JPH0761323B2 - Cardiac output measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to an examination room, an operating room, and the like in a medical facility such as a hospital.
The present invention relates to a cardiac output measuring device used for cardiac function tests and grasp of circulatory dynamics in ICU and the like.

[Prior Art] Conventionally, an indicator dilution method has been used to measure cardiac output by a right heart catheterization method for a cardiac function test.
The indicator dilution method includes a thermodilution method for obtaining a cardiac output from thermal diffusion and a dye dilution method for obtaining a cardiac output from a change in illuminance due to diffusion of a dye. Here, the thermodilution method will be described.

In the right heart catheterization method, a catheter is introduced from the jugular vein, femoral vein, cubital vein, etc., and is placed so that its tip is located in the pulmonary artery via the superior vena cava or inferior vena cava, right atrium, right ventricle. It The catheter has a discharge port located in the right atrium and a thermistor located in the pulmonary artery. Now, when a liquid having a temperature higher or lower than the blood temperature is injected into the right atrium from the discharge port, the liquid is diffused and diluted in the right atrium and the right ventricle. The temperature of this diluted liquid is detected by a thermistor located in the pulmonary artery, and after the dilution curve of temperature (diagram of temperature change with time), the area of the curve, etc., is calculated by the following equation by the Stewart-Hamilton method ( Calculate the cardiac output according to 1).

Where CO: cardiac output, S _i : specific gravity of infused liquid C _i : specific heat of infused liquid, V _i : amount of infused liquid T _i : temperature of infused liquid, T _b : blood temperature S _b : blood temperature Specific gravity, C _b : Specific heat of blood ∫ ₀ ^∞ ΔT _b dt: Area of thermodilution curve.

There is also a cardiac output measuring device capable of continuously measuring the cardiac output from the cardiac output obtained by the thermodilution method and the continuous blood flow velocity obtained by the thermal flow measurement (for example, , JP-A-61-125329).

[Problems to be Solved by the Present Invention] In the above-mentioned conventional example, for example, a cardiac output measuring apparatus using a thermodilution method or an indicator dilution method has intermittent measurement and continuous cardiac output measurement. However, it has the drawback that the total amount of the liquid to be injected increases if the measurement is frequently performed, the burden on the subject increases, and the risk of infection due to manipulation increases.

Further, in the cardiac output measuring device capable of continuously measuring cardiac output disclosed in JP-A-61-125329, it is necessary to measure the absolute value of the blood flow velocity, and In the measurement of the absolute value of the flow velocity, the probe output does not always change according to the theoretical formula, resulting in a measurement error.

[Means for Solving the Problems] The present invention has been made for the purpose of solving the above problems, and includes the following configuration as one means for solving the above problems.

That is, a blood temperature detecting means for detecting the temperature of blood, an equilibrium temperature detecting means for detecting a temperature which is heated by a constant current and cooled by the blood flow to reach an equilibrium state, and an indicator liquid is injected. It is equipped with a cardiac output measuring means for measuring cardiac output by measuring blood temperature, equilibrium temperature and cardiac output during calibration. And at least 3 obtained during the calibration
Combined with the three measured values, the formula CO = CO _CAL × ((Tt _R −K · (TB − TB _CAL )) / Tt _CAL ) ^{1 / A} where CO: cardiac output, CO _CAL : Cardiac output Tt _R : Equilibrium temperature during measurement TB: Blood temperature during measurement TB _CAL : Blood temperature during calibration, K: Temperature correction constant Tt _CAL : Equilibrium temperature during calibration, A: Continuous heart rate according to the constant Calculate the output.

[Operation] In the above configuration, the body temperature (blood temperature in the pulmonary artery) of the central portion during measurement and calibration, the equilibrium temperature when the equilibrium state is reached by being heated and cooled by the blood flow, and the heartbeat Output is obtained, the change in blood flow velocity is detected as a temperature change, the change in cardiac output is directly obtained from the temperature change information, and it is experimentally calculated by a function and parameter that match the probe output. The cardiac output can be continuously measured without measuring the absolute value of the blood flow velocity.

[Embodiment] A preferred embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a block diagram of a cardiac output measuring apparatus according to an embodiment of the present invention.

In FIG. 1, 1 is the main body of the cardiac output measuring device,
Externally exchangeable cardiac output measuring catheters 2 and 7
Connect. The catheter 2 is a catheter for injecting an indicator and detecting an indicator temperature based on a thermodilution method, and internally has a temperature sensitive element 3 for detecting an indicator temperature, and a correction resistor 4 for compensating for variations in characteristics of the temperature sensitive element. And an indicator temperature measuring probe circuit 15 composed of The indicator temperature measuring probe circuit 15 is electrically connected to the infusate temperature measuring circuit 24 of the measuring unit 20 of the cardiac output measuring apparatus main body via the connectors 5 and 6, and when measuring the cardiac output, the heart is measured. Located in the right atrium of.

