Apparatus, method and computer readable storage medium for compensating assessment of peripheral arterial tone

Abstract

A computer-implemented method for assessing peripheral arterial tone (100) (PAT) in an individual (1) monitored by photoplethysmography, comprising: an optical pulse signal (101) measured in a test volume (11); light intensities (102, 103) acquired at two or more points in time (12, 13) along the optical pulse signal (101); oxygen saturation estimate (104), and obtaining calibration data (105); determining a compensation function (14) from the oxygen saturation estimate (104) and the calibration data (105), the compensation function being a function of the oxygen saturation estimate (104); and determining a ratio (15) between the function of the light intensities (102, 103) and the compensation function (14) to evaluate the change in arterial blood volume (16) in the test volume (11) between the two or more time points (12, 13), thereby evaluating PAT (100).

Description

[Technical Field]

[0001] In particular, the present invention relates to methods and apparatus for assessing peripheral arterial tone (PAT), and more particularly to robustly monitoring peripheral arterial tone, for example, to detect sleep-related events. [Background technology]

[0002] During an individual's cardiac cycle, i.e., the period between two heartbeats, blood is pumped pulsatilely through the individual's vascular system. In other words, during the cardiac cycle, the amount of blood in, for example, the fingers, nostrils, ears, forehead, inside the mouth, toes, wrists, and ankles increases and decreases cyclically. Blood in arteries is called arterial blood. Blood in veins is called venous blood.

[0003] A common method for measuring such blood volume fluctuations is optical plethysmography (OPP) or photoplethysmography (PPG). Optical plethysmography (OPP) or photoplethysmography (PPG) is used to detect changes in blood volume in the microvascular bed of tissue. PPG is typically obtained by illuminating a test volume with light from one or more light sources (e.g., LEDs) and detecting collected light corresponding to the light reflected or transmitted within the test volume on a sensor. The sensor may include or correspond to, for example, a photodetector (e.g., a photodiode). For example, the light source and sensor may be positioned on opposite sides of an individual's finger to measure transmission-mode PPG or on the same side of the individual's finger to measure reflection-mode PPG. The heart pumps arterial blood into the test volume with each cardiac cycle. Optical plethysmography can capture physical events corresponding to changes in arterial blood volume in the test volume, for example, during the cardiac cycle.

[0004] In addition to cyclical fluctuations in arterial blood volume, arterial blood volume in tissue is also affected by the diameter of small arteries (arterioles) in the examined volume. These arterioles have muscular walls that can constrict, reducing their diameter. In other words, when these arterioles constrict, the arterial blood volume contained within the corresponding arteriole decreases significantly. Optical plethysmography is a measurement technique that can be used to monitor changes in the arterial blood volume contained within an arteriole as its diameter constricts. Therefore, monitoring changes in arterial blood volume with optical plethysmography empirically provides information about relative changes in arteriolar muscle tone, or smooth muscle tissue "tone" (also known as peripheral arterial tone or PAT).

[0005] Because arterial blood flow to the examined volume can be regulated by several other physiological phenomena, optical plethysmography can also be used to monitor respiration, hypovolemia, and other circulatory conditions, such as diagnosing sleep disorders. Sleep disorder diagnosis is a medical field in which a patient's sleep is monitored over a period of time, e.g., over one night or more. Based on the monitoring, different sleep-related events, such as apnea events, snoring, or limb movements, can be identified.

[0006] At the end of sleep apnea, breath reuptake typically coincides with the release of adrenaline. Adrenaline is released into the bloodstream and binds to adrenergic receptors in arterioles within the volume of interest. This induces an increase in arteriolar muscle tone, resulting in a decrease in arteriolar diameter and a decrease in arterial blood volume within the volume of interest. Therefore, monitoring peripheral arterial tone, such as with optical plethysmography, can provide valuable information regarding the occurrence of sleep-related events, such as sleep apnea.

[0007] Hemoglobin is the primary molecule that scatters light projected into the test volume during photoplethysmography measurements. Hemoglobin includes oxygenated hemoglobin (HbO2) and deoxygenated hemoglobin (Hb). The degree to which hemoglobin in arterial blood is oxygenated is called oxygen saturation (SpO2). The degree of light absorption and scattering by HbO2 differs significantly from that of Hb and also depends on the wavelength of light used in photoplethysmography.

[0008] As a result, optical plethysmography not only depends on the arterial blood volume in the test volume, but also on the hemoglobin composition of that arterial blood volume, as characterized by oxygen saturation. In other words, when measuring changes in PAT monitored by optical plethysmography, this measurement can be significantly affected by changes in the oxygen saturation of the monitored arterial blood volume. For example, during apnea, the proportion of HbO2 in the arterial blood volume in an individual's test volume decreases because less oxygen is delivered to the lungs.

[0009] For example, International Publication No. 98 / 04182 describes a method and device for detecting medical conditions by monitoring peripheral arterial tone. For example, as described in European Patent Application Publication No. 1534115, the device in European Patent Application Publication No. 1534115 performs photoplethysmography by relying on wavelengths at which the degree of absorption and scattering by HbO2 is the same as the degree of absorption and scattering by Hb. Such wavelengths are known as isosbestic wavelengths. Therefore, in European Patent Application Publication No. 1534115, the light intensity measured by photoplethysmography using this isosbestic wavelength is less dependent on the hemoglobin composition of arterial blood volume, i.e., the oxygen saturation value.

[0010] For example, the solution described in EP 1 534 115 A1 requires the use of three light sources to monitor PAT via photoplethysmography: two light sources that do not generate isosbestic wavelength light for estimating oxygen saturation, and one light source that generates isosbestic wavelength light for estimating peripheral arterial tone. The use of three light sources increases the cost and size of the device compared to a system that includes only two light sources. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] International Publication No. 98 / 04182 [Patent Document 2] European Patent Application Publication No. 1534115 Summary of the Invention

[0012] It is therefore an object of embodiments of the present invention to provide a computer-implemented method and apparatus that does not exhibit the inherent drawbacks of the prior art. More specifically, it is an object of embodiments of the present invention to provide a method and apparatus that accurately and robustly minimizes the effects on optical measurements of peripheral arterial tone due to changes in the hemoglobin composition of the monitored arterial blood volume without requiring the use of isosbestic wavelengths.

[0013] The scope of protection sought for various embodiments of the invention is defined by the independent claims.

[0014] To the extent that some embodiments and features described herein do not fall within the scope of the independent claims, they are to be construed as examples to facilitate understanding of various embodiments of the invention.

[0015] It is necessary to eliminate the influence of changes in oxygenated and deoxygenated hemoglobin concentrations on optical measurements of peripheral arterial tone.

[0016] Among other things, one object of embodiments of the present invention is to reduce the effect of changes in hemoglobin composition of monitored arterial blood volume on measurements of peripheral arterial tone by photoplethysmography.

[0017] According to a first exemplary aspect of the present disclosure, there is provided a computer-implemented method for assessing peripheral arterial tone (PAT) in an individual monitored by photoplethysmography, comprising: an optical pulse signal measured in a test volume of the individual; light intensities obtained by photoplethysmography at two or more points along the photoplethysmographic signal; oxygen saturation estimates, and obtaining calibration data; determining a compensation function from the oxygen saturation estimate and the calibration data, the compensation function being a function of the oxygen saturation estimate; This object is achieved by a computer-implemented method comprising the steps of: determining a ratio between the light intensity function and the compensation function to assess one or more changes in arterial blood volume in the test volume between the two or more time points, thereby assessing the individual's PAT.

