Thermal dilution injection measurement and control

Abstract

This application relates to thermodilution injection fluid measurement and control. Apparatus and methods for measuring, controlling (or both) the thermodilution injection fluid flow rate used to calculate a thermodilution pulmonary parameter. An injection fluid delivery system includes a syringe for containing injection fluid and a delivery tube configured at one end to connect to a catheter. A flow measurement device is inserted into the delivery tube to generate a signal used to determine the flow rate of fluid from the syringe to the catheter. A processor receives the signal from the flow measurement device and calculates the injection fluid volume to be used as an input for calculating a thermodilution pulmonary parameter such as cardiac output. A GUI is provided to guide the user as to whether the injection rate is too fast or too slow. The system can include a constant flow valve to provide a constant flow rate from the syringe rather than measuring or calculating the flow rate.

Description

[0001] This application is a divisional application of the original application with the filing date of October 21, 2015, the application number of 201580084984.9, and the invention title of "Thermodilution Infusate Measurement and Control". TECHNICAL FIELD

[0002] Aspects of the present disclosure generally relate to devices and methods for measurement, control, or both of fluid expelled from a syringe or other container, and in particular, can relate to accuracy of measured or calculated transpulmonary thermodilution parameters. BACKGROUND

[0003] Thermodilution is the most widely used technique for determining cardiac output. Thermodilution employs the principle of indicator dilution using temperature change as the indicator.

[0004] A known quantity of solution with a known temperature is rapidly injected into the right atrial lumen tube of the first catheter. This cooler solution mixes with and cools the surrounding blood, and the temperature downstream of the pulmonary artery is measured by a thermistor bead embedded in the second catheter. The resulting temperature change is then plotted on a time-temperature curve. This curve is similar to the curve produced by indicator dilution.

[0005] The normal curve is characteristically shown by a sharp rise from the self-injectate rapid injection. This is followed by a smooth curve, and a slightly elongated descent back to baseline. Since the curve represents a change from a warmer temperature to a cooler temperature and then back to a warmer temperature, the actual curve is in the opposite direction. In many illustrative and display graphs, the curve is generated in an upright manner so that the area under the curve is inversely proportional to cardiac output.

[0006] When cardiac output is low, more time is required for the temperature to return to baseline, producing a greater area under the curve. In the case of high cardiac output, the cooler injectate is carried more quickly through the heart, and the temperature returns to baseline more quickly. This produces a smaller area under the curve.

[0007] The key to this technique is the injectate temperature, volume, and flow rate. However, since the speed of injection varies between users performing the procedure, the actual volume and solution temperature of the injectate or injected bolus can vary greatly, losing accuracy and precision of the cardiac output measurement. Some users exert a great amount of force on the syringe to inject the bolus as quickly as possible, while others inject at a slower speed. Users can make mistakes when injecting the bolus, including injecting a different volume than the amount that goes into the monitoring device and upon which the calculation is based. SUMMARY

[0008] According to one embodiment of the concept disclosed herein, an injection fluid delivery system is provided. The system includes a container for containing a fluid injection fluid, a delivery tube in fluid communication with the container and configured at one end to connect to a catheter, and a manually or mechanically driven syringe, another type of syringe assembly, or other means for manually discharging fluid from the container into the delivery tube. A flow measurement device is inserted into the delivery tube and configured to generate a signal used in determining the flow rate of fluid from the container to the catheter. A processing device is adapted to receive the signal from the flow measurement device and is configured to calculate the volume of injection fluid to be used as input for calculating at least one parameter. In some embodiments, the at least one parameter to be calculated is a pulmonary thermodilution parameter, and in some such embodiments, the pulmonary thermodilution parameter is at least one of cardiac output, global end-diastolic volume, and extravascular pulmonary edema.

[0009] In some embodiments, and in combination with any of the above embodiments, the container is a syringe, and the device for manually discharging the fluid is the plunger of the syringe. In some such embodiments, the system also includes a conduit in fluid communication with the container, and in some of these embodiments, the conduit is manufactured and sold by Edwards Lifesciences. catheter.

