Abstract:
A medical treatment procedure and system that makes use of a bidirectional flow sensor unit to monitor, detect, and control the flow of one or more fluids to and from a patient. The sensor unit measures both flow rate and flow direction of a fluid of a conduit through which a first fluid flows to or from the patient in a first direction, and through which it is possible that the first fluid or a second fluid may flow in a reverse direction through the conduit from or to, respectively, the patient. The sensor unit measures the flow rate of the first fluid as the first fluid flows through the bidirectional flow sensor unit, and senses if the first fluid or the second fluid flows through the bidirectional flow sensor unit in the reverse direction. A signal is relayed to indicate the occurrence of a reverse flow condition.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of U.S. Provisional Application No. 60/639,406, filed Dec. 27, 2004, and U.S. Provisional Application No. 60/721,220, filed Sep. 29, 2005. The contents of these prior applications are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     The present invention generally relates to medical treatment systems that deliver fluids to a patient. More particularly, this invention relates to a bidirectional flow sensing device for use in medical treatment systems adapted to deliver one or more fluids to perform an infusion, transfusion, perfusion, catheterization, dialysis, respiration, or anesthetization procedure, and which may unintentionally or intentional entail bidirectional flow through a conduit delivering the fluid.  
         [0003]     A variety of drug infusion pumps, blood perfusion systems, dialysis, and catheter systems have been developed over the years that make use of elastomeric, gravity fed, syringe, electrical, and mechanical pumps. Valves and flow sensors have been incorporated into some infusion pump designs to improve dosage accuracy and control the flow of drugs from the system. Micromachined flow sensors, valves, and pumps have been developed that can replace traditional flow sensors, valves, and pumps used in drug delivery systems. A notable example of a micromachined flow sensor is commonly-assigned U.S. Pat. No. 6,477,901 to Tadigadapa et al.  
         [0004]     Various medical treatments entail intentionally delivering or withdrawing a fluid from a patient through a conduit, examples of which include but are not limited to drug infusion, blood transfusion, perfusion, catheterization, kidney dialysis, respiration assistance and monitoring, and delivery of anesthetics. In each case, a fluid (e.g., a drug, blood, urine, oxygen, expiration, anesthetic, etc.) is passed through a conduit to or from a patient. Such treatments may, either intentionally or unintentionally, result in both delivery and withdrawal of fluids. Examples of intentional withdrawal and delivery of fluids include dialysis, respiration assistance with oxygen, delivery of anesthetics, and retrograde infusion, transfusion, and perfusion procedures in which a body fluid is withdrawn, treated or supplemented, and then returned to the body. Retrograde drug infusion can also be employed to delivery multiple drugs that may otherwise be incompatible. Examples of unintentional withdrawal and delivery of fluids include drug infusion procedures during which, for one reason or another, body fluids are withdrawn through the conduit intended to delivery the drug, in which case bidirectional fluid flow occurs within the conduit.  
         [0005]     A number of medical problems may arise during procedures in which fluids are both withdrawn and delivered to a patient, such as air embolisms and high blood pressure as a result of inadequate control and accuracy of fluid flow, especially in neonatal and pediatric applications. In the past, flow rate measurements have been typically performed by ultrasonic flow sensors, optical sensors, and volumetric containers. To reduce the risk that a fluid will be improperly delivered or withdrawn, additional sensors, equipment, and procedures have been used to monitor the efficiency and progress of such procedures, including pressure sensors, air bubble detectors, temperature monitors, etc., each usually as a separate individual sensor. However, accurate flow measurement remains a challenge, particularly if bidirectional flow is or may be encountered.  
       BRIEF SUMMARY OF THE INVENTION  
       [0006]     The present invention provides a medical treatment procedure and system that make use of a bidirectional flow sensor to monitor, detect, and/or control the flow of fluids to and from a patient, as in the case of certain infusion, transfusion, and perfusion procedures, dialysis, respiration assistance and/or monitoring, and delivery of anesthetics. More particularly, the invention utilizes a bidirectional flow sensor unit to measure both flow rate and flow direction of a fluid. In treatments where bidirectional flow through a conduit is not desired, such as dialysis and infusion, transfusion, perfusion procedures, the bidirectional flow sensor unit can be used to detect, measure (if desired), and provide an appropriate warning of reverse (retrograde) flow of a fluid being delivered or withdrawn. In cases where both withdrawal and delivery of one or more fluids are desired, such as retrograde infusion, transfusion and perfusion procedures, respiration, and anesthetization, the bidirectional flow sensor unit allows the flow rate and flow direction to be measured and, when coupled with appropriate fluid control devices, controlled.  
