JPH0243364Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Field of Application) The present invention relates to a sensor for measuring tissue blood flow used when measuring tissue blood flow in a living body.

(Prior art) Various methods have been developed to measure tissue blood flow, including the thermal conductivity method, clearance method, and Doppler method. Of these, the thermal conductivity method has been widely applied clinically, especially in the field of neurosurgery. There is. This thermal conductivity method includes a constant current heating method (CC method) and a self-adjusting current heating method (SC method). The CC method applies a certain amount of heat to one of a pair of thermally conductive members that are brought into close contact with the tissue surface of a living body, and removes a certain amount of heat from the other.
Alternatively, a certain amount of heat is applied to only one of the pair of heat conductive members, and the temperature difference between the pair of heat conductive members is measured, and this temperature difference is inversely proportional to the thermal conductivity, and the thermal conductivity is the blood flow rate. This is a method of measuring blood flow since it is proportional to . In the SC method, heat is applied to one of a pair of thermally conductive members that are brought into close contact with the tissue surface of a living body, and heat is taken away from the other. Either the amount of heat given and the amount of heat taken away from the other heat conducting member is controlled and the blood flow rate is determined from these amounts of heat, or heat is applied to only one of the pair of heat conducting members and the temperature difference between the pair of heat conducting members is This is a method in which the amount of heat given to one of the above is controlled so as to be constant, and the blood flow rate is determined from this amount of heat. In these methods, for example, a Peltier stack is used as the element that applies heat to one of the pair of heat conductive members and removes heat from the other, and the element that applies heat only to one of the pair of heat conductive members is used. For example, a resistance wire or a thermistor is used.

FIGS. 5 and 6 show conventional sensors for measuring tissue blood flow using a Peltier stack. FIG. 5 is a sectional view of the sensor, and FIG. 6 is a diagram showing its bottom surface. A Peltier stack is a device that exhibits the Peltier effect, that is, heat is generated or absorbed when a current flows through the junction of two different metals. As shown in FIGS. 5 and 6, metal plates 2 and 3 each having an L-shaped cross section are attached to the heat generating side and the heat absorbing side of the Peltier stack 1, respectively. Inside the sensor, copper wires 9 and 10 are connected to both ends of the constantan wire 11, respectively.
0 constitute thermocouples 4 and 5, respectively, and their respective connection points are insulated and adhered to the center portions of the back sides of the bases of the metal plates 2 and 3 (inside the sensor). Copper wires 7 and 8 are drawn out from the Peltier stack 1. The copper wires 7, 8, 9, and 10 are put together to form a sensor cable 15. A portion of the Peltier stack 1, metal plates 2, 3, constantan wire 11, and copper wires 9, 10 are integrally molded and sealed with a cylindrical synthetic resin member 6.

When a constant current is passed through the Peltier stack 1 through the copper wires 7 and 8, the metal plate 2 generates a constant amount of heat, and the metal plate 3 absorbs a constant amount of heat.
A temperature gradient occurs between the two. When this sensor is brought into close contact with a measurement site of a biological tissue and energized, the temperature gradient between the metal plates 2 and 3 caused by the energization changes in accordance with the tissue blood flow rate. This blood flow rate is proportional to the thermal conductivity to the tissue, and since the thermal conductivity is inversely proportional to the temperature difference between the metal plates 2 and 3, the blood flow rate is inversely proportional to this temperature difference. Therefore, by measuring this temperature difference as a thermoelectromotive force difference using thermocouples 4 and 5, tissue blood flow can be measured. The above method is the CC
It is the law.

On the other hand, in the case of the SC method, the current applied to the Peltier stack 1 is controlled so that the temperature difference between the metal plates 2 and 3 is constant, and the blood flow rate is determined from this current value.

(Problem to be solved by the invention) The conventional sensor for measuring tissue blood flow described above weighs 0.6 gr when the diameter is 13 mm and the height is 3 mm.
It was extremely lightweight. Therefore, as shown in FIG. 5, in order to bring the metal plates 2 and 3 into close contact with the surface of the biological tissue 16, gauze 1 soaked in physiological saline is used.
7 (or cotton) must be placed on the sensor, pressed with a spring, or sewn to the hook with a thread to form a housing, making it difficult to attach the sensor to a living body. Another drawback was that if gauze or cotton was placed on the sensor, the state of contact between the sensor and the tissue could not be visually observed. Furthermore, during measurement, body fluids or blood may adhere to the sensor, which may change the surroundings of the sensor, or if saline gauze or the like becomes dry, the state of contact with the tissue surface may change, or the metal plate inside the sensor may change. There was a problem in that the Peltier stack or resistance wire was affected by heat from the surroundings, making accurate measurements impossible.

