Patent Publication Number: US-6336902-B1

Title: System for sensing a characteristic of fluid flowing to or from a body

Description:
This is a continuation of application Ser. No. 08/359,082, filed Dec. 14, 1994 now abandoned, which is a continuation of application Ser. No. 08/193,672, filed Feb. 7, 1994, now abandoned, which is a continuation of Ser. No. 08/071,612, filed Jun. 4, 1993, now abandoned, which is a continuation of Ser. No. 07/780,051, filed Oct. 21, 1991, now abandoned, which is a continuation of Ser. No. 06/786,999, filed Oct. 15, 1985, which is a continuation of Ser. No. 06/741,396, filed Jun. 5, 1985, now abandoned, which is a continuation of Ser. No. 06/399,330, filed Jul. 19, 1982, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     It is often necessary or desirable to measure the cardiac output of a patient. A common technique for accomplishing this is to inject a known volume of an injectate, such as a saline solution, into the right atrium. The injectate has a known temperature and it mixes with the blood to produce a temperature drop in the blood. The temperature of the blood is monitored at a suitable location downstream of the right atrium, and the data obtained can be used to determine cardiac output. This technique is commonly referred to as thermodilution, and the injection of the injectate and the downstream temperature measurement are carried out by a thermodilution catheter. 
     It is known to obtain the upstream temperature measurement of the injectate using a thermistor permanently mounted in the conduit which supplies the injectate. Although this system functions satisfactorily, it is necessary that the thermistor be initially sterile and be discarded after each usage. This increases the cost of using the thermodilution technique because the thermistor is a relatively expensive component. In addition, the thermistor bead material is subject to being attacked by the injectate. 
     The injectate may be at room temperature or at reduced temperatures. In the reduced temperature system, the injectate is cooled at one location and manually transported to the injection location near the proximal end of the thermodilution catheter. With this system, there is a risk of loss of sterility, the injectate may not be as cold as desired and there is an absence of a constant, ready supply of the injectate. 
     SUMMARY OF THE INVENTION 
     This invention provides for shielding the thermistor from the injectate and permits the thermistor to be reused even though other portions of the system may be disposable. This reduces the cost of the system, and the isolation of the thermistor from the injectate prevents the injectate from attacking the material of the thermistor bead. Furthermore, manual transport of the injectate is eliminated by providing a closed system in which a conduit carrier the cold injectate from a cooling container to the location where injection is to be carried out. 
     Although the concepts of this invention are particularly adapted for use in an injectate delivery system, in a broader sense, the concepts of the invention are also applicable to a system for sensing a characteristic of fluid flowing to or from the body of a human or animal. For example, the characteristic being sensed may be temperature, pressure or any characteristic that can be determined by an optical scan, such as the partial pressure of blood gases. This sensing can be carried out on any fluid, i.e., liquid or gas or mixture thereof, which is being injected into the body or being received from the body. 
     More particularly, the invention can be embodied in a system which includes a conduit having a first end adapted to be outside the body, a second end adapted to be received within the body and a flow passage through which fluid can flow between the first and second ends. The system also includes a probe, including means for sensing the desired characteristic of the fluid. Means is provided on the conduit for receiving at least the sensing means of the probe from the exterior of the conduit in the flow passage and isolating the probe from the fluid flowing through the flow passage. The probe can be mounted on the conduit with the sensing means in the flow passage and isolated from the fluid flowing in the flow passage so that the probe can sense the desired characteristic of the fluid in the conduit. 
     With this arrangement, the sensing means is isolated from the fluid flowing through the flow passage. For example, the sensing means may include a thermistor or fiber optics which can scan the fluid in the flow passage. Because the sensing means is isolated from the fluid in the flow passage, the probe need not be sterile. By removably mounting the probe on the conduit, at least the portion of the conduit having the receiving means can be disposed of without disposing of the probe. 
