JP3069128B2 - Cardiac output measurement device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a cardiac output measuring device capable of improving the cardiac output measurement accuracy.

[Related Art] In recent years, there is a demand for accurately grasping the quality of the function of the heart because it is necessary to promptly deal with heart disease, cardiovascular dysfunction and the like.

Therefore, according to this demand, the cardiac output is measured by a thermodilution method using a cardiac output measuring device. That is, by inserting a thermistor-equipped catheter provided with the thermistor of a cardiac output measuring device having a thermistor connected to a control device into a vena cava blood outlet portion of the heart, the blood temperature at the pulmonary artery blood inlet portion is determined. The temperature is measured based on the temperature detection signal of the thermistor, and then an indicator is injected into the blood outlet of the vena cava, and the indicator mixed blood temperature of the blood mixed with the indicator of the blood outlet of the vena cava is used as the temperature detection signal of the thermistor. , And the blood temperature detection signal of the thermistor and the indicator-mixed blood temperature detection signal are stored by the storage means of the control device, and the control device is provided with a Stewart-Hamilton as a flow measurement arithmetic expression.
formula, And the flow rate of the blood flowing through the right heart and the flow rate of the indicator-mixed blood is calculated from the equation (I) by the arithmetic means of the controller based on the blood temperature detection signal of the thermistor and the indicator-mixed blood temperature detection signal. And a cardiac output measurement method for measuring cardiac output.

By the way, in order to know the quality of the measurement by the cardiac output measurement method, the following cardiac output simulation measurement method is performed, and a catheter is inserted into the heart of the living body in comparison with the result by this method. All of the cardiac output measurement methods have been evaluated as being good.

To explain the method for simulating cardiac output, blood extracted from a living body is stored in a blood reservoir having an automatic temperature controller, and the automatically temperature-controlled blood is sent to a stirrer as a pulsating flow by a roller pump. The indicator (saline) is instantaneously injected into the stirrer with a syringe, and the blood and the saline in the stirrer are stirred, and the mixed fluid of the stirred blood and the saline in the stirrer is diluted with a measuring solution. At the same time as measuring the flow rate of this fluid with a graduated cylinder, a temperature sensor (thermistor) is attached to the tip and based on the output data (temperature signal) of the thermistor of the catheter inserted into the agitator, this data is obtained.
It is stored by a microcomputer via an A / D converter, and this microcomputer has a Stewart-Hamirlton formula as a flow measurement calculation formula, Is input, and the microcomputer calculates and records the flow rate of the fluid flowing out of the stirrer based on the stored data.
The information is recorded and displayed by the display means.

Here, Q _F is blood flow, V _I is the injection amount of saline indicator, [rho _I is the density of the saline, [rho _F is the density of blood, C _I
Denotes the heat capacity of the saline, C _F is the heat capacity of the blood, T _F is the blood temperature, T _I is saline temperature, [Delta] T _F is the change in blood temperature, the.

The catheter with a thermistor (Swan-Ganz catheter) used for the cardiac output measurement (commercial product name)
Although the time constant of the thermistor greatly affects the temperature measurement of the fluid, that is, greatly affects the cardiac output measurement, the conventional cardiac output measurement does not correct the time constant.

As an example, the injection amount of the physiological saline into the cardiac output simulation device is 0.77, 2.27, 4.27, 9.27 ml, the injection temperature is 274,27.
8,283,293 K, the infusion time is 2, 5, 10 seconds, and the flow rate of blood flowing into the stirrer is 1 to 6 / min.

[Problems to be Solved by the Invention] However, in the measurement method using the conventional cardiac output measuring device, the time constant of the thermistor (more precisely, the time constant of the catheter with a thermistor), that is, the catheter with each individual catheter The thermistor's time constant (response speed) changes for each individual catheter used, and this time constant greatly affects the temperature measurement accuracy of the fluid. Especially, the measurement error can be reduced by low flow rate, high indicator temperature, and long injection time of indicator. As a result, even when the cardiac output measurement conditions are the same except for the thermistor with a catheter, the flow rate measurement results of the blood flowing through the right heart and the indicator-mixed blood have different results. The measurement accuracy of the flow rate of the blood flowing out of the blood and the indicator-mixed blood was insufficient, and as a result, the cardiac output could not be measured accurately.

