WO2026003840A1

WO2026003840A1 - Device and method for measurment of oxigen saturation

Info

Publication number: WO2026003840A1
Application number: PCT/IL2025/050547
Authority: WO
Inventors: Eldad Shemesh
Original assignee: Cardiacsense Ltd
Current assignee: Cardiacsense Ltd
Priority date: 2024-06-24
Filing date: 2025-06-24
Publication date: 2026-01-02
Anticipated expiration: 2026-12-24
Also published as: IL313883A; IL313883B1

Abstract

Method and system for accurate measurement of blood oxygen saturation levels of a subject by manipulating respective DC components of first and second detection electrical signals associated with a detected light response of a body tissue being illuminated by a first and second wavelengths, and determining a respective correction factor for adjusting a modulation factor derived from the AC and DC components of first and second manipulated electrical signals (referred throughout the application as diminished electrical signals).

Description

DEVICE AND METHOD FOR MEASURMENT OF OXIGEN SATURATION

TECHNOLOGICAL FIELD

The present disclosure is generally in the field of medical measuring devices, and particularly relates to a blood saturation measurement devices.

BACKGROUND ART

Pulse oximetry is a noninvasive method for monitoring a person's blood oxygen saturation (SpO2) and is based on the principle that oxyhemoglobin and deoxyhemoglobin differentially absorb red and near-infrared (IR) light and measures this difference in the absorption spectra of these two forms of hemoglobin. The oxygen saturation (SpO2) of the hemoglobin in arterial blood is generally determined by the relative proportions of oxygenated hemoglobin and deoxyhemoglobin in the arterial blood. In commonly used methods of pulse oximetry, a subject’s tissue is illuminated by light selected to have at least two different wavelengths, typically one in the red band and one in the infrared band. The amount of light received after interacting with the tissue is detected by a detector and the intensity is measured for both wavelengths.

Fig. 1 shows extinction coefficient of HbCh, and Hb, across the visible and infrared light spectrum. The extinction coefficient is a measurement of how strongly a chemical substance absorbs light at a given wavelength. As can be seen, oxyhemoglobin absorbs more red light (650 nm) and allows more infrared light (940 nm) to pass through while deoxyhemoglobin absorbs more light at infrared wavelengths, which allows more red light to pass through than in oxyhemoglobin.

The detector generates signals which include a constant (non-pulsatile) component and a variable (pulsatile) component. The constant component is commonly referred to as the "DC component” . The measured DC component is influenced by several factors, such as the light absorbency of the biological tissue, constant reflective tissues such as skin, muscle and bone, and venous blood, capillary blood, and non-pulsatile arterial blood, the scattering properties of tissue, the intensity of the light source, and the sensitivity of the detector. The variable component results from the pulsatile flow of arterial blood through the tissue being probed. The variable component is commonly referred to as the "AC component” . This pulsatile flow, corresponding to the systole phase of the cardiac cycle, acts such that light absorption varies proportionately to the flow of blood. Since pulsing is a function of the fluctuating volume of arterial blood, the AC component represents the light absorption of the oxygenated and deoxygenated hemoglobin of arterial blood.

Perfusion index (PI) is the ratio of the pulsatile blood flow to the non-pulsatile static blood flow in a subject's peripheral tissue, such as finger, toe, or ear lobe. Perfusion index / level is an indication of the pulse strength at the sensor site. The Pi's values range from 0.01% for a very weak pulse to 20% for an extremely strong pulse. The perfusion index varies depending on patients, physiological conditions, and monitoring sites.

GENERAL DESCRIPTION

There is a need in the art to non-invasively, accurately and reliably, measure physiological parameters, such as blood oxygen saturation (SpO2) in a subject. In many medical monitoring scenarios it is required to measure blood oxygen saturation at various monitoring sites / tissues which are associated with a low perfusion index, such as a wrist of the subject. Further, there is developing interest to measure blood oxygen saturation non-invasively by incorporating such oxygen saturation measurement arrangements in wearable and / or portable devices for example, wrist band, watch or smartphone.

As mentioned above signals generated by the detector include a non-pulsatile (DC) component and a pulsatile (AC) component. The AC component carries most of the biomedical information. However, the desired AC component has a very small amplitude that rides on / biased by a relatively large DC offset signal. As such, the AC component typically constitutes only a small fraction of the signal. For example, when the SpCh measurement is performed over the finger the AC component may constitute roughly 10% of the signal. However, when the SpCh measurement is performed over the wrist the AC component is approximately 100 times lower and may be of less than 0.1% of the signal while the DC component may constitute, accordingly, more than 99.9% of the signal, generally depending on the monitoring site / tissue.

In many oxygen saturation measurement applications, the oxygen saturation level is being measured over the finger as perfusion level (AC/DC ratio) is very high over the finger and perfusion level is the parameter from which the AC component can be derived. Perfusion level measured over the wrist may have a value of less than 0.1% meaning hundreds of times smaller compared to perfusion level measured over a finger since the DC component is significantly increased due to the depth of the arteries below static reflective tissues such as skin, fat, and bone. As a result, in order to obtain a similar amplitude of the AC component over the wrist as in the case of a finger, much more energy is required. Increasing the driving current of the illumination source may result in an increased signal and accordingly in an increased amplitude of the AC component. However, this results in an increase of the DC component as well and thus may saturate the system.

The present application discloses techniques and arrangements to accurately measure blood oxygen saturation levels of a subject by manipulating respective DC components of first and second detection electrical signals associated with a detected light response of a body tissue being illuminated by a first and second wavelengths, and determining a respective correction factor for adjusting a modulation factor derived from the AC and DC components of first and second manipulated electrical signals (referred throughout the application as diminished electrical signals) . In some embodiments, the first and second manipulated electrical signals can be derived from the respective first and second detection electrical signals or amplification thereof.

In some embodiments, the DC components are manipulated by respective manipulation electrical signals controllably generated for at least partially reducing the respective DC components of the first and second detection electrical signals. The manipulation of the DC components results in variation / modification of the perfusion index associated with each wavelength. A correction factor can be determined based on the first and second manipulated electrical signals (z.e., the first and second detection electrical signals with the respective diminished / reduced DC components) and the first and second detection electrical signals for adjusting / correcting a modulation factor.

In some embodiments, manipulated electrical signals and the detection electrical signals may be averaged over a selected time interval for determining based thereon the correction factor. Namely, it is to be noted that the terms "manipulated electrical signal" and "detection electrical signal" throughout the application may be interpreted, in some embodiments, as average values of values obtained for each of the signals over a certain period of time. It is to be noted that a typical output of such a measurement system includes only an amplified product of the first and second manipulated/diminished electrical signals, while the gain factor of the amplification and the manipulation electrical signals are known (as they can be controlled). From this output, the first and second detection electrical signals can be calculated and restored.

In some embodiments, the modulation factor can be determined based on respective AC and DC components of the first and second manipulated/diminished electrical signals. The corrected modulation factor can be then used to determine the oxygen saturation level of the examined subject.

In possible embodiments, the adjusted modulation factor is a product of the modulation factor multiplied by the correction factor.

In some embodiments, the manipulated electrical signals are obtained by combining the first and second manipulation electrical signals with the respective first and second detection electrical signals. The manipulated / diminished electrical signals can thereafter be amplified and converted to voltage signals.

The first and second manipulation electrical signals can be in the form of first and second inverse electrical signals. In some embodiments, such first and second inverse signals electrical are generated in a direction opposite to direction of the first and second detection electrical signals and combined respectively therewith. Alternatively, the first and second manipulation electrical signals can have opposite polarities with respect to polarities of the respective first and second detection electrical signals.

In some embodiments, the manipulated electrical signals are obtained by subtracting each one of the first and second manipulation electrical signals form the respective each one of the first and second detection electrical signals. The resulting first and second manipulated electrical signals are thus indicative of this difference. In some embodiments, these manipulated / diminished electrical signals can be amplified thereafter and converted to voltage signals.

In some embodiments, the first and second amplified manipulated electrical signals and an amplification factor can be used for calculating the diminished electrical signals.

In some embodiments, the adjusted modulation factor is a product of the modulation factor multiplied by the correction factor. In some embodiments, (i) an intensity of illumination of said first and second wavelengths, (ii) the first and second manipulation signals, and (iii) gain value applied on the first and second diminished electrical signals are controlled to obtain (1) a ratio between the pulsatile and non- pulsatile components of the respective first and second diminished electrical signals within a selected range and (2) first and second diminished electrical signals in a selected intensity range below an amplification saturation threshold, The amplification saturation threshold is determined by the amplification.

The maximal amplification intensity should be as close as possible to the amplification saturation threshold of the amplifier so as to obtain the maximal signal intensity to reduce inaccuracies. The process can be iterative by setting values for the first and second diminished electrical signals and intensity values for the illumination and examining whether the ratio between the pulsatile component and the non-pulsatile component of the respective first and second diminished electrical signals is in a desired range and the diminished electrical signals are not saturated but are close to the saturation amplifier threshold, and correcting the first and second manipulation signals and intensity values until reaching the desired ratio range with a desired intensity without saturation.

Thus, according to one broad aspect of the present disclosure there is provided a method for determining an oxygen saturation level of an examined subject, the method comprising illuminating a tissue of the examined subject with first and second wavelengths; detecting a light response of the illuminated tissue for each of the first and second wavelengths and generating a respective first and second detection electrical signals indicative thereof, each of the detection electrical signals comprising a respective pulsatile component and non-pulsatile component; controllably generating respective first and second manipulation electrical signals to thereby at least partially diminish respective non-pulsatile components of the first and second detection electrical signals to obtain respective first and second diminished electrical signals; determining a modulation factor based on pulsatile components and non-pulsatile components of the first and second first and second diminished electrical signals or an amplified product thereof; determining a correction factor, based on the first and second diminished electrical signals and the first and second detection electrical signals, and adjusting the modulation factor based on the correction factor to obtain an adjusted modulation factor; and determining the oxygen saturation level of the examined subject based on the adjusted modulation factor. In some embodiments, the correction factor is indicative of variations of respective perfusion indices associated respectively with the first and second detection electrical signals due to the at least partial diminishing of the respective non-pulsatile components thereof.

In some embodiments, the generating of the respective manipulation electrical signals comprises generating respective inverse electrical signals, the inverse electrical signals are in a direction opposite to direction of the first and second detection electrical signals.

In some embodiments, the method further comprising amplifying the first and second diminished electrical signals, generating respective first and second amplified diminished electrical signals, and calculating the first and second diminished electrical signals based on the first and second amplified diminished electrical signals and gain factor of the amplifying.

In some embodiments, the first and second diminished electrical signals are calculated by the respective equations: I(kl)dim = V(Xi) / G and I(A2)dim = V(X2) / G, wherein I(Xl)dim and I(X2)dimare the first and second diminished electrical signals, V(Xi) and V(X₂) are the first and second amplified diminished electrical signals, and G in the gain factor.

In some embodiments, the method comprises calculating the first and second detection electrical signals based on the calculated first and second diminished electrical signals and the first and second manipulation electrical signals.

In some embodiments, the first and second detection electrical signals are calculated by the respective equations: Iu= I(Xl)dim + I(M) man and 1x2 — I( 2)dim + I(X2)man, wherein lu and lu are the first and second detection electrical, I(kl)dim and I(A2)dim are the first and second diminished electrical signals, and I(Xl)manand I(X2)man are the first and second manipulation electrical signals.

In some embodiments, the correction factor is calculated by the equation:

IWdim !