     The receiving means can be of various different constructions. For example, the receiving means may include a receiver projecting into the flow passage and having a receiver passage opening to the exterior of the flow passage for receiving the sensing means of the probe. Alternatively, the conduit may have a wall with a port leading to the fluid passage, and in this event, the receiving means may include a resilient membrane closing the port. The resilient membrane is deformable by the probe to permit at least the sensing means of the probe to be received in the flow passage. 
     The means for mounting the probe on the conduit preferably includes elongated telescoping members on the conduit and the probe, respectively. The telescoping members rigidly mount the probe and guide the sensing means into the receiving means. 
     When the system is used as an injectate delivery system, the conduit preferably has an inlet for receiving the injectate and an outlet through which the injectate can be delivered to the body. In this event, at least a downstream portion of the conduit includes a catheter for delivering the injectate to the interior of the body. 
     When the system is used to measure temperature, the projection of the receiving means into the flow passage creates turbulence adjacent the receiving means which assists heat transfer. To further increase heat transfer, the fluid passage can be restricted at the receiving means to increase the velocity of the injectate. 
     When using the system as a cold injectate system, the system preferably includes a cooling container, and the conduit leads from the receiving means to the cooling container with the cooling container being between the inlet and the receiving means. This provides a closed sterile system for the transfer of the cold injectate. In a preferred construction, the conduit includes several coils within the cooling container, and the storage volume within the cooling container is sufficient to store enough cold injectate for multiple injections. To reduce heat transfer to the injectate flowing from the cooling container, a length of the conduit downstream of the cooling container has a relatively low coefficient of heat transfer. 
     The injectate is forced through the conduit by a suitable pump, such as a syringe. By way of example, the conduit may include a first section coupled to the pump and extending past the receiving means and toward the outlet and an inlet section joined to the first section and leading to the inlet. A check valve is used for substantially preventing flow from the pump through the inlet section in a direction toward the inlet. 
     The invention, together with additional features and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying illustrative drawing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a system constructed in accordance with the teachings of this invention. 
     FIG. 2 is a longitudinal sectional view through the flow-through fitting and the probe. 
     FIG. 3 is a sectional view taken generally along line  3 — 3  of FIG.  2 . 
     FIG. 4 is an enlarged fragmentary sectional view of a portion of FIG.  2 . 
     FIG. 5 is a fragmentary sectional view showing a second preferred form of the flow-through fitting. 
     FIG. 6 is a sectional view of a probe and the flow-through fitting of FIG. 5 in the assembled condition. 
    
    
     BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows a system  11  for sensing a characteristic of fluid flowing to or from the body of a human or animal. In the form shown in FIG. 1, the system is an injectate delivery system, and more specifically, the system  11  is adapted to measure cardiac output. 
     The system  11  includes a conduit  13  having an inlet  15  and an outlet  17 , a pump in the form of a syringe  19 , a cooling container  21 , a probe  23  for making a temperature measurement, a flow-through fitting  25  adapted to cooperate with a probe  23  and a cardiac output computer  27 . In the embodiment illustrated, the conduit  13  is comprised of various sections or components, and in the form shown, the inlet  15  is defined by an IV spike  29  which is adapted to penetrate a conventional bottle  31  of injectate so that the inlet  15  can receive the injectate from the bottle. For example, the injectate may be a saline solution. 
     A snap clamp  33  may be provided on the conduit  13  immediately downstream of the IV spike  29 . A portion of the conduit  13  between the clamp  33  and the cooling container  21  is formed by a plurality of pull-apart coils  35 . Conduit of this type comprises coiled tubing which tends to remain together in coiled form until the coils are pulled away. This provides a more compact system. 
     The use of the cooling container  21  is optional and would not be used, for example, if room temperature injectate were to be utilized. In the embodiment illustrated, the cooling container  21  comprises a container  37  having radially extending tabs  39  adjacent its upper end, slots  41  extending axially through the tabs, and a notch  43  at the lower end of the container. The upper end of the container  37  can be closed by a lid  45 . The lid and the container  37  are preferably constructed of materials having a low coefficient of heat transfer. 
