Abstract:
A flow reversing device for performing blood treatment can include a flow reversing actuator. The flow reversing actuator can receive and engage a disposable tubing set with multiple branches that form forward and reverse blood flow paths respectively when blood the flow reversing actuator is selectively changed between forward and reverse configurations. The shape of the tubing can be such that during forward operation, dead regions of non-flowing blood are defined. The flow reversing actuator can have a controller configured to operate generally in forward mode. At first times, the controller can cause the flow reversing actuator to clear the dead regions. At second times, the controller can cause the flow reversing actuator to test for leaks by reversing the flow of blood for a period of time sufficient to cause air to be drawn into the tubing set and conveyed to an air sensor.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of U.S. application Ser. No. 13/075,454, filed Mar. 30, 2011, which is a division of U.S. application Ser. No. 10/578,600, filed May 8, 2006 (§371(c) date of Mar. 31, 2008), now U.S. Pat. No. 8,002,727, which is a U.S. national stage entry of International Application No. PCT/US2004/036933, filed Nov. 5, 2004, which claims the benefit of U.S. Provisional Application No. 60/518,122, filed Nov. 7, 2003. 
    
    
     FIELD 
     The present invention relates to the detection of leaks (including needle-disconnects and other causes of loss of integrity) in extracorporeal blood circuits and more particularly to the application of air infiltration detection techniques to the detection of leaks in positive pressure return lines. 
     BACKGROUND 
     Many medical procedures involve the extraction and replacement of flowing blood from, and back into, a donor or patient. The reasons for doing this vary, but generally, they involve subjecting the blood to some process that cannot be carried out inside the body. When the blood is outside the patient it is conducted through machinery that processes the blood. The various processes include, but are not limited to, hemodialysis, hemofiltration, hemodiafiltration, blood and blood component collection, plasmaphresis, aphresis, and blood oxygenation. 
     One technique for extracorporeal blood processing employs a single “access,” for example a single needle in the vein of the patient or a fistula. A volume of blood is cyclically drawn through the access at one time, processed, and then returned through the same access at another time. Single access systems are uncommon because they limit the rate of processing to half the capacity permitted by the access. As a result, two-access systems, in which blood is drawn from a first access, called an arterial access, and returned through a second access, called a venous access, are much faster and more common. These accesses include catheters, catheters with subcutaneous ports, fistulas, and grafts. 
     The processes listed above, and others, often involve the movement of large amounts of blood at a very high rate. For example, 500 ml of blood may be drawn out and replaced every minute, which is about 5% of the patient&#39;s entire supply. If a leak occurs in such a system, the patient could be drained of enough blood in a few minutes to cause loss of consciousness with death following soon thereafter. As a result, such extracorporeal blood circuits are normally used in very safe environments, such as hospitals and treatment centers, and attended by highly trained technicians and doctors nearby. Even with close supervision, a number of deaths occur in the United States every year due to undue blood loss from leaks. 
     Leaks present a very real risk. Leaks can occur for various reasons, among them: extraction of a needle, disconnection of a luer, poor manufacture of components, cuts in tubing, and leaks in a catheter. However, in terms of current technology, the most reliable solution to this risk, that of direct and constant trained supervision in a safe environment, has an enormous negative impact on the lifestyles of patients who require frequent treatment and on labor requirements of the institutions performing such therapies. Thus, there is a perennial need in the art for ultra-safe systems that can be used in a non-clinical setting and/or without the need for highly trained and expensive staff. Currently, there is great interest in ways of providing systems for patients to use at home. One of the risks for such systems is the danger of leaks. As a result, a number of companies have dedicated resources to the solution of the problem of leak detection. 
     In single-access systems, loss of blood through the patient access and blood circuit can be indirectly detected by detecting the infiltration of air during the draw cycle. Air is typically detected using an ultrasonic air detector on the tubing line, which detects air bubbles in the blood. The detection of air bubbles triggers the system to halt the pump and clamp the line to prevent air bubbles from being injected into the patient. Examples of such systems are described in U.S. Pat. Nos. 3,985,134, 4,614,590, and 5,120,303. 
