JP2621740B2 - Medical catheter flow meter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a medical catheter type flow meter, and more particularly, to a method for measuring a flow rate of a body fluid such as blood by a thermal effect.

[0002]

2. Description of the Related Art Techniques for measuring the flow rate of a body fluid, for example, blood, include a direct method and an indirect method, both of which are various. Currently, the most reliable is the direct method using an electromagnetic blood flow meter. This utilizes the fact that blood has conductivity, and a coil is wound around a blood vessel to apply a magnetic field perpendicular to the direction of blood flow. Then, an electromotive force is induced in the blood by electromagnetic induction, and the electromotive force is detected by a pair of electrodes arranged orthogonally to the direction of the blood flow and the direction of the magnetic field, and the blood flow is detected based on the detected electromotive force. Is calculated. However, this method requires that the blood vessels be extracted and can only be used during surgical procedures.

On the other hand, the center of the indirect method is to use an ultrasonic blood flow meter. It emits ultrasonic waves from outside the body to the blood and receives reflected waves from the blood. This reflected wave has a frequency different from that of the emitted ultrasonic wave due to the Doppler effect due to the blood flow. Therefore, the blood flow is obtained based on the change in the frequency. However, it is not clear by this indirect method where the blood flow in the living body is measured. Therefore, it is used to hear the heart sounds of the fetus and to find the position of the artery. Further, a device combining an ultrasonic sensor and a computer for calculation is extremely expensive. The ultrasonic sensor used for the indirect method is as large as several centimeters.
An ultrasonic sensor having a diameter of 3 mm has been put to practical use, and it is possible to measure the blood flow rate by a direct method by providing this ultrasonic sensor in a catheter. However, such a catheter is expensive, and the size of the ultrasonic sensor is large. For example, a coronary artery or the like is blocked by the catheter, so that it is impossible to measure the blood flow or the like.

[0004] Some indirect methods use a laser Doppler blood flow meter. This is similar in principle to an ultrasonic blood flow meter. However, the indirect method can only measure the blood flow in tissues such as earlobes and fingers that can transmit laser light at the periphery, and cannot measure the blood flow in other blood vessels. However, a laser Doppler blood flow meter can theoretically be made very thin using an optical fiber, and can be incorporated in a catheter to measure blood flow by a direct method. However, laser Doppler blood flow meters are disadvantageous in terms of cost.

Further, there is a thermal flow meter as a general flow meter. Among them, the hot-wire flowmeter generates heat by passing a current through a resistor, and obtains a flow rate from a temperature change when the resistor is cooled by a flow of a fluid. Measuring the flow rate from the temperature change when heat is applied to the fluid in this way is widely used in medical applications as a Swan-Ganz-type thermodilution (thermodilution) catheter.
For example, when measuring the blood flow in the heart, about 10 cm ³ of cold water of about 4 cm ³ is injected into the heart via a catheter, and the temperature of the tip of the pulmonary artery is measured by a thermistor provided on the catheter. The blood flow is obtained from the integrated value of the temperature change. More specifically, the thermodilution catheter has a structure in which a balloon is provided at a distal end, and a small thermistor is embedded behind the balloon. Then, when the catheter is inserted and fed from the vein on the side of the right hand, the distal end of the catheter enters the right atrium of the heart. When the balloon is inflated in the right atrium, the balloon flows by the blood flow and enters the pulmonary artery from the right ventricle, where the catheter is clogged. Here, when the balloon is compressed and fixed, the injection hole located on the side of the catheter and about 30 cm behind the distal end of the balloon is located in the right ventricle. Next, when 10 cm ^{3 of} 4 ° C. cold water is injected into the injection hole, the cold water spouts out into the right chamber and mixes with the blood in the right chamber, and the temperature of the blood in the right chamber falls. At the next heartbeat, the cold blood pushed out of the right ventricle flows through the thermistor. The temperature measured by the thermistor is as shown in FIG.
A change called a thermodilution curve as shown in FIG. The blood flow rate is determined from the thermodilution curve. The reason why a large amount of low-temperature cold water is injected as described above is that a large amount of heat change is required for measuring the blood flow volume of the heart. In other words, the heart requires about one second to measure the flow rate for pulsation, and the range of cardiac output is 1 to 10 liters. In such a case, a large amount of heat change occurs in the flow rate measurement. Required. However, such a conventional thermodilution catheter can be manufactured at a lower cost than an ultrasonic blood flow meter or a laser Doppler blood flow meter, but is still expensive and requires time and labor for injecting cold water. Above all, the error is large and the blood flow cannot be measured accurately. Furthermore, the blood flow in the coronary artery, which has recently been required to be measured, cannot be measured well. This is because the diameter of the blood vessel in the coronary artery is about 3 mm, which is thin, whereas the thermodilution catheter cannot be so small. In addition, the blood flow rate of the coronary artery
In the range of 100cm ^3, which is usually, every minute 20~30cm ^3-position.