[0010] In some embodiments and in combination with any of the above embodiments, the flow measurement device is configured to generate a signal to the processing device based on a pressure differential. In some embodiments and in combination with any of the above embodiments, the flow measurement device includes a pressure sensor for measuring the pressure drop across the orifice. In some embodiments and in combination with any of the above embodiments, the flow measurement device defines the area of ​​a contracting flow and includes a pressure sensor for measuring vortex differential pressure. In some embodiments and in combination with any of the above embodiments, the flow measurement device includes a venturi tube. In some embodiments and in combination with any of the above embodiments, the flow measurement device includes a pitot tube. In some embodiments and in combination with any of the above embodiments, the flow measurement device includes a hot-wire anemometer.

[0011] In some embodiments, and in combination with any of the above embodiments, a sensor inserted in the delivery tube is configured to detect changes in the pressure or temperature of the injection solution and to signal a timer to start at the beginning of the injection and stop at the end of the injection, thereby measuring the elapsed time of the injection.

[0012] According to another embodiment of the concepts disclosed herein, a method for determining an injection volume for use in determining transpulmonary thermodilution parameters is provided. The method includes starting a timer by a processor upon a signal of a pressure increase at a pressure sensor, the signal of the pressure increase at the pressure sensor indicating a start of an injection of a fluid injection fluid from a syringe into a delivery tube. A signal from a flow measurement device inserted into the delivery tube is received by the processor. The processor calculates a flow rate of the injection fluid. The timer is stopped to determine an elapsed time of the injection, and the processor calculates a volume of the injection fluid that has been injected. The calculated volume is used to calculate at least one transpulmonary thermodilution parameter.

[0013] In some embodiments and in combination with the above embodiments, the transpulmonary thermodilution parameter is at least one of cardiac output, global end-diastolic volume, and extravascular lung water. In some embodiments and in combination with any of the above embodiments, the method further includes graphically displaying a current flow rate of the injection fluid. In some such embodiments, the method further includes graphically displaying a predetermined minimum flow rate and a predetermined maximum flow rate, the predetermined minimum flow rate and the predetermined maximum flow rate defining limits within which the current flow rate is expected to occur.

[0014] According to another embodiment of the concepts disclosed herein, an injection fluid delivery system is provided. The injection fluid delivery system includes a container for containing a fluid injection fluid, a delivery tube in fluid communication with the container and configured at one end to connect to a catheter, and a syringe, a syringe device, or another device for manually expelling the fluid injection fluid from the container to the delivery tube during an injection. A constant flow control element is fluidly inserted into the delivery tube, and the constant flow control element is configured to maintain a substantially constant design flow rate during an injection of fluid from the container to the catheter. A sensor is inserted into the delivery tube, configured to detect a change in pressure or temperature of the injection fluid, and to signal a timer to start at the beginning of an injection and to stop at the end of an injection. A processing device is adapted to receive a signal from the sensor, wherein the processing device is configured to calculate a volume of the injection fluid based on the constant flow valve design flow rate and a measured injection elapsed time. The volume is to be used as an input for calculating at least one parameter. In some such embodiments, the at least one parameter to be calculated is a transpulmonary thermodilution parameter including at least one of cardiac output, global end-diastolic volume, and extravascular lung water.

[0015] In some embodiments and in combination with any of the above embodiments, the container includes a syringe, and the constant flow control element includes a constant flow valve fluidly inserted into the delivery tube. In other embodiments and in combination with any of the above embodiments, the container includes a syringe, and the syringe includes the constant flow control element as an integrated component of the syringe.

[0016] According to another embodiment of the concepts disclosed herein, a method of displaying relative flow rate of an infusion fluid delivery system is provided. The method includes calculating, by a processor, a flow rate of fluid in an infusion delivery tube for a heat dilution procedure using parameters measured by a flow measurement device. The processor graphically displays on a display device a predetermined minimum acceptable flow rate, a predetermined maximum acceptable flow rate, and an indication of a current flow rate relative to the minimum and maximum acceptable flow rates.

