JPS59160445A - Pulse oxygen densitometer - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to oximeters, and in particular to the photoelectric determination of human arterial oxygen saturation.

In particular, it takes at least 3 to 5 minutes to chemically determine the oxygen level in the blood. Patients whose blood is deprived of oxygen during such periods generally suffer irreversible brain damage, even if they do not die. Conventional life display methods such as pulse, blood pressure, and electrocardiogram cannot reliably warn of catastrophe phenomena in breathing or circulation. For example, in a sudden cessation of breathing, the heart rate may remain within normal limits until long after irreversible brain damage has occurred.

Non-invasive electronic techniques for determining the amount of oxygen are known. Wood, US Pat. No. 2,706,927, discloses a method for calculating oxygen saturation from measurements of the absorption of light in human tissue at two wavelengths. First, as much blood as possible is squeezed from the area where the measurement will be performed.
Perform measurements in a bloodless state. Blood from the arterial system is then passed through the tissue to restore normal blood flow. Information about the oxygen saturation rate of the subject's arterial system is obtained from the comparison results of light absorption in these two states. A series of devices and procedures have been proposed using this approach.

In procedures based on this technique, it has been experienced that it is difficult to determine the "bloodless" parameter with sufficient reliability, in part due to geometric distortions due to tissue compression, and the inconsistency of this parameter. Because it is a complete measurement, only incomplete results can be obtained.

The transmittance of each wavelength of light is a function of the thickness, color, and structure of the skin, flesh, bone, blood, and other materials through which the light passes. The attenuation of light in passage is Lambert-B
It has logarithmic characteristics according to Eers' law.

In a pulse oximeter, the main object of measurement is the blood in the arteries. Arterial blood is the only substance whose amount in tissues changes over time in synchrony with the arteries of the heart.

Variations in light transmittance are therefore indicative of blood flow variations, and it is possible to directly optically record the pulsatile component of arterial blood flow. This ability to separate out the absorption of light by arterial blood is useful for 'kt, and since the oxyhemoglobin component of blood is a substance whose absorption coefficient can be determined, it is possible to determine the oxyhemoglobin content in arterial blood. can.

Optical hemometry is well known. This type of blood meter measures the pulse rate (pulse rate) and provides information about the amount of blood delivered to tissues with each heartbeat.

However, with these blood volume meters, 1 sobestic poi
Optical frequencies at or near the optical frequency called nt (at which frequencies arterial flow measurements can be made independent of oxygen saturation) are commonly used.

As a result, information regarding the oxygen saturation rate cannot be obtained.

Following WOOd's aforementioned U.S. Pat. The optical absorption method uses measurements of fresh arterial blood as it enters the tissue in a naturally occurring "bloodless" state or an artificially created "bloodless" state during the resting state of the heart's beating cycle. It is necessary to compare and analyze the measured values. For example, a received signal may be separated into "alternating current" and "direct current" components and passed through a logarithmic amplifier before performing digital analysis of the signal. See US Pat. No. 8,998,550 to Kone'shi et al.

In a similar manner, difference outputs at both wavelengths are generated prior to digital analysis, and the DC component is removed from these difference outputs to approximate the logarithmic response according to prior art techniques. Harnagribri U.S. Pat. No. 4,266.55
Please refer to No. 4. Briefly, since only a small portion of the total signal of transmitted light is the pulsating component, numerous logarithm-based processes have been attempted to separate the stationary component from the signal prior to analysis.

However, schemes based on logarithms and logarithmic amplifiers are fraught with difficulties. One of these difficulties is the non-reproducibility of amplifiers due to mass production. Moreover, noise, semiconductor temperature dependence, and voltage sensitivity limit the practical application of such approximation techniques using logarithmic amplifiers.

U.S. Pat. No. 3,704,706 to Hertzfeld et al.
discloses the use of a single coherent red light source 5, preferably a laser. In the use of a single light source, i[
Information regarding rh pulse blood flow components cannot be separated from information regarding arterial oxygen components. The output of such a single red light source meter can simply indicate the product of the blood flow present and the saturation level. It is not possible to know only blood flow or only saturation.

Moreover, no calibration techniques are described or discussed in the prior art. Mass-produced instruments must be designed to allow initial calibration.

Similarly, maintenance of the calibration state is not described.

(Summary of the Invention) In the pulse oximeter according to the present invention, light of two different wavelengths is passed through human or animal tissues, such as fingers, ears, and scalp, to obtain transmitted light modulated by the pulsating component of the artery. blood flow (per, frbsi)
on) and pulse rate. The level of the incident light is continuously adjusted to compensate for varying attenuation due to skin color, flesh thickness, and other variables, as well as to provide optimal detection of pulsating components. At a point where the gradient of the pulsating component of the transmitted light changes from negative to positive or at a maximum point (indicating the maximum point of the waveform), a waveform analysis of the blood flow rate is performed.

To measure the ratio of the pulsating component to the constant component in the total transmitted light, each ratio of direct digital tracking of each of the two waveforms is then converted to a ratio. This ratio can later be fitted to an independently determined oxygen saturation curve. Calibration is performed by solving for four unknowns at at least four different saturation rates, or by fitting the ratios to independently determined curves to determine at least two coefficients of a polynomial. Outputs of pulse rate (number of pulses), pulse flow rate and oxygen saturation rate are given. The duty cycle of the incident light source is selected to be at least a factor of 4 to substantially eliminate the noise inevitably present in the signal.

