JPH0224138B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a pulse oximeter device,
An oximeter that photoelectrically determines the oxygen saturation of the arterial system of the human body by means of data initialization, processing of received data, configuring, and techniques for triggering alarms, as detailed below, in particular: Regarding equipment.

[Background of the invention]

Electrical non-invasive techniques for the determination of oxygen content are known. U.S. Pat. No. 2,706,927 to Wood discloses a method for calculating oxygen saturation from measurements of light absorption of human tissue at two wavelengths. First, as much blood as possible is squeezed from the area to be measured to perform a "bloodless" measurement. Arterial blood is then passed through the tissue to restore normal blood flow. Information about the oxygen saturation level of the subject's arterial system can be obtained from the comparison results of light absorption in these two states. Using this approach, a series of devices and procedures have been proposed.

In procedures based on this technique, it has been experienced that it is difficult to determine the parameters of the "bloodless" state with sufficient reliability, in part due to geometric distortions due to tissue compression. Incomplete results are obtained due to incomplete measurement of this parameter.

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. This transmittance attenuation has a logarithmic characteristic according to Lambert-Beer's law.

In a pulse oximeter, the main object of measurement is pulsating arterial blood. Arterial blood is the only substance whose amount in tissues changes over time in synchronization with the beating of the heart. Therefore,
Fluctuations in light transmission represent fluctuations in blood flow, allowing direct optical recording of the pulsatile component of arterial blood flow. This ability to isolate the optical absorption of arterial blood is particularly useful, since the oxidized hemoglobin component of blood is a substance whose absorption coefficient can be determined, making it possible to determine even a small amount of oxidized hemoglobin in arterial blood. Can be done.

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. Generally, these hemometers utilize optical frequencies near so-called isobestic points (frequency points at which measurements of arterial flow are made independent of oxygen saturation). As a result, no information regarding oxygen saturation can be obtained.

Following U.S. Pat. No. 2,706,927,
Many attempts have been made to eliminate the problems associated with measuring arterial saturation using optical absorption methods; of,
It is necessary to compare and analyze measurements in a naturally occurring "bloodless" state or an artificially created "bloodless" state during the resting state of the heart's beating cycle. For example, a received signal may be separated into "alternating current" and "direct current" components and passed through a logarithmic amplifier prior to digital analysis of the signal. See US Pat. No. 3,998,550 to Koneshi et al. In a similar manner, prior to digital analysis, difference outputs at both wavelengths are generated and the DC component is removed from these difference outputs to approximate the logarithmic response according to the prior art. U.S. Patent No. 4266554 for Hamaguri
Please refer to the issue. Briefly, since only a small portion of the total signal of transmitted light is the pulsating component, a number of logarithm-based treatments have been attempted to separate the stationary component from this signal prior to analysis.

Hertzfeld et al. US Patent No.
In issue 3704706, a single coherent red light source,
Preferably the use of lasers is disclosed. Using a single light source does not allow separation of information about arterial blood flow components from information about arterial oxygen components. The output of such a single red light source instrument simply reflects the blood flow present and saturation (saturation level)
It can only display the product of . It is not possible to know only blood flow or saturation.

In all the above-mentioned methods for measuring pulse rate, pulse flow and oxygen saturation, the variable or alternating current component is a small portion of the total absorption that occurs. In such situations, it is necessary to distinguish between the signal and noise due to other possible light sources. unconscious state,
Alternatively, measurements must be taken on patients who are unresponsive under local anesthesia or other methods, and these patients exhibit random and erratic movements (and heartbeats); It is important to establish thresholds for data reception (determining valid data) and analysis.

[Summary of the invention]

Light of two different wavelengths is passed through body tissues such as the fingers, ears, or scalp, and the light modulated by the pulsating components of arterial blood within the tissues is received to determine oxygen saturation (blood oxygen concentration). A display monitor for an oximeter is disclosed. This instrument is
First, it receives a signal and compares it with parameters to check for pulsed signals. If a pulsed signal is detected, a tone signal is emitted with a pitch proportional to oxygen saturation and with successive repetitions proportional to the pulse. A visual cue consisting of an LED array is provided by continuously blinking at a rate proportional to the pulse rate, increasing the number of light sources illuminated as the pulse size increases. By systematically removing irrelevant or irregular detection data, inappropriate alarm sounds are prevented.

[Other objects, features and advantages of the invention]

It is an object of the present invention to disclose an instrument capable of simultaneously tracking and displaying pulses as well as individual oxygen saturations. According to this aspect of the invention, at least one wavelength of light, preferably infrared, is monitored for changes in its slope. Proportional to, and typically synchronous with, the rate of change of the gradient, a signal is generated indicative of the heart's beating rate.
Another signal is generated containing pulse rate and oxygen saturation information.

One advantage of this feature of the invention is that each pulsation component is analyzed individually. The patient's heartbeat and arterial oxygen levels are continuously monitored.

Another object of the invention is the disclosure of a series of acoustic signals signaling pulse rate (pulse rate) and oxygen saturation. The pulse rate is displayed by emitting sequential tones at time intervals corresponding to the frequency of occurrence of negative slope inversions (representing the maximum value of the pulse waveform).
Oxygen saturation is indicated by decreasing pitch in proportion to the decrease in oxygen saturation.

An advantage of this feature of the invention is that the human ear is particularly sensitive to both changes in tone frequency of continuous acoustic signals and changes in timbre in continuous sounds. A simple pulse signal can make both the patient's pulse rate and oxygen saturation sufficiently visible to everyone in the immediate vicinity.

Yet another feature of the invention is the provision of visual signals conveying similar information. According to this feature of the invention, the array of light emitting diodes emits light at a height proportional to the magnitude of the pulse and at a frequency proportional to the pulse speed. The pulse characteristic representation is made because the human eye is particularly sensitive to changes in both the flash rate and the angular magnitude or height of a flashing LED array.

