Abstract:
A method of controlling a compression device controls a vent phase of a compression device having an inflatable bladder capable of being pressurized for applying compression to a part of a subject&#39;s body. The method includes delivering pressurized fluid from a source of pressurized fluid to a first inflatable bladder disposed about a portion of the subject&#39;s body and venting the pressurized fluid from the first inflatable bladder by opening a first valve. The method further includes monitoring fluid pressure in the first inflatable bladder during the venting of the first inflatable bladder. Based at least in part on the monitored fluid pressure, the first valve is selectively closed and selectively reopened to control fluid pressure in the first inflatable bladder to remain within a desired residual pressure range.

Description:
TECHNICAL FIELD 
     The present disclosure generally relates to pressure control and, more specifically, to controlling residual pressure in a bladder of a compression device. 
     BACKGROUND 
     The pooling of blood or stasis in a patient&#39;s extremities, particularly the legs, can occur when the patient is confined to bed for an extended period of time. Stasis is problematic because it is a significant cause leading to the formation of thrombi. To prevent this occurrence, it is desirable to move fluid out of interstitial spaces in the extremity tissues to enhance circulation. 
     Intermittent pneumatic compression (IPC) devices are used to improve circulation and minimize the formation of thrombi in the limbs of patients. These devices typically include a compression sleeve or garment having one or more inflatable bladders to provide a compressive pulse or compression therapy to the limb. 
     Pneumatic compression therapy is usually provided by a pneumatic pump and valves that control the flow of air into and out of specific bladders. Typically, inflation of the bladders is controlled by a microprocessor of the compression device to reach a set pressure providing the requisite therapeutic effect. Once the set pressure is reached, the bladders are usually vented until they reach ambient pressure. 
     SUMMARY 
     In one aspect, a method of controlling a compression device controls a vent phase of a compression device having an inflatable bladder capable of being pressurized for applying compression to a part of a subject&#39;s body. The method includes delivering pressurized fluid from a source of pressurized fluid to a first inflatable bladder disposed about a portion of the subject&#39;s body and venting the pressurized fluid from the first inflatable bladder by opening a first valve. The method further includes monitoring fluid pressure in the first inflatable bladder during the venting of the first inflatable bladder. Based at least in part on the monitored fluid pressure, the first valve is selectively closed and selectively reopened to control fluid pressure in the first inflatable bladder to remain within a desired residual pressure range. 
     In another aspect, a method of controlling a compression device includes controlling a vent phase of a compression device including an inflatable bladder capable of being pressurized for applying compression to apart of a subject&#39;s body. The method includes delivering pressurized fluid from a source of pressurized fluid to an inflatable bladder disposed about a portion of a subject&#39;s body and venting pressurized fluid from the inflatable bladder by partially opening a proportional valve. The method further includes monitoring fluid pressure in the inflatable bladder during the venting. Based at least in part on the monitored fluid pressure in the inflatable bladder, the proportional valve is closed when fluid pressure in the inflatable bladder is within a desired residual pressure range. 
     In yet another aspect, a compression device for applying compression treatment to a subject&#39;s body part, the device includes a controller, a first inflatable bladder in fluid communication with the first inflatable bladder, and a first 3-way/2-position, normally open, valve in fluid communication with the first inflatable bladder. The controller is configured to supply pressurized fluid, which is receivable by the first inflatable bladder. The first valve is actuatable by the controller to control venting of the pressurized fluid from the first inflatable bladder. 
     In still another aspect, a compression device for applying compression treatment to a subject&#39;s body part, the device includes a controller, a plurality of inflatable bladders, and a plurality of valves. The controller is configured to supply pressurized fluid. The plurality of inflatable bladders is in fluid communication with the controller, and the pressurized fluid from the controller is receivable by each of the plurality of inflatable bladders. Each of the plurality of valves is in fluid communication with a respective inflatable bladder. Less than all of the plurality of valves vents fluid from the plurality of inflatable bladders. This configuration can, for example, reduce the number of valves required to vent the bladders and, thus, reduce the overall size of the compression device. 