(Requires instrument operation) This instrument uses two light emitting diodes (CLED) as light sources, which emit light in a relatively narrow band and are easy to package.
use. Both LEDs sequentially strobe light at frequencies as far away as possible from the normal room light light frequency and its harmonics. By sequentially firing the LEDs, the signal produced at the photosensor (representing the reciprocal of the absorption) is split into two signals representing the transmittance in the body tissue for each wavelength.

These two signals are each generated by a phase detection circuit that cancels unstrobed ambient light in alternating half-cycles. A low-pass filter in the subsequent stage removes high-frequency noise and modulation (strobe) frequencies.

These two signals, representing the amount of tissue transmission for each wavelength, are converted to digital values by a microprocessor. To determine the change in transmission caused by pulsating changes in blood flow, the instantaneous voltage representing the total transmission of light must be stored. Care is taken to avoid offset voltages, waveform distortion, noise, etc. Generally, the amount of change due to pulsation is only a few inches of the total transmission amount, so there is no need to digitally convert the entire 10 volt range, but the upper 25% of the entire range is digitally converted. This conversion is electronically "multiplied" with a 4x gain.
and a 0-10 volt analog/digital converter with fixed 7, 5 volt fixed offset cancellation.

This results in a fourfold increase in resolution.

To avoid out-of-range signals due to variations in tissue density (Ctissue density), the LEDs can be controlled by the microprocessor so that the maximum transmission level received by the photosensor is within an optimal range. LE because variations in tissue density do not occur between patients but also depend on the physiological state of the same patient.
The brightness of D is continuously monitored and controlled.

The resulting signal is examined by a microprocessor for time-varying pulses.

Due to the characteristics of arterial flow, blood flows faster than its decline, so the start of a pulse can be identified by the maximum point of the signal (the extreme point, whose slope changes in the direction of increasing absorption). The pulse ends at the minimum point of the signal (the extreme point, the point where the slope changes representing the maximum amount of absorption).These values are preferably detected using an infrared signal.The difference from the maximum point to the minimum point is The change in the signal at
It represents the change in absorption rate that occurs when blood flows into tissue. Therefore, the saturation rate can be determined by analyzing the transmission ratio at each wavelength.

Logarithmic analysis becomes unnecessary.

(Objects, Features, and Advantages of the Invention) One object of the present invention is to provide a pulse oximeter that can directly analyze the pulsating component of transmitted light relative to incident light. With this material of the invention, logarithmic or analog calculations of the received signal are not required. Analysis of the pulses begins at the onset of an increase in light absorption, which can be seen by a reversal of the slope, and the pulses are then digitally tracked over time. Only the pulsating blood inflow is analyzed. During periods when pulses are not being analyzed, ie during venous flow of the analyzed tissue, the level of the incident light is adjusted to place the signal within the optimum amplitude range.

One advantage of the invention is that the pulsation component can be optimized by adjusting the level of the incident light. Optimization is possible for nearly all different patients, even though the non-pulsating component of the received light varies between patients due to differences in skin, bone, flesh texture, and venous blood. Although the arterial component makes up only a small portion of the transmitted light signal, it can be adjusted for optimal measurements.

Another advantage of the present invention is that adjustments to light levels can be made while monitoring the patient's condition. This allows optimization of changes in the patient's physiological state that affect the constant and pulsating components of the received light.

Yet another advantage of the meter is that it is self-adjusting during use. For example, the intensity of the incident light can be adjusted during operation of the meter without adversely affecting the meter's output.

Fourth, other advantages include faster response to changes and minimization of spurious components of motion (broadly defined noise) compared to conventional AC/DC techniques.

Another object of the present invention is the disclosure of an instrument that can simultaneously track and display pulse amplitude and an individual's oxygen saturation. According to this feature of the invention, at least one
The change in the slope of the amplitude of one wavelength of light (preferably infrared) is monitored.

A signal is generated proportional to the rate at which the gradient changes, indicating the rate of heartbeat. A second signal is emitted that is proportional to the intensity of the received light for the incident light at both wavelengths. Pulse rate and oxygen saturation can be displayed with visual and acoustic signals.

An advantage of this feature of the invention is that each pulsation component is analyzed individually. The patient's heartbeat, arterial oxygen content, and blood perfusion are continuously monitored. .

Yet another object of the present invention is to eliminate noise due to ambient light when amplifying transmitted optical signals within a critical range.

According to this aspect of the invention, the amplifier initially receives an optical signal containing a pulsating optical component (and noise due to ambient light) and amplifies it in a positive direction. Both LEDs are then shut off and the same amplifier receives only the noise due to ambient light and amplifies it in the negative direction. Ambient light noise causes both positive and negative signals to be switched to low frequencies? It is effectively removed by passing it through a filter (a filter that blocks high frequency noise and modulation frequency).

The remaining signal is amplified over the output range of the amplifier and input to a comparator circuit. 12-bit digital/analog signal that samples pulsating components within the range of 4096
A comparison is made by the converter. Accurate digital tracking of the signal is thus possible.

An advantage of this feature of the invention is that it can be used to eliminate ambient noise that is unavoidably present in such signals. For example, noise caused by surrounding indoor lighting can be removed.

Another object of the invention is to disclose a method for calibrating an instrument. According to this aspect of the invention, the received light ratio of two different frequencies is determined by an instrument.

At least four oxygen saturations are determined using at least four coefficients that are predetermined; these saturations are preferably determined experimentally. A fixed correction factor is then determined and then stored in the instrument's memory. Using these calibration values, an electronic reading is obtained that replicates the experimental data of blood oxygen saturation.

