Abstract:
A control unit for a medical device wherein the control unit comprises a pump, a conduit and control means for controlling the flow of fluid from the pump through the conduit; and wherein the conduit is a rigid internal passage located in the control unit.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This invention relates to a control unit assembly for use with a medical device and, particularly, a pneumatic medical device, such as a compression device for a limb. In particular, the invention relates to a control unit assembly for use with a mobile compression device suited for use in the treatment of venous leg ulcers, oedema, deep vein thrombosis and vascular disorders.  
         [0002]     Various medical devices are known that require inflation of one or more cells with fluid to a desired pressure, for example, compression devices which are used to apply pressure or pressure offloading devices such as mattresses or cushions which are used to even out pressure points. Compression devices are known for applying compressive pressure to a patient&#39;s limb. These types of devices are used to assist mainly in the prevention of deep vein thrombosis (DVT), vascular disorders and the reduction of oedema. Prior art devices are adapted for use in a hospital setting in which they are used predominantly for the prevention of DVT in patients with a high risk for developing this condition. U.S. Pat. Nos. 5,117,812; 5,022,387; 5,263,473; 6,231,532; 6,440,093 and 6,463,934 disclose such devices.  
         [0003]     Compression therapy is used in the treatment of venous leg ulcers. The treatment relies on the compression achieving a reduction in oedema and improved return of blood via the venous system. This in turn reduces the residence time for blood supplied to the lower limb and the severity of ischaemic episodes within the limb that can result in tissue breakdown.  
         [0004]     Compression of the limb can be achieved by a pneumatic or hydraulic compression device.  
         [0005]     WO 2004/084790 discloses one type of mobile compression device. By “mobile” it is meant that the user wearing the compression device has relative freedom to move about. The device of WO 2004/084790 comprises one or more fluid inflatable cuffs containing one or more cells arranged for fitting on to a leg or an arm. The device allows the adjustment of the pressure in the cells dependent on the pressure profile desired. The application of pressure by the cells in the sleeve or cuff is maintained by a pump and valves which are operated by an automatic control unit which detects the fall or rise in pressure in each cell throughout the device. Where excessive or deficient pressure is detected by a sensor located in the cell, the control unit activates the pump to restore the intended pressure.  
         [0006]     In the compression devices of the prior art, the control unit is a separate component which is typically not integral to the compression device and remotely operated. This is often on the user&#39;s belt, placed in a pocket or carried around by hand which is inconvenient for the user.  
         [0007]     As a control unit, generally, includes a pump, electronic circuitry, conduits for connecting the control unit to the compression device, valves, a source of power, etc., the control unit is usually quite large. Hence, the known control units are bulky and heavy. Therefore, positioning of the unit in the device has not been practical because attaching the known control units to an outer surface of the compression device would result in an excessive weight burden impairing the mobility of the user. Integral positioning is also unnecessary as most of the prior art devices are used in a hospital setting where mobility of the patient is not the main concern. Were the control unit to be positioned on the device, weight would be localized at the attachment point of the device resulting in a weight imbalance on the compression device. Also, a bulky control unit protruding from an outer surface of the compression device permits the unit to be knocked and possibly broken when the user is mobile and would not fit beneath clothing.  
         [0008]     There are barriers to reducing the size of the control unit. The conduits between the pump and the inflatable cells have in the past been external and would thus present a trip or tangle hazard. The power consumption by the components in a typical hospital device would make the battery too large to be carried on the device itself and would make it too bulky to fit under clothing.  
         [0009]     The above disadvantages may contribute to low patient compliance and limit use. A control unit which is an integral part of a device with a low profile and whose internal components are miniaturized sufficiently so as not to affect the performance of the control unit or the medical device has therefore been sought.  
       SUMMARY OF THE INVENTION  
       [0010]     According to a first aspect of the present invention, there is provided a control unit for a medical device wherein the control unit comprises a pump, a conduit and control means for controlling the flow of fluid from the pump through the conduit characterized in that the conduit is a rigid internal passage located in the control unit.  