Conventionally, a coronary sinus monitor has been used to measure the coronary blood flow. In this method, 8 with two thermistors
After inserting the catheter F into the blood vessel at the thick part of the entrance of the coronary artery, cold water is injected by a pump at a rate of about 15 cm ³ per minute. Then, the blood flow is determined from the time until the temperature detected by the thermistor reaches a certain equilibrium value. However, in such a coronary sinus monitor, the catheter used is expensive, and it takes a long time to measure, and the blood flow cannot be measured accurately. Most of all, since the blood flow is measured at the blood vessel at the entrance of the coronary artery, the blood flow to the lesion that one really wants to know is not known.

[0007]

As described above, the conventional methods for measuring blood flow have various problems.
First, electromagnetic blood flow meters can only be used during surgical procedures. In addition, the ultrasonic blood flow meter is expensive, and even if it is provided on a catheter, the blood flow cannot be measured in a thin blood vessel because it cannot be made thin. Also, laser Doppler blood flow meters are expensive. Furthermore, the conventional thermodilution catheter has a problem that it takes time to inject cold water, cannot measure blood flow accurately, and cannot measure blood flow in a thin blood vessel such as a coronary artery.

The present invention is intended to solve such a problem, and provides a medical catheter type flow meter which can easily and accurately measure a blood flow in a thick blood vessel or a thin blood vessel and can be inexpensive. The purpose is to:

[0009]

According to a first aspect of the present invention, there is provided a medical catheter type flow meter, wherein a catheter, a temperature measuring section provided at a distal end of the catheter, and a measuring section are provided. The heating unit includes a heating unit that converts a known amount of thermal energy from electric energy to the temperature unit and a temperature measurement unit that electrically measures a temperature change of the temperature measurement unit.

Further, in the medical catheter type flow meter according to the present invention, the temperature measuring means comprises a thermocouple,
The heating means includes the thermocouple and a high-frequency generator that applies a high-frequency voltage to the thermocouple, and includes a signal separator that separates a high-frequency voltage generated by the high-frequency generator and a thermoelectromotive force of the thermocouple. It is a thing.

[0011]

In the medical catheter type flow meter according to the first aspect of the present invention, when measuring the flow rate of a body fluid such as blood, the catheter is inserted into a living body, and the temperature measuring section at the distal end of the catheter is heated by the heating means. To convert a known amount of thermal energy from electrical energy. Then, a change in the temperature of the temperature measuring section is electrically measured by the temperature measuring means to determine the flow rate of the body fluid.

