Abstract:
A wound closure apparatus having a housing that contains a vacuum pump and a chamber for holding a disposable wound fluid collection canister. The canister resides within the chamber and connects at an outlet with the vacuum pump at an inlet with a porous wound pad. The pad is placed over or within a wound and adhesively secured thereto. When the vacuum pump activates, it evacuates air from the canister resulting in wound fluids flowing from the wound into the canister. Due to the negative effect that a vacuum can impose on tissue when granulation tissue is pulled into the pad, the pad contains multiple pore sizes to prevent granulation tissue from migrating into the pad. The pad has an outer surface adjacent the wound with pore sizes of a diameter of approximately 100 microns or less to prevent tissue from growing into the pad and is treated for biocompatibility.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation of U.S. patent application Ser. No. 09/545,339 filed Apr. 7, 2000, now U.S. Pat. No. 6,695,823 which claims the benefit of U.S. Provisional Application No. 60/128,567, filed Apr. 9, 1999, and any amendments thereof. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to the healing of wounds and, more particularly, but not by way of limitation, to an apparatus for closing wounds that is compact, self-contained, and includes a disposable wound fluids canister and a porous pad, which is biocompatible with the wound tissue to facilitate the healing of wounds, but does not adhere to the healing tissue. 
   2. Background Information 
   Wound closure involves epithelial and subcutaneous tissue adjacent to the wound migrating towards the center of the wound until it closes. Unfortunately, closure is difficult with large 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 bacterial infection and, thus are less able to close the wound naturally. Such wounds have presented difficulties to medical personnel for many years. 
   The most common technique for closing open wounds has been the use of sutures or staples. Although such mechanical closure techniques are widely practiced and often effective, they suffer a major disadvantage by providing tension on the skin tissue adjacent the wound. That is, the tensile force required to achieve closure using sutures or staples causes very high localized stresses at the suture or staple insertion point. Such stresses commonly result in the rupture of the tissue at those points, which can eventually cause dehiscence in wounds, providing additional tissue loss. 
   Moreover, some wounds harden and inflame to such a degree due to infection that closure by stapling or suturing is not feasible. Wounds not reparable by suturing or stapling generally require prolonged hospitalization with its attendant high cost, and major surgical procedures, such as grafts of surrounding tissues. Examples of wounds not readily treatable with staples or sutures include large, deep, open wounds; decubitus ulcers; ulcers resulting from chronic osteomyelitis; graft site wounds; and partial thickness burns that subsequently develop into full thickness burns. The use of skin grafts in these situations can result in the encapsulation of bacteria and other impurities. 
   The above problem is discussed in WO 93/09727 which proposes as a solution a procedure for draining the wound by applying a continuous negative pressure to the wound over an area sufficient to promote migration of epithelial and subcutaneous tissue toward the wound. Although WO 93/09727 deals in some detail with the clinical considerations of this kind of treatment, the apparatus described has certain practical shortcomings. 
   One problem with the apparatus described in the above prior document is that no means are disclosed for avoiding spread of infection from one patient to another or re-infection of the patient being treated. The pad in the wound drainage device can be modified with an antimicrobial agent, such as Neosporin, to limit the migration of bacteria through the pad and into the vacuum tubes and canister while negative air flow is engaged as well as into the patient when the air flow has been disengaged. 
   An objective is to have a pad that (a) is made from biocompatible material and (b) has sufficiently small pore size that granulation tissue does not migrate into the pad. Granulation tissue is a matrix of collagen, fibronectin and hyaluronic acid carrying microphages, fibroblasts and neovasculature that aids in healing. This objective may be accomplished by using a pad that (a) has a tissue compatible lubricious surface, (b) has a growth factor impregnated surface, (c) has a molecular graft on the pad surface, and/or (d) is antimicrobial. 
   The pad utilized in the wound drainage device can be formed by several different means with the ultimate goal of providing a vacuum compatible portion and a healing tissue compatible portion. It is known in the prior art that foam can be blown to form porous materials; however, it is not disclosed in the prior art that foam can be blown into a wound cavity to form a biocompatible porous pad which is both compatible with the healing tissue and compatible with the vacuum and negative air flow as in the present invention. It is known in the prior art that surgical dressings, such as teflon or rayon, are useful because they are compatible with healing tissue, but it is not disclosed in the prior art the use of porous surgical dressings in conjunction with a porous pad as in the present invention. It is known in the prior art that biocompatible substances such as Hydromers can be used as a coating material to increase lubricity and/or reduce pore size of pads; however, the prior art does not disclose the use of such substances to coat pads as used in the present invention. It is known in the prior art that antimicrobial agents can be used to deter bacterial growth; however, the prior art does not disclose the use of such agents in conjunction with the pad of the present invention. 
   SUMMARY OF THE INVENTION 
   It is a primary object of the present invention to provide a wound closure apparatus that closes wounds without stressing the surrounding skin. 
   It is another object of the present invention to render technology like that disclosed in WO 93/09727 in a convenient, compact and self-contained, efficient and economically feasible system. 
   It is a further object of the present invention to provide a wound closure apparatus that includes a removable and disposable wound fluids collection canister to protect the wound closure apparatus from contamination. 
   It is still a further object of the present invention to provide a wound closure apparatus which makes use of a porous pad with a smooth outer surface having pores of a diameter of approximately 100 microns or smaller so as to prevent skin regrowth therein. 
   It is another object of the present invention to provide a porous pad which can be used in conjunction with a wound closure apparatus which pad has a tissue compatible lubricious surface, has a growth factor impregnated surface, has a molecular grafted surface and/or is antimicrobial. 