An advantage of this feature of the invention is that it discloses multiple alarms that can all be set individually according to the patient's current state. According to this aspect of the invention, high pulse rates, low pulse rates and oxygen saturation levels can all be used as alarm limits.

An advantage of this feature of the invention is that the patient's alarm limit parameters can be adjusted to suit the patient by the anesthesiologist or other attending physician. Individual adjustments can be made to the particular physiological state at the time.

Yet another object of the invention is to disclose a combined handling method for this instrument to eliminate extraneous data. When this instrument is used,
Considering that patients are often in a state of unconsciousness or semi-consciousness, it will be appreciated that this instrument is not intended to be operated under satisfactory circumstances. Rocking or movement of the sensor head, or even local fluctuations in the patient's pulsation status, can unnecessarily trigger an alarm. According to this feature, the input processing data is compared with a confidence factor. If the data falls within the expected levels, the confidence factor remains unchanged or is promoted to the highest level. If the data does not fall within the expected level, the data itself is rejected. This confidence level is gradually lowered or widened in the range of data that can be processed. This process continues until data matching the confidence limits is received. If data is received that is consistent with the confidence factor, it is compared to the alarm limits.

An advantage of this feature of the invention is that small local variations in the received signal will not trigger an alarm.

Yet another feature of the invention is the disclosure of all the data used for pulse tracking. According to this aspect of the invention, the points of maximum light transmission (beginning of the incoming pulse) and maximum light absorption (end of the arterial pulse) are tracked for at least one wavelength. The maximum negative slope between the maximum and minimum is plotted to avoid Chongqing veins. Finally, the percentage of oxygen saturation is determined by comparing the amount of light transmission at both frequencies.

All of this data is analyzed against confidence limits for acceptance. 3 out of 6 data values
If the value exceeds this limit, all of the data is rejected. If four or more of the data values are within this limit, the data is accepted;
Confidence limits may be upgraded to acceptable limits or maintained at the narrowest limits. The confidence limits for unacceptable data are gradually lowered or widened.

An advantage of this feature of the invention is that data breaks often occur in one or more parameters. Because of such disruptions, the entire data block can be averaged to prevent premature alarms.

Another object of the invention is to disclose a simplified control for adjusting alarm limits. According to this feature, the adjustment is made to the encoder of the axis that is directly coupled to the adjustment knob of the alarm limit.
The alarm limit to be set is selected by pressing at least one selection button. Then, by rotating the alarm limit adjustment knob, this limit is updated with a sign that depends on the direction of rotation.
In the limit it depends on the amount of rotation. The current alarm limit being changed is displayed on the visual display. If the alarm limit does not change for a preset period of time, i.e. the knob is no longer rotated, this knob is disconnected to the alarm limit and reconnected to the initial coupled state and the display returns to the initial state.

An advantage of this feature of the invention is that control of the alarm limits is easily and simply adjusted. The complex environments of operating rooms and intensive care wards will now be equipped with easy-to-use instruments that are easily calibrated. In particular, the alarm can be controlled with one hand, which is important in terms of patient care. It is not necessary to manually reconfigure the instrument to its initial state of displaying saturation or pulse rate.

Other objects, features and advantages of the present invention will become more apparent upon consideration of the following description and drawings.

[Description of preferred embodiment]

FIG. 1 shows a housing 26 of an instrument according to the invention.
shows. This housing has, on the outside, a numerical display 1, a row of circuit selection buttons 2 to 5, alarm status indicator lights 6 to 9, an optically coupled adjustment knob 10, a synchronization status indicator 11, and an LED. Digital indicator 12 and power switch 13
Contains. A speaker 15 is positioned within the instrument housing facing downwardly.

Connector in housing 26 (not shown)
A lead wire 27 extends from there. 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.

[Oximeter operation]

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

In Figure 2, an ordinary microprocessor 1
6 has a bus 17 extending from this. bus 1
7 is connected to ordinary ROM 18 and RAM 19. Selection latch 21 and numerical display latch 2
2 is shown. Circuit selection button rows 2 to 5 (first
) and optically coupled control knob 10
(FIG. 1) is gated via a control device commonly referred to as gating circuit 24.

Now that we have covered some of the common parts of a microprocessor, we would like to draw your attention to the analog part of the circuit.

A detector 29 with a schematic detection circuit is shown on the finger 14 of the patient 28 . A first light emitting diode 32 in the red range and a second light emitting diode 30 in the infrared range are sequentially pulsed by amplifiers 31 and 33 to emit light at their respective frequencies. Typically, LED 32 is in the 6600A range and LED 30 is in the 9400A range.

All light from an activated light emitting diode is
It is necessary to pass through the flesh of the finger 14. Therefore, the barrier 36 that does not transmit light is the photo sensor 38.
and fingers 14. Barrier 36 terminating in contact with the flesh of finger 14 forms a path between each light emitting diode 30, 32 and light receiving diode 38 through only the flesh of finger 14.

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

First, in selecting the frequencies to be used, the two frequencies should be far enough apart that the light transmission changes appreciably as oxygen saturation (oxygen concentration) changes.

Next, choose a frequency that samples the same tissue. For example, ultraviolet light frequencies cannot be sampled from the same tissue due to scattering.

It is possible to use very close frequencies, but we did not choose to do so. They discovered that problems arise due to frequency drift in 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 and 42. Once amplified, the signals from each amplifier 41, 42 are sent in parallel through each phase detector 43, 44.
After that, it passes through each low-pass filter 45, 46. Next, offset amplifiers 47 and 48 perform amplification. The pulsating component of the output of this offset amplifier is sent to multiplexer 50.

