Abstract:
A system for therapeutically treating a desired region of a patient&#39;s body by circulating a nonambient temperature treatment fluid through a pad positioned on the treatment region. The system is provided with a fluid drive mechanism including a flow control assembly and a pump for delivering a drive fluid to the flow control assembly. The flow control assembly houses a pressurizing chamber having a drive fluid inlet and outlet and a treatment fluid inlet and outlet. A drive fluid outlet valve and treatment fluid inlet valve are provided to selectively restrict flow through the drive fluid outlet and treatment fluid inlet, respectively. Operation of the flow control assembly initiates with both the drive fluid outlet valve and treatment fluid inlet valve in an open position, enabling the pressurizing chamber to receive fresh treatment fluid in a receiving mode. When the drive pressure in the pressurizing chamber reaches a predetermined pressure value correlated to the volume of fresh treatment fluid in the pressurizing chamber, the flow control assembly automatically transitions to a discharging mode, wherein both the drive fluid outlet valve and the treatment fluid inlet valve assume a closed position. As a result the fresh treatment fluid is driven from the pressurizing chamber into the pad where it displaces treatment fluid residing therein.

Description:
TECHNICAL FIELD 
     The present invention relates generally to therapeutic treatment of the body and particularly to therapeutic treatment of the body provided by circulating a nonambient temperature treatment fluid over an affected body surface. More particularly, the invention relates to a mechanism for driving the fluid through a treatment pad of a therapeutic treatment system positioned on the body. 
     BACKGROUND OF THE INVENTION 
     Bodily injuries and ailments are commonly treated by applying a nonambient temperature material to the affected area of the body. For example, a low temperature material, typically applied in the form of ice or a cold liquid, may advantageously inhibit swelling in the region of the injury. A high temperature material, typically applied in the form of hot water or an active heating element, may advantageously reduce pain and promote healing. A number of splint devices are known in the art for applying nonambient temperature materials to injured or otherwise ailing areas of the body as evidenced by U.S. Pat. No. 3,548,819 to Davis et al; U.S. Pat. No. 3,901,225 to Sconce; and U.S. Pat. No. 4,706,658 to Cronin. One disadvantage of such devices is that the low temperature materials become warmer as they remain in contact with the body during treatment and the body transfers heat to the low temperature materials. Conversely, high temperature materials become cooler as they transfer heat to the body. This disadvantage can be remedied by periodically replacing the nonambient temperature materials. However, constant replenishment of these materials is cumbersome and inconvenient, and results in periodic treatment temperature fluctuations. 
     In response to this problem, a number of systems have been developed for continuously circulating a cooling fluid from a low temperature reservoir to a desired body location. Such systems are typified by U.S. Pat. No. 2,726,658 to Chessey; U.S. Pat. No. 3,683,902 to Artemenko et al; and U.S. Pat. No. 4,962,761 to Golden. These fluid circulation systems in general are relatively complex, rendering them costly to manufacture and maintain, as well as difficult to operate. Accordingly, the systems are not practical for widespread use. 
     U.S. Pat. No. 5,241,951 to Mason et al, incorporated herein by reference, discloses a therapeutic treatment system which rectifies the shortcomings of the above-referenced fluid circulation systems. The therapeutic treatment system of U.S. Pat. No. 5,241,951 is relatively simple, rendering it less costly to manufacture and maintain and enabling greater ease of operation than the prior systems. The system of U.S. Pat. No. 5,241,951 consists essentially of a fluid reservoir, a submersible pump, a pad having an internal fluid flowpath, fluid inlet and outlet lines connecting the pad to the pump and an in-line flow control valve. The system is operated by filling the reservoir with a nonambient temperature treatment fluid and submersing the pump in the fluid. The pad is positioned on the desired treatment region of the user and the pump is activated to deliver fresh treatment fluid from the reservoir to the pad via the fluid inlet line and return spent treatment fluid from the pad to the reservoir via the fluid outlet line. The user regulates the temperature of the pad by manually adjusting the valve to control the flow rate of fluid through the pad. 
     The system of U.S. Pat. No. 5,241,951 has been shown to provide effective therapeutic treatment to the body. Nevertheless, it has been found that the performance of the system is limited by the submersible pump. In particular, submersible pumps providing the required degree of reliability, i.e., durability and longevity, for the therapeutic treatment application of U.S. Pat. No. 5,241,951 are costly relative to the other system components. In addition, the electric motor of the submersible pump generates heat which is undesirably transferred to the cooling fluid in which the pump is submersed. Also submersion of the electrically-powered pump in the cooling fluid raises safety concerns for the user. Accordingly, the present invention recognizes the need for an improved fluid drive mechanism utilized within a fluid circulation-type therapeutic treatment system. It is an object of the present invention to provide a fluid drive mechanism for a therapeutic treatment system which is effective, safe and reliable, yet relatively inexpensive. It is another object of the present invention to provide a fluid drive mechanism which provides ease of operation and control for the user. These objects and others are achieved in accordance with the invention described hereafter. 
     SUMMARY OF THE INVENTION 
     The present invention is a fluid drive mechanism for conveying a nonambient temperature stored treatment fluid employed in a therapeutic treatment system. The fluid drive mechanism conveys the stored treatment fluid from a treatment fluid storage vessel to a treatment pad. The pad is positionable on a desired portion of the body and has a pad inlet, a pad outlet, and a continuous pad flowpath from the pad inlet to the pad outlet. A pad inlet line is connected to the pad inlet and a pad outlet line is connected to the pad outlet. 
     The fluid drive mechanism has a drive fluid pump and a pressurizing chamber. The pressurizing chamber has a drive fluid inlet for receiving a pressurized drive fluid from the drive fluid pump, a drive fluid outlet for periodically discharging the pressurized drive fluid to the atmosphere, a treatment fluid inlet for periodically receiving the stored treatment fluid from the treatment fluid storage vessel, and a treatment fluid outlet for periodically discharging the stored treatment fluid into the pad inlet line and thereafter to the pad flowpath where the stored treatment fluid displaces the treatment fluid already residing in the pad flowpath. The displaced treatment fluid from the pad flowpath is returned to the treatment fluid storage vessel by the pad outlet line. The receiving and discharging modes of operation occur sequentially and continuously to provide the fluid drive mechanism with a plurality of operating cycles in series. 