[0018] A computer-implemented method according to the present disclosure enables accurate and robust determination of peripheral arterial tone. Obtaining an estimate of an individual's oxygen saturation level monitored by photoplethysmography allows for the determination or estimation of the hemoglobin composition of the individual's arterial blood volume in the volume monitored by photoplethysmography. Thus, the computer-implemented method according to the present disclosure can adjust or otherwise compensate the optical plethysmography signal so that the light intensity more reliably reflects changes in the arterial blood volume under monitoring by minimizing the effects of changes in the hemoglobin composition of the monitored arterial blood volume. In other words, the computer-implemented method according to the present disclosure reduces the effect of changes in the hemoglobin composition of the arterial blood volume on the optical plethysmography signal, thereby minimizing or reducing the effect of changes in the hemoglobin composition of the arterial blood volume on the optical measurement of peripheral arterial tone. The computer-implemented method reliably determines a compensation function that is a function of the oxygen saturation estimate and divides a function of the light intensity measured by photoplethysmography by the compensation function of the oxygen saturation estimate. Therefore, the resulting estimate of changes in arterial blood volume in the examined volume provides a more accurate and robust assessment of an individual's peripheral arterial tone.

[0019] The computer-implemented method does not rely on the use of a light source emitting light at an isobestic wavelength. In contrast, the computer-implemented method is compatible with any conventional photoplethysmography setup, for example, including two light sources. The two light sources emit light at two different wavelengths, for example, one red wavelength and one infrared wavelength. In other words, the computer-implemented method accurately measures changes in arterial blood volume in the test volume using only two light sources, the minimum number of light sources required to determine an oxygen saturation estimate. Peripheral arterial tone is then mathematically derived from the two-light source photoplethysmography measurement. This allows for a smaller system size compared to a three-light source system, and further optimizes costs by eliminating the need for a third light source.

[0020] In the context of the present disclosure, the test volume of an individual is, for example, a volume defined in the test tissue of the individual. The individual is monitored by optical plethysmography, and light emitted by optical plethysmography propagates within the individual and is collected by an optical plethysmography sensor. In other words, the test volume of an individual is, for example, a volume defined in the test tissue of the individual from which an optical plethysmography signal is acquired. For example, the test volume is a volume of the peripheral tissue of the individual. For example, the test volume is a volume defined in the individual's fingers, fingertips, distal ends of fingers, nostrils, ears, forehead, inside of the mouth, toes, wrists, ankles, etc. In the context of the present disclosure, the test volume of an individual includes the individual's skin contained in the test volume and further includes the amount of arterial blood present in the test volume. In the context of the present disclosure, peripheral arterial tone is understood as a change in arterial tone of the test arterial bed in the test volume of the individual. In other words, by determining the pulsatile volume changes of the vascular bed in the test volume of an individual, information indicative of the muscle tone of the arterioles or the "tone" of the smooth muscle tissue in the test volume can be determined or evaluated, and thus the peripheral arterial tone regulated by the sympathetic nervous system can be determined or evaluated. Determining peripheral arterial tone is non-invasive and can be used to detect, for example, heart disease, erectile dysfunction, sleep apnea, obstructive sleep apnea, cardiovascular disease, etc.

[0021] In the context of the present disclosure, an optical plethysmography signal is a signal measured by optical plethysmography. For example, the optical plethysmography signal is an optical plethysmogram. For example, the optical plethysmography signal is a PPG. For example, the optical plethysmography signal is measured at an individual's fingertip by an optical plethysmography setup including at least two light sources and a sensor. In the context of the present disclosure, light intensity corresponds to the intensity of light collected on a sensor of the optical plethysmography setup, and the light collected on the sensor corresponds to light generated by one or two light sources and transmitted or reflected within the individual's test volume.

[0022] Blood in an artery is called arterial blood. Blood in a vein is called venous blood. In the context of the present disclosure, an oxygen saturation estimate (SpO2) or hemoglobin composition corresponds to the proportion of oxygenated hemoglobin to the total amount of hemoglobin in the arterial blood volume. For example, an oxygen saturation estimate (SpO2) or hemoglobin composition corresponds to the ratio of the oxygenated hemoglobin concentration to the sum of the oxygenated hemoglobin concentration and the deoxygenated hemoglobin concentration in the arterial blood volume monitored in the test volume. Alternatively, an oxygen saturation estimate (SpO2) or hemoglobin composition corresponds to the ratio of the volume fraction of oxygenated hemoglobin to the sum of the volume fractions of oxygenated hemoglobin and deoxygenated hemoglobin in the arterial blood volume monitored in the test volume.

[0023] In the context of this disclosure, deoxygenated hemoglobin is defined as a form of hemoglobin that is not bound to oxygen and does not have other bound molecules such as carbon monoxide, carbon dioxide, or iron. In the context of this disclosure, oxygenated hemoglobin is defined as a form of hemoglobin that has bound oxygen. In the context of the present invention, light emitted by a light source in a photoplethysmography setup includes photons that reach the sensor through a stochastic path of one or more scattering events. This light path is often assumed to be nonlinear, but rather to follow a curved spatial probability distribution. The test volume along this curved light path forms the volume sampled or interrogated by photoplethysmography. In the context of the present invention, the change in arterial blood volume in the test volume between two time points corresponds to the relative change between the amount of arterial blood present in the test volume at the first time point and the amount of arterial blood present in the test volume at the second time point.

[0024] According to an exemplary embodiment, the calibration data includes predetermined calibration coefficients and / or predefined coefficients; the step of identifying the compensation function corresponds to deriving the compensation function from the defined coefficients; or The step of identifying the compensation function corresponds to identifying the predetermined calibration factor by fitting the oxygen saturation estimate to a calibration ratio.

[0025] In the context of the present disclosure, the defined coefficients may be known or may be identified from literature, such as scientific publications. For example, the defined coefficients may include one or more extinction coefficients of a chromophore and / or one or more absorption coefficients of a chromophore and / or one or more scattering coefficients of a chromophore. In the context of the present disclosure, a chromophore is a molecular entity that absorbs or scatters light in the test volume. For example, in the context of the present disclosure, examples of chromophores include melanin molecules, oxygenated hemoglobin, deoxygenated hemoglobin, etc. In the test volume, the attenuation of the light intensity of incident light emitted from a light source in an optical plethysmography setup follows the Beer-Lambert law, which can be formulated as follows:

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[0026] Consider the following parameters: The Beer-Lambert law, formulated in equation (1), can be evaluated at the first and second time points. Taking the ratio of both equations, we obtain equation (2).

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[0027] Next, by taking the natural logarithm of both sides of equation (2), we obtain equation (3) as follows:

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[0028] If we use a logarithm with a base b other than Euler's number e, equation (3) becomes:

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[0029] JPEG0007811186000008.jpg8170

[0030] JPEG0007811186000009.jpg12170

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[0031] From equation (4), it can be seen that the logarithm of the ratio of light intensity at the first time point to the second time point is linearly related to the difference in volume fraction or concentration of chromophore i between the first time point and the second time point.

[0032] Between two time points along the optical plethysmography signal, some chromophores remain attached to the individual's epidermis. For example, between two time points along the optical plethysmography signal, melanin molecules remain fixed in the test volume. Therefore, the difference in volume fraction or concentration of such chromophores (e.g., melanin molecules) between the two time points is null. Therefore, the contribution of such chromophores to the right-hand side of equation (4) is null.

[0033] The primary chromophores whose volume fraction or concentration varies between two points in time along an optical plethysmography signal are oxygenated and deoxygenated hemoglobin in the arterial blood volume. In the context of this disclosure, the two major forms of hemoglobin, i.e., oxygenated and deoxygenated hemoglobin, exhibit significantly different absorption and scattering coefficients for most wavelengths of light.

[0034] JPEG0007811186000011.jpg32170

[0035] Taking the above into consideration, equation (4) can be rewritten as equation (5) as follows:

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[0036] It is known that the oxygen saturation estimate can be defined according to equation (6).

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[0037] JPEG0007811186000015.jpg17170

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[0038] Under normal circumstances, it is assumed that the volume fraction or sum of the oxygenated and deoxygenated hemoglobin concentrations in the arterial blood volume or the sum of the oxygenated and deoxygenated hemoglobin concentrations in the arterial blood volume remains approximately constant throughout the measurement of the photoplethysmography signal. In practice, only the ratio of oxygenated to deoxygenated hemoglobin, i.e., the oxygen saturation estimate, can change significantly during an individual being monitored by photoplethysmography, for example, during sleep apnea.

[0039] From equations (6) and (7), the following equation is obtained:

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[0040] By substituting equation (8) into equation (5), the following equation is obtained:

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[0041] JPEG0007811186000019.jpg6170

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[0042] JPEG0007811186000021.jpg15170

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[0043] Therefore, equation (11) is obtained.

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[0044] Therefore, the relation (12) is derived from the equation (11).

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[0045] JPEG0007811186000025.jpg41170

[0046] According to an exemplary embodiment, at least one of the time points corresponds to a diastolic phase in the individual's cardiac cycle, and / or at least one of the time points corresponds to a systolic phase in the individual's cardiac cycle.

[0047] During systole, the volume of arterial blood in the individual's test volume is greatest, resulting in the highest absorption and scattering of light at any given time during the cardiac cycle, i.e., the period between two heartbeats. Because hemoglobin is one of the primary absorbers and scatterers of photons in the test volume, the light intensity measured on the sensor of the photoplethysmography setup is lowest. Conversely, during diastole, the volume of arterial blood in the individual's test volume is smallest, resulting in the lowest absorption and scattering of light at any given time during the cardiac cycle, resulting in the highest light intensity measured on the sensor of the photoplethysmography setup. The at least one first time point may correspond, for example, to a diastole in a first cardiac cycle, and / or the at least one second time point may correspond, for example, to a systole in a second cardiac cycle different from the first cardiac cycle. Alternatively, the at least one first time point may correspond, for example, to a systole in a first cardiac cycle, and / or the at least one second time point may correspond, for example, to a diastole in a second cardiac cycle different from the first cardiac cycle. Alternatively, the at least one first time point corresponds to, for example, a systole or diastole in a cardiac cycle, and the at least one second time point corresponds to any time point within the same or a different cardiac cycle.

[0048] According to an exemplary embodiment, at least two of the two or more time points are within one cardiac cycle of the individual.

[0049] From equation (4), we can see that the logarithm of the ratio of systolic to diastolic light intensity is linearly related to the change in volume fraction or concentration of the chromophore between systole and diastole. To achieve the best signal-to-noise ratio during measurements with an optical plethysmography setup, it is preferable to measure at least two different time points within a cardiac cycle. These two time points indicate a large difference in light intensity on the sensor and, consequently, a large difference in arterial blood volume. The two time points corresponding to this largest difference are typically the diastole and the systole within a cardiac cycle.

[0050] According to an exemplary embodiment, the method further includes a step of determining an evaluation function that is a function of the light intensity, and the step of determining a ratio corresponds to determining a ratio between the evaluation function and the compensation function.

[0051] According to Equation (3), the evaluation function corresponds to the natural logarithm of the light intensity function. Alternatively, starting from Equation (2), any other evaluation function defined as a function of light intensity can be used, such as a linear approximation of the natural logarithm of the light intensity function, a Taylor series approximation of the light intensity function, or a linear approximation of another base logarithm of the light intensity function. Then, by determining the ratio between the evaluation function and the compensation function, the change in arterial blood volume in the test volume between two or more time points is evaluated, thereby evaluating peripheral arterial tone.

[0052] According to an exemplary embodiment, the evaluation function corresponds to the logarithm of the function of the light intensity.

[0053] According to Equation (3), the evaluation function corresponds to the natural logarithm of the function of light intensity. Alternatively, starting from Equation (2), any other evaluation function defined as a function of light intensity can be used, such as a linear approximation of the logarithm of the function of light intensity, a Taylor series approximation of the function of light intensity, or a linear approximation of another base logarithm of the function of light intensity. Alternatively, the evaluation function corresponds approximately to the ratio of the pulsatile waveform or alternating current (AC) component of the optical volume pulse wave signal to the slowly changing baseline or direct current (DC) component of the optical volume pulse wave signal, yielding Equation (13).

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[0054] According to an exemplary embodiment, the evaluation function corresponds to the logarithm of the ratio of the light intensities, and the evaluation function is optical path length, a function of the oxygen saturation estimate; and Dependent on one or more of said changes in arterial blood volume in said test volume.

[0055] Therefore, the left side of equation (10) corresponds to the evaluation function, ie the logarithm of the ratio of the light intensities measured by the sensors when investigating the examined volume of an individual with photoplethysmography.

[0056] According to an exemplary embodiment, the method comprises: providing a first light source configured to emit light at a first wavelength; providing a second light source configured to emit light at a second wavelength; providing a sensor; collecting propagated light on the sensor by optical plethysmography corresponding to light transmitted or reflected as it propagates through the distal end of the individual's finger at the two or more times; determining a first light intensity of the propagated light on the sensor at the two or more time points for the first wavelength; determining a second light intensity of the propagated light on the sensor at the two or more time points for the second wavelength; identifying a first ratio corresponding to the first light intensity ratio at the first wavelength; determining a second ratio corresponding to the second light intensity ratio at the second wavelength; and determining the predetermined calibration factor by fitting the oxygen saturation estimate to the calibration ratio.

[0057] JPEG0007811186000027.jpg51170

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[0058] JPEG0007811186000030.jpg10170

[0059] Alternatively, to account for nonlinearities not adequately captured by the above theory, equation (12) can be rewritten as equation (16) below:

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[0060] Then, considering equation (16), equation (14) can be rewritten as the following equation (17).

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[0061] Photoplethysmography technology uses a simple, non-invasive setup probe or biosensor. The photoplethysmography biosensor non-invasively measures pulsatile arterial volume changes in a test volume by collecting photoplethysmography signals, thereby assessing PAT. The first and / or second light sources may be, for example, LEDs or any other suitable light source that can be miniaturized to fit the photoplethysmography biosensor. The first wavelength may be different from the second wavelength. For example, the first wavelength and the second wavelength may be in the red spectrum. For example, the first wavelength may be in the red spectrum and the second wavelength may be in the infrared spectrum. The physical distance between the light source and the sensor may be, for example, a few millimeters, e.g., less than 3 mm.

[0062] According to an exemplary embodiment, the method comprises: collecting, on the sensor by optical plethysmography, propagated light corresponding to light at the first wavelength or the second wavelength that is transmitted or reflected as it propagates within the test volume of the individual at the two or more time points; and determining the light intensity of the propagated light on the sensor at the two or more times.

[0063] According to an exemplary embodiment, the oxygen saturation estimate depends on the ratio of the concentration of oxygenated hemoglobin to the total concentration of oxygenated and deoxygenated hemoglobin in the arterial blood volume.

[0064] According to an exemplary embodiment, the method further includes identifying the oxygen saturation estimate near the test volume of the individual, for example near a distal end of a finger of the individual.

[0065] According to an exemplary embodiment, the compensation function is derived from a regression that maps the oxygen saturation estimate to the predetermined calibration factor.

[0066] JPEG0007811186000035.jpg49170

[0067] According to an exemplary embodiment, the method further includes forcing the regression to use a linear rational map when evaluating the compensation function.

[0068] JPEG0007811186000036.jpg64170

[0069] JPEG0007811186000037.jpg25170

[0070] According to a second exemplary aspect, there is provided an apparatus including at least one processor and at least one memory including computer program code, the at least one memory and the computer program code being configured by the at least one processor to cause the apparatus to: an optical pulse signal measured in a test volume of the individual; light intensities obtained by photoplethysmography at two or more points along the photoplethysmographic signal; oxygen saturation estimates, and obtaining calibration data; determining a compensation function from the oxygen saturation estimate and the calibration data, the compensation function being a function of the oxygen saturation estimate; and determining a ratio between the light intensity function and the compensation function to assess one or more changes in arterial blood volume in the test volume between the two or more time points, thereby assessing the individual's PAT.

[0071] A computer-implemented method according to the present disclosure enables accurate and robust determination of peripheral arterial tone. Obtaining an estimate of an individual's oxygen saturation level monitored by photoplethysmography allows for the determination or estimation of the hemoglobin composition of the individual's arterial blood volume in the volume monitored by photoplethysmography. Thus, the computer-implemented method according to the present disclosure can adjust or otherwise compensate the optical plethysmography signal so that the light intensity more reliably reflects changes in the arterial blood volume under monitoring by minimizing the effects of changes in the hemoglobin composition of the monitored arterial blood volume. In other words, the computer-implemented method according to the present disclosure reduces the effect of changes in the hemoglobin composition of the arterial blood volume on the optical plethysmography signal, thereby minimizing or reducing the effect of changes in the hemoglobin composition of the arterial blood volume on the optical measurement of peripheral arterial tone. The computer-implemented method reliably determines a compensation function that is a function of the oxygen saturation estimate and divides a function of the light intensity measured by photoplethysmography by the compensation function of the oxygen saturation estimate. Therefore, the resulting estimate of changes in arterial blood volume in the examined volume provides a more accurate and robust assessment of an individual's peripheral arterial tone.

[0072] This device does not rely on the use of light sources emitting light at isoabsorption wavelengths. It is compatible with any conventional photoplethysmography setup, for example, one that includes two light sources. The two light sources emit light at two different wavelengths, for example, one red wavelength and one infrared wavelength. In other words, this device accurately measures changes in arterial blood volume in the test volume through a measurement setup using only two light sources, the minimum number of light sources required to determine an oxygen saturation estimate. The device then mathematically derives peripheral arterial tone from the two-light source photoplethysmography measurement. This allows for a smaller system size compared to photoplethysmography systems that include three light sources, and further optimizes costs by eliminating the need for a third light source.

[0073] According to an exemplary embodiment, there is provided an apparatus according to the second exemplary aspect of the present invention, a light source configured to emit light; and a sensor configured to collect propagated light corresponding to light transmitted or reflected as it propagates through a test volume of the individual at the two or more time points using optical plethysmography, and further configured to determine the light intensity of the propagated light at the two or more time points.

[0074] The sensor collects propagated light by optical plethysmography. The propagated light corresponds to light transmitted or reflected as it propagates through a test volume of the individual (e.g., the distal tip of the individual's finger) at two or more time points. Optionally, the system further comprises a wireless transmitter including a wireless communication interface. The wireless transmitter is configured to wirelessly transmit the determined peripheral arterial tone for further processing by the device. The wireless communication interface is preferably a low-power communication interface, such as a Bluetooth Low Energy (BLE) wireless interface.

[0075] According to a third exemplary aspect, the system includes at least an optical pulse signal measured in a test volume of the individual; light intensities obtained by photoplethysmography at two or more points along the photoplethysmographic signal; oxygen saturation estimates, and obtaining calibration data; determining a compensation function from the oxygen saturation estimate and the calibration data, the compensation function being a function of the oxygen saturation estimate; and assessing one or more changes in arterial blood volume in the test volume between the two or more time points by determining a ratio between the function of light intensity and the compensation function, thereby assessing the individual's PAT.

[0076] According to a fourth exemplary embodiment, when the program is executed on a computer, an optical pulse signal measured in a test volume of the individual; light intensities obtained by photoplethysmography at two or more points along the photoplethysmographic signal; oxygen saturation estimates, and obtaining calibration data; determining a compensation function from the oxygen saturation estimate and the calibration data, the compensation function being a function of the oxygen saturation estimate; and assessing one or more changes in arterial blood volume in the test volume between the two or more time points by determining a ratio between the function of light intensity and the compensation function, thereby assessing the individual's PAT.

[0077] Some exemplary embodiments will now be described with reference to the accompanying drawings. [Brief explanation of the drawings]

[0078] [Figure 1] 1 illustrates an exemplary embodiment of an apparatus according to the present disclosure. [Figure 2] 1 illustrates an exemplary embodiment of a system according to the present disclosure including an apparatus according to the present disclosure. [Figure 3] 1 illustrates an exemplary embodiment of a system according to the present disclosure including an apparatus according to the present disclosure. [Figure 4A] 1 illustrates an exemplary embodiment of a calibration of a device according to the present disclosure. [Figure 4B] 1 illustrates an exemplary embodiment of a calibration of a device according to the present disclosure. [Figure 5] 1 illustrates an exemplary embodiment of a PAT measurement of an individual assessed by a device according to the present disclosure. [Figure 6] 1 illustrates an exemplary embodiment of a computer-implemented method according to the present disclosure. [Figure 7] 1 illustrates an exemplary embodiment of a computing system suitable for performing one or more steps of embodiments of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0079] 1 illustrates an exemplary embodiment of an apparatus 10 according to the present disclosure. The apparatus 10 includes at least one memory 6 and at least one processor. The memory 6, by means of the at least one processor, causes the apparatus 10 to: an optical volume pulse signal 101 measured in a test volume 11 of an individual; light intensities 102, 103 acquired by photoplethysmography at two or more time points 12, 13 along an optical pulse wave signal 101 (light intensity 102 acquired at time point 12 and light intensity 103 acquired at time point 13); oxygen saturation estimate of 104, and obtaining calibration data 105; determining a compensation function 14 from the oxygen saturation estimate 104 and calibration data 105, the compensation function 14 being a function of the oxygen saturation estimate 104; The computer program code is configured to execute a step of evaluating one or more changes in arterial blood volume 16 in the test volume 11 between two or more time points 12, 13 by determining a ratio 15 between a function of light intensities 102, 103 and a compensation function 14, thereby evaluating the individual's PAT100. The device 10 obtains one or more of the optical volume pulse signal 101, the light intensities 102, 103, the oxygen saturation estimate 104, and the calibration data 105 from an external device. According to one alternative embodiment, the device 10 obtains one or more of the optical volume pulse signal 101, the light intensities 102, 103, the oxygen saturation estimate 104, and the calibration data 105 from the memory 6. According to another alternative embodiment, the device 10 obtains one or more of the optical volume pulse signal 101, the light intensities 102, 103, the oxygen saturation estimate 104, and the calibration data 105 from the memory 6 and / or the external device. The calibration data 105 includes predetermined calibration coefficients 25 and / or predefined coefficients 26. The device 10 is further configured to determine the compensation function 14 by deriving the compensation function 14 from the predefined coefficients 26. According to an alternative embodiment, the device 10 is configured to determine the compensation function 14 by fitting the oxygen saturation estimate 104 to a calibration ratio, thereby obtaining a predetermined calibration coefficient 25 and estimating the compensation function 14. Optionally, at least one time point 12 corresponds to a diastole in the individual's cardiac cycle and / or at least one time point 13 corresponds to a systole in the individual's cardiac cycle. The device 10 is configured to determine a cost function 17 that is a function of the light intensities 102, 103. The device then determines a ratio 15 that corresponds to the ratio of the cost function 17 to the compensation function 14. The cost function 17 corresponds, for example, to the logarithm of the function of the light intensities 102, 103. The cost function 17 corresponds, for example, to the logarithm of the ratio of the light intensities 102, 103. The cost function 17 depends on one or more of the optical path length, a function of the oxygen saturation estimate, and a change in arterial blood volume in the test volume.

[0080] FIG. 2 shows an exemplary embodiment of a system 20 according to the present disclosure. Components with the same reference numbers as those in FIG. 1 perform the same functions. The system 20 of FIG. 2 includes an apparatus 10 according to the present disclosure. Optionally, the system 20 further includes light sources 2, 3 and a sensor 4. The light sources 2, 3 are configured to emit light 40. The apparatus 10 includes: an optical volume pulse signal 101 measured in a test volume 11 of an individual 1; light intensities 102, 103 acquired by photoplethysmography at two or more time points 12, 13 along an optical pulse wave signal 101 (light intensity 102 acquired at time point 12 and light intensity 103 acquired at time point 13); oxygen saturation estimate of 104, and obtaining calibration data 105; determining a compensation function 14 from the oxygen saturation estimate 104 and calibration data 105, the compensation function 14 being a function of the oxygen saturation estimate 104; and evaluating one or more changes in arterial blood volume 16 in the test volume 11 between two or more time points 12, 13 by determining a ratio 15 between a function of light intensities 102, 103 and a compensation function 14, thereby evaluating the PAT100 of the individual 1. The apparatus 10 obtains one or more of an optical volume pulse signal 101, light intensities 102, 103, an oxygen saturation estimate 104, and calibration data 105 from an external device 200 that includes light sources 2, 3 and / or a sensor 4. For example, the external device 200 determines an arterial blood volume pulse in a test volume 11 of the individual 1. The external device 200 includes a battery for powering the different electrical components 2, 3, 4. The light sources 2, 3 are configured to emit light, i.e., transmit light 40, to the test volume 11 of the individual connected to the external device 200, for example, to a finger 11 of the individual 1 as shown, and more specifically to the distal end 11 of the individual's finger. The external device 200 further includes control circuitry for controlling the light sources 2, 3, i.e., for enabling or disabling the light sources 2, 3, and for receiving the measured arterial blood volume pulse value from the sensor 4. The control circuitry may further include a memory component for temporarily storing the obtained measurements. The control circuitry is further coupled to a wireless interfacing circuit 50 and configured to transfer the measurements to the wireless interfacing circuitry 50. The wireless interface 50 may support a short-range and / or low-power wireless communication protocol for efficiently transmitting the measurements to a receiver of the system. The wireless interface 50 may operate, for example, according to the Bluetooth Low Energy (BLE) protocol defined by the Bluetooth Special Interest Group (Bluetooth SIG) or the Near Field Communication (NFC) protocol. Operation according to such a protocol and transfer of the raw optical pulse signal 101 allows the external device 200 to be compact enough to fit on a finger or nostril and to operate over multiple nights. According to an alternative embodiment, the device 10 obtains one or more of the optical pulse signal 101, the light intensity 102, 103, the oxygen saturation estimate 104, and the calibration data 105 from the memory 6. According to another alternative embodiment, the device 10 obtains one or more of the optical pulse signal 101, light intensity 102, 103, oxygen saturation estimate 104, and calibration data 105 from a memory 6 and / or an external device including light sources 2, 3 and sensor 4.The calibration data 105 includes predetermined calibration coefficients 25 and / or predefined coefficients 26. The device 10 is further configured to determine the compensation function 14 by deriving the compensation function 14 from the predefined coefficients 26. According to an alternative embodiment, the device 10 is configured to determine the compensation function 14 by fitting the oxygen saturation estimate 104 to the predetermined calibration coefficients 25. Optionally, at least one time point 12 corresponds to a diastole in the individual's cardiac cycle, and / or at least one time point 13 corresponds to a systole in the individual's cardiac cycle. The device 10 is configured to determine an evaluation function 17 that is a function of the light intensities 102, 103. The device 10 collects, via photoplethysmography, propagated light 41 on the sensor 4 that corresponds to light 40 emitted by the first light source 2 or the second light source 3. This light 40 is transmitted or reflected by the test volume 11 as it propagates through the distal end of the individual's finger at two or more points in time 12, 13 along the optical plethysmography signal 101. In other words, the device 10 collects, by optical plethysmography, on the sensor 4 a light intensity 102 corresponding to the propagated light 41 corresponding to the light 40 emitted by the first light source 2 or the second light source 3. This light 40 is transmitted or reflected by the test volume 11 as it propagates through the distal end of the individual's finger and is collected by the sensor 4 at the first point in time 12. The device 10 collects, by optical plethysmography, on the sensor 4 a light intensity 103 corresponding to the propagated light 41 corresponding to the light 40 emitted by the same light source 2 or 3. This light 40 is transmitted or reflected by the test volume 11 as it propagates through the distal end of the individual's finger and is collected by the sensor 4 at the second point in time 13. The apparatus then determines a ratio 15 corresponding to the ratio of the evaluation function 17 and the compensation function 14. The evaluation function 17 corresponds, for example, to the logarithm of a function of the light intensities 102, 103. The evaluation function 17 corresponds, for example, to the logarithm of the ratio of the light intensities 102, 103. The evaluation function 17 depends on one or more of the optical path length, a function of the oxygen saturation estimate, and a change in arterial blood volume in the test volume. The apparatus 101 optionally determines an oxygen saturation estimate 104 near the distal end of the finger of the individual 1. Evaluating the compensation function 14 optionally corresponds to determining a regression that maps the oxygen saturation estimate 104 to predetermined calibration coefficients 25.Apparatus 10 optionally constrains the regression to use a linear rational map when evaluating compensation function 14 .

[0081] FIG. 3 shows an exemplary embodiment of a system 20 according to the present disclosure. Components with the same reference numbers as those in FIG. 1 or FIG. 2 perform the same functions. The system 20 of FIG. 3 includes an apparatus 10 according to the present disclosure. Optionally, the system 20 further includes light sources 2, 3 and a sensor 4. The light sources 2, 3 are configured to emit light 40. The apparatus 10 includes: an optical volume pulse signal 101 measured in a test volume 11 of an individual 1; light intensities 102, 103 acquired by photoplethysmography at two or more time points 12, 13 along an optical pulse wave signal 101 (light intensity 102 acquired at time point 12 and light intensity 103 acquired at time point 13); oxygen saturation estimate of 104, and obtaining calibration data 105; determining a compensation function 14 from the oxygen saturation estimate 104 and calibration data 105, the compensation function 14 being a function of the oxygen saturation estimate 104; The method is configured to perform a step of evaluating the change in arterial blood volume 16 in the test volume 11 between two or more time points 12, 13 by determining a ratio 15 between a function of light intensities 102, 103 and a compensation function 14, thereby evaluating the PAT100 of the individual 1. The device 10 obtains one or more of an optical volume pulse signal 101, light intensities 102, 103, an oxygen saturation estimate 104, and calibration data 105 from the light sources 2, 3 and / or the sensor 4. For example, the device 10 determines an arterial blood volume pulse in a test volume 11 of the individual 1. The device 10 includes a battery for powering the different electrical components 2, 3, 4. The light sources 2, 3 are configured to emit light, i.e., transmit light 40, into the test volume 11 of the individual connected to the device 10, for example, into a finger 11 of the individual 1 as shown, and more specifically, into the distal end 11 of the individual's finger as shown. The device 10 further includes control circuitry for controlling the light sources 2, 3, i.e., for enabling or disabling the light sources 2, 3, and for receiving the measured arterial blood volume pulse value from the sensor 4. The control circuitry may further include a memory component for temporarily storing the obtained measurements. The control circuitry is further coupled to a wireless interfacing circuit 50 and configured to transfer the measurements to the wireless interfacing circuitry 50. The wireless interface 50 may support a short-range and / or low-power wireless communication protocol for efficiently transmitting the measurements to a receiver of the system. The wireless interface 50 may operate, for example, according to the Bluetooth Low Energy (BLE) protocol defined by the Bluetooth Special Interest Group (Bluetooth SIG) or the Near Field Communication (NFC) protocol. Operation according to such a protocol and the transfer of the raw optical pulse signal 101 allows the device 10 to be compact enough to fit on a finger or nostril and to operate over multiple nights. According to an alternative embodiment, the device 10 obtains one or more of the optical pulse signal 101, the light intensity 102, 103, the oxygen saturation estimate 104, and the calibration data 105 from the memory 6. According to another alternative embodiment, the device 10 obtains one or more of the optical pulse signal 101, light intensity 102, 103, oxygen saturation estimate 104, and calibration data 105 from the light sources 2, 3 and / or sensor 4 and / or from the memory 6.The calibration data 105 includes predetermined calibration coefficients 25 and / or predefined coefficients 26. The device 10 is further configured to determine the compensation function 14 by deriving the compensation function 14 from the predefined coefficients 26. According to an alternative embodiment, the device 10 is configured to determine the compensation function 14 by fitting the oxygen saturation estimate 104 to the predetermined calibration coefficients 25. Optionally, at least one time point 12 corresponds to a diastole in the individual's cardiac cycle, and / or at least one time point 13 corresponds to a systole in the individual's cardiac cycle. The device 10 is configured to determine an evaluation function 17 that is a function of the light intensities 102, 103. The device 10 collects, via photoplethysmography, propagated light 41 on the sensor 4 that corresponds to light 40 emitted by the first light source 2 or the second light source 3. This light 40 is transmitted or reflected by the test volume 11 as it propagates through the distal end of the individual's finger at two or more points in time 12, 13 along the optical plethysmography signal 101. In other words, the device 10 collects, by optical plethysmography, on the sensor 4 a light intensity 102 corresponding to the propagated light 41 corresponding to the light 40 emitted by the first light source 2 or the second light source 3. This light 40 is transmitted or reflected by the test volume 11 as it propagates through the distal end of the individual's finger and is collected by the sensor 4 at the first point in time 12. The device 10 collects, by optical plethysmography, on the sensor 4 a light intensity 103 corresponding to the propagated light 41 corresponding to the light 40 emitted by the same light source 2 or 3. This light 40 is transmitted or reflected by the test volume 11 as it propagates through the distal end of the individual's finger and is collected by the sensor 4 at the second point in time 13. The apparatus then determines a ratio 15 corresponding to the ratio of the evaluation function 17 and the compensation function 14. The evaluation function 17 corresponds, for example, to the logarithm of a function of the light intensities 102, 103. The evaluation function 17 corresponds, for example, to the logarithm of the ratio of the light intensities 102, 103. The evaluation function 17 depends on one or more of the optical path length, a function of the oxygen saturation estimate, and a change in arterial blood volume in the test volume. The apparatus 101 optionally determines an oxygen saturation estimate 104 near the distal end of the finger of the individual 1. Evaluating the compensation function 14 optionally corresponds to determining a regression that maps the oxygen saturation estimate 104 to predetermined calibration coefficients 25.Apparatus 10 optionally constrains the regression to use a linear rational map when evaluating compensation function 14 .

[0082] 4A and 4B show an exemplary embodiment of calibration of a device according to the present disclosure. Components with the same reference numbers as those in FIG. 1, 2, or 3 perform the same functions. A first light source 2 is provided, emitting light 40 at a first wavelength. A second light source 3 is provided, emitting light 40 at a second wavelength, preferably different from the first wavelength. A sensor 4 is provided. By photoplethysmography, propagated light 41 is collected by the sensor 4 at two time points 2 and 3. This propagated light 41 corresponds to light 40 emitted by the first light source 2 or the second light source 3. As this light 40 propagates through the test volume 11 of the individual 1, it is transmitted or reflected by the test volume of the individual. As shown in FIG. 4A , light intensities 106, 107 corresponding to propagating light 41 collected by sensor 4 for a first wavelength emitted by light source 2 are measured by sensor 4 at first and second time points 12, 13, respectively. As shown in FIG. 4B , light intensities 108, 109 corresponding to propagating light 41 collected by sensor 4 for a second wavelength emitted by second light source 3 are measured by sensor 4 at first and second time points 12, 13, respectively. Sensor 4, or, in an alternative embodiment, apparatus 10 of FIG. 1 , 2, or 3 , then determines a first ratio corresponding to the ratio of first light intensities 106, 107 for the first wavelength in FIG. 4A . Sensor 4, or, in an alternative embodiment, apparatus 10 of FIG. 1 , 2, or 3 , then determines a second ratio corresponding to the ratio of second light intensities 108, 108 for the second wavelength in FIG. 4B . The sensor 4 or, in one alternative embodiment, the device 10 of FIG. 1, 2, or 3 determines a calibration ratio corresponding to the ratio of the function of the first ratio to the function of the second ratio. The sensor 4 or, in one alternative embodiment, the device 10 of FIG. 1, 2, or 3 determines a predetermined calibration factor by fitting the oxygen saturation estimate to the calibration ratio. According to another alternative embodiment, determining the first ratio and / or the second ratio and / or the calibration ratio and / or the predetermined calibration factor is performed by any other suitable external device including at least one processor and at least one memory containing computer program code.The at least one memory and computer program code are configured to cause the at least one processor to determine these values ​​to an appropriate external device.

[0083] FIG. 5 illustrates an exemplary embodiment of oxygen saturation estimate 104 measured simultaneously with test strain 100. As shown in FIG. 5, during time period 61, i.e., pre-vasoconstriction event period 61, the level of oxygen saturation estimate 104 is high, and uncompensated peripheral arterial tone 401 and compensated peripheral arterial tone 402 evolve in a similar manner and overlap as a function of time 60 at the pre-vasoconstriction event baseline value. During time period 62, the value of oxygen saturation estimate 104 slowly decreases, indicating the occurrence of an event in the individual under monitoring, such as a sleep-related event such as sleep apnea. As can be seen from FIG. 5, uncompensated peripheral arterial tone 401 and compensated peripheral arterial tone 402 evolve in a similar manner, but no longer overlap during corresponding time period 62. In effect, the average uncompensated baseline 403, which uncompensated peripheral arterial tone 401 evolves around during time period 62, is greater than the average compensated baseline 404, which compensated peripheral arterial tone 402 evolves around. This clearly illustrates the effect of compensating for the effects of changes in hemoglobin composition of the monitored arterial blood volume on the measurement of peripheral arterial tone. During time period 63, the value of oxygen saturation estimate 104 reaches a minimum, corresponding to the occurrence of an event in the monitored individual, such as a sleep-related event, e.g., sleep apnea. As can be seen from FIG. 5 , uncompensated peripheral arterial tone 401 and compensated peripheral arterial tone 402 evolve in a similar manner, but compensating for the effects of changes in hemoglobin composition of the monitored arterial blood volume on the measurement of peripheral arterial tone 100 allows for more accurate detection of the event. In effect, the decrease in peripheral arterial tone 100 indicates vasoconstriction of the arteries and arterioles in the monitored volume. This vasoconstriction event can be associated with the occurrence of an event in the monitored individual, such as a sleep-related event, e.g., sleep apnea. As can be seen from FIG. 5 , the decrease in uncompensated peripheral arterial tone 402 between the pre-vasoconstriction event baseline value and the lowest point of uncompensated peripheral arterial tone 402 is less than the decrease in compensated peripheral arterial tone 401 between the pre-vasoconstriction event baseline value and the lowest point of compensated peripheral arterial tone 401.For example, a predetermined threshold 400 of peripheral arterial tone 100 can be used to detect whether an event is occurring in an individual under monitoring, such as a sleep-related event, such as sleep apnea. If peripheral arterial tone 100 is above the predetermined threshold 400, an event is not detected, and if peripheral arterial tone 100 is below the predetermined threshold 400, an event is detected. A decrease in uncompensated peripheral arterial tone 402 between the pre-vasoconstriction event baseline value and the nadir of uncompensated peripheral arterial tone 402 will cause uncompensated peripheral arterial tone 402 to remain above the predetermined threshold 400, resulting in the failure to detect an event occurring in the individual under monitoring, such as a sleep-related event, such as sleep apnea. On the other hand, a decrease in compensated peripheral arterial tone 401 between the pre-vasoconstriction event baseline value and the nadir of compensated peripheral arterial tone 401 will cause compensated peripheral arterial tone 401 to fall below the predetermined threshold 400, resulting in the detection of an event occurring in the individual under monitoring, such as a sleep-related event, such as sleep apnea. Therefore, by compensating for the effect on the measurement of peripheral arterial tone 100 due to changes in the hemoglobin composition of the monitored arterial blood volume, it becomes possible to more accurately and robustly detect the occurrence of events occurring in the monitored individual, such as sleep-related events such as sleep apnea.

[0084] 6 illustrates an exemplary embodiment of a computer-implemented method for assessing peripheral arterial tone (PAT) in an individual monitored by photoplethysmography. The method comprises: an optical pulse signal measured in a test volume of the individual; light intensity obtained by photoplethysmography at two or more points along the photoplethysmographic signal; oxygen saturation estimates, and a first step 501 of obtaining calibration data; The first step 501 is followed by a second step 502 of determining, from the oxygen saturation estimate and the calibration data, a compensation function that is a function of the oxygen saturation estimate; The second step 502 is followed by a third step 503 of assessing one or more changes in arterial blood volume in the test volume between two or more time points by determining the ratio between the light intensity function and the compensation function, thereby assessing the individual's PAT.

[0085] FIG. 7 illustrates a suitable computing system 800 on which embodiments of the system may be implemented. The computing system 800 may generally be formed as a suitable general-purpose computer and may include a bus 810, a processor 802, a local memory 804, one or more optional input interfaces 814, one or more optional output interfaces 816, a communication interface 812, a storage element interface 806, and one or more storage elements 808. The bus 810 may include one or more conductors that enable communication between components of the computing system 800. The processor 802 may include any type of conventional processor or microprocessor that interprets and executes programming instructions. The local memory 804 may include random access memory (RAM) or another type of dynamic storage device that stores information and instructions executed by the processor 802, and / or read-only memory (ROM) or another type of static storage device that stores static information and instructions used by the processor 802. Input interface 814 may include one or more conventional mechanisms that allow an operator or user to input information into computing device 800, such as a keyboard 820, a mouse 830, a pen, a voice recognition and / or biometric mechanism, a camera, etc. Output interface 816 may include one or more conventional mechanisms that output information to an operator or user, such as a display 840. Communication interface 812 may include any transceiver-like mechanism, such as one or more Ethernet interfaces, that allows computing system 800 to communicate with other devices and / or systems, e.g., other computing devices 881, 882, 883, etc. Communication interface 812 of computing system 800 may be connected to such other computing systems via a local area network (LAN) or a wide area network (WAN), e.g., via the Internet.Storage element interface 806 may include a storage interface, such as a Serial Advanced Technology Attachment (SATA) interface or a Small Computer System Interface (SCSI), for connecting bus 810 to one or more storage elements 808, e.g., one or more local disks such as SATA disk drives, and may control the reading and writing of data to and / or from these storage elements 808. While storage element 808 is described above as a local disk, generally, any other suitable computer-readable medium may be used, such as a removable magnetic disk, an optical storage medium such as a CD or DVD, a ROM disk, a solid-state drive, a flash memory card, etc. Thus, computing system 800 may correspond to device 10 in the embodiments shown in FIGS. 1, 2, or 3.

[0086] As used herein, the term "circuitry" may refer to one or more or all of the following: (a) hardware-only circuit implementations, such as implementations in analog and / or digital circuitry only; (b) a combination of hardware circuitry and software, e.g., (where applicable) (i) a combination of analog and / or digital hardware circuitry and software / firmware; and (ii) hardware processor portions with software (including digital signal processors, software, and memory that work together to cause devices such as mobile phones and servers to perform various functions); and (c) Hardware circuitry and / or processors, such as microprocessors or portions of microprocessors, that require software (e.g., firmware) to operate but may not be present if not necessary for the software to operate. This definition of circuit applies to all uses of the term in this application, including any claims. As a further example, as used in this application, the term circuit also covers a hardware circuit alone, or a processor(s) alone, or a portion of a hardware circuit or processor and its(their) accompanying software and / or firmware implementation. The term circuit also covers, for example, a baseband integrated circuit or processor integrated circuit for a mobile terminal, or a similar integrated circuit in a server, cellular network device, or other computing or network device, if applicable to particular claim elements.

[0087] While the present invention has been described with reference to particular embodiments, it will be apparent to those skilled in the art that the invention is not limited to the details of the illustrative embodiments set forth above, and that the invention can be embodied in various changes and modifications without departing from the scope of the present invention. The present embodiments are therefore considered in all respects to be illustrative and not restrictive. The scope of the invention is indicated by the appended claims, rather than the foregoing description. Accordingly, all changes that come within the scope of the claims are intended to be embraced therein.

[0088] Furthermore, readers of this patent application will understand that the terms "comprising" or "comprise" do not exclude other elements or steps, and that the terms "a" or "an" do not exclude a plurality, and that a single element, such as a computer system, processor, or other integrated unit, may fulfill the functions of several means recited in the claims. Any reference signs in the claims should not be construed as limiting the respective claims to which they relate. Terms such as "first," "second," "third," "a," "b," "c," and the like, when used in the description or claims, are introduced to distinguish between similar elements or steps and do not necessarily describe an order or chronology. Similarly, terms such as "upper," "lower," "above," and "below" are introduced for explanatory purposes and do not necessarily indicate relative positions. It should be understood that terms used in this manner are interchangeable under appropriate circumstances, and that embodiments of the invention can operate according to the invention in other sequences or with orientations different from those described or illustrated above. In order to maintain the disclosure of the present application as originally filed, the contents of claims 1 to 15 as originally filed are added below. (Claim 1) 1. A computer-implemented method for assessing peripheral arterial tone (100) (PAT) in an individual (1) monitored by photoplethysmography, comprising: an optical pulse signal (101) measured in a test volume (11) of the individual (1); light intensities (102, 103) obtained by photoplethysmography at two or more points in time (12, 13) along said photoplethysmographic signal (101); oxygen saturation estimate (104), and obtaining calibration data (105); determining a compensation function (14) from the oxygen saturation estimate (104) and the calibration data (105), the compensation function being a function of the oxygen saturation estimate (104); and assessing a change in arterial blood volume (16) in the test volume (11) between the two or more time points (12, 13) by determining a ratio (15) between the function of the light intensities (102, 103) and the compensation function (14), thereby assessing the PAT (100) of the individual (1). (Claim 2) the calibration data (105) includes predetermined calibration coefficients (25) and / or predefined coefficients (26); the step of identifying the compensation function (14) corresponds to deriving the compensation function (14) from the defined coefficients (26); or 2. The method of claim 1, wherein the step of determining the compensation function corresponds to determining the predetermined calibration factor by fitting the oxygen saturation estimate to a calibration ratio. (Claim 3) 3. The method of claim 1 or 2, wherein at least one (12) of the time points (12, 13) corresponds to a diastolic phase in the cardiac cycle of the individual (1) and / or at least one (13) of the time points (12, 13) corresponds to a systolic phase in the cardiac cycle of the individual (1). (Claim 4) 4. The method according to claim 1, further comprising a step of determining an evaluation function (17) that is a function of the light intensities (102, 103), wherein the step of determining a ratio (15) corresponds to determining a ratio between the evaluation function (17) and the compensation function (14). (Claim 5) 5. The method according to claim 4, wherein the evaluation function (17) corresponds to the logarithm of a function of the light intensity (102, 103). (Claim 6) The evaluation function (17) corresponds to the logarithm of the ratio of the light intensities (102, 103), and the evaluation function (17) is optical path length, a function of the oxygen saturation estimate (104), and 6. The method according to claim 4 or 5, wherein the changes in the arterial blood volume (16) in the test volume (11) depend on one or more of the changes. (Claim 7) providing a first light source (2) configured to emit light at a first wavelength; providing a second light source (3) configured to emit light at a second wavelength; Providing a sensor (4); collecting, on the sensor (4) by optical plethysmography, propagated light corresponding to light transmitted or reflected as it propagates through the test volume (11) of the individual (1) at the two or more points in time (12, 13); determining a first light intensity (106, 107) of the propagated light on the sensor (4) at the two or more times (12, 13) for the first wavelength; determining a second light intensity (108, 109) of the propagated light on the sensor (4) at the two or more times (12, 13) for the second wavelength; determining a first ratio corresponding to a ratio of the first light intensities (106, 107) at the first wavelengths; determining a second ratio corresponding to the ratio of the second light intensities (108, 109) at the second wavelengths; determining the calibration ratio between the first ratio function and the second ratio function; The method of any one of claims 1 to 6, further comprising the step of: determining the predetermined calibration factor (25) by fitting the oxygen saturation estimate (104) to the calibration ratio. (Claim 8) collecting, on the sensor (4) by optical plethysmography, propagated light (41) corresponding to light (40) at the first wavelength or the second wavelength transmitted or reflected as it propagates within the test volume (11) of the individual (1) at the two or more time points (12, 13); 8. The method of claim 7, further comprising determining the light intensity (102, 103) of the propagated light on the sensor (4) at the two or more points in time (12, 13). (Claim 9) 9. The method according to claim 7 or 8, further comprising determining the oxygen saturation estimate (104) in the vicinity of the test volume (11) of the individual (1). (Claim 10) 10. The method of claim 1, wherein the step of evaluating the compensation function (14) corresponds to identifying a regression that maps the oxygen saturation estimate (104) to the predetermined calibration coefficients (25). (Claim 11) 11. The method of claim 10, further comprising the step of forcing the regression to use a linear rational map when evaluating the compensation function (14). (Claim 12) An apparatus (10) including at least one processor and at least one memory (6) containing computer program code, the at least one memory (6) and the computer program code being transmitted by the at least one processor to the apparatus (10): an optical pulse signal (101) measured in a test volume (11) of an individual (1); light intensities (102, 103) obtained by photoplethysmography at two or more points in time (12, 13) along said photoplethysmographic signal (101); oxygen saturation estimate (104), and obtaining calibration data (105); determining a compensation function (14) from the oxygen saturation estimate (104) and the calibration data (105), the compensation function being a function of the oxygen saturation estimate (104); and assessing a change in arterial blood volume (16) in the test volume (11) between the two or more time points (12, 13) by determining a ratio (15) between the function of the light intensities (102, 103) and the compensation function (14), thereby assessing the PAT (100) of the individual (1). (Claim 13) 13. A device according to claim 12, a light source (2, 3) configured to emit light; and a sensor (4) configured to collect propagated light corresponding to light transmitted or reflected as it propagates through the distal end of the finger of the individual (1) at the two or more points in time (12, 13) by optical plethysmography, and further configured to determine the light intensity (102, 103) of the propagated light at the two or more points in time (12, 13). (Claim 14) The system has at least an optical pulse signal (101) measured in a test volume (11) of an individual (1); light intensities (102, 103) obtained by photoplethysmography at two or more points in time (12, 13) along said photoplethysmographic signal (101); oxygen saturation estimate (104), and obtaining calibration data (105); determining a compensation function (14) from the oxygen saturation estimate (104) and the calibration data (105), the compensation function being a function of the oxygen saturation estimate (104); and assessing a change in arterial blood volume (16) in the test volume (11) between the two or more time points (12, 13) by determining a ratio (15) between the function of the light intensities (102, 103) and the compensation function (14), thereby assessing the PAT (100) of the individual (1). (Claim 15) When a program runs on a computer, an optical pulse signal (101) measured in a test volume (11) of an individual (1); light intensities (102, 103) obtained by photoplethysmography at two or more points in time (12, 13) along said photoplethysmographic signal (101); oxygen saturation estimate (104), and obtaining calibration data (105); determining a compensation function (14) from the oxygen saturation estimate (104) and the calibration data (105), the compensation function being a function of the oxygen saturation estimate (104); and assessing a change in arterial blood volume (16) in the test volume (11) between the two or more time points (12, 13) by determining a ratio (15) between the function of the light intensities (102, 103) and the compensation function (14), thereby assessing the PAT (100) of the individual (1).

Claims

1. A computer-readable medium containing computer-executable instructions that, when executed by one or more processors, perform a method for assessing peripheral arterial tone (PAT) in an individual monitored by photoplethysmography, comprising: The method comprises: a photoplethysmography signal measured in a test volume of the individual; and light intensity acquired by a photoplethysmograph at two or more points along the photoplethysmographic signal; and an oxygen saturation estimate; and obtaining calibration data; determining a compensation function from the oxygen saturation estimate and the calibration data, the compensation function being a function of the oxygen saturation estimate; determining a ratio between the function of light intensity and the compensation function to assess the change in arterial blood volume in the test volume between the two or more time points, thereby assessing PAT of the individual; 1. A computer-readable medium comprising:

2. the calibration data includes predetermined calibration coefficients and / or predefined coefficients; the step of identifying the compensation function corresponds to deriving the compensation function from the defined coefficients; or 2. The computer-readable medium of claim 1, wherein the step of identifying the compensation function corresponds to identifying the predetermined calibration factor by fitting the oxygen saturation estimate to a calibration ratio.

3. 3. The computer-readable medium of claim 1, wherein at least one of the time points corresponds to a diastole in the individual's cardiac cycle and / or at least one of the time points corresponds to a systole in the individual's cardiac cycle.

4. 4. The computer-readable medium according to claim 1, further comprising a step of specifying an evaluation function that is a function of the light intensity, wherein the step of specifying a ratio corresponds to specifying a ratio between the evaluation function and the compensation function.

5. The computer-readable medium of claim 4 , wherein the evaluation function corresponds to a logarithm of the function of the light intensity.

6. The evaluation function corresponds to the logarithm of the ratio of the light intensities, and the evaluation function is expressed as follows: The optical path length, a function of the oxygen saturation estimate; The computer-readable medium of claim 4 or 5, wherein the change in the arterial blood volume in the test volume depends on one or more of:

7. The method comprises: controlling a first light source configured to emit light at a first wavelength; controlling a second light source configured to emit light at a second wavelength; controlling the sensor; collecting and controlling propagated light on the sensor by photoplethysmography, the propagated light corresponding to light transmitted or reflected as it propagates through the test volume of the individual at the two or more time points; determining a first light intensity of the propagated light on the sensor at the two or more time points for the first wavelength; determining a second light intensity of the propagated light on the sensor at the two or more time points for the second wavelength; identifying a first ratio corresponding to the first light intensity ratio at the first wavelength; determining a second ratio corresponding to the second light intensity ratio at the second wavelength; determining the calibration ratio between the first ratio function and the second ratio function; determining the predetermined calibration factor by fitting the oxygen saturation estimate to the calibration ratio; The computer-readable medium according to claim 2, or the computer-readable medium according to any one of claims 3 to 6 which cites claim 2, further comprising:

8. The method comprises: collecting and controlling, on the sensor by photoplethysmography, propagated light corresponding to light at the first wavelength or the second wavelength that is transmitted or reflected as it propagates within the test volume of the individual at the two or more time points; determining the light intensity of the propagated light on the sensor at the two or more time points; The computer-readable medium of claim 7 further comprising:

9. The computer-readable medium of claim 7 or 8, further comprising determining the oxygen saturation estimate in the vicinity of the test volume of the individual.

10. The computer-readable medium of any one of claims 1 to 9, wherein the compensation function is derived from a regression that maps the oxygen saturation estimate to predetermined calibration coefficients of the calibration data.

11. A computer-readable medium as described in claim 10, wherein the method further includes a step of forcing the regression to use a linear rational mapping when evaluating the compensation function.

12. An apparatus including at least one processor and at least one memory containing computer program code, said at least one memory and said computer program code controlling operation of said apparatus by said at least one processor; The device comprises: a photoplethysmography signal measured in a test volume of the individual; and light intensity acquired by a photoplethysmograph at two or more points along the photoplethysmographic signal; and an oxygen saturation estimate; and Calibration data and determining a compensation function from the oxygen saturation estimate and the calibration data, the compensation function being a function of the oxygen saturation estimate; Identifying a ratio between the light intensity function and the compensation function evaluates the change in arterial blood volume in the test volume between the two or more time points, thereby evaluating the individual's PAT. The device is configured to:

13. The apparatus of claim 12, further comprising a computer-readable medium according to any one of claims 1 to 11, wherein the computer program code comprises the computer-executable instructions of the computer-readable medium.

14. 14. A device according to claim 12 or 13, a light source configured to emit light; a sensor configured to photoplethysmographically collect propagated light corresponding to light transmitted or reflected as it propagates through the distal end of the individual's finger at the two or more time points, and further configured to determine the light intensity of the propagated light at the two or more time points; The system further comprises:

15. A computer-readable storage medium containing computer-executable instructions for controlling the operation of a processor, The computer-executable instructions include: a photoplethysmography signal measured in a test volume of the individual; and light intensity acquired by a photoplethysmograph at two or more points along the photoplethysmographic signal; and an oxygen saturation estimate; and and instructions to obtain calibration data. instructions for determining, from the oxygen saturation estimate and the calibration data, a compensation function, the compensation function being a function of the oxygen saturation estimate; instructions to assess a change in arterial blood volume in the test volume between the two or more time points by determining a ratio between the function of light intensity and the compensation function, thereby assessing PAT of the individual; and A computer-readable storage medium comprising:

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