This multiplexer 50 provides its output to a comparator 52. Comparator 52 is ramped in half steps by a 12-bit digital-to-analog converter (hereinafter referred to as DAC) 54.

The DAC 54 sends a comparison signal representing one of the 4096 parts to a comparator 52.
and the comparator outputs to bus 17.

As is well known, not all human fingers and appendages are the same. In particular, even though the frequency and intensity of the optical signal output in each of the diodes 30, 32 are the same, due to differences between races, skin pigment, weight, age, maturity, and other factors. , different signals will be detected at the photo sensor 38.

Therefore, microprocessor 16 is programmed to receive signals from photo sensor 38 within an optimal range. As a second step of operation of the DAC 54, the individual LEDs 30, 32 are provided with the voltage outputs 60, 61 of the circuit 57 by sending a signal to the sample and hold circuit 57.
These voltage outputs 60, 61 are connected to the photo sensor 38.
is adjusted in each case to detect a signal well within the range of the DAC.

The clock circuit 70 includes light emitting diodes 30, 3.
The continuous light output from 2 is controlled at a duty cycle of 1/4. This is illustrated schematically by signals φ1 to φ4. Receipt of the signal at detector 43 occurs during periods φ1 and φ2, and reception of the signal at detector 44 occurs during periods φ3 and φ2.
Occurs between 4.

It will be readily seen that during each period φ1 and φ3, optical signals from the light emitting diodes 30, 32 are being received. 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 the schematically illustrated 1/4 duty cycle.

Having provided a general overview of the circuitry used in the invention, let us now discuss the invention in detail.

FIG. 3 shows microprocessor 100 with crystal 104 attached. This crystal works in conjunction with the clock circuitry built into the microprocessor 100 to generate the clock signals required by the microprocessor chip itself, as well as to the rest of the oximeter circuitry via an output 102. Provides clock pulses.

The microprocessor 100 is an 8085A CPU integrated circuit chip available from Intel Corporation of Santa Clara, Calif., USA. Remaining
Although the family identification suffixes of the IC components are shown in the drawings, these components are readily available from various manufacturers.

Address bus 103 consists of address lines A0 to A15. To accommodate an 8-bit processor, lines A0 through A7 on the address bus are connected to pins AD of the microprocessor so that these lines can be read during addressing time states.
It is latched from 0 to AD7. During another time state, lines AD0-AD7 become output data lines 104, OD0-OD7, and the lines configured at this time can only output data.

According to FIG. 4, it can be seen that the configuration of the ROM is standard. This ROM is ROM106,10
Line A addressing 7 and 108 in parallel
Addressed using a conventional address bus containing 0 through A10. Each of these ROMs is enabled by three decoded address bits from lines A11-A13 (see FIG. 6). As explained below with respect to FIG. 6, the enable output signals for reading the ROM include a read enable signal 110 (see FIGS. 3 and 4), and the address for a particular ROM selection is the ROM0 address 111. , ROM1 address 112 and ROM2 address 114. The ROM used in this example is an optically erasable programmable read only memory and includes an output data bus 115.

FIG. 5 shows two conventional RAMs 120, 121 addressed in parallel by address bits A0 through A9 which make up bus 125. These RAMs are connected to four bus lines AD0 to AD, which constitute address bus 127 of RAM 120.
3 and AD4 to AD7 that make up address bus 128 of RAM 121. RAM120,12
A 1 is read when enabled via enable port 129 in the absence of a write signal on port 130. These RAMs are written to when enabled by port 129 in the presence of a write signal via write port 130. Since each of both RAMs is connected to four separate data bits, there is no need to enable each RAM individually.

FIG. 6 shows a memory selection circuit according to the present invention. This memory selection has a 3-bit input 140 forming lines A11-A13. The output is the enable signal 111 of the memory ROM0,
This occurs when selected by the enable signal 112 of ROM1 and the enable signal 114 of ROM2.
The RAM enable signal 141 is sent through an inverter and a NAND gate to the read enable of RAMs 120, 121 for either reading or writing.

FIG. 8 shows a counter used as a frequency divider circuit. If we briefly consider Figure 3 again, we get
Microprocessor 100 is supplied with a clock signal designated at 102, typically operating at 2.5 MHz. The clock signal of this CPU is 102
is inputted to the counter 172 (see FIG. 8). The counter 172 receives a signal 1 based on the value 171.
02 and is not related to the frequency of the indoor light.
The output of counter 172 is output to binary counter 173 to generate an LED clock frequency of 1.827kHz.
is input to. The counter 173 has a signal LEDA1
91, LEDB192, LEDCLK190 and
Outputs DCLK189. This circuit works in conjunction with the circuit of FIG. 3 to provide light and detector switching to ensure phase relationships between the signals.

Although microprocessors have been generally described, it will be appreciated that much of the disclosure is already known in the art. In particular, for a detailed description of writing this microprocessor,
It can be found in the ``MCS-8085 Family User's Manual'' published by Intel in October 1979. Those skilled in the art are referred to this document if they have any questions regarding the circuits described above.

Briefly explaining FIG. 8, the outputs 190, 191, and 192 of the LED clocks 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 φ3 are output directly at clock driver 196. All four signals φ1' through φ4' comprising output 198 serve for timing as discussed below.

I mentioned the timer, but the rest of this disclosure is
divided into two separate parts. First, we discuss the timing for LED light emission. Emphasize the fact that the diode is locally switched.

Second, light reception will be explained. For reception, emphasis is placed on the fact that the signal is extracted digitally without any analog processing. Thereafter, the purely digital signals are 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 light transmission characteristics of the human body. It is pointed out that the amount of light emitted is adjusted to the amplifier circuit so that the sensor receives the appropriate amount.

Fourth, the setting of alarm limits is analyzed.
I will give an example.