The present invention has been made in view of the above circumstances, and has a low flow rate,
Under the measurement conditions such as high indicator temperature, long infusion time, and different time constant of the thermistor with catheter, accurate cardiac output measurement results can be obtained, and heart rate can be easily measured by any person. An object of the present invention is to provide a stroke volume measuring device.

“Means for Solving the Problems” The present invention has the following configuration to achieve the above object. That is, a cardiac output measuring apparatus having a storage means, an arithmetic means, and a display means connected to a cardiac output measuring device having a thermistor-equipped catheter, wherein the storage means comprises: T: measured temperature at time t , _T∞ : steady state temperature of mixing of blood and indicator, T _F : blood temperature, t _c : time constant of catheter, based on Newton's law of cooling And wherein, Q _F: Blood flow, V _I: injected amount of indicator, [rho _I: Density of the indicator, [rho _F: density of blood, C _I: heat capacity of the indicator, C _F: heat capacity of the blood, T _F: blood temperature , T _I: an indicator the temperature, T _∞: mixing steady state temperature of the blood and the indicator, t _I: when a injection time of the indicator,
Heat balance equation between the blood and the indicator _{Q F ρ F C F (T} F -T ∞) = V I ρ I C I (T ∞ -T I) / t from _I ...... (2) wherein said blood indicator The steady-state temperature reagent T _混合 mixed with The formula is stored, and the catheter with the thermistor is inserted into the inflow portion from the vena cava to the right atrium, and the blood temperature at the outflow side of the pulmonary valve or the pulmonary artery blood inlet portion is determined based on the temperature detection signal of the thermistor. Measured and stored, further, an indicator is injected into the blood outlet portion of the aorta, and the indicator mixed blood temperature of the blood mixed with the indicator at the aortic blood outlet portion is measured based on the temperature detection signal of the thermistor. The calculation means calculates the flow rates of the blood flowing through the right heart portion and the indicator-mixed blood from the equation (3) stored in the storage means, and calculates the calculated flow rates of the blood and the indicator-mixed blood. The stored flow rate of the stored blood and indicator mixed blood is retrieved and displayed on the display means.

[Operation] According to the measurement apparatus of the present invention, the expression (1) and the expression (2) are used.
The above equation (3) obtained from the equation is input and stored by the storage means. A catheter with a thermistor is inserted into the inflow portion from the vena cava to the right atrium, and the blood temperature at the outflow side of the pulmonary valve or at the pulmonary artery blood inlet portion is inserted. Is measured based on the temperature detection signal of the thermistor and stored by the storage means. An indicator is injected into the blood outlet portion of the vena cava, and the indicator mixed blood temperature of the blood mixed with the indicator at the pulmonary artery blood inlet portion is obtained. Is measured based on the temperature detection signal of the thermistor and stored by the storage means. The calculating means calculates the flow rates of the blood flowing through the right heart and the indicator mixed blood based on the equation (3). The flow rate of the mixed blood is recorded by the storage means, and the flow rates of the blood and the indicator mixed blood are displayed by the display means of the control device, whereby a low flow rate and a high indicator Time, long infusion times, can be obtained even precise cardiac output measurements in the measurement conditions of constants differ such as when the catheter with the thermistor, it is possible also to measure in any measurer. As a result, the quality of the heart function of the living body can be accurately grasped.

"Example" Hereinafter, the cardiac output measuring device of the present invention will be described.

First, the apparatus of the present invention will be described with reference to FIGS.

In FIG. 1, reference numeral 21 denotes a catheter with a thermistor (Swan-Ganz).
Catheter (commercial product, trade name)), and the catheter 21 with the thermistor is made of synthetic resin and has a flexible outer diameter of about
It consists of a solid striatum of 2.3 mm and length of about 1 m, and is configured as follows. That is, the thermistor 23 is fitted into a concave portion formed at an outer peripheral surface portion approximately 30 mm to 50 mm apart from the tip of the thermistor-equipped catheter 21. The outside is covered with a thin thick portion. In addition, the lead wire 23a of the thermistor 23 is buried in the rear end side of the thermistor-equipped catheter 21 from the attachment point of the thermistor 23 when the thermistor-equipped catheter 21 is molded, and protrudes outside from the rear end of the thermistor-equipped catheter 21. . In addition, a catheter 21 with a thermistor
An indicator injection hole 26a consisting of a long hole with a circular cross section is formed from a point about 300 mm away from the tip of the catheter 21 with the thermistor to the rear end of the catheter 21 with the thermistor, and the tip of the indicator injection hole 26a, that is, about 300 mm from the tip of the catheter 21 with the thermistor. An orifice 26b that connects the indicator injection hole 26a and the outside of the thermistor-equipped catheter 21 is formed at the separated location. The thermistor-equipped catheter 21 has a hollow portion (elongated hole) 26c. The fluid pressure applied to the distal end of the hollow portion 26c is transmitted to the rear end of the thermistor-equipped catheter 21.

