Methods, apparatus, storage media, and use of logarithmic or functional approximations thereof for evaluating peripheral arterial tone

Abstract

A computer-implemented method for assessing peripheral arterial tone (100), or PAT, of an individual (1) monitored by photoplethysmography and detecting the occurrence of a sleep-related event through said assessment, comprising the steps of acquiring a photoplethysmography signal (101) measured at a test volume (11) and light intensities (102, 103) acquired at two or more time points (12, 13) along said photoplethysmography signal (101); determining a change in arterial blood volume (16) within said test volume (11) between said two or more time points (12, 13) by determining a logarithm (17) of a function of said light intensities (102, 103) or an approximation (17) thereof, thereby assessing the PAT (100) of said individual (1); and detecting the occurrence of a sleep-related event by determining a decrease in said PAT (100), indicative of vasoconstriction of arteries and arterioles in said test volume (11).

Description

Technical Field

[0001] The present invention generally relates to methods and devices for evaluating Peripheral Arterial Tone (PAT). More specifically, the present invention relates to reliably monitoring peripheral arterial tone, for example, to detect sleep-related events.

Background Art

[0002] During an individual's cardiac cycle, that is, the period between two heartbeats, blood is pumped into the individual's vascular system in a pulsatile manner. In other words, during the cardiac cycle, the blood volume in, for example, the fingers, nostrils, ears, forehead, mouth, toes, wrists, ankles, etc. periodically increases and decreases. The blood in the arteries is called arterial blood. The blood in the veins is called venous blood.

[0003] A common method for measuring blood volume variations is optical plethysmography or photoplethysmography (also called PPG) that uses a photo-plethysmogram to detect changes in the blood volume in the microvascular bed of tissue. PPG is often obtained by irradiating the examination volume with light from one or more light sources such as LEDs and detecting the collected light corresponding to the light reflected or transmitted in the examination volume on a sensor. The sensor may include or correspond to a photodetector such as a photodiode. The light source and the sensor may be arranged on the opposite side of the individual's finger to enable measurement of transmission-mode PPG, or may be arranged on the same side of the individual's finger to enable measurement of reflection-mode PPG. During each cardiac cycle, the heart pumps arterial blood into the examination volume. For example, physical events corresponding to changes in the arterial blood volume in the examination volume during the cardiac cycle can be captured by optical plethysmography.

[0004] Arterial blood volume within a tissue is affected not only by periodic fluctuations in arterial blood volume but also by the diameter of arterioles or arterioles within the sample volume. These arterioles have muscular walls that can constrict, reducing their diameter. In other words, when these arterioles constrict and their diameter decreases, the amount of blood contained in the corresponding arteriole decreases significantly. Optical plethysmography is a measurement technique that can monitor changes in the amount of blood contained in an arteriole when its diameter constricts. Therefore, by monitoring changes in arterial blood volume using optical plethysmography, it is possible to empirically provide information about relative changes in the muscle tone or "tension" (also called peripheral arterial tone or PAT) of the smooth muscle tissue of arterioles.

[0005] Because arterial blood flow to the volume being examined can be regulated by several other physiological phenomena, optical plethysmography may be used to monitor respiration, hypovolemia, and other cardiovascular diseases, such as in the diagnosis of sleep disorders. The diagnosis of sleep disorders is a medical field and involves monitoring a patient's sleep over a certain period, for example, one night or more. Based on the monitoring, various sleep-related events such as apnea episodes, snoring, or limb movements can be identified.

[0006] The resumption of breathing in the terminal stages of sleep apnea typically occurs simultaneously with the release of adrenaline. Adrenaline is released into the bloodstream and binds to adrenaline receptors in the arterioles of the volume being examined. This increases the muscle tone of the arterioles, reduces the diameter of the arterioles of the volume being examined, and decreases arterial blood volume. For this reason, monitoring peripheral arterial tone using optical plethysmography, for example, can provide important information regarding the occurrence of sleep-related events such as sleep apnea. It has been widely reported in several scientific publications that signals obtained by optical plethysmography provide information about changes in arterial tone through changes in the pulse amplitude of the signal. For example, a scientific publication by Hamunen et al., titled "Effect of pain on autonomic nervous system indices derived from photoplethysmography in healthy volunteities," published on May 1, 2012, in the British Journal of Anesthesia, Vol. 108, No. 5, pp. 838-844, reports that the pulse plethysmographic amplitude (also known as PPGA) of photoplethysmography is due to pulsatile changes in tissue volume (mainly arterial blood), and that PPGA decreases during sympathetic nerve activation or vasoconstriction.

[0007] However, monitoring changes in the pulse amplitude of signals obtained by optical plethysmography does not accurately reflect changes in arterial tone. In other words, even if the pulse amplitude of the signal is taken into consideration and its changes are monitored, it is not possible to accurately determine changes in sympathetic nerve tone. [Overview of the project] [Problems that the invention aims to solve]

[0008] Therefore, embodiments of the present invention aim to propose computer-implementable methods and apparatus that do not exhibit the inherent drawbacks of the prior art. More specifically, embodiments of the present invention aim to propose methods and apparatus for accurately and reliably determining changes in peripheral arterial tone by optically measuring changes in arterial blood volume within a test volume. [Means for solving the problem]

[0009] The scope of protection required for various embodiments of the present invention is defined by the independent claims.

[0010] Embodiments and features not included in the independent claims described herein should be interpreted as examples to facilitate understanding of the various embodiments of the present invention.

[0011] In optical measurements of peripheral arterial tone, it is necessary to accurately and reliably determine changes in monitored arterial blood volume.

[0012] According to a first exemplary aspect of the present disclosure, this objective is achieved by a computer-implemented method for evaluating peripheral arterial tone (PAT) of an individual monitored by optical plethysmography and for detecting the occurrence of sleep-related events in the individual as a result of the evaluation, the computer-implemented method is The optical plate measured in the inspection volume of the aforementioned individual Chis Imagery signals and, A step of acquiring the light intensity obtained by optical plethysmography at two or more time points along the optical plethysmography signal, A step of determining the logarithm of the function of light intensity or its function approximation to determine the change in arterial blood volume in the test volume between two or more time points, and thereby evaluating the PAT of the individual, The step includes detecting the occurrence of sleep-related events by determining a decrease in the PAT, which indicates vasoconstriction of arteries and arterioles in the aforementioned examination volume.