The catheter 7 detects the temperature of blood or the temperature of a temperature-sensitive element (hereinafter referred to as equilibrium temperature) which is heated by a constant current from the constant current source circuit 23 and cooled by blood flow. Blood temperature / equilibrium temperature detection catheter, which includes a thermistor 8 for detecting the temperature of blood diluted in the right atrium and the right ventricle and a correction resistor 9 for correcting the characteristics of the thermistor. A circuit 16 and an equilibrium temperature detection probe circuit 17 including a thermistor 10 (preferably a self-heating type thermistor) for detecting a blood flow rate change as an equilibrium temperature by a thermal flow rate measuring method are provided.

Blood temperature probe circuit 16 and equilibrium temperature probe probe circuit
17 is electrically connected to the blood temperature measuring circuit 25 and the equilibrium temperature measuring circuit 26 of the measuring unit 20 of the cardiac output measuring apparatus main body via the connectors 11 and 12, respectively, and is used for measuring the cardiac output. It is located in the pulmonary artery and detects the body temperature of the central part as a blood temperature signal. The catheter 2 and the catheter 7 described above are manufactured as a single unit in appearance.

Next, the operation of the cardiac output measuring apparatus according to the embodiment will be described with reference to FIG.

The cardiac output measuring device 1 is divided as follows in terms of function. That is, a measuring unit 20 that performs various temperature measurements through the catheters 2 and 7, an opto-isolation communication circuit 35 that transmits measurement data measured by the measuring unit 20 by optical means, and an opto-isolation communication. Based on the measurement data input via the circuit 35, the main CPU section 40 that calculates and outputs the cardiac output intermittently by the thermodilution method or continuously by the equilibrium temperature measurement, and the main CPU section 40 calculates It is divided into a display unit 51 for displaying the cardiac output value thus obtained, and a power supply unit 60 for supplying a DC power supply to each of the above units.

In the measuring unit 20, the infusate temperature measuring circuit 24 detects the temperature of the indicator discharged from the opening of the catheter 2 to the right atrium,
A voltage signal corresponding to the temperature is output. Further, the blood temperature measuring circuit 25 detects the blood temperature in the pulmonary artery and outputs a corresponding voltage signal, and the equilibrium temperature measuring circuit 26 determines, for example, the amount of heat applied to the self-heating type thermistor and the flow velocity of the surrounding blood. The equilibrium temperature is detected from the relationship with the amount of heat taken away and the corresponding voltage signal is output.

The main CPU 44 measures the local CPU 30 according to the program stored in the ROM 45, for example, according to the program shown in FIG. 3 to each of the measurement circuits (injection liquid temperature measurement circuit 24, blood temperature measurement circuit 25, equilibrium temperature measurement circuit 26). Sends a signal that instructs execution and controls the measurement operation. The RAM 46 temporarily stores data required for control. These signals are transmitted via an opto-isolation communication circuit in a transmission format described later. Further, the local CPU 30 sends a selection signal to the analog switch 27 in order to select the measurement data from each of the measurement circuits. As a result, the measurement data from each measurement circuit reaches the A / D converter 28 via the analog switch, is converted into digital data there, and is then fetched by the local CPU 30. Then, the local CPU 30 sends the received data as serial data to the opto-isolation communication circuit 35 by its own serial communication function according to the program stored in the ROM 29.

The opto-isolation communication circuit 35 performs transmission / reception of data between the measurement unit 20 and the main CPU unit 40 in a completely electrically insulated state, and a photodiode circuit and a photo diode are provided on the measurement unit 20 side and the main CPU 40 side, respectively. The optical transmitter / receiver circuits 36 and 37 are composed of transistor circuits, and the optical fiber glass 38 is a signal transmission medium for electrically insulating the optical transmitter / receiver circuits from each other. Therefore, the electrical connection between the voltage signal of the measuring unit 20 and the voltage signal of the main CPU unit 40 is completely cut off, and no closed loop is formed between the human body of the subject and the main CPU side, so a safe measurement is possible. Can be done.

Next, the operation of the main CPU section 40 will be described. The serial data from the optoisolation communication circuit 35 is
Received by CPU44. Taking the case where the cardiac output is calibrated by the thermodilution method as an example, the cardiac output calibration means 41 measures the temperature of the blood generated by the injection of the cooled or warmed infusate. From the blood temperature measuring circuit 25 for measuring the change, a signal relating to the temperature of the blood diluted with heat is received from the main CPU 44. At the same time, the cardiac output calibration means 41,
Injectate temperature, infusate specific heat, infusate specific gravity, blood specific gravity, blood specific heat, based on Stewart-Hamilton equation (1),
Also, a thermodiluted cardiac output is calculated from the thermodiluted blood temperature, and the result is output to the calibration signal storage means 42 as a calibration cardiac output signal. If the thermodilution method cannot be used to inject the indicator in a serious patient, the appropriate cardiac output can be adjusted using the cardiac output input means 50 consisting of a setting switch such as a thumbwheel switch or a digital switch, and a keyboard. Is input and is output to the calibration signal storage means 42 as a cardiac output value at the time of calibration.