An advantage of this feature of the invention is that experimentally derived constants can be regenerated to the instrument. There is no need to individually calibrate instruments for traditional laboratory blood tests.

Yet another object of the present invention is to disclose an apparatus for adjusting the ratio of light transmission determined by an instrument. According to this aspect of the invention, at least one filter segment is used, which is mounted on and driven by an electric motor with a rotational speed proportional to the pulse rate. It comprises two LEDs and one photosensor. The detector is connected to the light pipe (
For example, the light emitted from the LED passes through a rotating filter and is received by the sensor. With this configuration, it is possible to create an artificial pulse, and this can be used to adjust the ratio of the amount of light transmitted. An advantage of this feature of the invention is that it facilitates calibration of the meter, either during manufacture or after installation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, a housing 26 of the instrument of the present invention is shown. This housing has, on the outside, a numerical display 1, a row of circuit selection buttons 2 to 5, alarm status indicators 6 to 9, and an optically coupled adjustment knob 1.
0, a synchronization status indicator light 11, an LED digital indicator 12, and a power switch 18. A speaker 15 is located inside the instrument housing facing downwards.

From a connector (not shown) in the housing 26,
The lead wire 27 is extended. Line 27 extends to probe 29 of the detector. Detector 29 is placed on finger 14 of patient's hand 28. By placing this detector 29 on the finger 14, all readings in the present invention are possible.

A careful examination of the circuit of FIG. 2 provides a comprehensive understanding of the operation of the present invention.

In FIG. 2, a conventional microprocessor 16 has a bus 17 extending therefrom. ROM on bus 17
18 and RAM 19 are combined. An LED display 20 is shown having a selection latch 21 and a numerical display latch 22. This circuit consists of the circuit selection button rows 2-5 (FIG. 1) shown previously and the optically coupled control
10 (FIG. 1) includes a control device (generally indicated by 24).
gated circuit).

Although I have described the ordinary parts of a microprocessor,
Next, please pay attention to the analog part of one circuit.

A detector 29 with a simple detection circuit is shown on the finger 14 of the patient 28. The first light emitting diode 82 in the red range and the second light emitting diode 80 in the infrared range are sequentially pulsed to emit light at their respective frequencies by the amplifiers 31,33. Typically, LED 82 is in the 6600A range and LED 82 is in the 9400A range.

All light from the active side light emitting diode needs to pass through the flesh of the finger 14. Therefore, a light-tight barrier 36 is placed between the photosensor 38 and the finger 14. Barrier 36 terminating in contact with the flesh of finger 14
A path is formed between each light emitting diode 80 and the light receiving diode 38 through only the flesh of the finger 14.

This instrument uses two different frequencies. These frequencies are 670rLm (red) and 940rLrIL
(infrared). It may also be useful to have a little discussion in relation to these parameters.

When choosing the frequencies to be used, first, ensure that the two frequencies are sufficiently far apart from each other so that the transmission or transmittance of light changes clearly with changes in oxygen saturation (oxygen concentration), and second, that the same tissue can be sampled. For example, ultraviolet frequencies cannot sample individual tissues due to scattering.

It is possible to use very close frequencies, but we did not choose to do so. We have discovered that a problem arises due to the frequency drift of the light source.

The signal received from each light emitting diode is first passed through a preamplifier 40 . This signal is then amplified in parallel in amplifiers 41,42. The signals from each amplifier 41.42 are sent in parallel via each phase detector 43.44.

It then passes through each low-pass filter 45,46. It is then sent to offset amplifiers 47 and 48. The pulsating component which is the output of the offset amplifier is sent to the multiplexer 5o.

This multiplexer 50 sends its output to a comparator 52.
give to Comparator 52 is a 12-bit digital-to-analog converter (hereinafter referred to as DAC).
(referred to as ) 54, the half stave is tilted. DAC
54 provides an analog comparison signal representing one of 4096 values to comparator 51. Comparator is bus 17
Output for.

As is well known, not all human fingers and associated membranes are the same. Specifically, are the frequencies and intensities of the optical signal outputs in each of the diodes 3o and 32 the same? Even though
Due to differences in race, skin pigment, weight, age, maturity and other factors.

Different signals will be detected on the photosensor 38 side.

Accordingly, microprocessor 16 is programmed to receive signals from sensor 38 within an optimal range. 1 light emitting diode 8 by sending a signal to the sample and hold circuit 57 in the second operating phase of the DAC 54.
0.82 is given the voltage output 60% 61 of the circuit 57, respectively.

These voltage outputs 60.61 are
It is adjusted to detect a signal that causes conversion in AC to take place within a range.

Clock 70 controls the sequential light output from light emitting diodes 80.82 with a duty cycle of y. This is approximately controlled by the signals φ1 to φ4. detection 648
Receipt of signals at detector 44 occurs during periods φ1 and φ2, and reception of signals at detector 44 occurs during periods φ3 and φ4.

In each period φ1 and φ8, the light emitting diode 80
．． It will be readily seen that the optical signal from 82 is being received. During periods φ2 and φ4, only noise (such as noise due to ambient light) is received, rather than a signal. As will become clear below, by amplifying the negative signal before passing through the low-pass filter, noise can be removed using a 1:4 duty cycle.

Having provided the reader with an overview of the circuitry used in the invention, the invention will now be discussed in detail.