[0013] The computer-implemented method according to this disclosure allows for accurate and reliable determination of peripheral artery tone. Compared to methods that monitor changes in the pulse amplitude of optical plethysmography signals, the computer-implemented method according to this disclosure can more accurately determine changes in arterial blood volume within the examination volume between two time points by determining the logarithm of the function of light intensity or its functional approximation. Therefore, compared to conventional solutions, the computer-implemented method according to this disclosure allows for more accurate and reliable evaluation of an individual's PAT. In other words, by evaluating changes in arterial blood volume within the examination volume obtained by determining the logarithm of the function of light intensity or its functional approximation, an individual's peripheral artery tone can be evaluated more accurately and reliably.

[0014] In the context of this disclosure, the examination volume of an individual is, for example, a volume defined in the examination tissue of the individual, which is monitored by optical plethysmography, through which light emitted by optical plethysmography propagates and is collected by a sensor for optical plethysmography. In other words, the examination volume of an individual is, for example, a volume defined in the examination tissue of the individual from which the optical plethysmography signal is acquired. For example, the examination volume is the volume of the peripheral tissue of the individual. For example, the examination volume is the volume defined in the individual's fingers, fingertips, distal ends of fingers, nostrils, ears, forehead, mouth, toes, toe tips, wrists, and ankles. In the context of this disclosure, the examination volume of an individual includes the individual's skin contained within the examination volume, and further includes the amount of blood within the examination volume. In the context of this disclosure, peripheral arterial tone is understood as a change in arterial tone of the examination bed of arteries in the examination volume of the individual. In other words, by determining changes in pulsatile blood volume in the vascular bed of an individual's test volume, information indicating muscle tone or "tension" in the smooth muscle tissue of arterioles within the test volume can be determined or evaluated. This allows for the determination or evaluation of peripheral arterial tone regulated by the sympathetic nervous system. Determining peripheral arterial tone is non-invasive and can be used, for example, to detect heart disease, erectile dysfunction, sleep apnea, obstructive sleep apnea, cardiovascular disease, sleep-related respiratory events, etc.

[0015] In the context of this disclosure, an optical plethysmography signal is a signal measured by optical plethysmography. For example, an optical plethysmography signal is an optical plethysmogram. For example, an optical plethysmography signal is a PPG. An optical plethysmography signal is measured at the fingertip of an individual by an optical plethysmography apparatus comprising, for example, at least one light source and a sensor. In the context of this disclosure, light intensity corresponds to the intensity of light collected by the sensor of the optical plethysmography apparatus, and the light collected by the sensor corresponds to light generated by one or more light sources transmitted through or reflected from the inspection volume of the individual.

[0016] In the context of this disclosure, the oxygen saturation estimate, SpO2, or hemoglobin composition corresponds to the proportion of oxygenated hemoglobin related to the total amount of hemoglobin in the arterial blood volume within the test volume. For example, the oxygen saturation estimate, SpO2, or hemoglobin composition corresponds to the ratio of the concentration of oxygenated hemoglobin to the sum of the concentrations of oxygenated and deoxygenated hemoglobin in the arterial blood volume being monitored within the test volume. Alternatively, the 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 and deoxygenated hemoglobin in the arterial blood volume being monitored within the test volume.

[0017] In the context of this disclosure, deoxygenated hemoglobin is defined as a form of hemoglobin that does not contain bound oxygen and 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 contains bound oxygen. In the context of this disclosure, light emitted by the light source of an optical plethysmography apparatus includes photons that reach the sensor through a stochastic path of one or more scattering events. This optical path is often assumed to be not linear but set according to a curved spatial probability distribution. The volume examined along this curved optical path forms the volume sampled or examined by optical plethysmography. The computer implementation method according to this disclosure evaluates an individual's PAT by evaluating one or more changes in arterial blood volume in the examination volume between two or more time points. In the context of this disclosure, the change in arterial blood volume in the examination volume between two time points corresponds to the relative change between the arterial blood volume present in the examination volume at a first time point and the arterial blood volume present in the examination volume at a second time point different from the first time point. Blood contained within arteries is called arterial blood. Blood contained within veins is called venous blood.

[0018] In the context of this disclosure, a chromophore is a molecular unit that absorbs or scatters light in the inspection volume. For example, in the context of this disclosure, chromophores include melanin molecules, oxygenated hemoglobin, and deoxygenated hemoglobin. In the inspection volume, the attenuation of the light intensity of incident light emitted from the light source of the optical plethysmography apparatus follows the Beer-Lambert law, which can be formulated as shown in equation (1).

number

[0019] The following parameters are given. JPEG0007879054000004.jpg43170The Beer - Lambert law formulated in Equation (1) can be evaluated at the first point and the second point. Taking the ratio of both equations, Equation (2) is obtained.

Number

[0020] Next, by taking the natural logarithm of both sides of Equation (2), the following Equation (3) is obtained.

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[0021] JPEG0007879054000007.jpg6170

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[0022] JPEG0007879054000009.jpg9170

[0023] JPEG0007879054000010.jpg13170

number

[0024] JPEG0007879054000012.jpg14170

[0025] 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 sample volume. Therefore, the difference in either the volume fraction or concentration of chromophores such as melanin molecules between the two time points is NULL. Consequently, the contribution of such chromophores to the right-hand side of equation (4) is NULL.

[0026] The main chromophores whose volume fraction or concentration fluctuates between two time points along an optical plethysmography signal are oxygenated hemoglobin and deoxygenated hemoglobin in arterial blood volume. In the context of this disclosure, the two main forms of hemoglobin, namely oxygenated hemoglobin and deoxygenated hemoglobin, exhibit significantly different absorption and scattering coefficients for most wavelengths of light.

[0027] JPEG0007879054000013.jpg24170

[0028] Considering the above, equation (4) can be rewritten as equation (5) as follows.

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[0029] It is known that an estimate of oxygen saturation can be defined based on the following equation (6).

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[0030] JPEG0007879054000017.jpg15170

number

[0031] Under normal circumstances, it is assumed that the volume fraction or sum of oxygenated and deoxygenated hemoglobin in arterial blood volume, or the sum of oxygenated and deoxygenated hemoglobin concentrations in arterial blood volume, remains approximately constant during the measurement of optical plethysmography signals. In reality, during the process of monitoring an individual using optical plethysmography, for example, during sleep apnea, only the ratio of oxygenated to deoxygenated hemoglobin, i.e., only the estimated oxygen saturation, can change significantly.