Further, in the medical catheter type flow meter according to the second aspect of the present invention, a high frequency voltage is applied to the thermocouple from the high frequency generator to apply heat energy to the temperature measuring section. The thermocouple generates an electromotive force corresponding to the temperature of the temperature measuring unit, but separates the high-frequency voltage by the high-frequency generator and the thermoelectromotive force of the thermocouple by a signal separator, and from the separated thermoelectromotive force, Obtain the temperature of the temperature measuring section.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the medical catheter type flow meter according to the present invention will be described below with reference to FIGS. The flow meter according to the present embodiment basically includes a temperature measuring unit 1 provided at the distal end of a catheter, as shown in FIG.
Then, a known amount of thermal energy is converted from electric energy by the heating means 2 and given, and the temperature change of the temperature measuring section 1 is electrically measured by the temperature measuring means 3 to obtain the blood flow. As shown in FIG. 1B, the temperature measuring means 3 includes a thermocouple 4, and the heating means 2 includes the thermocouple 4 and the extracorporeal electrode 5, and the thermocouple 4 and the extracorporeal electrode. And a high-frequency generator 6 for applying a high-frequency voltage to the high-frequency generator 5. Further, the temperature measuring means 3 includes a signal separator 7 for separating a high-frequency voltage generated by the high-frequency generator 6 and a thermoelectromotive force of the thermocouple 4, and detects the temperature of the temperature measuring unit 1 based on the thermoelectromotive force. A thermometer main body 8 for obtaining a temperature is provided. Further, there is a calculator 9 for calculating the flow rate from the temperature change thus obtained. In FIG. 1B, a portion surrounded by a chain line is provided on the catheter 10.

Next, a guide wire for PTCA (percutaneous transluminal coronary angioplasty) used as the catheter 10 will be described.
The configuration of the eleventh embodiment will be described with reference to FIGS. This PT
The CA guide wire 11 has a core wire 13 housed in a long thin coil 12 serving as the signal separator 7 and has flexibility and can be inserted into a thin, meandering blood vessel. I have. The reason why the dense coil 12 having a spring property is used is to provide appropriate flexibility, and the reason why the core wire 13 is passed through the coil 12 is to enhance operability. The dense coil 12, SUS304 stainless steel coil, length 1600mm, wire diameter 50μm, outer winding diameter 500μm,
It has an inner diameter of 400 µm and is coated with Teflon for the purpose of enhancing smoothness and insulation. Core wire 13
Although a stainless steel wire is used for the ordinary guide wire 11 for PTCA, in this embodiment, a beryllium bronze wire is used in order to obtain sufficient hardness and a large thermoelectromotive force. Its diameter is 200 μm. A tip 14 is provided at the tip of the guide wire 11. The tip 14 is made of stainless steel, but has a gold plating 15 on the outer surface. And chips
14 has a cylindrical shape, and a head 16 and a base 17 are arranged in the axial direction. Head 16 has an outer diameter of 500 μm and a length of 1 m
m, and the base 17 has an outer diameter of 400 μm and a length of 1 mm.
The inner diameter of the tip 14 is 200 μm. Then, one end of the coil 12 is fitted on the outer peripheral side of the base 17 and welded, and the chip 14 and the coil 12 are electrically connected. At the same time, the core wire 13 is inserted into the chip 14, welded and electrically connected. The tip 14 serves as the temperature measuring element 1 and serves as a measurement contact point between the stainless steel coil 12 and the beryllium bronze core wire 13 forming the thermocouple 4. On the other hand, on the near side of the guide wire 11,
A pair of terminals 23 and 24 are provided via insulating tubes 21 and 22. One insulating tube 21 is made of Teflon, has a length of 30 mm, an outer diameter of 300 μm, and an inner diameter of 200 μm, and is covered on the outer peripheral side of the other end of the core wire 13. Also, one terminal 23
Is made of stainless steel, has a cylindrical shape with an inner diameter of 300 μm, and a small-diameter portion 25 and a large-diameter portion 26 are arranged in the axial direction. The small diameter portion 25 has an outer diameter of 400 μm, a length of 6 mm, and a large diameter portion 26.
Has an outer diameter of 500 μm and a length of 4 mm. And small diameter part 25
The other end of the coil 12 is fitted to the outer peripheral side of the coil and welded, and the coil 12 and the terminal 23 are electrically connected. At the same time, the terminal 23 is placed on one end of the outer periphery of the insulating tube 21. The other insulating tube 22
Consists of Teflon, length 20mm, outer diameter 500μm, inner diameter
At 300 μm, it covers the one end of the outer periphery of the one insulating tube 21 and coaxially abuts the end face of the one terminal 23 on the large diameter portion 26 side. The other terminal 24 is a tube made of beryllium bronze, having a length of 4 mm, an outer diameter of 500 μm, and an inner diameter of 200 μm. The other terminal 24 is put on the outer peripheral side of the core wire 13 and welded and joined.
13 is electrically connected. Further, the two terminals 23,
24 is connected to an external electric circuit via connectors 27 and 28. The beryllium bronze is preferably made of constantan if it can exhibit a higher hardness. The two terminals 23 and 24 are electrically connected to the thermometer body 8 as shown in FIG.
Is electrically connected to the high-frequency generator 6 together with the extracorporeal electrode 5.