In FIG. 8, a microprocessor 100 having a crystal 104 is shown. This crystal is
It cooperates with the clock circuitry contained in the microprocessor 100 to produce the required clock signals for the microprocessor chip itself and provides clock pulses to the rest of the oximeter circuitry via the output 102. .

Microprocessor 100 is an 808 microprocessor available from Inte 1, Inc., Sunta Clara, California, USA.
It is a 5.4-inch CPU integrated circuit chip. The 7-Ami'Ji identification suffixes of the remaining IC components are shown in the drawings;
These components are readily available from various manufacturers.

Address bus 108 connects address circuits AO to A15.
Consists of. To accommodate an 8-pit processor, lines AO through A7 on the address bus are latched from pins ADO through AD7 of the microprocessor, allowing readout of these lines in the addressing time state. In another time state, lines ADO through AD7 become output data lines 104, opo through OD'l, which can only output data as shown in this example.

In FIG. 4, it can be seen that the form of the ROM is standard. This ROM has lines AO to AIO that address ROM2O3°107 and 108 in parallel.
Addressing is done using a normal address bus including Each of these ROMs is connected to lines A11 to A18' (sixth
It is enabled by three decoded address pits from (see figure). As described below with respect to FIG. 6, the output of the ROM read enable state includes a read enable signal 110 (see FIGS. 3 and 4).
, the address for specific ROM selection is ROM0 add 1
11, ROM1 address 112 and ROM2 address 114. The ROM used in this example is an optically erasable programmable read only memory and refers to the output data bus 115.

In FIG. 5, two conventional RAMs 120, 121 are shown addressed in parallel by address bits AO through A9 which make up bus 125. 4 that constitute the bus 127 of these RAKc-1 RAM 120
8 bus lines ADO to AD8 and AD4 to ADT which constitute bus 128 of RAM 121.
It is written and read through two pits. RAM120
121 is read when enabled via enabled port 129 in the absence of a write signal on port 130. These RAMs are written to when enabled by baud 129 when a write signal is present via write port 130. Since each of both RAMs is associated with four separate data pits, there is no need to individually enable each RAM.

In FIG. 6, a memory selection circuit of the present invention is shown. This memory selection has an 8-bit input 140 that constitutes lines A11 through A18. Memory is RO
M0 available signal 111.80 M1 available signal 112
, an output occurs when selected by the ROM2 enable signal 114.

RAM enable signal 14 passes through an inverter and a NAND gate to enable RAM1°20.121 for either reading or writing.

In FIG. 8, a counter used as a frequency divider circuit is shown. Returning briefly to FIG. 3, microprocessor 100 generates a clock signal designated generally at 102 operating at 2.5 MHz. The clock signal of the CPU- is outputted at 102 to a counter 172 (see the eighth column). counter 1
72 divides the signal 102 by a number 171 and outputs it to a binary counter 173 to generate an LED clock frequency of 1.827 KHz, which is unrelated to the frequency of the interior light. The counter 173 has a signal LEDA191°L
F: Output DB192, r, gvQr, g190.

This circuit cooperates with the circuit of FIG. 13 to provide light and detector switching to ensure a predetermined phase relationship between the signals.

Although microprocessors have been described generally, it will be appreciated that much of the disclosure is already known in the art. In particular, a detailed description of the programming of this microprocessor was published by Intel in 1979.
[Can be found in the McS-8085 Family User's Manual, published October 2013. Those skilled in the art should refer to this document if they have any doubts about the circuit described above.

Briefly referring to FIG. 8, the LED clock outputs 190, 191, and 192 are input to the clock frequency divider circuit 194 of FIG. 13. The frequency divider circuit 194 sequentially outputs four duty cycle status signals indicated by φ1' to φ4'. The complements of signals φ1 and φ8 are output at direct clock divider output 196. Output 198
All four signals φ1' through φ4' that make up the signal φ1' to φ4' serve for timing as discussed below.

Having mentioned the timer, the remainder of the invention is divided into three separate parts. 1st K, discusses the timing for LED light emission. It will be emphasized that the diodes are locally switched.

Second, let's describe the reception of light. Regarding reception, it may be emphasized that the signal is extracted digitally without any analog processing.

The purely digital signals are then processed and used here to form the light curve. Efforts were made to eliminate all variables to be analyzed, such as changes in meat quality and noise due to ambient light.

Thirdly, the light level adjustment circuit of the present invention will be described as a measure against changes in the light transmission characteristics of the human body. It will be pointed out that the amount of incident light is adjusted so that the sensor receives the appropriate amount to the amplifier circuit.

In FIG. 14, sufficient voltage is applied to lead 1, 301.30.
2, an appropriate level of current is provided to each of the light emitting diodes 81,88.

These diodes are shown schematically across connector 305 and are switched by respective transistors 307 and 309. Receiving a negative pulse turns off the transistor, a voltage appears across each diode 81.33, and light is emitted.

The emitted light passes through the flesh of the finger 14, and is then received by a light-receiving sensor 38.

In FIG. 12, a photosensor 38 is shown. This is coupled to both ends of connector 305. connector 8
05 further sends its signal through a preamplifier 40. This signal is then split and sent to voltage amplifiers 41, 42 where amplification occurs in parallel to create the gain difference between red and infrared signal processing. . Each phase detector 43.44 is the 13th
It is clocked by inputs φ1' to φ4' from the clock circuit shown in the figure. Four signals φ1゜φ that are clock periods
The duty cycle of each of 2, φ3, and φ4 is % and is gated by each of these signals. In detail, the period φ
1, a negative amplification of all optical signals including pulsating components and noise is performed in amplifier 201, and the resulting signal is passed through low-pass filter 45.

