Abstract:
The invention relates to a therapeutic device to promote the healing of a wound, comprising a porous paid which is permeable for fluids to place on the wound, a bandage to cover the wound and to provide an essentially airtight seal around the wound, a drainage line connecting the pad with a suction pump so that suction can be applied to the wound to draw the fluids away from it, whereby the line is connected to the suction pump via a canister to collect fluid sucked from the wound, a connector to connect the pad to the drainage line, means to determine a prevailing wound pressure basically comprising the wound and this surrounding skin area, as well as a control unit to control the wound pressure. In order to generally improve metrology with the goal of making possible a more reliable and more secure dressing of the wound, and also to design metrology in an especially simple and error-free way, it is proposed that the pad interconnect the suction pump solely via the drainage line.

Description:
CROSS REFERENCE TO RELATED PATENT APPLICATIONS  
       [0001]     This application is the National Phase Application under 35 USC §371 of International Application No. PCT/EP2006/002623, filed Mar. 22, 2006, which claims priority to German Patent Application 10 2005 014 420.9, filed Mar. 24, 2005. 
     
    
     BACKGROUND  
       [0002]     A. Technical Field  
         [0003]     The present invention relates to a therapeutic device to promote the healing of a wound, comprising:  
         [0004]     an essentially airtight cover around the wound, whereby a liquid-permeable pad is preferably provided between the wound and cover, a drainage line connecting the cover with a suction pump,  
         [0005]     a drainage line connecting the cover with a suction pump so that the wound can be suctioned to draw fluids from it, whereby a distal end of the drainage line is connected indirectly to the suction pump through a reservoir to collect the fluid suctioned from the wound,  
         [0006]     pressure disposal means for the direct or indirect definition of a wound pressure prevailing in the area between the wound and the cover and  
         [0007]     a control unit to regulate the wound pressure.  
         [0008]     The present invention also relates to a procedure for operating a class-appropriate therapy device.  
         [0009]     B. Background of the Invention  
         [0010]     Wound healing devices are used to treat secondary healing chronic or acute wounds, in particular in humans. Using the negative pressure present in the skin area around the wound is supposed to remove fluid, that is, in particular wound exudation, from the wound to thereby shorten the healing period. In many cases, the use of such a wound healing device makes wound healing possible at all in the first place.  
         [0011]     For example, a class-appropriate wound healing device is described in EP 0 865 304. In the device described therein it is in particular provided that the device comprises an additional line which connects the porous pad to a pressure gage. Using the additional line, it is possible to monitor the pressure at the wound site. For this purpose in the referenced therapy equipment, the pressure sensor will be provided in the housing of the wound healing device. The wound pressure measured by the additional line should be adjusted to the desired value using a control means also provided in the housing.  
         [0012]     A disadvantage of this known wound healing device is that it is relatively complex to provide an additional tube line with the drainage line. Such a tube generally increases the complexity of the apparatus. It is true that it has been proposed to use a multi-lumen tube whose main tube is used as a drainage tube and from which a secondary tube is used as a probe tube to measure pressure. However, this results for example in increasing the external diameter of the tube connection between the housing and the wound dressing in an undesirable fashion. It also cannot be excluded that the additional line becomes blocked or e.g. is cut off from the prevailing pressure due to crimping or some other way at the wound site. In such a case, the pressure reading taken by the known therapy device would be incorrect without the cause being an error in the drainage tube or the wound site. Accordingly, the control of the wound pressure would fail.  
       SUMMARY OF THE INVENTION  
       [0013]     The task of the present invention is therefore to provide a class-appropriate therapy device to promote the healing of a wound in which the metrology is generally improved to make possible a more reliable and secure wound dressing. The invention is also intended to make the metrology of a class-appropriate therapeutic device particularly simple and error-resistant.  
         [0014]     This task is solved according to the invention in that the pressure sensor means comprise at least one pressure sensor on the distal end of the drainage tube. By measuring this distal pressure, advantageously an additional line between canister and the wound can be eliminated if the distal pressure can be used in a suitable way as measurement for the wound pressure. This can be done by prior calibration. In this fashion, the control of the wound pressure can be advantageously done in a particularly simple way. That is, according to the invention, beside the drainage line no additional tube line is needed between the pad and the suction pump and/or collecting canister. The result is simpler equipment design. Therefore to determine wound pressure a measuring procedure is used that requires no additional probe tube to the wound area.  