   In accordance with the present invention, there is provided a therapeutic apparatus for stimulating healing of wounds, said apparatus including a housing that contains a vacuum pump and a chamber for holding a disposable wound drainage collection cannister. The cannister preferably resides within the chamber and connects at an outlet with the vacuum pump and at an inlet with a pad. The pad is of a porous, compliant material which works well for distributing gas pressure in the wound environment and which also complies with the negative air flow. The pad has a smooth outer surface that has pores close enough together so that the healing tissue will not grow into the pad. The pores on the outer surface of this pad less than one millimeter, normally in the approximate upper range of 100 microns (or less) in diameter in areas where the pad is in contact with the wound. The outer surface of the pad can consist of the outer portion of the pad itself, a material adhered to the pad, or a material placed over the pad. The pad is placed over the wound or pressed into the wound and adhesively secured thereto to create a sealed environment at the wound. The pad is designed such that when the pad is removed it does not disrupt the healing tissue. Thus, when the vacuum pump activates, it evacuates air from the canister and thence the wound environment, resulting in the application of negative pressure to the wound, which in turn tends to promote drainage of fluids flowing from the wound into the canister. After the canister is filled, it is removed from the chamber, disposed of, and replaced with another canister to continue therapy. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view depicting the vacuum pump unit of a wound closure apparatus constructed according to the teachings of the present invention. 
       FIG. 2  is a right side plan view depicting the vacuum pump unit of  FIG. 1 . 
       FIG. 2A  is a detail view of the latch  26  portion of  FIG. 2 , partially cutaway to eliminate guide (or “key”)  29  from the view and to show portions of latch  26  in sagital cross section. 
       FIG. 3  is a perspective view depicting a wound drainage collection canister for use in conjunction with the vacuum pump unit of  FIG. 1 . 
       FIG. 4  is a rear plan view depicting the wound drainage collection canister of  FIG. 3 . 
       FIG. 5  is a perspective view depicting the connection of a wound drainage collection canister of  FIG. 3  to a wound coverage pad. 
       FIG. 6  is a front plan view in partial cross section depicting the connection of the wound drainage collection canister of  FIG. 3  within the housing of the vacuum pump of  FIG. 1 . 
       FIG. 6A  is a partial view of the apparatus shown in  FIG. 6  except the canister is removed. 
       FIG. 7  is a perspective view depicting the filter carrier of the wound drainage collection canister. 
       FIG. 8  is a top plan view depicting the filter cap of the wound drainage collection canister. 
       FIG. 9  is a schematic view depicting the control system for a wound closure apparatus constructed according to the teachings of the present invention. 
       FIG. 10  is a section through a wound showing the wound pad in place. 
       FIG. 11  is a porous wound pad being dipped into a solution. 
       FIG. 12  is a porous wound pad with varying porosity on two sides (with tube). 
       FIG. 13  is a side of a porous wound pad being melted by a heat source. 
       FIG. 14A  is a cross section of chemical being sprayed into the wound. 
       FIG. 14B  is a cross section of chemical being sprayed into the wound (with tube). 
       FIG. 15  is a cross section of a wound where spraying of the chemical has been completed (with tube). 
       FIG. 16  is a cross section of a wound where the sprayed chemical has hardened into the contours of the wound (with tube). 
       FIG. 17  is a porous sock wrapped around the porous wound pad (with tube). 
       FIG. 18  is a porous wound pad with a removable micropore layer (with tube). 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   As illustrated in  FIGS. 1 and 2 , front housing  11  and rear housing  12  connect together using any suitable means such as screws and fasteners to provide wound closure vacuum pump  10  with a small, compact, and easily portable carrying case. Consequently, front housing  11  and rear housing  12  connect together to form handle  13  that permits easy carrying of the wound closure apparatus  10 . Except as may be otherwise evident from this description, the carrying case of the vacuum pump  10  is substantially as described and shown in WIPO Design No. DM/032185. 
   Front housing  11  includes power switch  15  that is movable between an on and off position to permit user control of the delivery of power to the wound closure apparatus  10 . Keypad  16  and liquid crystal display (LCD)  17  mount to front housing  11  to permit the programming of the wound closure apparatus  10 . Chamber  18  is defined by integrally formed interior side walls  100  and  101 , top wall  102 , bottom wall  103  and rear wall  104 . Side wall  100  is dependently attached to the interior of the front housing  11  by standard mounting hardware (not shown). The wound fluids collection canister  19 , illustrated in  FIGS. 3-5 , is received within chamber  18 . Side walls  100  and  101  each include a key  29  and  30 , respectively, that aid in the alignment of wound fluids collection canister  19  within chamber  18 . Furthermore, front housing  11  includes latch  26  to secure the wound fluids collection canister  19  within chamber  18 . 
   Rear housing  12  includes arm  14  pivotally mounted to it within recess  110 . An identical arm pivotally mounts to the opposite side of rear housing  12  within an identical recess. Arm  14  and its corresponding arm mounted on the opposite side of the rear housing  12  pivot from within their recesses to a position where they support the wound closure apparatus  10  at an angle. Arm  14  and its corresponding arm angularly support the wound closure apparatus  10  to permit easier user access to keypad  16 . Arm  14  and its corresponding arm may also be used to permit hanging of apparatus  10  from a hospital bed foot board. 