[0017] According to another embodiment of the concepts disclosed herein, a system for displaying relative flow rate of an infusion fluid delivery system is provided. The system includes a display device, a processor operably connected to the display device; and a memory. The memory is operably connected with the processor to store a predetermined minimum acceptable flow rate and a predetermined maximum acceptable flow rate, and is further operably connected to store computer program code that, when executed, causes the processor to calculate a flow rate of fluid in an infusion delivery tube for a heat dilution procedure using parameters measured by a flow measurement device, and to graphically present on the display device a predetermined minimum acceptable flow rate, a predetermined maximum acceptable flow rate, and an indication of a current flow rate relative to the minimum and maximum acceptable flow rates.

[0018] According to another embodiment of the concepts disclosed herein, an apparatus for displaying relative flow rate of an infusion fluid delivery system is provided. The apparatus includes means for storing a predetermined minimum acceptable flow rate and a predetermined maximum acceptable flow rate, means for calculating a flow rate of fluid in an infusion delivery tube for a heat dilution procedure using parameters measured by a flow measurement device, and means for graphically displaying a predetermined minimum acceptable flow rate, a predetermined maximum acceptable flow rate, and an indication of a current flow rate relative to the minimum and maximum acceptable flow rates. BRIEF DESCRIPTION OF DRAWINGS

[0019] For a more complete understanding, reference is now made to the embodiments shown in the accompanying drawings and described below. In the drawings;

[0020] Figure 1 is a perspective view of a prior art infusion fluid delivery system.

[0021] Figure 2 is a schematic diagram of an infusion fluid delivery system according to an example embodiment of the present invention.

[0022] Figure 3 is a flowchart of an example process that can be performed by an example embodiment of the present invention.

[0023] Figure 4 is a screen shot of a screen of a display device that is part of a system. Such a screen can be produced by an embodiment of the present invention. Figure 2

[0024] ​Figure 5 is a block diagram of a system according to an example embodiment of the present application.

[0025] Figure 6 is a schematic diagram of another injection fluid delivery system according to an example embodiment of the present application.

[0026] Figures 7-9 is a graph representing the effect of an incorrect injection fluid volume being injected or recorded on transpulmonary thermodilution parameters. DETAILED DESCRIPTION

[0027] The following detailed description of implementations refers to the accompanying drawings that depict specific embodiments. Other implementations can not include all of the features noted in connection with the figures.

[0028] Embodiments of the concepts disclosed herein relate to devices and methods for measuring, controlling (or both) characteristics of an injection bolus. Characteristics can include, for example, pressure, temperature, and flow, and although the disclosed devices and methods can be applied to automated devices such as syringe pumps, they are discussed herein with respect to manually operated syringes and containers. Additionally, real-time feedback can be provided to a user to help reduce variability in injection technique, as well as reduce the likelihood of user error in entering data into a monitoring device.

[0029] As those skilled in the art will appreciate, the present application can be embodied as a method, apparatus, article of manufacture, system, computer program product, or combination of the foregoing. Any suitable computer-usable or computer-readable medium can be utilized for the computer program product including non-transitory computer program code to implement all or part of the embodiments of the present application. The computer-usable or computer-readable medium can be, for example but not limited to, a tangible electronic, magnetic, optical, electromagnetic, or semiconductor system, apparatus, or device.

[0030] There are two main types of injection fluid delivery systems for thermodilution procedures. One is an open system that utilizes a syringe pre-filled with ice-cold or room temperature injection fluid. The other is a closed system, also for ice-cold or room temperature injection fluid, that is maintained in a closed loop fashion to reduce multiple access to the sterile system. Available data suggest that variability in cardiac output determination will be reduced if ice-cold solution is used. Optionally, injection fluid temperatures warmer than body temperature can be used. The computer records the patient's baseline temperature variation (which can be through a signal), which can be noise. In some cases, a temperature variation of 0.05°C can occur with respiration. This reduces the "signal-to-noise" ratio and can produce abnormally low cardiac output values. Other cases where increased signal-to-noise ratio can be beneficial include febrile patients, low cardiac output states, and patients with wide respiratory variation.