         [0011]     The control unit of the invention has the advantage that, as the conduits are rigid it is possible to make a detachable connection between the control unit and a docking unit which is part of the medical device. This also makes it possible for there to be no external conduits between the control unit and the docking unit on the medical device. In this way, the control unit can be readily attached and detached from the medical device.  
         [0012]     According to a second aspect of the present invention, there is provided a control unit assembly for a medical device wherein the assembly comprises a control unit and a docking unit, the docking unit located on the medical device wherein 
        a. the control unit comprises a pump, a conduit and control means for controlling the flow of fluid from the pump through the conduit; and     b. the docking unit comprises a detachable fluid transfer connector which connects the conduit to an inflatable cell of the device.        
 
         [0015]     Preferably, the docking unit also comprises a backing plate and the connector is a relatively inflexible connector of the plug and socket type. The connector, preferably, forms an air tight seal and allows the repeated attachment and removal of the control unit. The number and arrangement of the connectors will be adapted to suit the number of cells present in the device.  
         [0016]     The provision of the backing plate with rigid connectors permits direct insertion of the control unit into the device and allows it to be removed and re-inserted. This overcomes the need for remote positioning of the control unit assembly. Instead, the pump draws air or fluid from an external source into the conduits and to the rigid fluid transfer connectors of the backing plate into the cells of the compression device.  
         [0017]     The rigid connectors, where present, act to hold to the control unit assembly securely while permitting the control unit to be readily detached from the compression device. To assist in the securement of the control unit to the device, an additional press-fit retaining means which acts against a spring bias and can be released by the pressing of a button on the control unit may be provided.  
         [0018]     The presence of the docking unit and the detachable fluid connectors gives the advantage that the control unit is removable and, therefore, reusable. This is because typically the control unit assembly is significantly more costly to produce. Designed as a separate unit, it can have a working life of many years and can be transferred between devices and between patients. For cost-effective treatment of patients, the recycling of the control unit, rather than its disposal after each patient, is desirable. In contrast, the medical device whose inner surfaces come into contact with the patient&#39;s skin are typically single use and disposed of once no longer required by a particular patient. In any case, compression devices will typically have a working life of no longer than six months. Hence, the easy removal of the control unit assembly from the medical device and replacement on another medical device is advantageous.  
         [0019]     The invention further provides that the conduits in the control unit are preferably rigid internal passages wholly located within the control unit in the form of a manifold.  
         [0020]     The term “manifold” means the fluid transfer conduits that form a labyrinth of passages in the rigid material of the control unit. Preferably, the conduits terminate in connectors suitable for making connections with other components of the control unit assembly and compression device. The manifold replaces the plurality of tubes between the pump and device and makes the control unit compact enough to be received in the docking unit. The docking unit is, preferably, a pouch within the outer contour of the device.  
         [0021]     Preferably, the control unit further comprises a plurality of valves located between the pump and the conduits, the plurality of valves being arranged in a ranked or tiered hierarchical structure  
         [0022]     The term “hierarchical or ranked valve tree structure” means the that valves are arranged in ranks according to their proximity in the direction of fluid flow from the pump. The valve closest to the pump directs fluid flow to a further rank or ranks of valves. In this manner, the number of valves needed in the control unit to control the plurality of inflatable cells is reduced.  
         [0023]     The provision of the ranked valve arrangement permits size reduction of the control unit by reducing the number of valves and, therefore, the space that they occupy and their power consumption. This permits the proximal positioning of the control unit assembly on or within an outer sleeve of a compression device. When placed discretely within an outer sleeve of the compression device, there are no external edges of the control unit which can be knocked or damaged during use resulting in improved patient safety, quality of patient life and control unit life. Furthermore, improved patient compliance is expected with such a discretely concealed unit.  
         [0024]     The ranked valve tree structure of the valve assembly where present, advantageously provides a means of selectively varying the air or fluid pressure of individual cells in the compression device without simultaneously activating all of the valves. Furthermore, the ranked valve tree structure reduces the number of valves required to achieve pressure variation. The tree structure thus permits size reduction in the control unit as fewer valves are needed. Hence, this arrangement is particularly amenable to portable power sources such as a battery. The valves are preferably latching valves as they further reduce the power consumption in the device.  