In FIG. 14, in the next period, transistor 309 is no longer on (LED 80 is disabled) and transistor 31 is grounded. At the same time, during one period φ2, the gate portion of the phase detector 43 is opened to positively amplify the received signal. However, this received component does not include the LED emission component and represents entirely electronic or optical noise.

Therefore, the timing of this circuit is to first generate a signal representing light containing a pulsating component and noise at an equal time pace, and then generate a signal representing light containing a pulsating component and noise. - Amplifier 201 amplifies one signal in the positive direction and another signal in the negative direction with the same gain. It is output from amplifier 201. The signal over all four periods of the clock contains two identical but different polarity noise components that will be canceled and a signal component that will not be canceled. By taking each intermittent pulse and passing them through a low pass filter 45, the result is noise cancellation and a signal of only the valid signal components.

The same goes for the remaining channels. In detail, the period φ.

8, the noise and optical signals are amplified in the negative direction and passed through the low-pass filter 46. During one period φ4, only the noise is amplified in the positive direction and passed through the low-pass filter 46.
It is canceled while passing 6. ``The output signals VA and VB of the circuit of FIG. 12 can be described as having two components.

The first component is a constant. This is the component of transmitted light that remains approximately constant. This signal component is due to components absorbed by skin pigments, bones, flesh, and venous blood. The second component represents the pulsatile flow of blood in the artery.

The instrument determines the ratio of the second component to the first component. What is sought here is the ratio of the pulsating component of the artery to the total absorption component of the tissue. The arterial component of blood has a permeability that depends on the oxygen saturation of hemoglobin in the blood.

In FIG. 11, the amplification of the signal to an idealized state is shown. Specifically, in the process of extracting each signal VA', VB2, an offset voltage VOFF is introduced. The offset voltage is a constant voltage that removes a portion of the constant component of the received light signal related to passage through an unaltered portion of flesh. Since it is known that the ripple component is always very small compared to the total signal, its removal can improve the accuracy of the digital conversion. However, it is necessary for the microprocessor program to mathematically reinsert this removed voltage prior to processing the signal. This removal and amplification occurs in each amplifier 330, 331, and signals VA' and VB' are output.

Note that the rejection does not vary as a function of the detected pulsation signal. The role of this removal is simply to allow only the detected signal-related portion to be separated and amplified.

When converting these signals from digital to analog, it is necessary to combine the pulsating component with the remainder of the constant component. This is best seen in the circuit of FIG.

In FIG. 9, multiplexer 50 is shown. During the analysis operation shown here, this multiplexer 5
0 samples signals VA' and VB'. The signal is sent to the negative side of comparator 52. The signals to drive the multiplexers pass through lines OD4-OD6 in the DAC high latch 860. The DAC's low latch 862 is then activated in response to an enable signal on the enable line 863 and is output on a 12-bit basis and input to the digital-to-analog converter 54. One of 4096 types occurs.

Typically, the signals are compared half by half. The output of DAC 54 is sent via lead 865 to comparator 52 and the output 366 is sent to the microprocessor. Depending on whether a high or low state signal is received, the stepping operation of the 12-pin DAC 54 occurs in half, allowing the 12-bit division to occur quickly.

As a result, the output level of the voltage of the receiving photosensor can be quickly determined and the pulsation component can be quickly followed and determined. This process is repeated for both signals VA' and VB' at a rate that allows the microprocessor to faithfully track both signals VA' and VB'.

Having described the light receiving circuit (light receiving circuit) of the present invention, attention should now be paid to the brightness adjustment level.

Recall that each patient will exhibit a certain patient-specific light transmission component at both wavelengths due to flesh texture, skin pigment, skin thickness, bone, venous blood, and other constant components. . For this reason, it is necessary (for each patient) to adjust the level of current applied to the light source 31. This is accomplished by the DAC circuit of FIG. 9 and the sample and hold circuit of FIG.

Sampling of optical signals by a microprocessor was previously discussed. If the signal is not within the useful range of the conversion circuit, the level of the incident light must be adjusted up or down as necessary to bring the signal level into the acceptable voltage range for analog-to-digital conversion. In FIG. 9, the program outputs the desired voltage level and corresponding code to launch 362,860 via its data bus.
Set the output of 4 to the voltage corresponding to the required LED current. Note that this is only done during periods when the DAC is not used for input conversion (outside input conversion periods). The program then uses the same bus to send the bit output corresponding to the selected LED to latch 370 in FIG.
give to This pit or selection signal is converted to a voltage compatible with voltage converter 871 and applied to one of eight analog switches 872, 874. As a result, after the input is removed, the voltage from the DAC corresponding to the desired LED current level is applied to the storage capacitor and the voltage is latched. This voltage is applied to amplifiers 875, 8
76 and provided to the LED circuit. Thus, depending on the strength of the signal received by the photosensor, each light emitting diode can be driven with an adjusted high or low voltage to produce an optimal light output.

It turns out that only two of the eight available channels of this sample and hold circuit are needed to adjust the strength of L'ED. The remaining channels provide general purpose analog outputs from the microprocessor for various unrelated functions. The output of amplifier 377 provides a fixed offset voltage to the aforementioned offset amplifier (FIG. 11).
The output of amplifier 60 provides volume control for the alarm and
The outputs of 1°602 and 603 provide external outputs to any chart recorder, and the output of amplifier 604 provides control over the pitch of the alarm.

