JPH021230A - Flow rate measuring catheter - Google Patents

Abstract

PURPOSE:To accurately measure a flow rate by largely reducing a measuring error by providing a thermometric part for measuring the temp. of a fluid in a state thermally insulated from a catheter main body. CONSTITUTION:In a catheter 22, a sensor 8 for measuring a blood flow rate is provided in a state thermally insulated from the catheter main body 13. That is, a ring-shape recessed part 50 is formed to the outer periphery of the main body 13 at a predetermined place and filled with a porous heat insulating material 51 and the sensor 8 is fixed to the heat insulating material 51. Therefore, the sensor 8 is fixed in a state thermally insulated from the catheter main body 13 by the heat insulating material 51 and, at the time of measurement, the heat conductance between the sensor 8 and blood is not performed through the catheter main body 13 but performed therebetween directly or through a cover material 53. As a result, the sensor 8 rapidly responds to a change in the temp. of blood to make it possible to detect the same and the time required to reach predetermined temp. becomes markedly short and measuring accuracy is enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a catheter for measuring flow rate, and particularly to a catheter for measuring blood flow rate based on a thermodilution method.

Conventional techniques Conventionally, methods for measuring blood flow velocity include laser Doppler method, pulse modulation Doppler method, ultrasound Doppler method,
There are pitot tube catheterization methods, hot film methods, etc. Further, as methods that can theoretically measure cardiac output (total flow rate), there are impedance method, electromagnetic flow one-meter method, admittance spresmography, and the like.

On the other hand, thermodilution and dye dilution using Fick's law are excellent methods for measuring blood flow (particularly cardiac output) without being affected by changes in blood vessel diameter or intravascular flow velocity distribution. law is used.

These methods measure the rate at which a physical quantity injected from outside the body, such as the low temperature caused by a cold water mass or the coloring caused by a dye, is diluted by blood, and the cardiac output is determined from this measured value.

According to the thermodilution method, as shown in FIG. 7, a catheter 2 is guided through the vena cava 1 to the right atrium 4 of the heart 3, further through the right ventricle 5 to the pulmonary artery 6, and cold water 7 is injected into the right atrium 4. death,
A sensor (usually a thermistor) 8 near the tip measures blood temperature changes. That is, the recovery from the low temperature state caused by the cold water 7 due to the blood flow is measured by the thermistor 8 as a change in resistance. In the figure, 9 is the left atrium, 10 is the left ventricle, 11 is the pulmonary vein, and 12 is the aorta. As shown in FIGS. 7, 8, 9, and 10, the catheter 2 has a main body 13 including a side hole 14 for injecting cold water.
Thermistor 8, balloon 16, air supply to balloon 16
Side holes 31 for exhaust are provided, and correspondingly a lumen (not shown) for supplying cold water, a lumen 18 for wiring 34 of the thermistor 8, and a lumen 19 for pressure measurement.
, a lumen 20 for feeding air into the balloon 16, and a second pressure measurement lumen (not shown) for measuring blood pressure on the upstream side.

Then, as shown in FIG. 9, when inserting the catheter 2 (usually by percutaneous insertion) and placing it in the bloodstream, the balloon 16 is inflated (as shown by the dashed line in FIG. 10).
carry.

Connector 3 to catheter 2 inserted into the living body
3, 35, and 36 respectively, the blood flow rate calculation display device 37
, syringe 41 for balloon expansion/deflation, infusion bottle 4
2 (includes syringe barrel 43 and sterilization filter 44) is connected. The blood flow calculation display device 37 includes a blood flow needle 47.
, a condition setting key 46, etc. are provided. The injection liquid 7 used above is cooled to a predetermined temperature and then injected, and it is preferable to use a maintenance liquid used for maintaining body fluids of a patient or an infusion liquid for nutritional supplementation. In other words, by using such maintenance fluids or infusions, it is possible to replenish maintenance fluids, etc. at the same time as measuring blood flow, which is very efficient and allows for the injection necessary for thermodilution without losing the balance of body fluids. liquid can be supplied.

In the above, the blood temperature change obtained by the sensor 8 is converted into cardiac output using the following equation (1).