         [0007]     The procedure of this invention includes placing a conduit for flowing a first fluid to or from a living body in a first direction and through which it is possible that the first fluid or a second fluid may flow in a reverse direction through the conduit from or to, respectively, the living body. A bidirectional flow sensor unit is fluidically coupled to the conduit so that the first fluid and optionally the second fluid are able to flow therethrough in the first and reverse directions. The bidirectional flow sensor unit comprises means for sensing the flow rate and flow direction of the first fluid and optionally the second fluid flowing through the bidirectional flow sensor unit. The sensing means is then used to measure the flow rate of the first fluid as the first fluid flows through the bidirectional flow sensor unit, and sense if the first fluid or the second fluid flows through the bidirectional flow sensor unit in the reverse direction. A signal is then relayed to indicate the occurrence of the first fluid or the second fluid flowing through the bidirectional flow sensor unit in the reverse direction.  
         [0008]     The system of this invention includes a conduit placed for flowing a first fluid to or from a living body in a first direction and through which it is possible that the first fluid or a second fluid may flow in a reverse direction through the conduit from or to, respectively, the living body. A bidirectional flow sensor unit is fluidically coupled to the conduit so that the first fluid and optionally the second fluid are able to flow therethrough in the first and reverse directions. The bidirectional flow sensor unit comprises means for sensing the flow rate and flow direction of the first fluid and optionally the second fluid flowing through the bidirectional flow sensor unit. The system further includes means for relaying a signal indicating the occurrence of the first fluid or the second fluid flowing through the bidirectional flow sensor unit in the reverse direction.  
         [0009]     A significant advantage of this invention is that various sensors and devices previously required in medical treatment procedures and systems to measure fluid flow rates and monitor or safeguard against retrograde flow can be replaced by a bidirectional flow sensor unit capable of accurately sensing both. In the context of a treatment where bidirectional flow through the same conduit is not desired, such as dialysis and infusion, transfusion, perfusion procedures, the bidirectional flow sensor unit can be used to detect, measure (if desired), and provide an appropriate warning of reverse (retrograde) flow of a fluid being delivered or withdrawn. In the context of a treatment where both withdrawal and delivery of one or more fluids are desired, such as retrograde infusion, transfusion and perfusion procedures, respiration, and anesthetization, the bidirectional flow sensor unit allows the flow rate and flow direction to be measured, monitored, and, if coupled with appropriate fluid control devices, controlled.  
         [0010]     Other objects and advantages of this invention will be better appreciated from the following detailed description. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  is a schematic representation of a fluid delivery system mounted to an intravenous pole and adapted to infuse, transfuse, or perfuse a drug, blood, or other bodily or medicinal fluid through an intravenous tube in accordance with certain embodiments of the invention.  
         [0012]      FIGS. 2 and 3  are schematic representations of systems adapted to assist and/or monitor respiration and/or deliver an anesthetic in accordance with additional embodiments of the invention.  
         [0013]      FIG. 4  is a perspective view of a bidirectional flow sensing unit for use in the treatment system of  FIG. 1 .  
         [0014]      FIGS. 5 and 6  are perspective and cross-sectional views, respectively, of a Coriolis-type mass flow rate sensor suitable for use in the sensing unit of  FIG. 2 .  