         [0025]     Further, according to the invention, a compression device for use on a limb comprising a control unit assembly according to the first and second aspects of the present invention is provided.  
         [0026]     Preferably, the one or more detachable fluid transfer connectors of one aspect of the invention is adapted for connection with the air or fluid transfer conduits in the control unit and in the compression device. More preferably, this is achieved by a male connector tube on the control unit assembly being engageable with a female connector slot on the compression device or a female connector slot on the control unit assembly being engageable with a male connector tube on the compression device.  
         [0027]     A latch can be used to retain the male and female parts in place in order to secure the control unit. Preferably, the latch can be easily released so that the control unit assembly can be removed from the compression device, for example, by pushing a button on the exterior of the compression device.  
         [0028]     Any number of rigid air or fluid transfer connectors can be employed. However, preferably, four or five connectors will be present and this will be dependent on the requirements of the compression device. Preferably, the air or fluid transfer connectors are made of a rigid plastics material which can be integrally formed as part of the backing plate. This may be achieved, for example, by means of injection molding techniques during the manufacture of the docking unit or backing plate.  
         [0029]     The control unit assembly of the first and second aspects of the invention may comprise an additional (booster) portable battery as a power source. This may be a re-chargeable nickel cadmium, nickel metal hydride or lithium ion battery or any other lightweight battery that provides sufficient power.  
         [0030]     Preferably, the control unit is attached to the backing plate in a sliding press-fit to engage the connectors and the latch.  
         [0031]     The compression device, preferably, has an outer surface with a pouch for receiving and holding the control unit assembly. The docking unit is positioned in the pouch and can conveniently be in the form of a backing plate.  
         [0032]     The compression device may contain many inflatable cells dependent on the individual needs of a patient and may be adapted for an arm or a leg. In a preferred embodiment, the device is adapted for use below the knee of a patient and comprises three inflatable cells located in the region between the knee and the ankle and two inflatable cells located in the heel and foot region.  
         [0033]     In another embodiment, the invention provides a control unit assembly for a medical device wherein the assembly comprises a control unit and a docking unit, the docking unit located on the medical device wherein the control unit comprises a pump, a conduit and control means for controlling the flow of air through the conduit and the docking unit comprises a detachable air inlet connector which provides air to the pump, the connector being provided with a filter.  
         [0034]     In this way, the air inlet to the pump is provided with a filter on the device side of the assembly. Thus, when the device has reached the end of its useful life and is replaced, the control unit is indirectly provided with a new filter. If the filter were placed in the control unit, it would not be replaced during the lifetime of the control unit without servicing of the unit. In addition, the provision of the filter on the device side of the assembly means that contamination of the control unit and its electrical circuitry is limited. If the filter were present in the control unit, during operation of the device unfiltered air would be drawn into the control unit at least as far as the filter. As the filter is external to the control unit, only filtered air is drawn into the control unit. This gives the advantage that reliability of the control unit may be improved. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0035]      FIG. 1  is a perspective view of the control unit assembly of the invention integrated in a mobile compression device worn on the limb of a patient.  
         [0036]      FIG. 2  is a perspective view of a backing plate for receiving a control unit to form the assembly of the invention.  
         [0037]      FIG. 3  is a perspective view of one end of the control unit of the invention showing the connectors which engage the connectors of the backing plate in use.  
         [0038]      FIG. 4  is a perspective view of the backing plate and control unit of the assembly removed from the compression device to show the coming together of the connectors and the springs which bias the assembly apart for detachment of the control unit.  
         [0039]      FIG. 5  is a schematic air flow logic diagram of the assembly of the invention.  