[0032] From equations (6) and (7), we can deduce the following:

number

[0033] Substituting equation (8) into equation (5), we get the following:

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[0034] JPEG0007879054000021.jpg16170

[0035] JPEG0007879054000022.jpg15170

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[0036] Equation (10) emphasizes the term on the left side, called the evaluation function, which is, Optical path length d and JPEG0007879054000024.jpg15170

[0037] JPEG0007879054000025.jpg15170

[0038] Assuming a constant estimated oxygen saturation level, the change in arterial blood volume of the test volume between two time points is evaluated by determining the logarithm of the ratio of light intensities collected by the sensor when measured by optical plethysmography at the two time points.

number

[0039] JPEG0007879054000027.jpg17170

[0040] JPEG0007879054000028.jpg10170

[0041] According to the exemplary embodiment, the function of light intensity corresponds to the ratio of light intensities.

[0042] 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 basis logarithm of the function of light intensity. Alternatively, the evaluation function corresponds approximately to the ratio of the pulsating waveform or AC component of the optical plethysmography signal to the slowly changing baseline or DC component of the optical plethysmography signal, thereby yielding equation (13).

number

[0043] According to an exemplary embodiment, at least one of the time points corresponds to the diastole phase of the individual's cardiac cycle, at least one of the time points corresponds to the systole phase of the individual's cardiac cycle, or two or more time points correspond to each of them.

[0044] During systole, the arterial blood volume within the individual's test volume is maximum, resulting in maximum light absorption and scattering at any given time in the cardiac cycle, i.e., during the period between two heartbeats. Since hemoglobin is one of the main absorbers and scatterers of photons within the test volume, the light intensity measured by the optical plethysmography device's sensor is minimum. Conversely, during diastole, the arterial blood volume within the individual's test volume is minimum, resulting in minimum light absorption and scattering at any given time in the cardiac cycle. Therefore, the light intensity measured by the optical plethysmography device's sensor is maximum. At least one first time point corresponds, for example, to diastole in the first cardiac cycle, and at least one second time point corresponds, for example, to systole in a second cardiac cycle different from the first cardiac cycle, or the first and second time points correspond to these diastole or systole, respectively. Alternatively, at least one first time point corresponds, for example, to systole in a first cardiac cycle, and / or at least one second time point corresponds, for example, to diastole in a second cardiac cycle different from the first cardiac cycle. Alternatively, at least one first time point corresponds, for example, to systole or diastole in a cardiac cycle, and at least one second time point corresponds to any time point within the same or different cardiac cycles.

[0045] According to an exemplary embodiment, this method, A step of providing a light source configured to emit light of a certain wavelength, The process of providing sensors, A step of collecting, on the sensor, the propagating light corresponding to the wavelength of light transmitted or reflected as it propagates through the inspection volume of the individual at two or more time points, using optical plethysmography, The process includes determining the light intensity of the light propagating on the sensor at two or more of the aforementioned time points.

[0046] Optical plethysmography technology uses a simple, non-invasive setup probe or biosensor. The optical plethysmography biosensor non-invasively measures changes in pulsatile arterial volume within the examination volume by collecting optical plethysmography signals, thereby evaluating PAT. The light source is, for example, an LED or any other suitable light source that can be miniaturized to fit the optical plethysmography biosensor. This wavelength is, for example, in the red spectrum. Alternatively, this wavelength is in the infrared spectrum. The physical distance between the light source and the sensor is, for example, a few millimeters, or less than 3 mm.

[0047] According to a second exemplary embodiment, an apparatus is disclosed comprising at least one processor and at least one memory containing computer program code, wherein the at least one memory and the computer program code are provided to the apparatus by the at least one processor, The optical plate measured in the inspection volume of the aforementioned individual Chis Imagery signals and, Acquire the light intensity obtained by optical plethysmography at two or more time points along the aforementioned optical plethysmography signal, By determining the logarithm of the function of light intensity or an approximation thereof, the change in arterial blood volume within the examination volume between the two or more time points is determined, and thereby the PAT of the individual is evaluated. The system is configured to detect the occurrence of sleep-related events by determining a decrease in PAT, which indicates vasoconstriction of arteries and arterioles in the aforementioned examination volume.

[0048] The apparatus according to this disclosure allows for accurate and reliable determination of peripheral artery tone. Compared to methods that monitor changes in the pulse amplitude of an optical plethysmography signal, the apparatus according to this disclosure can more accurately determine changes in arterial blood volume within the examination volume between two time points by determining the logarithm of the function of light intensity or its functional approximation. Therefore, compared to conventional solutions, the apparatus according to this disclosure allows for more accurate and reliable evaluation of an individual's PAT. In other words, by evaluating changes in arterial blood volume within the examination volume obtained by determining the logarithm of the function of light intensity or its functional approximation, an individual's peripheral artery tone can be evaluated more accurately and reliably.

[0049] According to an exemplary embodiment, a system comprising an apparatus according to a second exemplary embodiment of the present invention, A light source configured to emit light, A system is provided which is configured to collect, by optical plethysmography, propagating light corresponding to the light transmitted or reflected as it propagates through the inspection volume of the individual at two or more time points, and which is further configured to determine the light intensity of the propagating light at two or more time points.

[0050] The sensor collects propagating light by optical plethysmography, and the propagating light corresponds to the light transmitted or reflected as it propagates through the examination volume of the individual (e.g., the distal end of the individual's finger) at two or more time points. Optionally, the system further includes a wireless communication interface and a wireless transmitter 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.

[0051] According to a third exemplary embodiment, a computer program product comprising instructions that can be executed by a computer, wherein the instructions that can be executed by the computer are at least: The optical plate measured in the inspection volume of the aforementioned individual Chis Imagery signals and, Acquire the light intensity obtained by optical plethysmography at two or more time points along the aforementioned optical plethysmography signal, By determining the logarithm of the function of light intensity or an approximation thereof, the change in arterial blood volume within the examination volume between the two or more time points is determined, and thereby the PAT of the individual is evaluated. A computer program product is provided that is used to detect the occurrence of sleep-related events by determining a decrease in PAT, which indicates vasoconstriction of arteries and arterioles in the aforementioned examination volume.

[0052] According to a fourth exemplary embodiment, a computer-readable storage medium containing instructions that can be executed by a computer, wherein the instructions that can be executed by the computer are, when the program is executed on the computer, The optical plate measured in the inspection volume of the aforementioned individual Chis Imagery signals and, A step of acquiring the light intensity obtained by optical plethysmography at two or more time points along the optical plethysmography signal, A step of determining the logarithm of the function of light intensity or an approximation thereof to determine the change in arterial blood volume in the test volume between two or more time points, and thereby evaluating the PAT of the individual, A computer-readable storage medium is provided for performing the steps of detecting the occurrence of sleep-related events by determining a decrease in PAT, which indicates vasoconstriction of arteries and arterioles in the aforementioned examination volume.