Fifth, or finally, program alerts are discussed. In particular, the use of "confidence limits" and the totality of data received in a monitoring program as a means of screening out irrelevant data and also allowing timely warnings to be issued to prevent physiological catastrophes. will be disclosed.

In FIG. 14, sufficient voltage on leads 301 and 302 provides an appropriate level of current to each of light emitting diodes 30 and 32. These diodes are shown here schematically connected with connector 305 and each transistor 307,
309. Specifically, upon receipt of a negative pulse in each transistor, the transistor turns off, a voltage appears across each diode 30, 32, and light is emitted.

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

FIG. 12 shows the photo sensor 38. This is connected to connector 305. Connector 305 further routes the signal through preamplifier 40. This signal is then split and sent to voltage amplifiers 41, 42 where amplification is performed in parallel to create a gain difference between red and infrared signal processing. Each phase detector 43, 44 is clocked by inputs φ1' through φ4' from the clock circuit of FIG. Four signals φ1, φ2, φ3, φ4 which are clock periods
The duty cycle of each is 1/4 and is gated by these signals. In detail, the period φ
1, negative amplification of all optical signals including pulsation components and noise is performed in amplifier 201, and the resulting signal is passed through low-pass filter 45.

In FIG. 14, the signal φ1 no longer appears in the next period, so the transistor 3
09 is turned on, and the current to the diode 30 is shunted and grounded. At the same time, during the period φ2, the gate section of the phase detector 43 is opened to amplify the received positive signal component. However, this received component does not include the LED light emission component, but represents pure electronic or optical noise. Therefore, the timing of this circuit is to first generate a signal representing light containing a pulsating component and a noise component on an equal time basis, and then generate a signal containing only noise. Amplifier 201 amplifies one signal in the positive direction and the other signal in the negative direction by the same amount. amplifier 20
When combined over all four periods of the clock through 1, the instrument will see equal magnitude noise components that can be canceled and signal components of unequal magnitude that cannot be canceled. By taking each intermittent pulse and passing them through a low pass filter 45, noise is canceled and a signal containing only valid signals is output as a result.

The same goes for the remaining channels. Specifically, during the period φ3, the noise and optical signals are amplified in the negative direction and passed through the low-pass filter 46. During period φ4, only noise is amplified in the positive direction and canceled while passing through the low-pass filter 46.

The output signals VA and VB of the circuit in FIG. 12 are:
It can be described as having two components. The first component is constant. This is the component of the transmitted light that remains essentially unchanged. This signal component is due to components absorbed by skin pigment, bone, meat, and venous blood. The second component represents the pulsatile flow of arterial blood.

The ratio of the second component to the first component is determined by this meter. What is sought here is the ratio of the pulsating component of the artery to the total absorption component of the tissue. The color of the arterial component of blood gives rise to differential light absorption that depends on the oxygen saturation of hemoglobin. The instrument must separate this component.

In FIG. 11, the amplification of the signal is shown for an idealized situation. To explain in detail, in the process of extracting each signal VA', VB', the offset voltage is
VOFF is introduced. This offset voltage is a constant voltage that removes a portion of the constant component of the received light signal associated with passage through a constant 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, for microprocessor programming, it is necessary to mathematically reinsert this removed voltage prior to processing the signal. This removal and amplification is performed by each amplifier 33.
0,331 and the signals VA' and
VB′ is output.

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.

FIG. 9 shows the microplexer 50. During the analysis operation shown here, this multiplexer 50
samples signals VA' and VB'. The signal is sent to the negative side of comparator 52. The signals for driving the multiplexers pass through lines OD4-OD6 in the high latch 360 of the DAC. The DAC roller latch 362 is then activated in response to an enable signal on the enable line 363, and the output is input to the digital/analog converter 54 in 12-bit units. 4096 divisions are performed.

Typically, the signals are compared half by half.
The output of DAC 54 is sent via lead 365 to comparator 52, whose output 366 is sent to the microprocessor. 12 bits, depending on whether a high or low signal is received.
The stepping operation of DAC54 occurs in half,
Allows 12-bit splits to occur quickly. As a result, the output level of the received photo sensor voltage can be determined quickly, 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 of the present invention, attention should now be paid to the light adjustment level.

Each patient's flesh quality, skin pigment, skin thickness, bones,
Recall that due to the presence of venous blood and other constant components, the patient will exhibit a constant light absorption specific to the patient at both wavelengths. For this reason,
It is necessary to adjust the level of applied current (to the light source for each patient). This is the 9th
This is performed by the DAC circuit shown in the figure and the sample hold circuit shown in FIG.

Sampling of optical signals by a microprocessor was previously discussed. If the signal is not within the valid range of the conversion circuit, the incident light level must be adjusted to increase or decrease as necessary to bring the signal level back into the acceptable voltage range for analog-to-digital conversion. . In Figure 9, the program will output the desired voltage level and corresponding code to latches 362 and 360 via its data bus, setting the output of DAC 54 to the voltage corresponding to the desired LED current. . Note that this is only done during periods when the DAC is not being used to convert inputs (outside the input conversion period). The program then connects the bit output corresponding to the selected LED to latch 37 in Figure 10 using the same bus.
Give to 0. This bit or selection signal is converted to a suitable voltage by voltage converter 371 and applied to one of eight analog switches 372,374. This results in a signal that corresponds to the desired LED current level after the input is removed.
The voltage from the DAC is given to the storage capacitor,
Voltage is latched. This voltage is applied to amplifier 37
5,376 and applied to the LED circuit. Thus, depending on the strength of the signal received by the photo sensor, each light emitting diode can be driven with a regulated 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 intensity of the LED. The remaining channels are
Provides general purpose analog output from the microprocessor for various unrelated functions. The output of the amplifier 377 is connected to the offset amplifier (11th
A voltage with a fixed offset is applied to the amplifier 37
The output VVOL of 8 provides volume control for the alarm, the output of amplifiers 601, 602, 603 provides external output to any chart recorder, and the output of amplifier 604 provides control for the pitch of the alarm.