Theory of Operation The method of operation involves measuring the amount of light transmission through tissue for two different wavelengths (red and infrared) at any two points in time. However, the two time points are only a very short time compared to one entire pulse. The waveform of a single pulse of blood within the human body is digitally plotted. Measurements are made by considering changes in the amount of light transmitted by inflowing arterial blood.

The amount of light transmitted increases as the amount of light absorbed increases when blood flows in. As a result, the photodetector, ie, photosensor 38, detects less light. 4 In this way, the presence of a pulsating component can be seen from the decrease in the amount of light received by the photosensor.

The amount of ambient light transmitted (approximately 99 inches of signal) is represented by the symbol I, and the change in the amount of transmission due to pulses is represented by the symbol △I.
The relational expression for expressing the amount of change in the amount of light transmission with respect to the unchanged part of the meat quality is expressed by the following expression. That is.

ΔI/IOoΔM (1) where 6M is the change in material during the duration of the pulse.

If we insert a constant to make the equation equal, we get the following formula. That is.

△I/I=6M(2) Here, K is a proportionality constant.

The change in mass is due to the fact that blood (whose optical absorption is greater than that of tissue) consists of blood, which has two forms of hemoglobin: oxyhemoglobin (hemoglobin with associated oxygen) and deoxyhemoglobin (hemoglobin without oxygen). (hemoglobin), the above equation can be extended to the equation for two variable components as shown below. Immediately.

△I / I = KA△MA + KB△MB (8) Here, %KA is a constant for oxyhemoglobin.

△MA is the amount of change due to the influx of oxyhemoglobin,
KB is a constant for reduced hemoglobin.

'ΔMB is the amount of change in deoxyhemoglobin.

Recall that we are performing tests at two different wavelengths. In this case, the above relationship can be extended to include the applicable constants at each wavelength. Therefore, KAl and KBl have the first wavelength λ1 (e.g.
KA2 and KB2 are constants for oxygen-modarbin and deoxyhemoglobin, respectively, at the red wavelength), and KA2 and KB2 are constants at the second wavelength λ1.

It can be seen that each constant of the form Kxy relates to the relationship between the total absorption of light and the change in matter due to the pulsating flow for a particular color of change in absorption of light.

The ratio of oxyhemoglobin to the total hemoglobin amount S (
If you know the saturation level), you will know the following. That is, △MA=S△M
(5α)ΔMB=CI-8)6M
(5b) However, ΔM = ΔMA + ΔuB
(6) Here, S is the saturation degree of oxyhemoglobin, and (1-8) is the fraction of deoxyhemoglobin. Substituting this into the previous formula gives the following result.

That is, ゛λ2 From the above equation, it can be seen that one degree of saturation is determined,
The solution for blood perfusion (6M) is trivial.

At this crossroads, the amount of light transmitted at two different wavelengths and the associated ratios have all been defined. In defining this ratio, the reader will find that no logarithmic proportionality calculations are necessary. That is, the wavelength λl and the wavelength λ
In No. 2, the ratio between the amounts of light through 314 light was defined as follows. That is.

By substituting equations 6(α) and 6(b) representing the change in the amount of light absorption with respect to the total amount of light transmission at each wavelength λ1 and λ2, the following equation is obtained. That is.

R=cKAIS1KB1-8KB1)/CKA2S+K
B2-8KB2) (8) Similarly, if you solve for S, you will get the following formula. That is, 5=CKB1-RKB2)/R
CKA2-KH2)-(KAx-xBl)
(9) Thus, it can be seen that a certain relationship exists for both the ratio R and the degree of saturation S.

As will be appreciated by those skilled in the medical arts, values determined electronically by light absorption methods can also be determined by laboratory tests. In fact, there are numerous experimental protocols or tests for determining saturation. In this case, the procedure for the calibration of all instruments is immediately obvious.

Specifically, specific ratios R1, R2, R3, R4 can be determined by experimentally obtaining arterial oxygen saturations from individuals with different saturations S1, R2, R3, R4. In order to obtain these ratios R1 reliably, the instrument itself is used, especially in the parts of the apparatus that are relevant to ensuring reliable measurement results in this example.Then, the coefficients for both oxyhemoglobin and deoxyhemoglobin are determined. First assumptions can be made.

Taking one of the aforementioned coefficients KAl, this constant can be decomposed into two individual components. First, one component is obtained from the previously determined value and is denoted by A'. Second, for each instrument, this constant has to be changed fJS. This variation is due to observation conditions, electronic parts of individual instruments, etc.

This value can be expressed as ΔCA1. Each of the four constants in the above equation can be expanded in the same way as well.

(CA2+△CA2) (S i Ri)+(CB
2+ΔCB2)C1li-8iRi)=CCA1+Δ
CA1)(Si)+(CB1+△CBl)'(1-, S
') '' (10) where i is an index associated with the ratio of at least four measured saturations and permeations (i-1, 2, 8, 4, . . . ).

Those skilled in mathematics and instrumental calculations will recognize that it is possible to solve for the quantity and wavelength of ΔC in all states simultaneously, assuming the use of four independent degrees of saturation. . Thus, a set of constants is obtained, which can be used to program the instrument made individually for all values of S.

The aforementioned relationships can be determined in other ways. It has been discovered that the relationship between R (transmission ratio) and S (oxygen saturation of hemoglobin) matches a simple curve. In particular, a constant and predictable curve of S versus R can be obtained, at least for humans. A plot of this curve is shown in FIG.

By using this relationship in the traction table, patient saturation can be quickly calculated.