[0053] According to a fifth exemplary embodiment, the use of logarithmic or functional approximations thereof is provided for evaluating peripheral arterial tone (PAT) of an individual monitored by optical plethysmography and for detecting the occurrence of sleep-related events in the individual by said evaluation, The assessment of peripheral artery tone is, The optical plate measured in the inspection volume of the aforementioned individual Chis Imagery signals and, The light intensity obtained by optical plethysmography at two or more time points along the aforementioned optical plethysmography signal and The process of obtaining, A step of determining the logarithm of the function of light intensity or an approximation thereof to determine the change in arterial blood volume in the test volume between two or more time points, and thereby evaluating the PAT of the individual, The step includes detecting the occurrence of sleep-related events by determining a decrease in the PAT, which indicates vasoconstriction of arteries and arterioles in the aforementioned examination volume. [Brief explanation of the drawing]

[0054] Several exemplary embodiments will be described below with reference to the attached drawings.

[0055] [Figure 1] Exemplary embodiments of the apparatus relating to this disclosure are shown. [Figure 2] This document provides exemplary embodiments of the system relating to this disclosure, including the device relating to this disclosure. [Figure 3] This document provides exemplary embodiments of the system relating to this disclosure, including the device relating to this disclosure. [Figure 4] This document illustrates an exemplary embodiment of comparing PAT measurements of an individual evaluated using the apparatus described herein with PAT measurements of an individual evaluated without determining the logarithm of the function of light intensity. [Figure 5] Exemplary embodiments of the computer implementation method relating to this disclosure are shown. [Figure 6]This document illustrates an exemplary embodiment of a suitable computing system for performing one or more steps in an embodiment of the present invention. [Modes for carrying out the invention]

[0056] Figure 1 shows an exemplary embodiment of the apparatus 10 according to the present disclosure. The apparatus 10 includes at least one memory 6 and at least one processor, and the memory 6 is provided to the apparatus 10 by at least one processor. Optical plethysmography signal 101 measured in the sample volume of the individual, The light intensities 102 and 103 obtained by optical plethysmography at two or more time points 12 and 13 along the optical plethysmography signal 101 and This involves obtaining the following: the light intensity 102 is obtained at time 12, and the light intensity 103 is obtained at time 13. By determining the logarithm 17 of the function of light intensity 102, 103 or its function approximation 17, the change in arterial blood volume 16 in the test volume between the two or more time points 12, 13 is determined, and thereby the individual's PAT 100 is evaluated. The computer program code is configured to detect the occurrence of a sleep-related event in the individual 1 by determining a decrease in PAT 100, which indicates vasoconstriction of arteries and arterioles in the aforementioned examination volume 11. The device 10 acquires the optical plethysmography signal 101 or the light intensities 102, 103 or both from an external device. According to an alternative embodiment, the device 10 acquires the optical plethysmography signal 101 and / or the light intensities 102, 103 (optical plethysmography signal or light intensities or both) from memory 6. According to a further alternative embodiment, the device 10 acquires the optical plethysmography signal 101 and / or the light intensities 102, 103 from memory 6 and / or an external device. Optionally, at least one time point 12 corresponds to diastole in the individual's cardiac cycle, and / or at least one time point 13 corresponds to systole in the individual's cardiac cycle. The device 10 is configured to determine an evaluation function 17 corresponding to the logarithm 17 of the function of the light intensities 102, 103 or a function approximation 17 thereof. The evaluation function 17 depends on one or more of the following: optical path length, a function of the estimated oxygen saturation, and changes in arterial blood volume within the examination volume.

[0057] Figure 2 shows an exemplary embodiment of the system 20 according to the present disclosure. Components having the same reference numerals as in Figure 1 perform the same function. The system 20 in Figure 2 includes the apparatus 10 according to the present disclosure. Optionally, the system 20 further includes a light source 2 and a sensor 4. The light source 2 is configured to emit light 40. The apparatus 10 is, The optical plethysmography signal 101 measured in the individual's inspection volume 11, The light intensities 102 and 103 obtained by optical plethysmography at two or more time points 12 and 13 along the optical plethysmography signal 101 and Here, light intensity 102 is obtained at time 12, and light intensity 103 is obtained at time 13. By determining the logarithm 17 of the function of light intensity 102, 103 or its approximation 17, the change in arterial blood volume 16 in the examination volume 11 between two or more time points 12, 13 is determined, and thereby the PAT 100 of individual 1 is evaluated. The system is configured to detect the occurrence of sleep-related events in individual 1 by determining a decrease in PAT100, which indicates vasoconstriction of arteries and arterioles in the examination volume 11. Apparatus 10 acquires optical plethysmography signals 101 and / or light intensities 102, 103 from an external device 200 which includes at least one light source 2 and / or a sensor 4. For example, the external device 200 determines the arterial blood volume pulse in the examination volume 11 of individual 1. The external device 200 includes a battery for supplying power to different electrical components 2, 4. The light source 2 is configured to emit light, i.e., to transmit light 40 to the examination volume 11 of an individual connected to the external device 200, for example, the finger 11 of individual 1 as shown, more specifically the distal end 11 of the individual's finger. The external device 200 further includes a control circuit for controlling the light source 2, i.e., for enabling or deactivating the light source 2, and for receiving measurements from the sensor 4, for example, light intensity measurements. The control circuit may further include a memory component for temporarily storing the obtained measurements. The control circuit is further coupled to a wireless interface circuit 50 and configured to transfer the measurements to the wireless interface circuit 50. The wireless interface 50 may support short-range and / or low-power wireless communication protocols to efficiently transmit measurements to the system's receiver. The wireless interface 50 may operate, for example, according to the BLE protocol or Near Field Communication (NFC) protocol as defined by the Bluetooth Special Interest Group. Operation according to such protocols and the transmission of the raw optical plethysmography signal 101 allows the external device 200 to be miniaturized to fit in a finger or nostril and to operate for multiple nights. According to an alternative embodiment, the device 10 acquires the optical plethysmography signal 101 and / or light intensities 102, 103 from memory 6. According to a further alternative embodiment, the device 10 acquires the optical plethysmography signal 101 and / or light intensities 102, 103 from memory 6 and / or the external device. Optionally, at least one time point 12 corresponds to diastole in the individual's cardiac cycle, and / or at least one time point 13 corresponds to systole in the individual's cardiac cycle. The device 10 is configured to determine an evaluation function 17, which is a function of the light intensities 102 and 103.The external device 200 collects propagating light 41 corresponding to the light 40 emitted from the light source 2 on the sensor 4 using optical plethysmography, and this light 40 is transmitted or reflected by the inspection volume 11 as it propagates along the distal end of the finger of individual 1 at two or more time points 12, 13 along the optical plethysmography signal 101. In other words, the external device 200 collects light intensity 102 corresponding to the propagating light 41 corresponding to the light 40 emitted from the light source 2 on the sensor 4 using optical plethysmography, and this light 40 is transmitted or reflected by the inspection volume 11 as it propagates along the distal end of the finger of individual 1 and is collected on the sensor 4 at a first time point 12. The external device 200 collects light intensity 103 corresponding to propagating light 41 corresponding to light 40 emitted from the same light source 2 on the sensor 4 using optical plethysmography. This light 40 is transmitted or reflected by the examination volume 11 as it propagates along the distal end of the finger of individual 1 and is collected on the sensor 4 at a second time point 13. The device then determines an evaluation function 17. The evaluation function 17 corresponds, for example, to the logarithm of a function of light intensities 102 and 103. The evaluation function 17 corresponds, for example, to the logarithm of the ratio of light intensities 102 and 103. The evaluation function 17 depends on one or more of the following: optical path length, an estimate of oxygen saturation, and changes in arterial blood volume within the examination volume.