     The cooling container  21  can be supported on a horizontal surface or mounted on an IV pole by a bracket  47 . The bracket  47  has a ledge  49  and a post  50  which can be received in the notch  43  and one of the slots  41 , respectively. The bracket  47  also has a pole mounting section  51  which can be slid onto an IV pole and retained in position on the pole by a screw  53 . 
     A section of the conduit  13  is formed into coils  55  within the container  37 , and the coils are elevated above the floor of the cooling container  21  by a partition  57 . The coils  55  are constructed of thin-walled metal to provide good heat transfer, and the coils may be held together by a band (not shown). The container  37  may be filled with ice  59 , water or other cold substance to reduce the temperature of the injectate within the coils  55 . Preferably, the interior volume of the coils is sufficient to provide multiple injections of the injectate. 
     The conduit  13  also includes a section  61  of relatively low coefficient of heat transfer coupled to the coils  55  by an inline tubing connector  63 . The section  61  extends downstream of the coils  55  to a check valve  65 , and the latter is coupled to a fitting  67  to the flow-through fitting  25  and by an appropriate fitting to the syringe  19 . The syringe  19  is of conventional construction and includes a housing  69  and a plunger  71  which can be withdrawn to draw injectate from the coils  55  through the check valve  65  and into the housing  69 . Movement of the plunger  71  inwardly of the housing  69  expels the injectate through the downstream portions of the conduit  13  and out the outlet  17 . During this time, the probe  23  is coupled to the flow-through fitting  25  to make a temperature measurement as described more particularly hereinbelow. The check valve  65  substantially prevents the injectate pumped by the syringe from flowing in the section  61  of the conduit back toward the inlet  15 . 
     The downstream end of the flow-through fitting  25  is coupled to a conventional thermodilution catheter  73  which forms a portion of the conduit  13 . More specifically, the catheter  73  has a proximal injectate hub  75  coupled to the downstream end of the flow-through fitting  25  by a fitting  77 . The catheter  73  also includes a balloon  79 , a balloon inflation valve  81  through which the balloon can be inflated and a distal lumen hub  83 , a downstream thermistor (not shown) between the balloon  79  and the outlet  17  and a thermistor lead  85 . The hub  83  is connectable to a suitable pressure monitor (not shown) for monitoring the pressure at the distal end of the catheter  73 . For example, a thermodilution catheter of this type is available from American Edwards Laboratories, Santa Ana, Calif., as Model No. 93A-131-7F. The cardiac output computer  27  is coupled to the thermistor lead  85  and to leads  86  which are coupled to the probe  23 . 
     In use, the catheter  73  is inserted, utilizing known techniques, into the heart and pulmonary artery with the outlet  17  being in the right atrium, and with the balloon being in the pulmonary artery. With the IV spike  29  coupled to the bottle  31 , a ready supply of cold injectate is available in the coils  55 . By moving the plunger  71  in a direction outwardly of the housing  69 , a known amount of cold injectate can be drawn into the housing  69 . By pushing the plunger  71  forwardly, this known volume of injectate is forced through the flow-through fitting  25 , a length of the catheter  73  and the outlet  17  into the right atrium where it mixes with the blood and proceeds through the heart. The probe  23  measures the temperature of the injectate as it passes through the flow-through fitting  25 , and the temperature of the blood-injectate mixture in the pulmonary artery is measured by the downstream thermistor adjacent the balloon  79 . The cardiac output computer  27  processes this data in accordance with known techniques to ascertain cardiac output. 
     FIGS. 2-4 show one preferred construction for the probe  23  and the flow-through fitting  25 . The flow through fitting  25  which may be constructed of a suitable polymeric material, includes a tube section  87  which forms a portion of the conduit  13  and which has a passage  89  therein forming a portion of the flow passage of the conduit. An upstanding, elongated boss  91  is integrally joined to the tube section  87  and communication between the boss and the passage  89  is provided by a port  93  in the wall of the tube section. A pressure transducer  97  may, if desired, be mounted on the wall of the tube section  87 . 
