JP2511153B2 - Cardiac output measuring device - Google Patents

Description

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

[Prior Art] Conventionally, an indicator dilution method has been used to measure cardiac output by a right heart catheterization method for cardiac mechanics examination, and this indicator dilution method uses cardiac diffusion from thermal diffusion. There are a thermodilution method for obtaining the amount and a dye dilution method for obtaining the cardiac output from the change in illuminance due to the diffusion of the pigment. Here, the thermodilution method will be described.

In the right heart catheterization method, a catheter is introduced from the jugular vein, femoral vein, elbow cord 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, a dilution curve of that temperature (a diagram of temperature change with time) is obtained, and from the area of the curve, etc., the following by Stewart-Hamilton method ( The cardiac output is calculated by the equation 1).

The cardiac output is calculated by the following equation (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 Specific gravity, C _b : Specific heat of blood ∫ _o ^∞ 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 Invention] In the above-mentioned conventional example, for example, a cardiac output measuring apparatus using a thermodilution method or an indicator dilution method is intermittent in measurement and is used for continuous measurement of cardiac output. Cannot be used, and if it is frequently measured, the total amount of liquid to be injected increases, increasing the burden on the subject and increasing the risk of infection due to operation.

Further, in the cardiac output measuring device capable of continuously measuring cardiac output disclosed in Japanese Patent Laid-Open No. 61-125329, it is necessary to measure the absolute value of the blood flow velocity and the blood flow. In the measurement of the absolute value of the velocity, the probe output does not always change according to the theoretical formula, which causes a measurement error.

Furthermore, when the change in blood flow velocity is detected as a temperature change and the cardiac output is calculated from the temperature change information by a unique function and parameter (constant), the temperature change information and the cardiac output are not always calculated. If there is a measurement error in the calculated value of cardiac output because the values do not match, or if the characteristics of the standard probe and the characteristics of the individual probes are different, the difference in the characteristics also causes a difference in the calculated value of cardiac output. There is a drawback that the measurement accuracy of the cardiac output decreases due to this.

[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, means for detecting the blood temperature during calibration and measurement, and means for detecting the equilibrium temperature at the time of calibration and measurement when warmed by a constant current and cooled by blood to reach an equilibrium state. When,
Means for measuring the cardiac output during calibration by injecting an indicator liquid, means for determining the constants A and B of the equation logTt = A · logv + B which defines the relationship between the blood flow velocity v and the equilibrium temperature Tt, The detected equilibrium temperature and cardiac output during calibration are Tt _CAL and C, respectively.
O _CAL , where CO is the cardiac output set as the reference, means for obtaining the first equilibrium temperature Tt from the first equation Tt = Tt _CAL (CO / CO _CAL ) ^A including the constant A, The blood temperature at the time of the detected calibration TB _CAL , the blood temperature and the equilibrium temperature at the time of the detected measurement TB, Tt _R , respectively,
If the correction constant set to K, and means for determining a second equation _{Tt = Tt R -K (TB-} TB CAL) than the second equilibrium temperature Tt, measured on the basis of the cardiac output at the time of the detected calibration A unit for dividing the range into a plurality of units; a unit for dividing the constant A into a plurality of constants as a value depending on the flow velocity based on the detected cardiac output during calibration; In each of the measured ranges, the second equilibrium temperature Tt and the case were divided into a third equation CO = CO _CAL (Tt / Tt _CAL ) ^{1 / A} obtained by modifying the first equation. Means for determining a continuous cardiac output from the third equation by applying a plurality of constants.

[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, and the change in cardiac output is directly obtained from the temperature change information, and the function and parameter (constant) experimentally matched to the probe output
By automatically selecting and calculating multiple characteristics of each probe, cardiac output can be continuously measured without measuring the absolute value of blood flow velocity. It is a thing.

[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 device according to an embodiment of the present invention.

In FIG. 1, reference numeral 1 is a main body of a cardiac output measuring apparatus, and externally connectable exchangeable cardiac output measuring catheters 2 and 7. 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. Circuit 16, and a thermistor 10 (preferably a self-heated thermistor) that detects changes in blood flow rate as an equilibrium temperature by a thermal flow measurement method.
The equilibrium temperature detection probe circuit 17 is provided. Also,
A resistor 13 is provided as an electrically passive element, and the characteristic of the probe is recognized by its characteristic value.

The blood temperature measuring probe circuit 16 and the equilibrium temperature measuring probe circuit 17 are 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 device main body via the connectors 11 and 12, respectively. It is connected and is located in the pulmonary artery during cardiac output measurement and detects the body temperature of the central part as a blood temperature signal. In addition, the catheter 2 and the catheter 7 described above are
Each is 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, a main CPU unit 40 that calculates and outputs cardiac output intermittently by thermodilution method or continuously by equilibrium temperature measurement, and the main CPU unit 40.
Is divided into a display unit 51 for displaying the cardiac output value obtained by calculation, and a power supply unit 60 for supplying a DC power supply to each unit.