     The drive fluid outlet is fitted with a drive fluid outlet valve which enables the fluid drive mechanism to transition between the receiving and discharging modes of operation. In particular, the drive fluid outlet valve selectively controls discharge of the drive fluid from the pressurizing chamber to the atmosphere. The drive fluid outlet valve opens when a predetermined substantial volume decrease of stored treatment fluid occurs in the pressurizing chamber, which creates a pressure drop enabling stored treatment fluid to enter the pressurizing chamber from the treatment fluid storage vessel. Conversely, the drive fluid outlet valve closes when a predetermined substantial volume increase of stored treatment fluid occurs in the pressurizing chamber, which creates a pressure buildup driving stored treatment fluid from the pressurizing chamber to the pad flowpath. Thus, opening the drive fluid outlet valve transitions the fluid drive mechanism to the receiving mode of operation and closing the drive fluid outlet valve transitions the fluid drive mechanism to the discharging mode of operation. Since the drive fluid outlet valve opens and closes in response to the volume of stored treatment fluid in the pressurizing chamber, the operating modes of the fluid drive mechanism are likewise correlated to the volume of stored treatment fluid in the pressurizing chamber. It is also noted that the treatment fluid inlet is fitted with a treatment fluid inlet valve to substantially inhibit back flow of the stored treatment fluid from the pressurizing chamber to the treatment fluid storage vessel. 
     A number of alternate embodiments are employed in the present fluid drive mechanism to effect opening and closing of the drive fluid outlet valve in response to the volume of stored treatment fluid in the pressurizing chamber. In accordance with each of these embodiments, a displacement member is positioned within the pressurizing chamber and is displaced in response to changes in the stored treatment fluid volume or the drive fluid pressure. Displacing the displacement member to a maximum downward level actuates opening of the drive fluid outlet valve, while displacing the displacement member to a maximum upward level actuates closing of the drive fluid outlet valve. In accordance with one embodiment, the displacement member is a buoyant float which need not engage the walls of the pressurizing chamber. In accordance with another embodiment, the displacement member is a piston which slidably engages the walls of the pressurizing chamber. In accordance with yet another embodiment, the displacement member is a flexible diaphragm which is anchored to the walls of the pressurizing chamber. 
     The invention will be further understood from the accompanying drawings and description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a therapeutic treatment system including a partially exploded view of a fluid drive mechanism of the present invention. 
     FIG. 2 is a partial cross-sectional view of a flow control assembly included within the fluid drive mechanism of FIG.  1 . 
     FIG. 3 is a partial cross-sectional view of an alternate embodiment of a flow control assembly included within the fluid drive mechanism of FIG.  1 . 
     FIG. 4 is a partial cross-sectional view of yet another alternate embodiment of a flow control assembly included within the fluid drive mechanism of FIG.  1 . 
     FIGS.  5 A- 5 D are partial cross-sectional views of the flow control assembly of FIG. 2 in a series of operating modes comprising a single operating cycle. 
     FIG. 6 is a perspective view of a therapeutic treatment system including a partially exploded perspective view of an alternate embodiment of a fluid drive mechanism. 
     FIG. 7 is a partial cross-sectional view of a flow control assembly included within the fluid drive mechanism of FIG.  6 . 
     FIG. 8 is a partial cross-sectional view of an alternate embodiment of a flow control assembly included within the fluid drive mechanism of FIG.  6 . 
     FIGS.  9 A- 9 D are partial cross-sectional views of the flow control assembly of FIG. 7 in a series of operating modes comprising a single operating cycle. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring initially to FIG. 1, a therapeutic treatment system including a fluid drive mechanism is shown and generally designated  10 . For purposes of illustration, the therapeutic fluid circulation system  10  is described below as used in low temperature cooling applications. However, it is apparent to the skilled artisan that the system  10  can be adapted for high temperature heating applications simply by substituting a high temperature treatment fluid for the low temperature treatment fluid described hereafter. 
     The system  10  comprises a treatment pad  12  positionable on the body of a patient at the point where therapeutic cooling treatment is desired. The treatment pad  12  is shown positioned on the knee  14 , but it is understood that the pad  12  can alternatively be positioned substantially anywhere on the body where the treatment is desired. The treatment pad  12  is preferably a substantially planar member made up of a thin flexible heat-conductive material, forming a bladder which encloses an internal flowpath for the treatment fluid. Although not shown, the flowpath can contain a plurality of baffles to increase the tortuosity of the flowpath. The treatment pad  12  is readily conformable to the body contours of the patient, having a plurality of slits  16  formed therein to enhance conformance. Treatment pads of the type having utility in the present system  10  are disclosed in U.S. Pat. No. 5,417,720, incorporated herein by reference. 
     The treatment pad  12  has a pad inlet port  18  and a pad outlet port  20  connected to a pad inlet line  22  and a pad outlet line  24 , respectively. The pad inlet and outlet lines  22 ,  24  and pad inlet and outlet ports  18 ,  20  have substantially the same inside diameter and are connected at a joint  26  having snap-action locking inlet and outlet couplings  28 ,  30  which are manually selectively releasable. More specifically, the pad inlet port  18  is connected to the proximal end of  22   a  of the pad inlet line  22  by means of the inlet coupling  28  and the pad outlet port  20  is connected to the proximal end  24   a  of the pad outlet line  24  by means of the outlet coupling  30 . The terms “proximal” and “distal” are used herein relative to the treatment pad  12 . 
     An insulative sheath  32  covers the pad inlet and outlet lines  22 ,  24  (shown in cut-away), enclosing the lines  22 ,  24  in a single tubular unit. The sheath  32 , pad inlet line  22  and pad outlet line  24  are formed from supple materials which render them fully flexible. The sheath  32  has a strong and resilient plastic exterior skin and an insulating foam interior which minimizes heat exchange between the pad inlet line  22  and the pad outlet line  24  or between the lines  22 ,  24  and the surrounding environment. The sheath  32  also prevents condensate formation on the exterior of the pad inlet and outlet lines  22 ,  24 . An insulative sheath  34  having a similar composition can also be provided over the fluid inlet and outlet ports  18 ,  20  extending between the joint  26  and the treatment pad  12 . 