The thermistor 23 includes a lead wire 23a and the lead wire 23a.
A / D converter (analog / analog) connected to connector 23b
Controller 25 via digital converter) 24
Is electrically connected to

At the rear end of the thermistor-equipped catheter 21, an indicator injection device 26 connected to communicate with the indicator injection hole 26a is attached.

The indicator injection device 26 is provided with a timer 27, and the timer 27 is connected to the controller 25 so that the fluid in the indicator injection device 26 can be discharged for a set time of the timer 27.

As shown in FIG. 3, the controller 25 includes a CPU (central processing unit) 28 for controlling each unit of the apparatus, a ROM 29 storing a control program used in the CPU 28, a RAM 30 for temporarily storing data, and a CPU 28. It comprises an interface 33 for connecting each part of the device (thermistor 23 of catheter 21 with thermistor, A / D converter 24, timer 27 of indicator injector 26, display means 31, keyboard 32).

In use, the catheter 21 with the thermistor is inserted into the inflow part from the vena cava 34 to the right atrium from the distal end side where the thermistor 23 is attached, and is operated under X-ray monitoring, as shown in FIG. Side penetrates through the right heart 35 of the heart to the pulmonary artery.
The orifice 26b for injecting the indicator is located at the blood outlet of the vena cava or the inlet 37 of the right atrium.

Next, the operation of the cardiac output measuring device configured as described above will be described with reference to the flowchart shown in FIG.

SP1; storage means for cardiac output measuring device is connected with a thermistor catheter 21, the calculating means, the Kon'ntorora 25 having a display unit, T: measured at time t temperature, T _∞: mixing steady blood indicator Temperature, T _F : blood temperature, t _c : time constant of catheter, based on Newton's cooling law And wherein, Q _F: Blood flow, V _I: injected amount of indicator, [rho _I: Density of the indicator, [rho _F: density of blood, C _I: heat capacity of the indicator, C _F: heat capacity of the blood, T _F: blood temperature , T _I : indicator temperature, T _：: steady-state temperature of mixing of blood and indicator, t _I : heat-injection time of indicator and heat balance equation of blood and indicator Q _F ρ _F C _F (T _F −T _∞ ) from _{= V I ρ I C I (} T ∞ -T I) / t I ...... (2) equation, to erase the mixture constant temperature T _∞ of said blood indicator SP2; The catheter 21 with the thermistor is inserted into the blood outlet of the vena cava 34 of the heart.

SP3: The blood temperature of the blood inlet portion 36 of the pulmonary artery is measured based on the temperature detection signal of the thermistor 23 and stored by the storage means of the controller 25.

SP4: The indicator is injected into the blood outlet of the vena cava 34 by the indicator injector 26.

SP5: The indicator mixed blood temperature of the blood mixed with the indicator at the blood outlet portion of the vena cava 34 is measured based on the temperature detection signal of the thermistor 23 and stored by the storage means of the controller 25; SP6; by the arithmetic means of the control device wherein (1), (2) said erasing the mixture constant temperature T _∞ of blood and an indicator (3) blood flowing through the Migishin unit 35 from the equation, calculates the flow rate of the indicator mixture blood from the equation, and stores .

SP7: The stored measurement flow rates of the blood and the indicator-mixed blood are displayed by the display means 31 of the controller 25.

 Thus, the measurement of the cardiac output is completed.

By the way, since there is a problem of whether the measured value measured in this way is reliable, the inventor of the present invention has determined whether or not the above-mentioned cardiac output measurement method of the present invention is good or not by the simulated cardiac output measurement described below. Confirmed by method. Next, a method of measuring the simulated cardiac output will be described.

FIG. 5 is a schematic piping diagram of a simulated cardiac output measuring device for confirming and evaluating the quality of the method of the present invention by comparing it with the measurement result of the cardiac output measuring device of the present invention.