     In one or more aspects, a manifold can be in fluid communication with each bladder, and a single pressure transducer can be in fluid communication with the manifold for measuring a fluid pressure in each bladder. In some aspects, a check valve can be upstream from and in fluid communication with the manifold. Additionally or alternatively, in certain aspects, the manifold can define a fail-safe orifice. 
     Embodiments can include one or more of the following advantages. 
     In some embodiments, methods of controlling the vent phase of a compression device include selectively closing and selectively reopening a valve, based at least in part on measured fluid pressure in a bladder, to control fluid pressure in the bladder to remain with a desired residual pressure range (e.g., a pressure range above ambient pressure and below a compression pressure for treating the subject). Such control of fluid within the bladder during the vent phase can, for example, reduce the amount of fluid (e.g., air) needed to inflate the bladder during a subsequent phase of treatment. Reducing the amount of fluid needed to inflate the bladder can reduce the total cycle time of the compression and venting process to facilitate improved treatment of the portion of the subject&#39;s body. Additionally or alternatively, reducing the amount of fluid needed to inflate the bladder can reduce the size of the air supply associated with inflating the bladder, which can facilitate, for example, portability of the compression device and/or reduce the amount of space taken by the compression device in the vicinity of the subject. 
     In certain embodiments, methods of controlling the vent phase of compression device include controlling one or more valves to control the residual pressure in one or more bladders. In some implementations, such control of the residual pressure in three bladders can facilitate the use of a gradient of residual pressures in the three bladders. For example, a first bladder positionable about an ankle of the subject can have a residual pressure of about 4 mmHg, a second bladder positionable about a calf of the subject can have a residual pressure of about 2 mmHg, and a third bladder positionable about a thigh of the subject can have a residual pressure of about 0 mm Hg. Such a gradient in residual pressures can reduce the respective inflation times and/or the respective inflation volumes of each of the bladders as the bladders are inflated to apply a gradient of compression pressures to the subject. 
     Other objects and features will be apparent from the description and drawings, and from the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic of a compression device. 
         FIG. 2  is a graphical illustration of a pressure profile of the compression device of  FIG. 1 . 
         FIG. 3  is a schematic of a compression device including bladders each having dedicated valves. 
         FIG. 4  is a schematic of a compression device including bladders each having dedicated valves and dedicated pressure transducers. 
         FIG. 5  is a schematic of a compression device including a valve controlling pressure in a common manifold and dedicated valves for certain bladders. 
         FIG. 6  is a schematic of another embodiment of a compression device including a valve controlling pressure in a common manifold and dedicated valves for certain bladders. 
         FIG. 7  is a schematic of a compression device including a passive check valve. 
         FIG. 8  is a schematic of a compression device including normally open and normally closed valves. 
         FIG. 9  is a perspective of a controller and compression sleeve. 
     
    
    
     Corresponding reference characters indicate corresponding parts throughout the drawings. 
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , a pneumatic circuit of an intermittent pneumatic compression (IPC) device  1  includes a bladder  3  and a controller  5  for controlling a residual pressure in the bladder. In the IPC device  1 , a compression sleeve  13  including the bladder  3  is connected, for example, via tubing  15 , to the controller  5  having a processor  19  operatively connected to an air supply  21  (e.g., a compressor) that provides compressed air to the bladder. A valve  23  is provided between the sleeve  13  and the air supply  21 . A pressure transducer  25 , downstream from the valve  23 , monitors the pressure in the bladder  3 . The transducer  25  may be connected directly to the bladder  3  or a manifold (not shown) in communication with the bladder. The sleeve  13  can have two or more bladders. For example, the sleeve  113  shown in  FIG. 3  has three bladders. 