     While detection of air infiltration is a reliable technique for detecting leaks in single access systems, the more attractive two-access systems, in which blood is drawn continuously from one access and returned continuously through another, present problems. While a disconnection or leak in the draw line can be sensed by detecting air infiltration, just as with the single needle system, a leak in the return line cannot be so detected. This problem has been addressed in a number of different ways, some of which are generally accepted in the industry. 
     The first level of protection against return line blood loss is the use of locking luers on all connections, as described in International Standard ISO 594-2 which help to minimize the possibility of spontaneous disconnection during treatment. Care in the connection and taping of lines to the patient&#39;s bodies is also a known strategy for minimizing this risk. 
     A higher level of protection is the provision of venous pressure monitoring, which detects a precipitous decrease in the venous line pressure. This technique is outlined in International Standard IEC 60601-2-16. This approach, although providing some additional protection, is not very robust, because most of the pressure loss in the venous line is in the needle used to access the patient. There is very little pressure change in the venous return line that can be detected in the event of a disconnection, so long as the needle remains attached to the return line. Thus, the pressure signal is very weak. The signal is no stronger for small leaks in the return line, where the pressure changes are too small to be detected with any reliability. One way to compensate for the low pressure signal is to make the system more sensitive, as described in U.S. Pat. No. 6,221,040, but this strategy can cause many false positives. It is inevitable that the sensitivity of the system will have to be traded against the burden of monitoring false alarms. Inevitably this leads to compromises in safety. In addition, pressure sensing methods cannot be used at all for detecting small leaks. 
     Yet another approach, described for example in PCT application US98/19266, is to place fluid detectors near the patient&#39;s access and/or on the floor under the patient. The system responds only after blood has leaked and collected in the vicinity of a fluid detector. A misplaced detector can defeat such a system and the path of a leak cannot be reliably predicted. For instance, a rivulet of blood may adhere to the patient&#39;s body and transfer blood to points remote from the detector. Even efforts to avoid this situation can be defeated by movement of the patient, deliberate or inadvertent (e.g., the unconscious movement of a sleeping patient). 
     Still another device for detecting leaks is described in U.S. Pat. No. 6,044,691. According to the description, the circuit is checked for leaks prior to the treatment operation. For example, a heated fluid may be run through the circuit and its leakage detected by means of a thermistor. The weakness of this approach is immediately apparent: there is no assurance that the system&#39;s integrity will persist, throughout the treatment cycle, as confirmed by the pre-treatment test. Thus, this method also fails to address the entire risk. 
     Yet another device for checking for leaks in return lines is described in U.S. Pat. No. 6,090,048. In the disclosed system, a pressure signal is sensed at the access and used to infer its integrity. The pressure wave may be the patient&#39;s pulse or it may be artificially generated by the pump. This approach cannot detect small leaks and is not very sensitive unless powerful pressure waves are used, in which case the effect can produce considerable discomfort in the patient. 
     Clearly detection of leaks by prior art methods fails to reduce the risk of dangerous blood loss to an acceptable level. In general, the risk of leakage-related deaths increases with the decrease in medical staff per patient driven by the high cost of trained staff. Currently, with lower staffing levels comes the increased risk of unattended leaks. Thus, there has been, and continues to be, a need in the prior art for a foolproof approach to detection of a return line leak or disconnection. 
     In an area unrelated to leak detection, U.S. Pat. No. 6,177,049 B1 suggests the idea of reversing the direction of blood flow for purposes of patency testing. The patent also states that flow reversal may be used to improve patency by clearing obstructed flow. 
     U.S. Pat. No. 6,572,576 discusses various embodiments of a blood treatment device where blood flow is reversed to provide leak detection. According to the inventions described, a leak detector effective to ensure detection of leaks in the venous blood line (the line returning blood to the patient) is provided by periodically generating a negative pressure, which may be brief or at a 50% duty cycle, in the blood return line. This draws air into the venous line which can be revealed by an air sensor in the blood treatment machine. During the negative pressure cycle, any air drawn in the venous blood line is detected, the system is shut down and an alarm generated. U.S. Pat. No. 6,572,576, filed Jul. 7, 2001 entitled “Method and apparatus for leak detection in a fluid line” is hereby incorporated by reference as if fully set forth in its entirety herein. 