C = ^,Z1 wherein Cr is the correction factor, I(Xl)dim and I(X2)dimare the first and second diminished electrical signals, and l and lu are the first and second detection electrical. In some embodiments, the adjusted modulation factor is calculated by the equation: wherein Radj is the adjusted modulation factor, Cr is the correction factor, R is the modulation factor.

In some embodiments, comprising controlling (i) an intensity of illumination of the first and second wavelengths, (ii) the first and second manipulation electrical signals, and (iii) gain value applied on the first and second diminished electrical signals to obtain (1) a ratio between the pulsatile and non-pulsatile components of the respective first and second diminished electrical signals within a selected range and (2) first and second diminished electrical signals in a selected intensity range below an amplification saturation threshold.

According to one broad aspect of the present disclosure there is provided a system for determining an oxygen saturation level of an examined subject, the system comprising at least one light source configured and operable to emit light in first and second wavelengths; at least one photodetector configured to detect a light response of the illuminated tissue for each of the first and second wavelengths and generating a respective first and second detection electrical signals indicative thereof, each of the detection electrical signals comprising a respective pulsatile component and non-pulsatile component; a signal manipulation unit configured and operable to controllably generate respective first and second manipulation electrical signals and to combine the respective first and second detection electrical signals with the first and second manipulation electrical signals to thereby at least partially diminish respective non-pulsatile components of the first and second detection electric signals to obtain respective first and second diminished electrical signals; and a processing utility configured to determine the respective pulsatile and non-pulsatile components of the first and second diminished electrical signals or an amplified product thereof and determine based thereon a modulation factor; determine a correction factor, based on the first and second diminished electrical signals and the first and second detection electrical signals, for adjusting the modulation factor based on the correction factor to obtain an adjusted modulation factor; and determine the oxygen saturation level of the examined subject based on the adjusted modulation factor. In some embodiments, the first and second wavelengths are in the red and infrared spectral ranges, respectively.

In some embodiments, the respective first and second manipulation electrical signals comprise respective first and second inverse electrical signals being generated in a direction opposite to direction of the first and second detection electrical signals.

In some embodiments, the signal manipulation unit comprises a signal combiner configured to combine the respective first and second detection electrical signals with the first and second manipulation electrical signals.

In some embodiments, the signal manipulation unit comprising an amplification unit configured and operable for generating first and second amplified diminished electrical signals.

In some embodiments, the amplification unit comprises a transimpedance amplifier configured to receive the first and second detection signals and the first and second manipulation signals, and to generate first and second amplified diminished electrical signals.

In some embodiments, the processing utility is configured for calculating the first and second diminished electrical signals based on the amplified diminished electrical signals and gain factor of the amplification unit.

In some embodiments, the processing utility is configured to calculate the first and second diminished electrical signals by the respective equations: I(kl)dim = V(Xi) / G and I(A2)dim = V(X2) / G, wherein I(Xl)dim and I(A2)dim are the first and second diminished electrical signals, V(Xi) and V(X2) are the first and second amplified diminished electrical signals, and G in the gain factor.

In some embodiments, the processing utility is further configured for calculating the first and second detection electrical signals based on the calculated first and second diminished electrical signals and the first and second manipulation electrical signals.

In some embodiments, the processing utility is configured to calculate the first and second detection electrical signals by the respective equations: Ixi= I(kl)dim + I(M) man and 1x2 — I( 2)dim + I( 2)man, wherein Ixi and 1x2 are the first and second detection electrical I(kl)dim and I(A2)dim are the first and second diminished electrical signals, and I(M) man and I(X2)man are the first and second manipulation electrical signals. In some embodiments, the processing utility is configured for calculating the correction factor by the equation: wherein Cf is the correction factor, I(Xl)dim and I(X2)dimare the first and second diminished electrical signals, and lu and h.2 are the first and second detection electrical.

In some embodiments, the processing utility is configured for calculating the adjusted modulation factor by the equation: R_adj = R * = * wherein Radj is the adjusted modulation factor, Cf is the correction factor and R is the modulation factor.

In some embodiments, the processing utility is configured for controlling (i) an intensity of illumination of the first and second wavelengths, (ii) the first and second electrical manipulation signals, and (iii) gain value applied on the first and second diminished electrical signals to obtain (1) a ratio between the pulsatile and non-pulsatile components of the respective first and second diminished electrical signals within a selected range and (2) first and second diminished electrical signals in a selected intensity range below an amplification saturation threshold.

It is to be noted that any combination of the described embodiments with respect to any aspect of this present disclosure is applicable. In other words, any aspect of the present disclosure can be defined by any combination of the described embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to better understand the subject matter that is disclosed herein and to exemplify how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

Fig. 1 shows extinction coefficient plots for deoxyhemoglobin (deHb) and oxyhemoglobin (HbO2) in the red and infrared light wavelength ranges; Fig. 2 is a block diagram schematically illustrating a system for determining oxygen saturation levels according to some possible embodiments;

Fig. 3A and 3B are block diagrams schematically illustrate system for determining oxygen saturation utilizing a transimpedance amplifier;

Fig. 4 is a flowchart of oxygen saturation measurement procedure according to some possible embodiments.

DETAILED DESCRIPTION

One or more specific and/or alternative embodiments of the present disclosure will be described below with reference to the drawings, which are to be considered in all aspects as illustrative only and not restrictive in any manner. It shall be apparent to one skilled in the art that these embodiments may be practiced without such specific details. In an effort to provide a concise description of these embodiments, not all features or details of an actual implementation are described at length in the specification. Elements illustrated in the drawings are not necessarily to scale, or in correct proportional relationships, which are not critical. Emphasis instead being placed upon clearly illustrating the principles of the invention such that persons skilled in the art will be able to make and use the oxygen saturation measurement devices and/or methods once they understand its features. This invention may be provided in other specific forms and embodiments without departing from the essential characteristics described herein.

For an overview of several example features, process stages, and principles of the invention, the examples illustrated schematically and diagrammatically in the figures are intended oxygen saturation measurement. These oxygen saturation measurement devices are shown as one example implementation that demonstrates a number of features, processes, and principles used to such procedures, but they are also useful for other applications and can be made in different variations. Therefore, this description will proceed with reference to the shown examples, but with the understanding that the invention recited in the claims below can also be implemented in myriad other ways, once the principles are understood from the descriptions, explanations, and drawings herein. All such variations, as well as any other modifications apparent to one of ordinary skill in the art and useful oxygen saturation measurement applications may be suitably employed and are intended to fall within the scope of this disclosure. Reference is made to Fig. 2 schematically illustrates an oxygen saturation measurement system 10 according to possible embodiments of the present disclosure. The oxygen saturation measurement device 10 comprises an optical setup 12 including at least one light source (e.g., coherent light source), two such coherent light sources 12a and 12b are shown herein, each configured to irradiate / illuminate a living tissue 15 (e.g., a wrist of the examined subject) with light of respective first and second wavelengths (z/.z?). and a detector unit 14 (e.g., using a single photodetector responsive to multiple wavelength ranges or respective Xi,Z,2 photodetectors) configured / positioned to detect a light response received (e.g., transmitted through and/or reflected through) from the tissue 15, and generating a respective first and second detection electrical signals (hi, I22) indicative thereof, each of the detection electrical signals (h.i,hh) includes a respective pulsatile (AC) component AC(hi), AC(h2) and non-pulsatile (DC) component DC(hi), DC(h2) such that Zu = DC(hi) + AC(hi) and Zu = DC( 2) + ACfl ).

Also provided in the oxygen saturation measurement system 10 is a signal manipulation unit 16 configured to at least partially diminish respective non-pulsatile components DC(hi), DC(h,2) of the first and second detection electric signals (hi, I22) to obtain respective first and second diminished electrical signals (also referred to herein as DC-reduced signals) I( l)dim, I(2.2)dtm, and a processing utility 18 configured to process the diminished signals I( l)dim , I(2.2)dim from the signal manipulation unit 16 to determine based thereon a correction factor for adjusting a modulation factor derived from respective AC and DC components of the first and second diminished electrical signals l( l)dim , I( 2)dim.

Optionally, but in some embodiments preferably, the coherent light sources 12a and 12b are operated in the red to infrared spectral ranges. A single wavelength, or several wavelengths, can be emitted by each of the light sources 12a and 12b, sequentially or simultaneously. The light sources 12a and 12b can be implemented utilizing one or more laser devices, and/or laser diodes, and/or light emitting diodes. Each of the light sources 12a and 12b can be operated continuously, intermittently or modulated at a specific frequency.

The optical setup 12 can be optically coupled to the tissue 15 (e.g., skin) of the examined subject e.g., using optical fibers (not shown), and/or other optical elements (not shown), such as lenses or prisms, or by free-space coupling. The examined tissue/body part 15can be for example, an earlobe, an ear auricle, a finger or a toe, a wrist, a nostril, the forehead, limbs, chest or abdomen. The detector unit 14is implemented in possible embodiments, for example, but without limiting, a photodiode, and/or an avalanche photodiode, and/or a photomultiplier, and/or a camera, and/or by an array of such (or different) light detectors. A detector array with optical filters (not shown) can be used in possible embodiments wherein the protocol for illuminating the examined the tissue 15 includes simultaneous use of multiple light sources.

The signal manipulation unit 16 is configured and operable to controllably generate respective first and second manipulation electrical signals (1(2.1) man , W man) and to combine the respective first and second detection electric signals with the first and second manipulation electrical signals, e.g. , by a signal combiner 16c. Optionally, but in some embodiments preferably, such manipulation electrical signals may have only a DC component (e.g. , direct current signals).

The combining results in at least partial diminish of respective non-pulsatile components DC(hi), DCfl ) of the first and second detection electric signals (hi, IP) to obtain respective first and second diminished electrical signals 1(2.1) dim , 1(2.2) dim. The respective pulsatile (AC) component AC(hi), AC(hd) are maintained unaffected by the combination. Accordingly:

I(2.1)dim = DC[I(2.1)dim] + ACp(2.1)dim], and

I(2.2)dim = DCP(2.2)dim] + ACP(2.2)dim] wherein

ACp(2.1)dim]= AC(hi), and

ACp(2.2)dtm]= AC(h₂), hence

I(2.1)dim = DCp(2.1)dtm] + AC(hi), and

I(2.2)dim = DCP(2.2)dim] + AC(h₂).

In some embodiments, the first and second manipulation electrical signals (l(2.1)man , 1(2.2) man ) may have substantially the same magnitude as the respective non- pulsatile components DC(hi), DC(hd) of the detection electrical signals, i.e., . Accordingly, after the combining, the first and second diminished electrical signals (I(2.1)dim , I(2.2)dim) have only respective pure pulsatile (AC), namely the pulsatile components AC(hi), AC(hd) of the respective first and second detection electrical signals (hi, hi) such that I(2.1)dim = AC(hi), I(2.2)dim = AC(h,2). In possible embodiments, the first and second manipulation electrical signals (I(21)man , 1(22) man ) are generated in the form of respective first and second inverse electrical signals in a direction opposite to direction of the first and second detection electrical signals (hi, Ip). In some other embodiments, the first and second manipulation electrical signals (1(21) man , 1(22) man ) may have opposite polarities with respect to polarities of the respective first and second detection electrical signals IM, IP). Accordingly, first and second diminished electrical signals (I(21)dtm , I(22)dim are indicative of of difference between a respective one of the first and second detection electrical signals and a respective one of the first and second manipulation electrical signals, as follows: I(21)dim = hi - I(21)man and I(22)dim = In - I(22)_man.

The processing utility 18 includes in some embodiments, one or more processors 18p and memories 18e configured for storing and executing program code configured to orchestrate the operation of the processing utility 18, a communication interface (I/F) unit 18i configured to communicate data between the signal manipulation unit 16 and for receiving data from the detector unit 14, e.g. , over serial/parallel data communication bus, and/or wirelessly, and/or over one or more data networks, with external units/systems.

Also provided in the processing utility 18 is an analyser 18n configured and operable to receive and process the first and second diminished electrical signals (I(21)dim , I(22)dim) generated by signal manipulation unit 16and extract respective pulsatile and non-pulsatile components (e.g., average values over a certain period of time) DC[I(21)d,m], DCp(22)dim], ACp(21)dim], AC P(22)dim] thereof

The processing utility 18 further includes a modulation factor module 18d configured to determine, based on the respective pulsatile and non-pulsatile components of the first and second diminished electrical signals (I(21)dtm , I(22)dim), a modulation factor / parameter R (also referred to as ratio-of ratios). In some embodiments, the modulation factor R is computed by the equation: wherein A Cp(21)dim]= AC(hi), and

ACp(22)_dim]= AC p, hence (1), wherein AC(hi)] '/DC [I(21)dim] and AC(Ix2)] '/DC [I(22)dim] are perfusion indices associated with the respective first and second diminished electrical signals (I(21)dim , I(22)dim)

The processing utility 18 can further include a correction factor module 18c configured to receive and process the first and second diminished electrical signals (I(21)dim , I(22)dim) and the first and second detection electrical signals (hi, 1x2) for determining based thereon a correction factor Cf. In some embodiments, the correction factor Cf can be calculated / computed as follows:

In some embodiments, the correction factor module 18c can be configured to obtain averaged values of the first and second diminished electrical signals (1(21) dim , 1(22) dim) and the averaged values of the first and second detection electrical signals (hi, h ) over a selected time interval (e.g., 20 sec) and to determine based thereon the correction factor Cf based.

Optionally, but in some embodiments preferably, the correction factor module 18c can use the correction factor Cf for adjusting the modulation factor J? to obtain an adjusted modulation factor Radj. In some embodiments, the adjusted modulation factor Radj may be a product of the modulation factor R and the correction factor Cf and thus may be computed as follows:

When the non-pulsatile components DCxi, DC x of the respective first and second detection electrical signals (hi, hi) are manipulated (i.e., at least partially reduced) by the first and second manipulation electrical signals (1(21) man , 1(22) man ), the perfusion indices AC(hi)/DC(hi) and AC(h.2)/DC(h2) associated the respective first and second detection electrical signals (hi, 1x2), and consequently the modulation factor R, are affected by this manipulation since the DC components DC(hi), DC(h2) are modified (z.e., reduced) to DC[I( l)dim], DC P( 2)dim] . As Equation (2) shows, this manipulation on the DC i, DC components is accounted for by the correction factor Cf. Thus, the correction factor Cf is indicative of variation of respective perfusion indices AC(hi)/DC(hi) andACf dJ/DCf d) associated respectively with the first and second detection electric signals (hi, h.2) due to the manipulation (i.e., at least partial cancellation) of the respective non-pulsatile components DC u, DC .

The processing utility 18 can also include a saturation module 18s configured determining the oxygen saturation level of the examined subject based on the adjusted modulation factor Radj. In some embodiments, the processing unit 18 can determine the oxygen saturation level by implementing one or more calibration schemes such as Maxim’s calibration scheme. In this calibration scheme, the SpCh levels are obtained by a quadratic regression in the form ofS_p0₂ = aR² + bR + c, wherein a, b, and c are calibration coefficients. Due to the adjustment / correction of the modulation factor R the adjusted modulation factor Radj can be used, hence the quadratic regression takes the form

This calibration method is known in the art and therefore will not be described in detail herein. Generally, in the calibration lab, the SpCh level of the test subjects are varied in a controlled manner and the signals measured from the test subjects are recorded. During data collection, the test subjects may use a gas mask to control their SpCh level. Through the gas mask, the blood oxygen content is reduced incrementally by changing the oxygen level of the test subject from 100% SpCh and lowering to 70% SpCh. After collecting enough data, the recorded signals are used to find (calculate) the R values. Then, a second (or first) order curve / line is fitted to obtain the calibration coefficients a, b, and c for the SpCh measurement algorithm.

In some embodiments, the processing utility 18 can be operatively coupled to the optical setup 12 for controlling operation of the light sources 12a and 12b. For example, the the processing utility 18 can be configured to control at least one of the following: the measurement(s) repetition rate, the electric supply and/or optical power / magnitude of light generated by the light sources 12a and 12b.

In possible embodiment, the processing utility 18 can be further configured to control one or more of the operating parameters of the detector 14, such as, but not limited to, gain or filtering. In possible embodiments, the processing utility 18 can be also operatively coupled to the signal manipulation unit 16 for controlling operation thereof. For example, the processing utility 18 can be configured to control repetition rate and/or magnitude of the manipulation electrical signals and possibly synchronization / timing of the light generated by light sources 12a and 12b and manipulation signals generated by the signal manipulation unit 16 to achieve the desired DC reduction effect.

For example, in some embodiments, the magnitude of the manipulation electrical signals can be determined in accordance with average magnitude of the detection electrical signals (e.g. , form a selected number of illumination sessions or over a selected time frame of illumination). Alternatively or additionally, one or more control loops may be implemented by the signal manipulation unit 16 or by the processing utility 18 for iteratively modifying the magnitude of the manipulation signals until the diminished electrical signals have required (e.g., small enough) DC component or until its complete cancellation, namely until a desired ratio between the respective DC and AC components of the first and second diminished electrical signals is achieved.

To facilitate understanding, in all the figures, the same reference numbers are used to identify functionally similar elements of the oxygen saturation measurement system. Reference is made to Figs. 3A and 3B schematically illustrate system configurations usable for measuring oxygen saturation level according to some possible embodiments of the present disclosure . In the system 10’ and 10’ ’ shown in Figs. 3A and 3B, respectively, the signal manipulation unit 16 can include or be associated with an amplification unit (e.g, a transimpedance amplifier (TIA) 16t/16t’) configured to amplify the first and second diminished electrical signals (I(21)dim , 1(22) dim) and to convert them to first and second voltage signals. The first and second amplified diminished electrical signals (voltage signals) V(2i), V(2 ), generated by the amplification unit, can be relayed to the processing utility 18 and thereby used for calculating the correction factor Cf as described more in detail further below.

As show in Fig. 3A, the first and second detection electrical signals (hi, I ) are provided to a TIA 16t via its non-inverting (positive) input terminal/port 16n from the detector 14. Optionally, but in some embodiments preferably, the first and second manipulation electrical signals (1(21) man , W man ) may be generated by an electrical signal source / generator 16g which sinks the first and second manipulation electrical signals (1(21) man , W man ) into the inverting input terminal/port 16i of the TIA 16t. Consequently, the detection electrical signals and the manipulation electrical signals have opposite polarities.

The TIA 16t is configured for combining the the detection electrical signals with the manipulation electrical signals for at least partially diminishing / reducing the respective DC components DC (hi), DC (h ) of the detection electrical signals (hi,h.2) to obtain the first and second diminished electrical signals (1(11) dim , 1( 2) dim). In particular, in some embodiments, a respective one of the first and second detection electrical signals (hi, h) is added to / subtracted from a respective one of the first and second manipulation electrical signals (1(11) man , 1(22) man ) to thereby at least partially diminish / reduce their respective DC components DC(hi), DC(hi) for obtaining the respective first and second diminished electrical signals (l(ll)dim , l(12)dim) as follows. l(ll)dim hi 1(11) man and I( 2)dim ⁼ 12 W man. The first and second diminished electrical signals (DC-reduced signals) I(ll)dim , I(12)dim are thereafter amplified and converted to respective voltage signals V(li), V(li).

In Fig. 3B, the first and second manipulation electrical signals (1(11) man , 1(22) man) may be generated by an electrical signal generator 16g’ in the form of inverse electrical signals in an opposite direction of the respective first and second detection electrical signals (hijh) and introduced to a signal propagation path thereof. This results in combination (e.g., addition or subtraction) of each respective one of the first and second detection electrical signals (hi,h.2) and a respective one of the first and second manipulation electrical signals (I(ll)man, 1(12) man ) to thereby at least partially diminish / reduce their respective DC components DC(hi), DC(hi) for obtain the respective first and second diminished electrical signals (I(ll)dim, 1(12) dim . As shown, the obtained first and second diminished electrical signals (I(ll)dim , I(12)dim are received in the TIA 16t which amplifies the diminished electrical signals and converted them to respective voltage signals V(li), V(li).

Optionally, in some embodiments, the signal generator 16g/16g’ can be controlled by the processing utility 18 or by a control unit (not shown) of the signal manipulation unit 16 for setting magnitudes (and possibly timing) of the first and second manipulation electrical signals (1(11) man , 1(22) man ) so as to achieve the required DC reduction of the the first and second detection electrical signals (hi, h ).

The correction factor module 18c can be configured to receive and process the first and second amplified diminished electrical signals V(li), V(li) indicative of voltage levels of the amplified diminished electrical signals for computing based thereon the correction factor Cf. The correction factor Cf can be calculated / computed as follows:

In some embodiments, 1(11) dim and 1(12) dim are a quotient of the respective first and second amplified diminished electrical signals (voltage signals) V(li), V(li) divided by a gain factor G of the TIA 16t, typically set by the resistor(s) of the TIA. The correction factor module 18c can be configured for computing the first and second diminished electrical signals I(ll)dim and Az2//„» as follows: I(ll)dim = V(li) / G and I(12)dtm = V(12) / G. The first and second detection electrical signals (hi, 12) can be calculated by using the relation: l(ll)dim ⁼ hl - I(ll)man and 1(12) dim ⁼ 112 ~ I(12)man, hence hl ⁼ l(ll)dim + W man and 1x2= I(12)dim + 1(12) man.

Optionally, but in some embodiments preferably, the correction factor Cf can be calculated based on averaged values of the first and second detection electrical signals (hi, 1 2) and averaged values of the first and second diminished electrical signals 1(11) dim and I(12)dim over time. More specifically, the voltage measurement of V(l ) may be performed over a selected time interval (e.g., 20 sec). This way, average values of the first and second diminished electrical signals I(ll)dim and I(12)dtm can be determined by the correction factor module 18c based on the averaged voltage signals V(li), V(li), each of the averaged diminished electrical signals may include respective averaged DC components and averaged AC components (e.g., a DC component and !ri of respective the AC component). The correction factor module 18c can be further configured for calculating the average values of the first and second detection electrical signals (hi, 1 2) based on the respective averaged first and second diminished electrical signals 1(11) dim and 1(12) dim.

It should be noted that the present disclosure is not limited with respect to the circuit configuration of the DC offset cancellation circuitry. As will be understood by persons of skill in the art, in view of the description provided herein, a variety of circuit configurations may be used in the signal manipulation unit 16 to perform DC offset cancellation and/or amplification. For example, but without limiting, in some embodiments the signal manipulation unit 16 may comprise one or more analog frontends such as ADPD6000/ADPD7000 chips.

The the processing utility 18 may be configured for controlling parameters of the amplification unit, for example, gain factor G associated therewith. Preferably, the maximal gain factor can be increased to be below (but as close as practically possible) a saturation threshold of the amplification unit for obtaining the maximal signal intensity to reduce inaccuracies. Thus, the processing utility 18 may be configured for controlling (e.g, by iterative modification) the magnitude of the manipulation electrical signal and intensity of the illumination of the light sources 12a and 12b for attaining maximal signal intensity without risk of saturation.

Reference is made to Figs. 4 illustrating a flowchart of process 40 for measuring oxygen saturation levels of an examined subject, according to some possible embodiments of the present disclosure. The process 40 is commenced by illuminating / irradiating (si) a tissue (e.g, wrist) of the examined subject with first and second wavelengths (z/ .?). Next, a light response of the illuminated tissue (e.g., transmitted through and/or reflected through) is detected (s2) and a respective first and second detection electrical signals (hi, IM) indicative thereof are generated. Each of the detection electrical signals (hi, I ) comprising a respective pulsatile component DC(hi), DC(I ) and non-pulsatile component AC(hi), AC (I ).

Then, respective first and second manipulation electrical signals (I(ll)man , 1( 2) man ) are controllably generated (s3) to thereby at least partially diminish respective non-pulsatile components DC(hi), DC(IM) of the first and second detection electric signals (hi, IM) to obtain respective first and second diminished electrical signals (I(ll)dim , 1( 2) dim). Optionally, the first and second manipulation signals (1(11) man , w man ) can include or be in the form of inverse electrical signals generated in a direction opposite to direction of the respective first and second detection electrical signals (In, IM) and introduced to a signal propagation path thereof.

The process 40 further includes determining (s4) a modulation factor R based on non-pulsatile components DC [I(ll)dim] ', DC[I(12)dim] and pulsatile components AC[I(ll)dim], AC[I(12)dim] of the first and second diminished electrical signals (I(ll)dtm , 1(12) dim). Optionally, the modulation factor R can be calculated by equation (1) above.

The process 40 also includes determining (s5) a correction factor Cf, based on the first and second diminished electrical signals (I(ll)dim , 1(12) dim) and the first and second detection electrical signals (hi, hi), for adjusting the modulation factor R. In some embodiments, the correction factor Cf can be calculated / computed in accordance with equation (2). The adjusted modulation factor is determined based on the correction factor Cf and the modulation factor R. Finally, the oxygen saturation levels of the examined subject are determined (s6) based on the adjusted modulation factor. In some embodiments, the adjusted modulation factor can be calculated in accordance with equations (3a) and (3b).

Optionally, in some embodiments, the process 40 also includes, after step s3, amplifying (s7) the first and second diminished electrical signals (I(21)dim , 1(22) dim , generating respective first and second measurement data signals indicative of voltage levels of the first and second amplified electrical signals, and calculating (s8) the first and second diminished electrical signals (I(21)dtm , 1(22) dim) based on the first and second measurement data signals and gain factor G of the amplification. In some embodiments, the first and second diminished electrical signals (I(21)dim , 1(22) dim) can be calculated as follows: 1(21) dim = V(2i) / G and 1(22) dim = V( 2) / G.

In some embodiments, process 40 further includes calculating (s9) the first and second detection electrical signals (hi, i) based on the calculated first and second diminished electrical signals (I(21)dim , 1(22) dim) and the first and second manipulation electrical signals (1(21) man , W man ). For example, the the first and second detection electrical signals (hi, i) can be computed as follows: hi= I(21)dim + I(21)man wi h.i I(22)dim + 1(22) man.

The flowcharts and block diagrams in the different depicted embodiments illustrate the architecture, functionality, and operation of some possible implementations of apparatuses / devices and methods according to an illustrative embodiment. In this regard, each block in the flowcharts or block diagrams may represent a module, segment, function, and/or a portion of an operation or step. For example, one or more of the blocks may be implemented as program code, in hardware, or as a combination of the two. When implemented in hardware, the hardware may, for example, take the form of integrated circuits that are manufactured or configured to perform one or more operations in the flowcharts or block diagrams.

It should also be understood that throughout this disclosure, where a process or method is shown or described, the steps/acts of the method may be performed in any order and/or simultaneously, and/or with other steps/acts not-illustrated/de scribed herein, unless it is clear from the context that one step depends on another being performed first. In possible embodiments not all of the illustrated/described steps/acts are required to carry out the method.

While particular embodiments of the invention have been described, it will be understood, however, that the invention is not limited thereto, since modifications may be made by those skilled in the art, particularly in light of the foregoing teachings. As will be appreciated by the skilled person, the invention can be carried out in a great variety of ways, employing more than one technique from those described above, all without exceeding the scope of the claims.

Claims

CLAIMS:

1. A method for determining an oxygen saturation level of an examined subject, the method comprising:

(a) illuminating a tissue of the examined subject with first and second wavelengths;

(b) detecting a light response of said illuminated tissue for each of the first and second wavelengths and generating a respective first and second detection electrical signals indicative thereof, each of said detection electrical signals comprising a respective pulsatile component and non-pulsatile component;

(c) controllably generating respective first and second manipulation electrical signals to thereby at least partially diminish respective non-pulsatile components of the first and second detection electrical signals to obtain respective first and second diminished electrical signals;

(d) determining a modulation factor based on pulsatile components and non- pulsatile components of said first and second first and second diminished electrical signals or an amplified product thereof;

(e) determining a correction factor, based on the first and second diminished electrical signals and the first and second detection electrical signals, and adjusting said modulation factor based on the correction factor to obtain an adjusted modulation factor;

(f) determining the oxygen saturation level of the examined subject based on the adjusted modulation factor.

2. The method of claim 1, wherein the correction factor is indicative of variations of respective perfusion indices associated respectively with the first and second detection electrical signals due to said at least partial diminishing of the respective non-pulsatile components thereof.

3. The method of claims 1 or 2, wherein the generating of the respective manipulation electrical signals comprises generating respective inverse electrical signals, said inverse electrical signals are in a direction opposite to direction of the first and second detection electrical signals.

4. The method of any one of the preceding claims, further comprising amplifying the first and second diminished electrical signals, generating respective first and second amplified diminished electrical signals, and calculating the first and second diminished electrical signals based on said first and second amplified diminished electrical signals and gain factor of said amplifying.

5. The method of claim 4, wherein the first and second diminished electrical signals are calculated by the respective equations: I(kl)dim = V(Xi) / G and I(A2)dim = V(A,2) / G, wherein I(kl)dim and I(A2)dim are the first and second diminished electrical signals, V(Xi) and V(X₂) are the first and second amplified diminished electrical signals, and G in the gain factor.

6. The method claims 4 or 5, comprising calculating the first and second detection electrical signals based on the calculated first and second diminished electrical signals and said first and second manipulation electrical signals.

7. The method of claim 6, wherein the first and second detection electrical signals are calculated by the respective equations: Iu= I ( l )dim + I(M) man and 1x2 — I( 2)dim + I(X2)man, wherein lu and lu are the first and second detection electrical, I(kl)dim and I(A2)dim are the first and second diminished electrical signals, and I(A1 )manand I(X2)man are the first and second manipulation electrical signals.

8. The method of any one of the preceding claims, wherein the correction factor is calculated by the equation: wherein Cris the correction factor, I(Xl)dim and I(A2)dim are the first and second diminished electrical signals, and l and lu are the first and second detection electrical.

9. The method of any one of the preceding claims, wherein the adjusted modulation factor is calculated by the equation: wherein Radj is the adjusted modulation factor, Cr is the correction factor, R is the modulation factor.

10. The method of any one of claims 4-8, comprising controlling (i) an intensity of illumination of said first and second wavelengths, (ii) the first and second manipulation electrical signals, and (iii) gain value applied on the first and second diminished electrical signals to obtain (1) a ratio between the pulsatile and non-pulsatile components of the respective first and second diminished electrical signals within a selected range and (2) first and second diminished electrical signals in a selected intensity range below an amplification saturation threshold.

11. A system for determining an oxygen saturation level of an examined subject, the system comprising: at least one light source configured and operable to emit light in first and second wavelengths; at least one photodetector configured to detect a light response of said illuminated tissue for each of the first and second wavelengths and generating a respective first and second detection electrical signals indicative thereof, each of said detection electrical signals comprising a respective pulsatile component and non-pulsatile component; a signal manipulation unit configured and operable to controllably generate respective first and second manipulation electrical signals and to combine said respective first and second detection electrical signals with said first and second manipulation electrical signals to thereby at least partially diminish respective non-pulsatile components of the first and second detection electric signals to obtain respective first and second diminished electrical signals; a processing utility configured to:

(i) determine the respective pulsatile and non-pulsatile components of said first and second diminished electrical signals or an amplified product thereof and determine based thereon a modulation factor;

(ii) determine a correction factor, based on the first and second diminished electrical signals and the first and second detection electrical signals, for adjusting said modulation factor based on the correction factor to obtain an adjusted modulation factor; and

(iii) determine the oxygen saturation level of the examined subject based on the adjusted modulation factor.

12. The system of claim 11, wherein the first and second wavelengths are in the red and infrared spectral ranges, respectively.

13. The system of claims 11 or 12, wherein the correction factor is indicative of variations of respective perfusion indices associated respectively with the first and second detection electrical signals due to said at least partial diminishing of the respective non- pulsatile components thereof.

14. The system of any one of claims 11 to 13, wherein the respective first and second manipulation electrical signals comprise respective first and second inverse electrical signals being generated in a direction opposite to direction of the first and second detection electrical signals.

15. The system of any one of claim 11 to 14, wherein signal manipulation unit comprises a signal combiner configured to combine said respective first and second detection electrical signals with said first and second manipulation electrical signals.

16. The system of any one of claims 11 to 15, wherein the signal manipulation unit comprising an amplification unit configured and operable for generating first and second amplified diminished electrical signals.

17. The system of claim 16, wherein the amplification unit comprises a transimpedance amplifier configured to receive the first and second detection signals and the first and second manipulation signals, and to generate first and second amplified diminished electrical signals.

18. The system of claims 16 or 17, wherein the processing utility is configured for calculating the first and second diminished electrical signals based on said amplified diminished electrical signals and gain factor of said amplification unit.

19. The system of claim 18, wherein the processing utility is configured to calculate the first and second diminished electrical signals by the respective equations: I(kl)dim = V(Xi) / G and I(A2)dim = V(A,2) / G, wherein I(Xl)dim and I(X2)dimare the first and second diminished electrical signals, V(Xi) and V(A,2) are the first and second amplified diminished electrical signals, and G in the gain factor.

20. The system of claim 18 or 19, wherein the processing utility is further configured for calculating the first and second detection electrical signals based on the calculated first and second diminished electrical signals and said first and second manipulation electrical signals.

21. The system of claim 20, wherein the processing utility is configured to calculate the first and second detection electrical signals by the respective equations: Ixi= I(kl)dim + I(M) man and 1x2 — I( 2)dim + I( 2)man, wherein Ixi and 1x2 are the first and second detection electrical I(kl)dim and I(A2)dim are the first and second diminished electrical signals, and I(Xl)manand I(X2)man are the first and second manipulation electrical signals.

22. The system of any one of claims 11 to 21, wherein the processing utility is configured for calculating the correction factor by the equation: wherein Cr is the correction factor, I(Xl)dim and I(A2)dim are the first and second diminished electrical signals, and lu and I;.2 are the first and second detection electrical.

23. The system of any one of claims 11 to 22, wherein the processing utility is configured for calculating the adjusted modulation factor by the equation: wherein Radj is the adjusted modulation factor, Cr is the correction factor and R is the modulation factor.

24. The system of any one of claims 11-23, wherein the processing utility is configured for controlling (i) an intensity of illumination of said first and second wavelengths, (ii) the first and second electrical manipulation signals, and (iii) gain value applied on the first and second diminished electrical signals to obtain (1) a ratio between the pulsatile and non-pulsatile components of the respective first and second diminished electrical signals within a selected range and (2) first and second diminished electrical signals in a selected intensity range below an amplification saturation threshold.