[Monitor operation]

A method for providing signal information obtained by an oximeter device to an attending physician through the oximeter monitor of the present invention will now be described.

In FIG. 1, when the power of the instrument is turned on via the power switch 13, the numerical display 1 (digital display) and
Both LED digital display meters 12 light up momentarily until the microprocessor 16 begins its operation. The speaker 15 also emits a signal tone (beep). When the microprocessor 16 is able to control the instrument in about milliseconds, the numeric display 1 is cleared and the zero is placed in digit 7.
Flashes about 94-796. When the power is turned on, the oximeter is not in operation, so the audible alarm is prohibited, and the alarm prohibition indicator LED9
starts lighting up. Synchronization with the patient's 28 pulse rate via the detection probe 29 has not yet been established. Therefore, the asynchronous state indicator light 11 lights up to indicate the asynchronous state. Microprocessor 1
6 begins sampling the signal of the photo sensor 38 and, upon determining that a valid pulse is being received, displays digit 794 on the numerical display 1.
-796, the oxygen saturation level in the blood of the patient 28 is displayed as a percentage in decimal notation. Digits 797-79
9 digitally displays the pulse rate (pulse rate). The LED digital display meter 12 begins flashing in synchronization with the pulse rate, and the vertical height of the flashing is proportional to the strength of the received pulse. After approximately 4 or 5 valid pulses are received, the asynchronous LED indicator 1
1 is deenergized and turns off. The alarm, which when triggered via the speaker 15, can be manually enabled from this point on using the alarm button 5. When button 5 is pressed,
The alarm prohibition indicator light 9 goes out. An alarm sounds when the alarm limit is exceeded, as discussed in detail below.

When synchronization with the pulse is established, the speaker 15
begins beeping at a frequency that is synchronized with the frequency of the identified pulse rate and at a pitch that is proportional to oxygen saturation. Defaults give an initial volume and pitch to these signals.

This information is continuously and regularly updated by the microprocessor 16 and modified only by a digital filter whose function is to average recent pulse history with current information. This easily eliminates small transient fluctuations in pulse rate and oxygen saturation due to physiological and artifactual noise changes.

Microprocessor 16 continues to sample data and compares it to current alarm limits within the instrument. In this embodiment, when the power is turned on, the alarm limits are set to default values of 85% for the oxygen saturation lower limit, 55 for the pulse rate (pulse rate) lower limit, and 140 for the pulse rate upper limit.

Default value of this alarm limit and speaker 1
The acoustic signal from 5 can be modified as follows. The volume of the alarm (beep) sound from the speaker 15 can be set by turning an optically coupled control knob 10. control knob 10
By rotating the knob 10 clockwise, the volume can be maximized, and by rotating the knob 10 counterclockwise, the sound output of the speaker 15 can be completely inhibited.

To change the alarm limit parameters, press Button 2
~Press one of 4. For example, saturation limit button 2
When pressed, the alarm limits for the current saturation level are displayed on digits 794-796. Initially, the default value is 85, which is the lower limit. The oxygen saturation limit value can then be adjusted by turning the optical effect knob 10. By rotating the knob 10 in either direction, this limit can be adjusted anywhere between 0 and 100%, depending on the clinician's determination of the appropriate saturation as the alarm limit depending on the condition of the patient 28. Can be changed. If the knob 10 is not moved for about 2 seconds, the knob 10 automatically becomes unable to adjust the saturation limit value and returns to the volume adjustment mode. At the same time, display 1 is switched back to display the current oxygen saturation level and current pulse rate. The pulse rate upper limit button 3 and pulse rate lower limit button 4 operate in a similar manner. The alarm status indicators 6, 7, 8 flash when the corresponding physiological parameter exceeds its alarm limit. The indicator lights 6 to 8 emit light regardless of whether the alarm prohibition button 5 enables or disables the acoustic signal.

As previously mentioned, if no parameters exceed the alarm limits, the speaker 15 emits a pulsed tone whose repetition frequency is equal to the patient's pulse rate and whose pitch is proportional to the oxygen saturation. If an alarm is enabled by button 5, the speaker 15 will emit a continuous tone of constant pitch when any parameter exceeds its respective alarm limit (disabling the corresponding alarm). or until the corresponding parameter returns within the set range). When the alarm is disabled again, LED9
lights up to indicate to the user that no acoustic warning will be issued.

The monitoring operation of the oximeter discussed above may be further understood with reference to the circuits of FIGS. 15-18. For further details, please refer to the computer program at the end.

FIG. 15 shows optically coupled control knob 1.
FIG. 2 is a circuit diagram showing the operation of 0. The axis of the knob 10 is coupled to an axis encoder 793. Axial encoder 793 is perforated by windows 790 at regular intervals. LED-photo sensor pair 79
1,792 are placed close to each other on both sides of encoder 793. LED-photo sensor pair 7
92 is shown optically coupled via window 790, and LED-photo sensor pair 791 is shown closed by encoder 793. The width of each slot (window) is half the spacing between slots. For each LED-photo sensor pair,
A narrow slit is provided to improve resolution. LED-photo sensor pair 791 and 792
The relationship between slot-to-slot angle
A relationship separated by an angle representing 25%, i.e. 1/
This is a relationship called a quadrature.

If encoder 793 is rotated clockwise, pair 792 will be in the unclosed condition at the time pair 791 is in the closed condition, but if encoder 793 is rotated counterclockwise, the opposite is also true. That is,
When 792 is in the closed state, 791 is in the non-closed state. Two LEDs for each edge of each window -
Such a clear relationship exists between pairs of photo sensors. Thus, a signal is sent to the microprocessor 16 indicating the direction and step of rotation of the knob 10.