     Referring now to  FIGS. 1 and 9 , the controller  5  is disposed in a housing  22 . A control panel  24  on the housing  22  includes controls and indicators, for example, for inputting parameters to the controller  5 . An output connector  26  is positioned on the housing  22  and is engageable with the tubing  15  for connecting the controller  5  and the air supply  21  to the sleeve  13 . The sleeve  13  includes three bladders  3  that, in use, apply compression to the subject&#39;s ankle, calf, and thigh, respectively. It should be appreciated that the sleeve  13  can include fewer or additional bladders, as required for applying a particular compression treatment protocol to a portion (e.g., a limb) of a subject. 
     The sleeve  13  is configured to be wrapped around a subject&#39;s limb (e.g., leg) ( FIG. 9 ). To provide a compressive pulse to the limb, the controller  5  opens the valve  23  and activates the air supply  21  to provide compressed air to the bladder  3  until the pressure in the bladder reaches a suitable value for operation in a compression cycle. In embodiments in which the sleeves having two or more bladders, sequential compression therapy can be applied to the subject&#39;s limb. When pressurization is complete, the air supply  21  is deactivated and the bladder  3  is allowed to depressurize by, for example, venting back through the tubing  15  to the controller  5 . Air may be vented to the atmosphere through the valve  23 . It may be desirable to retain some pressure (i.e., residual pressure) in the bladder  3  after venting. Controlling residual pressure in the bladder  3  reduces the flow requirement of the device  1 , and in particular the air supply  21 , by reducing air required for subsequent pressurization. In some embodiments, a desired residual pressure range is between about 0 and about 15 mmHg (e.g., about 1 mmHg and about 10 mmHg). 
     The processor  19  executes computer-executable instruction to pressurize (e.g., inflate) the bladder  3  to provide compression pressure to a wearer&#39;s limb. For example, the processor  19  may execute instructions to pressurize the bladder  3  to a first compression pressure (e.g., 20 mmHg) to move the blood in the limb from a region (e.g., calf) underlying the bladder  3 . This phase of the compression cycle is known as the inflation phase. After pressurizing the bladder  3  to the first compression pressure, the processor  19  may execute instructions to reduce the pressure in the bladder to a residual pressure (e.g., 10 mmHg), allowing the blood to reenter the region of the limb underlying the bladder. This phase of the compression cycle is known as the vent phase. During the vent phase, the pressure in the bladder  3  can be sensed by the pressure transducer  25  until the pressure in the bladder reaches a desired residual pressure (e.g., a predetermined residual pressure). 
     To control the pressure in the bladder  3  during the vent phase, the processor  19  can execute instructions to operate the valve  23  to vent the bladder to the desired residual pressure. For example, the processor  19  can open and close the valve  23  as fluid is being vented from the bladder  3  until the pressure in the bladder is within a predetermined residual pressure range. 
     Referring to  FIG. 2 , once the inflation phase is completed, the processor  19  executes instructions to open the valve  23  and the pressure in the bladder  3  begins to drop, starting the vent phase. Predetermined pressure values P 1 , P 2  can be set such that the valve  23  remains open until the pressure transducer  25  senses pressure in the bladder  3  has reached a bottom range pressure P 1  (e.g., the bottom pressure range P 1  can be above ambient pressure). When the transducer  25  measures a pressure of P 1  or less, the processor  19  executes instructions to close the valve  23 , causing the pressure in the bladder  3  to rise. When the pressure transducer  25  senses pressure in the bladder  3  has reached or exceeded a top range pressure P 2 , the processor  19  executes instructions to open the valve  23 , causing the pressure in the bladder to drop. The processor  19  can execute instructions to operate the valve in this manner (i.e., repeatedly opening and closing the valve  23 ) until the pressure in the bladder  3  levels out within the pressure range between P 1  and P 2 . The processor  19  can also execute instructions to open and close the valve  23  at regular intervals using a timer  31  operatively connected to the processor. For instance, the processor  19  can open and close the valve  23  about every 200 ms until the desired residual pressure is maintained in the bladder  3 . Although  FIG. 2  illustrates residual pressure as a function of time for a single bladder, it will be understood that the process can be used in compression devices having multiple bladders. 