     Hemofiltration, dialysis, hemodiafiltration, and other extracorporeal blood treatments may employ flow selector valves such as Y-valves, four-way valves, and other such devices for redirecting the flow of blood and other fluids such as replacement fluids. For example, the direction of the flow of blood through certain types of filters may be reversed repeatedly to prevent coagulation of blood in regions where the mean flow slows to very low rates. For example, where blood is circulated through tubular media in the context of a dialysis filter, it has been proposed that blood may coagulate on the surface of the inlet header leading to the progressive coagulation of blood. U.S. Pat. No. 5,605,630, proposes occasionally reversing the flow of blood through the filter. A four-way valve is proposed for changing over the flow direction. 
     In other references, the idea of reversing the flow of blood through a tubular media filter is discussed in connection with other issues. For example, in U.S. Pat. No. 5,894,011, the known technique of switching access lines in the patient to improve the flow through an occluded fistula is automated by the addition of a four-way valve on the patient-side blood circuit. In single-access systems in general, for example as described in U.S. Pat. No. 5,120,303, flow is conventionally reversed through the filter during each draw/return cycle. In the &#39;303 reference, the specification observes that the efficiency of filtration is increased due to the double-passing of the same blood through the filter; that is, each volume of drawn blood is filtered twice. Yet another reference, U.S. Pat. No. 6,189,388 B1, discusses reversing the flow direction of blood through the patient access occasionally in order to quantify an undesirable short-circuit effect that attends their long term use. Still another U.S. Pat. No. 6,177,049 B1 suggests reversing flow through the draw access before treatment while an observer is present to test the accesses for patency or to clear blockage in the accesses. 
     Referring to  FIGS. 1A through 1E , a number of alternative designs for four-way valves have been developed for blood circuits. Referring to  FIG. 1A , U.S. Pat. No. 5,894,011, discloses a valve that swaps the connections between pairs of lines  905  and  906  via a pair of rotatably connected disks  901  and  902 , each of which supports one of the pairs of lines  905  and  906 . A seal must be maintained between the disks  901  and  902  and between the respective lines. The device is intended to be operated manually. 
     Referring to  FIG. 1B , another four-way valve, disclosed in U.S. Pat. No. 5,605,630, which has been proposed for use in blood lines, has a rotating wheel  910  with channels  911  and  912  defined between the wheel  910  and the inside of a housing  913 . When the wheel is rotated, the channels  911  and  912  shift to join a different pair of lines. This device also has seals. 
     Referring to  FIG. 1C , another arrangement is proposed in U.S. Pat. No. 6,177,049. This device has a rotating component  915  with channels  921  and  922  defined within it. As the rotating component  915  is rotated, the channels defined between pairs of lines  917  and  919  change from parallel lines joining one set of corresponding lines to U-shaped channels joining a different set. 
     Referring to FIGS.  1 D 1  and  1 D 2 , a design, disclosed in U.S. Pat. No. 4,885,087, is very similar to that of  FIG. 1B . This design has a rotator  925  that connects different pairs of lines depending on the position thereby defining two different sets of possible flow channels  926  and  929  or  927  and  931 . 
     In all of the above designs, the valves are not hermetically sealed. Any seal can be compromised, particularly by microorganisms. Thus, each of the foregoing designs suffers from that drawback. Also, many are expensive and do not lend themselves to automation. 
     Referring to  FIG. 1E , another type of four-way valve is formed by interconnecting two tubes  937  and  938  with crossover lines  935  and  936 . This design is disclosed in U.S. Pat. No. 6,189,388 (Hereafter, “U.S. Pat. No. &#39;388”). Tube pinching actuators  941 - 944  are used to force fluid through different channels, depending on which actuators are closed. This device provides a hermetic seal and can be fairly inexpensive, but in a given configuration, significant no-flow areas are defined. These dead spaces can lead to the coagulation of blood, which is undesirable. Also, the interconnection of tubes in this does not lend itself to automated manufacturing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A, 1B, 1C ,  1 D 1 ,  1 D 2 , and  1 E illustrate various flow reversing devices according to the prior art. 
         FIG. 2A  illustrates a flow circuit including a blood treatment machine and a sensor module. 
         FIG. 2B  illustrates a flow reversing portion of the blood treatment machine of  FIG. 2A . 