   Canister  19  has a shape as shown in  FIGS. 3 to 6 . As illustrated in  FIGS. 3  to  6 , canister  19  includes side walls  20  and  21 , top wall  23 , bottom wall  24 , back wall  22  and front wall  25  that define the rectangular chamber for receiving blood, pus, and other fluids emitted from a wound. Side walls  20  and  21  include key ways  27  and  31  respectively, that receive a respective one of keys  29  and  30  to provide easy alignment of canister  19  within chamber  18 . Furthermore, key way  27  includes recess  28  that receives latch  26  to fasten canister  19  within chamber  18 . 
   Front wall  25  of canister  19  includes raised portion  32  extending therefrom to furnish a window that permits a user to determine the level of wound fluids within canister  19 . Accordingly, raised portion  32  is transparent so that the level of wound fluids within canister  19  may be visually determined. Raised portion  32  includes side walls  110  and  111 , top wall  112 , bottom wall  113 , and front face  114  that define a chamber which opens into the chamber defined by side walls  20  and  21 , top wall  23 , bottom wall  24 , back wall  22  and front wall  25  of canister  19 . Front face  114  of raised portion  32  includes graduations that demarcate the volume of wound fluid within canister  19 . Additionally, side walls  110  and  111  of raised portion  32  include ridges that provide a gripping surface for the user during the insertion and removal of canister  19  from chamber  18 . 
   Although raised portion  32  is transparent to permit the determination of the level of wound fluids within canister  19 , side walls  20  and  21 , back wall  22 , top wall  23 , bottom wall  24 , and front wall  25  are opaque so that they are only translucent. As an alternative, the portions of canister  19  surrounding filter  46  may also be transparent. This enables a user to visually check for signs of contamination of filter  46 . In this preferred embodiment, side walls  20  and  21 , back wall  22 , top wall  23 , bottom wall  24 , front wall  25 , and raised portion  32  of canister  19  are fabricated from a plastic material. 
   Canister  19  includes inlet  35  that is formed integrally with top wall  112  of raised portion  32 . Inlet  35  is cylindrical in shape and communicates with the interior of canister  19  to permit the transfer of wound fluids into canister  19 . In this preferred embodiment, inlet  35  is also fabricated from a plastic material. 
   In order to prevent liquids sucked into the canister  19  from splashing directly onto cap  49 , which mask the outlet  44 , and to reduce foaming within the canister  19 , inlet  35  has a blind inner end. Inlet  35  has a slot  35 A so that drainage fluid is deflected downwardly into the raised handle portion  32  of the canister  19 . Handle portion  32  may communicate with the main part of the canister  19  through one or more holes in wall  25 . It is desirable to avoid foaming because this can give a false reading when a capacitance sensing device is used to sense when the canister  19  is filled. An anti-foaming material, e.g. a silicone, may be added to the canister  19 , e.g. by coating the interior walls. It may also be advantageous to include a gel-forming substance, e.g. a polyacrylamide of modified starch in order to immobilize the drainage fluid. This is particularly useful if the apparatus is likely to be tilted. 
   Wound fluids (i.e. drainage) are communicated through inlet  35  into canister  19  via pad  36  and hoses  37  and  38 . In this preferred embodiment, the portion of the pad  36  next to the vacuum tube  37  (i.e. inner portion or surface) is fabricated from an open cell polyurethane or polyether foam. The outer surface of the pad  36  in contact with the wound cavity  216  can consist of the same material as the inner portion or surface next to the vacuum tube  37  where the size of the pores is 100 microns of less. Hose  37  is inserted within pad  36  by making an incision in pad  36  and inserting the end of hose  37 . Hose  37  can then be secured within pad  36  using any suitable means such as an adhesive or a flange. Preferably, the porous pad  36  has an elongated hole  300  (See  FIG. 11 ) for the drainage tube  37  which is an interference fit with the tube  37 . The hoses  37  and  38  are preferably made from medical grade PVC tube. Hose  38  mounts within inlet  35  using any suitable means such as adhesive or welding. Hoses  37  and  38  include luer lock connectors  39  and  40 , respectively, (or the equivalent, such as any known quick disconnect type coupling) that attach together to permit communication between hoses  37  and  38 . Furthermore, hoses  37  and  38  include pinch clamps  41  and  42 , respectively, that are capable of sealing their respective hose  37  or  38  to prevent the flow of wound fluids. The porous pad  36  is preferably packaged in a sterile container together with its connector and clamp. When packaged, the clamps will be in their open condition. 
   The communication of wound fluids into canister  19  requires the securing of pad  36  over a wound. Pad  36  is secured over a wound using cover  43  which is fabricated from a plastic material and includes an adhesive on one side that sticks to human skin. Wound cover  43  is conveniently a surgical drape material comprising a sheet of elastomeric material coated peripherally or overall with a pressure-sensitive adhesive, such as an acrylic adhesive. The elastomeric or rubbery nature of the wound cover  43  is important because it accommodates changes in pressure in the wound area during intermittent operation of the vacuum pump  84 . The wound cover  43  is preferably a polyurethane film with a removable backing sheet, i.e. of polythene to protect the adhesive surface. 
   A high degree of reticulation in the inner portion or surface of the porous pad  36  next to the vacuum tube  37  is desirable to achieve good permeability when the pad  36  is under suction. The outer surface of the pad  36  next to the wound, however, is smooth and contains pores of approximately 100 microns in diameter to allow for vacuum air flow through the pad  36  while preventing the healing tissue from cross linking with the pad  36 . While the upper range of pore size is not exactly known, it is between 100 microns and 1000 microns (one millimeter). The lower end of the pore size is simply large enough to allow air and fluids to flow therethrough which could be as small as one micron. 