[0058] Figure 3 shows an exemplary embodiment of the system 20 according to the present disclosure. Components having the same reference numerals as those in Figure 1 or Figure 2 perform the same function. The system 20 in Figure 3 includes the apparatus 10 according to the present disclosure. Optionally, the system 20 further includes at least one light source 2 and a sensor 4, which are included in the apparatus 10. The light source 2 is configured to emit light 40. The apparatus 10 is, The optical plethysmography signal 101 measured in the individual's inspection volume 11, The optical plethysmography signals 101 are used to obtain the optical plethysmography signals 102 and 103 at two or more time points 12 and 13, where the optical intensity 102 is obtained at time point 12 and the optical intensity 103 is obtained at time point 13. By determining the logarithm 17 of the function of light intensity 102, 103 or its approximation 17, the change in arterial blood volume 16 in the examination volume 11 between two or more time points 12, 13 is determined, and thereby the PAT 100 of individual 1 is evaluated. The system is configured to detect the occurrence of sleep-related events in individual 1 by determining a decrease in PAT100, which indicates vasoconstriction of arteries and arterioles in the examination volume 11. The device 10 acquires optical plethysmography signals 101 and / or light intensities 102, 103 from the light source 2 and / or sensor 4. For example, the external device 10 determines the arterial blood volume pulse in the examination volume 11 of individual 1. The external device 10 includes a battery for supplying power to different electrical components 2, 3, and 4. The light source 2 is configured to emit light, i.e., to transmit light 40 to the examination volume 11 of an individual connected to the external device 10, for example, the finger 11 of individual 1 as shown, more specifically the distal end 11 of the individual's finger as shown. The device 10 further includes a control circuit for controlling the light source 2, i.e., for enabling or deactivating the light source 2, and for receiving arterial blood volume pulse values ​​measured from sensor 4. The control circuit may further include a memory component for temporarily storing the obtained measurements. The control circuit is further coupled to a wireless interface circuit 50 and configured to transfer the measurements to the wireless interface circuit 50. The wireless interface 50 may support short-range and / or low-power wireless communication protocols to efficiently transmit measurements to the system's receiver. The wireless interface 50 may operate, for example, according to the Bluetooth Low Energy (BLE) protocol or the Near Field Communication (NFC) protocol as defined by the Bluetooth Special Interest Group. Operation according to such protocols and the transfer of the raw optical plethysmography signal 101 allows the external device 10 to be miniaturized to fit into a finger or nostril and to operate for multiple nights. According to an alternative embodiment, the device 10 acquires one or more of the optical plethysmography signal 101, light intensity 102, and 103 from the memory 6. According to a further alternative embodiment, the device 10 acquires one or more of the optical plethysmography signal 101, light intensity 102, and 103 from the light source 2 and / or sensor 4 and / or from the memory 6. Optionally, at least one time point 12 corresponds to the diastole phase of the individual's cardiac cycle, and / or at least one time point 13 corresponds to the systole phase of the individual's cardiac cycle.The device 10 is configured to determine an evaluation function 17, which is a function of light intensities 102 and 103. The device 10 collects propagating light 41 corresponding to light 40 emitted from light source 2 by optical plethysmography on sensor 4, and this light 40 is transmitted or reflected by the inspection volume 11 as it propagates along the distal end of the individual's finger at two or more time points 12 and 13 along the optical plethysmography signal 101. In other words, the device 10 collects light intensity 102 corresponding to propagating light 41 corresponding to light 40 emitted from light source 2 by optical plethysmography on sensor 4, and this propagating light 41 is transmitted or reflected by the inspection volume 11 as it propagates along the distal end of the individual's finger and is collected on sensor 4 at a first time point 12. The device 10 collects light intensity 103 corresponding to propagating light 41 corresponding to light 40 emitted from the same light source 2 by optical plethysmography on sensor 4. This light 40 is transmitted or reflected by the examination volume 11 as it propagates through the distal end of the finger of individual 1 and is collected on sensor 4 at a second time point 13. The device then determines an evaluation function 17. The evaluation function 17 corresponds, for example, to the logarithm of a function of light intensities 102 and 103. The evaluation function 17 corresponds, for example, to the logarithm of the ratio of light intensities 102 and 103. The evaluation function 17 depends on one or more of the following: optical path length, an estimate of oxygen saturation, and changes in arterial blood volume within the examination volume.