In this device, unlike the conventional technology, the device uses equal pressure (
Note that the device does not require logarithmic calculations (see Equation 7); .

The reader will appreciate that the pulse oximeter or hemometer described above is typically intended for use on a human finger. However, it should be known that this pulse oximeter works equally well anywhere on the skin. The ideal preferred application for the very small localized sensor of the present invention is on the scalp of a child during childbirth. One possibility is to avoid the oxygen deprivation conditions during childbirth that lead to cerebral palsy. Similarly, other skin locations may be used, such as the nasal septum.

Meter Calibration In FIG. 15, an apparatus for in-situ calibration of the meter is disclosed. In particular, the device of FIG. 15 allows adjustment of the ratio H and uses a rotating filter 400 in place of the pulsatile component of human blood.

Referring to the apparatus of FIG. 15, an electric motor 4 with a conventional power source 403, schematically shown as a battery in the figure.
8 variable resistor 404, labeled 01, drives the motor at variable rotational speeds. Typically, this rotational speed is chosen to emulate a human pulse. Although only one filter element is shown, many variations of multiple elements may be used.

Red light source 30 and infrared light source 32 are connected to light pipe 430.
432 valleys. Each of these light pipes (optical fibers) forms a path of light and directs the light to a location 435 in close proximity to the rotating filter 400. At the same time, photosensor 38 is coupled to second light pipe 438.

As it rotates, light pipe 438 first receives undattenuated light and then receives light that is attenuated by filter 400 .

The filter 400 includes a rotor 402 that rotates together with an electric motor 401.
It is rotated by the rotation of . In such rotational motion, the filter passes between each light beam in a manner that emulates a pulsating signal.

Since the pulsating component of the blood flow is represented by an increasing amount of absorption, it can be seen that the pulsating component of the finger can be emulated with a simple device such as the rotating filter 400. Of course, intermediate vendors will find that customization of filter 400 is possible. For example, by placing a neutral filter with varying absorption (with a concentration gradient) along the rotating surface of filter 400, this filter can also be made sensitive to the red and infrared components used in the above embodiments. This allows for good approximation to the finger pulsation response. Similarly, color can be completely excluded, but the limitation is that the color (wavelength) of the light source is not examined.

Second, in the case of a neutral filter in which the red and infrared light patterns are the same, the ratio R of each is constant. Therefore, a rotating filter can be used to calibrate the calculated ratio R. The reader can also vary the filter density radially and by changing the position of the light pipe.

It will be seen that various values of H are obtained.

In FIG. 16, a blot of the ratio iR to the experimentally determined blood oxygen saturation St/C is shown. Those skilled in the art will appreciate that the constants necessary to correlate a ratio "4R" to a saturation WE can be readily determined by suitable graphical techniques.

The reader will find that the use of red and infrared light is desirable. Although any two colors that produce a non-redundant set of values R and S can be used, these colors are preferred. Below is the bow computer program.

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[Brief explanation of drawings]

FIG. 1 is a perspective view of the instrument of the present invention showing the instrument housing and the connection of the sensor to the patient's finger; FIG. 2 is an overall circuit diagram showing the circuit of the present invention; and FIG. 3 is the circuit in the vicinity of the microprocessor. FIG. 4 is a circuit diagram in the vicinity of the read-only memory, ie, ROM, of the present invention;
FIG. 5 is a circuit diagram in the vicinity of the read-only memory or ROM of the present invention, FIG. 6 is a circuit diagram showing memory selection, FIG. 7 is a circuit diagram showing input/output selection states, and FIG. 8 is a circuit diagram of the present invention. 9 is a circuit diagram showing a comparator circuit that performs 12-bit digital/analog conversion, FIG. 10 is a circuit diagram showing a sample holding circuit of the present invention, and FIG. 11 is a circuit diagram showing a sample holding circuit of the present invention. 12 is a circuit diagram showing a detector of the present invention; FIG. 13 is a detailed diagram of a clock circuit with an output for energizing a light emitting diode; FIG. Detailed diagram of the circuit for energizing and switching the diodes, Figure 15, used in the manufacturing company and later in the field for the adjustment of the meter's light ratio detector to allow complete adjustment of the meter. A diagram illustrating an apparatus to be used, and a first
Figure 6 is a graph showing the light transmittance (CR) versus the tested oxygen saturation (S). DESCRIPTION OF SYMBOLS 1... Numerical display, 2-5-... Circuit selection button, 6-9... Alarm status indicator light, 10... Control knob, 11... Synchronization status indicator light, 12. ...Digital indication meter, 13...0 switch, 14...finger %
15...Speaker, 16...Microprocessor,
17...Bus, 18...ROM, 19...RA
M, 20... LED display, 21... Selection latch, 22... Numerical display latch % 24... Control device, 26... Housing, 27... Lead wire, 28
...Patient, 29...Detector, 30...Light emitting diode, 31...Amplifier, 32...Light emitting diode,
88... Amplifier, 36... Barrier, 38... Photo sensor, 40... Preamplifier, 41.42... Amplifier, 43.44... Phase detector, 45.46... Low-pass filter, 47, 48...offcent amplifier,
50... Multiplexer, 52... Comparator. 54... Disaster/analog converter, 57...
...Sample holding circuit, 60.61...Voltage output, 7
0...Clock, 100...Microprocessor. 102... Clock, 103... Address bus,
104...Crystal, 1o6...ROM% 10
7...ROM, 108...ROM, 115...Output data bus, 120.121...RAM, 127
,128... Bus, 129.180... Port, 1
72...Counter, 173...Binary counter, 19
4... Clock divider, 201... Amplifier, 805
...Connector, 307.309...Transistor,
360% 262...Latch, 870...Latch,
371... Voltage converter, 872, 874... Analog switch, 378... Amplifier, 400...
Filter, 402... Rotor, 401... Electric motor,
430.482...Light pipe, 794-799...
Number. Patent applicant: Nelcor Inc.
Name) Engraving of drawings (no changes in content) FI6. 1 FIG, II -〇Fl, 9゜) coFIG,
/6゜Procedural amendment (method) Showa, ge, March 1, 2011, case description Showa is the year ＞iτ da petition No. /6/'7? R Nogurusu too ho 5 fti Chi 4, Agent 5, Date of amendment order Showa, February 2J, 2008 (shipment date) Contents of Z amendment