         [0015]      FIGS. 7 through 9  illustrate the Coriolis effect on the sensor of  FIGS. 4 and 5 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0016]      FIG. 1  represents a medical treatment system  10  that can be employed in an infusion, transfusion, perfusion, or dialysis procedure. The system  10  is shown as comprising a console  14  mounted to a pole  16 , alongside which a tube  18  is secured for delivering or withdrawing a fluid from a patient. As an example, the tube  18  may be an intravenous (IV) tube or other suitable conduit suitable for the treatment being performed, and terminated with any suitable delivery device, such as a cannula, catheter, etc. As will be appreciated by those skilled in the art from the following discussion, the fluid may be a medicinal drug, nutritional solution, or body fluid if the procedure is an infusion, transfusion, perfusion treatment, blood if the procedure is a dialysis treatment, etc. A sensor unit  12  is fluidically in line with the tube  18  and communicates with the console  14  through a connector  20 . According to a preferred embodiment of the invention, the sensing unit  12  is a bidirectional flow sensor unit  12 , such as of a type represented in  FIG. 4  and described in greater detail below. Suitable electronic circuitry (not shown) for communicating with the sensor unit  12  may be located on the unit  12  or console  14 . The console  14  is equipped with a display  22  for providing a visual indication of the operation of the system  10 . An AC power cord (not shown) or rechargeable battery (not shown) may be employed to power both the console  14  and the sensor unit  12 . The console  14  is also shown as being equipped with audible and visual alarms  24  for warning nearby caregivers of any errors encountered during operation of the system  14 , e.g., an improper flow rate, flow direction, or fluid density for the fluid flowing through the tube  18 , as well as other appropriate notifications that can be initiated by the sensor unit  12 . The console  14  can be further equipped with other warning indicators and controls, such as a low battery warning light, reset/confirm buttons, etc. A flow device  26  is shown as being mounted to the side of the console  14 . Depending on the particular operation mode of the system  10 , the flow device  26  may be a shut-off valve for stopping flow of the fluid through the tube  18  in response to the output of the sensor unit  12  or console  14 , or a pump to induce and/or reverse flow through the tube  18 . The console  14  is preferable connected to a computer  28  by which the operation and status of the console  14  can be controlled and monitored. While the sensor unit  12 , console  14 , and computer  28  are represented as physically interconnected for communication, it is also within the scope of this invention that wireless communication techniques could be used, including IR, RF, optical, magnetic, etc.  
         [0017]     A preferred configuration for the sensing unit  12  of this invention is represented in  FIG. 4 . The unit  12  is shown as comprising a housing  44  adapted for inline installation, though other configurations are also possible and within the scope of this invention. The housing  44  is formed to have a fluid inlet  46  and outlet  48 , both of which can be adapted for a fluidic connection through such fittings as a Luer, threaded, compression, barbed, lock or other type of fitting. The housing  44  contains a sensor  50  and electronic circuitry  52  located and enclosed within a cavity defined within the housing  44  and closable with a cover (not shown). The sensor  50  is the structure through which the fluid flowing through the tube  18  is sensed, and is therefore adapted to provide a measurable response to various properties of the fluid, which in accordance with the invention include at least the flow rate and flow direction of the fluid through the sensor unit  12 . The circuitry  52  is preferably configured to communicate with and control the sensor  50  and output information regarding the operation of the sensing unit  12  to the console  14 . The unit  12  further includes an electrical connector  54  by which the circuitry  52  can be coupled to the console  14 , as well as to a computer or another suitable electronic device capable of controlling and receiving signals from the sensing unit  12 . As noted above, an alternative to the connector  54  is a wireless communication device. Power for the sensor  50  and circuitry  52  can be provided with a battery (not shown) within the housing  44 , delivered through a cable connected via the connector  54 , or delivered telemetrically using known tele-powering techniques. The console  14  is equipped with a display  22  for providing a visual indication of the operation of the system  10 . An AC power cord (not shown) or rechargeable battery (not shown) may be employed to power both the console  14  and the sensor unit  12 . Similar to the console  14 , the sensor unit  12  can be equipped with a display, audible and visual alarms in response to the operation of the unit  12 , power indicators, reset/confirm buttons, etc.  