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 and outputs a voltage signal corresponding to the temperature. In addition, 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
Detects the equilibrium temperature from the relationship between the amount of heat applied to the self-heating type thermistor and the amount of heat taken away by the flow velocity of the surrounding blood, and outputs a corresponding voltage signal. Then, the characteristic value measuring circuit 22 reads the characteristic of the resistor 13, recognizes the characteristic of the probe from the value, and generates a signal representing the characteristic of the probe.

With respect to the local CPU 30, the main CPU 44 stores the measurement circuits (the infusate temperature measurement circuit 24, the blood temperature measurement circuit 25, etc.) stored in the ROM 45 according to the program shown in FIG. 3, for example.
The equilibrium temperature measuring circuit 26 and the characteristic value measuring circuit 22) are instructed to execute the measurement, and a signal for controlling the measuring operation is sent. RAM46
Temporarily stores the data necessary 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 is converted to A / D via the analog switch.
It reaches the converter 28, where it is converted into digital data and then taken into the local CPU 30. And the local CPU30
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 serves as a signal transmission medium for electrically insulating the optical transmitter / receiver circuits from each other. Therefore, the measuring unit 20
Since the electrical connection between the voltage signal of and the voltage signal of the main CPU section 40 is completely cut off and no closed loop is formed between the subject and the main CPU side, safe measurement can be performed.

Next, the operation of the main CPU section 40 will be described. The serial data from the opto-isolation communication circuit 35 is received by the main CPU 44. 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
Calculates the thermodilution cardiac output from the temperature of the infusate, the specific heat of the infusate, the specific gravity of the infusate, the specific gravity of the blood, the specific heat of the blood, and the temperature of the heat-diluted blood based on the Stewart-Hamilton equation (1). Is output to the calibration signal storage means 42 as the 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 stores and holds the cardiac output value by the thermodilution method or 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 constant selection means 47 selects a constant used for calculating the continuous cardiac output based on the calibration cardiac output stored and held in the calibration signal storage means 42, and calculates the result as the continuous cardiac output calculation. Send to means 43.

The continuous cardiac output calculation means 43 is the calibration signal storage means.
Based on the following calculation formula, the cardiac output during calibration, the blood temperature during calibration, the equilibrium temperature during calibration, the blood temperature during measurement, and the equilibrium temperature during measurement, which are stored in 42 Calculate stroke volume.

CO = CO _CAL × ((Tt _R- K · (TB-TB _CAL )) / Tt _CAL ) as the calculation formula for continuous cardiac output
^{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: There are constants, and it can be seen from this formula that the equilibrium temperature change due to blood temperature change from calibration is also corrected.

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 blood flow velocity And the equilibrium temperature can be experimentally determined as follows.

logTt = A · logv + B (4) However, Tt: equilibrium temperature, A, B: constant From the above formulas (3) and (4), the cardiac output at the time of 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.

In order to further improve the accuracy of the calculation of the continuous cardiac output obtained by the equation (2), the case of the constant A is classified according to the magnitude of the calibration value of the cardiac output. That is, equation (2),
Although A is set as one constant in (4) and (5), it is treated as a characteristic value that depends on the flow velocity, and in this embodiment, there is a certain cardiac output value at the time of calibration (2.75 in this embodiment). ) Is large, AH is large, and small is AL. Then, a case where the constant divided into these two is used for the calculation will be described.

By transforming the above equation (5), Tt = Tt _CAL · (CO / CO _CAL ) ^A (7) is obtained, so the continuous cardiac output is calculated when the calibration value of cardiac output is CO _CAL ≥ 2.75. The formula is shown below.

The equilibrium temperature Tt _2.75 when the cardiac output CO is 2.75 is (7)
From the formula, Tt _2.75 = Tt _CAL · (2.75 / CO _CAL ) ^AH (8) with constant A as AH. Then, at the time of actual measurement, the equilibrium temperature Tt can be easily obtained by the equation (6), so the following cases are divided according to the result of comparing the value of Tt with the value of Tt _2.75 obtained from the above equation (8), Calculates continuous cardiac output. That is, (a) When Tt ≥ Tt _2.75 , and CO _CAL = 2.75, (8)
From the formula, Tt _CAL = Tt _2.75 , so CO = 2.75 · (Tt / Tt _2.75 ) ^{1 / AL} (9) is obtained, and (b) When Tt ≤ Tt _2.75 , CO _CAL is the value at the time of calibration. As it is, calculate continuous cardiac output by CO = CO _CAL · (Tt / Tt _CAL ) ^{1 / AH} (10).

On the other hand, the calculation formula of continuous cardiac output when the calibration value of cardiac output is CO _CAL <2.75 is as follows.

In this case, the equilibrium temperature Tt _2.75 when the cardiac output CO is _2.75.
Is Tt _2.75 = Tt _CAL · (2.75 / CO _CAL ) ^AL (11), where AL is the constant A in the equation (7). Then, at the time of actual measurement, the equilibrium temperature Tt is calculated by the equation (6), and the value of the Tt and the Tt obtained by the equation (11) are obtained.
_Based on the result of comparing the values of _2.75 , make the following cases,
Calculates continuous cardiac output. That is, (a) When Tt ≥ Tt _2.75 , CO _CAL uses the value at the time of calibration, and CO = CO _CAL · (Tt / Tt _CAL ) ^{1 / AL} (12) is obtained, and (b) Tt <Tt _If CO _CAL = 2.75 when _2.75 , Tt _CAL = Tt _2.75 from equation (8), so calculate continuous cardiac output by CO = 2.75 · (Tt / Tt _2.75 ) ^{1 / AH} (13) . Therefore, it is possible to continuously measure the cardiac output with high accuracy without measuring the absolute value of the blood flow velocity.