[0031] Using the modified Stewart-Hamilton equation to calculate cardiac output, taking into account temperature changes as an indicator. The modifications include the measured temperature of the injectate and the patient's blood temperature, as well as the specific gravity of the injected solution. The Stewart-Hamilton equation is as follows:

[0032] CO = (V x (T B - T I ) / A) x (S I x C I ) / (S B x C B ) x (60 x C x K)

[0033] Where:

[0034] CO = cardiac output

[0035] V = volume of injectate (mL)

[0036] A = area of thermodilution curve (mm squared) divided by chart speed (mm / sec)

[0037] T B , T I = temperature of blood (B) and injectate (I)

[0038] S B , S I = specific gravity of blood and injectate

[0039] C B , C I = specific heat of blood and injectate

[0040] (S I x C I ) / (S B x C B ) = 1.08 when using 5% dextrose

[0041] 60 = 60 sec / min

[0042] C T = correction factor for injectate warming

[0043] Dilution devices, methods, and computer programs applicable to thermodilution methods are disclosed in U.S. Patent No. 8,343,058 to Pfeiffer et al. issued January 1, 2013 and assigned to Edwards Lifesciences IPRM AG, the contents of which are incorporated by reference herein in their entirety. At least three key thermodilution parameters, cardiac output, global end-diastolic volume, and extravascular lung water, can be affected by the volume of injectate.

[0044] Referring to the drawings, wherein like reference numerals refer to like or similar parts throughout, Figure 1 An existing art infusion delivery system 20 is shown, which in this embodiment is an open system. The system 20 includes a sterile infusion solution container 22 connected to the outlet of a syringe 26 or to tubing connected to the outlet of the syringe 26 via an infusion delivery tubing 24. A non-vented IV spike 28 and a device to stop flow from the tubing, such as a snap clamp 30, can be provided along the infusion delivery tubing 24. A check valve 34 can be provided near the connection of the tubing 24 to the syringe outlet to allow flow from the container 22 to the syringe 26, but not back to the container 22.

[0045] Downstream of the check valve 34 connection to the syringe outlet, a flow-through housing 36 can be provided that receives a temperature probe 40. The temperature probe 40 is one of several components that are electrically connected to a computer 42, which can include a processor or processing device, CPU, monitor, and control unit associated with a cable 44 and catheter connector 46. A three-way stopcock and continuous flush device 48 can be connected downstream of the flow-through housing 36 of the temperature probe 40. The most downstream element can be a catheter 50, which can be, for example, a Swan-Ganz catheter. The catheter 50 can include a proximal infusion hub 52. At the distal end of the catheter 50, there can be a balloon 54 and a distal lumen 56, with a thermistor 58 proximal to the balloon 54 and spaced from a proximal infusion port 60. At the proximal end of the catheter 50, in addition to the proximal infusion hub 52, there can be a balloon inflation valve 62, an IV / pressure monitoring line 64, and a thermistor connector 66 connected to the computer 42 via the catheter connector 46.

[0046] An example embodiment of an infusion delivery system 70 according to the present application is shown schematically in Figure 2 In this embodiment, a flow measurement device can be provided. In the flow measurement device, a differential pressure can be measured across a pressure-reducing component such as, for example, an orifice, a constricted flow area that causes a vortex differential pressure, a differential pressure transducer, or a Venturi tube, to calculate the flow rate of the infusion. The flow measurement device can optionally include a Pitot tube or hot wire anemometer type device. The flow rate can be used to calculate the volume of the infusion, which in turn can be used in the Stewart-Hamilton equation and the equation of incorporated U.S. Patent No. 8,343,058, and can provide more accurate results than otherwise achievable.

[0047] Figure 2The injectate delivery system 70 can include a reservoir such as a syringe 26 which can draw from the injectate reservoir 22 with a check valve 34 allowing flow from the reservoir 22 but preventing flow back into the reservoir 22. Alternatively, the reservoir 22, tubing 24 and check valve 34 can be omitted, leaving the system closed with only the syringe 26 as the source of injectate; the syringe 26 can be pre-filled and self-cooled. Another check valve 72 can be provided which allows flow of injectate out of the syringe 26 but prevents backflow from the tubing 24 into the syringe 26 when the syringe 26 is being drawn upon to draw injectate from the reservoir 22. As described above, a flow measurement device 74 can be inserted linearly with the tubing 24. Pressure sensors 78, 80 can be provided upstream and downstream of the flow measurement device 74, and preferably a temperature sensor 82, which can be a thermistor, can also be provided downstream of the flow measurement device 74. The pressure sensors 78, 80 and temperature sensor 82 can be connected to the computer 42 via the cable 44. A stopcock 84 or other valve can be provided and can be connected to a proximal injectate hub (not shown). The catheter 50 is represented in Figure 2 by a single line, but it should be understood that multiple connecting lines can be incorporated into the catheter for various functions, as Figure 1 illustrated.