         [0015]     The task according to the invention is solved inventively by having the pressure sensor means comprise at least one wound pressure sensor provided under the cover and means for transferring the readings to the control unit. The advantage is that the wound pressure can be measured directly at the wound site. Errors which can occur in the indirect taking of wound pressure are thus advantageously avoided. The application of a pressure sensor directly on the wound site is also advantageous compared to the state of the art procedure for measuring wound pressure in which an additional probe tube is run from the wound to a sensor located in the base unit because pressure gradients can be generated inside the sensor tube which can systematically distort the wound pressure measurement. Instead, according to the present invention, the wound pressure is measured directly at the wound site and transferred to the control unit by, for example, an electric cable or by radio. Overall, according to this feature of the present invention, the error susceptibility of controlling wound pressure can be significantly improved. It is possible, for example, to recognize blockages in the drainage tube if the directly measured wound pressure is compared to another measured quantity, whereby the second measure quantity can be, for example, pump output or a pressure on the distal end of the drainage tube. Similarly, it is possible in this way to recognize a drop in wound pressure due to a crimping of the drainage tube.  
         [0016]     According to an advantageous embodiment of the inventive therapeutic device, the means to determine wound pressure comprise at least one strain gage provided in direct proximity to the skin area. Strain gages are robust and therefore particularly suited to being used directly on the patient. In addition to measuring wound pressure, strain gages can also measure patient movement artifacts. Since they produce a signal with a significantly higher frequency than the wound pressure fluctuations, they are easily distinguished from wound pressure variations by the control unit if suitable band pass filters are used. By combining the inventive wound pressure measurement by strain gages at the wound site with other pressure measurement procedures, the only qualitative alternative to reducing strain gage costs is to use them purely qualitatively. In this way, for example, the exceeding of a minimum pressure value can be established only qualitatively. In this way, the cost of the strain gage can be reduced sharply compared to a quantitative evaluated sensor. This is particularly advantageous if all of the components which are in contact with the patient are designed as disposable items so that the strain gage is also a disposable item.  
         [0017]     An especially advantageous further development of the invention is obtained by providing the strain gage in an interactive connection with a connector to connect the cover with the drainage line. Such connectors are used in class-appropriate therapy devices in order to obtain a better distribution of the negative pressure input through the drainage tube over the wound. Since the connector is more or less stretched between the drainage tube and the porous paid depending on the negative pressure prevailing on the wound, with the help of the strain gage this measurement of this strain can be used as the measurement for the wound pressure.  
         [0018]     For the fine adjustment to various wound pressure levels it is advantageous according to another embodiment of the invention if a control pump is provided in addition to the suction pump. With this configuration, the suction pump which, for example has a substantially greater suction power than the control pump can be used to set a basic pressure value. The higher suction power of the suction pump compared to the suction power of the control pump can be used to extract the wound exudation. As suction pumps with such strong suction power often have the disadvantage of not being able to be finely adjusted or being too sluggish, the use of an additional control pump effectively provides a possibility for fine adjustment.  
         [0019]     In a special embodiment of the invention, the therapeutic device comprises a wound pressure sensor provided under the cover to measure the prevailing distal pressure on the distal end of the drainage tube and a suction pump pressure sensor to measure the suction pump-side pressure p 2 . The advantage of this is that three pressure measurements are present at three different locations on the device. These measurements make possible the gathering of a large quantity of vacuum therapy operating data. By evaluating the absolute values of the three pressure measurements and the differences between these measured values important input quantities can be obtained for optimized setting and control. Also, all three pressure values can be evaluated together, for example, to calculate an indicator for the trouble-free operation of vacuum therapy.  
         [0020]     The inventive task is also solved by a procedure to operate a therapeutic device to promote the healing of a wound, comprising:  
         [0021]     an essentially airtight cover around the wound, whereby a fluid-permeable pad is preferably provided between the wood and the cover,  
         [0022]     a drainage line connecting the cover with a suction pump can be suctioned on the wound to removed fluids from there, whereby a distal end of the drainage line is indirectly connected with the suction pump via a reservoir to collect the fluid suctioned from the wound,  
         [0023]     pressure sensor means for the direct or indirect definition of a prevailing wound pressure in the area between the wound the cover and  
         [0024]     a control unit to control wound pressure.  