     Referring to  FIG. 3 , a pneumatic circuit  101  includes three bladders  103 A,  103 B,  103 C, each in fluid communication with a dedicated valve  123 A,  123 B,  123 C. Parts of the circuit  101  generally corresponding to those of the circuit  1  will be given the same number, plus “100.” A single pressure transducer  125  fluidly communicates with a manifold  127  in communication with the bladders  103 A,  103 B,  103 C. An air supply  121  delivers compressed air to the bladders  103 A,  103 B,  103 C through tubing  115 . The circuit  101  can vent the bladders  103 A,  103 B,  103 C to a desired residual pressure as described above. For example, each time the valves are opened, the pressure transducer  125  measures pressure in the corresponding bladder until the targeted residual pressure is reached. Each valve  123 A,  123 B,  123 C is a 3-way/2-position, normally closed, solenoid valve. Each of these valves includes three ports and is actuatable to place a first port (i.e., inlet port) in fluid communication with a second port (i.e., bladder port) in a first position. Each valve is further actuatable to place the second port in fluid communication with a third port (i.e., vent port) in a second position. The first port of each valve  123 A,  123 B,  123 C is in fluid communication with the air supply  121 . The second port of each valve  123 A,  123 B,  123 C is in fluid communication with a respective bladder  103 A,  103 B,  103 C and the third port is in fluid communication with ambient atmosphere. The valves  123 A,  123 E,  123 C could also be other types. 
     The pressure in each bladder  103 A,  103 B,  103 C can be controlled to a common or different residual pressure. To control each bladder to a common residual pressure, the controller  105  vents the bladders  103 A,  103 B,  103 C at the same time to produce a uniform pressure at the manifold  127 . The manifold pressure is controlled by opening and closing the valves  123 A,  123 B,  123 C simultaneously until the targeted residual pressure is reached. 
     The pressure in each bladder  103 A,  103 B,  103 C can be controlled to different residual pressures. To control the pressures in the bladders  103 A,  103 B,  103 C to different residual pressures, the controller  105  vents each bladder separately (for example, the controller can control the process of opening and closing each valve separately). This can, for example, facilitate the use of a single pressure transducer to monitor pressure in each bladder  103 A,  103 B,  103 C. 
     In some embodiments, the controller  105  sequentially vents the bladders  103 A,  103 B,  103 C to respective residual pressures. In such embodiments, a first bladder  103 A is vented by repeatedly opening and closing the corresponding valve  123 A. The pressure transducer  125  measures the pressure in the manifold  127  corresponding to the first bladder  103 A and the bladder is vented until the pressure reaches a desired residual pressure for the first bladder at which time the valve  123 A is closed. The controller  105  then indexes to a second bladder  103 B and vents the second bladder until the pressure in the manifold  127  reaches a desired residual pressure for the second bladder. Finally, the controller  105  indexes to a third bladder  103 C and vents the third bladder until the pressure in the manifold  127  reaches a desired residual pressure for the third bladder. The controller  105  can index between bladders  103 A,  103 B,  103 C prior to the targeted residual pressure being reached in any of the bladders. The controller  105  can also sequentially vent each bladder  103 A,  103 B,  103 C to the same or different residual pressure. Additionally or alternatively, the controller  105  can index between the bladders  103 A,  103 B,  103 C in non-sequential order. 
     Referring to  FIG. 4 , a pneumatic circuit  201  is similar to the circuit  101  ( FIG. 3 ) except each bladder  203 A,  203 B,  203 C has a dedicated valve  223 A,  223 B,  223 C and a dedicated pressure transducer  225 A,  225 B,  225 C, respectively. Parts of the circuit  201  generally corresponding to those of the circuit  1  will be given the same number, plus “200.” 