   There are several different ways to prepare a pad  36  for use with the wound drainage apparatus  10  which contains an outer surface with the preferred specifications. One way is to make a porous pad  36  out of a material which consists entirely of micropores (not shown) with a diameter of approximately 100 microns or less, or blow the pad  36  in such a way that the portion to be inserted into the wound cavity contains the micropores of a diameter of approximately 100 microns or less as will be subsequently described. A micropore is an opening in the pad  36  of approximately 100 microns or less. 
   Referring to  FIGS. 11 and 12 , a second way to create the pad  36  is to dip the portion of the pad  36  which is to be placed inside the wound in a liquid coating material  201  which dries into the pad  36  acting as a bulking agent thereby reducing the diameter of the pad pores  205  to approximately 100 microns or less. This effectively creates a smooth outer surface with a pore size of approximately 100 microns or less, hereinafter called micropores  207 , to be placed in the wound cavity  216 . An inner surface can have pores  205  of a size of greater than 100 microns which have a greater vacuum compatibility with the vacuum tube  37 . 
   In  FIG. 11 , a porous wound pad being dipped into a solution  201  is shown.  FIG. 11  shows a porous wound pad  36 , with top  203 , bottom  204 , and side  206 . The pores  205  of the porous wound pad  36  are a vacuum compatible size. A vacuum tube  37  is shown in the side  206  of the porous wound pad  36 . The pad  36  is being dipped to approximately 1 millimeter into a liquid coating material  201 , such as a liquid hydrophilic foam solution, held in a flat tray  202 , which when hardened acts as a bulking agent to form a smooth micropore layer  211  with micropores  207  of a diameter of approximately 100 microns or less. This allows for the flow of negative air pressure and fluids through the pad  36  without compromising the healing tissue surface. The coating of the pad  36  can occur directly before insertion into the wound cavity  216 , allowing enough time for drying, or the pad  36  can be coated during manufacturing. Furthermore, for certain types of wounds it may be necessary to mix an antimicrobial agent such as Neosporin with the liquid coating material  201  so as to create a modified pad surface which is difficult for bacteria to stick to thus preventing bacterial migration through the pad  36 . The addition of the coating to the pad  36  does not hamper the ability to trim the pad  36  to conform to the wound cavity  216 . 
     FIG. 12  shows a cross section of a porous wound pad  36  with varying porosity on one surface (with tube). This varying porosity can result from the porous pad  36 , with top  203 , bottom  204  and side  206 , being dipped in the liquid coating material  201  as described in  FIG. 11 . This pad  36  contains an upper pore layer  212  with vacuum compatible pores  205  and a smooth micropore layer  211  with healing compatible pores  207  which have a diameter of approximately 100 microns or less. By having a size of approximately 100 microns or less, tissue cannot grow into the micropore layer  211 . Again the liquid coating material  201  (a) can be modified with an antimicrobial agent such as Neosporin to deter bacterial migration through the pad  36 , or (b) forms a tissue compatible lubricious surface that is growth factor impregnated or is a molecular graft. 
   Referring to  FIG. 13 , another way of creating the optimum outer pad surface is to take a porous pad  36  with pores  205  that may have a diameter greater than 100 microns and heat that pad  36  on the side to be placed inside the wound cavity  216  with a heat source  208  so as to shrink or melt the pore size to a diameter of approximately 100 microns or less while maintaining a smooth texture. In  FIG. 13 , a side of a porous wound pad being melted by a heat source is shown. The pad  36 , with top  203 , bottom  204 , and side  206  and containing pores  205  of vacuum compatible pore size, is shown on a hot plate  208 . This hot plate  208  has a standard current adapter  209  and plug  210 . While a hot plate  208  was used in this illustration, any heat source could be used. The heat source  208  was simply necessary to melt the surface of the pad  36  partially so as to create a smooth micropore layer  211  with healing compatible micropores  207  of approximately 100 microns or less. 
   Referring to  FIGS. 17 and 18 , the porous pad  36  can be made with a smooth outer surface of approximately 100 microns or less by taking a pad  36  with vacuum compatible pores  205  and placing the pad  36  within a porous sock  213  which is smooth and contains pores  207  with a diameter of approximately 100 microns or less. The sock-covered pad  36  is then placed inside the wound cavity (not shown in this Figure).  FIG. 17  shows a porous wound pad  36  situated within a porous sock  213 . The pad  36 , with top  203 , bottom  204 , and side  206 , has vacuum compatible pores  205  and a vacuum tube  37  for use in extending the negative air pressure through the pad  36 . The porous sock  213  contains healing compatible pores  207  of a diameter of approximately 100 microns or less and acts as a covering being placed over the porous wound pad  36  before insertion into the wound cavity  216 . If any trimming of the pad  36  is needed it can be done before the pad  36  is placed in the sock  213  before insertion into the wound cavity  216 . 
   Referring specifically to  FIG. 18 , a variation of the technique demonstrated in  FIG. 17  would be to affix a smooth porous membrane  219  only to the face of the pad  36  that is to be placed into the wound cavity  216 . This membrane  219  contains pores of a diameter of approximately 100 microns or less. The porous sock  213  or membrane  219  may be composed of TEFLON, rayon, or a similar material. Knit rayon film is often used for conventional dressings to try to accelerate the growth of granulation tissue. The membrane  219  may form a tissue compatible lubricious surface that is growth factor impregnated and antimicrobial. In  FIG. 18 , a porous wound pad  36  with a removable membrane  219  is shown. The pad  36 , with top  203 , bottom  204 , and side  206  and vacuum compatible pores  205 , contains a vacuum tube  37  for use in extending the negative air pressure through the pad  36  for aspiration of the wound cavity  216 . The removable membrane material  219 , such as teflon or rayon, contains healing compatible micropores  207  of a diameter of 100 microns or less. This membrane material  219  can be placed around the portion of the pad  36  which is to go into the wound cavity  216 . The membrane  219  can be held in place on the pad  36  by any biocompatible means such as an adhesive. 