FIG. 2 shows the relationship between the flow velocity and the equilibrium temperature. However, I _c : current value, V _o : output potential T _b : blood temperature, K: constant, and T _b is a characteristic curve obtained from a constant, and (2), (9), (10),
The characteristic curves obtained from equation (4), which was experimentally determined by the basic equations for introducing equations (12) and (13), and the actual measurement data (black circles in the figure) are shown. It can be seen that the above equation better agrees 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 smooths the AC output voltage from the power supply transformer and converts it into a stabilized DC voltage, and the DC / DC converter circuit 6
The DC voltage for the measuring unit 20 is shown in 3, and the main CP is shown in the main CPU.
Supply DC voltage for U part respectively.

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.

When starting measurement of continuous cardiac output, step S1
Determines whether cardiac output calibration is required. 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 results are stored as a calibration value of cardiac output, a calibration value of blood temperature, and a calibration value of equilibrium temperature in the calibration signal storage means in steps S6, S7, and S8, and the calibration process is completed. Further, in step S14, a constant for cardiac output calculation is selected based on the calibration value of the equilibrium temperature.

If it is determined that calibration is unnecessary in step S1, immediately measure the blood temperature in the blood temperature measuring circuit of step S10,
Then, the equilibrium temperature measurement circuit of step S11 starts to measure the equilibrium temperature. The continuous cardiac output is calculated in step S12 based on these measurement results and calculation constants, and the calculated 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. The cardiac output can be continuously measured without measuring the absolute value of, and the measurement accuracy can be improved because a constant according to the measurement range is used for calculation.

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, without manufacturing the catheter 2 and the catheter 7 as a single body in appearance, only the indicator injection mechanism of the catheter 2 is provided integrally with the catheter 7, and the indicator thermometer probe circuit is configured independently to provide an indicator injection tank. It may be inserted into.

[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, 13 …… Resistor, 15 …… Indicator thermometer probe circuit, 16
...... Blood temperature probe circuit, 17 …… Equilibrium temperature probe circuit, 20 …… Measuring section, 21 …… Constant voltage circuit, 22 …… Characteristic value measurement circuit, 23 …… Constant current source circuit, 24 …… Injection liquid Temperature measuring circuit, 25 …… Blood temperature measuring circuit, 26 …… Balanced temperature measuring circuit, 27 …… Analog switch, 28 …… A / D converter, 29,
45 …… ROM, 30 …… Local CPU, 31,46 …… RAM, 35 ……
Opto-isolation communication circuit, 36,37 …… Optical transceiver circuit, 38 …… Optical fiberglass, 40 …… Main CPU section, 4
1 …… Cardiac output calibration means, 42 …… Calibration signal storage means, 4
3 …… Continuous cardiac output calculation means, 44 …… Main CPU, 47 ……
Constant selection means, 50 ... cardiac output input means, 51 ... indicator, 60 ... power supply section, 61 ... power transformer, 62 ... DC power supply circuit, 63 ... DC / DC converter circuit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-61-125329 (JP, A) JP-A-62-207435 (JP, A) JP-A-63-216536 (JP, A) JP-A-1- 70024 (JP, A)

Claims (1)

(57) [Claims] 1. Means for detecting blood temperature during calibration and measurement, respectively, and equilibrium temperature at the time of calibration and measurement when warmed by a constant current and cooled by blood to reach an equilibrium state, respectively. A means for detecting, a means for injecting an indicator liquid to measure the cardiac output during calibration, and an equation that defines the relationship between the blood flow velocity v and the equilibrium temperature Tt logTt = A · logv + B constants A and B are determined. Means for calculating the equilibrium temperature and the cardiac output at the time of calibration detected as Tt _CAL and CO _CAL respectively, and the cardiac output set as the reference as CO, the first equation including the constant A Tt = Tt _CAL (CO / CO _CAL ) ^A means for determining the first equilibrium temperature Tt, the detected blood temperature at the time of calibration TB _CAL , and the detected blood temperature and equilibrium temperature at the time of measurement, respectively. TB, Tt _R , correction constant K If it, dividing means for obtaining a second equation _{Tt = Tt R -K (TB-} TB CAL) than the second equilibrium temperature Tt, the measurement range on the basis of the cardiac output at the time the detected calibrated to multiple Means for dividing the constant A into a plurality of constants as a value depending on the flow velocity based on the detected cardiac output at the time of calibration; In each case, the third equation CO = CO _CAL (Tt / Tt _CAL ) ^{1 / A} obtained by modifying the first equation is given the second equilibrium temperature Tt and the plurality of constants classified according to the case. A means for determining continuous cardiac output from the third equation by applying the method, the cardiac output measuring device.