JPH05176916A - Tissue oxygen flowmeter - Google Patents

Abstract

PURPOSE:To simultaneously measure the rate between the blood quantity, the blood flow rate and oxygenated type erythrocytes in a tissue by synthesizing laser beams having different wavelengths and outputting as one composite laser beam to the tissue, demultiplexing the laser beam scattered and reflected from the tissue and executing mutually an arithmetic processing. CONSTITUTION:A laser oscillator A 11 oscillates the laser beams of the same wavelength as the absorbing point wavelength of an erythrocyte, etc., and a laser oscillator B 12 oscillates a laser beam having absorbing point wavelength being different from that of the laser oscillator A 11. In such a state, two or more laser inputs are mixed and multiplexed by a synthesizer 13 and outputted as one laser beam. The laser beam reflected from a tissue is divided and outputted at every wavelength by a spectroscope 17, passes through filters A18, B19 and amplifiers 20, 21, and a tissual blood flow rate A and a tissual blood quantity, and a tissual blood quantity B are outputted by an arithmetic circuit A22, and an arithmetic circuit B 23, respectively. Subsequently, by an arithmetic circuit C24, and arithmetic circuits D25, E26, a signal (e) for indicating the ratio of oxygenated type erythrocytes from the tissual blood quantities A, B, and tissual oxygen content; tissual oxygen flow rate signal (d) are outputted, respectively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tissue oxygen flow meter for simultaneously measuring the blood flow of living tissue and the proportion of oxidized red blood cells in the blood.

[0002]

2. Description of the Related Art Currently, an apparatus as shown in FIG. 5 has been proposed as an apparatus for measuring blood flow using laser light. The laser light output from the laser oscillator (51) is guided to the optical fiber for light transmission (52), and the tissue (54) is irradiated through the probe (53). Receiving fiber (55) that pairs part of the light scattered by the tissue (54) with the sending fiber in the probe
To receive light. This light is guided to the photodetector (56) and the amplifier (5
After being amplified in 7), ∫ωP (ω) dω as tissue blood flow (5a) and ∫P as tissue blood volume (5b) in the arithmetic circuit (58).
(Ω) dω is calculated. In this device, the wavelength of the light of the laser oscillator (51) is such that the red blood cells have little absorption.

A pulse oximeter as shown in FIG. 6 has been proposed as a device for measuring the oxygen saturation level in arterial blood. The red LED (62) and the near infrared LED (63) are driven by the driver (61) of the near infrared LED (63).
3) is lit up alternately. These lights are fiber optics (64)
Is radiated to your finger through the
It is taken in by (65) and guided to the photodetector (66). This is amplified by the amplifier (67) and is calculated by the arithmetic circuit (68) to output it as the oxygen saturation (6a) of arterial blood. Red wavelength is about 660
A wavelength of around 805 nm is used for the near infrared wavelength. This corresponds to the isosbestic point (805 nm) and the isosbestic point (660 nm).

[0004]

The conventional laser blood flow meter can measure the blood volume and blood flow in the tissue.
The proportion of oxidized red blood cells is unknown.

A pulse oximeter can measure the oxygen saturation in arterial blood, but cannot measure the blood flow velocity because it uses an LED. Therefore, it can be measured as a delivery amount per unit time. Can not. Moreover, since it is not the oxygen saturation in the actual tissue, it is possible to confirm the functions of the heart and lungs, but it is unclear whether oxygen has been sent to the terminal tissues.

[0006]

In view of the above, according to the present invention, the laser beams having different wavelengths are combined and output as one combined laser beam to the tissue, and the laser beams scattered and reflected from the tissue are demultiplexed. By performing the arithmetic processing on (1) and (2), the tissue blood volume and the blood flow volume are extracted, and the device that can obtain the oxygen blood volume and the tissue oxygen blood flow volume is realized.

The features of the present invention are as follows. A blood flow meter using laser light is widely used because it can continuously and non-invasively measure a tissue blood flow rate. However, blood simultaneously contains red blood cells containing oxygenated hemoglobin (oxidized red blood cells) and red blood cells containing non-oxygenated hemoglobin (reduced red blood cells). The ratio of this oxidized red blood cell and reduced red blood cell is measured using a two-wavelength laser light,
The oxidized blood volume and the oxidized blood flow, that is, the tissue oxygen content and the oxygen flow rate are obtained from the relationship between the tissue blood volume and the blood flow that have been measured at one wavelength until now.