[0059] Figure 4 shows an exemplary comparison between peripheral arterial tension 401 based on PPG amplitude as a function of time 60 for an individual and peripheral arterial tension 402 based on an evaluation function as a function of time 60 for the same individual, wherein the peripheral arterial tension 401 based on PPG amplitude is evaluated considering the change in pulse amplitude of the optical plethysmography signal, as described in the prior art, and the peripheral arterial tension 402 based on the evaluation function is determined by the computer implementation method or apparatus according to the disclosure, that is, the peripheral arterial tension 402 based on the evaluation function is evaluated by determining the logarithm of the ratio of light intensities measured from the optical plethysmography signal. The plot is labeled JPEG0007879054000030.jpg17170. As can be seen from Figure 4, peripheral arterial tone 401 based on PPG amplitude and peripheral arterial tone 402 based on the evaluation function change similarly as a function of time 60 at the baseline value before the vasoconstriction event. However, during periods 61 and 62, i.e., during events such as sleep-related events, for example, sleep-related respiratory events, as can be seen from Figure 4, peripheral arterial tone 401 based on PPG amplitude and peripheral arterial tone 402 based on the evaluation function change similarly, but do not overlap in the corresponding periods 61 and 62. In fact, during period 61, peripheral arterial tone 401 based on PPG amplitude decreases to level 403, and this value at level 403 is higher than the value at level 404 where peripheral arterial tone 402 based on the evaluation function decreases. Similarly, during period 62, peripheral arterial tone 401 based on PPG amplitude decreased to level 405, a value higher than the value at level 406 where peripheral arterial tone 402 based on the evaluation function decreased. As can be seen from Figure 4, by evaluating peripheral arterial tone 100 by determining the logarithm of the function of light intensity obtained by optical plethysmography, the events that occurred can be detected more accurately. In practice, a decrease in peripheral arterial tone 100 indicates vasoconstriction of arteries and arterioles in the monitored examination volume. This vasoconstriction may be related to events occurring in the monitored individual, such as sleep-related events such as sleep apnea. As can be seen from Figure 4, the decrease in peripheral arterial tone 401 based on PPG amplitude between the baseline value before the vasoconstriction event and the lowest point of peripheral arterial tone 401 based on PPG amplitude is smaller than the decrease in peripheral arterial tone 402 based on the evaluation function between the baseline value before the vasoconstriction event and the lowest point of peripheral arterial tone 402 based on the evaluation function. For example, a predetermined threshold 407 for peripheral arterial tone 100 can be used to detect whether or not an event such as a sleep-related event, such as sleep apnea, is occurring in the monitored individual. If the peripheral arterial tone 100 is above this predetermined threshold 407, no event is detected, but if the peripheral arterial tone 100 is below this predetermined threshold 407, an event is detected.A decrease in peripheral arterial tone 401 based on PPG amplitude, between the baseline value before a vasoconstriction event and the lowest point of peripheral arterial tone 401 based on PPG amplitude, maintains that peripheral arterial tone 401 based on PPG amplitude above a predetermined threshold 407. As a result, sleep-related events such as sleep apnea occurring in the monitored individual become undetectable. On the other hand, a decrease in peripheral arterial tone 402 based on the evaluation function, between the baseline value before a vasoconstriction event and the lowest point of peripheral arterial tone 402 based on the evaluation function, causes peripheral arterial tone 402 based on the evaluation function to fall below a predetermined threshold 407. As a result, sleep-related events such as sleep apnea occurring in the monitored individual become undetectable. Therefore, it can be seen that by evaluating peripheral arterial tone 100 by determining the logarithm of the function of light intensity obtained by optical plethysmography, it becomes possible to detect sleep-related events such as sleep apnea occurring in the monitored individual more accurately and reliably.

[0060] Figure 5 shows an exemplary embodiment of a computer-implemented method for evaluating peripheral arterial tone (PAT) in an individual monitored by optical plethysmography, and this method is, The optical plethysmography signal 101 measured in the inspection volume 11 of individual 1, The light intensities 102 and 103 obtained by optical plethysmography at two or more time points 12 and 13 along the optical plethysmography signal 101 and The first step 501 is to obtain, A second step 502 follows a first step 501, in which a change in arterial blood volume 16 in the examination volume 11 is determined between two or more time points 12, 13 by determining the logarithm 17 of the function of light intensity 102, 103 or an approximation thereof, and thereby the PAT 100 of individual 1 is evaluated. The procedure includes a third step 503, following a second step 502, which involves detecting the occurrence of a sleep-related event in individual 1 by determining a decrease in PAT 100, which indicates vasoconstriction of arteries and arterioles in the examination volume 11.

[0061] Figure 6 shows a suitable computing system 800 that enables the implementation of an embodiment of the system. This computing system 800 can generally be configured as a suitable general-purpose computer and may include 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 memory interface 806, and one or more memory 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 memory that stores information and instructions executed by the processor 802, and / or read-only memory (ROM) or another type of static memory that stores static information and instructions used by the processor 802. The input interface 814 may include one or more conventional mechanisms, such as a keyboard 820, a mouse 830, a pen, a voice recognition and / or biometric authentication mechanism, a camera, etc., that enable an operator or user to input information into the computing device 800. The output interface 816 may include one or more conventional mechanisms, such as a display 840, for outputting information to an operator or user. The communication interface 812 may include one or more mechanisms, such as any transceiver, such as an Ethernet interface, that enable the computing system 800 to communicate with other devices and / or systems, such as other computing devices 881, 882, 883, etc. The communication interface 812 of the computing system 800 can be connected to such other computing systems by a local area network (LAN) or a wide area network (WAN) such as the Internet.The memory element interface 806 may include a Serial ATA (Serial Advanced Technology Attachment, SATA) interface or a SCSI (Small Computer System Interface) memory interface for connecting the bus 810 to one or more memory elements 808, one or more local disks such as SATA disk drives, and for controlling the reading of data from and / or writing of data to these memory elements 808. Although the memory elements 808 are described as local disks, any other suitable computer-readable medium can generally be used, such as removable magnetic disks, optical storage media such as CDs or DVDs, ROM disks, solid-state drives, or flash memory cards. Thus, the computing system 800 may correspond to the device 10 in the embodiment illustrated in Figure 1, Figure 2, or Figure 3.

[0062] As used in this application, the term “circuit” may refer to one or more or all of the following: (a) Hardware-only circuit implementations, such as implementations using only analog and / or digital circuits. (b) A combination of hardware circuitry and software (if applicable), for example, (i) combinations of analog and / or digital hardware circuits and software / firmware, (ii) Any part of a hardware processor (including a digital signal processor) having software and memory that works in conjunction with a device such as a mobile phone or server to perform various functions, (c) Hardware circuits and / or processors, such as microprocessors or parts of microprocessors, which require software (such as firmware) to operate, or which do not require software to operate. This definition of “circuit” applies in all instances where the term is used in this application, including in the claims. As a further example, as used in this application, the term “circuit” encompasses not only a mere hardware circuit, a processor (or more processors), a part of a hardware circuit or processor, and the implementation of its (or their) accompanying software and / or firmware. The term “circuit” may also include, for example, certain elements described in the claims. For instance, it may mean a baseband integrated circuit or application processor integrated circuit in a mobile phone, or a similar integrated circuit in a server, cellular network device, or other network device.