In FIG. 5, reference numeral 1 denotes a blood reservoir having an automatic temperature controller and a stirring device. Blood collected from a living body (bovine blood in this embodiment) is stored in the blood reservoir 1 in a stirring state.

The blood reservoir 1 is connected to a roller pump 2 by a pipe 1a, and the roller pump 2 is connected by a pipe 2a to a stirrer 3 having a stirrer (corresponding to the right heart of a living heart, which is a substitute simulated heart for a living heart). Have been.

A catheter with a thermistor (Swan-Ga
nz catheter) (commercial product name) 5 is inserted, and this Sw
A temperature sensor (thermistor) 4 is attached to the tip of the an-Ganz catheter 5, and a syringe 9 is attached to the rear end of the Swan-Ganz catheter 5 so that an indicator (saline) can be injected into the agitator 3. Are in communication.

The inside of the upper part of the stirrer 3 is connected to the measuring cylinder 6 by a pipe 5a. The measuring cylinder 6 is connected to a predetermined location by a pipe 6a.

An A / D converter (analog / digital converter) 7 is connected to the thermistor 4 of the stirrer 3. A controller 12 is connected to the A / D converter 7 as described later.
The recording device 8 is connected to the controller 12.

As shown in FIG. 7, the controller 12 includes a CPU (Central Processing Unit) 13 for controlling each unit of the apparatus, a ROM 14 storing a control program used in the CPU 13, a RAM 15 for temporarily storing data, a CPU 13 Each part (a stirring motor of blood reservoir 1, an automatic temperature controller built in blood reservoir 1, a motor of roller pump 2, a stirring motor of stirrer 3,
An A / D converter 7 connected to a temperature sensor (thermistor) 4 of a catheter 5 with a thermistor inserted into the agitator 3;
It comprises a record display device 8, a keyboard 16, and an interface 11 for connecting to an A / D converter 10) connected to a temperature sensor (thermistor) 1b of the blood reservoir 1.

Next, the operation when the simulated cardiac output is measured by the cardiac output measuring device configured as described above will be described with reference to the flowchart shown in FIG. Before starting the flow measurement described below, the following expression (3) is input from the keyboard 16 to the CPU via the interface 11 and stored therein.

SP1; blood (bovine blood in this embodiment) extracted from a living body is stored in a blood reservoir 1, and the blood is automatically temperature-controlled via a temperature sensor (thermistor) 1a and a controller 12, and blood in the blood reservoir 1 is stored. It is determined whether or not the temperature has been adjusted to the predetermined temperature.
Proceed to.

 SP2: Roller pump 2 is turned on.

SP3: The blood automatically temperature-controlled by the blood reservoir 1 is made into a steady flow or a pulsating flow by the roller pump 2 and the agitator 3
Send to

SP4: A low-temperature indicator (physiological saline) is injected into the stirrer 3 from the syringe 9.

 SP5: The blood and the physiological saline in the agitator 3 are agitated.

SP6: The mixed fluid of the blood and the physiological saline in the agitator 3 stirred in SP5 is caused to flow out to the measuring cylinder 6, and the flow rate of the fluid is measured by the measuring cylinder 6.

At the same time, the output data (temperature signal) of the thermistor 4 is input to the A / D converter 7.

SP7: The temperature data of the thermistor 4 is input to the controller 12 via the A / D converter 7.

SP8: Based on the temperature data of the thermistor 4, the flow rate of the fluid flowing out of the agitator 3 via the catheter 5 is calculated by the calculation means of the controller 12 using the following calculation formula (3).

SP9; The calculation result of SP8 is stored by the controller 12.

SP10: The calculation result of SP8 is recorded and displayed by the recording and display device 8.

In addition, as an example, as in the conventional example, the injection amount of the physiological saline is 0.77, 2.27, 4.27, 9.27 ml, the injection temperature is 274,278,283,
At 293 K, the injection time is 2, 5, 10 seconds, and the blood flow rate from the roller pump 2 to the agitator 3 is 1 to 6 / min.

By the way, the data of the thermodilution curve includes Newton's cooling law shown in the following equation (1) (the law that the amount of heat lost by an object due to radiation is proportional to the difference between the temperature of the object and its surroundings, and the approximate law I (Found by .Newton).

Here, T is the measured temperature at time t, T _∞ is mixed steady state temperature of the blood and the indicator, T _F is the blood temperature, the t _c indicates the time constant of the catheter.