     A receiver  95  is mounted on the tube section  87  and extends diametrically completely across the passage  89 . In this embodiment, the receiver  95  is a rigid, thin-wall, metal tube of high thermal conductivity that may be constructed, for example, of silver-plated copper. The receiver  95  has a receiver passage  97  which is sealed from the injectate in the passage  89 . More specifically, the receiver  95  has an end wall  99  and a peripheral wall  101 , both of which are imperforate and a flange  103  for assisting in sealing the receiver to the tube section  87 . Although various methods of attachment may be used, in the embodiment illustrated, the receiver  95  is attached to the tube section  87  by insert molding. When so attached, the boss  91  and the receiver passage  97  are coaxial. 
     As best seen in FIG. 3, the flow-through fitting  25  includes a restriction  105  for restricting the flow passage  89  at the receiver  95 . Also, for use in attaching the probe  23 , the flow-through fitting  25  includes a pair of arms  107  with inwardly directed lugs  109  spaced outwardly from the boss  91 . The arms  107  are sufficiently resilient so that the lugs  109  can be moved away from the boss  91  by pushing on ears  111  integrally joined to the arms  107 , respectively. 
     The probe  23  includes a probe housing  113 , which may be constructed of a suitable thermoplastic, and a thermistor  115 . Although various constructions are possible, in the embodiment illustrated, the probe housing  113  has opposed mounting arms  117  adapted to telescopically receive the boss  91 , and a tubular mounting section  119  in which the thermistor  115  is mounted. The probe housing  113  has an axial bore  121  through which the leads  86  extent and are coupled to the thermistor  115 . The thermistor  115  projects from the outer end of the tubular mounting section  119  and is received within the receiver passage  97 . The thermistor  115  may be pressed into the mounting section  119 . The exterior of the probe housing  113  has outwardly projecting lugs  123  receivable beneath the lugs  109  to releasably mount the probe  23  on the flow-through fitting  25 . When so mounted, the thermistor  115 , which is of conventional construction, is housed within the receiver  95 . The receiver  95  serves as an enclosure in which the thermistor  115  is sealed and isolated from the injectate in the passage  89 . 
     FIGS. 5 and 6 show a second preferred form for the probe  23   a  and the flow-through fitting  25   a.  Portions of the probe  23   a  and fitting  25   a  corresponding to portions of the probe  23  and the fitting  25  are designated by corresponding reference numerals followed by the letter “a.” The probe  23   a  and the fitting  25   a  are identical to the probe  23  and the fitting  25 , respectively, in all respects not shown or described herein. 
     The primary difference between the fittings  25   a  and  25  is that the former has a receiver  95   a  in the form of a thin, resilient membrane of a suitable rubber. The receiver  95   a  in the form illustrated is in the form of a sock having an imperforate end wall  131  and a peripheral wall  133  with the latter being firmly held between the boss  91   a  and a tubular insert  135  which is suitably mounted within the boss. 
     The probe housing  113   a  includes a rigid section  136  and a pliable section  138 . The probe housing is removably attached to the fitting  25   a  by resilient arms  117   a  which partially embrance the tube section  87   a.  The thermistor  115   a  is mounted on a support  137  of plastic or other suitable material, and the support  137  is suitably mounted on a mounting section  139  of the probe housing  113   a.    
     With the probe  23   a  detached from the fitting  25   a,  the end wall  131  lies in the port  93   a  out of the passage  89   a.  However, when the probe  23   a  is mounted on the fitting  25   a  as shown in FIG. 6, the end of the thermistor  115   a  engages the end wall  131  and resiliently deforms it to permit the thermistor to project a substantial distance into the passage  89   a.  In this position, the thermistor  115   a  is isolated and sealed from the injectate in the passage  89   a  by the membrane-like receiver  95   a.  The membrane can be extremely thin so that it is a very effective heat transfer member which enables the thermistor  115   a  to provide a very accurate temperature reading. 
     Although exemplary embodiments of the invention have been shown and described, many changes, modifications and substitutions may be made by one having ordinary skill in the art without necessarily departing from the spirit and scope of this invention.