the plurality of markings  1810  may have a different color or texture to provide a user with color or tactile-aided indications of the position of the top casing portion  1802 . 
     The user may be alerted to a state of the reduced pressure treatment system  1800  based on the number of the plurality of markings  1810  that are exposed to the user. For example, the more of the plurality of markings  1810  that are exposed, the more urgent may be the need for a user to perform an action to the reduced pressure treatment system  1800 , such as to compress the top casing portion  1802  into a compressed position to maintain a reduced pressure that is being generated or delivered by the reduced pressure treatment system  1800 . 
     Referring to  FIG. 19 , a process that may be implemented by a manually-actuated pump, such as pump  102  in  FIG. 1  or any other illustrative embodiment of the reduced pressure treatment system described above, is shown in accordance with an illustrative embodiment. 
     The process compresses a variable volume chamber having a variable volume from an uncompressed position to a compressed position (step  1905 ). The process determines whether the compressed position yields a threshold level of reduced pressure as indicated by an indicator, such as visual indicators  1608  in  FIG. 16  (step  1910 ). If the process determines that the compressed position does not yield a threshold level of reduced pressure as indicated by an, indicator, the process further compresses or expands the variable volume chamber (step  1915 ). The process then returns to step  1910 . 
     If the process determines that the compressed position yields a threshold level of reduced pressure as indicated by an indicator, the process may then expand the variable volume chamber from the compressed position to the uncompressed position (step  1920 ). The process transfers reduced pressure from the variable volume chamber to a fixed volume chamber (step  1925 ). The process may then transfer the reduced pressure to a tissue site via a manifold and delivery tube (step  1930 ). 
     The flowcharts and block diagrams in the different depicted embodiments illustrate the architecture, functionality, and operation of some possible implementations of the apparatus and methods. In some alternative implementations, the function or functions noted in the block may occur out of the order noted in the figures. For example, in some cases, two blocks shown in succession may be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. 
     The illustrative embodiments described herein separate the chambers in which exudates and other liquids are collected from the reduced-pressure-generating chamber. Thus, the compressible pumps are capable of being re-charged (i.e. the flexible bellows can be re-depressed) even when liquids are present in the fixed volume chamber. When the fixed volume chamber becomes completely full of exudate or other liquids, the fixed volume chamber may then be emptied before additional reduced pressure may be applied by the compressible pump. Also, the illustrative embodiments, unlike traditional manually-activated systems, are capable of delivering a measured and consistent amount of pressure to a tissue site during a particular reduced pressure treatment cycle. The illustrative embodiments are further capable of consistently repeating the targeted pressure each time the compressible pump is recharged. These pressure delivery capabilities exist regardless of the orientation or location of the fixed volume chamber. 
     The illustrative embodiments are also capable of alerting a user as to the need to perform an action on a reduced pressure source. For example, the illustrative embodiments may include a visual indicator that, when exposed, alerts a user that the reduced pressure source needs to be compressed or otherwise charged.