[0048] The flow measurement device 74 can have known flow characteristics and flow area which provide a relationship between pressure loss and injectate velocity, so that when the pressure loss is known, the velocity can be determined. In addition, the initial change in pressure - or, if desired, temperature - when the bolus is expelled from the syringe 26 can trigger a timer to start in the computer 42. With the velocity of the injectate known and the fluid characteristics, and the elapsed time measured, the volume of injectate can be calculated.

[0049] An embodiment of a method 88 for determining the volume of injectate used in determining transpulmonary thermodilution parameters is shown in Figure 3 First, the injectate is expelled from the syringe 90. A timer is started 92 upon receiving a signal of an increase in pressure at a pressure sensor, such as in the line from the syringe; which pressure sensor (or both) to use can be selected as desired to accommodate the application and equipment. A signal is received 94 from a flow measurement device in the line from the syringe, which can be on both sides of a pressure reduction device (upstream and downstream), or alternatively from the flow which generates a signal from a cooled hot wire anemometer. The flow rate can then be calculated 96 by, for example, the differential pressure across the pressure reduction device, Pitot tube, or by the hot wire anemometer.

[0050] Optionally, a graphical user interface (GUI) can be provided that graphically displays the real-time flow rate 98 of the injectate. The display can include limits within which the flow rate should occur. Upon receiving a signal that the pressure drop at the selected one or both pressure sensors has occurred, the timer 100 can be stopped. The flow rate and the elapsed time measured are used to calculate the volume 102. A signal from the temperature sensor is received to indicate the temperature of the injectate 104, and the volume and temperature are used to calculate at least one transpulmonary thermodilution parameter 106.

[0051] Figure 4 A monitor 120 associated with the computer 42 Figure 1 and 2 is shown. The monitor 120 can display a GUI of the flow rate of the injectate from the syringe 26 into the catheter 50. The flow rate can be displayed in real time, as represented in this embodiment by a bubble 122a. In Figure 3 the flow rate increases from left to right. Minimum limits 124 and maximum limits 126 of the flow rate can be displayed on the monitor 120. A target 130 can be centered, and various example positions of the bubble are shown in dashed lines. A second bubble 122b shows that the flow rate is too slow, as it is outside of the acceptable range and below the minimum limit 124. A third bubble 122c shows that the flow rate is acceptable, but should be increased, as it is just within the acceptable range and above the minimum limit 124. A fourth bubble 122d shows that the flow rate is too fast, as it is outside of the acceptable range and above the maximum limit 126. A fifth bubble 122e shows that the flow rate is acceptable, but should be decreased, as it is just within the acceptable range and below the maximum limit 124. A user applying force to the syringe 26 can observe the monitor 120 to guide as to how fast the plunger of the syringe 26 should be pressed, and what force should be applied accordingly to cause an acceptable flow rate.

[0052] Figure 5 Details of the computer 42 Figure 1 and associated CPU, monitor and control unit are schematically illustrated, as are other components of the selected injectate delivery system and the patient 200. The system includes an I / O interface 202, which in turn can include appropriate connectors, and circuitry to monitor signals from the sensor system. The circuitry can include analog-to-digital converters, encoders, decoders, etc. The I / O interface 202 is coupled to a central processing unit (CPU) 204 that controls the operation of the entire system.

[0053] The I / O interface receives sensor signals from pressure sensors, temperature sensors, and / or flow rate detectors 205, etc. The CPU 204 is further operatively connected to a memory 206. The memory 206 stores all information required for the system to operate. Such information can be stored in a temporary manner, or can be stored more permanently. The memory can comprise a single or multiple types of memory. For example, a portion of the memory connected to the CPU 204 can be "flash" memory ("flash") that semi-permanently stores information for use by the system. In either case, the memory 206 in this example embodiment includes computer program code 208 that, when executed by the CPU 204, causes the system to perform various processes to graphically display information according to example embodiments disclosed herein. The memory 206 also stores data 210 that, in example embodiments, includes historical values of pressure, temperature, time, flow rate, and injection volume. Figure 5 The memory 206 in this example embodiment includes computer program code 208 that, when executed by the CPU 204, causes the system to perform various processes to graphically display information according to example embodiments disclosed herein. The memory 206 also stores data 210 that, in example embodiments, includes historical values of pressure, temperature, time, flow rate, and injection volume.