         [0025]     The following procedure is followed to determine wound pressure in the inventive procedure  
         [0026]     in a first step, the suction pump is temporarily turned off,  
         [0027]     in a second step, a distal pressure is measured with a pressure sensor provided on the distal end of the drainage tube.  
         [0028]     Using this procedure it is surprisingly simple to measure the pressure at the wound site, that is, the wound pressure without having to apply a measuring head directly to the wound site or to the pad. In addition, no addition tube is required as probe tube to measure the wound pressure. Instead, according to the invention, the circumstance is used that a uniform pressure is set inside the drainage tube, on the wound-side end of the drainage tube and on the distal end of the drainage tube if the suction pump is turned off and so that no fluidic pressure gradients are created. It cannot be excluded however that leakage in the system or leaks in particular at the wound site can cause slight residual flow. In practice, however, this slight residual flow results in a negligible dynamic pressure gradient in the absence of an extreme leak, which would endanger the success of the therapy in any case.  
         [0029]     Therefore after switching off the suction pump, the same pressure will be measured on the distal end of the drainage tube as at the wound site.  
         [0030]     After the pressure on the distal end has been measured in this way which equals the wound pressure when applying the inventive procedure, the suction pump can be turned on again if it is immediately necessary to maintain the target pressure. The measurement can, for example, be taken at regular time intervals in order to control the wound pressure.  
         [0031]     The procedure described above is further improved in a special embodiment of the invention if a relaxation period is observed between the first and second step, during which a largely uniform pressure is set between the distal and proximal end of the drainage tube. During the relaxation period, the fluidic pressure gradients balance each other out. The relaxation period can be determined in advance by tests.  
         [0032]     The inventive task can be solved according to the invention by a procedure to operate a class-appropriate therapeutic device in which to determine the wound pressure at a given suction power of the suction pump a distal pressure is first measured at the pressure sensor provided on the distal end of the drainage tube, and a pressure value is then calculated from a calibration table stored in the control unit using a pair of values taken from the distal pressure and the suction power; this pressure value essentially corresponds to the wound pressure.  
         [0033]     An advantage of this procedure to determine wound pressure according to the invention is that it enables continuous measurement of pressure. This is made possible by the fact that a drop in pressure which may be caused by a flow resistance in the drainage tube is considered in the measurement due to the calibration. In this fashion, the wound pressure can be measured advantageously without a pressure sensor being provided at the site of the wound, that is, for example, on the pad. In addition, a probe tube or similar does not have to be run to the wound to enable measurement of the wound pressure. The evaluation of the distal pressure measured by the pressure sensor provided on the distal end of the drainage tube can readily be done. That is where the calibration table is stored which is used to convert the distal pressure into a wound pressure. Using the calibration table, each pair of wound pressure values from the suction power of the suction pump and inside the airtight cover is assigned a distal pressure. On the other hand, the simple assignment of a wound pressure simply to distal pressure without taking into account the pump output in the case of a running pump would not be sufficient due to the suction dependency of the dynamic pressure gradients. The control unit should be provided with suitable interpolation algorithms to calculate the table interim values.  
         [0034]     In a special embodiment of the above inventive procedure it is provided that the definition of the calibration table comprises the following steps:  
         [0035]     the suction pump is operated with various predetermined constant suctions;  
         [0036]     of each suction power the wound pressure is simultaneously measured using a wound pressure sensor provided inside the airtight cover and the distal pressure measured by a distal pressure sensor provided on the distal end of the drainage tube;  
         [0037]     the measured wound pressure and distal pressure as well as the associated suction power are entered in the calibration table as a triple value.  
         [0038]     This procedure to determine the calibration table is particularly well suited to systematically record the necessary value area.  
         [0039]     In addition, the inventive task is similarly solved by the invention with the help of a procedure to operate a class-appropriate therapeutic device which comprises the following steps to report errors in the drainage tube:  
         [0040]     simultaneous direct measurement of wound pressure with a running suction pump inside the airtight cover and the distal pressure on the distal end of the drainage tube;  
         [0041]     calculation of a difference between the wound pressure and the distal pressure;  
         [0042]     comparing the difference with a reference difference;  
         [0043]     determining an error in the drainage tube in the event of a deviation from the reference difference by a predetermined threshold value.  