   Referring to  FIGS. 14 through 16 , another way in which the pad  36  is made is by spraying a nontoxic chemical substance  215  directly into the wound cavity  216 . The chemical substance  215  hardens into the shape of the wound cavity  216  when placed directly into the wound  216 . This forms a pad  36  such that the surface of the pad  36  next to the healing tissue is smooth and has pores of a diameter of approximately 100 microns or less. A chemical substance (not shown) can also be sprayed in a sterile environment before insertion into the wound cavity  216 . When the pad  36  is formed on an external sterile surface it is allowed to harden slightly into a foam like substance and then pressed into the wound cavity  216  so as to conform to the wound. The chemical substances used in these circumstances are sprayed so as to make a pad  36  with a smooth outer surface containing pores with a diameter of approximately 100 microns or less. 
     FIG. 14A  shows a cross section of chemical being sprayed into a wound. A nontoxic chemical substance  215  is sprayed from the spray nozzle  218  of a container (not shown). The chemical substance  215  is under pressure such that when it is sprayed into the wound cavity  216  of the body  214  the gas is expelled from the chemical substance  215  which allows the chemical substance  215  to expand from a liquid phase to a solid porous phase which conforms to the shape of the wound cavity  216  (See  FIG. 15  where the solidification of the pad  36  is shown with a wound cover  43  placed over the pad  36  and tube  37  assembly.). The vacuum tube  37  should be placed in the cavity  216  during the spraying of the chemical substance  215  before solidification occurs (See  FIG. 14B ). This porous pad  36  which is formed (See  FIG. 16 ) is equally vacuum compatible next to the vacuum tube  37  as well as compatible with the healing tissue containing a smooth surface and only micropores  207  of approximately 100 microns of less in diameter in contact with the wound cavity  216 . 
   The type of pad  36  can vary based on the type of wound involved. In addition, the type of wound may dictate that an antimicrobial agent, such as Neosporin, be used in the pad  36  entirely or on the surface which is in contact with the wound so as to give a topical antimicrobial effect. 
   In use, the porous pad  36  is cut to a size which corresponds closely to the edge of the wound with the objective of packing the pad  36  into the wound cavity  216  so that it contacts the surface of the cavity  216 , rather than bridging the cavity  216 . As depicted in  FIG. 10 , the cavity  216  may be extensive and there may be little or no tissue coverage to the bone  212 . This is illustrated diagrammatically in  FIG. 10 .  FIG. 10  is a cross-section through a wound showing the porous pad  36  packed in the wound cavity  216 . It is important that the pad  36  should be firmly packed into the recesses of the wound cavity  216 . Drainage tube  37  terminates within the center of the porous pad  36 . Surgical drape  43  extends over the porous pad  36  and is adhered to intact skin around the periphery of the wound. Drape  43  is also firmly adhered around the tube  37  to prevent leakage of air. A wound cover  43  is then adhered to the surrounding skin and around the drainage tube  37  to provide an air-tight seal around the wound. 
   As illustrated in  FIGS. 2 ,  4  and  6 , canister  19  includes outlet  44  that mounts over port  45  to permit wound closure apparatus  10  to draw wound fluids into canister  19 . Outlet  44  is cylindrically shaped and formed as an integral part of back wall  22  by outer wall  33  and inner wall  50  which are interconnected by end wall  34 . Passageway  52 , defined in part by interior wall  50  and in part by filter cap  49 , provides the actual conduit for outlet  44  between the interior and exterior of canister  19 . The placement of canister  19  within recess  18  such that outlet  44  resides over port  45  couples canister  19  to a vacuum pump  84 . The vacuum pump  84  removes air from canister  19  to create a vacuum pressure within canister  19 . That vacuum pressure is then transmitted to a wound site through hoses  37  and  38 , thereby not only enabling therapeutic use of system  10 , but also tending to promote wound drainage. Any wound drainage fluid is then drawn through pad  36  and hoses  37  and  38  into canister  19 . 
   Outlet  44  resides near top wall  23  of canister  19  to ensure efficient operation of the vacuum pump  84 . That is, the vacuum pump  84  removes the most air from canister  19  when the air does not have to first bubble through wound fluids contained in canister  19 . Consequently, with outlet  44  positioned near the top of canister  19 , the vacuum pump  84  removes air directly from canister  19 , and it is only during the final filling of canister  19  that air must bubble through wound fluids. Preferably, as described below, the apparatus includes detecting and warning means which operates before the level of drainage fluid reaches either the inlet or outlet tube so that a fresh canister  19  can be installed. 
   In removing fluids from a wound utilizing wound closure apparatus  10 , a major safety concern is preventing wound fluids from contaminating the vacuum pump  84 . Accordingly, filter  46  mounts over outlet  44  utilizing filter carrier  48  and filter cap  49  to block the flow of wound fluids to outlet  44  so that wound fluids remain within canister  19  and do not flow into the vacuum pump  84 . In this preferred embodiment, filter  46  is a 0.2 micron hydrophobic membrane filter providing a bacterial barrier, although other filters may be substituted as appropriate. 