Next, the operation of the above configuration will be described. For example, when measuring the flow rate of blood, the guide wire 11 is inserted percutaneously into a blood vessel, and the tip 14 of the distal end of the guide wire 11 is positioned at a measurement point in the blood vessel. Then, as shown in FIG. 1C, a 13.56 MHz high frequency voltage of 10 μW is applied between the chip 14 via the core wire 13 and the extracorporeal electrode 5 located outside the living body, for example, on the back, from the high frequency generator 6. And continues to be applied. As a result, chip 14
The vicinity is dielectrically heated, and the temperature of the chip 14 rises, but the temperature of the chip 14 eventually reaches an equilibrium temperature. The equilibrium temperature is determined according to the blood flow. As shown in FIG. 5, there is a linear relationship between the log of the equilibrium temperature and the log of the blood flow. On the other hand, a thermoelectromotive force corresponding to the temperature of the chip 14 is generated at the measurement contact between the stainless steel coil 12 and the core wire 13 made of beryllium bronze, that is, the chip 14, based on the reference contact. This thermoelectromotive force is measured in the thermometer main body 8 connected to the coil 12 and the core wire 13. At this time, a high frequency of 13.56 MHz
The thermoelectromotive force which is damped by the coil 12 as a signal separator and separated from the high frequency voltage is measured in the thermometer main body 8. Then, the blood flow is determined from the equilibrium temperature determined based on the thermoelectromotive force. For example, when treating a thrombus, first, the guide wire 11 is inserted into a blood vessel, and the blood flow is measured just before the stenosis of the blood vessel. Next, the shaft of the PTCA catheter is inserted through the guide wire 11, and the balloon provided at the distal end of the shaft is inflated to expand the blood vessel. Thereafter, the shaft is removed from the guide wire 11, and the blood flow in the expanded blood vessel is measured. In this way, the position of the stenosis can be reliably specified, and whether the treatment has been successfully performed can be confirmed. In particular, in the case of a coronary bifurcation, a pre-treatment measurement of its blood flow is very important to know which bifurcation is blocked. The position of the stenosis may not be easily understood by X-ray examination alone. Measurement of blood flow after vasodilation is also important to confirm that treatment was actually successfully performed. Further, in the coronary artery, since blood is pulsating, a ripple as shown in FIG. 6 appears in the temperature change in accordance with the pulsation, and this ripple is interesting as physiological data.
In the graph of FIG. 6, the peaks correspond to the time when the heart stops, and the valleys correspond to the time when the heart moves. Assuming that the temperature measuring means is a conventional thermistor, the thermistor has a large heat capacity and poor response, so that a fine phenomenon such as the ripple cannot be detected. On the other hand, according to the temperature measuring means 3 as in the present embodiment, the above-described ripple can be detected.

In this method of measuring the flow rate, if the power is not increased as the flow rate increases, the equilibrium temperature decreases due to washing with a blood flow of about 37 ° C. and accurate measurement cannot be performed. become. On the other hand, if the maximum temperature in the vicinity of the chip 14 is suppressed to 42 ° C. or less, the problem of hemolysis does not occur from the beginning, but since the area of the chip 14 is small,
It is OK even if the temperature rises.

According to the configuration of the first embodiment, heat energy is applied to the tip 14 provided at the distal end of the guide wire 11 by high-frequency heating, and the temperature change of the tip 14 is measured by the thermocouple 4 to obtain the blood. Since the flow rate of the body fluid is measured, the flow rate of the body fluid can be easily and accurately measured without any trouble. The guide wire 11 has a diameter of 0.5 mm.
The blood flow can be freely measured not only for a thick blood vessel but also for a thin blood vessel such as a coronary artery. Further, the guide wire 11 as in the present embodiment can be inexpensive.
Then, while the high-frequency heating is performed via the thermocouple, the signal separator 7 separates the thermo-electromotive force from the high-frequency voltage, so that the heating means 2 and the temperature measuring means 3 can be shared. Thereby, the number of conducting wires incorporated in the guide wire 11 can be reduced, the structure of the guide wire 11 can be simplified, and the guide wire 11 can be made thin. That is,
The blood flow can be measured by the guide wire 11 having the same thickness as the conventional guide wire for PTCA.