         [0044]     This procedure can be used advantageously, for example, to report blockages in the drainage tube. It is also possible with the inventive procedure to determine that the drainage tube is crimped and acts to constrict the pressure. In particular, it is advantageous in this procedure that the wound pressure is measured simultaneously by two different procedures. The direct measurement of wound pressure inside the airtight cover is not influenced by the pressure gradients in the drainage tube influenced by dynamic effects. Conversely, on the other side, the distal pressure on the distal end of the drainage tube is influenced by the dynamic effects in the drainage tube. Measuring both pressure quantities at the same time therefore makes it possible according to the invention to isolate changes in dynamic pressure drops from other effects. That is, if the distal pressure changes without a change in the wound pressure or the suction power of the suction pump, the cause is an error in the drainage tube, such as blockage with wound exudation or similar or a crimping of the tube. This improvement in the metrology of the vacuum therapy device is an enormous advantage in the optimum patient care.  
         [0045]     According to an especially advantageous embodiment of the above inventive procedure, the wound pressure is evaluated only on a qualitative basis. To do this, an especially inexpensive sensor—such as a strain gage—can be used to measure wound pressure which is only used as a pressure switch, for example, to detect the exceeding of a minimum negative pressure requires for the therapy. In particular, in the event that the wound bandage unit is designed with the wound pressure sensor as a disposable item, the result is substantial cost savings potential.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0046]     The invention is described in a preferred embodiment using a drawing, whereby other advantageous details can be found in the drawing figures.  
         [0047]     Parts having the same function are labeled with the same reference numbers.  
         [0048]     The figures of the drawings show:  
         [0049]      FIG. 1  is a schematic representation of the inventive wound healing device and its operating mode.  
         [0050]      FIG. 2  is a detailed representation of the inventive wound healing device with the suction tube  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0051]      FIG. 1  schematically shows an embodiment of an inventive wound healing device  1 . The wound healing device  1  comprises a base unit  2  and a wound dressing unit  3 . The base unit  2  contains a replaceable collecting container  4 , a suction pump  5  and a control device  6 . The base unit  2  is enclosed by a housing  7 . A carrying strap  8  is attached to the housing  7 .  
         [0052]     The collecting container  4  contains a mixture  9  consisting of wound exudation and gelling agent. The collecting container  4  comprises a suction opening  11  on one of the inner walls  10  facing the housing  7 . The suction opening  11  is connected to the suction pump  5  by the filter  12  and a suction tube  13 . A pump-side probe tube  14  branches off from the suction tube  13 . The pump-side probe tube  14  carries the prevailing pressure p 2  contained in the suction tube  13  to a suction-pump-side pressure sensor  15  which is located in the control device  6 . The control device  6  also contains the distal pressure sensor  16 , which interconnects the prevailing pressure p 1  prevailing on the distal end of the suction tube  17  via the probe tube  17  and the distal probe tube  36 . A 3/2-way valve  35  is installed in both the probe tube  17  and in the probe tube  14 . The distal probe tube  36  runs along the replaceable collecting container  4  inside the housing  7  to a suction opening  19  located in the outer wall  18  of the collecting container  4  in the housing  7  of the base unit  2 . Also, the distal probe tube  36  can optionally be run through a black box  33 .  
         [0053]     The wound dressing unit  3  comprises the wound exudation suction tube  20 , a sponge  21  and a film foil  23  through which the wound exudation suction tube  20  and the sponge  21  are fastened to skin  24  surrounding the wound  22  in such a way that an airtight connection is created. The sponge  21  is able to absorb and store fluids. Using the stretched film foil  23 , the sponge  21  is applied with a certain contact pressure to the wound  22 .  
         [0054]     Further, a strain gage  30  is fastened in the wound dressing  3  between the film foil  23  and the sponge  21  near the tube connector  31 . The strain gage  30  is used to measure the wound pressure on the wound  22 . The strain gage  30  with connected to an electrical cable  29 . The electrical cable  29  is connected to the outer edge of the suction tube  20  and in this way connected to the evaluation device  32  for the wound pressure P 3  by means of a plug-type connector  34  in the housing  7  of the base unit  2 . The evaluation device  32  is part of the control device  6 .  
         [0055]     The collecting container  4 , the wound exudation suction tube  20 , the sponge  21  and the film foil  23  are respectively sterile and replaceable for disposable use. The wound exudation is located in the wound  22 .  