     Each bladder  203 A,  203 B,  203 C can be controlled to a desired residual pressure using pressure readings from each dedicated pressure transducer  225 A,  225 B,  225 C. Having a dedicated pressure transducer can also allow the controller  205  to simultaneously vent each bladder  203 A,  203 B,  203 C to a common or different residual pressure. 
     Referring to  FIG. 5 , a pneumatic circuit  301  includes a first valve  323 A controlling the pressure in a common manifold  327 , a second valve  332 B dedicated to a second bladder  303 B, and a third valve  323 C dedicated to a third bladder  303 C. A single pressure transducer  325  measures residual pressure in the manifold  327  and the three bladders  303 A,  303 B,  303 C. The first valve  323 A functions as a “vent valve” for venting air from each bladder out of the circuit. In the illustrated embodiment, each valve  323 A,  323 B,  323 C is a 2-way/2-position, normally closed, solenoid valve. These valves include two ports, an inlet port and an outlet port, and are closed until the valve is energized. The valves  323 A,  323 B,  323 C could also be other types of valves. Parts of the circuit  301  generally corresponding to those of the circuit  1  will be given the same number, plus “300.” 
     During a vent phase, the controller  305  uses the first valve  323 A to control the residual pressure in the manifold  327  and the three bladders  303 A,  303 B,  303 C. During compression treatment, the bladders  303 A,  303 B,  303 C and manifold  327  may all be open to each other or, in certain instances, may be controlled for timed operation during treatment. For example, the second valve  323 B and the third valve  323 C can be instructed by the controller  305  to remain open during venting. The controller  305  can open and close the first valve  323 A to control the residual pressure in all three bladders during the vent phase. The controller  305  can also instruct the second valve  323 B and the third valve  323 C to remain open during venting and open and close the first valve  323 A. While this configuration does not allow independent control of the residual pressure in each bladder  303 A,  303 B,  303 C,this configuration can be implemented with a single pressure transducer  325 , which reduces cost as compared to implementations requiring additional pressure transducers. 
     The circuit  301  can also be operated by keeping only the vent valve  323 A open during the vent phase and independently opening and closing the second and third valves  323 B,  323 C. In these embodiments, when the third valve  323 C is closed and the second valve is opened and closed by the controller  305 , the pressure in the first and second bladders  303 A,  303 B will normalize to the pressure in the manifold  327  and the residual pressure in the first and second bladders will be the same. When the controller  305  closes the second valve  323 B and indexes to the third valve  323 C, the opening and closing of the third valve will cause the pressure in the third bladder  303 C to normalize to the pressure in the manifold  327 , causing the residual pressure in the first and third bladders  303 A,  3030  to be the same. This pressure may be the same or different from the pressure in the second bladder  303 B. Valves  323 A,  323 B,  323 C can be normally open or normally closed, depending on the length of the vent time compared to compression treatment time, to optimize valve power consumption. 
     Referring to  FIG. 6 , a pneumatic circuit  401  is similar to the circuit  301  ( FIG. 5 ) except the vent valve  323 A of circuit  301  is replaced with a proportional control vent valve  423 A. Parts of the circuit  401  generally corresponding to those of the circuit  1  will be given the same number, plus “400.” 
     In the illustrated embodiment, the proportional control valve  423 A is a 3-way/3-position, piezo valve. However, the valve could be a 3-way/2-position, piezo valve (not shown) or any other suitable proportional control valve. A proportional valve such as the valve  423 A can be partially opened and closed to vary the amount and rate of fluid passing through the valve. The controller  405  can control the degree to which the valve  423 A is opened during the vent phase to control the residual pressure in the bladders  403 A,  403 B,  403 C. The controller  405  may partially open the vent valve  423 A so the rate at which air is vented from the bladders  403 A,  403 B,  403 C is proportional to the difference between a measured pressure in the bladders/manifold  427  and a desired residual pressure. Additionally or alternatively, the controller  405  may partially open the vent valve  423 A so that the rate at which the air is vented from the bladders/manifold is proportional to a rate of change of the pressure in the bladders/manifold. As compared to a conventional solenoid valve, proportional control using the valve  423 A uses less power and can facilitate a smoother transition between the therapeutic compression pressure in the bladders  403 A,  403 B,  403 C and the desired residual pressure. Additionally or alternatively, proportional control using the valve  423 A can modify the residual pressure in the bladders  403 A,  403 B,  403 C from cycle to cycle as needed. As compared to solenoid valves, this valve does not need to be closed or opened repeatedly to control residual pressure. 
