Apparatus and method for compensating for peripheral arterial tone assessment

Abstract

A computer-implemented method for evaluating peripheral arterial tension (PAT) (100) in an individual (1) monitored by optical plethysmography, comprising: - obtaining: o an optical plethysmography signal (101) measured at a study volume (11); o light intensity (102; 103) acquired at two or more time points (12; 13) along the optical plethysmography signal (101); o oxygen saturation estimation (104); o calibration data (105); - determining a compensation function (14) from the oxygen saturation estimation (104) and the calibration data (105); wherein the compensation function (14) is a function of the oxygen saturation estimation (104); and - determining a ratio (15) of the function of the light intensity (102; 103) to the compensation function (14) to assess changes in arterial blood volume (16) in the study volume (11) between the two or more time points (12; 13), and thereby assessing PAT (100).

Description

Technical Field

[0001] This invention generally relates to methods and apparatus for assessing peripheral arterial tension, or PAT. More specifically, this invention relates to robustly monitoring peripheral arterial tension to detect, for example, sleep-related events. Background Technology

[0002] During an individual's cardiac cycle, that is, the period between two heartbeats, blood is pumped through the individual's vascular system in a pulsating manner. In other words, during the cardiac cycle, the amount of blood in various parts of the body, such as the fingers, nostrils, ears, forehead, inside the mouth, toes, wrists, and ankles, cyclically increases and decreases. The blood contained in arteries is called arterial blood. The blood contained in veins is called venous blood.

[0003] A common method for measuring such fluctuations in blood volume is optical plethysmography (OPG), in which changes in blood volume in the tissue microvascular bed are detected using an optical plethysmogram or photoplethysmogram (PPG). PPG is typically obtained by illuminating a study volume with light from one or more light sources (e.g., LEDs) and detecting the collected light corresponding to the light reflected or transmitted in the study volume on a sensor, which may include or correspond to a photodetector, such as a photodiode. The light source and sensor may be arranged, for example, on opposite sides of an individual's finger, allowing measurement of the transmission pattern PPG, or on the same side of the individual's finger, allowing measurement of the reflection pattern PPG. During each cardiac cycle, the heart pumps arterial blood to the study volume. Physical events corresponding to, for example, changes in arterial blood volume in the study volume during a cardiac cycle can be captured by optical plethysmography.

[0004] In addition to the periodic fluctuations in arterial blood volume, the arterial blood volume in tissues is also affected by the diameter of the arterioles or small arteries within the study volume. These small arteries have muscular walls that can contract to reduce their diameter. In other words, when these small arteries contract and their diameter decreases, the volume of arterial blood contained within the corresponding arteriole decreases significantly. Optical plethysmography (OPP) is a measurement technique used to monitor changes in arterial blood volume in small arteries as their diameter contracts. Therefore, monitoring changes in arterial blood volume via OPP can empirically provide information on the relative changes in muscle tone, or “tension,” of the smooth muscle tissue of small arteries, also known as peripheral arterial tension (PAT).

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

[0006] Reabsorption of breath at the end of sleep apnea typically coincides with the release of adrenaline. Adrenaline is released into the bloodstream and binds to adrenergic receptors in the arterioles of the study volume. This triggers an increase in arteriolar tone, leading to a decrease in arteriolar diameter and arterial blood volume in the study volume. Therefore, monitoring peripheral arterial tone via, for example, optical plethysmography can provide valuable information about the occurrence of sleep-related events such as sleep apnea.

[0007] Hemoglobin is the primary molecule that scatters emitted light onto the volume under study during optical plethysmography (OPP). Hemoglobin comprises oxyhemoglobin (also known as HbO2) and deoxyhemoglobin (also known as Hb). The degree of oxygenation of hemoglobin in arterial blood is called oxygen saturation or SpO2. The degree of light absorption and scattering caused by HbO2 differs significantly from that of Hb and also depends on the wavelength of the light used in the OPP.

[0008] As a result, optical plethysmography depends not only on the arterial blood volume within the studied volume but also on the hemoglobin composition of that arterial blood volume, characterized by oxygen saturation. In other words, when attempting to measure changes in PAT monitored by optical plethysmography, the measurement can be greatly influenced by changes in the oxygen saturation of the monitored arterial blood volume. For example, during apnea, when less oxygen is supplied to the lungs, the proportion of HbO2 in the arterial blood volume within the studied individual volume decreases.

[0009] For example, WO98 / 04182 describes a method and apparatus for detecting medical conditions by monitoring peripheral arterial tension. As described, for example, in EP1534115A2, the apparatus of EP1534115A2 relies on a wavelength for performing optical plethysmography, for which the degree of absorption and scattering caused by HbO2 at that particular wavelength is the same as the degree of absorption and scattering caused by Hb at that particular wavelength. This wavelength is called the isoabsorption wavelength. Therefore, the light intensity measured by optical plethysmography in EP1534115A2 depends less on the hemoglobin composition of arterial blood volume, in other words, on the value of oxygen saturation, when dependent on this isoabsorption wavelength.

[0010] For example, the solution described in EP1534115A2 requires the use of three light sources to monitor PAT via optical plethysmography: two light sources do not produce light of isoabsorption wavelengths to estimate oxygen saturation, and a third light source produces light of isoabsorption wavelengths to estimate peripheral arterial tension. Using three light sources increases the cost and size of the device compared to a system that includes only two light sources. Summary of the Invention

[0011] Therefore, the object of embodiments of the present invention is to provide a computer-implemented method and apparatus that does not exhibit the inherent disadvantages of the prior art. More specifically, the object of embodiments of the present invention is to provide a method and apparatus for accurately and robustly minimizing the influence of changes in the hemoglobin composition of the monitored arterial blood volume on the optical measurement of peripheral arterial tension, without the need for isoabsorption wavelengths.

[0012] The scope of protection sought by the various embodiments of the present invention is given by the independent claims.

[0013] Embodiments and features described in this specification that are not within the scope of the independent claims (if any) shall be interpreted as examples useful for understanding the various embodiments of the invention.

[0014] It is necessary to eliminate the influence of changes in oxygenation and deoxygenated hemoglobin concentrations on optical measurements of peripheral arterial tension.

[0015] The purpose of embodiments of the present invention is to reduce the impact of changes in the hemoglobin composition of the monitored arterial blood volume on the measurement of peripheral arterial tension using optical plethysmography.

[0016] According to a first exemplary aspect of the invention, this objective is achieved by a computer-implemented method for evaluating peripheral arterial tension (PAT) in an individual monitored by optical plethysmography, wherein the method comprises the following steps:

[0017] -get:

[0018] o Optical volumetric recording signal measured at the individual's study volume;

[0019] o The light intensity acquired by optical volumetric imaging at two or more time points along the optical volumetric imaging signal;

[0020] Oxygen saturation estimation;

[0021] o Calibration data;

[0022] - Determine a compensation function from the oxygen saturation estimate and the calibration data; wherein the compensation function is a function of the oxygen saturation estimate; and

[0023] - Determine the ratio of a function of light intensity to a compensation function to assess one or more changes in arterial blood volume in the study volume between two or more time points, and thereby assess an individual's PAT.

[0024] The computer-implemented method according to the invention allows for the accurate and robust determination of peripheral arterial tension. By obtaining an estimate of the oxygen saturation of an individual monitored using optical plethysmography, the hemoglobin composition of the arterial blood volume of the individual in the study volume monitored by optical plethysmography can be determined or estimated. Therefore, the computer-implemented method according to the invention can modulate, or in other words compensate, the optical plethysmography signal by minimizing the influence caused by changes in the hemoglobin composition of the monitored arterial blood volume, so that the light intensity more reliably reflects changes in the monitored arterial blood volume. In other words, the computer-implemented method according to the invention reduces the influence of changes in the hemoglobin composition of arterial blood volume on the optical plethysmography signal, and thereby minimizes or reduces the influence of changes in the hemoglobin composition of arterial blood volume on the optical measurement of peripheral arterial tension. The computer-implemented method actually determines a compensation function, which is a function of the oxygen saturation estimate, and divides the function of the light intensity measured by optical plethysmography by this compensation function of the oxygen saturation estimate. Therefore, the resulting assessment of changes in arterial blood volume in the study volume provides a more accurate and robust assessment of the individual's peripheral arterial tension.