[0054] Still referring to Figure 5 , the monitoring and control unit 12 can also include a network interface 213. This network interface can allow the system to connect to a wired or wireless network to allow monitoring on a remote display (not shown). For example, the remote display can duplicate or be used in place of the local display panel. In Figure 5 example embodiments, a local display device 217 (which can be the same as the monitor 120 of Figure 4 ) is connected to the CPU 204 via a graphics engine 224. The local display device can be an LCD panel, a plasma panel, or any other type of display component along with the accompanying circuitry that interfaces the display device to the graphics engine 224. The graphics engine 224 can be located on its own chip, or in some embodiments it can be located on the same chip as the CPU 204. Note that the display device 217 can include user input functionality, such as an optical or capacitive touch screen on the display screen. In this case, the monitoring control unit 42 can include additional circuitry to process such input. Alternatively, such circuitry can be included in the display device itself, the graphics engine, or the CPU 204.

[0055] Figure 6 Another example embodiment of an injection fluid delivery system 300 according to the present application is schematically shown. Similar to the injection fluid delivery system 70 of Figure 2 , the injection fluid delivery system 300 includes a monitoring and control unit 42, a pump 44, a pressure sensor 46, a temperature sensor 48, a flow rate detector 50, and a local display panel 52. The monitoring and control unit 42 includes a CPU 204, an I / O interface 206, a memory 208, and a network interface 210. The CPU 204 is connected to the I / O interface 206, the memory 208, and the network interface 210. The I / O interface receives sensor signals from pressure sensors, temperature sensors, and / or flow rate detectors 205, etc. The CPU 204 is further operatively connected to a memory 206. The memory 206 stores all information required for the system to operate. Such information can be stored in a temporary manner, or can be stored more permanently. The memory can comprise a single or multiple types of memory. For example, a portion of the memory connected to the CPU 204 can be "flash" memory ("flash") that semi-permanently stores information for use by the system. In either case, the memory 206 in this example embodiment includes computer program code 208 that, when executed by the CPU 204, causes the system to perform various processes to graphically display information according to example embodiments disclosed herein. The memory 206 also stores data 210 that, in example embodiments, includes historical values of pressure, temperature, time, flow rate, and injection volume. Figure 6The injectate delivery system 300 can include a container such as a syringe 26 which can be drawn from the injectate container 22 with a check valve 34 allowing flow from the container 22 but preventing flow back into the container 22. Alternatively, the container 22, tubing 24 and check valve 34 can be omitted, leaving the system closed with only the syringe 26 as the source of injectate; the syringe 26 can be pre-filled and self-cooled. Another check valve 72 can be provided which allows flow of injectate out of the syringe 26 but prevents backflow from the tubing 24 into the syringe 26 when the syringe 26 is drawn to extract injectate from the container 22. In this embodiment, however, the constant flow valve 302 can be inserted linearly with the tubing 24. The constant flow valve 302 will remain closed until an "opening pressure" is reached by the plunger actuating the syringe 26, at which point the seal will open and flow will begin, held at the same constant flow rate based on the design of the valve. The pressure required to break the seal can be approximately, for example, one pound. Alternatively, a constant flow syringe can be provided which combines a syringe and constant flow valve.

[0056] A pressure sensor 306 and a temperature sensor 308, which can be a thermistor, can be provided linearly with the constant flow valve 302, and preferably downstream of the constant flow valve 302. The pressure sensor 306 and the temperature sensor 308 can be connected to the computer 42 via the cable 44. The pressure sensor 306 can be used to start and stop the timer to allow volume calculation based on the valve's flow rate times elapsed time, while the temperature sensor 308 is required for the thermal dilution calculation. A stopcock 84 or other valve can be provided and can be connected to a proximal injectate hub (not shown). The catheter 50 is shown in Figure 6 with a single line, but it should be understood that multiple connecting lines can be incorporated into the catheter for various functions, as exemplified in Figure 1 .