One of the purposes of blood circulation is the delivery of oxygen to tissues, a device for measuring this flow rate. Blood flow in the brain is also controlled by the amount of oxygen sent to it. Normally, when the proportion of oxygen in the air decreases, the blood flow increases to secure the amount of oxygen to the brain. In this case, the cause of the change cannot be grasped by measuring only the change in blood flow. However, if the ratio of oxidized red blood cells is measured at the same time, one factor of blood flow change can be investigated. In order to perform this measurement, there is a point where the absorption cross sections of oxidized red blood cells and reduced red blood cells differ according to wavelength (different absorption point) and the same point (isosorption point). Then, the total tissue blood volume and tissue blood flow volume are obtained, and the ratio of oxidized red blood cells is obtained from the relationship between different absorption points and isosbestic points. The absorption cross section and the scattering cross section are measured by another method in advance, or the values of already published data are used.

[0009]

[Embodiment] (11) is a laser oscillator A which oscillates a laser beam having the same wavelength as the wavelength of the isosbestic point of red blood cells. Reference numeral (12) is a laser oscillator B, which oscillates laser light having an absorption point wavelength different from that of the laser oscillator A (1). (13) is a multiplexer, which mixes and combines two or more laser inputs and outputs as one laser beam. Reference numeral (14) is an optical fiber, which is composed of an optical fiber. Reference numeral (15) is a light receiving fiber, which is made of an optical fiber like the light transmitting fiber. Reference numeral (16) is a probe, which is a bundle of the output port of the light-transmitting fiber and the input port of the light-receiving fiber and which forms a contact surface with the living tissue. The probe (16) has a shape that facilitates measurement depending on the measurement site. Reference numeral (17) is a demultiplexer, which divides one laser input [laser transmitted through the light receiving fiber (15)] for each wavelength and outputs it. Reference numeral (18) is a filter A, which filters and detects laser light having a target wavelength. Filter A (18) is connected to one of the outputs of the duplexer (17). Reference numeral (19) is a filter B, which filters and detects laser light having a desired wavelength. Filter B (19) is connected to the other output of the duplexer (17). (2
0) and (21) are amplifiers that perform electric amplification after photoelectric conversion. The input of the amplifier (20) is connected to the output of the filter A (18), and the input of the amplifier (21) is connected to the output of the filter B (19). Reference numeral (22) is an arithmetic circuit A, which is connected to the output of the amplifier (20) to output the tissue blood flow volume A to the output end (a) and the tissue blood volume A to the output end (b). (23) is the arithmetic circuit B,
It is connected to the output of the amplifier (21) and outputs the tissue blood volume B. (2
Reference numeral 4) is an arithmetic circuit C, which outputs a signal (e) indicating the proportion of oxidized red blood cells from the tissue blood volume A and the tissue blood volume B. (25) is a calculating means D, which outputs a signal (c) indicating the tissue oxygen content from the signal indicating the tissue blood volume A and the signal (e) indicating the ratio of oxidized red blood cells. (26) is an arithmetic circuit E which outputs a tissue oxygen flow rate signal (d) from a signal (e) indicating the tissue blood volume A and the ratio of oxidized red blood cells.

Laser light oscillator A of the wavelength of the isosbestic point of red blood cells A
(11) and the two laser beams output from the laser oscillator B (12) with different absorption point wavelengths respectively pass through the optical fiber,
The light is guided to one light transmitting fiber (14) by the multiplexer (13) and is irradiated onto the tissue (MM) by the probe (16). Some of the light scattered by the tissue will be absorbed by the receiving fiber (1
It passes through 5) and is split into two optical fibers by a demultiplexer (17). After that, after passing through the filter A (18) that passes the laser wavelength at the isosbestic point and the filter B (19) that passes the laser wavelength at the different absorption point, after each photoelectric conversion by the amplifiers (20) and (21). Is amplified. The signal of the wavelength at the isosbestic point is calculated by the calculation circuit A (22) to obtain the tissue blood flow volume A and the tissue blood volume A. The tissue blood volume B is obtained from the signal of the different absorption point wavelength calculated by the arithmetic circuit B (23), and the ratio of oxidized red blood cells is obtained from the tissue blood volumes A and B by the arithmetic circuit C (24). The tissue oxygen content is obtained from the arithmetic circuit D (25) from this ratio and the tissue blood volume A, and the tissue oxygen flow rate is obtained from the tissue blood flow A by the arithmetic circuit E (26).

Next, an example of a concrete algorithm of the arithmetic means will be shown below. The integrated intensity (IIPS) of the power spectrum of scattered light is expressed by equation (1), where m is proportional to the ratio of red blood cell amount in the tissue by the number of parallel equilibrium collisions between photons and red blood cells. IIPS = ∫S (ω) dω = I-exp (-m) (1) Here, m is also expressed as follows.

[Equation 1] (2) The number density ρ is the number of red blood cells per unit tissue volume,

[Outer 1] Is the scattering cross section of red blood cells, and L is the optical path length. Since the effect of absorption is not taken into consideration in Eq. (1), it becomes as shown in Eq. (3) considering the effect of absorption.