[However, vb i b i b b i Cardiac output (blood flow rate) Amount of injected cold water (ml) Temperature of blood before cold water injection (°C) Temperature of injected cold water (°C) Blood Specific heat of blood Specific gravity of injected water Specific heat Si: Specific gravity of injected water L 2 hours (seconds) ΔTb: Temperature change of blood In this case, signals are processed according to the flow shown in FIG. 9 in measuring blood flow. That is, the measured value of the temperature measurement unit 21 that measures the temperature of the liquid injected into the catheter 2 is input to the A/D converter 26 and digitized, and the thermistor 8 of the catheter 2 detects the blood temperature as a change in electrical resistance. This signal is extracted as a current signal by a bridge circuit 23, amplified by an underground circuit 24, and further inputted to the A/D converter 26 through an automatic zero adjustment circuit 25 that compensates for drift over time. The output of the A/D converter 26 is processed by a central processing unit (CPU) 45, and the blood flow rate is displayed on the display 3.
7 and is further recorded by the printer 27.

By the way, in the above catheter 2, the temperature measuring section 28
As shown in FIGS. 9 and 10, the sensor 8 constituting the catheter body 13 is fixed with an adhesive 29 in direct contact with the catheter body 13, so that there is a gap between the sensor 8 and the blood flowing outside. Temperature measurement by the sensor 8 is performed by heat conduction (that is, heat is transferred from the blood to the sensor 8 via the main body 13 and the adhesive 29).

However, in heat transfer via the main body 13 and the adhesive, a portion of the heat transfer amount is used to heat or cool the main body 13 and the adhesive 29, resulting in a reduction in the heat transfer rate. Therefore, the response time required until the sensor 8 consisting of a thermistor detects a predetermined temperature becomes longer. That is, since the sensor 8 has a structure that makes it difficult to respond, for example, as shown in FIG.
As shown in the figure, the time T required to reach the temperature L1 is 1.0~
It takes a long time of 2.0 seconds (here, the maximum temperature t, I
When 1.0, let T be the time it takes for the temperature to reach from 0 to (1-4-)).

Therefore, due to the poor responsiveness of the sensor 8, the temperature output (detected temperature information) by the sensor 8 deviates greatly from the true blood temperature, as shown in Figure 4 (B), and the temperature changes during operation. Measuring the temperature inside a blood vessel, where the temperature changes every beat (every second for 60 bρm), can only yield results that include large errors. In other words, even if we integrate the temperature output shown in Figure 4 (Sunday) and calculate the blood flow volume based on Fick's law mentioned above, this is true blood: 4. There is a considerable error from the amount. It becomes. This tendency becomes particularly noticeable as the heart rate increases.

OBJECTS OF THE INVENTION An object of the present invention is to provide a flow rate measuring catheter that greatly reduces measurement errors and enables accurate measurements.

20 Structure of the Invention That is, the present invention provides a catheter used for measuring the flow rate of a fluid by a thermodilution method, in which a temperature measuring section for measuring the temperature of the fluid is provided in a state substantially insulated from the catheter body. The present invention relates to a flow rate measuring catheter characterized in that:

E, Example The present invention will be explained in detail below.

1 and 2 show a blood flow measurement catheter 22 based on a thermodilution method according to a first embodiment of the present invention. However, parts common to those described in FIGS. 7 to 10 are given common reference numerals, and their explanations may be omitted.

This catheter 22 is fundamentally different from the conventional catheter 2 described above, in that a sensor (i.e., a thermistor) 8 for measuring blood flow is provided in a state substantially insulated from the catheter body 13. This is characteristic.

That is, a ring-shaped recess 50 is formed on the outer periphery of the main body 13 at a predetermined location, and a porous heat insulating material 51 (for example, a foam made of a polymeric material or an inorganic material) is filled into the recess, and a thermistor is installed. A sensor 8 consisting of the following is fixed to a heat insulating material 51. A wiring 34 extending from the thermistor 8 leads to the measurement circuit system described above. The thermistor 8 may be exposed to the blood side as shown by the solid line, but if a non-insulating cover material 53 (for example, a stainless steel plate) is attached near the thermistor as shown by the imaginary line, the heat conductivity can be improved. It also has the effect of flattening the circumferential surface while keeping it in good condition.

As described above, according to the structure of this embodiment, the sensor 8 (therefore, the blood temperature measuring section 28) is fixed in a substantially insulated state from the catheter body 13 by the heat insulating material 51. During measurements, the heat transfer between the sensor 8 and the blood no longer takes place via the catheter body 13, but directly with the blood or via the covering material 53 (this (This is done for both heating and cooling). As a result, the sensor 8 can quickly respond to and detect changes in blood temperature, so that the thermal time constant during temperature measurement becomes smaller, for example,
As shown in Figure (A), the time T required to reach the predetermined temperature is 0.2
~1,0 sec, which is significantly shorter. Considering that the thermal time constant of a single thermistor is approximately 0.05 to 0.5 seconds, this means that the time constant is close to or equal to this time constant, and the measurement accuracy is improved.