         [0018]     The sensor  50  is represented as comprising a tube  56  that serves as a conduit through which the fluid flows as it flows between the inlet  46  and outlet  48  of the housing  44 . In a preferred embodiment of the invention, the sensor  50  and its tube  56  are part of a Coriolis mass flow sensor.  FIGS. 5 and 6  depict a preferred Coriolis mass flow sensor  50  taught in commonly-assigned U.S. Pat. No. 6,477,901 to Tadigadapa et al., whose discussion of the construction and operation of a Coriolis flow sensor is incorporated herein by reference. In Tadigadapa et al., wafer bonding and silicon etching techniques are used to micromachine the tube  56  and its freestanding portion  58 , which is suspended over a silicon substrate  60 . While the freestanding portion  58  of the tube  56  is represented as generally U-shaped, other shapes, both simpler and more complex, are within the scope of this invention. In accordance with Tadigadapa et al, the freestanding portion  58  can be vibrated in a direction perpendicular to the underlying surface of the substrate  60 . Fluid flows through an internal passage  62  within the tube  56 , and enters and exits the tube  56  through fluid inlet and outlet passages (one of which is identified with reference number  64  in  FIG. 6 ) provided in the substrate  60 . During half of the vibration cycle in which the freestanding portion  58  of the tube  56  moves upward, the freestanding portion  58  has upward momentum as the fluid travels around the tube bends, and the fluid flowing out of the freestanding portion  58  resists having its vertical motion decreased by pushing up on that part of the freestanding portion  58  nearest the fluid outlet. The resulting force causes the freestanding portion  58  of the tube  56  to twist. As the tube  56  moves downward during the second half of its vibration cycle, the freestanding portion  58  twists in the opposite direction. This twisting characteristic, illustrated in  FIGS. 7 through 9 , is referred to as the Coriolis effect. As explained in Tadigadapa et al., the degree to which the freestanding portion  58  of the tube  56  twists (deflects) during a vibration cycle as a result of the Coriolis effect can be correlated to the mass flow rate of the fluid flowing through the tube  56 . In addition, the density of the fluid is proportional to the natural frequency of the fluid-filled freestanding portion  58 , such that controlling the vibration of the portion  58  to maintain a frequency at or near its resonant frequency will result in the vibration frequency changing if the density of the fluid flowing through the tube  56  changes.  
         [0019]     The resonant frequency of the freestanding tube portion  58  is determined in part by its mechanical design (shape, size, construction and materials). Suitable frequencies are in the range of 1 kHz to over 100 kHz, depending on the particular fluid being analyzed. Under most circumstances, frequencies above 10 kHz, including ultrasonic frequencies (those in excess of 20 kHz), will be preferred. The amplitude of vibration is preferably adjusted through means used to vibrate the tube portion  58 . For this purpose,  FIG. 5  shows an electrode  66  located beneath the freestanding portion  58  on the surface of the substrate  60 . In the embodiment shown, the tube  56  serves as an electrode (e.g., is formed of doped silicon) that is capacitively coupled to the electrode  66 , enabling the electrode  66  to electrostatically drive the freestanding portion  58 . However, it is foreseeable that the tube  56  could be formed of a nonconductive material, requiring a separate electrode formed on the freestanding portion  58  opposite the electrode  66  for vibrating the freestanding portion  58  electrostatically. Furthermore, the freestanding portion  58  could be driven capacitively, piezoelectrically, piezoresistively, acoustically, ultrasonically, magnetically, optically, or by another actuation technique. Also shown in  FIGS. 5 and 6  are sensing electrodes  68  for providing feedback to enable the vibration frequency and amplitude to be controlled with the circuitry  52  within the sensing unit  12 . While capacitive sensing is preferred, the sensing elements  68  could sense the proximity and motion of the freestanding portion  58  in any other suitable manner.  
         [0020]     In order to provide a temperature-sensing capability, the sensor  50  is shown in  FIG. 5  as including an on-chip thin film temperature sensor  72 , such as a resistance temperature detector (RTD), in close proximity to the resonating tube  56 . The temperature sensor  72  is shown integrated onto the same substrate  60  as the tube  56  to provide an accurate fluid temperature output, which in addition to providing useful temperature data also enables temperature to be factored into the fluid density measured by the sensor  50 . Alternatively, a temperature sensing capability can be achieved by fabricating a second cantilevered tube on the substrate  60 . According to commonly-assigned U.S. Pat. No. 6,647,778 to Sparks, vibrating the cantilevered tube at resonance enables the tube to measure the temperature of the fluid flowing therethrough on the basis that the Young&#39;s and shear modulus of the materials used to form the tube change with temperature, causing the resonant frequency of the tube to detectably shift with temperature.  
         [0021]      FIG. 6  schematically represents the micromachined tube  56  enclosed by a cap  70  bonded or otherwise attached to the substrate  60 . In a preferred embodiment, the bond between the cap  70  and substrate  60  is hermetic, and the resulting enclosure is evacuated to enable the freestanding portion  58  to be driven efficiently at high Q values without damping. A suitable material for the cap  70  is silicon, allowing silicon-to-silicon bonding techniques to be used, though other cap materials and bonding techniques are possible and within the scope of the invention.  