Signals from optically coupled pairs 791 and 792 are provided to comparators 720 and 721. Through control logic 722, knob 1
Both the direction of rotation and the step of 0 are presented to the microprocessor. The signal at output DIR 724 allows microprocessor 16 to calculate the direction of rotation and output STEP 725.
The signal at allows the step to be determined.
The advantage of such an arrangement is that the absolute position of the knob 10 is not critical. The position of knob 10 is significant only when microprocessor 16 receives a signal that the adjustment knob is moving.

As shown in FIG. 16, a direction signal 724 and a step signal 725 are sent to the input gates of chip 732. Chip 732 is enabled via control logic 734. Inputs from buttons 2-5 include direction signal 724 and step signal 72.
5 is output via buses AD0 to AD7 to provide direction and alarm limit correction amounts to the RAM memory.

FIG. 17 shows an LED display circuit. The digit selection data present on data lines OD0 to OD7 is
Display selection DSPSEL 717 enters latch 701 which is enabled. This data is output to driver 702 and driver 711 to obtain numerical digit selection signals SEL0 to SEL7. Signal SEL0~
SEL5 (705-710) is 7 segments
LED decimal numeric display 794-799
make it available for use.

The data representing the numerical values to be displayed on the numerical displays 794 to 799 is displayed in the display digit DSPDIG718.
latch 703 is entered, which is enabled by .
The output of latch 703 is connected to drivers 704 and 714.
is input. BIT0 of drivers 704 and 714
The BIT7 output switches ON each individually selected segment of a standard 7-segment LED display and displays either the current oxygen saturation level or a single decimal value of the limit value, or the current pulse rate level or Display limit values. Other digits are displayed in a similar manner in sequence.

SEL7 (715) and SEL6 (716) are
8 for each LED chip 712, 713 chip
Activate two LEDs. Each chip that emits light
The number of LEDs is determined by bits 0 through 7. As mentioned above, the number of emitting LEDs is proportional to the intensity of the pulse, and the flash rate of the display is synchronized with the heartbeat rate.

Finally, FIG. 18 shows a control circuit for controlling the sound output of the speaker 15. Voltage levels VVOL 378 and VBEEP 604 (see FIG. 10) correspond to the desired volume and pitch, respectively. signal
VBEEP 604 is transmitted from timer 740 and transistor 743 to speaker 1 via connector 741.
5 results in a repetition of the modulated pitch and tone. The signal VVOL378 is
The signal is sent to the speaker 15 via a transistor 742 and a connector 741 to modulate the volume.

[Operation theory]

The method of operation involves measuring the amount of light transmission through tissue for two different wavelengths (red light and infrared light) at any two points in time. However, the two time points are only a very short time period compared to one entire pulse. The pulse waveform 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.

Regarding the amount of light transmitted, the amount of light absorbed increases when blood flows in. As a result, the photodetector,
That is, the photo sensor 38 detects a small amount of light. Therefore, a decrease in the amount of light received by the photo sensor indicates a pulsating component.

If the amount of light transmission in the surrounding area (approximately 99% of the signal) is represented by a symbol, and the change in transmission amount due to pulses is represented by Δ, then the relational expression to express the change in the amount of light transmission with respect to the unchanged part of the flesh is as follows. It is expressed by the following formula. That is: ΔI/I∞ΔM (1) where ΔM is the change in substance within the flesh during the duration of the pulse.

Inserting a constant to make it equal, we get the following formula. That is, ΔI/I=KΔM (2) where K is a proportionality constant.

The change in mass is due to the fact that blood (whose optical absorption is greater than tissue) consists of two forms of hemoglobin: oxyhemoglobin (hemoglobin with associated oxygen) and deoxyhemoglobin (hemoglobin with associated oxygen). The above equation can be extended to the equation for two variable components as shown below. That is, ΔI/I=K _A ΔM _A +K _B ΔM _B (3) Here, K _A is a constant for oxidized hemoglobin,
ΔM _A is the amount of change due to the influx of oxygenated hemoglobin, K _B is the constant for deoxyhemoglobin,
ΔM _B is the amount of change in reduced hemoglobin.

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 , ΔI / I | _ _ _ _ _ _} wavelength λ1 (e.g.
are the constants of oxyhemoglobin and deoxyhemoglobin at red wavelength), K _A2 and
K _B2 is a constant at the second wavelength λ2.

It can be seen that each constant in the form _K

If we know the ratio S (saturation degree) of oxidized hemoglobin to the total amount of hemoglobin, we will know the following. That is, ΔM _A = SΔM (5a) ΔM _B = (1-S) ΔM (5b) However, ΔM = ΔM _A + ΔM _B (6) Here, S is the saturation degree of oxidized hemoglobin, and (1-S) is the percentage of reduced hemoglobin.
Substituting this into the previous equation gives the following result. That is, ΔI/I|〓 ₁ =K _A1 SΔM+K _B1 (1-S)ΔM (6a) ΔI/I|〓 ₂ =K _A2 SΔM+K _B2 (1-S)ΔM (6b) From the above equation, one saturation The solution for blood perfusion (ΔM) is trivial.

At this time, a ratio related to the amount of light transmitted at two different wavelengths is suddenly defined. By defining this ratio, it will be seen that calculations based on logarithmic proportionality are not necessary. In particular, the ratio between the amount of transmitted light at wavelength λ1 and wavelength λ2 is defined as follows.