That is, since the response speed of the sensor 8 is fast, as shown in FIG.
As such, the temperature output approximately tracks the true blood temperature with significantly less error.

This becomes especially noticeable when the heart rate increases, and as shown in Figure 5, while in the conventional case the measurement error increases depending on the heart rate, the measurement error using the catheter based on the present invention increases the measurement error. It was found that not only the error becomes smaller, but also the error distribution range becomes smaller.

In this example, since the contact area of the fixed area of the sensor 8 with the metal plate 53 described above is small (that is, even if adhesive is used for fixing, the amount of adhesive used is small), so it is difficult to measure using adhesive. There is no effect at all.

FIG. 6 shows another embodiment of the invention.

According to this example, unlike the example shown in FIG.
Only the periphery of the cover material 53 is bonded to the catheter body 13. In this example as well, the thermal response is improved, measurement errors are reduced, and the sensor 8 can be attached via the cover material 53, making the attachment easy.

Although the present invention has been illustrated above, the above-mentioned example can be further modified based on the technical idea of the present invention.

For example, the structure of the temperature measuring section described above may be modified in various ways, and the sensor 8 may be fitted and fixed into an opening (not shown) provided in the cover material 53. The area where the heat insulating material 51 and the metal plate 53 are provided is not limited to the area where the sensor 8 exists and its vicinity as in the above example, but may be provided all around the outer peripheral surface of the catheter body. The metal plate 53 may be attached by fitting,
Adhesion may also be used.

The metal plate 53 itself is preferably made of a material with good thermal conductivity in order to promote the thermal responsiveness of the sensor 8, and is preferably made of stainless steel (for example, S U 3304.316.316L).
Other examples include gold, silver, platinum, etc.

In addition to the heat insulating material 51, a foam made of a polymeric material or an inorganic material can be used. Further, the sensor 8 can also use a thermocouple instead of a thermistor. The metal plate 53 described above may not be used depending on the case.

Further, the type, size, structure, material, etc. of each part of the catheter can be changed in various ways.

Note that the catheter of the present invention is not only inserted into the heart as described above, but can also be applied to other sites.

1. Effects of the Invention As described above, the temperature measuring part of the fluid such as blood is provided in a state that is substantially insulated from the catheter body, so that there is no temperature difference between the temperature measuring part and the fluid during measurement. Heat transfer will no longer take place through the catheter body, but will take place effectively with the fluid. As a result, it is possible to quickly respond to and detect changes in the temperature of the fluid, thereby reducing errors and accurately measuring the flow rate.

[Brief explanation of the drawing]

1 to 6 show embodiments of the present invention, in which FIG. 1 is an enlarged sectional view of the main part of the catheter, FIG. 2 is a sectional view taken along the line ■-■ in FIG. 1, and FIG. Figure 4 is a graph comparing thermal responsiveness, Figure 4 is a graph comparing temperature output, Figure 5 is a graph comparing measurement errors due to heart rate, and Figure 6 is based on another example. FIG. 2 is a cross-sectional view similar to FIG. 1 of the catheter. 7 to 10 show conventional examples, in which FIG. 7 is a schematic sectional view showing the state of catheter insertion during blood flow measurement, FIG. 8 is a schematic front view of the catheter, and FIG. 9 is a blood vessel. No. 8 showing the catheter with its circuitry within the
Figure 10 is an enlarged sectional view taken along the line IX-IX in Figure 8.
It is an X-ray enlarged sectional view. In addition, in the symbols shown in the drawings, 1...Aorta 2.22...Catheter 4...
・・・Right atrium 5・・・・・・Right ventricle 6・・・・・・Pulmonary artery 7・・・・・・Infusion fluid 8・・・・・・・・・Sensor (thermistor) 13...
... Catheter body 28 ... Temperature measuring part 34 ... Wiring 50 ... Recessed part 51 ... . . . Insulating material 53 . . . Covering material.

Claims (1)

[Claims] 1. A catheter used for measuring the flow rate of a fluid by a thermodilution method, characterized in that a temperature measuring section for measuring the temperature of the fluid is provided in a state substantially insulated from the catheter body. Measuring catheter.