         FIG. 3A  illustrates a flow circuit including a blood treatment machine, a flow reversing module. 
         FIG. 3B  illustrates features of the flow reversing module of  FIG. 3A . 
         FIG. 3C  illustrates a flow circuit including a blood treatment machine, a flow reversing module, and a sensor module. 
         FIG. 3D  illustrates details of a sensor module. 
         FIG. 3E  illustrates a detail of a flow circuit with a flow reversing module and separate sensor modules. 
         FIG. 4A  illustrates a portion of a fluid circuit that is interoperable with an actuator to form a flow reversing device. 
         FIG. 4B  illustrates an actuator interoperable with the fluid circuit portion illustrated in  FIG. 4A . 
         FIGS. 5A and 5B  illustrate two operating modes of a flow reverser defined by the combination of the devices of  FIGS. 4A and 4B . 
         FIG. 6  illustrate a flow reversing actuator according to an alternative embodiment to that of  FIGS. 4A, 4B, 5A, and 5B . 
         FIG. 7  illustrates a flow reversing device according to an alternative embodiment to that of  FIGS. 4A, 4B, 5A, and 5B . 
         FIG. 8A  illustrates a sensor module embedded in a soft outer casing. 
         FIG. 8B  illustrates a compact longitudinal reversing module. 
         FIGS. 9A-9C  illustrate a first embodiment of a fluid circuit portion and an actuator for providing a compact longitudinal flow reverser. 
         FIGS. 10A and 10B  illustrate a second embodiment of an actuator for providing a compact longitudinal flow reverser. 
         FIG. 11  is a flow chart for describing a control embodiment in which blood flow is reversed according to multiple schedules. 
         FIG. 12  is a time plot of blood flow for use in describing the control regime of  FIG. 11 . 
         FIG. 13  is an illustration of stagnant flow regions for illustrating the flow control regime of  FIGS. 11 and 12 . 
         FIGS. 14A and 14B  illustrate control responses to air detection, according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to  FIG. 2A , a patient  130  is connected by an access  139  to a blood processing machine  315 . The latter draws blood through an arterial blood line  305  and returns treated blood to the patient  130  through a venous blood line  307 . The blood processing machine  315  may be any treatment device such as a hemodialysis machine, a hemofiltration machine, an infusion pump (in which case no arterial line  305  would be present), etc. 
     Access  139  may consist of various devices such as a fistula (not shown) and catheter (not shown) combination or other type of access which may be disconnected by various means. For example, a catheter (not shown) may be withdrawn from a fistula (not shown) and/or the catheter (not shown) disconnected from the arterial  307  and venous  305  lines by means of a luer connector (not shown). The above are conventional features of which a variety of alternatives are known. 
     One or more bubble or air sensors (not shown) are provided in a sensor module  311 . The sensor module  311  is connected to the blood processing machine  315  by means of a signal line  302 . The signal line  302  applies a signal indicating the presence of air or bubbles in one or both of the arterial  307  and venous  305  lines. The sensor module  311  may be lightweight snap-on module that clamps onto the arterial  307  and venous  305  lines. As is common in blood treatment systems, the arterial  307  and venous  305  lines are clear plastic such as PVC. The sensor module  311  may also include a sensor to indicate the presence of blood in the arterial  307  and venous  305  lines as well. The latter signal may be used for indicating and controlling a transition from a priming mode where the arterial  307  and venous  305  lines carry sterile fluid to a treatment mode where the arterial  307  and venous  305  lines carry blood. 
     Referring now also to  FIG. 2B , the blood processing machine  315  may include, along with various other hardware elements, a flow reversing valve  327 . The flow reversing valve  327  may be controlled by an electronic controller  323  to cause the flow through the arterial  307  and venous  305  lines to reverse. In a normal treatment mode, the flow may be as indicated by arrows  301 A and during a test mode, in which flow is reversed, blood flow may be as indicated by arrows  301 B. During both treatment and test modes, the flow of blood on the other side of the reversing valve  327  may remain as indicated by arrows  301 C. 