The calibration signal storage means 42 is a cardiac output value by the thermodilution method,
Alternatively, while storing the cardiac output value input by the cardiac output input means 50 as the calibration cardiac output,
The blood temperature signal from the blood temperature measuring circuit 25 and the equilibrium temperature signal from the equilibrium temperature measuring circuit 26 are retained and stored as the blood temperature during calibration and the equilibrium temperature during calibration, respectively. Then, when there is a request from the continuous cardiac output calculation means 43, the stored and held data is output.

The continuous cardiac output calculation means 43 includes the calibration signal storage means 42.
Calibration-related cardiac output, calibration blood temperature,
From the equilibrium temperature during calibration, the blood temperature during measurement, and the equilibrium temperature during measurement, the continuous cardiac output is calculated based on the following equation (2).

CO = CO _CAL × ((Tt _R- K ・ (TB-TB _CAL )) / Tt _CAL ) ^{1 / A} (2) where CO: cardiac output, CO _CAL : cardiac output during calibration Tt _R : Equilibrium temperature during measurement, TB: Blood temperature TB _CAL : Blood temperature during calibration, K: Temperature correction constant Tt _CAL : Equilibrium temperature during calibration, A: Constant From equation (2) above, blood from calibration It can be seen that the equilibrium temperature change accompanying the temperature change is also corrected. Therefore, it is possible to continuously measure the cardiac output with high accuracy without measuring the absolute value of the blood flow velocity.

Therefore, the process of obtaining the above equation (2) will be described with reference to a series of related equations.

Cardiac output is generally expressed as CO = sv (3) where CO: cardiac output, s: blood vessel cross-sectional area v: blood flow velocity, and equilibrium with blood flow velocity. The temperature can be experimentally determined as follows.

logT _t = A · logv + B (4) However, T _t : Equilibrium temperature, A, B: Constant From the above equations (3) and (4), the cardiac output during calibration is C
When O _CAL and the equilibrium temperature during calibration are Tt _CAL , the following relational expression is obtained.

CO = CO _CAL · (Tt / Tt _CAL ) ^{1 / A} (5) On the other hand, the equilibrium temperature change due to the blood temperature change from the time of calibration is corrected by the following formula.

Tt = Tt _R- K ・ (TB-TB _CAL ) (6) where Tt _R : Equilibrium temperature during measurement TB: Blood temperature, K: Temperature correction constant TB _CAL : Blood temperature during calibration (5) When the temperature correction of the expression (6) is performed on the expression, the expression (2), which is an arithmetic expression of the continuous cardiac output, is obtained.

FIG. 2 shows the relationship between the flow velocity and the equilibrium temperature,
Conventional theoretical formula, Here, I _{c is the} current value, V _{o is the} output potential T _{b is the} blood temperature, and K is a constant, and T _b is a characteristic curve obtained from a constant and the basic equation for introducing equation (2) Shows the characteristic curve obtained from the equation (4) defined in the above, as well as the measured data (black circles in the figure),
It can be seen that the experimentally determined formula agrees better with the measured value.

In the power supply unit 60, the power transformer 61 steps down the AC power from the outside and supplies it to the DC power circuit 62. The DC power supply circuit smoothes the AC output voltage from the power supply transformer and converts it into a stabilized DC voltage, and the DC / DC converter circuit 63
Is the DC voltage for the measuring unit 20 and the main CPU is the main CPU
DC voltage for each part is supplied.

Here, the procedure for measuring the continuous cardiac output in the cardiac output measuring apparatus of the present embodiment will be described with reference to the flow chart shown in FIG.

At the start of continuous cardiac output measurement, it is determined in step S1 whether cardiac output calibration is necessary. If calibration is required, select the calibration method in step S2, and measure cardiac output by the indicator dilution method in step S3.

On the other hand, if the indicator dilution method cannot be executed even if it is determined that the calibration is necessary, the corresponding cardiac output is manually input using the cardiac output inputting means in step S9.

Next, in step S4, the blood temperature measuring circuit measures the blood temperature, and in step S5, the equilibrium temperature measuring circuit measures the equilibrium temperature. The above measurement result is the calibration value of cardiac output,
As the blood temperature calibration value and equilibrium temperature calibration value,
In S6, S7, S8, the calibration signal storage means stores and holds it, and the calibration process ends.