The present invention was devised in view of the shortcomings of conventional sensors, and its purpose is to ensure that a pair of heat conductive members for detecting temperature differences are in close contact with the tissue surface of the living body, and to prevent such heat conduction. The goal is to ensure that the members and the elements that heat or cool them are not easily affected by ambient heat.

(Means for solving the problem) Therefore, in the present invention, a pair of heat conductive members for detecting a temperature difference are arranged at a predetermined interval, and
A heat-absorbing and heat-generating element that heats one of the pair of heat-conducting members and cools the other, or a heat-generating element that heats only one of the pair of heat-conducting members, is placed inside a metal housing and between the inner wall of the housing. The opening of the housing is sealed with the surfaces of the pair of thermally conductive members that come in contact with the living body exposed to the outside of the housing for use in tissue blood flow measurement. I created a sensor.

(Function) When the sensor with the above configuration is attached to the surface of the tissue of a living body, the weight of the housing will push the heat conduction member toward the living body, so the heat conduction member can be brought into close contact with the tissue with a constant pressure. Can be done. In addition, since an air layer is formed between the heat conduction member and the heat absorption/heat element or the heat conduction member and heat generation element and the inner wall of the housing, the heat insulation effect is good, and body fluids and blood may adhere to the area around the sensor. Even if the conditions change, the effect on the measurement results will be very small.

(Example) Hereinafter, an example of the sensor for measuring tissue blood flow according to the present invention will be described with reference to the drawings.

An embodiment of the present invention is shown in FIGS. 1 and 2.
FIG. 2 is a perspective view of the sensor for measuring tissue blood flow of the present invention, and FIG. 1 is a sectional view thereof. In these figures, the same or equivalent parts as those of the conventional example shown in FIGS. 5 and 6 are denoted by the same reference numerals. A Peltier stack 1 is housed in a housing 22 made of stainless steel and formed in the shape of a hollow cylinder with a bottom. Metal plates 2 and 3 each having an L-shaped cross section are provided on the heat generating side and the heat absorbing side of the Peltier stack 1, respectively. installed. In this embodiment, gold is used as the heat conductive member for detecting the temperature difference. The bases of these metal plates 2 and 3 are fixed to a synthetic resin plate 23 with their bottom surfaces exposed to the outside. This synthetic resin plate 23 is similar to the ring 2 made of synthetic resin.
6 to the inner periphery of the housing 22. By the synthetic resin plate 23 and ring 26,
The opening of the housing 22 is sealed. In this way, the synthetic resin plate 23 and the ring 26 serve both as a fixing means for fixing the Peltier stack 1 and the metal plates 2 and 3 to the housing 22, and as a sealing means for sealing the opening of the housing 22. Metal plates 2, 3, Peltier stack 1 and housing 22
An air layer is formed between the inner wall of the Copper wires 7 and 8 are drawn out from the Peltier stack 1. Inside the sensor, copper wires 9 and 10 are connected to both ends of the constantan wire 11, respectively, and the constantan wire 11 and the copper wire 9, and the constantan wire 11 and the copper wire 10 constitute thermocouples 4 and 5, respectively, and the respective connection points is bonded in an insulated manner to the central part of the back side (inside the sensor) of the base of the metal plates 2 and 3. Copper wires 7, 8, 9, 10 are sensor cables 15
The sensor cable 15 is pulled out from a hole 17 provided in the housing 22 to the outside of the housing 22. Hole 1
7, the sensor cable 15 and the housing 2
2 is filled with a synthetic resin filler 18. In this embodiment, the housing 22 has an outer diameter of 12
mm, height 6 mm, thickness 2 mm, and the total weight of this sensor is approximately 4 g.

When using the sensor configured as described above, the sensor is placed on a measurement site of living tissue. The sensor placed on the measurement site is pressed against the living tissue by its own weight, and the metal plates 2 and 3 provided on the bottom of the sensor are brought into close contact with the living tissue.