[0063] Although the present invention has been described with reference to specific embodiments, it will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be embodied with various changes and modifications without departing from its scope. These embodiments should be considered in all respects to be exemplary and not limiting, and the scope of the present invention is indicated not by the above description but by the appended claims, and so all changes that fall within the scope of the claims are intended to be encompassed therein.

[0064] Readers of this patent application will understand that the words “comprising” or “comprise” do not exclude other elements or processes, that the words “a” or “an” do not exclude plurals, and that a single element, such as a computer system, processor, or another integrated unit, may perform the functions of several means described in the claims. All reference numerals in the claims should not be construed as limiting each claim. Terms such as “first,” “second,” “third,” “a,” “b,” and “c,” when used herein or in the claims, are introduced to distinguish similar elements or processes and do not necessarily describe a sequential or chronological order. Similarly, terms such as “up,” “down,” “above,” and “below” are introduced for illustrative purposes and do not necessarily indicate relative positions. Terms used in this manner are interchangeable in appropriate contexts, and embodiments of the invention may operate in accordance with the invention in other orders or in directions different from those described or illustrated above. Furthermore, in order to maintain the disclosures made at the time of filing this application, the contents of claims 1 to 10 at the time of filing this application are added below. (Claim 1) A method implemented in a computer for evaluating peripheral arterial tone (100), i.e., PAT, of an individual (1) monitored by optical plethysmography, and for detecting the occurrence of sleep-related events in the individual (1) based on the evaluation, A step of acquiring an optical plethysmography signal (101) measured at the inspection volume (11) of the individual (1), and light intensity (102, 103) obtained by optical plethysmography at two or more time points (12, 13) along the optical plethysmography signal (101), A step of determining the logarithm (17) of the function of the light intensity (102, 103) or its function approximation (17) to determine the change in arterial blood volume (16) in the test volume (11) between two or more time points (12, 13), and thereby evaluating the PAT (100) of the individual (1), The process involves determining the decrease in PAT(100), which indicates vasoconstriction of arteries and arterioles in the aforementioned examination volume (11), thereby detecting the occurrence of sleep-related events in the individual (1). A method implemented in a computer, characterized by including [a certain element]. (Claim 2) The method according to claim 1, characterized in that the function of the light intensity (102, 103) corresponds to the ratio of the light intensity (102, 103). (Claim 3) 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 and, The function (104) for estimating oxygen saturation, The method according to claim 1 or 2, characterized in that it depends on one or more of the following: the change in arterial blood volume (16) in the test volume (11). (Claim 4) The method according to any one of claims 1 to 3, characterized in that at least one (12) of the aforementioned time points (12, 13) corresponds to the diastole phase in the cardiac cycle of the individual (1), and / or at least one (13) of the aforementioned time points (12, 13) corresponds to the systole phase in the cardiac cycle of the individual (1). (Claim 5) The aforementioned method, A step of providing a light source (2) configured to emit light (40) of a certain wavelength, The process of providing the sensor (4), A step of collecting, on the sensor (4), propagating light (41) corresponding to the wavelength of light (40) that is transmitted or reflected when propagating through the inspection volume (11) of the individual (1) at two or more time points (12, 13) using optical plethysmography, A step of determining the light intensity (102, 103) of the propagating light on the sensor (4) at two or more of the aforementioned time points (12, 13) The method according to any one of claims 1 to 4, further comprising: (Claim 6) A device (10) comprising at least one processor and at least one memory (6) containing computer program code, wherein the at least one memory (6) and the computer program code are provided to the device (10) by the at least one processor, The optical plethysmography signal (101) measured in the inspection volume (11) of the individual (1), The process involves acquiring the light intensity (102, 103) obtained by optical plethysmography at two or more time points (12, 13) along the optical plethysmography signal (101), By determining the logarithm (17) of the function of the light intensity (102, 103) or its function approximation (17), the change in arterial blood volume (16) in the examination volume (11) between the two or more time points (12, 13) is determined, and thereby the PAT (100) of the individual (1) is evaluated. By determining the decrease in PAT(100), which indicates vasoconstriction of arteries and arterioles in the aforementioned examination volume (11), the occurrence of sleep-related events in the individual (1) is detected. A device (10) characterized by being configured to perform the following. (Claim 7) A system (20) comprising the apparatus described in claim 6, Light sources (2, 3) configured to emit light, A sensor (4) is configured to collect propagating light corresponding to the light transmitted or reflected as it propagates through the inspection volume (11) of the individual (1) at two or more time points (12, 13) using optical plethysmography, and to determine the light intensity (102, 103) of the propagating light at two or more time points (12, 13). A system (20) further characterized by having the following: (Claim 8) A computer program that includes instructions that a computer can execute, wherein the instructions that the computer can execute are, at a minimum, The optical plethysmography signal (101) measured in the inspection volume (11) of the individual (1), The process involves acquiring the light intensity (102, 103) obtained by optical plethysmography at two or more time points (12, 13) along the optical plethysmography signal (101), By determining the logarithm of the function of the light intensity (102, 103) or its approximation (17), the change in arterial blood volume (16) within the examination volume (11) between the two or more time points (12, 13) is determined, and thereby the PAT (100) of the individual (1) is evaluated. By determining the decrease in PAT(100), which indicates vasoconstriction of arteries and arterioles in the aforementioned examination volume (11), the occurrence of sleep-related events in the individual (1) is detected. A computer program characterized by being used to execute [something]. (Claim 9) A computer-readable storage medium containing instructions that a computer can execute, wherein the instructions that the computer can execute are, when the program is executed on the computer, A step of acquiring an optical plethysmography signal (101) measured at the inspection volume (11) of the individual (1), and light intensity (102, 103) obtained by optical plethysmography at two or more time points (12, 13) along the optical plethysmography signal (101), A step of determining the logarithm (17) of the function of the light intensity (102, 103) or its function approximation (17) to determine the change in arterial blood volume (16) in the test volume (11) between the two or more time points (12, 13), and thereby evaluating the PAT (100) of the individual (1), The process involves detecting the occurrence of sleep-related events in the individual (1) by determining a decrease in the PAT (100) which indicates vasoconstriction of arteries and arterioles in the aforementioned examination volume (11), and A computer-readable storage medium characterized by being used to perform the following actions. (Claim 10) The use of a logarithmic or functional approximation (17) for evaluating peripheral arterial tone (100), i.e., PAT, of an individual (1) monitored by optical plethysmography, and for detecting the occurrence of sleep-related events in the individual (1) by said evaluation, wherein the evaluation of peripheral arterial tone (100) is A step of acquiring an optical plethysmography signal (101) measured at the inspection volume (11) of the individual (1), and light intensity (102, 103) obtained by optical plethysmography at two or more time points (12, 13) along the optical plethysmography signal (101), A step of determining the logarithm (17) of the function of the light intensity (102, 103) or its function approximation (17) to determine the change in arterial blood volume (16) in the test volume (11) between two or more time points (12, 13), and thereby evaluating the PAT (100) of the individual (1), The process involves determining the decrease in PAT(100), which indicates vasoconstriction of arteries and arterioles in the aforementioned examination volume (11), thereby detecting the occurrence of sleep-related events in the individual (1). The use of logarithmic or logarithmic function approximation (17), characterized by comprising the above.