[0025] The computer-implemented method does not rely on the use of a light source that emits light of equal absorption wavelengths. Instead, it is compatible with any conventional setup for optical plethysmography that includes, for example, two light sources, emitting light of two different wavelengths, such as a red wavelength and an infrared wavelength. In other words, the computer-implemented method accurately measures changes in arterial blood volume in a study volume with only two light sources, which is the minimum number of light sources required to determine an oxygen saturation estimate. Peripheral arterial tension is then mathematically derived from the optical plethysmography measurement with two light sources. This allows for miniaturization compared to systems with three light sources and further allows for cost optimization by eliminating the need for a third light source.

[0026] In the context of this invention, the study volume of an individual is, for example, a volume defined in the individual's tissue under study, which is monitored by optical plethysmography, wherein light emitted by optical plethysmography propagates and is collected on a sensor used for optical plethysmography. In other words, the study volume of an individual is, for example, a volume defined in the individual's tissue under study, for which an optical plethysmography signal is acquired. For example, the study volume is the volume of the individual's peripheral tissue. For example, the study volume is a volume defined in the fingers, fingertips, distal ends of the individual's fingers, nostrils, ears, forehead, inside the mouth, toes, tips of the toes, wrists, and the individual's ankles. In the context of this invention, the study volume of an individual includes the individual's skin contained within the study volume, and also includes the arterial blood volume present in the study volume. In the context of this invention, peripheral arterial tension is understood as the change in arterial tension in the study arterial bed within the study volume of an individual. In other words, determining the change in pulsatile volume in the vascular bed of the individual's study volume allows for the determination or assessment of information indicating the muscle tension or 'tonality' of the smooth muscle tissue of the small arteries in the study volume, and thus allows for the determination or assessment of peripheral arterial tension regulated by the sympathetic nervous system. Determining peripheral arterial tension is non-invasive and can be used, for example, to detect heart disease, erectile dysfunction, sleep apnea, obstructive sleep apnea, cardiovascular disease, etc.

[0027] In the context of this invention, an optical volumetric signal is a signal measured by optical volumetric imaging. For example, an optical volumetric signal is an optical volumetric map. For example, an optical volumetric signal is a PPG. An optical volumetric signal is measured, for example, at the fingertip of an individual using an optical volumetric imaging device comprising at least two light sources and sensors. In the context of this invention, light intensity corresponds to the intensity of light collected on the sensors of the optical volumetric imaging device, wherein the light collected on the sensors corresponds to light generated by one or two light sources that is transmitted through or reflected in the studied volume of the individual.

[0028] Blood contained in arteries is called arterial blood. Blood contained in veins is called venous blood. In the context of this invention, an oxygen saturation estimate, or SpO2, or hemoglobin composition corresponds to the fraction of oxyhemoglobin associated with the total amount of hemoglobin in arterial blood volume. For example, an oxygen saturation estimate, or SpO2, or hemoglobin composition corresponds to the ratio of the sum of the concentrations of oxyhemoglobin and deoxyhemoglobin in the arterial blood volume monitored in the study volume. Alternatively, an oxygen saturation estimate, or SpO2, or hemoglobin composition corresponds to the ratio of the volume fraction of oxyhemoglobin to the sum of the volume fractions of deoxyhemoglobin in the arterial blood volume monitored in the study volume.

[0029] In the context of this invention, deoxyhemoglobin is defined as a form of hemoglobin that does not have bound oxygen and does not have any other bound molecules (e.g., carbon monoxide, carbon dioxide, or iron). In the context of this invention, oxyhemoglobin is defined as a form of hemoglobin that has bound oxygen. In the context of this invention, light emitted by a light source of an optical volumetric imaging device comprises photons arriving at a sensor via a probabilistic path through one or more scattering events. This optical path is not straight and is generally assumed to follow a curved spatial probability distribution. The study volume along this curved optical path forms the volume sampled or studied by optical volumetric imaging. In the context of this invention, the change in arterial blood volume in the study volume between two time points corresponds to the relative change between the arterial blood volume present in the study volume at a first time point and the arterial blood volume present in the study volume at a second time point.

[0030] According to the example embodiment, the calibration data includes predetermined calibration coefficients and / or predetermined coefficients; and:

[0031] - Determine the compensation function to correspond to the compensation function derived from predefined coefficients; or

[0032] - Determine the compensation function corresponding to the predetermined calibration coefficient by fitting the oxygen saturation estimate to the calibration ratio.

[0033] In the context of this invention, predetermined coefficients are, for example, known or can be determined from the literature, such as from scientific publications. For example, predetermined coefficients 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 this invention, a chromophore is a molecular unit that absorbs or scatters light in a study volume. For example, examples of chromophores in the context of this invention are melanin molecules, oxyhemoglobin, deoxyhemoglobin, etc. In the study volume, the attenuation of the light intensity of incident light emitted by a light source set by optical volumetric plethysmography follows the Beer-Lambert law, which can be formulated as in equation (1):

[0034]

[0035] in,

[0036] -I0 corresponds to the intensity of the incident light emitted by the light source of the optical volumetric recording device;

[0037] -ε i The extinction coefficient corresponding to chromophore i;

[0038] -V i Corresponding to the volume fraction or concentration of chromophore i in the study volume;

[0039] -d corresponds to the optical path length, which is the length of the path a photon travels before reaching the sensor of an optical volumetric imaging device. The optical path length is a function of the wavelength of the incident light and the composition of the chromophores in the study volume, and the optical path length depends on the distance between the light source emitting the photon and the sensor. In the paper “Montecarlo analysis of optical interactions in Reflectance and transmission finger Photoplethysmography” published by Chatterjee et al. on February 15, 2019 in Sensors (Basel) 19(4):789, doi: 10.3390 / s19040789, the distance between the light source emitting the photon and the sensor is a few millimeters, such as 3 mm or less, and the optical path length can be approximated as constant.

[0040] -G corresponds to the light intensity loss parameter that depends on the scattering, and it depends on the wavelength λ of the incident light emitted by the light source.

[0041] Consider the following parameters:

[0042] -V i，d This corresponds to the volume fraction or concentration of chromophore i in the study volume at the first moment along the optical volume recording signal;

[0043] -V i，s This corresponds to the volume fraction or concentration of chromophore i in the study volume at the second time along the optical volume recording signal;

[0044] -I h This corresponds to the light intensity measured by the sensor of the optical volumetric device at the first time point;

[0045] -I l The light intensity corresponds to the light intensity measured by the sensor of the optical volumetric device at the second time point;

[0046] The Beer-Lambert law expressed in formula (1) can be evaluated at both the first and second time points. When a ratio of these two representations is taken, equation (2) is obtained:

[0047]

[0048] Then, by taking the natural logarithm of both sides of equation (2), we obtain equation (3) as follows:

[0049]

[0050] If we use the base b instead of the logarithm of Euler's number e, equation (3) becomes:

[0051]

[0052] It can be seen that the above equation (3') is equal to equation (3) multiplied by a constant.

[0053] When the difference V i，s -V i，d renamed ΔV i Then, equation (3) can be simplified to equation (4), thus obtaining:

[0054]

[0055] As can be seen from equation (4), the logarithm of the light intensity fraction at the first time point and 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.

[0056] Some chromophores remain attached to the epidermis of an individual between two time points along the optical volumetric signature. For example, melanin molecules remain fixed to the study volume between two time points along the optical volumetric signature. Therefore, the difference in volume fraction or concentration of such chromophores (e.g., melanin molecules) between these two time points is zero. Consequently, the contribution of such chromophores to the right-hand side of equation (4) is zero.