[0057] The materials of construction of the components of the devices disclosed herein can be selected by one of ordinary skill in the art of medical device design.

[0058] As discussed above, the thermal dilution algorithm is sensitive to the volume of injectate applied to the patient. If the volume of injectate is incorrectly entered into the system, or the volume applied to the patient is different, the calculated values are inaccurate. To demonstrate the effect of the volume of injectate on the results of key transpulmonary thermal dilution parameters, an analysis was performed. Using thermal dilution boluses from a clinical study, the output parameters were recalculated using a range of injectate volumes between 10 mL and 20 mL to allow for the examination of the range and error in the parameter values resulting from incorrect injectate volumes. The effect of the volume of injectate on the three main transpulmonary thermal dilution parameters of cardiac output, global end-diastolic volume, and extravascular lung water was considered.

[0059] The procedure used hot dilution boluses from a clinical study to recalculate the output parameters using a range of injection fluid volumes between 10 mL and 20 mL, and then studied the range and error in the parameter values resulting from incorrect injection fluid volumes. The results were as follows:

[0060] Injection volume (mL) CO (L / min) GEDV (mL) EVLW (mL) 10 3.28 1005.7 304.2 11 3.64 1105.6 332.7 12 4 1205.4 316.3 13 4.35 1305.2 389.8 14 4.71 1405.1 418.4 15 5.07 1504.9 447 16 5.43 1604.7 475.5 17 5.79 1704.6 504.1 18 6.15 1804.4 532.6 19 6.51 1904.3 561.2 20 7.01 2004.1 589.7

[0061] Figures 7-9 The results are shown plotted with the parameters, each as a function of injection fluid volume. The graphs and tables above show that, assuming the initial 10 mL value is correct, if 20 mL is incorrectly injected instead of the expected 10 mL, there can be an error of up to 114% in CO Figure 7 , an error of up to 99% in GEDV Figure 8 , and an error of up to 94% in EVLW Figure 9 .

[0062] While specific embodiments have been illustrated and described herein, it will be appreciated that any arrangement calculated to achieve the same purpose can be substituted for the specific embodiments shown and that the embodiments described herein have other applications in other environments. This application is intended to cover any adaptations or variations of the present disclosure. The following claims are in no way intended to limit the scope of the present disclosure to the specific embodiments described herein. Although the foregoing has been described in some detail for purposes of clarity, it will be apparent that certain changes and modifications can be made to the embodiments without departing from the scope of the application. Accordingly, the application is not limited to the specific embodiments described herein, but includes all alterations and modifications that fall within the scope of the claims.

Claims

1. An injectate delivery system comprising: a container for containing a fluid injectate; a delivery tube in fluid communication with the container and configured at one end to connect to a catheter, the delivery tube comprising an elongated conduit configured to receive the injectate expelled from the container; an injection device configured to expel the fluid injectate from the container to the delivery tube; a first pressure sensor linearly connected with the delivery tube, wherein the first pressure sensor is configured to generate a first signal; a second pressure sensor linearly connected with the delivery tube; a flow measurement device inserted in the delivery tube downstream of a first connection point between the first pressure sensor and the delivery tube and upstream of a second connection point between the second pressure sensor and the delivery tube, wherein the flow measurement device comprises a pressure reducing component and is configured to generate a third signal; and a processing device adapted to receive the third signal from the flow measurement device, wherein: the first pressure sensor is further configured to generate the first signal in response to detecting an increase in pressure; the first pressure sensor or the second pressure sensor is configured to generate a second signal in response to detecting a decrease in pressure; and the processing device is further configured to: start a timer upon receipt of the first signal; receive the second signal; stop the timer upon receipt of the second signal; receive the third signal; calculate a flow rate of the fluid injectate from the container to the catheter based at least in part on the third signal; and determine an injectate volume based at least in part on the calculated flow rate and an elapsed time between the first signal and the second signal, the injectate volume to be used as an input in calculating at least one parameter.

2. The system of claim 1, wherein the at least one parameter is cardiac output.

3. The system of claim 1, wherein the container is a container of a syringe comprising a manually operable plunger as the injection device.