[Equation 2] (3) where

[Outside 2] Is the respiratory cross section of red blood cells. Using laser light (eg, 805 nm) having a wavelength at the same absorption point of oxidized red blood cells and reduced red blood cells and laser light (eg, 633 nm) having different absorption wavelengths,
Each IIPS is represented by the following equation.

[Equation 3]

[Equation 4] (4) where

[Outside 3] : IIPS measured at different absorption wavelengths

[Outside 4] : IIPS measured at isosbestic wavelength

[Outside 5] : Number density of oxidized red blood cells

[Outside 6] : Absorption cross section of oxidized red blood cells at different absorption wavelengths

[Outside 7] : Absorption cross section of reduced red blood cells at different absorption wavelengths

[Outside 8] : Absorption cross section of red blood cells at isosbestic wavelength

[Outside 9] : Scattering cross section of red blood cells at different absorption wavelengths

[Outside 10] : Scattering cross section of red blood cells at the isosbestic wavelength. Since the scattering cross section of red blood cells does not depend on the degree of oxidation between 600 nm and 1000 nm, one scattering cross section per wavelength is used. In the near infrared wavelength range,

[Outside 11] Since ρ is small, ρ is given by the following equation.

[Equation 5] (5) If the distance between the two wavelengths is small,

[Outside 12] If so, the proportion of oxidized red blood cells

[Outside 13] Is

[Equation 6] Required by. From this ratio and the tissue blood volume, the tissue oxidized blood volume or tissue oxygen content is

[Equation 7] And the tissue oxygen flow rate is

[Equation 8] Can be sought in. Here, <ω> is the first moment of the power spectrum of the signal and is proportional to the average blood flow velocity.

Next, an example of an experiment conducted by using one embodiment of the present invention will be described. FIG. 2 shows a diagram of a model system of tissue blood flow. FIG. 3 is a sectional view taken along line XX ′. This model system consists of polyethylene tubes (215) and polyacetal (213) (214) plates,
(215) has an outer diameter of 0.8 mm and an inner diameter of 0.5 mm. The 0.8 μm red and blue polystyrene particle dispersion liquid was directly flowed into the tube (215) by a micro feeder (212). Red particles and blue particles have almost the same absorption cross section in the near-infrared region, but they differ greatly in red light, so red particles were used as a model of oxidized red blood cells and blue particles were used as a model of reduced red blood cells. Both particles were mixed to a ratio of 10: 0.8: 2.5: 5.2: 8.0: 10 and the total particle dispersion concentration was adjusted to 0.064% and 0.13%. .. A fiber optic probe (16) to illuminate the tissue and receive some of the scattered light and direct it to the photodiode.
It was used. The probe (16) contains an optical fiber for irradiation (14) and an optical fiber for reception (15) in parallel, and the center distance between them is 0.
It is 5 mm. The core diameter of the optical fiber is 100 μm. HeNe laser light with output of about 2 mW (632.8n
m) and the semiconductor laser light (780 nm) are irradiation fibers
The model system is illuminated through (14). Scattered light from the model system is guided to the photodiode through the receiving fiber (15) and amplified to 0.25Hz to 20K.
The integrated intensity (IIPS) of the power spectrum up to Hz and the first moment <ω> are obtained from the FFT analyzer (211). The scattering cross section and the absorption cross section were measured using a spectrophotometer and an integrating sphere. Figure 4 shows the result of this experiment.
Shown in. It was determined from the blue particle number ratio (horizontal axis) and the measurement results.

[Outside 14] The relationship (vertical axis) was proportional.

[0013]

As described above in detail, the present invention has the effect that the accurate tissue oxygen flow rate can be detected by laser light.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

[Fig. 2]

FIG. 3 is a diagram illustrating an experiment using an embodiment of the present invention.

FIG. 4 is a diagram showing the results of the experiment shown in FIG.

[Figure 5]

FIG. 6 is a diagram showing a conventional example.

[Explanation of symbols]

 11 Laser Oscillator A 12 Laser Oscillator B 13 Multiplexer 14 Transmitter Fiber 15 Receiving Fiber 16 Probe 17 Splitter 18 Filter A 19 Filter B 20, 21 Amplifier 22 Arithmetic Circuit A 23 Arithmetic Circuit B 24 Arithmetic Circuit C 25 Arithmetic Circuit D 26 arithmetic circuit E MM biological tissue

Claims (1)

[Claims] 1. A laser beam output means for outputting a plurality of laser beams having different wavelengths, a probe for irradiating a living tissue with the laser beam output means, and detecting a laser beam scattered and reflected from the tissue, Demultiplexing means for demultiplexing the laser light detected by the probe, and detection means for detecting the tissue blood flow rate, tissue blood volume, tissue oxygen content, tissue oxygen flow rate from each of the demultiplexed laser light A tissue oxygen flow meter.