   As illustrated in  FIG. 7 , filter carrier  48  includes face  53  formed integrally with lip  54 . Face  53  includes groove  56  formed therein, while lip  54  supports brace  55  in its interior. Filter  46  fits within groove  56  of face  53  and is supported within filter carrier  48  by brace  55  of lip  54 . An O ring  53 A is fitted in peripheral recess of filter carrier  48  to accommodate manufacturing tolerances and ensure a fluid tight seal with filter cap  49 . 
   As illustrated in  FIGS. 6 and 8 , filter cap  49  includes cylindrical portions  57  and  58 , which are formed integrally (with annulus  57 ′ spanning there between), to hold filter carrier  48  within passageway  52  of outlet  44 . To mount filter  46  over passageway  52 , filter  46  is first placed within filter carrier  48  as described above. Filter carrier  48  is then positioned within filter cap  49  such that face  53  abuts annulus  57 ′ of filter cap  49  and lip  54  of filter carrier  48  resides within annular lip  50 ′ of outlet  44 . Accordingly, when cylindrical portion  57  of filter cap  49  mounts over outlet  44 , the front face  53  of filter carrier  48  and the outer edges of filter  46  abut annulus  57 ′ to secure filter  46  within passageway  52 . Filter cap  49  attaches to outlet  44  using any suitable means such as an adhesive or welding. Filter cap  49  is completely sealed except for aperture  51  positioned on top of filter cap  49 . Aperture  51  communicates with port  45  via passageway  52  of outlet  44  to permit the vacuum pump  84  to draw air from the interior of canister  19 . 
   As illustrated in  FIGS. 2 and 6 , port  45  includes O-ring  59  mounted thereabout to provide a fluid tight seal between port  45  and inner wall  50  of outlet  44 . Port  45  mounts through rear wall  104  of chamber  18  using any suitable means such as nuts  60  and  61 . Furthermore, line  62  attaches to the rear of port  45  using any suitable means such as a clamp to couple port  45  to the vacuum pump  84 . 
   Switch  63  protrudes through rear wall  104  of chamber  18  to produce a signal indicating when canister  19  properly and securely resides within chamber  18 . In this preferred embodiment, switch  63  is a normally open push button switch that mounts on rear wall  104  of chamber  18  using any suitable means such as a bracket. When canister  19  is properly positioned within chamber  18 , its rear wall  22  presses the head of switch  63 , closing switch  63  so that it provides a signal indicating that canister  19  properly resides within chamber  18 . 
   Fill sensor  64  resides adjacent side wall  101 , exterior to chamber  18 . Fill sensor  64  provides a signal that indicates when canister  19  is filled with wound debris. In this preferred embodiment, fill sensor  64  is a capacitive sensor that mounts on side wall  101  of chamber  18  using any suitable means such as a bracket or appropriate adhesive material. Fill sensor  64  has a sensing profile  64 A which determines the point at which the capacitance measurement is made. When wound fluids have reached the level within canister  19  which corresponds to the location of the sensing profile  64 A, the capacitance within canister  19  as ‘seen’ by fill sensor  64  changes, resulting in fill sensor  64  outputting a signal indicating that canister  19  is filled with wound fluids to the level at which the sensing profile is located. The position of this sensing profile behind wall  101  can be changed (see  FIG. 6A ) to provide an optimum balance of space and volume utility. 
   As illustrated in  FIG. 2A , latch  26  generally comprises latch pin  65 , handle  66 , latch guide sleeve  68 A and spring  67 . Latch pin  65  comprises a proximal end  65 A and distal end  65 B. Latch guide sleeve  68 A abuts the inner surface of front housing  11  and is held securely in place from the outer side of front housing  11  by nut  68 B. Handle  66  screws onto the proximal end  65 A of latch pin  65  and is locked in position by nut  69 A. In the preferred embodiment, cover  68  over nuts  69 A and  68 B provides a surface against which handle  66  abuts, thus preventing end  65 B from excessively entering chamber  18  as will be understood further herein. Cover  68  also provides aesthetic enclosure of nuts  69 A and  68 B. Dependent attachment of side wall  100  (chamber  18 ), as described herein above, is such that side wall  100  abuts latch guide sleeve  68 A on the side distal front housing  11 . Further, this arrangement causes distal end  65 B of latch pin  65  to project into chamber  18  under the force of spring  67  (shown partially cut away). Spring  67  resides circumferentially about latch pin  65  within an axial bore of latch pin guide  68 A. Spring  67  exerts force between distal end  65 B of latch pin  65  and an annulus within the axial bore of latch pin guide  68 A. A transverse slot in the distal end of latch pin guide  68 A receives end  65 B of latch pin  65 , providing rotational alignment of end  65 B and further recess for end  65 B when a user “pulls” handle  66  in an axial direction. 
   Latch  26  operates to ensure canister  19  remains secured within chamber  18 . End  65 B of latch  26  terminates in a point that protrudes through key  29  into chamber  18 . During the placing of canister  19  within chamber  18 , key way  27  of canister  19  forces the point  65 B of the latch pin within key  29 . However, once canister  19  has been properly positioned within chamber  18 , recess  28  resides below latch pin end  65 B so that spring  67  biases the point  65 B of latch pin  65  into recess  28  to prevent the removal of canister  19  from chamber  18 . The removal of canister  19  from chamber  18  is accomplished by grasping handle  66  and pulling the point  65 B of latch pin  65  from recess  28 . With the point of latch pin  65  no longer within recess  28 , canister  19  may be pulled from chamber  18  using its raised portion  32 . 