         [0022]     As discussed above and represented in  FIGS. 7 through 9 , the direction of twist of the freestanding portion  58  depends on the direction of fluid flow through the tube  56 . In accordance with this invention, the circuitry  52  and sensing elements  68  of the sensor  50  cooperate to sense the direction of twist of the tube  56  relative to the drive electrode  66  or phase differences between the laterally opposite side portions of the tube  56  or other parts of the tube resulting from the Coriolis effect, which can then be correlated to the direction of flow through the tube  56  and, therefore, the sensor unit  12  containing the tube  56 . As such, it can be appreciated that the resonating tube flow sensor  50  is well suited for use in the sensing unit  12  of this invention for the purpose of sensing both flow rate and flow direction, though it is foreseeable that other types of flow sensors could be employed, such as hot-wire, thin-film, drag force, ultrasonic, pressure, or another type of flow sensor. However, particularly advantageous aspects of the resonating tube sensor  50  include its very small size, its ability to precisely measure extremely small amounts of fluids, and, of particular interest to the present invention, its ability to sense bidirectional fluid flow, in contrast to prior art flow sensors that, if not inherently bidirectional, would require the use of more than one flow sensor per tube  18  to provide a bidirectional capability. Furthermore, the preferred flow sensor  50  can attain flow rate measurement accuracies of under ±1%, in contrast to other types of infusion pumps whose accuracies can range from about ±15% for volumetric pumps and ±3% for syringe pumps. While the high cost and the high flow rate requirements for prior art Coriolis-type flow sensors have restricted their use in the drug delivery arena, the flow sensor  50  is able to sense the extremely low flow rates (e.g., less than 1 ml/hr) required by infusion therapy applications, and can be used to sense the flow rates associated with the treatment system  10  of  FIG. 1 .  
         [0023]     From the above, it can be appreciated that sensor units  12  equipped with the sensor  50  can be advantageously employed in the treatment system  10  of  FIG. 1 . If a fluid is being delivered, the sensing unit  12  is placed downstream of any type of drug delivery device, including but not limited to an IV bag, IV set, peristaltic pump, syringe, syringe pump, electromechanical pump, pressurized pump, implanted pump, etc., enabling the flow rate of the fluid to be accurately monitored to ensure a proper amount of fluid is delivered. Dose and dose rates can also be calculated based on the flow rate measured with the sensor unit  12 . With the addition of one or more sensor units  12 , multiple fluids can be delivered with the treatment system  10 . In addition to sensing the flow rate of the fluid flowing through the tube  18 , and therefore being administered to or withdrawn from a patient, the sensor  50  is able to sense in which direction the fluid is flowing, either in the intended direction or the reverse direction, by sensing the direction of twist of the freestanding portion  58  of the sensor tube  56 . As such, if bidirectional flow through the fluid tube  18  is not desired, such as during dialysis and infusion, transfusion, perfusion procedures, the sensor unit  12  can be used to detect, measure (if desired), and provide an appropriate warning of reverse (retrograde) flow of the fluid occurs, such as with the alarm  24  of the console  14 . Alternatively, if the tube  18  is intended to selectively withdraw and deliver of one or more fluids, such as during a retrograde infusion, transfusion or perfusion procedure, respiration assistance and monitoring, and delivery of anesthetics, the sensor unit  12  allows the flow rate and flow direction of the one or more fluids to be measured, monitored, and, if coupled with appropriate fluid control devices, controlled. In view of these benefits, the sensor unit  12  of this invention can be employed to improve the safety of a variety of medical treatment procedures, especially for neonatal and pediatric applications in which dose sensitivity is particularly critical. The sensor unit  12  also enables multiple drugs to be delivered with a single conduit  18  through the ability to detect barrier solutions delivered between incompatible drugs based on changes in density (as indicated by changes in the resonant frequency of the sensor tube  56 ).  
         [0024]     The above-noted density and temperature-sensing capabilities of the sensing unit  12  can also be utilized with the present invention to sense and monitor the specific gravity/density of the fluid to confirm that the correct fluid, drug concentration, etc., is being delivered or withdrawn, as well as detect the presence of undesired components in the fluid. In particular, the sensing unit  12  can be sufficiently sensitive to detect occlusions and fine air bubbles that could cause air embolisms, as reported in commonly-assigned U.S. patent application Ser. Nos. 10/248,839 and 10/708,509.  