     Referring to  FIG. 7 , a pneumatic circuit  501  is similar to the circuit  301  ( FIG. 5 ) except a passive check valve  529  is downstream from a vent valve  523 A. The controller  505  controls the check valve  529  to control the residual pressure in each bladder  503 A,  503 B,  503 C. Parts of the circuit  501  generally corresponding to those of the circuit  1  will be given the same number, plus “500.” 
     During the vent phase, when the controller  505  opens the vent valve  523 A, air passes through the check valve  529  until pressure in the manifold  527  drops below a check valve cracking pressure (e.g., a pressure set during manufacture of the check valve). The cracking pressure can be selected, for example, based on desired residual pressure in the bladders  503 A,  503 B,  503 C. When the pressure in the manifold  527  drops below the cracking pressure of the check valve  529 , the check valve closes, causing pressure in the manifold to increase. When the pressure in the manifold  527  rises to a level greater than the cracking pressure, the check valve  529  opens, reducing pressure in the manifold. Thus, the check valve  529  controls residual pressure in the bladders  503 A,  503 B,  503 C through its cracking pressure. 
     Referring again to  FIG. 3 , a passive check valve (not shown) can be added to the outlet of each valve  223 A,  223 B,  223 C of the circuit  201  (e.g., between the manifold  227  and each valve). By using three check valves, each bladder  203 A,  203 B,  203 C can be controlled to a common or different residual pressure. Because the check valves are passive, no power is consumed to control the residual pressure. In these embodiments, in which the cracking pressure of the check valve is fixed, the residual pressure for the bladder is a constant value. 
     Referring to  FIG. 8 , a pneumatic circuit  601  is similar to the circuit  101  ( FIG. 3 ) except valves  623 A and  623 B are 3-way/2-position, normally open, solenoid valves. Parts of the circuit  601  generally corresponding to those of the circuit  1  will be given the same number, plus “600.” Valve  623 C is a 3-way/2-position, normally closed, solenoid valve. Valves  623 A,  623 B,  623 C are associated with bladders  603 A,  603 B,  603 C, respectively. A check valve  629  is disposed between the air supply  621  and the manifold  627 . The bladder  603 A can apply compression to a subject&#39;s ankle, the bladder  603 B can apply compression to a subject&#39;s calf, and the bladder  603 C can apply compression to the subject&#39;s thigh. The 3-way/2-position valves associated with the bladders  603 A,  603 B (e.g., bladders disposed about the ankle and the calf of a patient&#39;s leg) allow residual pressure to be held in these bladders between inflation phases. An orifice  633  in the manifold  627  may provide a fail-safe mechanism to vent fluid from the bladders  603 A,  603 B,  603 C. The orifice  633  is a small opening in the manifold  627  to help vent the manifold in case valves fail during the inflation cycle. The orifice  633  could be, for example, about 0.005 inches in diameter to about 0.2 inches in diameter. 
     It will be apparent that modifications and variations are possible without departing from the scope of the disclosure. 
     When introducing elements of the present invention or the preferred embodiments(s) thereof, the articles “a”, “an”, “the”, and “said” are intended to mean that there are one or more of the elements. The terms “comprising”, “including”, “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. 
     In view of the above, it will be seen that several objects are achieved and other advantageous results attained.
         As various changes could be made in the above constructions and methods without departing from the scope of this disclosure, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.