R=ΔI/I｜〓 ₁ /ΔI/I｜〓 ₂ (7) By substituting equations (6a) and (6b) that express the change in the amount of light absorption with respect to the total amount of light transmission at each wavelength λ1 and λ2, we get , we get the following formula. That is, R=K _A1 S+K _B1 −SK _B1 /K _A2 S+K _B2 −SK _B2 (8) Similarly, by solving for S, the following equation is obtained. That is, S=K _B1 −RK _B2 /R(K _A2 −K _B2 )−(K _A1 −K _B1 ) (9) In this way, a certain relationship exists for both the ratio R and the degree of saturation S. I understand that.

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

In detail, different oxygen saturations S ₁ , S ₂ , S ₃ , S ₄
Specific ratios R ₁ , R ₂ , R ₃ , and R ₄ can be determined by experimentally obtaining arterial oxygen saturation from individuals with . In order to obtain these ratios R ₁ reliably, the instrument itself is used, especially in the part of the apparatus concerned with ensuring reliable measurement results in this example. Initial assumptions can then be made about the coefficients for both oxyhemoglobin and deoxyhemoglobin.

If we take one of the coefficients mentioned above, K _A1 , this constant becomes 2
It can be broken down into two individual components. 1st
Then, one component is obtained from the previously determined value and is denoted by C _A1 . Second, this constant needs to vary from instrument to instrument. This variation is due to observation conditions, electronic parts of individual instruments, etc.
This value can be expressed as ΔC _A1 . Each of the four constants in the above equation can be expanded in the same way as well.

(C _A2 + ΔC _A2 ) (S ₁ R ₁ ) + (C _B2 + ΔC _B2 ) (R ₁ − S ₁ R ₁ ) = (C _A1 + ΔC _A1 ) (S ₁ ) + (C _B1 + ΔC _B1 ) (1−S ₁ ) (10) where i is an index associated with at least four measured saturations and transmittances (i=1,
2, 3, 4,…).

For those skilled in mathematics and instrumental calculations, assuming the use of four independent saturation levels,
It will be seen that it is possible to solve for the quantity and wavelength of ΔC in all states simultaneously. 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. R for S (oxygen saturation of hemoglobin)
We discovered that the relationship between (transmission ratio) can be fitted into a simple curve. In particular, a constant and predictable curve of S versus R can be obtained, at least for humans. By using this relationship in a lookup table, patient saturation can be quickly calculated.

Unlike the prior art, this device does not use a light source with an isobaric wavelength;
Note that the device does not require logarithmic calculations (see Equation 7).

It will be appreciated that the pulse oximeter or hemometer described above is typically intended for use on a human finger. However, it should be noted that this pulse oximeter works equally well anywhere on the skin. The ideal desired 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.

[Theory of monitor confidence limits]

To "intelligently" separate patient pulses from noise and motion artifacts, a method is used that stores expected pulse characteristics and compares them to the voltage pulse waveform. This method requires a list of five "vectors" or parameters. These parameters are ΔI〓 ₁ ,
I〓 ₁ , ΔI〓 ₂ , I〓 ₂ and pulse rate (pulse rate), which are schematically shown in the memory 400 of FIG. These parameters are 16-bit 2
Note that it is the same as the transmittance parameter described above with scaling appropriate for the base operation.

One set of historical values for each parameter is
Stored in RAM, ie, history list. Each of these lists is five elements long in this example, but can be shortened or expanded as needed. This history list is used as a reference against which to compare the current parameters under test stored in RAM. This comparison results in a set of differences, which are also stored in encoded form as difference codes. Also, in relation to each parameter,
There is a "confidence" code, which is essentially the level of tolerance for each parameter at present, as described below.

The first step in the reliability check is to store the current parameters and then compare the values of these parameters with the values stored in the history list. The contents of this history list probably consist of the parameters of previous good pulses.
At startup, the parameters of these pulses are loaded with arbitrary initial values and associated with low reliability codes that allow a wide range of data. Here, the parameter of the total amount of light transmission I〓 ₁ is the memory 4
02 is shown.

Once the difference code is calculated and placed in memory 403, the difference code is compared with the corresponding confidence code stored in memory 404. These reliability codes, which have the same range as the difference codes, are
A description of how close the current parameters are to the history that is considered acceptable. Both the difference code and the reliability code are such that a code of 0 represents a difference or tolerance of 0 to 12%, and a code of 1 represents a difference or tolerance of 13 to 12%.
The 25% is coded in such a way that 2 represents 26-37% and so on up to a code of 8 representing 100% disagreement.

The meaning of such a code with respect to this difference is simply the ratio of the current parameter to the historical parameter, and with respect to the reliability code it represents the tolerance to this parameter.

Once reliability codes are calculated for each parameter, these codes are summed in register 405 to generate a reliability score for the set of parameters. Then, all these evaluation points are
It is compared to a threshold or maximum acceptable score. Note that a low score indicates good agreement with expectations and activates enable 407 to enable data acceptance.

If the overall reliability evaluation score is less than the threshold, the program assumes that the current pulse is indeed a good pulse, takes a branch to update the reliability code, and continues processing the pulse. Get into the process. If this reliability code is higher than the threshold, all data are rejected.

The reliability code is adjusted individually by comparing the difference code for each parameter to the reliability code. If the difference code is smaller,
The confidence code is decremented by one count to represent a higher confidence level for the next test. If the difference code is larger (the parameter itself is not within tolerance even though the overall result is satisfactory), the confidence level is decreased by incrementing its confidence code. represents what has been done. If the pulse is good so that the reliability code converges quickly for the good pulse, this process of increasing and decreasing is repeated twice.

If the score is not acceptable, the program checks all parameters again, except during pulse periods where parameters are likely to be out of range due to artifacts caused by motion. If the retest is still not good, the reliability code is readjusted as described above to slightly lower the reliability level in preparation for the next test.

The program then performs one final check on these updated reliability codes before moving on and rejecting the pulses. The reason for the final check is that the confidence code applied to the next pulse is applied even if the current pulse is slightly outside the acceptance window. This approach provides good response under varying pulse conditions.