     The therapeutic treatment system  10  has a treatment fluid storage vessel  36  which is preferably a fluid-tight, thermally-passive container, such as a conventional insulated plastic picnic cooler. The term “thermally passive”, as used herein, characterizes a structure which is free of any active cooling elements, such as refrigeration coils or the like. Thus, the entirety of the therapeutic treatment system  10  is likewise characterized as thermally passive. The treatment fluid storage vessel  36  serves as a fresh storage reservoir, having a selectively removable cover  38  for the addition of fresh treatment fluid into the vessel  36  or the withdrawal of stored treatment fluid  40  from the vessel  36 . The cover  38  aids in maintaining the low temperature of the stored treatment fluid  40  in the treatment fluid storage vessel  36 . The stored treatment fluid  40  is a low temperature fluid, i.e., below ambient room temperature, and preferably a cold liquid. 
     The system  10  further comprises a fluid drive mechanism generally designated  42  which includes a flow control assembly  44  and a pump  46 . The treatment fluid storage vessel  36 , cover  38 , and flow control assembly  44  are shown in an exploded view for purposes of illustration. It is understood that these components are assembled with one another in a manner described hereafter to provide the system  10  with an integrated structure during operation. The flow control assembly  44  has a housing  48  formed from a durable, water-proof, rigid, hard plastic which encloses the internal components of the flow control assembly  44 . The housing  48  includes a lower section  50  and an attached upper section  52 , wherein the upper section  52  has a wider cross section than the lower section  50 . An aperture  54  is provided in the cover  38  of the treatment fluid storage vessel  36 . The aperture  54  has a cross section wider than that of the lower section  50 , but narrower than that of the upper section  52 . When the system  10  is assembled for operation, the narrower lower section  50  is received through the aperture  54  and extends into the treatment fluid storage vessel  36 , while the wider upper section  52  is retained atop the cover  38  external to the treatment fluid storage vessel  36  because of its wider cross section. 
     The pump  46  is substantially any means for compressing a drive fluid received into the pump  46  via a pump inlet port  56  and delivering the pressurized drive fluid to the flow control assembly  44  via a drive fluid line  58 . The drive fluid is preferably an ambient temperature gas and is more preferably ambient temperature air drawn into the pump inlet port  56  from the surrounding environment and discharged from the pump  46  via the end  58   a  of the drive fluid line  58  engaging the pump  46 . A preferred pump having utility in the present system  10  is a conventional electrically-powered air pump, such as is typically used in small household aquarium applications. The preferred pump is driven by an ac-powered, single-speed electric motor (not shown) having an external power line  60  connectable to an ac power source via a conventional ac wall outlet  62 . 
     Although a preferred pump is described above, the present invention is not limited to any one type of pump. For example, the pump can alternatively be an ac-powered, variable-speed pump. In other alternatives, the pump can be a dc-powered, variable- or single-speed pump employing a transformer to convert the ac power from the ac wall outlet  62  to dc power. The dc-powered pump can alternatively obtain its power directly from a dc power source, such as an automobile battery or a portable external or internal battery pack consisting of one or more disposable dry cell batteries or rechargeable batteries. In still another alternative, the pump can be a canister (not shown) of a compressed gas, such as carbon dioxide, which serves as the drive fluid. The cannister is in fluid communication with the pressurizing chamber  64  via a regulator valve positioned across the drive fluid line  58 . In yet another alternative, the pump can be a manually operated pump. Manually operated pumps, such as a bulb-type pump commonly used in an arm cuff for blood pressure measuring applications, are well known to the skilled artisan. A manually operated pump is the preferred pump of the therapeutic treatment system  10  when an electric power source or compressed gas cannister is unavailable. 
     Referring to FIG. 2, the flow control assembly  44  is described in further detail. The upper section  52  of the housing  48  is open to the atmosphere through a vent  63 , while the lower section  50  encloses a fluid-tight pressurizing chamber  64 . The upper section  52 , in cooperation with the lower section  50 , serves generally as a mount which maintains the flow control assembly  44  in engagement with the treatment fluid storage vessel  36  and in proper position with relation to the stored treatment fluid  40  in the treatment fluid storage vessel  36 . The upper section  52  also serves as a guide for the distal ends  22   b ,  24   b  of the pad inlet and outlet lines  22 ,  24 , respectively, and for the end  58   b  of the drive fluid line  58  opposite the pump  46 . The upper section  52  receives and retains each of the lines  22 ,  24 ,  58 . The lower section  50  defines the walls of the pressurizing chamber  64  which are rigidly configured and have a fixed geometry. The pressurizing chamber  64  is essentially impermeable to the stored treatment fluid  40  or the drive fluid with the exception of controlled fluid flow permitted through drive fluid inlet and outlet ports and treatment fluid inlet and outlet ports as described hereafter. 
     The drive fluid inlet port  66  is a first opening in the top of the lower section  50  which engages the end  58   b  of the drive fluid line  58 . The drive fluid outlet port  68  is a second opening in the top of the lower section  50  of the housing  48  adjacent to the drive fluid inlet port  66 . The treatment fluid inlet port  70  is a plurality of first openings in the bottom of the lower section  50 . The treatment fluid outlet port  72  is a second opening in the bottom of the lower section  50  adjacent to the treatment fluid outlet port  72  which engages the distal end  22   b  of the pad inlet line  22 . 
     A flapper valve  74  is positioned at the treatment fluid inlet port  70 , functioning as a treatment fluid inlet valve to selectively permit flow of treatment fluid  40  from the treatment fluid storage vessel  36  into the pressurizing chamber  64  or prevent back flow of treatment fluid  40  from the pressurizing chamber  64  into the treatment fluid storage vessel  36 . A check valve  76  is intermediately positioned within the pad inlet line  22 , functioning as a treatment fluid outlet valve to selectively permit flow of treatment fluid  40  into the pad  12  from the pressurizing chamber  64  via the distal end  22   b  of the pad inlet line  22  or to prevent back flow of treatment fluid  40  into the pressurizing chamber  64  from the treatment pad  12 . Although not shown, the pad outlet line  24  has a flow restriction positioned at some point in the pad outlet line  24  or pad outlet port  20 . The flow restriction can be substantially any element which restricts the cross-sectional area of the pad outlet line  24  or pad outlet port  20 , such as a reduction orifice, a crimp in the line, a pressure relief valve or a selectively adjustable valve. Alternatively, the flow restriction can be provided by sizing the pad outlet line  24  smaller than the pad inlet line  22 . 