If it is determined that the calibration is unnecessary in step S1, the blood temperature measurement in the blood temperature measurement circuit in step S10 and the equilibrium temperature measurement in the equilibrium temperature measurement circuit in step S11 are immediately started. Based on these measurement results, the continuous cardiac output is calculated in step S12, and the calculation result is displayed on the display as continuous cardiac output in the next step S13.

As described above, according to this embodiment, catheters having different interchangeable uses are prepared, and the indicator temperature (injection liquid temperature) is calibrated on the one hand based on the thermodilution method, and the blood temperature and the equilibrium temperature are calibrated on the other hand. At the same time, there is an effect that continuous cardiac output can be obtained by measuring at the time of measurement, converting the obtained value into an electric signal, and performing electrical calculation.

In addition, the change in blood flow velocity is detected as a temperature change, and the change in cardiac output is directly obtained from the temperature change information, and is calculated by a function and parameter experimentally matched to the probe output. There is an effect that the cardiac output can be continuously measured without measuring the absolute value of, and the measurement accuracy can be improved.

In addition, if the test subject cannot be infused with the thermodilution indicator, the cardiac output can be manually input, and the measurement unit directly related to the human body and the main CPU unit that executes electrical calculations can be electrically operated. Since it is cut off, the burden on the subject for measurement can be reduced, the risk of infection can be reduced, and safe measurement can be performed.

It should be noted that only the indicator injection mechanism of the catheter 2 is integrally provided with the catheter 7 without manufacturing the catheter 2 and the catheter 7 as a single unit in appearance, and the indicator temperature measuring probe circuit has an independent structure for injecting the indicator. It may be inserted into the tank.

[Effects of the Invention] As described above, according to the present invention, there is an effect that the cardiac output can be continuously and accurately measured without measuring the absolute value of the blood flow velocity.

[Brief description of drawings]

FIG. 1 is a block diagram of a cardiac output measuring apparatus according to an embodiment of the present invention, FIG. 2 is a diagram showing a relationship between an equilibrium temperature and a flow velocity, and FIG. 3 is a cardiac output according to the present embodiment. It is a flow chart which shows the measurement processing procedure of the continuous cardiac output of a measuring device. In the figure, 1 ... Cardiac output measuring device, 2 ... Catheter for indicator injection and indicator temperature detection, 3 ... Temperature sensing element, 4, 9
...... Correction resistor, 5,6,11,12 ...... Connector, 7 …… Blood temperature / equilibrium temperature detection catheter, 8,10 …… Thermistor, 15 …… Indicator thermometer probe circuit, 16 …… Blood thermometer probe Circuit, 17 …… Equilibrium temperature probe probe circuit, 20 ……
Measuring unit, 21,22 …… Constant voltage circuit, 23 …… Constant current source circuit, 2
4 …… Injection fluid temperature measuring circuit, 25 …… Blood temperature measuring circuit, 2
6 …… Equilibrium temperature measuring circuit, 27 …… Analog switch, 28
...... A / D converter, 29,45 …… ROM, 30 …… Local CPU, 3
1,46 …… RAM, 35 …… Opto-isolation communication circuit, 36,37 …… Optical transceiver circuit, 38 …… Optical fiber glass, 40 …… Main CPU section, 41 …… Cardiac output calibration means, 42
...... Calibration signal storage means, 43 …… Continuous cardiac output calculation means, 44 …… Main CPU, 50 …… Cardiac output input means, 51 ・ ・ ・
… Display unit, 60 …… Power unit, 61 …… Power transformer, 62 ……
DC power supply circuit, 63 ... DC / DC converter circuit.

Claims (3)

[Claims] 1. A blood temperature detecting means for detecting the temperature of blood, an equilibrium temperature detecting means for detecting a temperature which is heated by a constant current and cooled by a bloodstream to reach an equilibrium state, and an indicator liquid. It is equipped with a cardiac output measuring means for injecting blood to measure the cardiac output, and measures blood temperature, equilibrium temperature and cardiac output during calibration, and the blood temperature at that time is newly added for subsequent measurements. , Equilibrium temperature is calculated, and combined with at least three measured values obtained in the calibration, the formula CO = CO _CAL × ((Tt _R −K · (TB − TB _CAL )) / Tt _CAL ) ^{1 / A} where: CO: Cardiac output, CO _CAL : Cardiac output during calibration Tt _R : Equilibrium temperature during measurement TB: Blood temperature during measurement TB _CAL : Blood temperature during calibration, K: Temperature correction constant Tt _CAL : Calibration A cardiac output measuring device, which calculates a continuous cardiac output according to a time equilibrium temperature and A: constant. 2. The cardiac output measuring device according to claim 1, wherein the cardiac output measuring means comprises a blood temperature measuring means and a thermodilution method cardiac output calculating means. 3. The cardiac output measuring device according to claim 1, wherein the cardiac output during calibration can be set by the operator without depending on the measurement.