Claims (1)

[Claims] 1. first and second light sources for emitting sequential light pulses in red light and infrared light to an image quality of a human being; at least one sensor sensitive to each of the light sources having an indirect path of light through the flesh, each of the light sources comprising:
having a duty cycle smaller than -γS of a portion with respect to time, the sensor receives the amount of indirect light transmission from each light source during a first portion of the duty cycle of each light source; receiving ambient light during a second portion of the duty cycle, the sensor outputting a signal to an amplifier, the amplifier processing the signal from the received light source during the first portion of the duty cycle; and processing the ambient light signal in a second portion of the duty cycle to remove noise signals from the received light signal by subtracting one of the amplified signals from the other of the amplified signals. A pulse oximeter characterized in that it is provided with a device. 2. The pulse oximeter of claim 1, wherein each light source has a duty cycle of -4. 3. The amplifier has a positive input and a negative input. further comprising means for switching to one of the inputs of the amplifier during a first portion of the duty cycle of each light source and to an input of the opposite sign of the amplifier during a second portion of the duty cycle of each light source. A pulse oximeter according to claim 1, characterized in that: 4. at least one light source outputting light of a preselected wavelength to the human flesh, and having an indirect path from the light source through the human flesh adjacent to the input of the light source; at least one optical sensor addressed to said fleshy substance; an increase in the amount of light absorbed in a first period due to the inflow of arterial blood to said fleshy body and a decrease in the amount of light absorbed in a second period due to the outflow of arterial blood to said fleshy substance; a device for continuously monitoring the intensity of light received by said light source for detecting said light source; and adjusting the light output intensity of said light source during one of said light transit periods to detect during said arterial pulsating flow. A pulse oximeter further comprising a device for maintaining the intensity of light at the optical sensor within a predetermined range. 5. first and second light sources in the red light and infrared ranges, respectively, addressed to human flesh and at least one adjacent to said light source for receiving passing indirect light; one optical sensor is provided, detects light from the light source, and sequentially outputs a first signal from the first light source and a second signal from the second light source, and each of the light sources -sequentially alternating duty cycles of shorter periods of time, such that the light sensor first samples light from the first light source passing through the human flesh, and then samples the light from the first light source passing through the human flesh; samples the ambient light that passes through the human flesh second, samples the light from the second light source that passes through the human flesh third, and samples the ambient light that passes through the human flesh fourth. sample,
A comparison circuit is provided connected to the output of the sensor, the comparison circuit comparing the output of the digital-to-analog converter to the light received from the light source and determining the ratio of the changing portion of the light signal to the unchanged portion of the same signal. A pulse oximeter characterized by being equipped with a oxidation device. 6. A first and a second circuit connected to the output of the comparison circuit.
further comprising an amplifier for receiving an offset signal constituting an invariant portion of the output of the comparator circuit and for amplifying the offset signal in the negative direction, each of the first and second amplifiers and a second optical signal, such that the outputs of the first and second amplifiers constitute a changing portion of the optical signal, and the outputs of the first and second amplifiers eliminate a substantial portion of the unchanged portion. The pulse oximeter according to claim 5, characterized in that: 7. first and second light emission sources for emitting sequential light pulses in red light and infrared light into the human flesh, and an indirect light path from the first and second light sources through the human flesh; a sensor responsive to each of the light sources, the sensor sequentially outputs a signal from each light source to an amplifier, and a device for digitally tracking the state of light absorption; and a device for digitally tracking the state of absorption of light; A device that determines the absorption quotient for each wavelength in order to determine the flow of blood by dividing the change in the amount of light transmitted due to the pulsating component of the flow, and a device that is directly related to each aspect of the amount of light transmitted at each frequency. and a device that allows optical determination of the saturation amount by adapting the ratio of the amount of light transmission to the saturation amount experimentally determined in the ratio. Pulse oximeter to determine oxygen saturation. 8. for calibrating a Sulhars oximeter comprising first and second light sources that sequentially emit pulses of light and at least one photosensor that detects light transmitted through human flesh by the light sources; In the apparatus, at least one light path communicates with the light source at a light receiving end and a light emitting end with respect to a spatial interval overlapping the path of the filter, and a first light pipe for transmitting light from the outlet to the oxygen concentration. at least one light path in communication with a photosensor of the meter, and a device for passing said light through said spacing between said pipes to a filter having an absorption disposition to emulate said pulses. Instrument to do. 9. The instrument of claim 8, wherein said filter is mounted to a rotor of an electric motor and rotates within a gap between said optical paths. 9. An instrument as claimed in claim 8, characterized in that the speed of said rotational movement of said filter is adjustable to emulate a varying pulse rate.