Next, a second embodiment of the present invention will be described with reference to FIG. In the second embodiment, in the thermodilution catheter 30, high-frequency heating is performed by the heating means 2 instead of injecting cold water as in the related art, and the temperature is measured by the thermocouple 4 instead of the thermistor. is there. The thermodilution catheter 30 is provided with a balloon 32 that can be inflated and deflated at a distal end of a flexible plastic shaft 31. Although not shown, the shaft 31 has:
A liquid passage for taking liquid in and out of the balloon 32 is formed, and an indeflator is connected to the liquid passage on the hand side of the catheter 30. At the rear (hand side) position of the balloon 32 on the shaft 31, a metal ring 33 serving as the temperature measuring unit 1 is provided. A wire 34 similar to the guide wire 11 of the first embodiment is connected to the metal ring 33. This wire 34 passing through the shaft 31
It is a copper constantan thermocouple wire and high-frequency heating wire.

When measuring the flow rate of a body fluid, for example, blood, a catheter is inserted into a blood vessel, a metal ring 33 is positioned at a measurement point, and a 13.56 MHz frequency is applied between the metal ring 33 and the extracorporeal electrode 5. A high-frequency voltage is applied for 100 ms with a power of 100 μW. As a result, the metal ring 33 becomes 62
Heated to ° C. After this heating, the metal ring 33
Although the temperature decreases due to the blood flow, as shown in FIG.
The differential value of the temperature drop curve corresponds to the blood flow, and thus the blood flow is obtained.

In such a method for measuring blood flow,
If the temperature drop curve after one short heating period drops too fast, accurate measurement cannot be performed, so that the metal ring 33 has a somewhat large size, for example, a length of 5 mm.
It is necessary to use something of the order.

On the other hand, as in the first embodiment,
It is also possible to continuously apply heat to the metal ring 33 and determine the blood flow rate from the equilibrium temperature reached during that time.

Next, a third embodiment of the present invention will be described with reference to FIGS. The medical catheter type flow meter of the third embodiment measures the amount of urine generated per minute. The balloon catheter 41 has a shaft 42
Has a balloon 43 at its tip. In the shaft 42, a urine passage 46 having an inflow port 44 at its tip and an outflow port 45 at a middle portion of the side surface is formed. A temperature measuring unit 47 is attached to the inner surface of the urine passage 46. A wire 48 similar to the guide wire 11 of the first embodiment is connected to the temperature measuring section 47. This wire 48 which is both a wire for thermocouple and a wire for high frequency heating
Passes through the inside of the shaft 42 and reaches its proximal end, and connectors 49 and 50 are connected. In addition, 51 is
This is an indeflator for taking liquid in and out of the balloon 32 through a liquid passage formed in the shaft 42.

When measuring the flow rate of urine, the catheter 41 is inserted through the urethra 52 and the bladder 53 into the ureter 54 above it. Therefore, the balloon 43 is first inflated, and the ureter 54 is closed by the balloon 43. Therefore, urine that gradually flows down through the ureter 54 falls into the urine passage 46 from the inlet 44 at the tip of the shaft 42, passes therethrough, and flows out from the outlet 45 located in the bladder 53. Return into the bladder 53. In the meantime, the flow rate of urine is determined by heating the temperature measuring unit 47 located in the urine passage 46 and measuring the temperature of the temperature measuring unit 47.

The medical catheter type flow meter of the present invention can be widely applied to measurement of various body fluids at various sites. For example, the present invention can be applied to measurement of blood flow in a blood vessel of a brain having a cerebral infarction, renal blood flow, hepatic blood flow, pancreatic pancreatic juice flow, liver bile flow, spinal fluid flow, and the like.