     The flow restriction in the pad outlet line  24  or pad outlet port  20  creates a back pressure in the treatment pad  12  which is desirable for effective operation of the therapeutic treatment system  10 . It is also apparent that the flow restriction can be effectively employed to directly control the flow rate of the stored treatment fluid  40  from the pressurizing chamber  64  through the treatment pad  12 , and hence control the temperature of the treatment pad  12 . Alternatively, a flow restriction can be placed in the pad inlet line  22  or pad inlet port  18 , such as the selectively adjustable valve disclosed in U.S. Pat. No. 5,241,951, to directly control the flow rate of the stored treatment fluid  40  from the pressurizing chamber  64  through the treatment pad  12   
     The drive fluid line  58  opens into the pressurizing chamber  64  via the drive fluid inlet port  66 . Drive fluid flow into the pressurizing chamber  64  is controlled by operation of the pump  46 , either increasing or decreasing the pump speed and correspondingly the drive fluid flow rate, if the pump  46  is adjustable, or initially sizing the pump for a desired drive fluid flow rate, if the pump  46  is not adjustable. Alternatively, a fixed or selectively adjustable flow restriction (not shown) can be positioned in the drive fluid line  58  to control the drive fluid flow rate into the pressurizing chamber  64 . As will be apparent below in describing operation of the fluid drive mechanism  42 , the flow rate of the stored treatment fluid  40  from the pressurizing chamber  64  through the treatment pad  12  can be controlled indirectly by controlling the drive fluid flow rate using one of the above-described techniques. These indirect techniques are an alternative to the direct techniques described above for controlling the treatment fluid flow rate through the treatment pad  12 . 
     A drive fluid outlet valve  78  is positioned in the drive fluid outlet port  68  to selectively permit or prevent drive fluid flow from the pressurizing chamber  64  into the surrounding atmosphere. The drive fluid outlet valve  78  comprises a valve pin  80  selectively displaceable against a valve seat  82  which is the perimeter of the drive fluid outlet port  68 . The free cross-sectional area of the drive fluid outlet port  68  is substantially greater than the free cross-sectional area of the drive fluid inlet port  66  when the drive fluid outlet valve  78  is open. A displacement member  84  enclosed within the pressurizing chamber  64  is provided to actuate the drive fluid outlet valve  78 . The displacement member  84  is either hollow or formed from a relatively low density material such that the displacement member  84  is substantially buoyant in the stored treatment fluid  40 , functioning as a float. In the present embodiment, the displacement member  84  is a rigid body having a substantially fixed geometry which approximates the cross section of the pressurizing chamber  64 , but is slightly smaller, so that vertical displacement of the displacement member  84  within the pressurizing chamber 64  is not substantially impeded by the sides of the lower section  50 , nor is flow of the stored treatment fluid  40  and drive fluid between the displacement member  84  and the sides of the lower section  50  blocked. 
     The displacement member  84  is provided with an upper extension  86  which is connected to the valve pin  80  by a connective member  90 . The connective member  90  is a flexible link such as a length of string, cord or chain. The valve pin  80  is rotatably joined to one end of a rigid alignment arm  92  and the opposite end of the alignment arm  92  is rotatably joined to a pivot  94  which is integral with the top of the lower section  50 . The alignment arm  92  rotates about the valve pin  80  and pivot  94  in correspondence with vertical movement of the valve pin  80  up and down. The alignment arm  92  maintains the alignment of the valve pin  80  with respect to the drive fluid outlet port  68  as the valve pin  80  moves vertically. 
     It is apparent from the present construction that when the displacement member  84  of the drive fluid outlet valve  78  is displaced upward, the displacement member  84  ultimately reaches an upward transition level where the upper extension  86  is in abutment with the valve pin  80  and the connective member  90  is relaxed. Once this upward transition level is reached, continued upward displacement of the displacement member  84  to a maximum upward level causes the upper extension  86  to urge the valve pin  80  upward into the valve seat  82  closing the drive fluid outlet valve  78 . Conversely, when the displacement member  84  is displaced downward, the displacement member  84  ultimately reaches a downward transition level where the upper extension  86  separates from the valve pin  80  by a length corresponding to that of the connective member  90  and the connective member  90  is pulled taut. Once this downward transition level is reached, continued downward displacement of the displacement member  84  to a maximum downward level causes the connective member  90  to pull the valve pin  80  downward away from the valve seat  82  reopening the drive fluid outlet valve  78 . Alignment of the upper extension  86  with the valve pin  80  is maintained during vertical displacement of the displacement by the close spatial relation between the displacement member  84  and the lower section  50 . In contrast to the drive fluid outlet valve  78 , both the flapper valve  74  and check valves  76  are passive valves which only operate in response to pressure changes caused by the action of the drive fluid outlet valve  78 , as will be apparent below in describing operation of the fluid drive mechanism  42 . 
     Referring to FIG. 3, an alternate embodiment of the flow control assembly is shown and generally designated  100 . The flow control assembly  100  has a number of components substantially identical to those of FIG. 2 which are identified in FIG. 3 by the same reference characters as FIG.  2 . The flow control assembly  100  differs from the flow control assembly  44  primarily in the characteristics of the lower section and the connective and displacement members. The connective member  102  of the flow control assembly  100  is a rigid lever arm having a construction similar to the alignment arm  92 . The connective member  102  is rotatably connected at one end to the pivot  94  and rotatably connected at the opposite end to the upper extension  104  while an intermediate point of the connective member  102  is rotatably connected to the valve pin  80 . The upper extension  104  is positioned on the displacement member  106  out of direct alignment with the valve pin  80 . The displacement member  106  and lower section  108  are dimensioned such that the displacement member  106  has a cross section substantially less than the cross section of the pressurizing chamber  110 . This configuration provides a substantial annular space  112  in the pressurizing chamber  110  between the displacement member  106  and lower section  108 . The pad inlet line  22  enters the pressurizing chamber  110  through a third opening  114  in the top of the lower section  108  and extends through the annular space  112  to the bottom of the pressurizing chamber  110 . The distal end  22   b  of the pad inlet line  22  serves as the treatment fluid outlet port and no second opening is provided in the bottom of the lower section  108 . 