The above description provides a rough overview of the processing of reliability codes used in oximeters to provide an intelligent processor for signals based on physiological conditions. A more detailed description can be found in the computer section at the end.
written in the program.

It will be appreciated that the process disclosed herein is an intermediate step in the overall process of displaying measurement results.

Furthermore, for the purpose of determining the calibration of an instrument in human subjects, a method for determining the measured value _R1 with a high level of confidence can determine the calibration parameters using the instrument itself, as described in the text. That will be understood.

In summary, it will be appreciated that the pulse oximeter monitor of the present invention provides a wide range of important information to the attending physician in a variety of visual and acoustic formats. Although the foregoing provides a complete disclosure of the preferred embodiments of the invention, various modifications, alternative constructions, and equivalents are possible without departing from the spirit and scope of the invention. For example, high oxygen saturation limits are required in neonatal applications to prevent bronchopulmonary dysplasia and retrolental fibroplasia. Adding a warning limit for high oxygen saturation is well within the scope of this invention. Accordingly, the foregoing description and illustrations in the text should not be construed as limiting the scope of the invention, which is instead defined by the following claims.
Below is a computer program.

[Brief explanation of drawings]

FIG. 1 is a perspective view of the instrument of the present invention showing the housing of the instrument and the state of 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. The circuit diagram, FIG. 4, shows the read-only memory of the invention, namely
A circuit diagram showing the vicinity of the ROM, FIG. 5, is a circuit diagram of the present invention.
A circuit diagram showing the vicinity of RAM, Fig. 6 is a circuit diagram showing memory selection, Fig. 7 is a circuit diagram showing input/output selection, Fig. 8 is a circuit diagram showing the counter of the present invention, and Fig. 9 is a circuit diagram showing 12 FIG. 10 is a circuit diagram showing a comparator circuit in which bit digital/analog conversion is performed. FIG. 10 is a circuit diagram showing a sample holding circuit of the present invention.
1 is a circuit diagram showing an offset amplifier circuit according to the invention, FIG. 12 is a circuit diagram showing a detector according to the invention, FIG. 13 is a detailed diagram of a clock circuit with an output for energizing a light emitting diode, and FIG. 14 15 is a detailed diagram of the circuit for energizing and switching the diodes at a point near the detector; FIG. 15 is a circuit diagram showing the action of an optically coupled adjustment knob; FIG. 16 is a control of the invention. The circuit diagram of the button circuit, Figure 17, is
FIG. 18 is a circuit diagram of the LED output circuit, FIG. 18 is a circuit diagram of the audio output circuit, and FIG. 19 is a logic diagram of the blocks of numerical processing steps that produce the meter output. 1...Numeric display, 2-5...Circuit selection button, 6-9...Alarm status indicator light, 10...Control knob, 11...Synchronization status indicator light, 12...Digital indicator meter, 13...Power supply switch, 1
4...Finger, 15...Speaker, 16...Microprocessor, 17...Bus, 18...ROM, 1
9...RAM, 20...LED display, 21
...Selection latch, 22...Numerical display latch, 24
...Gate circuit, 26...Housing, 27...
Lead wire, 28...patient, 29...detector, 30
...Light emitting diode, 31...Amplifier, 32...
Light emitting diode, 33...Amplifier, 36...Barrier, 38...Photo sensor, 40...Preamplifier, 41, 42...Amplifier, 43, 44...Phase detector, 45, 46...Low pass filter ,4
7, 48...Offset amplifier, 50...Multiplexer, 52...Comparator, 54...Digital/analog converter, 57...Sample holding circuit, 60, 61...Voltage output, 70...
Clock circuit, 100... microprocessor,
102...Clock, 103...Address bus, 104...Crystal, 106-108...
ROM, 115...Output data bus, 120,
121...RAM, 127,128...Bus, 1
29,130...port, 172...counter,
173...Binary counter, 194...Clock frequency divider, 201...Amplifier, 305...Connector,
307,309...transistor, 360,36
2...Latch, 370...Latch, 371...Voltage converter, 372, 374...Analog switch, 378...Amplifier, 601-604...
Amplifier, 701... Latch, 702, 711...
Driver, 703...Latch, 704, 714...
...Driver, 712,713...LED chip,
722...Control logic, 724...Output DIR,
740...Timer, 741...Connector, 74
2,743...transistor, 790...slot, 791,792...LED-photo sensor pair,
793...Encoder, 794-799...Numeric value.

Claims (1)

[Scope of Claims] 1. In an oximeter device that measures the pulse rate and oxygen saturation of blood by absorption of irradiated light passing through living tissue, a first oximeter that emits light at first and second wavelengths, respectively;
and a second light source, and a light sensor, the light source and the light sensor being adapted to be addressed to the tissue to determine the path of light through the tissue between the light source and the light sensor. , detecting a signal corresponding to light received by the optical sensor at each of the first and second wavelengths, and deriving from the signal a pulsatile signal corresponding to a pulsating characteristic of arterial blood flow; means for generating a signal corresponding to oxygen saturation; and means responsive to said pulsating signal for controlling generation of an acoustic tone signal; and means for continuously varying the tone frequency of said acoustic signal using oxygen saturation. means for generating an intermittent acoustic tone signal, comprising means corresponding to the oxygen saturation signal for generating an intermittent acoustic tone signal. 2. The means for changing the tone frequency of the acoustic signal is a means for decreasing the tone frequency with decreasing oxygen saturation.
Apparatus described in section. 3. an array of lights; means coupled to receive the pulsating signal from the detection means for flashing the lights; and circuitry for varying the number of lights flashed in relation to the strength of the pulsating signal. 2. The apparatus of claim 1, further comprising means.