It should be noted that the present invention is not limited to the above embodiment, and various modifications can be made. For example,
In the first embodiment, the coil 12 of the guide wire 11 is also used as the signal separator 7, and the high frequency is actually damped by the coil 12, so that the temperature can be measured without a special filter. Alternatively, a band reject filter may be separately provided. In the above embodiment, the heating means 2 and the temperature detecting means 3 are partially used, but they may be provided independently. Further, in the above embodiment, the heating means 2 is based on high-frequency heating, and the temperature detecting means 3 is the thermocouple 4, but the heating means and the temperature detecting means may be thermistors. That is, a thermistor is provided at the temperature measuring section at the distal end of the catheter, and at the time of measurement, a DC current of several mA is first passed through the thermistor to raise the temperature to 62 ° C. Of course, at this time, since the temperature cannot be usually measured, the temperature is measured by repeatedly turning on and off the thermistor to some extent. That is, heating is performed by turning on the power to the thermistor, and the temperature is measured when the power is turned off. This is repeated, and when the temperature of the temperature measuring section reaches, for example, 62 ° C., the heat radiation curve may be checked. However, a thermistor cannot be made smaller than a thermocouple, so a thermocouple is more advantageous for miniaturization. In addition, the present invention can be applied not only to ordinary catheters but also to guidewire puncture needles and the like.

[0026]

According to the first aspect of the present invention, a known amount of thermal energy is converted from electric energy and given to a temperature measuring section provided at the distal end of the catheter, and the temperature change of the temperature measuring section is electrically measured. Then, since the flow rate of bodily fluids such as blood is measured, the flow rate of bodily fluid can be easily and accurately measured, and the catheter can be made thin, so that not only thick blood vessels,
The blood flow can be measured even in a small blood vessel, and the cost can be reduced.

Further, according to the second aspect of the present invention, the temperature measuring means is a thermocouple, and the heating means is constituted by the thermocouple and a high-frequency generator for applying a high-frequency voltage to the thermocouple. Since the high-frequency voltage and the thermoelectromotive force of the thermocouple are separated from each other and the temperature of the temperature measuring section is obtained from this thermoelectromotive force, the structure can be simplified by using the heating means and the temperature measurement means together, and the catheter can be used. Can be thinner.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of a medical catheter type flow meter of the present invention.

FIG. 2 is a side view of the same guide wire.

FIG. 3 is an enlarged sectional view of the same guide wire.

FIG. 4 is an enlarged exploded sectional view of the guide wire.

FIG. 5 is a graph showing a relationship between temperature and blood flow.

FIG. 6 is a graph showing a change in temperature of blood according to the first embodiment.

FIG. 7 is a cross-sectional view of a distal end portion of a catheter according to a second embodiment of the medical catheter type flow meter of the present invention.

FIG. 8 is a graph showing the relationship between temperature and blood flow.

FIG. 9 is a schematic view showing a third embodiment of the medical catheter type flow meter according to the present invention.

FIG. 10 is a cross-sectional view of a distal end portion of the catheter.

FIG. 11 is a graph showing a change in blood temperature when measuring a blood flow rate using a conventional thermodilution catheter.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Temperature measuring part 2 Heating means 3 Temperature measuring means 4 Thermocouple 6 High frequency generator 7 Signal separator 10 Catheter 30 Thermodilution catheter (catheter) 33 Metal ring (temperature measuring part) 41 Balloon catheter (catheter) 47 Temperature measurement Department

Claims (2)

(57) [Claims] 1. A catheter, a temperature measuring unit provided at a distal end of the catheter, and heating means for converting a known amount of heat energy from electric energy to the temperature measuring unit,
A medical catheter-type flowmeter, comprising: a temperature measuring means for electrically measuring a temperature change of the temperature measuring section. 2. The temperature measuring means comprises a thermocouple,
The heating means includes the thermocouple and a high-frequency generator that applies a high-frequency voltage to the thermocouple, and includes a signal separator that separates a high-frequency voltage generated by the high-frequency generator and a thermoelectromotive force of the thermocouple. The medical catheter type flow meter according to claim 1, wherein: