JP4844291B2 - Time division pulse oximetry and pulse oximeter - Google Patents

Description

  The present invention relates to pulse oximetry for continuously and non-invasively measuring arterial oxygen saturation (SaO2) by utilizing blood volume fluctuations of intraarterial blood due to pulse, and a pulse oximeter for performing the same. Time-division pulses that can accurately eliminate artefacts due to body movements and obtain high-precision oxygen saturation of arterial blood by processing the time-series data of tissue transmitted light according to the required time. It relates to oximetry and pulse oximeters.

Today, in a technique called pulse oximetry, the following procedure is generally used when determining oxygen saturation (SaO2) of arterial blood.
(1) The tissue transmitted light is continuously measured with a plurality of wavelengths.
(2) The peak and valley of the pulsation of the tissue transmitted light to be measured are determined, and the transmitted light is set as L + ΔL and L, respectively.
(3) ΔA≡log [(L + ΔL) / L] ≈ΔL / L is obtained.
(4) Find Φij≡ΔAi / ΔAj.
(5) Since Φij has a one-to-one correspondence with SaO2, it is converted to SaO2.

  In a device for measuring oxygen saturation of arterial blood currently on the market, a conversion table is used when converting the above-mentioned Φij to SaO2. The use of the conversion table is not particularly problematic in the case of a two-wavelength type apparatus, but in order to improve the measurement accuracy, it is obtained theoretically and experimentally in the case of an apparatus using a larger number of wavelengths. It is necessary to use the calculated formula.

  For example, the present applicant previously used five different wavelengths of light as biological tissue as a device that continuously and non-invasively measures arterial blood oxygen saturation by utilizing arterial blood volume fluctuations due to pulse. Proposed a five-wavelength pulse oximeter for irradiating (see Patent Document 1).

  That is, the pulse oximeter described in Patent Document 1 receives a light emitting unit that irradiates a living tissue with light of five different wavelengths, and receives light emitted from the light emitting unit and transmitted or reflected through the living tissue. A light receiving unit for converting each into an electric signal, a light intensity variation calculation unit for obtaining a light intensity variation for a living tissue based on a variation of transmitted light or reflected light of each wavelength output from the light receiving unit, and A dimming degree fluctuation ratio calculating part for obtaining at least four ratios of the five dimming degree fluctuations obtained by the dimming degree fluctuation calculating part, and a dimming degree fluctuation obtained by the dimming degree fluctuation ratio calculating part. An oxygen saturation calculator that calculates oxygen saturation in the blood using arterial blood oxygen saturation, venous blood oxygen saturation, arterial blood to venous blood ratio, and tissue terms as unknowns With To erase the effects of variation of the variation of the venous blood and tissue is characterized in that it has configured to determine the oxygen saturation of arterial blood.

  Therefore, the pulse oximeter described in Patent Document 1 having such a configuration reliably eliminates the influence when venous blood is pulsating for some reason, and oxygen saturation of arterial blood Can be measured with high accuracy without causing time delay and smoothing. In addition, when the pulse wave is small and pulse oximetry is impossible, it is possible to intentionally give a body motion and obtain the oxygen saturation of arterial blood included at that time. Furthermore, the oxygen saturation of venous blood has the advantage that it can be measured simultaneously.

  A long-standing problem in pulse oximetry is that transmitted light is disturbed by mechanical disturbances such as body movements. That is, it becomes difficult to properly find the peaks and valleys of the pulsation waveform measured by the disturbance of the transmitted light. In addition, it is necessary to correct the peaks and valleys of the measured pulsation waveform. If the correction is not made, the time series data of arterial blood oxygen saturation (SaO2) finally obtained not only has the disadvantage of increasing the error, but can also use information other than the value of the valley. Indispensable for body movement elimination.

As a countermeasure for solving such a problem, a conventionally proposed or adopted method is a statistical method in which a correct value of SaO2 is estimated from previous and subsequent data. However, in this case, the following problem occurs.
(1) Since a large time delay occurs, for example, it is delayed to find that SaO2 starts to decrease.
(2) Since the change in SaO2 is smoothed, for example, when SaO2 is drastically reduced, it is unclear how much it was.

JP-A-2005-95606

In the above-described conventional pulse oximetry method, what is expected further in the future is to quickly find out the change in SaO2 for the patient and cope with it quickly, but make use of the original features of such pulse oximetry method. In other words, the above-mentioned problems must be solved.
Further, it has been found that when the patient's body movement is very intense, the conventional pulse oximetry technique based on the determination of the peak and valley of the pulsation waveform of the transmitted light to be measured cannot obtain a sufficient measurement result. That is, when the body movement is intense, the determination of the peaks and valleys of the measurement waveform is not uniquely determined, so that a method using baseline correction for the measurement waveform cannot be expected to have a sufficient effect.

Accordingly, as a result of various examinations and trials, the present inventors have appropriately determined the oxygen saturation (SaO2) of arterial blood by using the entire transmitted light signal for the measured pulsation waveform of the transmitted light. I found out that it can be measured.
That is, by using not only the points of the peaks and valleys of the pulsation waveform of the transmitted light to be measured but also the entire time series data of the transmitted light, it is not necessary to determine the peaks and valleys of the measured waveform.

  The object of the present invention is to eliminate the influence of body motion and improve the measurement accuracy of arterial oxygen saturation (SaO2) by using the entire time-series data of transmitted light for the pulsation waveform of transmitted light to be measured. It is to provide a time segmented pulse oximetry and pulse oximeter that can contribute.

  In order to achieve the above object, the pulse oximetry according to claim 1 of the present invention irradiates a living tissue with light of a plurality of different wavelengths by a light emitting element, and transmits light reflected or reflected by the living tissue. Light is received by the light receiving element and converted into electric signals, and the time series data of the electric signal obtained by the light receiving element is divided at regular intervals, and the time series data divided at regular intervals is between two different wavelengths. Calculate the slope value of the regression line and convert the calculated slope value to SaO2, respectively, and smooth it, or smooth the time series of the slope value and convert it to SaO2 to eliminate the influence of body movement, and oxygen in arterial blood It is characterized by obtaining saturation.

  A pulse oximeter according to claim 2 of the present invention receives a light emitting unit that irradiates a living tissue with a plurality of light beams having different wavelengths, and light that is transmitted from or reflected by the living tissue. A light receiving unit for converting each into an electric signal, a processing device for dividing time-series data consisting of electric signals of transmitted light or reflected light of each wavelength converted and output from the light receiving unit at regular intervals, and a divided time An inclination value calculating device for calculating an inclination value of a regression line between two different wavelengths for each time-series data, and smoothing the calculated inclination value by converting each of the calculated inclination values to SaO2, or the calculated inclination value And a conversion smoothing device for smoothing and converting to SaO2, and determining the oxygen saturation of arterial blood from which the influence of body motion has been eliminated.

  According to the time-segment pulse oximetry and the pulse oximeter of the present invention, by using the entire time-series data of transmitted light without determining the peaks and valleys of the pulsation waveform of the transmitted light to be measured, While eliminating the influence, it contributes to the improvement of the measurement accuracy of arterial blood oxygen saturation (SaO2), and the degree of freedom of the measurement site can be expanded.

  Next, an embodiment of the time-division pulse oximetry according to the present invention will be described in detail below with reference to the accompanying drawings in relation to the apparatus configuration of a pulse oximeter that implements this.

I. Outline of Apparatus Configuration of Pulse Oximeter FIG. 1 is a schematic explanatory diagram showing an apparatus configuration as a pulse oximeter for carrying out time segmented pulse oximetry according to the present invention. That is, in FIG. 1, reference numeral 10 denotes a light emitting unit, and five light emitting elements LED1 to LED5 that respectively irradiate a living tissue with light of five different wavelengths are provided. Reference numeral 12 indicates a living tissue irradiated by light emitted from the light emitting unit 10. Reference numeral 14 denotes a light receiving unit, which includes a light receiving element PD that receives light transmitted through the living tissue 12, a current-voltage converter 16, and an AD converter 18.

  Reference numeral 20 denotes a storage unit, which is composed of transmitted light signal temporary storage devices 20A to 20E that temporarily store a transmitted light signal obtained by the light receiving element PD of the light receiving unit 14 in time series for each wavelength. Yes.

  Reference numeral 30 denotes a calculation unit. Based on the transmitted light signals L1 to L5 temporarily stored in time series in the transmitted light signal temporary storage devices 20A to 20E, respectively, (1) the transmitted light signals L1 to L5 are stored. (2) Next, calculate the slope of the regression line between the time-series data of different wavelengths for the time-series data of the transmitted light signals L1 to L5 divided every fixed time, and (3) Calculate The calculated slope values are converted into SaO2 (arterial blood oxygen saturation), respectively, and (4) oxygen saturation in blood is calculated by smoothing the converted time series data of SaO2 [SpO2]. It has a function as a calculator. Note that the order of conversion to SaO2 and smoothing may be reversed.

  Reference numeral 22 denotes a timing device, the light emission timing by each of the light emitting elements LED1 to LED5 of the light emitting unit 10, and the transmission light signal storage holding timing in each of the transmitted light signal temporary storage devices 20A to 20E of the storage unit 20. It is comprised so that control may be performed.

  FIG. 2 shows a system configuration diagram for performing the above-described calculation processing in the oxygen saturation calculator as the calculation unit 30. That is, in FIG. 2, reference numeral 32 denotes a transmitted light signal section storage unit, and the transmitted light signals L1 to L5 inputted from the transmitted light signal temporary storage devices 20A to 20E are set to a predetermined time (for example, 0.5 seconds). Each of the divided storage circuits 32A to 32E stores the transmitted light signal sequentially in time series for each divided time.

  Reference numeral 34 denotes a regression line slope value calculation unit, and the regression line slope value Φ12 for the transmitted light signals L1 to L5 that are stored in the transmitted light signal section storage unit 32 at regular intervals. , Φ32, Φ42, and Φ52 are configured as inclination value calculation circuits 34a, 34b, 34c, and 34d, respectively.

  Reference numeral 36 indicates a first calculation circuit for obtaining a solution of simultaneous equations with respect to the slope values Φ12, Φ32, Φ42, and Φ52 of the regression line obtained by the slope value calculation circuits 34a, 34b, 34c, and 34d. Reference numeral 38 denotes a second calculation circuit for smoothing the solution of the simultaneous equations. Therefore, in the second calculation circuit 38, the blood oxygen saturation [SpO2] is calculated. Note that the solution may be obtained after smoothing the slope value.

II. Pulse oximeter calculation processing operation ( time division pulse oximetry )
Next, the calculation processing operation of the arterial blood oxygen saturation by the above-described apparatus configuration of the pulse oximeter, that is, the time segmented pulse oximetry according to the present invention will be described together with the operation of the pulse oximeter.

(1) Time division processing of transmitted light signal First, the five light emitting elements LED1 to LED5 of the light emitting unit 10 are sequentially and alternately changed to wavelengths λ1, λ2, λ3, λ4, and λ5 based on the signals of the timing device 22, respectively. Light up with. As a result, the light transmitted through the living tissue 12 is received by the light receiving unit 14, and the transmitted light signals L1, L2, L3, L4, and L5 are respectively transmitted to predetermined wavelengths corresponding to the wavelengths of the light emitting elements LED1 to LED5. At each timing, the transmitted light signal temporary storage devices 20A to 20E of the storage unit 20 are stored and held. In addition, these transmitted light signal temporary storage devices 20A to 20E store data for a certain period of time (data as digital values) of the AD converter 18 of the light receiving unit 14 (see FIG. 1).

  In this way, the transmitted light signals L1 to L5 stored and held in the transmitted light signal temporary storage devices 20A to 20E, respectively, are input to the respective division storage circuits 32A to 32E of the division storage unit 32 in the calculation unit 30. Then, it is divided every fixed time (for example, 0.5 seconds), and the transmitted light signal is sequentially stored in time series for each divided time (see FIG. 2).

(2) Calculation processing for obtaining the slope value of the regression line relating to the time- divided transmitted light signal The oxygen saturation (SpO2) in the blood is calculated by, for example, the change in attenuation (ΔAi) obtained for transmitted light of 5 wavelengths. Based on this, the ratio of these dimming fluctuations (Φij: i, j is the wavelength) is obtained by the following equation.
The elements constituting the pulsation of transmitted light are arterial blood (a), venous blood (v), and tissues other than blood, that is, pure tissue (t).

Φij≡ΔAi / ΔAj
= [√Eai (Eai + F) + √Evi (Evi + F) * V + Exi]
/ [√Eaj (Eaj + F) + √Evj (Evj + F) * V + Exj]
However,
ΔAi≡log [(Li + ΔLi) / Li] ≈ΔLi / Li
Eai≡SaEoi + (1-Sa) Eri
Evi≡SvEoi + (1-Sv) Eri
V≡ΔDv / ΔDa
Exi≡ZtiΔDt / (HbΔDa) ≡AiEx2 + Bi

In the above formula, Li is the tissue transmitted light, ΔAi is the change in attenuation, Eoi is the extinction coefficient of oxygenated hemoglobin, Eri is the extinction coefficient of deoxygenated hemoglobin, Sa is the oxygen saturation of arterial blood (SaO2), and Sv is the peripheral. Venous blood oxygen saturation (SvO2), ΔDa is the change in effective arterial thickness, ΔDv is the change in effective venous blood thickness, ΔDt is the change in pure tissue thickness, and Zti is the attenuation of pure tissue , Ex2 is the value of Exi at the second wavelength, and Ai, Bi are tissue constants (determined by actual measurement).
Therefore, in the above formula, there are four unknowns, Sa, Sv, V, and Ex2.

  In this case, in order to measure SaO2 with high accuracy and to eliminate the influence of body movement and the like, tissue transmitted light is measured at an appropriate five wavelengths, a quaternary simultaneous equation is established with respect to the above equation, and the solution is Sa. Can be requested. For example, λ1 = 805 nm, λ2 = 875 nm, λ3 = 660 nm, λ4 = 700 nm, and λ5 = 730 nm are preferable examples of wavelength selection.

  Therefore, in the time division oximetry of the present invention, the slope values of the regression lines are respectively obtained based on the transmitted light signals L1 to L5 of the five wavelengths (λ1 to λ5) stored in the division storage circuit 32 by time division. (Φij: where i and j are wavelengths) is obtained by the following equation. That is, the slope value (Φij) in this case corresponds to the aforementioned Φij = ΔAi / ΔAj. In the following equation, n is the number of data in the time segment, t is the segmented time (for example, 0.5 seconds), and Σ is the sum of the data in the time segment.

Φij≡ {nΣ [Li (t) * Lj (t)] − ΣLi (t) * ΣLj (t)}
/ {NΣLj (t) ² − [ΣLj (t)] ² }

(3) Calculation processing for obtaining solutions of simultaneous equations related to inclination values 4 on the inclination values (Φ12, Φ32, Φ42, Φ52) of regression lines for tissue transmitted light of 5 wavelengths (λ1 to λ5), respectively The former simultaneous equations are set up and a calculation for obtaining Sa as a solution thereof is performed (see FIG. 2).

(4) Calculation processing for smoothing the solution of simultaneous equations The Sa value obtained as the solution of the quaternary simultaneous equations is calculated by time-dividing data that is continuous over time. Since a large change is shown, this is smoothed. Thereby, a natural change of SaO2 can be obtained.

  An example of calculation processing of arterial blood oxygen saturation (SaO2) by a subject using the time-segmented pulse oximetry according to the present invention described above will be described together with a graph showing respective measurement results as compared with the case of conventional pulse oximetry.

The light emitting unit 10 and the light receiving unit 14 were attached to the subject's fingertips, and SaO2 was lowered by holding the breath, and SpO2 was measured while shaking the tip of the wrist vigorously. FIG. 3 shows the change in SpO2 measured by the time segmented pulse oximetry of the present invention using 5 wavelengths. FIG. 4 shows the change in SpO2 measured by the conventional two-wavelength calculation (in this case, the body motion elimination operation is not performed). FIG. 5 shows the change in SpO2 measured with a commercially available pulse oximeter attached to the opposite hand.
Thus, according to the time-segment pulse oximetry of the present invention, the influence of body movement is sufficiently eliminated, and a rapid change in SaO2 is clearly measured. In particular, it was confirmed that the point in time at which SaO2 starts to decrease can be found early.

  6 (a), 6 (b), and 6 (c) show SpO2 values calculated by the first calculation circuit 36 as solutions of simultaneous equations relating to the slope values Φ12, Φ32, Φ42, and Φ52 of the regression line. (A) shows a state where smoothing is not performed, (b) shows a state where 10 data are averaged and smoothed by the second calculation circuit 38, and (c) is the same. This shows a state in which 20 data are averaged and smoothed.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments. For example, the case where five wavelengths are used has been described, but the number of wavelengths is larger or smaller than that. In addition to being applicable to the case, the measurement object can be applied to the measurement of all pulsating with arterial blood such as CO hemoglobin in blood or a diluted state of dye injected from outside the body. Many design changes can be made without departing from the spirit.

It is a schematic block diagram which shows the apparatus structure as a pulse oximeter which implements the time division pulse oximetry which concerns on this invention. It is explanatory drawing which shows the system structure of the pulse oximetry in the calculation part of the pulse oximeter shown in FIG. It is a wave form diagram which shows the change of SpO2 measured by the time division pulse oximetry which concerns on this invention. It is a wave form diagram which shows the change of SpO2 measured by the conventional 2 wavelength type pulse oximetry. It is a wave form diagram which shows the change of SpO2 measured with the commercially available pulse oximeter. (A)-(c) is a wave form diagram which shows the change of SpO2 measured by the time division pulse oximetry which concerns on this invention, Comprising: (a) is a wave form diagram in the state which has not performed the smoothing process, (b) ) Is a waveform diagram in a state in which smoothing processing is performed to average 10 data, and (c) is a waveform diagram in a state in which smoothing processing is performed to average 20 data.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Light emission part 12 Biological tissue 14 Light reception part 16 Current voltage converter 18 AD converter 20 Memory | storage parts 20A-20E Transmitted light signal temporary storage 22 Timing unit 30 Calculation part 32 Transmitted light signal division | segmentation memory | storage parts 32A-32E 34. Regression line inclination value calculation units 34a to 34d Inclination value calculation circuit 36 First calculation circuit 38 Second calculation circuit LED1 to LED5

Claims (2)

Irradiate a living tissue with light of a plurality of different wavelengths by a light emitting element,
The light transmitted through or reflected by the living tissue is received by a light receiving element and converted into electrical signals, respectively.
The time series data of the electrical signal obtained by the light receiving element is divided at regular intervals,
Calculate the slope of the regression line between two different wavelengths for each time-series data divided at regular intervals.
Each calculated slope value is converted into SaO2, smoothed,
Alternatively, the time series of slope values is converted into SaO2 after smoothing,
Pulse oximetry characterized by determining the oxygen saturation of arterial blood that has eliminated the effects of body movement. A light emitting unit for irradiating a living tissue with light of different wavelengths,
A light receiving unit that receives light emitted from the light emitting unit and transmitted or reflected through the living tissue, and converts the light into electrical signals;
A processing device that divides time-series data composed of electrical signals of transmitted light or reflected light of each wavelength converted and output from the light receiving unit at regular intervals;
An inclination value calculation device for calculating an inclination value of a regression line between two different wavelengths for the time-series data for each divided time;
Each of the calculated slope values is converted to SaO2 for smoothing, or the calculated slope value is smoothed and converted to SaO2 for smoothing,
A pulse oximeter characterized by obtaining the oxygen saturation of arterial blood from which the influence of body movement has been eliminated.