     During treatment, the reversing valve  327  is periodically actuated to place the reversing valve  327  in the test mode. This generates a negative gage pressure in the venous line  305 . If any leaks are present in the venous line  305  between the patient  130  and the sensor module  311 , air will infiltrate the venous line  305  and be detected by the air or bubble detector within the sensor module  311 . The resulting signal may be applied to the controller  323 . The controller  323  may be configured to respond by controlling one or more line clamps as indicated at  317  to stop the flow of blood and trigger an over-pressure alarm in the blood processing machine  315  if the latter is provided with one. The controller may also activate an alarm (not shown). The controller may alternatively maintain the test mode to continue flow in the reversed direction in which case, if the blood processing machine  315  is provided with an internal air or bubble detector (not shown), the latter will be triggered by the infiltrating air as if the air had been drawn by the arterial line in the first instance. 
     Although a flow reversing valve  327  is illustrated in  FIG. 2B , alternative mechanisms for generating a negative pressure in the venous line  305  as discussed in references incorporated by reference in the instant specification. Also, while one line clamp  317  is illustrated, more clamps may be employed to prevent the loss of blood. For example, a clamp may be provided in the venous line  305 . Note that the use of a sensor module  311  as illustrated allows the sensors to be located close to the patient. consequently, the system can respond quickly to a disconnection of the arterial  307  or venous  305  lines. One of the common types of leaks the system may protect against is an improperly installed or defective connection between the venous  305  or arterial  307  line and the catheter (not shown). 
     Referring now to  FIGS. 3A and 3B , a combined flow reversing and sensor module  333  houses a flow reversing valve  351  and at least one sensor  352 A. Flow through venous  325  and arterial  327  lines may be reversed in portions  337  and  335 , respectively, by reversing the flow reversing valve  351 . The sensor  352 A may include a bubble or air sensor, a blood sensor, or both. The sensor module  333  or any of the other sensor modules described herein may include other types of sensors such as pressure sensors to detect a loss of patency at any point in the system. In the foregoing embodiments, the blood or air (or bubble) sensors may include non-wetted conductivity sensors or non-wetted conductivity cells such as optical (opacity or hue) sensors or any sensor suitable for detecting the presence of air or blood in a clear liquid. The sensor module may also be used to detect other properties or conditions near the patient access such as a sudden acceleration (by means of an accelerometer) due to detachment and subsequent falling out of a catheter, for example. An additional sensor  352 B, which may be identical to sensor  352 A, may be employed to provide an indication of air infiltration during normal operation in a forward blood-flow direction. 
     A controller  349  may be provided to periodically control the flow reversing valve  351 . The controller may activate a line clamp  326 . The controller may respond to the detection of air in the same manner as described with respect to the foregoing embodiments or as described in the references incorporated in the instant specification, for example, by clamping the line. A signal line  329  may be provided to transmit detector and/or controller signals to the blood processing machine  320 . Blood processing machine  320  may be similar to that described with reference to the previous embodiments (e.g.  315  in  FIGS. 2A and 2B ), but preferably it does not include the reversing valve  351 . As in previous embodiment, in a normal treatment mode, the flow may be as indicated by arrows  301 A and during a test mode, in which flow is reversed; blood flow may be as indicated by arrows  301 B. During both treatment and test modes, the flow of blood on the other side of the reversing valve  351  may remain as indicated by arrows  301 C. 
     Referring now to  FIG. 3C , the blood processing machine  320 , the same as the one described with reference to  FIG. 3A , is linked by venous  373  and arterial  375  blood lines to a flow reversing module  370 . A sensor module  377  is located close to the access  139  and is coupled to the reversing module  370  by a signal line  378 . Venous  374 A and arterial  376 A lines link the reversing module  370  to the access  139  for supply and return flows of blood (with reference to the patient  130 ), respectively. Portions of venous  374 B and arterial  376 B lines pass through the sensor module  377  to the access  139 . The configuration of  FIG. 3C , as in the configuration of  FIGS. 2A and 2B  allows the sensor module  377  to be located close to the patient  130  and for the reversing module  370  to be retrofitted to a blood treatment machine  315  that is otherwise not configured for leak detection in the fashion described. Thus  FIGS. 3A-3C  are attractive for retrofit applications where leak detection capability is to be added to a blood processing machine  315  otherwise not configured for it. 