   As illustrated in  FIG. 9 , wound closure apparatus  10  preferably plugs into a standard 115/120 VAC power source (e.g. an outlet) to supply power to control system  70 . Alternative embodiments (not shown, although similar) are readily adapted for 220 VAC power by changing the power cord and appropriately rewiring the taps of the transformer within DC power supply  71 , as is readily known in the art. The application of power to control system  70  is regulated by power switch  15  which is a standard push button on/off switch. With power switch  15  depressed, DC power supply  71  receives the 115/120 VAC signal and converts it into a 12 VDC signal for use by fan  74  and vacuum pump  84 . A conventional voltage regulator  96  steps down the voltage to +5V for use by each of the other DC components  16 ,  17 ,  63 ,  64 ,  72 , and  75 . Voltage regulator  96  connects to keypad  16 , LCD  17 , switch  63 , fill sensor  64 , microcontroller  72 , transducer  75 , and tilt sensor  82  to supply each of them with the +5V DC signal. Microcontroller  72  links to solid state relays (MOSFETs)  97  and  98  for controlling the provision of the 12 VDC power supply to fan  74  and pump motor  83 , respectively. 
   As illustrated in  FIG. 1 , once power switch  15  is depressed, a user employs keypad  16  and LCD  17  to select the operating parameters for wound closure apparatus  10 . Wound closure apparatus  10  stores the previously selected operating parameters so that upon power initialization, LCD  17  displays the phrase “NEW PATIENT” with the word “NO” over arrow button  76 , and the word “YES” over arrow button  77 . If the user presses arrow button  76  to answer no, wound closure apparatus  10  will operate at the previously selected parameters. After answer no, the user pressures on/off button  78  to begin operation of wound closure apparatus  10 . 
   Conversely, if the user presses arrow button  77  to indicate a new patient, wound closure apparatus  10  will operate either under default values or allow the user to select the operating parameters. To operate under default parameters, the user presses on/off button  78  after pressing arrow button  77 . However, to select his or her own values, the user presses option button  79  after pressing arrow button  77 . 
   Upon the pressing of options button  79 , LCD  17  displays a bar graph representing the spectrum of available vacuum pump pressures and a numerical representation of the vacuum pump pressure presently displayed by the bar graph. The user changes vacuum pump pressure using arrow buttons  76  and  77 . The pressing of arrow button  76  reduces vacuum pump pressure, while the pressing of arrow button  77  increases vacuum pump pressure. After selecting the desired vacuum pump pressure, the user presses option button  79  to save the selected vacuum pump pressure. 
   Once the selected vacuum pump pressure has been saved, LCD  17  displays the pump operation times available to the user. The user may program wound closure apparatus  10  to pump either continuously or intermittently. Thus, LCD  17  displays the word “CONTINUOUS” over arrow button  76   b  and “INTERMITTENT” over arrow button  77 . The user selects continuous operation by pressing arrow button  76  followed by on/off button  78  to activate the vacuum pump  84 . In its continuous mode, wound closure apparatus  10  runs its vacuum pump  84  continuously until on/off button  78  is pressed again. 
   If the user presses arrow button  77  to select intermittent operation, LCD  17  displays a bar graph representing the minimum and maximum on times for the vacuum pump  84 . LCD  17  also displays the phase “ON TIME” and the numerical value presently displayed by the bar graph. A user decreases the on time of the vacuum pump  84  by pressing arrow button  76  and increases the on time of the vacuum pump  84  by pressing arrow button  77 . After selecting the desired on time, the user presses options button  79  to save the selected on time value. 
   LCD  17  then displays a second bar graph representing the off time for the vacuum pump  84  with the phrase “OFF TIME” and the numerical value presently depicted by the bar graph. Again, arrow buttons  76  and  77  are pressed to increase or decrease, respectively, the off time for the vacuum pump  84 . After selecting the off time, the user presses options button  79  followed by on/off button  78  to operate wound closure apparatus  10  using the selected parameters. 
   Keypad  16  includes setting button  80  to permit the user to sequentially display the currently selected operating parameters of wound closure apparatus  10 . Keypad  16  further includes delay button  81  to permit the user to deactivate an alarm sounded in response to an improper operating condition of wound closure apparatus  10 . Delay button  81  provides the user with the ability to silence alarms so that the alarm will not have to be listened to during the correction of the problem. 
   Any new alarm conditions occurring within the fifteen minute period (“delay period”) after the pressing of delay button  81  will not be indicated by an audible alarm. However, the pump will still be deactivated when appropriate, even during the delay period. 
   Again referring to  FIG. 9 , microcontroller  72  is a multi-port microprocessor with a ten-bit analog to digital (“A/D”) converter having associated memory that stores the program directing microcontroller  72  during its controls of wound closure apparatus  10 . After receiving and storing the user selected operational parameters and receiving an on signal due to the pressing of on/off button  78 , microcontroller  72  activates pump motor  83  which, in turn, drives vacuum pump  84  to begin the removal of air from canister  19 . 
   As vacuum pump  84  operates, it draws air from within canister  19 , into line  62  via outlet  44  of canister  19  and port  45 . Line  62  connects to filter  85  and transducer  75  via T-junction  91 . Filter  85  is similar to filter  46  and thus ensures no wound fluids contaminate vacuum pump  84 . Filter  85  communicates with pump  84  via T-junction  88  and one arm of the latter is connected to bleed valve  86 . Bleed valve  86  communicates with the atmosphere to release pressure developed within line  62  by vacuum pump  84  after microcontroller  72  deactivates vacuum pump  84 . Bleed valve  86  is sufficiently small to ensure that it generally does not affect the vacuum pressure levels achieved by vacuum pump  84  as it evacuates air from canister  19 , except to prevent overpressurization beyond 250 mm Hg and to prevent erratic operation of the vacuum pump  84  at very low pressure settings. 