4. The system of claim 3, wherein the catheter is in fluid communication with the container.

5. The system of claim 4, wherein the catheter is a Swan-Ganz catheter.

6. The system of claim 1, wherein the flow measurement device is configured to generate the signal based on a pressure differential.

7. The system of claim 1, wherein: the first pressure sensor is located upstream of the flow measurement device and in line with the elongated conduit; the second pressure sensor is located downstream of the flow measurement device and in line with the elongated conduit; and the first and second pressure sensors are configured to measure a pressure drop across the flow measurement device.

8. The system of claim 1, wherein: the first pressure sensor is located upstream of the flow measurement device and in line with the elongated conduit; the second pressure sensor is located downstream of the flow measurement device and in line with the elongated conduit; ​ The first and second pressure sensors are configured to measure a differential pressure of the swirl, and The flow measurement device defines an area of constriction flow.

9. The system of claim 1, wherein the flow measurement device comprises a Venturi tube.

10. The system of claim 1, wherein the flow measurement device comprises one or more Pitot tubes.

11. The system of claim 1, wherein the flow measurement device comprises a hot wire anemometer.

12. The system of claim 1, further comprising a temperature sensor inserted in the delivery tube downstream of the flow measurement device, wherein the temperature sensor is configured to detect a change in temperature of the fluid bolus and to signal a timer to start at the beginning of the injection of the bolus and to stop at the end of the injection to measure the elapsed time of the injection.

13. The system of claim 1, wherein the processing device is further configured to display the calculated flow rate of the fluid bolus in real time.

14. The system of claim 1, further comprising a valve that allows the bolus to be expelled from the container, wherein the flow measurement device is located downstream of the valve.

15. The system of claim 1, wherein the flow measurement device is not located within the container or the injection device.

16. The system of claim 1, wherein the flow measurement device is entirely within the elongated tube.

17. A bolus delivery system, comprising a container for containing a fluid bolus, a delivery tube in fluid communication with the container and configured at one end to connect to a catheter; an injection device configured to expel the fluid bolus from the container to the delivery tube; a first pressure sensor linearly connected with the delivery tube, wherein the first pressure sensor is configured to generate a first signal; a second pressure sensor linearly connected with the delivery tube; a flow measurement device inserted in the delivery tube downstream of a first connection point between the first pressure sensor and the delivery tube and upstream of a second connection point between the second pressure sensor and the delivery tube, the flow measurement device comprising a pressure-reducing component and being configured to generate a third signal; and a processing device adapted to receive the third signal from the flow measurement device; wherein: the first pressure sensor is further configured to generate the first signal in response to detecting an increase in pressure; the first pressure sensor or the second pressure sensor is configured to generate a second signal in response to detecting a decrease in pressure; and the processing device is further configured to: start a timer upon receipt of the first signal; receive the second signal; stop the timer upon receipt of the second signal; receive the third signal; calculate a flow rate of the bolus based at least in part on the third signal; determine cardiac output based at least in part on: the elapsed time between the first signal and the second signal; and the calculated flow rate.

18. The injectate delivery system of claim 17, further comprising: a constant flow valve in line with the delivery tube and configured to maintain a constant flow rate at the delivery tube; and a temperature sensor configured to generate a fourth signal; wherein the processing device is further configured to determine cardiac output based at least in part on the first signal, the fourth signal, and the constant flow rate.

19. The injectate delivery system of claim 17, further comprising: a constant flow valve in line with the delivery tube and configured to maintain a constant flow rate at the delivery tube, wherein: the first pressure sensor is further configured to generate the second signal in response to detecting a pressure decrease; and the processing device is further configured to: start the timer upon receipt of the first signal; receive the second signal; stop the timer upon receipt of the second signal; and calculate a volume of the injectate based at least in part on the constant flow rate and an elapsed time between the first signal and the second signal.

20. The injectate delivery system of claim 19, wherein: the first pressure sensor is further configured to generate the second signal in response to detecting a pressure decrease; and the processing device is further configured to: start the timer upon receipt of the first signal; receive the second signal; stop the timer upon receipt of the second signal; and calculate a volume of the injectate based at least in part on the constant flow rate and an elapsed time between the first signal and the second signal.

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