     Internally, the flow reversing module  370  may be identical to that shown in  FIG. 3B . The sensor(s)  352  may or may not be present to protect against leaks in the portions of the venous and arterial lines  374 A and  376 A as well as the portions  374 B and  376 B which are protected by sensors in the sensor module  377 . Note also that signal line  378  or any of the foregoing signal lines may represent wireless links, acoustical signal links, or any suitable means of communication. Also, the various devices may be powered by battery or by electrical lines. 
     Referring to  FIG. 3D , a sensor module  380  has features which may be employed in sensor modules  311  ( FIG. 2A ) and  377  ( FIG. 3C ) described above. Air detectors  401  and  407  detect air passing through lines  374  and  376 , respectively. Blood sensors  403  and  405  may be included in the sensor module  380  to detect blood in lines  374  and  376 , respectively. Note that in another embodiment, the sensor module  380  only contains sensors for a single line  374 , which is preferably the venous line of the foregoing embodiments. In yet another embodiment, the entire sensor module  380  is connected around a single line  374 , which is preferably the venous line of the foregoing embodiments. In the latter case, only the upper part  380 A is present and the other half  380 B on the other side of line  380 C is not present. Note that alternatively, both lines may be provided with separate sensor modules  390 A and  390 B in an alternative embodiment as illustrated at  FIG. 3E . Note also that two adjacent flow lines may be protected by a single air detector or blood detector or both. 
     A key  409  of any desired shape may be placed on one of the lines  374  or  376  which fits into a slot  411  and engages a detector  410  to indicate its proper insertion into the slot  411 . The key  409  and slot  411  ensure that if only one line  374  is protected by air sensor  401 , that it is the venous line. Otherwise the protection system wherein flow is reversed to indicate a leak would serve no purpose. The detector  410  may send a signal along the signal line  378  to indicate proper insertion. A failure of proper insertion while attempting to operate the system may cause the system to generate an alarm. A door  406  may be closed over the lines  374  and/or  376  to lock them in place. Electronic equivalents of key  409  and sensor  410  may also be provided. 
     Referring to  FIGS. 4A and 4B , in an embodiment of a compact and reliable flow reversing device, a portion of a fluid circuit  224  includes a toroidal portion  226  with ports A, B, C, and D linked by segments  221 A,  221 B,  221 C, and  221 D as illustrated. Fluid lines  203 ,  205 ,  207 , and  209  connect with respective ones of ports A, B, C, and D. The toroidal portion and portions of fluid lines  203 ,  205 ,  207 , and  209  fit into channels  211 ,  215 ,  211 , and  217  of an actuator  221 . The actuator  221  contains a rotatable clamp  222  with two edges  238  and  237  which selectively pinch segments  221 A,  221 B,  221 C, and  221 D between the edges  238  and  237  and edges  231 ,  229 ,  235 , and  233  of the actuator  221 , respectively as illustrated in  FIGS. 5A and 5B . 
     Referring now to  FIG. 5A , the toroidal portion  226  may be of a compliant and stretchable material that permits it to be forced into position in the actuator  221  and partly deformed as illustrated. The clamp  22  may be in the neutral position illustrated in  FIG. 4B  when this is done. During operation, when clamp  222  is in a first position indicated in  FIG. 5A , segments  221 B and  221 D are clamped closed allowing a flow between line  209  to  207  and from line  205  to line  203  as indicated by arrows  225 A and  227 A. As will be observed, segment  221 B is pinched between edges  238  and  231  while segment  221 D is pinched between edges  237  and  235 . The path of lines  209  to  207  may correspond to flow through the venous lines of the previous embodiments. For example, with reference to  FIG. 3A , line  209  may correspond to line  325  and line  207  to line  337 . Similarly, the path of lines  205  to  203  may correspond to flow through the arterial lines of the previous embodiments. For example, with reference to  FIG. 3A , line  205  may correspond to line  335  and line  203  to line  329 . In the configuration of  FIG. 5A , the flow may then provide for normal blood flow for treatment by allowing  207  to flow blood to a patient and return through line  205  to pass through the flow reverser back to a blood treatment machine. 