On the other hand, the following heat balance equation (2) is established from the physiological balance of the indicator and the heat balance of the blood.

_{Q F ρ F C F (T} F -T ∞) = V I ρ I C I (T ∞ -T I) / t I ...... (2) where, Q _F is blood flow, V _I is the physiological indicators injection volume of saline, [rho _I is the density of the saline, [rho _F is the density of blood, C _I
Is the heat capacity of saline, C _F is the heat capacity of blood, T _F is the blood temperature, T _I is the temperature of saline, _T∞ is the steady temperature of mixing of blood and indicator, and t _I is the injection time of saline, respectively. Show.

However, not be T _∞ is measured using the heat balance equation (2).

This is because when the cardiac output of the living body is actually measured as described above, the time at which the low-temperature indicator is injected from the orifice 26b is instantaneous. mixing and constant temperature T time until _∞, by a very short time until the temperature is as followed blood flows immediately indicator mixed blood after passing through the T _∞ rises, the thermistor with This is because 23 is not able to detect the above _T∞ .

Therefore, the blood, in order to calculate the flow rate without using the indicator mixture temperature T _∞, the formula (1), wherein T (2)
_{When ∞} is eliminated, the following flow rate calculation formula (3) can be used to calculate the blood flow rate based on the thermodilution curve.

Here, Q _F is blood flow, V _I is the injection amount of saline indicator, [rho _I is the density of the saline, [rho _F is the density of blood, C _I
Is the heat capacity of saline, C _F is the heat capacity of blood, T _F is the blood temperature, T _I is the temperature of saline, _T∞ is the steady temperature of mixing of blood and indicator, and t _I is the injection time of saline, respectively. Show.

This flow rate calculation formula (3) is a cardiac output calculation formula considering the time constant of the catheter, and the blood flow rate from this formula (3) is calculated at each time within the range of time t = 0.3 to 0.7 seconds, for example, 0.3 times. Second,
It is calculated from each sensing temperature T at each predetermined sensing time, such as 0.4 seconds and 0.5 seconds. The physical property value is 1.08 as before.

Here, when the time constant of the thermistor-equipped catheter that needs to be used in the flow rate calculation formula (3) is known in advance, the flow rate can be calculated using the time constant.
When the time constant of the catheter with a thermistor is unknown, the flow rate cannot be calculated from the flow rate calculation equation (3) until the time constant of the catheter is checked.

Then, the following experiment was performed in order to know the time constant of the catheter with a thermistor.

First, a catheter with a thermistor is immersed in a constant temperature bath at a certain liquid temperature _TF filled with liquid. Then, the catheter with a thermistor exhibits a resistance value corresponding to the liquid temperature _TF . Then, replace the thermistor catheter in bovine blood vessel of a low-temperature T _∞ where bovine blood is filled in a certain moment. After a lapse of a certain time, the temperature of the thermistor-equipped catheter becomes the above-mentioned _T∞ , and shows a resistance value corresponding to the temperature _T∞ .

This situation is shown graphically in FIG. That is, the environmental temperature of the thermistor catheter was inserted (liquid temperature) of FIG. 10 (horizontal axis Δ time and the vertical axis represents the environmental temperature T of the thermistor) as shown in, to a temperature T _∞ in the certain temperature T _F instantaneously alter, change as shown in FIG. 10 proceeds the temperature of the thermistor catheter is toward the ambient temperature T _∞. Δt in FIG. 10 differs depending on the time constant of the thermistor.

From the above experiment, the sensing time of the thermistor (se
c) The relationship between the (horizontal axis) and the indicated dimensionless temperature of the catheter with a thermistor ( _TT− / _TF - _T∞ ) (vertical axis) is shown in the graph of FIG. 9 and the sensing of these thermistors is performed. It was found that the time and the indicated dimensionless temperature of the catheter with the thermistor had a linear relationship. Then, the time constant of the thermistor-equipped catheter can be obtained from a graph showing the relationship between the thermistor sensing time and the indicated dimensionless temperature of the thermistor-equipped catheter.

The time constant obtained from the slope of the straight line shown in FIG.
It varied from 1.69 to 2.27. This is due to the difference in heat transfer characteristics between each thermistor and the polymer-coated portion.