     It is apparent from the present construction that when the displacement member  106  of the drive fluid outlet valve  78  is displaced upward, the displacement member  106  ultimately reaches an upward transition level where the connective member  102  begins to upwardly displace the valve pin  80  as it rotates in a first direction. Once this upward transition level is reached, continued upward displacement of the displacement member  106  to a maximum upward level causes the connective member  102  to urge the valve pin  80  upward into the valve seat  82  closing the drive fluid outlet valve  78 . Conversely, when the displacement member  106  is displaced downward, the displacement member  106  ultimately reaches a downward transition level where the connective member  102  begins to downwardly displace the valve pin  80  as it rotates in a second direction substantially opposite the first direction. Once this downward transition level is reached, continued downward displacement of the displacement member  106  to a maximum downward level causes the connective member  102  to pull the valve pin  80  downward away from the valve seat  82  reopening the drive fluid outlet valve  78 . Alignment of the displacement member  106  within the pressurizing chamber  110  is maintained by the connective member  102 . 
     Referring to FIG. 4, another alternate embodiment of the flow control assembly is shown and generally designated  120 . The flow control assembly  120  has a number of components substantially identical to those of FIG. 2 which are identified in FIG. 4 by the same reference characters as FIG.  2 . The flow control assembly  120  differs from the flow control assembly  44  primarily in the characteristics of the displacement member. The displacement member  122  of the flow control assembly  120  is a piston formed from a material which may or may not be buoyant in the stored treatment fluid  40 . In either case, the displacement member  122  and lower section  50  are dimensioned such that the displacement member  122  has a cross section nearly the same as the cross section of the pressurizing chamber  64 , but incrementally smaller. The cross section of the displacement member  122  is incrementally smaller only by a sufficient degree to enable slidable displacement of the displacement member  122  relative to the lower section  50 , while maintaining a fluid seal between the displacement member  122  and the lower section  50 . This configuration enables the flow control assembly  120  to establish a pressure differential on opposite sides of the displacement member  122  within the pressurizing chamber  64 . It is apparent from the present construction that the displacement member  122  effects opening and closing of the drive fluid outlet valve  78  in substantially the same manner as the drive fluid outlet valve  78  of FIG. 2 except that the displacement member  122  is driven primarily by the pressure of the stored treatment fluid  40  or drive fluid on the displacement member  122  in the pressurizing chamber  64  (particularly where the displacement member  122  is not buoyant in the stored treatment fluid  40 ), while the displacement member  84  is driven primarily by the buoyant force of the stored treatment fluid  40  on the displacement member  84  in the pressurizing chamber  64 . 
     Three alternate embodiments of flow control assemblies  44 , 100 , 120  have been shown above. It is apparent to the skilled artisan from this teaching that other embodiments of flow control assemblies are possible within the scope of the present invention by configuring the elements of the flow control assemblies  44 ,  100 ,  120  in alternate combinations not expressly shown herein. For example, the connective member  102  of the flow control assembly  100  can be combined with the displacement member  122  and lower section  50  of the flow control assembly  120  to achieve another alternate flow control assembly within the scope of the present invention. Similarly, the connective member  90  of the flow control assembly  44  can be combined with the displacement member  106  and lower section  108  of the flow control assembly  100  to achieve still another alternate flow control assembly within the scope of the present invention. In this embodiment it may be desirable to further modify the displacement member  106 , coupling it with a vertical displacement guide, such as a rail, within the pressurizing chamber  110  to maintain the desired alignment of the upper extension and valve pin  80 . 
     Operation of the flow control assemblies  44 ,  100 ,  120  is substantially similar. For purposes of illustration, a method of operation is described below for the flow control assembly  44  as utilized within the fluid drive mechanism  42  and, more generally, as utilized within the therapeutic treatment system  10 . However, it is readily within the purview of the skilled artisan to adapt the following operating method to the alternate flow control assemblies  100 ,  120  described above or to other flow control assemblies which are within the scope of the present invention. 
     Referring to FIGS.  1  and  5 A- 5 D, operation of the therapeutic treatment system  10  employing the fluid drive mechanism  42  is initiated by filling the treatment fluid storage vessel  36  with a fresh cold treatment fluid  40  from a remote source (not shown). The fresh cold treatment fluid  40  is preferably ice water at a temperature approaching its freezing point. After filling the treatment fluid storage vessel  36  with a desired volume of the fresh cold treatment fluid  40 , which is several times greater than the volumetric capacity of the flowpath within the treatment pad  12 , the cover  38  is positioned on the treatment fluid storage vessel  36  to reduce heat loss from the cold treatment fluid  40  to the surrounding atmosphere. The joint  26  is secured and the treatment pad  12  is placed on the skin of the patient at the point on the body where therapeutic treatment is desired and preferably secured to the body by a wrap or straps integral with the construction of the treatment pad  12 . An additional padding material, such as a soft cloth, can be placed on the skin between the treatment pad  12  and the skin for the comfort of the patient or such padding material can be integral with the construction of the treatment pad  12 . Typically residual ambient temperature treatment fluid is already present in the flowpath of the treatment pad  12  from a prior treatment. 
     The flow control assembly  44  is positioned in close fitting engagement with the cover  38  by placing the lower section  50  of the housing  48  through the aperture  54  so that it extends into the treatment fluid storage vessel  36 , while the upper section  52  of the housing  48  remains fixedly positioned atop the cover  38 . The system  10  is activated by connecting the external power line  60  to the ac wall outlet  62 , actuating the pump  46  in continuous uninterrupted operation. FIG. 5A shows the flow control assembly  44  at the outset of an operating cycle. Specifically, FIG. 5A shows the flow control assembly  44  at the precise time when the assembly  44  has just completed the treatment fluid discharging mode of operation and is transitioning to the treatment fluid receiving mode of operation. It is noted that the terms “discharging” and “receiving” as used herein are only with reference to flow of the stored treatment fluid  40  through the pressurizing chamber  64 . The terms are not used to reference the flow of treatment fluid  40  through the treatment pad  12  because the treatment pad  12  is simultaneously in the receiving and discharging modes of operation when the flow control assembly  44  is in the discharging mode of operation. The treatment pad  12  is essentially inactive when the assembly  44  is in the receiving mode of operation except for a minor volume of warmer treatment fluid which preferably continuously leaks from the treatment pad  12  through the open flow restriction in the pad outlet line  24 . 
     At the outset of the receiving mode of operation, the low treatment fluid level  130  in the pressurizing chamber  64  has just dropped the displacement member  84  to a maximum downward level toward the bottom of the pressurizing chamber  64 . The valve pin  80  has transitioned to an open position below the valve seat  82  in response to the downward pulling force of the taut connective member  90  which results from the low treatment fluid level  130 . The pressurized drive fluid, preferably air, is fed by the continuously-operating pump  46  into the pressurizing chamber 64  via the drive fluid line  58 . However, the pressurizing chamber  64  remains substantially at ambient atmospheric pressure because the pressurized drive fluid immediately exits the pressurizing chamber  64  via the open drive fluid outlet valve  78  into the surrounding atmosphere. Drive fluid flow is indicated by the directional arrows. As noted above, the free cross-sectional area of the drive fluid outlet port  68  is substantially greater than the free cross-sectional area of the drive fluid inlet port  66  when the drive fluid outlet valve  78  is open, preventing a substantial pressure buildup in the pressurizing chamber  64  during the receiving mode. 
     The check valve  76  is going from the open position to the closed position in response to the pressure drop in the pressurizing chamber and the treatment fluid back pressure in the treatment pad  12 . The treatment fluid back pressure is substantially greater than the hydrostatic head of the treatment fluid level  130  in the pressurizing chamber  64 . Thus, the check valve  76  prevents the back flow of treatment fluid  40  from the treatment pad  12  into the pressurizing chamber  64  via the pad inlet line  22  when the pressurizing chamber  64  is at ambient pressure. The flapper valve  74  is going from the closed position to the open position in response to an upward force through the treatment fluid inlet port  70  produced by the hydrostatic head of the treatment fluid level  132  in the treatment fluid storage vessel  36  indicated by the directional arrows. 
     FIG. 5B shows the flow control assembly  44  at an intermediate point in the treatment fluid receiving mode of operation. The hydrostatic head of the treatment fluid level  132  in the treatment fluid storage vessel  36  has more fully opened the flapper valve  74  enabling a significant volume of treatment fluid  40  to enter the pressurizing chamber  64  from the treatment fluid storage vessel  36 . It is noted that a conventional stop (not shown) is provided in association with the flapper valve  74  to restrict the flapper valve  74  from opening too far, i.e., 90° or more. As the treatment fluid  40  enters the pressurizing chamber  64 , the treatment fluid level  130  in the pressurizing chamber  64  rises. However, the treatment fluid level  132  in the treatment fluid storage vessel  36  does not drop significantly due to the relative volume disparity between the treatment fluid storage vessel  36  and the pressurizing chamber  64 . Treatment fluid flow is indicated by the directional arrows. The stored treatment fluid  40  entering the pressurizing chamber  64  displaces the displacement member  84  upward as the result of buoyant forces, partially relaxing the connective member  90  and causing it to randomly coil. However, the valve pin  80  stays in the open position below the valve seat  82  due to the absence of any significant upward force on the valve pin  80 . Thus, the pressurized drive fluid continues to pass from the drive fluid line  58  through the pressurizing chamber  64 , indicated by the directional arrows, and the pressurizing chamber  64  remains at ambient atmospheric pressure. The check valve  76  in the pad inlet line  22  remains closed in response to the treatment fluid back pressure in the treatment pad  12 . 
     FIG. 5C shows the flow control assembly  44  at the precise time when the flow control assembly  44  has just completed the treatment fluid receiving mode of operation and is transitioning to the treatment fluid discharging mode of operation. At the outset of the discharging mode of operation, the high treatment fluid level  130  in the pressurizing chamber  64  and the resulting increased buoyant force has just raised the displacement member  84  to a maximum upward level toward the top of the pressurizing chamber  64 . The valve pin  80  has transitioned to a closed position in the valve seat  82  in response to the upward pushing force of the upper extension  86  abutting the valve pin  80  which results from the high treatment fluid level  130 . The connective member  90  is deformed in a fully relaxed random coil. The pressurized drive fluid, which continues to be fed from the pump  46  into the pressurizing chamber  64  via the drive fluid line  58 , begins to build up in the pressurizing chamber  64  due to closure of the drive fluid outlet valve  78 . The drive fluid buildup causes a drive fluid pressure increase in the head space  134  of the pressurizing chamber  64  which is substantially greater than the treatment fluid back pressure in the treatment pad  12 . The drive fluid pressure exerts a substantial downward force on the treatment fluid level  130  in the pressurizing chamber  64  indicated by the directional arrows. The flapper valve  74  is going from the open position to the closed position, indicated by the directional arrow, in response to the increased drive fluid pressure which acts on the stored treatment fluid  40 . Upon closure of the flapper valve  74 , the check valve  76  goes to the open position in response to the pressure of the stored treatment fluid  40  which is driven into the pad inlet line  22  because it is unable to escape from the pressurizing chamber  64  through the closed flapper valve  74 . 
     FIG. 5D shows the flow control assembly  44  at an intermediate point in the treatment fluid discharging mode of operation. The valve pin  80  remains in the closed position below the valve seat  82  due to the elevated drive fluid pressure in the pressurizing chamber  64  which exceeds the ambient atmospheric pressure external to the pressurizing chamber  64 . There is also an absence of any significant downward pulling force on the valve pin  80  from the still partially relaxed connective member  90 . With the drive fluid outlet valve  78  closed, the pump  46  continues to deliver pressurized drive fluid to the pressurizing chamber  64  indicated by the directional arrows. As a result, a significant volume of fresh cold treatment fluid  40  is displaced from the pressurizing chamber  64  through the open check valve  76  into the treatment pad  12  indicated by the directional arrows, while the flapper valve  74  is closed. The treatment fluid level  130  in the pressurizing chamber  64  consequently drops, causing a declining buoyant force and a corresponding drop in the displacement member  84 . 
     The fresh cold treatment fluid  40 , which is displaced into the treatment pad  12  at a treatment fluid displacement pressure exceeding the resistive back pressure of the treatment pad  12 , subsequently displaces the warmer treatment fluid residing in the treatment pad  12 . The resistive back pressure is a function of the flow restriction in the pad outlet line  24 . The warmer treatment fluid displaced from the treatment pad  12  is returned to the treatment fluid storage vessel  36  via the pad outlet line  24  and discharged into the fresh cold treatment fluid  40  from the distal end  24   b  as shown by the directional arrow in the pad outlet line  24 . The warmer treatment fluid is renewed in the treatment fluid storage vessel  36  by mixing with the fresh cold treatment fluid  40  because the volume of fresh cold treatment fluid  40  is several times greater than the volume of warmer treatment fluid from the treatment pad  12 . 
     Ultimately the falling treatment fluid level  130  in the pressurizing chamber  64  drops the displacement member  84  to the maximum downward level, retransitioning the flow control assembly  44  from the treatment fluid discharging mode shown in FIG. 5D back to the treatment fluid receiving mode shown in FIG.  5 A and completing one operational cycle of the flow control assembly  44 . The operational cycles are performed continuously and repeatedly for the duration of the desired treatment period. Operation of the flow control assembly  44  is terminated by terminating operation of the pump  46 . 
     Although not shown, it is within the purview of the skilled artisan to construct an alternate embodiment of a flow control assembly employing the present teaching which omits the connective member mechanically linking the displacement member and valve pin. A switch is provided in this embodiment which transitions the drive fluid outlet valve between the open and closed positions in the absence of a mechanical linkage between the displacement member and valve pin. For example, one or more sensors may be positioned in the lower section which are in electrical communication with a valve switch. The switch electromechanically or electronically transitions the drive fluid outlet valve when the sensor indicates that the displacement member has reached its maximum downward or upward level. It is further within the purview of the skilled artisan to construct an alternate embodiment of a flow control assembly employing the present teaching which omits the connective member and the drive fluid outlet valve. A switch is provided in this embodiment which activates or deactivates the pump, respectively, in response to the position of the displacement member. For example, one or more sensors may be positioned in the lower section which are in electrical communication with a pump switch. The switch electromechanically or electronically activates or deactivates the pump when the sensor indicates that the displacement member has reached its maximum downward or upward level. 
     An alternate embodiment of a fluid drive mechanism is described below with reference to FIGS. 6 and 7. Referring initially to FIG. 6, a therapeutic treatment system is shown and generally designated  140 . The system  140  employs the fluid drive mechanism  142  having a flow control assembly  144  and pump  46 . The system  140  is substantially the same as the system  10  with the exception of the fluid drive mechanism  142 . The components of FIG. 6 which are substantially identical to those of FIG. 1 are identified in FIG. 6 by the same reference characters as FIG.  1 . 
     The flow control assembly  144  is adapted for in-line mounting intermediately along the length of the pad inlet line  22  remote from the treatment fluid storage vessel  36 . The distal ends  22   b ,  24   b  of the pad inlet and outlet lines  22 ,  24 , respectively, extend directly into the treatment fluid storage vessel  36  remote from the flow control assembly  144 . A slot  146  is provided in the cover  148  of the treatment fluid storage vessel  36  to receive the pad inlet and outlet lines  22 ,  24  into the treatment fluid storage vessel  36  when the cover  148  is in place. 
     Details of the flow control assembly  144  are described below with reference to FIG.  7 . The components of FIG. 7 which are substantially identical to those of FIG. 2 are identified in FIG. 7 by the same reference characters as FIG.  2 . The flow control assembly  144  comprises a housing  150  formed from a durable, waterproof, rigid, hard plastic which encloses a pressurizing chamber  152 . The housing  150  defines the sidewalls of the pressurizing chamber  152 , which are rigidly configured and have a fixed geometry. The interior of the pressurizing chamber  152  is divided into a drive fluid compartment  154  and a treatment fluid compartment  156  by a displacement member  158 . The displacement member  158  is a continuous fluid-impermeable flexible diaphragm, preferably formed from an elastomeric material, which is anchored and sealed along its outer edge to the sidewall of the pressurizing chamber  152 . The drive fluid and treatment fluid compartments  154 ,  156  are in fluid isolation from one another and have variable volumes depending on the position of the displacement member  158 . 
     The flow control assembly  144  is provided with treatment fluid inlet and outlet valves  160 , 76  which are one-way check valves. The flow control assembly  144  is also provided with a drive fluid outlet valve  78  comprising a valve pin  80  and a valve seat  82 . It is noted that both the fluid inlet and outlet valves  160 ,  76  are passive valves which only operate in response to pressure changes caused by the action of the drive fluid outlet valve  78 , as will be apparent below in describing operation of the flow control assembly  144 . The displacement member  158  is centrally anchored to the valve pin  80  by means of a connective member  164  in the form of a rigid bracket which slidably retains the base of the valve pin  80 . A biasing member  166  is provided in the form of a coiled spring which is riveted to the connective member  164 . The biasing member  166  biases the displacement member  158  upward. It is apparent that the upward force of the biasing member  166  is analogous to the upward force produced by the hydrostatic head of the treatment fluid level  132  in the treatment fluid storage vessel  36  of the therapeutic treatment system  10 . 
     Although not shown, it is apparent to the skilled artisan from the present teaching that the flow control assembly  44  can also be adapted to utilize the above-described displacement member  158 . Similarly, the flow control assembly  144  can be adapted to utilize the displacement member  84 . 
     Referring to FIG. 8, an alternate flow control assembly is shown and generally designated  170 . The flow control assembly  170  is preferably employed in the therapeutic treatment system  140  of FIG. 6, as an alternative to the flow control assembly  144  shown in FIG.  7 . The components of FIG. 8 which are substantially identical to those of FIG. 7 are identified in FIG. 8 by the same reference characters as FIG.  7 . The flow control assembly  170  employs a rigid slidable piston as the displacement member  172  of the drive fluid outlet valve  78 . The displacement member  172  slidably engages the sidewall of the pressurizing chamber  152 , dividing the interior into the drive fluid and treatment fluid compartments  154 ,  156  which are in fluid isolation from one another. In all other respects, the flow control assemblies  144 , 170  are substantially identical, both structurally and operationally. 