     Referring now to  FIG. 5B , when clamp  222  is in a first position indicated in  FIG. 5B , segments  221 A and  221 C are clamped closed allowing a flow between line  209  to  205  and from line  207  to line  203  as indicated by arrows  225 B and  227 B. In the configuration of  FIG. 5B , the flow may then provide for reverse blood flow for testing by allowing line  205  to flow blood to a patient and return through line  207  to pass through the flow reverser back to a blood treatment machine. This results in a negative pressure in line  207  whereupon if any disconnections or leaks occur, air will be drawn into line  207  which may be revealed by a sensor, as discussed with reference to the figures above. 
     Referring now to  FIGS. 6 and 7 , in alternative embodiments of the flow reverser of  FIGS. 5A and 5B  a clamp  427  may be passively mounted on a door  424  and engaged with a drive bolt  443  in a chassis portion  421  of a flow reverser. The drive bolt  443  may fit as a key in a recess  441  thereby driving the clamp. The closure of the door  424  may be indicated by a detector which may send a signal to a controller permitting the drive bolt  443  to be operated according to the configuration of a controller (e.g.,  349  of  FIG. 3B ). Instead of a single rotating clamp located at a center of a flow reverser, respective clamps  451 A,  451 B,  451 C, and  451 D may pinch respective portions of the flow circuit toroidal portion  226  by means of a shaped boss  449  that fits into the center of the toroidal portion  226 . The claims  451 A,  451 B,  451 C, and  451 D may be operated by respective drives such as solenoids (not shown) or coupled to be operable with one or two drives as desired. 
     Referring to  FIG. 8A , to permit a flow reverser or sensor module to be placed close to the patient but allow for patient comfort, the flow reverser or sensor module  379  may be fitted into a soft shell  501 . The latter may have a shape such as a teddy bear or other stuffed animal or ornament. 
     Referring to  FIG. 8B , preferably the flow reverser is of a compact longitudinal shape with the lines  667  and  669  leading to the blood treatment machine stemming from one end and the lines and the lines  663  and  665  leading to the patient access stemming from the opposite end. This may allow the flow reverser  661  to lie close to the patient access and self-orient in a comfortable and unobtrusive manner. 
     Referring to  FIGS. 9A, 9B, and 9C , two Y-junctions  503  and  505  may be connected to a patient access and two other Y-junctions may be connected to a blood treatment machine or remainder thereof. Two double edged clamps  519  and  521  are driven by a double-axis motor drive  527  that rotates one clamp  519  in one direction and the other clamp  521  in the opposite direction, for example by providing that one clamp is connected to the stator and one connected to the rotor of the motor. It is contemplated that a reduction drive would be employed to increase the torque of the primary motor within the drive  527  and allow a small motor (not shown separately) to be used. A support stalk  502  holds the drive  527  so that it is free to rotate with respect to it, thereby providing a mounting to a housing such as illustrated in  FIG. 8B . Each segment  511 ,  513 ,  515 , and  517  may be selectively pinched by as illustrated in  FIGS. 9B and 9C  to provide for forward and reverse flow between one pair of junctions  505 / 503  or  509 / 507 . The clamps may be tapered to provide a high clamping pressure as indicated at  535 ,  533 ,  523 , and  525  and similarly on portions opposite the edges indicated at  535 ,  533 ,  523 , and  525 . 
     Note that the tubing structure of  FIG. 9A  which includes parallel segments  511 ,  513 ,  515 , and  517 , and the four Y-junctions  503  and  505 ,  507 , and  509 , is toroidal in shape, which can be confirmed by inspection. It will be observed that a planar projection (that is, a mapping or projection, as of a shadow, onto a plane, as of a shadow onto a surface) of the structure  511 ,  513 ,  515 , and  517 ,  503 ,  505 , and  507  with a plane perpendicular to parallel segments  511 ,  513 ,  515 , and  517  and a projection direction parallel to parallel segments  511 ,  513 ,  515 , and  517 , is shaped as a ring. 