   In the preferred embodiment, an orifice of 0.5 mm diameter is especially preferred for bleed valve  86 . Valve  86  or the equivalent is particularly important for enabling intermittent application of negative pressure, as the orifice  86  allows for gradual release of the negative pressure (over a period of about fifteen seconds) when the pump motor  83  is de-actuated. Bleed valve  86  is positioned outside housing  11  to facilitate un-clogging of aperture  86  in the event of a blockage. An aperture is provided in bleed valve  86 , which is machined from stainless steel. Flow control orifices would be alternatives. 
   Line  62  also includes T-connector  91  to connect it with line  92 . Line  92  is connected to tank  94  which acts as a damper to pressure changes in line  62 . This dampening effect, facilitated by restrictor  89  in line  93  between transducer  75  and T-junction  91 , causes the pressure measured by transducer  75  to be an accurate indication of actual wound site pressure. Transducer  75  communicates with line  62  via line  93  to measure tank  94  pressure and produce an electrical signal representative of that pressure. Transducer  75  outputs its pressure signal to microcontroller  72 . 
   Microcontroller  72  utilizes the pressure signal to control the speed of pump motor  83 . As previously described, the user selects either a default vacuum pump pressure or a desired vacuum pump pressure for the operation of wound closure apparatus  10 . After receiving the wound pressure signal from transducer  75 , microcontroller  72  compares the wound pressure with the user selected pressure. If the wound pressure is higher than the user selected vacuum pump pressure, microcontroller  72  reduces pump motor speed to decrease vacuum pump pressure and thus the pressure at the wound. Conversely, if the wound pressure is less than the user selected vacuum pump pressure, microcontroller  72  increases the speed of pump motor  83  resulting in an increase in the vacuum pressure applied at the wound. 
   Microcontroller  72  controls pump motor  83  by varying the amount of voltage received by pump motor  83 . That is, microcontroller  72  receives the 12 VDC signal from DC power supply  71  and outputs a voltage between 0 and 12 VDC to pump motor  83  to control its speed in accordance wit the user selected vacuum pump pressure value. Accordingly, microcontroller  72  employs feedback to ensure that the wound experiences the user selected vacuum pump pressure. If the target pressure is not reached after a period of five minutes, microcontroller  72  deactivates motor  83  and sounds the audible alarm. Additionally, the feedback signal prevents maximum vacuum pump pressure from being exceeded. If the wound pressure measured by transducer  75  exceeds a maximum safe vacuum pump pressure microcontroller  72  deactivates pump motor  83  and activates alarm  95  to signal a malfunction. 
   Wound closure apparatus  10  includes fan  74  to cool pump motor  83  and printed circuit (“PC”) board  200  during the operation of the wound closure apparatus  10 . In the preferred embodiment, microcontroller  72  controls fan  74  to always operate while power is being supplied. In alternative embodiments, however, microcontroller  72  controls fan  74  to operate only in relation to motor  83 , because it is only necessary for fan  74  to operate if motor  83  is also operating. In such alternative, as long as pump motor  83  operates, microcontroller  72  runs fan  74 . However, when microcontroller  72  deactivates pump motor  83  it also deactivates fan  74 . 
   Control system  70  includes fill sensor  64  to provide a signal to microcontroller  72  that indicates when canister  19  is completely filled with wound fluids. After receiving a signal from fill sensor  64 , microcontroller  72  deactivates pump motor  83  and fan  74  and activates alarm  95  to signal the user that canister  19  must be replaced. 
   Control system  70  includes switch  63  to prevent users from operating wound closure apparatus  10  without a canister properly installed. If a canister is not properly installed, switch  63  remains open and therefore outputs no signal to microcontroller  72 . If microcontroller  72  receives no signal from switch  63 , indicating no canister within chamber  18 , it will not supply power to pump motor  83  even after a user has pressed on/off button  78 . Furthermore, microcontroller  72  activates alarm  95  to signal the user that either a canister is not properly installed or is improperly installed within chamber  81 . Microcontroller  72  operates pump motor  83  only if switch  63  is depressed to provide a signal indicating the proper placement of a canister within chamber  18 . 
   Control system  70  includes tilt sensor  82  to prevent operation of wound closure apparatus  10  if it is tilted excessively. Excessive tilting of wound closure apparatus  10  during operating diminishes the efficiency of removal of wound fluids and, more importantly, might result in either the contamination of vacuum pump  84  or the spilling of wound fluids. Thus, if wound closure apparatus  10  tilts along any of its axes beyond a predetermined angle (approximately 45° in this preferred embodiment), tilt sensor  82  outputs a signal to microcontroller  72 . In response, microcontroller  72  deactivates pump motor  83  and activates alarm  95  to signal the user of the excessive tilt situation. In this preferred embodiment, tilt sensor  82  may be implemented with any standard mercury switch. A predetermined delay (e.g. 30 seconds) may be incorporated in the circuitry so that the tilt alarm does not operate immediately. 
   Although the invention has been described with reference to specific embodiments, this description is not meant to be construed in a limited sense. Various modifications of the disclosed embodiments, as well as alternative embodiments of the inventions will become apparent to persons skilled in the art upon the reference to the description of the invention. It is, therefore, contemplated that the appended claims will cover such modifications that fall within the scope of the invention.