     Since operation of the flow control assemblies  144 ,  170  is substantially similar. a method of operating the flow control assembly  144  is described below with reference to FIGS.  6  and  9 A- 9 D. It is readily within the purview of the skilled artisan, however, to adapt the following operating method to the alternate flow control assembly  170 . Operation is initiated by conducting a startup of the system  140  in a substantially similar manner as described above for startup of the system  10 . FIG. 9A shows the flow control assembly  144  at the outset of an operating cycle. Specifically, FIG. 9A shows the flow control assembly  144  at the precise time when the assembly  144  has just completed the treatment fluid discharging mode of operation and is transitioning to the treatment fluid receiving mode of operation. 
     At the outset of the receiving mode of operation, the displacement member  158  has been flexed to a maximum downward level toward the bottom of the pressurizing chamber  152 . The valve pin  80  has transitioned to an open position resting against the bottom of the connective member  164 . The valve pin  80  has disengaged the valve seat  82  in response to the downward pulling force of the connective member  164  which is greater than the expansion force of the biasing member  166 . This transition point occurs when the volume of the treatment fluid compartment  156  is minimized and the displacement member  158  is at the maximum downward level. The pressurized drive fluid is fed by the continuously-operating pump  46  into the drive fluid compartment  154  via the drive fluid line  58 . However, the drive fluid compartment  154  remains substantially at ambient atmospheric pressure because the pressurized drive fluid immediately exits the drive fluid compartment  154  via the open drive fluid outlet valve  78  into the surrounding atmosphere indicated by the directional arrows. The free cross-sectional area of the drive fluid outlet port  68  is substantially greater than the free cross-sectional area of the drive fluid inlet port  66  when the drive fluid outlet valve  78  is open, preventing a substantial pressure buildup in the pressurizing chamber  152  during the receiving mode. 
     The treatment fluid outlet valve  76  is going from the open position to the closed position in response to the treatment fluid back pressure in the treatment pad  12  and the suction force of the displacement member  158 . The displacement member  158  is initiating its upward flex in response to the expansion force of the biasing member  166  indicated by the directional arrow. Conversely, the treatment fluid inlet valve  160  is going from the closed to the open position in response to the upward suction force of the displacement member  158 . 
     FIG. 9B shows the flow control assembly  144  at an intermediate point in the treatment fluid receiving mode of operation. The suction force of the displacement member  158  caused by the expansion force of the biasing member  166  has opened the treatment fluid inlet valve  160 , drawing a significant volume of treatment fluid  40  into the treatment fluid compartment  156  from the treatment fluid storage vessel  36  indicated by the directional arrows. The valve pin  80  stays in the open position below the valve seat  82 . Thus, the pressurized drive fluid continues to pass from the drive fluid line  58  through the drive fluid compartment  154  indicated by the directional arrows and the drive fluid compartment  154  remains at ambient atmospheric pressure. The treatment fluid outlet valve  76  in the pad inlet line  22  remains closed in response to the treatment fluid back pressure in the treatment pad  12 . 
     FIG. 9C shows the flow control assembly  144  at the precise time when the flow control assembly  144  has just completed the treatment fluid receiving mode of operation and is transitioning to the treatment fluid discharging mode of operation. At the outset of the discharging mode of operation, the displacement member  158  has been flexed to a maximum upward level toward the top of the pressurizing chamber  152 . The valve pin  80  has transitioned to a closed position in the valve seat  82  in response to the upward force of the bottom of the connective member  164  abutting the valve pin  80  which results from the expansion force of the biasing member  166 . This transition point occurs when the volume of the treatment fluid compartment  156  is maximized and the displacement member  158  is positioned at the maximum upward level. The pressurized drive fluid, which continues to be fed from the pump  46  into the drive fluid compartment  154  via the drive fluid line  58 , begins to build up in the drive fluid compartment  154  due to closure of the drive fluid outlet valve  78 . The drive fluid buildup causes a drive fluid pressure increase in the drive fluid compartment  154  which is substantially greater than the treatment fluid back pressure in the pad  12  and the expansion force of the biasing member  166 . The drive fluid pressure exerts a substantial downward force on the displacement member  158  indicated by the directional arrows. The drive fluid pressure initiates a downward flex in the displacement member  158 . The treatment fluid outlet valve  76  is going from the closed position to the open position in response to the drive fluid pressure increase which acts on the stored treatment fluid  40 . The treatment fluid inlet valve  160  is going from the open position to the closed position in response to the back pressure in the treatment fluid compartment  156 . 
     FIG. 9D shows the flow control assembly  144  at an intermediate point in the treatment fluid discharging mode of operation. The valve pin  80  remains in the closed position below the valve seat  82  due to the elevated drive fluid pressure in the drive fluid compartment  154  which exceeds the ambient atmospheric pressure external to the drive fluid compartment  154 . There is also an absence of any significant downward pulling force on the valve pin  80 . With the drive fluid outlet valve  78  closed, the pump  46  continues to deliver pressurized drive fluid to the drive fluid compartment  154  indicated by the directional arrows. As a result, a significant volume of fresh cold treatment fluid  40  is displaced from the treatment fluid compartment  156  through the open treatment fluid outlet valve  76  into the treatment pad  12  indicated by the directional arrows. 
     The fresh cold treatment fluid  40 , which is displaced into the treatment pad  12  at a treatment fluid displacement pressure exceeding the resistive back pressure of the treatment pad  12 , subsequently displaces the warmer treatment fluid residing in the treatment pad  12 . The warmer treatment fluid displaced from the treatment pad  12  is returned to the treatment fluid storage vessel  36  via the pad outlet line  24  and discharged into the fresh cold treatment fluid  40  from the distal end  24   b . Ultimately the displacement member  158  flexes to the maximum downward level, retransitioning the flow control assembly  144  from the treatment fluid discharging mode shown in FIG. 9D back to the treatment fluid receiving mode shown in FIG.  9 A and completing one operational cycle of the flow control assembly  144 . The operational cycles are performed continuously and repeatedly for the duration of the desired treatment period. Operation of the flow control assembly  144  is terminated by disconnecting the pump  46  from the power source. 
     While the foregoing preferred embodiments of the invention have been described and shown, it is understood that all alternatives and modifications, such as those suggested and others, may be made thereto and fall within the scope of the invention.