[0057] The primary chromophores whose volume fraction or concentration fluctuates between two time points along the optical volumetric plethysmography signal are oxyhemoglobin and deoxyhemoglobin in arterial blood volume. In the context of this invention, the two main forms of hemoglobin, namely oxyhemoglobin and deoxyhemoglobin, exhibit significantly different absorption and scattering coefficients for most wavelengths of light.

[0058] All other chromophores are neither the effects of oxyhemoglobin nor deoxyhemoglobin, and their volume fraction or concentration fluctuates between two time points along the optical volumetric recording signal, which can be written as their combined extinction coefficient ε. other , and the product of one minus the sum of the volume fractions or concentrations of deoxyhemoglobin and deoxyhemoglobin, where the sum of all volume fractions or concentrations equals 1.

[0059] Taking into account the above factors, equation (4) can then be rewritten as equation (5):

[0060]

[0061]

[0062]

[0063]

[0064] The estimated value of oxygen saturation can be defined according to equation (6):

[0065]

[0066] in,

[0067] - This corresponds to the volume fraction or concentration of oxyhemoglobin contained in arterial blood within the study volume.

[0068] -V Hb This corresponds to the volume fraction or concentration of deoxyhemoglobin contained in arterial blood within the study volume.

[0069] Additionally, V blood Defined as the total volume fraction or total concentration of oxygenated and deoxygenated hemoglobin contained in arterial blood within the study volume, and defined in equation (7) as follows:

[0070]

[0071] It is assumed that under normal circumstances, the sum of the volume fractions or concentrations of oxygenated and deoxyhemoglobin within the arterial blood volume, or the sum of the concentrations of oxygenated and deoxyhemoglobin within the arterial blood volume, remains approximately constant throughout the measurement of the optical plethysmography signal. In reality, during individual monitoring via optical plethysmography, such as during sleep apnea, only the ratio of oxygenated to deoxyhemoglobin, i.e., only the oxygen saturation estimate, may change significantly.

[0072] From equations (6) and (7), we can obtain the following equation:

[0073]

[0074] (1-SpO2)V blood =V Hb (8)

[0075] By substituting expression (8) into equation (5), we can obtain the following:

[0076]

[0077] Two predetermined calibration coefficients, Q1 and Q2, and two constants can be defined as follows:

[0078]

[0079] Q2=ε Hb -ε other

[0080] After rewriting equation (9) with two predetermined calibration coefficients Q1 and Q2 in mind, equation (10) can be obtained, where the left-hand side of equation (10) corresponds to the evaluation function, and Q1SpO2+Q2 corresponds to the compensation function as a function of oxygen saturation estimation:

[0081]

[0082] Therefore, we can obtain equation (11):

[0083]

[0084] Therefore, subtract relation (12) from equation (11):

[0085]

[0086] Relationship (12) is highlighted on the left-hand side, which shows the change ΔV between the first and second time points and the total volume fraction or concentration of oxygenated and deoxygenated hemoglobin in the study volume. blood The linear relationship. Under the assumption of a constant volume fraction or concentration of the total oxygenated and deoxygenated hemoglobin in arterial blood, ΔV blood It is a linear representation of fluctuations in arterial blood volume within a study volume. Therefore, changes in arterial blood volume within a study volume are evaluated by determining the ratio of the light intensity collected on the sensor as a function of oxygen saturation estimation when measured using optical plethysmography.

[0087] According to an exemplary embodiment, at least one of these time points corresponds to cardiac diastole during the individual's cardiac cycle, and / or at least one of these time points corresponds to cardiac contraction during the individual's cardiac cycle.

[0088] During cardiac systole, the volume of arterial blood in the individual's study volume is at its maximum, resulting in maximum absorption and scattering of light at any point in time within the cardiac cycle (i.e., the period between two heartbeats), because hemoglobin is one of the main absorbers and scatterers of photons in the study volume, thus leading to the lowest measurable light intensity on the sensor of the optical volumetric plethysmography device. Conversely, during cardiac diastole, the volume of arterial blood in the individual's study volume is at its minimum, resulting in minimum absorption and scattering of light at any point in time within the cardiac cycle, and thus leading to the highest measurable light intensity on the sensor of the optical volumetric plethysmography device. At least one first time point corresponds, for example, to the diastolic phase of a first cardiac cycle, and / or at least one second time point corresponds, for example, to the systolic phase of a second cardiac cycle different from the first cardiac cycle. Alternatively, at least one first time point corresponds, for example, to the systolic phase of a first cardiac cycle, and / or at least one second time point corresponds, for example, to the diastolic phase of a second cardiac cycle different from the first cardiac cycle. Alternatively, at least one first time point corresponds, for example, to the systolic or diastolic phase of a cardiac cycle, and at least one second time point corresponds to any point in time within the same cardiac cycle or different cardiac cycles.

[0089] According to the example embodiment, at least two of the two or more time points are within one cardiac cycle of the individual.

[0090] From equation (4), the logarithm of the light intensity fractions during systole and diastole is linearly correlated with the change in the integral number or concentration of the chromophore between systole and diastole. To achieve the highest signal-to-noise ratio during measurements using an optical plethysmography device, it is preferable to perform measurements at at least two distinct time points within a cardiac cycle, where these at least two time points indicate a large difference in light intensity on the sensor, and therefore a large difference in arterial blood volume. The two time points corresponding to this maximum difference typically fall during diastole and systole within a cardiac cycle.

[0091] According to an exemplary embodiment, the method further includes the steps of: determining an evaluation function as a function of light intensity; and wherein determining the ratio corresponds to determining the ratio of the evaluation function to the compensation function.

[0092] 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 natural logarithm of the function of light intensity, or a Taylor series approximation of the function of light intensity, or a linear approximation of other fundamental logarithms of the function of light intensity. The change in arterial blood volume in the study volume between two or more time points is then evaluated by determining the ratio of the evaluation function to the compensation function, thereby assessing peripheral arterial tension.

[0093] According to the example embodiment, the evaluation function corresponds to the logarithm of the function of light intensity.

[0094] 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, or a Taylor series approximation of the function of light intensity, or a linear approximation of other fundamental logarithms of the function of light intensity. Alternatively, the evaluation function roughly corresponds to the ratio of the pulsating waveform or AC component of the optical volumetric signal to the slowly varying baseline or DC component of the optical volumetric signal, resulting in equation (13):

[0095]

[0096] According to an exemplary embodiment, the evaluation function corresponds to the logarithm of the ratio of light intensity; and wherein the evaluation function depends on one or more of the following:

[0097] - Optical path length;

[0098] - A function for estimating oxygen saturation;

[0099] - Changes in arterial blood volume within the study volume.

[0100] Therefore, the left-hand side of equation (10) corresponds to the evaluation function, which is the logarithm of the ratio of light intensity measured by the sensor when studying the study volume of an individual using optical volumetric plethysmography.

[0101] According to an exemplary embodiment, the method further includes the following steps:

[0102] - Provide a first light source configured to emit light of a first wavelength;

[0103] - Provide a second light source configured to emit light of a second wavelength;

[0104] - Provide sensors;

[0105] - By using optical volumetric plethysmography and collecting the propagating light on a sensor, the propagating light corresponds to the light that is transmitted or reflected when propagating at two or more time points at the distal end of an individual's finger;

[0106] - For a first wavelength, determine the first light intensity of the light propagating on the sensor at the two or more time points;

[0107] - For the second wavelength, determine the second light intensity of the light propagating on the sensor at the two or more time points;

[0108] - Determine a first ratio corresponding to the ratio of the first light intensity at the first wavelength;

[0109] - Determine a second ratio corresponding to the ratio of the second light intensity at the second wavelength; and

[0110] - Fit the oxygen saturation estimate to the calibration ratio to determine the predetermined calibration coefficient.