         [0025]     Because micromachining technologies are employed to fabricate the sensor tube  56 , the size of the tube  56  can be extremely small, such as lengths of about 0.5 mm and cross-sectional areas of about 250 square micrometers, with smaller and larger tubes also being within the scope of this invention. Because of the ability to produce the sensor tube  56  at such miniaturized sizes, the sensor unit  12  can be used to process very small quantities of fluid for analysis. However, because miniaturization can render the sensor  50  unsuited for applications in which measurements of properties are desired for a fluid flowing at relatively high flow rates, the sensor  50  can be configured to have an internal bypass passage in accordance with the teachings of commonly-assigned U.S. patent application Ser. No. 11/164,374, whose teachings regarding the fabrication of bypass passages are incorporated herein by reference.  
         [0026]     Illustrated in  FIG. 2  is another system  30  configured in accordance with this invention to employ the bidirectional flow sensor unit  12 . The system  30  differs from the system  10  of  FIG. 1  in the manner in which it is specifically adapted to both deliver and withdraw one or more fluids within the same conduit. As represented, the system  30  is adapted to assist and/or monitor the respiration of a patient, including such procedures as supplying and monitoring supplemental respiratory oxygen, monitoring and/or preventing sleep apnea, and delivering an anesthetic to a patient. A source  32  of a breathable gas mixture, oxygen, or anesthetic is shown fluidically interconnected with the bidirectional flow sensor unit  12  of this invention through a suitable conduit  34 . In turn, the sensor unit  12  is connected through a pair of tubes  36  to a cannula  38 , which is represented as being a nasal cannula though other delivery devices could be used, such as a throat, mouth, or trachea cannula. Flow of the gas mixture, oxygen, or anesthetic from the source  32  is preferably regulated with a suitable device (not shown) controlled with a controller  42  that also communicates with the sensor unit  12 . As a patient inhales through the cannula  38 , the gas mixture, oxygen, or anesthetic is drawn through the sensor unit  12  and tubes  36 . During exhalation, the patient&#39;s expiration may also be exhaled through the tubes  36  and the sensor unit  12  before being exhausted through an outlet  40  on the sensor unit  12 , with the result that the sensor unit  12  is not only able to sense flow rate, but also detect the change in flow direction and, if so desired, provide an appropriate output, such as a visual or audible signal generated on the sensor unit  12  or by the controller  42 , indicating a change in flow direction and therefore the completion of a respiration cycle. Because of the typically limited flow capacity of its sensor tube  56 , the sensor unit  12  used in the embodiment of  FIG. 2  is preferably configured with a bypass passage such that only a fraction of the gases being inhaled and exhaled passes through the sensor tube  56 .  
         [0027]      FIG. 3  shows another embodiment of the system  30 , in which the sensor unit  12  is coupled to the conduit  34  and tubes  36  with a bypass tube  43  connected with a splitter on the conduit  34 . The bypass tube  43  is equipped with a filter  45  that prevents bacteria, viruses, etc., exhaled by the patent from contaminating the sensor unit  12 . In this manner, the conduit  34 , tubes  36 , cannula  38 , bypass tube  43 , and filter  45  constitute a disposable unit while the sensor unit  12  is reusable.  
         [0028]     With each embodiment of  FIGS. 2 and 3 , the flow rates of the inhalation and exhalation of the patient can be monitored, as well as the frequency of the patient&#39;s breaths as sensed by a change in the direction of flow through the sensor unit  12 . The temperature sensor  72  on the sensor  50  further permits the temperature of the patient&#39;s exhalation to be monitored. Because of the ability of the sensor unit  12  to measure density, the sensor unit  12  is also capable of monitoring the gas mixtures inhaled and exhaled by the patient.  
         [0029]     In view of the foregoing, it can be appreciated that the present invention is also applicable to other treatment systems in which one or more fluids are delivered to or withdrawn from the human body, including retrograde (reverse) infusion, transfusion, and perfusion procedures. In such applications, both the delivery and withdrawal of the fluids can be controlled in a closed-loop system through the fluid sensor  12 , controller  42 , and appropriate devices under the control of the controller  42 , such as valves, pumps, motors, fluid actuators, etc.  
         [0030]     While the invention has been described in terms of a preferred embodiment, it is apparent that other forms could be adopted by one skilled in the art. Therefore, the scope of the invention is to be limited only by the following claims.