         [0056]     To use the inventive wound healing device  1 , the sponge  21  is introduced into the wound  22 . One end of the wound exudation suction tube  20  is connected to the sponge  21 , and then both the wound exudation suction tube  20  and the sponge  21  are affixed to the wound  22  with the help of the film foil  23  in such a way that the system is made airtight.  
         [0057]     The other end of the wound exudation suction tube  20  is also connected to the suction opening  19  contained in the outer wall  18  of the collecting container  4  in an airtight fashion. Due to the property of the sponge  21  to absorb and store fluids, the wound exudation  25  is removed from the wound  22  into the sponge  21 . The wound exudation quantity that exceeds the storage capacity of the sponge  21  is suctioned into the collecting container  4  through the wound exudation suction tube  20 . The negative pressure needed for the suction is produced by the suction pump  5 .  
         [0058]     For this purpose the suction tube  13  of the suction pump  5  interconnects the collecting container  4 . The filter  12  arranged between the collecting container  4  prevents the wound exudation  25  from entering the suction tube  13 , the suction pump  5 , the suction-pump-side probe tube  14  or even the suction-pump-side pressure sensor  15 .  
         [0059]     The excess wound exudation  25  collected in the collecting container  4  in the manner described above is thickened by a gelling agent. This effectively prevents the moistening of the filter  12  even when the base unit  2  is moved. As a result, for example, the filter  12  is prevented from being moistened and germs are prevented from getting into the control device  6 . Also, it is possible to dispose of the potentially contaminating wound fluid in the solid aggregate state in a more hygienic fashion.  
         [0060]     The negative pressure produced by the suction pump  5  is continuously received on the one hand by the suction-pump-side pressure sensor  15  and by the wound-side strain gage  30  on the other and also via the distal pressure sensor  16 , which measures the distal pressure p 1 . Then, the pressure p 3  taken from the wound-side strain gage  30 , the pressure p 2  taken from the suction-pump-side pressure sensor  15  and the pressure p 1  taken from the distal end of the suction tube  20  are used in the microprocessor of the control device  6  as input data for control.  
         [0061]     In order to maintain a moist wound environment, the pressure level in the wound dressing unit  3  is set according to the individual needs of the patient, the properties of the wound  22  and according to the criteria of compatibility (pain by the patient). The setting is done using a software menu mode on a display unit  26  on the microprocessor-controlled control device  6 . The software menu mode makes it possible for the user to select different languages. Also, the desired control program for the negative pressure on wound dressing unit  3  can be selected using the software menu mode. The microprocessor of the control device  6  processes the signal of the wound-side strain gage  30 , that is pressure signal p 3 , of suction-pump-side pressure sensor  15 , that is pressure signal p 2  and distal pressure sensor  16 , that is the distal pressure p 1 —according to the selected control algorithm at output readings. The output readings are fed by the control device  6  to the control valve  27  and, optionally, also directly to the suction pump  5 .  
         [0062]     Assisted by the control valve  27 , which is located in the suction tube  13  between the suction pump  5  and the filter  12 , various pressure control programs can be physically realized as the control valve  27  can be opened and closed quickly according to the control signals of the control device  6 .  
         [0063]     The user can also run a fixed pressure control program through the display unit and the software menu mode. Assessing the pressure signals p 1 , p 2  and p 3  sent from the pressure sensors  15 ,  16 ,  30 / 32 , the control device  6  influences the valve  27  and/or the suction pump  5  as outputs for the pressure areas and control times. In term of control, only slightly deviations are permitted of the actual value from the target value.  
         [0064]     With the carrying strap  8 , the base unit  2  can be carried by the patient on whose wound  22  the wound dressing unit  3  is applied. This makes the patient mobile even during use of the inventive wound healing device  1 .  
         [0065]     For service and for patient documentation purposes, the control device  6  is equipped with a computer interface  28 . It can be used, for example, to input new control algorithms using an external computer or to forward patient information to a central administration.  
         [0066]      FIG. 2  depicts a preferred option of connecting the electrical cable  29  to the base unit  2 . As shown in the figure, the suction tube  20  represented in cross section comprises an interior  20   a  and an exterior  20   b  tube wall. The electrical cable  29 , which connects the strain gage  30  with the control unit  6  in the base unit  2  is run in the cavity  20   c  between the interior  20   a  and an exterior  20   b  tube wall. The electrical cable  29  runs out of the cavity  20   c  near the base unit  2  and it is connected with the control device in the base unit  2  via the plug-type connector  34 . In this fashion, the signal of the strain gage  30  is sent to the evaluation device  32  for the wound pressure p 3 .  