According to this embodiment, the metal plates 2 and 3 can be brought into close contact with the tissue with constant pressure. Therefore, there is no need to place gauze, cotton, etc. on the sensor as in the conventional case, and fluctuations due to drying of these items can be eliminated. Another advantage is that the state of contact between the sensor and the tissue surface can be directly confirmed visually. Furthermore, when the sensor is placed on the brain tissue, for example, even after the brain pressure goes up and down or the body moves, the sensor's own weight will cause the metal plates 2 and 3 to be placed on the tissue surface with the same pressure as before the change. Can be placed in close contact. Furthermore, even if bodily fluids or blood adhere to the sensor during measurement, the air layer formed within the housing 22 provides a heat insulating effect, and the influence of these on the sensor output is minimized.

The effects of the embodiments described above are the same in both the CC method and the SC method. Although the above-described embodiment uses a sensor using a Peltier stack, the same effect can be obtained with a sensor using a resistance wire or a thermistor if the structure is equivalent to that of this embodiment. In this embodiment, a case has been described in which the housing 22 is made of stainless steel and the metal plates 2 and 3 are made of gold, but these materials are not limited to stainless steel and gold. Furthermore, the shape of the housing 22 is not limited to a cylindrical shape, but may be polygonal, for example. Incidentally, if a double-sided adhesive tape is provided on the peripheral edge of the bottom surface of the housing 22, the mounting of this sensor will be more stable.

FIG. 4 shows the results of an experiment conducted to obtain the relationship between the weight of a sensor used in the thermal conductivity method and the output voltage of the sensor. In this experiment, as shown in Fig. 3, a sensor 30 is placed on a thermally conductive plate 31 that has been calibrated using a sensor that has been calibrated in advance in an animal experiment, a weight 32 is placed on top of it, and the weight of the weight 32 is calculated. This is a record of the change in the reciprocal of the sensor output voltage as the voltage is increased. This sensor 30
It has a diameter of 8 mm, a height of 4 mm, a weight of 0.5 g, and a lead wire that runs sideways. Neoprene rubber is used for the heat conductive plate 31. As shown in FIG. 4, since the contact between the bottom surface of the sensor 30 and the heat conductive plate 31 cannot be ensured only by its own weight (0.5 g), the sensor output voltage becomes high. For this reason, the blood flow equivalent value takes a lower value than the actual blood flow. Next, when the weight 32 is set to 1g (total weight is 1.5g), the sensor output voltage becomes stable, but the sensor output voltage becomes more stable than when the weight 32 is set to 2g (total weight is 2.5g). The reciprocal number is getting lower. When the weight 32 is 2 g or more (total weight 2.5 g or more), the sensor output voltage is approximately constant. Therefore, from this result, if the total weight is 2.5 g or more, an accurate and stable sensor output voltage can be obtained. However, biological experiments have shown that when the amount exceeds 5.5g, the pressure on the brain is too strong, causing the brain to collapse. Therefore, the appropriate total weight of the sensor is about 2.5 g to 5 g.

[Effects of the invention] As described above, according to the invention, since the pair of heat conduction members in which a temperature difference occurs is pressed toward the living body by the weight of the housing, these heat conduction members can be reliably It can be brought into close contact with living tissue. Furthermore, these heat conductive members and an element that heats one of these heat conductive members and cools the other, or a heating element that heats only one of these heat conductive members, are covered with a housing via an air insulating layer. Therefore, the influence of heat received from the outside on these heat conductive members and elements can be reduced. Therefore, according to the present invention, tissue blood flow can be accurately measured.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an embodiment of the sensor for measuring tissue blood flow according to the present invention, FIG. 2 is an external perspective view of the sensor shown in FIG. 1, and FIG. 3 is a cross-sectional view of the sensor for measuring tissue blood flow. An explanatory diagram of an experiment conducted to clarify the relationship between weight and output voltage, Figure 4 is a diagram showing the experimental results, and Figures 5 and 6 are diagrams showing conventional sensors for measuring tissue blood flow. It is. 1... Peltier stack, 2, 3... Metal plate (thermal conductive member), 4, 5... Thermocouple, 22... Housing,
23...Synthetic resin plate, 26...Ring.

Claims (1)

[Scope of utility model registration request] A pair of heat conductive members arranged at a predetermined interval, and an heat absorbing/heating element that heats one of the pair of heat conductive members and cools the other, or heats only one of the pair of heat conductive members. A sensor for measuring tissue blood flow including a heat generating element includes a metal housing having an opening, the pair of heat conducting members and the heat absorbing/heating element, or the pair of heat conducting members and the heat generating element being connected to the housing. a fixing means for fixing with a heat insulating material so as to have a gap between the housing and the inner wall of the housing; A sensor for measuring tissue blood flow, comprising a sealing means for sealing an opening.