Claims

1. A method for operating a device equipped with one or more processors that evaluates peripheral arterial tone, i.e., PAT, of an individual monitored by optical plethysmography, and detects the occurrence of sleep-related events in the individual based on the evaluation, The apparatus includes the steps of acquiring an optical plethysmography signal measured at the inspection volume of the individual and the light intensity obtained by optical plethysmography at two or more time points along the optical plethysmography signal, The apparatus comprises a step of determining the change in arterial blood volume in the test volume between two or more time points by determining the logarithmic or logarithmic approximation of the function of the light intensity, thereby evaluating the PAT of the individual, wherein at least one of the time points corresponds to the diastolic phase of the individual's cardiac cycle, and / or at least one of the time points corresponds to the systolic phase of the individual's cardiac cycle, The apparatus performs the step of detecting the occurrence of sleep-related events in the individual by determining a decrease in the PAT, which indicates vasoconstriction of arteries and arterioles in the examination volume. A method for operating a device, comprising the following:

2. The method according to claim 1, characterized in that the function of light intensity corresponds to the ratio of light intensities.

3. The method according to claim 1 or 2, wherein the function of light intensity includes a first measurement corresponding to the light intensity measured by the sensor of the optical plethysmography apparatus at a first time point, and a second measurement corresponding to the light intensity measured by the sensor of the optical plethysmography apparatus at a second time point.

4. The method according to claim 2, wherein the function of light intensity corresponding to the ratio of light intensities is the ratio of a first measurement corresponding to the light intensity measured by the sensor of the optical plethysmography apparatus at a first time point to a second measurement corresponding to the light intensity measured by the sensor of the optical plethysmography apparatus at a second time point.

5. The method according to claim 4, wherein the first time point corresponds to the diastole phase in a first cardiac cycle, and the second time point corresponds to the systole phase in a second cardiac cycle different from the first cardiac cycle.

6. The method according to claim 4, wherein the first time point corresponds to the systole phase in a first cardiac cycle, and the second time point corresponds to the diastole phase in a second cardiac cycle different from the first cardiac cycle.

7. The method according to claim 4, wherein the first time point corresponds to the diastole phase of the cardiac cycle, and the second time point corresponds to the systole phase of the same cardiac cycle.

8. The method according to claim 4, wherein the first time point corresponds to the systolic phase of the cardiac cycle, and the second time point corresponds to the diastolic phase of the same cardiac cycle.

9. The aforementioned method, The process of controlling the operation of a light source configured to emit light of a certain wavelength, The aforementioned device includes a step of controlling the operation of the sensor, The process involves the apparatus collecting, on the sensor, the propagating light corresponding to the wavelength of light transmitted or reflected as it propagates through the inspection volume of the individual at two or more time points, using optical plethysmography; The apparatus includes the step of determining the light intensity of the propagating light on the sensor at two or more time points in time. The method according to any one of claims 1 to 8, further comprising:

10. The method according to any one of claims 1 to 9, further comprising the step of detecting the occurrence of the sleep-related event in the monitored individual by determining that the logarithmic or logarithmic approximation of the function of the light intensity has fallen to a value below a predetermined threshold.

11. The method according to claim 10, wherein the sleep-related event is detected when the PAT is below a predetermined threshold, and the sleep-related event is not detected when the PAT is above a predetermined threshold.

12. The method according to claim 11, wherein the sleep-related event is sleep apnea.

13. An apparatus comprising at least one processor and at least one memory containing computer program code, wherein the at least one memory and the computer program code are provided to the apparatus by the at least one processor, Optical plethysmography signals measured in the individual's sample volume, To acquire the light intensity obtained by optical plethysmography at two or more time points along the optical plethysmography signal, By determining the logarithmic or logarithmic approximation of the light intensity function, the change in arterial blood volume within the test volume between the two or more time points is determined, and the PAT of the individual is evaluated accordingly. By determining the decrease in PAT, which indicates vasoconstriction of arteries and arterioles in the aforementioned examination volume, the occurrence of sleep-related events in the individual is detected. A device that performs an action.

14. The apparatus according to claim 13, wherein the computer program code is configured to perform the method according to any one of claims 1 to 12 by the at least one processor.

15. A system comprising the apparatus described in claim 13 or 14, A light source configured to emit light, A sensor configured to collect propagating light corresponding to the light transmitted or reflected as it propagates through the inspection volume of the individual at two or more time points, and further configured to determine the light intensity of the propagating light at two or more time points, A system that further enhances this feature.

16. A computer-readable storage medium containing executable instructions for executing a program when run on a computing device, wherein the executable instructions are: A command to acquire an optical plethysmography signal measured at the inspection volume of an individual, and the light intensity obtained by optical plethysmography at two or more time points along the optical plethysmography signal, A command to determine the logarithmic or logarithmic approximation of the light intensity function, thereby determining the change in arterial blood volume in the test volume between the two or more time points, and thereby evaluating the PAT of the individual, A command is given to detect the occurrence of sleep-related events in the individual by determining the decrease in PAT, which indicates vasoconstriction of arteries and arterioles in the aforementioned examination volume. A computer-readable storage medium that includes [the specified element].

17. The computer-readable storage medium according to claim 16, wherein the executable instruction is configured to perform the method described in any one of claims 1 to 12 when the executable instruction is executed on the computing device.

18. The computing device is a computer, wherein the computer-readable storage medium is as described in claim 17.

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