as illustrated in fig1 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 fig3 - 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 fig3 to 6 . as illustrated in fig3 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 fig1 ) 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 fig1 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 fig1 , a porous wound pad being dipped into a solution 201 is shown . fig1 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 . fig1 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 fig1 . 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 fig1 , 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 fig1 , 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 fig1 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 ). fig1 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 fig1 , a variation of the technique demonstrated in fig1 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 fig1 , 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 fig1 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 . fig1 a 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 fig1 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 fig1 b ). this porous pad 36 which is formed ( see fig1 ) 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 fig1 , the cavity 216 may be extensive and there may be little or no tissue coverage to the bone 212 . this is illustrated diagrammatically in fig1 . fig1 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 fig2 , 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 fig7 , 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 fig6 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 fig2 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 fig6 a ) to provide an optimum balance of space and volume utility . as illustrated in fig2 a , 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 fig9 , 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 fig1 , 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 fig9 , 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 .
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 .