     Referring to  FIGS. 10A and 10B , another flow reversing device using a fluid circuit portion as illustrated in  FIG. 9A  producing four parallel segments  511 ,  513 ,  515 , and  517  is driven by a linear drive (not shown) that moves a stalk  607  along an axis thereof. Cams  617  and  619  are forced into an opposing pair of tube segments  605  and  611  when a large diameter portion  627  of the stalk  607  is forced between the cams  617  and  619  by pushing the stalk  607  in a first direction (to the left). Cams  617  and  619  are forced into an opposing pair of tube segments  633  and  635  when a large diameter portion  627  of the stalk  607  is forced between the cams  610  and  621  by pushing the stalk  607  in a second opposite direction (to the right). The segments may be held in position by a frame of two portions  613  and  615  which close around a cam frame  607 . Edges  609  and  611  are provided to amplify the pinching stress and cooperative with cams  617  and  619  to clamp the tubes segments  603  and  609 . 
     Referring to  FIG. 11 , an operating regimen begins with a priming of a fluid circuit at step S 10 . The priming mode is initiated by a priming command being received by the flow reverser controller at step S 10 . The flow reverser controller places the flow reverser in forward mode so that fluid is pumped in a single direction. The controller may be configured to operate for flow in a single direction continuously as long as no blood is detected by blood sensors in the sensor module or in the blood treatment machine. The pump may be operated at step S 20  for a desired period of time to prime the blood circuit and other portions of the fluid circuit used for treatment. At some point during the priming mode, the operator may halt the pump, clamp various lines, and make certain connections in preparation for treatment and restart the pump. All these steps are assumed to fall within step S 20 . 
     When the flow reverser controller detects blood in step S 25 , control flow exits to step S 30  and flow continues in the same direction for a specified period of time which may be proportional to the mass flow rate of blood. The blood will ordinarily be detected because of the connection changes of the operator who has determined that the system is adequately primed and has remade connections as required. This may also be an automated process as well depending on the blood processing system and the level of automation. Referring now also to  FIG. 12 , once the initial forward operation period has elapsed at step S 30 , the flow reverser control may go into an operating mode where it periodically reverses flow  830  for a fixed interval test cycle  820  to generate a temporary negative pressure and reverse flow to test the venous line and then returns to forward operation  835 . Generally, the test cycle  820  interval will be shorter than the normal forward treatment  825  interval. In addition to the test cycle, short duration reverse cycles  810  are a higher frequency may be included to clear the dead legs of the flow reversing device. Referring momentarily to  FIG. 13 , the shaded regions  815  in the embodiment of  FIGS. 5A and 5B  in the normal flow direction represent areas with no flow. If the blood in these regions is allowed to stagnate for an extended time, clotting may occur. To help prevent this, the flow may be reversed for very short intervals to cause a flow in these otherwise continuously non-flow regions  855 . A train of such dead-leg clearing cycles is shown in  FIG. 12  at  810 . 
     Returning to  FIG. 11 , the cyclical operation of  FIG. 12  may continue until a treatment is completed or until air is detected (or some other malfunction causes treatment to be terminated). For retrofit embodiments of the flow reversing leak detection system such as illustrated in  FIGS. 3A and 3C  for example, it is desirable for the flow reversing controller to respond to air detection in a manner that ensures an appropriate response without some sort of control connection or control collaboration between the flow reversing module (e.g.  370 ,  FIG. 3C ) and the blood treatment machine  320 . Thus, preferably the flow reversing module control&#39;s  349  response should ensure appropriate action. Referring now to  FIG. 14A , to that end a response S 45 A for step S 45 , when air is detected at step S 40 , the blood lines may be clamped at step S 60  to induce a high pressure in the blood treatment machine which in most type of blood treatment machines would trigger a shutdown and error indication by the machine. This may be provided by means of a clamp as indicated at  326  or  317  in  FIGS. 3B and 2B  respectively, for example. Referring to  FIG. 14B , another response for step S 45  is step S 45 A in which a shutdown by the main processing machine is induced in step S 65  to continue operating in reverse mode until the air that was detected by the flow reversing module triggers an air detection by the blood processing machine. 
     Note that by placing the air sensor close to a patient as described in the foregoing embodiments, the reverse cycle may be kept to a minimum duration. Preferably this duration is established to provide the minimum volume displacement needed to cause any air bubbles leaking into the blood line to reach the air sensor in the sensor module. This may be established in the flow reverser by means of an input from a user or by calculating from a measured flow rate. Thus, a flow rate sensor may be included in the flow reversing module and the controller configured to calculate the amount of time, based on flow rate, to ensure the minimum volume is displaced.