         [0067]     The device can use the following different procedures to measure wound pressure:  
         [0068]     Firstly, the pressure can be taken directly using the strain gage  30  on the wound site around the airtight covering of the wound. The evaluation of the measurement p 3  for the wound pressure of the strain gage  30  is done using the evaluation device  32  inside the control device  6 .  
         [0069]     Further, the wound pressure can be determined by measuring the distal pressure p 1  with the distal pressure sensor  16 , which reads the pressure on the distal end of the suction tube  20 . This method takes into account the dynamic pressure gradient caused by the suction flow by calibrating with the help of the control device  6 . The calibration is done by evaluating the wound pressure p 3  measured by the strain gage  30  in conjunction with the equivalent values for p 1 . This pair of values must be produced by different pump powers and input into the calibration curve. After the calibration curve is determined, the strain gage  30  on the wound site is no longer required. Therefore, normally, the wound dressing could be supplied without measuring equipment. Only for calibration purposes could a calibration wound dressing be used which comprises a strain gage or other pressure sensors. In this way the manufacturing costs of the normally used disposable wound dressings can be kept advantageously low.  
         [0070]     Finally, the wound pressure can also be determined by measuring the distal pressure p 1  without having to take into account dynamic effects. In this case, before each measurement the suction pump  5  can be switched off and a relaxation period can be observed. During the relaxation period, a stationary condition is created in which the pressure p 3  at the wound site which is the same as the pressure p 1  at the distal end of the drainage tube  20 . In this case, a simple measurement of the pressure p 1  by the pressure sensor  16  via the probe tube  36  already provides the sought wound pressure. To undertake control, this reading should be taken at regular intervals.  
         [0071]     In addition, the described processes for measuring wound pressure can be used simultaneously. On the one hand, this can result in an improvement in the reliability of the measurement. Also, error diagnosis procedures can also be conducted in this fashion to, for example, determine a blockage of the drainage tube. Blockage exists when there is a change of the pressure p 1  with a constant measurement p 3 , whereby p 1  can be measured either with the dynamic or the static methods described above.  
         [0072]     In order to determine a blockage of the filter  12 , the prevailing pressure p 2  in the suction tube  13  can be measured on the suction side of the suction pump  5  with the help of the suction-pump-side pressure sensor  15  and at the same time with the distal pressure sensor  16  via the probe tube  17  and the prevailing pressure p 1  on the end of the suction tube  13  distal probe tube  36 . The difference between p 1  and p 2  assessed in the control device  6  is then correlated with the degree of blockage of the filter. When a certain degree of blockage is reached, the user can be requested to change the filter.  
         [0073]     Further, the measurement of the pressure p 2  can also be used to measure the suction power of the suction pump  5 .  
         [0074]     Therefore a device is proposed to promote wound healing entailing a significant improvement in metrology and which results in a major improvement over conventional devices and which makes possible more reliable control.  
       LIST OF DRAWING REFERENCES  
       [0000]    
       
           1  Wound healing device  
           2  Base unit  
           3  Wound dressing unit  
           4  Collecting container  
           5  Suction pump  
           6  Control device  
           7  Housing  
           8  Carrying strap  
           9  Mixture  
           10  Inside wall  
           11  Suction opening  
           12  Filter  
           13  Suction tube  
           14  Suction-pump-side probe tube  
           15  Suction-pump-side pressure sensor  
           16  Wound-side pressure sensor  
           17  Wound-side probe tube  
           18  Outer wall  
           19  Suction opening  
           20  Wound exudation suction tube  
           20   a  Interior tube wall  
           20   b  Exterior tube wall  
           20   c  Cavity  
           21  Sponge  
           22  Wound  
           23  Film foil  
           24  Skin  
           25  Wound exudation  
           26  Display unit  
           27  Control valve  
           28  Computer interface  
           29  Electrical cable  
           30  Strain gage 
         31  Tube connector      32  P3 evaluation device      33  Black box      34  Plug-type connector      35  3/2-way valve      36  Distal probe tube