         [0040]      FIG. 6  is a schematic view of the interior of the control unit of the assembly of  FIG. 1  showing the air manifold.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0041]     In  FIG. 1 a  control unit assembly and compression device according to an embodiment of the invention is shown worn on the leg of a patient. The device comprises a sleeve  2  having a leg cuff  4  connected to a foot cuff  6 . The device also comprises a control unit assembly  8  comprising a control unit  10 . The control unit  10  is small and when removed from the sleeve  2  may be hand held. The control unit  10  is battery powered and rechargeable so that it can be recharged when attached to or detached from the sleeve  2 .  FIG. 1  also shows the pouch  12  provided on sleeve  2  for receiving the control unit  10  and the low profile of the assembly. The control unit assembly follows the contour of the device and integrates the assembly into the device.  
         [0042]      FIG. 2  is a perspective view taken from above the device with the control unit  10  removed showing the interior of the pouch  12  and the backing plate  14 . The control unit  10  may be slidably engaged in the pouch  12  and retained in position by a latching means.  FIG. 1  shows a release button  22  positioned on the pouch  12  of the device which when depressed releases the control unit  10  from the pouch  12 .  
         [0043]      FIG. 3  is a perspective view of the control unit  10  removed from the pouch  12  and viewed from the bottom, showing the connectors  16  for engagement with the rigid connectors  18  of the backing plate  14 .  
         [0044]      FIG. 4  is a perspective view of the backing plate  14 , removed from the device for the purposes of illustration, showing the rigid connectors  18  for engagement with the connectors  16  of the control unit  10 .  FIG. 4  shows the control unit  10  being slid into engagement with the backing plate  14 . As the control unit  10  is slid into the backing plate  14 , it begins to compress two springs  20  which act to bias the control unit  10  and backing plate  14  apart. Further sliding movement of the control unit  10  causes the connectors  16 ,  18  to engage in a fluid tight seal and the control unit  10  to engage a latch (not shown) which retains the control unit  10  in the pouch  12  against the springs  20 . The control unit  10  is released from the pouch  12  by depressing button  22  ( FIG. 1 ), the outline of which is visible on the sleeve  2 . The springs  20  then cause the control unit  10  and backing plate  14  to spring apart and the control unit  10  can be removed from the device. The springs  20  can be in the form of a leaf spring located in the backing plate  14  which similarly biases the parts of the assembly apart.  
         [0045]      FIG. 4  also shows air filter  24  provided on the air inlet/outlet connector of the backing plate  14 . As the air filter  24  is provided on the backing plate  14 , it is naturally replaced when the control unit  10  is used with a new device. This reduces the service requirements of the control unit  10 .  
         [0046]     Referring to  FIGS. 5 and 6 , the control unit  10  has fluid flow conduits  40 ,  42 ,  44 ,  46 ,  48  which terminate in connectors C 1 , C 2 , C 3 , C 4  and an air inlet/outlet C 5 . When a cell is required to be inflated, air is taken in via the conduit  48  by the operation of pump (labeled “PUMP”) and valves V 4  and V 5  under instruction from a processor (not shown). The processor instructs valves V 3 , V 1  and V 2  which are arranged between the air inlet/outlet C 5  and the conduits  40 ,  42 ,  44 ,  46  such that only one of the conduits  40 ,  42 ,  44 ,  46  is operational at any one time. From  FIG. 5  it can be seen that valve V 3  directs fluid from/to the air inlet/outlet C 5  to/from either valve V 1  or V 2  which in turn selectively open or close fluid paths to connectors C 1  or C 2 , or C 3  or C 4 . The valves are preferably latching valves.  
         [0047]     A sensor S 1  ( FIG. 6 ) is located in conduit  40  between connector C 1  and valve V 1  in the control unit  10 . Similarly, sensors S 2 , S 3  and S 4  are located in conduits  42 ,  44 ,  46 , respectively. Sensors S 1  to S 4  are all fluid pressure sensors controlled by a processor (not shown) and arranged to provide an indication of pressure exerted by the respective cells in the device. S 5  independently monitors the pressure in the fluid flow system of the device.  
         [0048]      FIG. 6  also shows the air manifold  50  with its labyrinth of passages that supplies air from the pump to each of the connectors C 1  to C 5 . The air manifold  50  replaces the external tubes needed with prior art devices between a distal control unit and the connectors of the device.