Incidentally, the (3) to calculate the flow rate Q _F from the equation This equation (3) of the time t, it takes a measured temperature T value at time t, the flow rate Q _F which calculates the equation (3) is a time t Since it is a function of the temperature T, if the temperature at a certain time of the thermodilution curve can be measured, the flow rate at that time can be calculated.

Therefore, if the time constant of the catheter to be used is checked and notified in advance, the sensing temperature T of the thermistor at a predetermined time (for example, 0.3 seconds, 0.4 seconds, 0.5 seconds, etc.) t in the falling curve range of the thermodilution curve is measured. Thus, the flow rate of the indicator-mixed blood that has passed through the right heart can be calculated.

Therefore, the indicator-mixed blood flow rate at that time is calculated from the sensing measured temperature T by the thermistor at the predetermined time t among the five points of the sampling interval of 0.1 second from the falling point of the thermodilution curve after the injection of the indicator. If the average value of the flow rates is obtained, the cardiac output can be calculated.

Next, a conventional flow rate measurement result using the formula (I),
Table 1 shows the results of flow rate measurement using equation (3). (I) in Table 1 shows the measurement results using the above formula (I), and (3) in Table 1 shows the measurement results using the above formula (3). Also,
In Table 1, * indicates that the measured values are not statistically valid but are statistically valid by comparison with those measured with a measuring cylinder as described above.

In these measurements, the indicator injection amount was 4.27 ml, the injection temperature was 274K, and the injection time was 2 seconds.

From Table 1, the measured flow rate according to the formula (I) increases with the time constant, and a catheter having a smaller time constant has a value closer to the actually measured flow rate. The maximum error at low flow rate was 31%, and the maximum error at high flow rate was 9% for catheters with a large time constant. The time constant is indicative of the heat transfer characteristics of the catheter. A catheter with a small time constant exhibits a high responsiveness to changes in blood temperature, and is therefore suitable for accurate cardiac output measurement. However, commercially available Swan-Ganz catheters have different time constants depending on the object, and high accuracy cardiac output cannot be measured without correcting the time constant by the measurement using the formula (I).

On the other hand, the measured flow rate according to the formula (3) of the present invention has a maximum error of 14% and a correlation coefficient of 0.999 in the range of the measured flow rate of 1 to 6 / min.
The flow rate coincided with the measured flow rate.

The above is the result when blood is flowed from the pump to the stirring tank 3 at a constant flow rate in the above apparatus. The flow rate is measured in the state closest to the actual condition of the living body, and the flow rate is calculated using the above equation (3). Therefore, a pulsating flow (pulsating flow) was applied from the pump 2 to the stirring tank 3 in the above apparatus, and the controller measured the flow rate at a beat number of 1.25 _S ^-1 and a Duration of 75%, and the quality was confirmed. Table 2 shows the flow measurement results using the above formula (I) and the flow measurement results using the above formula (3) in this case. In Table 2, * indicates that the measured values are statistically valid by comparing with those actually measured with a graduated cylinder as described above, although no biological experiments were performed.
As a result, the measured flow rate by the above equation (3) has a maximum error of 16%,
The correlation coefficient was 0.996, which was consistent with the measured flow rate. From these results, it was confirmed that the flow measurement method of the present invention represented by the formula (3) is effective in both a steady flow and a pulsating flow.

By the way, there is a concern that the measured flow rate may be different even if the same amount and the same temperature of the indicator is injected between the time when the indicator is injected into the blood for a long time and the time when the indicator is injected into the blood for a short time. dynamic flow rate _{Q F = 4 (n = 5} ), injection volume V _I = 4.27 ml saline, saline infusion temperature T _I = 274 K
Confirm the effect of injection time on the measured flow rate as
The results shown in FIG. 6 were obtained.

FIG. 6 shows the effect of the injection time on the measured flow rate according to the formulas (I) and (3).

The vertical axis of FIG. 6 shows the ratio of the flow rate measured by the formulas (I) and (3) to the flow rate actually measured by the measuring cylinder, and the vertical axis shows the injection time of the indicator. In FIG. 6, a solid white bar graph shows the flow rate measurement result by the above formula (I), and a hatched bar graph shows the flow rate measurement result by the above formula (3).

According to FIG. 6, the measured flow rate according to the above formula (I) had a maximum error of 20% at an injection time of 10 seconds, which was significantly different from the actually measured flow rate.

On the other hand, the measured flow rate according to the formula (3) was in good agreement with the actually measured flow rate, and a result was obtained which was not affected by the injection time. That is, in FIG. 6, the ratio of the measured flow rate to the actually measured flow rate is
As the value approaches 1.0, the measured flow rate is closer to the actual measured flow rate, indicating that the measurement has been performed with high accuracy.

As described above, the cardiac output measurement method according to the equation (3) is not affected by the heat transfer characteristics of each catheter and the conditions such as the indicator injection amount, the indicator injection temperature, and the indicator injection time. It was also confirmed that accurate cardiac output measurement was possible.

The ability to measure the flow rate with high accuracy without being influenced by the conditions such as the indicator injection amount, indicator injection temperature, and indicator injection time
This means that the operability of the flow measurement has been improved without requiring any operation technique and without choosing the operator.

[Effects of the Invention] According to the device of the present invention, the time constant of the catheter greatly affects the accuracy of measuring the temperature of the fluid, and a measurement error occurs particularly at a low flow rate, a high indicator temperature, and a long injection time of the indicator. Insufficient accuracy, and thus the inability to accurately measure cardiac output, eliminates the problem of low flow rates, high indicator temperatures, long infusion times, and different time constants for thermistors with catheters. A precise cardiac output measurement result can be obtained, which can be measured by any measurer, so that the measurement accuracy is improved and the measurement operation is facilitated.

[Brief description of the drawings]

1 and 2 are schematic diagrams showing the device of the present invention, FIG. 3 is a diagram showing the electrical configuration of the control device, FIG. 4 is a flowchart showing the operation of the device of the present invention, and FIG. FIG. 6 is a piping diagram of a simulated cardiac output measuring device for evaluating the cardiac output measuring device of FIG. 6, FIG. 6 is a diagram showing the relationship between the ratio of the measured flow rate to the actually measured flow rate and the physiological saline injection time, and FIG. FIG. 8 is a diagram showing the electrical configuration of the controller, FIG. 8 is a flowchart thereof, FIG. 9 is a diagram showing the relationship between the sensing time of the thermistor and the indicated dimensionless temperature of the catheter, and FIG. It is a figure showing the relation of the thermistor under change. 21 ... Thermistor-equipped catheter, 23 ... Thermistor,
25: controller, 26: indicator injection device, 34: vena cava, 36: pulmonary artery entrance, 37: right atrium entrance.

────────────────────────────────────────────────── ─── Continued on the front page (58) Fields investigated (Int. Cl. ⁷ , DB name) A61B 5/02-5/0295 G01K 1/00-19/00 Practical file (PATOLIS) Patent file (PATOLIS)

Claims (1)

(57) [Claims] 1. A cardiac output measuring apparatus having a storage means, an arithmetic means, and a display means connected to a cardiac output measuring device having a catheter with a thermistor, wherein: T: time t measured temperature in, T _∞: mixing steady state temperature of the blood and the indicator, T _F: blood temperature, t _c: when the time constant of the catheter, based on the cooling Newton's law Equation: Q _F : blood flow, V _I : indicator injection volume, ρ _I : indicator density,
ρ _F : density of blood, C _I : heat capacity of indicator, C _F : heat capacity of blood, T _F : blood temperature, T _I : indicator temperature, T _：: steady mixing temperature of blood and indicator, t _I : injection of indicator when it is time, the thermal balance equation _{Q F ρ F C F (T} F -T ∞) of blood and an indicator from _{= V I ρ I C I (} T ∞ -T I) / t I ...... (2) formula It was erased mixture constant temperature reagent T _∞ of said blood indicator The formula is stored, and the catheter with the thermistor is inserted into the inflow portion from the vena cava to the right atrium, and the blood temperature at the outflow side of the pulmonary valve or the pulmonary artery blood inlet portion is determined based on the temperature detection signal of the thermistor. Measured and stored, further, an indicator is injected into the blood outlet portion of the aorta, and the indicator mixed blood temperature of the blood mixed with the indicator at the aortic blood outlet portion is measured based on the temperature detection signal of the thermistor. The calculation means calculates the flow rates of the blood flowing through the right heart portion and the indicator-mixed blood from the equation (3) stored in the storage means, and calculates the calculated flow rates of the blood and the indicator-mixed blood. The cardiac output is stored in a storage means, and the display means retrieves and displays the stored flow rates of the blood and the indicator-mixed blood. Constant apparatus.