[0111] Oxygen saturation estimation can be obtained, for example, from a reference measurement obtained by optical plethysmography. Alternatively, oxygen saturation estimation can be obtained, for example, by any other suitable device or method for measuring oxygen saturation near the studied volume being evaluated. For example, the evaluation function can be measured by a sensor of an optical plethysmography device. Using the light intensity collected by optical plethysmography for a first wavelength λ1 and the light intensity collected by optical plethysmography for a second wavelength λ2, a predetermined calibration coefficient for the compensation function for the first wavelength λ1 is determined by calculating the following equation (14). and and the predetermined calibration coefficient for the first wavelength λ2 and compensation function Become possible:

[0112]

[0113] It simplifies to equation (15):

[0114]

[0115] The left-hand side of equation (15), namely the calibration ratio, can be calculated from the measurements of the sensors of the optical volumetric recording devices with two wavelengths λ1 and λ2.

[0116] Alternatively, to illustrate the nonlinearity not properly captured by the above theory, equation (12) can be rewritten in equation (16) as follows:

[0117]

[0118] in It is the compensation function corresponding to the first wavelength λ1, and it is an invariant function of SpO2.

[0119] Then, given equation (16), equation (14) can be rewritten in equation (17) as follows:

[0120]

[0121] in It is the compensation function corresponding to the second wavelength λ2.

[0122] Optical plethysmography (OPP) utilizes simple and non-invasive devices, such as probes or biosensors. OPP biosensors non-invasively measure changes in pulsatile arterial volume within a study volume by collecting optical plethysmography signals, thereby assessing PAT (pulsatile arterial volume). The first and / or second light source is, for example, an LED or any other suitable light source, which can be miniaturized to fit the OPP biosensor. The first wavelength is different from the second wavelength. For example, the first and second wavelengths are included in the red spectrum. Alternatively, the first wavelength may be included in the red spectrum, and the second wavelength in the infrared spectrum. The physical distance between the light source and the sensor is, for example, a few millimeters, such as less than 3 mm.

[0123] According to an exemplary embodiment, the method further includes the following steps:

[0124] - Light propagating on the sensor is collected by optical volumetric imaging, the propagating light corresponding to the first or second wavelength transmitted or reflected when propagating within the study volume of the individual at two or more time points; and

[0125] - Determine the light intensity of the light propagating on the sensor at two or more time points.

[0126] According to the example embodiment, oxygen saturation estimation depends on the ratio of the concentration of oxyhemoglobin in arterial blood volume to the total concentration of oxyhemoglobin and deoxyhemoglobin.

[0127] According to an example embodiment, the method further includes the step of determining an estimate of oxygen saturation in the vicinity of the individual's study volume (e.g., near the distal end of the individual's finger).

[0128] According to the example embodiment, the compensation function is derived from a regression that maps oxygen saturation estimates to predetermined calibration coefficients.

[0129] The estimated compensation function corresponds to a least-squares regression that maps, for example, the oxygen saturation estimate to predetermined calibration coefficients. After data collection, for example in a clinical trial, the oxygen saturation estimate can be fitted to the left-hand side of equation (15) to determine the predetermined calibration coefficients, thereby estimating the compensation function. In other words, the least-squares regression maps the oxygen saturation estimate to the left-hand side of equation (15).

[0130] According to an example embodiment, the method further includes the step of: forcing the regression to use a first-order rational mapping when evaluating the compensation function.

[0131] For example, the method also includes a step of forcing least squares regression to use a first-order rational mapping when estimating the compensation function. In the least squares regression mapping of oxygen saturation estimates to equation (15)... Subsequently, predetermined calibration coefficients are generated by forced linear regression using first-order rational mappings (i.e., first-order polynomials in the numerator and denominator) and least-squares fitting. and The best estimate is obtained down to a constant scalar. This is due to the measurable parameter and ΔV. blood The linear relationship between them is relevant, so it is sufficient to determine the predetermined calibration coefficients to achieve the constant factor.

[0132] Alternatively, referring to equation (17), the compensation function can be determined again through least squares regression. and compensation function This least-squares regression maps the measured reference oxygen saturation estimate to the known right-hand side of equation (17). The only restriction to the regression is that the mapping utilizes factorless functions of the oxygen saturation estimate in the numerator and denominator.

[0133] According to a second example aspect, an apparatus is disclosed, wherein the apparatus includes 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 to cause the apparatus to execute using the at least one processor:

[0134] -get:

[0135] o Optical volumetric recording signal measured at the individual's study volume;

[0136] o The light intensity acquired by optical volumetric imaging at two or more time points along the optical volumetric imaging signal;

[0137] Oxygen saturation estimation;

[0138] o Calibration data;

[0139] - Determine a compensation function from the oxygen saturation estimate and the calibration data; wherein the compensation function is a function of the oxygen saturation estimate; and

[0140] - Determine the ratio of a function of light intensity to a compensation function to assess one or more changes in arterial blood volume in the study volume between two or more time points, and thereby assess an individual's PAT.

[0141] The computer-implemented method according to the invention allows for the accurate and robust determination of peripheral arterial tension. By obtaining an estimate of the oxygen saturation of an individual monitored using optical plethysmography, the hemoglobin composition of the arterial blood volume of the individual in the study volume monitored by optical plethysmography can be determined or estimated. Therefore, the computer-implemented method according to the invention can adjust, or in other words, compensate the optical plethysmography signal measured by optical plethysmography, such that the light intensity more reliably reflects changes in the monitored arterial blood volume by minimizing the influence caused by changes in the hemoglobin composition of the monitored arterial blood volume. In other words, the computer-implemented method according to the invention reduces the influence of changes in the hemoglobin composition of the arterial blood volume on the optical plethysmography signal, and thereby minimizes or reduces the influence of changes in the hemoglobin composition of the arterial blood volume on the optical measurement of peripheral arterial tension. The computer-implemented method actually determines a compensation function, which is a function of the oxygen saturation estimate, and divides the function of the light intensity measured by optical plethysmography by this compensation function of the oxygen saturation estimate. Therefore, the resulting assessment of changes in arterial blood volume in the study volume provides a more accurate and robust assessment of the individual's peripheral arterial tension.

[0142] This device does not rely on a light source that emits light at the same absorption wavelength. It is compatible with any conventional setup for optical plethysmography that includes, for example, two light sources, emitting light at two different wavelengths, such as a red wavelength and an infrared wavelength. In other words, the device accurately measures changes in arterial blood volume in the study volume using a measurement setup with only two light sources—the minimum number of light sources required to determine an estimate of oxygen saturation. Peripheral arterial tension is then mathematically derived from the optical plethysmography measurement with two light sources using this device. This allows for miniaturization compared to optical plethysmography systems that include three light sources, and also allows for cost optimization by eliminating the need for a third light source.

[0143] According to an exemplary embodiment, a system is provided, wherein the system includes apparatus according to a second exemplary aspect of the invention, and further includes:

[0144] - A light source configured to emit light; and

[0145] - A sensor configured to collect propagating light by optical volumetric plethysmography, the propagating light corresponding to light transmitted or reflected when propagating in the study volume of the individual at two or more time points; and further configured to determine the light intensity of the light propagating at the two or more time points.

[0146] The sensor collects propagating light via optical plethysmography, where the propagating light corresponds to light transmitted or reflected as it propagates within the study volume of the individual (e.g., the distal end of the individual's finger) at two or more time points. The system may also optionally include a wireless transmitter comprising a wireless communication interface, wherein the wireless transmitter is configured to wirelessly transmit the determined peripheral arterial tension 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.

[0147] According to a third example aspect, a computer program product is provided, which includes computer-executable instructions for causing a system to perform at least the following operations:

[0148] -get:

[0149] o Optical volumetric recording signal measured at the individual's study volume;

[0150] o The light intensity acquired by optical volumetric imaging at two or more time points along the optical volumetric imaging signal;

[0151] Oxygen saturation estimation;

[0152] o Calibration data;

[0153] - Determine a compensation function from the oxygen saturation estimate and the calibration data; wherein the compensation function is a function of the oxygen saturation estimate; and

[0154] - Determine the ratio of a function of light intensity to a compensation function to assess one or more changes in arterial blood volume in the study volume between two or more time points, and thereby assess an individual's PAT.

[0155] According to a fourth example aspect, a computer-readable storage medium is provided, wherein the computer-readable storage medium includes computer-executable instructions for performing the following steps when the program is run on a computer:

[0156] -get:

[0157] o Optical volumetric recording signal measured at the individual's study volume;

[0158] o The light intensity acquired by optical volumetric imaging at two or more time points along the optical volumetric imaging signal;

[0159] Oxygen saturation estimation;

[0160] o Calibration data;

[0161] - Determine a compensation function from the oxygen saturation estimate and the calibration data; wherein the compensation function is a function of the oxygen saturation estimate; and

[0162] - Determine the ratio of a function of light intensity to a compensation function to assess one or more changes in arterial blood volume in the study volume between two or more time points, and thereby assess an individual's PAT. Attached Figure Description

[0163] Some exemplary embodiments will now be described with reference to the accompanying drawings.

[0164] Figure 1 An example embodiment of the device according to the invention is depicted.

[0165] Figure 2 An example embodiment of a system according to the invention, including the apparatus according to the invention, is described.

[0166] Figure 3 An example embodiment of a system according to the invention, including the apparatus according to the invention, is described.

[0167] Figure 4A and 4B An example embodiment of the calibration of the device according to the invention is depicted.

[0168] Figure 5 An example embodiment of PAT measurement of an individual evaluated by the device according to the invention is depicted.

[0169] Figure 6 An example embodiment of a computer-implemented method according to the present invention is described.

[0170] Figure 7 Example embodiments of suitable computing systems for performing one or more steps in the embodiments of the present invention are shown. Detailed Implementation

[0171] Figure 1 An exemplary embodiment of the device 10 according to the present invention is described. The device 10 includes at least one memory 6 and at least one processor, wherein the memory 6 includes computer program code configured to, together with the at least one processor, cause the device 10 to perform the following:

[0172] -get:

[0173] o Optical volumetric recording signal 101 measured at 11 of the individual's study volume;

[0174] o Light intensities 102 and 103 are collected at two or more time points 12 and 13 along the optical volume recording signal 101 by optical volume recording, wherein light intensity 102 is collected at time point 12 and light intensity 103 is collected at time point 13.

[0175] Oxygen saturation estimated at 104;

[0176] o Calibration data 105;

[0177] - Determine the compensation function 14 from the oxygen saturation estimate 104 and calibration data 105; wherein the compensation function 14 is a function of the oxygen saturation estimate 104; and

[0178] - Determine the ratio 15 of the light intensity 102, 103 as a function of the compensation function 14, thereby assessing one or more changes in the arterial blood volume 16 in the study volume 11 between two or more time points 12, 13, and thereby assessing the individual's PAT100.

[0179] The device 10 acquires one or more of the following: optical volumetric signal 101, light intensity 102, 103, oxygen saturation estimate 104, and calibration data 105 from an external device. According to an alternative embodiment, the device 10 acquires one or more of the following: optical volumetric signal 101, light intensity 102, 103, oxygen saturation estimate 104, and calibration data 105 from memory 6. According to another alternative embodiment, the device 10 acquires one or more of the following: optical volumetric signal 101, light intensity 102, 103, oxygen saturation estimate 104, and calibration data 105 from memory 6 and / or from an external device. The calibration data 105 includes predetermined calibration coefficients 25 and / or predetermined coefficients 26. The device 10 is then further configured to determine a compensation function 14 by deriving a compensation function 14 from the predetermined coefficients 26. According to an optional 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 predetermined calibration coefficients 25 and thus estimating the compensation function 14. Optionally, at least one time point 12 corresponds to the diastolic phase of an individual's cardiac cycle and / or at least one time point 13 corresponds to the systolic phase of an individual's cardiac cycle. The device 10 is configured to determine an evaluation function 17 as a function of light intensities 102, 103. The device then determines a ratio 15 corresponding to the ratio of the evaluation function 17 to the compensation function 14. The evaluation function 17, for example, corresponds to the logarithm of a function of light intensities 102, 103. The evaluation function 17, for example, corresponds to the ratio of functions of light intensities 102, 103. The evaluation function 17 depends on one or more of the following: optical path length, a function of the oxygen saturation estimate, and changes in arterial blood volume in the study volume.

[0180] Figure 2An example embodiment of the system 20 according to the present invention is described. It has the characteristics of... Figure 1 Components with the same label on them perform the same function. Figure 2 The system 20 includes the device 10 according to the invention. Optionally, the system 20 further includes light sources 2 and 3 and a sensor 4. The light sources 2 and 3 are configured to emit light 40. The device 10 is configured to:

[0181] -get:

[0182] o Optical volumetric recording signal 101 measured at the study volume 11 of individual 1;

[0183] o Light intensities 102 and 103 are collected at two or more time points 12 and 13 along the optical volume recording signal 101 by optical volume recording, wherein light intensity 102 is collected at time point 12 and light intensity 103 is collected at time point 13.

[0184] Oxygen saturation estimated at 104;

[0185] o Calibration data 105;

[0186] - Determine the compensation function 14 from the oxygen saturation estimate 104 and calibration data 105; wherein the compensation function 14 is a function of the oxygen saturation estimate 104; and

[0187] - Determine the ratio 15 of the function of light intensity 102, 103 and the compensation function 14, thereby assessing one or more changes in arterial blood volume 16 in study volume 11 between two or more time points 12, 13; and thereby assessing PAT 100 of individual 1.

[0188] The device 10 acquires one or more of the following: optical volumetric signal 101, light intensity 102, 103, oxygen saturation estimate 104, and calibration data 105 from an external device 200 including light sources 2, 3 and / or sensor 4. For example, the external device 200 determines the arterial blood volume pulse in the study volume 11 of individual 1. The external device 200 includes batteries for powering various electrical components 2, 3, 4. The light sources 2, 3 are configured to emit light, i.e., to transmit light 40 to the study volume 11 of the individual attached to the external device 200, for example, to the finger 11 of individual 1 as shown, and more specifically to the distal end 11 of the individual's finger. The external device 200 also 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 sensor 4. The control circuitry may also include memory components for temporarily storing the acquired measurement values. The control circuitry is also coupled to and configured to forward measurement results to wireless interface circuitry 50. Wireless interface 50 may support short-range and / or low-power wireless communication protocols for efficiently transmitting measurements to the receiving section of the system. Wireless interface 50 may operate, for example, according to the Bluetooth Low Energy (BLE) protocol defined by the Bluetooth Special Interest Group or according to the Near Field Communication (NFC) protocol. Operation via such protocols, along with the forwarding of the raw optical volumetric signal 101, allows for miniaturization of the external device 200, making it suitable for use with a finger or nostril and allowing operation over multiple nights. According to an alternative embodiment, device 10 obtains one or more of the optical volumetric signal 101, light intensity 102, 103, oxygen saturation estimate 104, and calibration data 105 from memory 6. According to another alternative embodiment, device 10 obtains one or more of the optical volumetric signal 101, light intensity 102, 103, oxygen saturation estimate 104, and calibration data 105 from memory 6 and / or from external devices including light sources 2, 3 and / or sensors 4. Calibration data 105 includes predetermined calibration coefficients 25 and / or 26. The device 10 is then further configured to determine the compensation function 14 by deriving the compensation function 14 from predetermined coefficients 26. According to an alternative embodiment, the device 10 is configured to determine the compensation function 14 by fitting an oxygen saturation estimate 104 to predetermined calibration coefficients 25. Optionally, at least one time point 12 corresponds to the diastolic phase of an individual's cardiac cycle and / or at least one time point 13 corresponds to the systolic phase of an individual's cardiac cycle. The device 10 is configured to determine an evaluation function 17 as a function of light intensities 102, 103. The device 10 collects propagating light 41 corresponding to light 40 emitted by the first light source 2 or the second light source 3 via optical volumetric plethysmography on the sensor 4, wherein, as it propagates along the distal end of an individual's finger, the light 40 is studied for volumetric transmission or reflection at two or more time points 12, 13 along the optical volumetric plethysmography signal 101.In other words, device 10 collects the light intensity 102 corresponding to the propagating light 41 via optical volumetric plethysmography on sensor 4. This propagating light corresponds to light 40 emitted by the first light source 2 or the second light source 3, wherein when propagating at the distal end of the finger of individual 1, light 40 is transmitted or reflected by the study volume 11, and is collected on sensor 4 at a first time point 12; and device 10 collects the light intensity 103 corresponding to the propagating light 41 via optical volumetric plethysmography on sensor 4. This propagating light corresponds to light 40 emitted by the same light source 2 or 3, wherein when propagating at the distal end of the finger of individual 1, light 40 is transmitted or reflected by the study volume 11, and is collected on sensor 4 at a second time point 13. The device then determines a ratio 15 corresponding to the ratio of the evaluation function 17 and the compensation function 14. Evaluation function 17 is, for example, the logarithm of the function of light intensities 102 and 103. Evaluation function 17 is, for example, the ratio of the function of light intensities 102 and 103. The evaluation function 17 depends on one or more of the following: optical path length, a function of the oxygen saturation estimate, and changes in arterial blood volume in the study volume. Device 101 optionally determines an oxygen saturation estimate 104 near the distal end of the finger of individual 1. The estimated compensation function 14 optionally corresponds to determining a regression that maps the oxygen saturation estimate 104 to a predetermined calibration coefficient 25. When evaluating the compensation function 14, device 10 optionally forces the regression to use a first-order rational mapping.

[0189] Figure 3 An example embodiment of the system 20 according to the present invention is described. It has the characteristics of... Figure 1 or Figure 2 Components with the same label on them perform the same function. Figure 3 The system 20 includes the device 10 according to the invention. Optionally, the system 20 further includes light sources 2 and 3 and a sensor 4. The light sources 2 and 3 are configured to emit light 40. The device 10 is configured to:

[0190] -get:

[0191] o Optical volumetric recording signal 101 measured at the study volume 11 of individual 1;

[0192] o Light intensities 102 and 103 are collected at two or more time points 12 and 13 along the optical volume recording signal 101 by optical volume recording, wherein light intensity 102 is collected at time point 12 and light intensity 103 is collected at time point 13.

[0193] Oxygen saturation estimated at 104;

[0194] o Calibration data 105;

[0195] - Determine the compensation function 14 from the oxygen saturation estimate 104 and calibration data 105; wherein the compensation function 14 is a function of the oxygen saturation estimate 104; and

[0196] - Determine the ratio 15 of the function of light intensity 102, 103 and the compensation function 14, thereby assessing the change in arterial blood volume 16 in study volume 11 between two or more time points 12, 13; and thereby assessing the PAT 100 of individual 1.

[0197] Device 10 acquires optical volumetric recording signals 101, light intensities 102, 103, oxygen saturation estimates 104, and calibration data 105 from one or more of the following: light sources 2, 3, and / or sensor 4. For example, device 10 determines the arterial blood volume pulse in the study volume 11 of individual 1. Device 10 includes batteries for powering various electrical components 2, 3, 4. Light sources 2, 3 are configured to emit light, i.e., to transmit light 40 to the study volume 11 of the individual attached to device 10, for example, to the finger 11 of individual 1 as shown, and more specifically to the distal end 11 of the finger of the individual as shown. Device 10 also includes control circuitry for controlling light sources 2, 3, i.e., for enabling or disabling light sources 2, 3, and for receiving the measured arterial blood volume pulse value from sensor 4. The control circuitry may also include memory components for temporarily storing the acquired measurement values. The control circuitry is also coupled to wireless interface circuitry 50 and configured to forward measurement results to wireless interface circuitry 50. Wireless interface 50 may support short-range and / or low-power wireless communication protocols for efficiently transmitting measurements to the receiving section of the system. Wireless interface 50 may operate, for example, according to the Bluetooth Low Energy (BLE) protocol defined by the Bluetooth Special Interest Group or according to the Near Field Communication (NFC) protocol. Operation via such protocols, along with the forwarding of the raw optical volumetric signal 101, allows for miniaturization of device 10, making it suitable for use with a finger or nostril and allowing operation over multiple nights. According to an alternative embodiment, device 10 obtains one or more of the following: optical volumetric signal 101, light intensity 102, 103, oxygen saturation estimate 104, and calibration data 105 from memory 6. According to another alternative embodiment, device 10 obtains one or more of the following: optical volumetric signal 101, light intensity 102, 103, oxygen saturation estimate 104, and calibration data 105 from light sources 2, 3 and / or sensor 4 and / or from memory 6. Calibration data 105 includes predetermined calibration coefficients 25 and / or 26. The device 10 is then further configured to determine the compensation function 14 by deriving the compensation function 14 from predetermined coefficients 26. According to an alternative embodiment, the device 10 is configured to determine the compensation function 14 by fitting an oxygen saturation estimate 104 to predetermined calibration coefficients 25. Optionally, at least one time point 12 corresponds to the diastolic phase of an individual's cardiac cycle and / or at least one time point 13 corresponds to the systolic phase of an individual's cardiac cycle. The device 10 is configured to determine an evaluation function 17 as a function of light intensities 102, 103. The device 10 collects propagating light 41 corresponding to light 40 emitted by the first light source 2 or the second light source 3 via optical volumetric plethysmography on the sensor 4, wherein, as it propagates along the distal end of an individual's finger, the light 40 is transmitted or reflected by the studied volume 11 at two or more time points 12, 13 along the optical volumetric plethysmography signal 101.In other words, device 10 collects the light intensity 102 corresponding to the propagating light 41 via optical volumetric plethysmography on sensor 4. This propagating light corresponds to light 40 emitted by the first light source 2 or the second light source 3, wherein when propagating at the distal end of the finger of individual 1, light 40 is transmitted or reflected by the study volume 11, and is collected on sensor 4 at a first time point 12; and device 10 collects the light intensity 103 corresponding to the propagating light 41 via optical volumetric plethysmography on sensor 4. This propagating light corresponds to light 40 emitted by the same light source 2 or 3, wherein when propagating at the distal end of the finger of individual 1, light 40 is transmitted or reflected by the study volume 11, and is collected on sensor 4 at a second time point 13. The device then determines a ratio 15 corresponding to the ratio of the evaluation function 17 and the compensation function 14. Evaluation function 17 is, for example, the logarithm of the function of light intensities 102 and 103. Evaluation function 17 is, for example, the ratio of the function of light intensities 102 and 103. The evaluation function 17 depends on one or more of the following: optical path length, a function of the oxygen saturation estimate, and changes in arterial blood volume in the study volume. Device 101 optionally determines an oxygen saturation estimate 104 near the distal end of the finger of individual 1. The estimated compensation function 14 optionally corresponds to determining a regression that maps the oxygen saturation estimate 104 to a predetermined calibration coefficient 25. When evaluating the compensation function 14, device 10 optionally forces the regression to use a first-order rational mapping.

[0198] Figure 4A and 4B An example embodiment of the calibration of the device according to the present invention is shown. It has the characteristics of... Figure 1 or Figure 2 or Figure 3 Components with the same designation on the label perform the same function. A first light source 2 is provided and emits light 40 of a first wavelength. A second light source 3 is provided and emits light 40 of a second wavelength. The second wavelength is preferably different from the first wavelength. A sensor 4 is provided. By means of optical volumetric imaging, the propagated light 41 is collected on the sensor 4 at two time points 2 and 3, wherein the propagated light 41 corresponds to the light 40 emitted by the first light source 2 or the second light source 3, and when propagating in the study volume 11 of the individual 1, the light 40 is transmitted or reflected by the study volume of the individual. Figure 4A As shown, for the first wavelength emitted by the light source 2, corresponding to the propagating light 41 collected on the sensor 4, the light intensities of 10⁶ and 10⁷ are measured by the sensor 4 at the first time point 12 and the second time point 13, respectively. Figure 4B As shown, for the second wavelength emitted by the second light source 3, corresponding to the propagating light 41 collected on the sensor 4, the light intensities of 10⁸ and 10⁹ are measured by the sensor 4 at the first time point 12 and the second time point 13, respectively. According to Figure 1 or Figure 2 or Figure 3Alternative embodiments of device 10, for Figure 4A The sensor 4 then determines a first ratio corresponding to the ratio of the first light intensity of 10⁶ to 10⁷ based on the first wavelength. Figure 1 or Figure 2 or Figure 3 Alternative embodiments of device 10, for Figure 4B The sensor 4 then determines a second ratio corresponding to the ratio of the second light intensity 10⁸ to 10⁸, based on the second wavelength. Then, according to... Figure 1 or Figure 2 or Figure 3 In an optional embodiment of device 10, sensor 4 determines a calibration ratio corresponding to a ratio that is a function of a first ratio and a function of a second ratio. According to Figure 1 or Figure 2 or Figure 3 In an alternative embodiment of device 10, sensor 4 then determines a predetermined calibration coefficient by fitting the oxygen saturation estimate to a calibration ratio. According to another alternative embodiment, the determination of the first ratio and / or the second ratio and / or the calibration ratio and / or the predetermined calibration coefficient is performed by any other suitable external device including at least one processor and at least one memory including computer program code, said at least one memory and computer program code being configured to utilize said at least one processor to enable said suitable external device to determine these values.

[0199] Figure 5 An exemplary comparison is shown between uncompensated peripheral arterial tension 401 as a function of time 60 in an individual and compensated peripheral arterial tension 402 as a function of time 60 in the same individual, wherein the uncompensated peripheral arterial tension 401 is determined by optical plethysmography without compensating for the influence of changes in the hemoglobin composition of the monitored arterial blood volume on the measurement of peripheral arterial tension. The compensated peripheral arterial tension 402 is determined by a computer-implemented method according to the invention or by a device according to the invention, i.e., wherein the compensated peripheral arterial tension 402 compensates for the influence of changes in the hemoglobin composition of the monitored arterial blood volume on the measurement of peripheral arterial tension. For clarity, by calculation... Peripheral arterial tension estimation is plotted. According to an alternative embodiment, this is achieved through calculation... Draw a peripheral artery tension estimate. Figure 5 An exemplary embodiment of the oxygen saturation estimation 104, measured simultaneously with the study tension 100, is also shown. Figure 5As shown, during time period 61, i.e., the period before the vasoconstrictive event, the oxygen saturation estimate 104 was high, and uncompensated peripheral arterial tension 401 and compensated peripheral arterial tension 402 evolved in a similar manner and overlapped as a function of time 60 at the baseline value before the vasoconstrictive event. During time period 62, the value of the oxygen saturation estimate 104 decreased slowly, serving as an indication of an event (e.g., a sleep-related event, such as sleep apnea) occurring in the monitored individuals. Figure 5 As can be seen, uncompensated peripheral arterial tension 401 and compensated peripheral arterial tension 402 develop in a similar manner, but no longer overlap in the corresponding time period 62. In fact, the mean uncompensated baseline 403 of the evolution of uncompensated peripheral arterial tension 401 during time period 62 is greater than the mean compensated baseline 404 of the evolution of compensated peripheral arterial tension 402. This clearly demonstrates the effect of compensating for the influence of changes in the hemoglobin composition of the monitored arterial blood volume on the measurement of peripheral arterial tension. During time period 63, the value of oxygen saturation estimate 104 reaches its slowest point, corresponding to events occurring at the monitored individuals, such as sleep-related events, such as sleep apnea. Figure 5 As can be seen, uncompensated peripheral arterial tension 401 and compensated peripheral arterial tension 402 develop in a similar manner, but compensating for the impact of changes in hemoglobin composition of the monitored arterial blood volume on the measurement of peripheral arterial tension 100 allows for more accurate detection of events. In fact, a decrease in peripheral arterial tension 100 indicates vasoconstriction in the arteries and arterioles within the monitored study volume. This vasoconstriction event can be correlated with the occurrence of events in the monitored individual, such as sleep-related events like sleep apnea. Figure 5As shown, the decrease in uncompensated peripheral arterial tension 402 between the pre-vasoconstriction baseline value and the minimum point of uncompensated peripheral arterial tension 402 is less than the decrease in compensated peripheral arterial tension 401 between the pre-vasoconstriction baseline value and the minimum point of compensated peripheral arterial tension 401. For example, a predetermined threshold 400 for peripheral arterial tension 100 can be used to detect whether an event, such as a sleep-related event, such as sleep apnea, has occurred at the monitored individual: when peripheral arterial tension 100 is above the predetermined threshold 400, no event is detected, but when peripheral arterial tension 100 is below the predetermined threshold 400, an event is detected. The decrease in uncompensated peripheral arterial tension 402 between the pre-vasoconstriction event baseline value and the minimum point of uncompensated peripheral arterial tension 402 keeps uncompensated peripheral arterial tension 402 above the predetermined threshold 400, resulting in no detection of events, such as sleep-related events, such as sleep apnea, occurring at the monitored individual. On the other hand, the decrease in compensated peripheral arterial tension 401 between the baseline value of the pre-vasoconstriction event and the lowest point of the compensated peripheral arterial tension 401 causes the compensated peripheral arterial tension 401 to drop below a predetermined threshold 400, which leads to the detection of events occurring at the monitored individual, such as sleep-related events, such as sleep apnea. Therefore, it can be seen that compensating for the effect of changes in the hemoglobin composition of the monitored arterial blood volume on the measurement of peripheral arterial tension 100 allows for more accurate and robust detection of events occurring at the monitored individual, such as sleep-related events, such as sleep apnea.

[0200] Figure 6 An exemplary embodiment of a computer-implemented method for evaluating peripheral arterial tension (PAT) in an individual monitored by optical plethysmography is shown, wherein the method includes the following steps:

[0201] - In step 501, we obtain:

[0202] o Optical volumetric recording signal measured at the study volume of the individual;

[0203] o The light intensity acquired by optical volumetric imaging at two or more time points along the optical volumetric imaging signal;

[0204] Oxygen saturation estimation;

[0205] o Calibration data;

[0206] - In a second step 502, which follows the first step 501, a compensation function is determined from the oxygen saturation estimate and the calibration data; wherein the compensation function is a function of the oxygen saturation estimate; and

[0207] - In a third step 503, which follows the second step 502, the ratio of the light intensity as a function of the compensation function is determined, thereby assessing one or more changes in arterial blood volume in the study volume between the two or more time points, and thereby assessing the individual's PAT.

[0208] Figure 7 A suitable computing system 800 capable of implementing various embodiments of the system is illustrated. The computing system 800 can generally be configured as a suitable general-purpose computer and includes a bus 810, a processor 802, 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 wires allowing communication between components of the computing system 800. The processor 802 may include any type of conventional processor or microprocessor that interprets and executes programmed instructions. The local memory 804 may include random access memory (RAM) or another type of dynamic storage device storing information and instructions for execution by the processor 802, and / or read-only memory (ROM) or another type of static storage device storing static information and instructions for use by the processor 802. The input interface 814 may include one or more conventional mechanisms allowing an operator or user to input information into the computing device 800, such as a keyboard 820, a mouse 830, a pen, voice identification and / or biometric devices, a camera, etc. Output interface 816 may include one or more conventional mechanisms, such as display 840, for outputting information to an operator or user. Communication interface 812 may include any transceiver-like mechanism, such as one or more Ethernet interfaces enabling computing system 800 to communicate with other devices and / or systems (e.g., other computing devices 881, 882, 883). The communication interface 812 of computing system 800 can be connected to another computing system via a local area network (LAN) or wide area network (WAN) (e.g., 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, such as one or more local disks, such as SATA disk drives, and controlling data reading from and / or writing to these storage elements 808. While the storage element 808 is described as a local disk, any other suitable computer-readable medium may be used, such as a removable disk, optical storage media such as CDs or DVDs, ROM disks, solid-state drives, or flash memory cards. Therefore, computing system 800 may correspond to... Figure 1 or Figure 2 or Figure 3 The apparatus 10 in the illustrated embodiment.

[0209] As used in this application, the term "circuit" may refer to one or more or all of the following:

[0210] (a) Hardware circuit implementation only, such as implementation only in analog and / or digital circuits, and

[0211] (b) A combination of hardware circuitry and software, such as (if applicable):

[0212] (i) A combination of analog and / or digital hardware circuitry with software / firmware, and

[0213] (ii) Any part of a hardware processor having software (including digital signal processors), software, and memory, which work together to enable a device such as a mobile phone or server to perform various functions.

[0214] (c) Hardware circuitry and / or processors (e.g., microprocessors or a portion thereof) that require software (e.g., firmware) to operate, but which may not exist when software is not required to operate.

[0215] This definition of "circuit" applies to all uses of the term in this application, including in any claim. As another example, as used in this application, the term "circuit" also covers implementations of hardware circuitry or processors (or processors in general) or a portion thereof and their accompanying software and / or firmware. The term "circuit" also includes, for example and if applicable to elements of a particular claim, baseband integrated circuits or processor integrated circuits for mobile devices or similar integrated circuits in servers, cellular network devices, or other computing or networking devices.

[0216] Although the invention has been described with reference to specific embodiments, it will be apparent to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that various changes and modifications can be made to implement the invention without departing from its scope. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description; thus, all variations falling within the scope of the claims are intended to be included within the invention.

[0217] The reader of this patent application will also understand that the words “comprising” or “including” do not exclude other elements or steps, the words “a” or “an” do not exclude a plurality, and a single element such as a computer system, processor, or other integrated unit can perform the functions of the plurality of means described in the claims. No reference numerals in the claims shall be construed as limiting the related claims. When used in the specification or claims, the terms “first,” “second,” “third,” “a,” “b,” “c,” etc., are introduced to distinguish similar elements or steps, and do not necessarily describe an order or chronological sequence. Similarly, the terms “top,” “bottom,” “above,” “below,” etc., are introduced for descriptive purposes and are not necessarily intended to indicate relative positions. It should be understood that such terms are interchangeable where appropriate, and embodiments of the invention can operate in other orders or in directions different from those described or illustrated according to the invention.

Claims

1. A computer-implemented method for assessing peripheral arterial tone, PAT, of an individual monitored by photoplethysmography, wherein the method comprises: - obtaining: o a photoplethysmographic signal measured at a study volume of the individual; o light intensities collected by photoplethysmography at two or more time points along the photoplethysmographic signal; o an oxygen saturation estimate; o calibration data; - determining a compensation function from the oxygen saturation estimate and the calibration data; wherein the compensation function is a function of the oxygen saturation estimate; and - determining a ratio of (a) a function of the light intensities and (b) the compensation function, thereby assessing a change in arterial blood volume in the study volume between the two or more time points, and thereby assessing PAT of the individual.

2. The method according to claim 1, wherein the calibration data comprises predetermined calibration coefficients and / or predefined coefficients; and wherein: - the determining the compensation function derives the compensation function from the predefined coefficients; or - the determining the compensation function corresponds to determining the predetermined calibration coefficients by fitting the oxygen saturation estimate to calibration ratios.

3. The method according to claim 1, wherein at least one of the time points corresponds to diastole in a cardiac cycle of the individual, and / or wherein at least one of the time points corresponds to systole in a cardiac cycle of the individual.

4. The method of any one of claims 1 to 3, wherein the method further comprises: determining an assessment function as a function of the light intensities; and wherein determining the ratio determines a ratio of the assessment function and the compensation function.

5. The method according to claim 4, wherein the assessment function corresponds to the light intensities.

6. The method according to claim 4, wherein the assessment function corresponds to a logarithm of a ratio of the light intensities; and wherein the assessment function depends on one or more of: - a light path length; - a function of the oxygen saturation estimate; and - the change in arterial blood volume in the study volume.

7. The method according to claim 2, wherein the method further comprises: - providing a first light source configured to emit light of a first wavelength; - providing a second light source configured to emit light of a second wavelength; - providing a sensor; - collecting, by photoplethysmography and on the sensor, propagated light corresponding to the light transmitted or reflected when propagating in the study volume of the individual at the two or more time points; - determining, for the first wavelength, first light intensities of the light propagated on the sensor at the two or more time points; - determining, for the second wavelength, second light intensities of the light propagated on the sensor at the two or more time points; - determining a first ratio corresponding to a ratio of the first light intensities at the first wavelength; - determining a second ratio corresponding to a ratio of the second light intensities at the second wavelength; - determining the calibration ratios of the function of the first ratio and the function of the second ratio; and - fitting the oxygen saturation estimate to the calibration ratios, thereby determining the predetermined calibration coefficients.

8. The method according to claim 7, wherein the method further comprises the steps of: - collecting, by photoplethysmography and on the sensor, propagated light corresponding to light of the first or second wavelength that is transmitted or reflected when propagating in the study 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 time points.

9. The method according to claim 7 or 8, wherein the method further comprises the step of determining the oxygen saturation estimate near the study volume of the individual.

10. The method according to any one of claims 1 to 3, 7 and 8, wherein the compensation function is derived from a regression that maps the oxygen saturation estimate onto predetermined calibration coefficients of the calibration data.

11. The method according to claim 10, wherein the method further comprises the step of forcing the regression to use a first order rational mapping when evaluating the compensation function.

12. An apparatus for evaluating the peripheral arterial tone, PAT, of an individual, comprising at least one processor and at least one memory including computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus to perform: - obtaining: o an optical plethysmography signal measured at a study volume of an individual; o a light intensity acquired by photoplethysmography at two or more time points along the optical plethysmography signal; o an oxygen saturation estimate; o calibration data; - determining a compensation function from the oxygen saturation estimate and the calibration data; wherein the compensation function is a function of the oxygen saturation estimate; and - determining a ratio of (a) a function of the light intensity and (b) the compensation function, thereby evaluating a change in arterial blood volume in the study volume between the two or more time points and thereby evaluating the PAT of the individual.

13. A system for evaluating the peripheral arterial tone, PAT, of an individual, comprising the apparatus according to claim 12, and further comprising: - a light source configured to emit light; and - a sensor configured to collect, by photoplethysmography, propagated light corresponding to the light that is transmitted or reflected when propagating in a distal part of a finger of the individual at the two or more time points; and further configured to determine the light intensity at the two or more time points.

14. A computer program product comprising computer executable instructions for causing a system to perform at least the following: - obtaining: o an optical plethysmography signal measured at a study volume of an individual; o a light intensity acquired by photoplethysmography at two or more time points along the optical plethysmography signal; o an oxygen saturation estimate; o calibration data; - determining a compensation function from the oxygen saturation estimate and the calibration data; wherein the compensation function is a function of the oxygen saturation estimate; and - determining a ratio of (a) a function of the light intensity and (b) the compensation function, thereby assessing a change in arterial blood volume in the investigation volume between the two or more points in time, and thereby assessing the PAT of the individual.

15. A computer readable storage medium comprising computer executable instructions for performing the following steps when a program comprising the computer executable instructions is run on a computer: - obtaining: o an optical plethysmography signal measured at an investigation volume of an individual; o a light intensity acquired by optical plethysmography at two or more points in time along the optical plethysmography signal; o an oxygen saturation estimate; o calibration data; - determining a compensation function from the oxygen saturation estimate and the calibration data; wherein the compensation function is a function of the oxygen saturation estimate; and - determining a ratio of (a) a function of the light intensity and (b) the compensation function, thereby assessing a change in arterial blood volume in the investigation volume between the two or more points in time, and thereby assessing the PAT of the individual.

Images