Device for measuring the functionality of the arterial system

Abstract

To provide an easy-to-use apparatus for measuring functionality of arterial system for measuring blood pressure and / or for obtaining indications of endothelial dysfunction.SOLUTION: An apparatus for measuring functionality of an arterial system of an individual includes a photoplethysmography sensor (101) for emitting, to the arterial system, electromagnetic radiation having a wavelength in the range from 475 nm to 600 nm and for receiving a part of the electromagnetic radiation reflected off the arterial system. The apparatus further includes a pressure instrument (102) for managing mechanical pressure applied to the arterial system when the photoplethysmography sensor emits and receives the electromagnetic radiation to and from the arterial system. The effect of the mechanical pressure on the envelope of the reflected electromagnetic radiation can be used for determining diastolic blood pressure of arteries or for determining whether there is a normal endothelial function.SELECTED DRAWING: Figure 1a

Description

[Technical field]

[0001] The present disclosure relates to an apparatus and a method for measuring the functionality of the arterial system. The measured functionality may be, for example, the arterial diastolic pressure "DBP" (lowest blood pressure, minimum blood pressure) or the endothelial function, which represents the ability of the blood circulation to respond to vasomotor changes. Furthermore, the present disclosure relates to a computer program for measuring the functionality of the arterial system. [Background technology]

[0002] Possible abnormalities in the arterial system, if not diagnosed and properly treated and / or treated, can gradually undermine the health of an individual. For example, hypertension is a significant risk factor for cardiovascular disease. Thus, blood pressure measurement has become a routine procedure in many medical examinations. For the last few decades, automated non-invasive blood pressure "NIBP" measurement techniques, which are typical of oscillometric methods, have become widespread. In this technique, a cuff (a piece of fabric wrapped around the upper arm with a blood pressure monitor) is placed over the brachial artery, and blood flow is completely blocked when air is pumped into the cuff to exceed the systolic pressure. When the air pressure in the cuff is released, the pulsation, or oscillation, measured in the cuff increases to the point of mean arterial blood pressure "MAP" and then starts to decrease. The bell-shaped envelope of the pulsation is presented in the time domain along with the corresponding decreasing blood pressure curve. Systolic and diastolic blood pressure are then calculated from the MAP using pre-fixed percentages derived from population studies. The systolic blood pressure is typically considered to correspond to the point on the blood pressure curve where the blood pressure is above the MAP and the envelope value is 50% of the maximum envelope value, i.e., 50% of the envelope value corresponding to the MAP, and the diastolic blood pressure is typically considered to correspond to the point on the blood pressure curve where the blood pressure is below the MAP and the envelope value is 80% of the maximum envelope value.

[0003] Another example of an abnormality in the arterial system is endothelial dysfunction, which is feared to be a precursor to atherosclerosis, caused by the formation of plaque in the arteries. In clinical trials, endothelial function is induced by occluding the brachial artery for a few minutes; when released, blood flow to the artery increases and endothelial cells begin to excrete nitric oxide (NO), which then dilates the artery to allow more blood to flow. Arteries with endothelial dysfunction do not dilate in the same way.

[0004] In many cases it would be advantageous for abnormalities of the above kind to be detected at an early stage.Therefore, there is a demand for easy-to-use techniques for measuring, for example, blood pressure and / or obtaining an indication of endothelial dysfunction. Summary of the Invention

[0005] The following presents a simplified summary in order to provide a basic understanding of some aspects of various invention embodiments. The summary is not an extensive overview of the invention. It is not intended to identify key or critical elements of the invention or to delineate the scope of the invention. The following summary merely presents some concepts of the invention in a simplified form as a prelude to a more detailed description of example embodiments of the invention.

[0006] According to the present invention, a new device is provided for measuring the functionality of an individual's arterial system. The device according to the present invention comprises a photoplethysmography (optical plethysmography) "PPG" sensor for emitting electromagnetic radiation having a wavelength in the range of 475 nm to 600 nm to the arterial system and for receiving a portion of the electromagnetic radiation reflected from the arterial system. The device further comprises a pressure device for managing a mechanical pressure applied to the arterial system when the photoplethysmography sensor emits electromagnetic radiation to the arterial system and receives electromagnetic radiation from the arterial system.

[0007] In this document, the verb "manage" should be understood broadly so that managing does not necessarily include controlling or modifying the entity being managed, such as, for example, the mechanical pressure mentioned above, and managing can only include measuring the entity being managed.

[0008] The wavelength range of 475 nm to 600 nm is selected such that the electromagnetic radiation can only reach the more superficial cutaneous arterioles located in the reticular dermis, but not the arteries located in the subcutaneous tissue. The wavelength may be, for example, but is not necessarily, about 537 nm, in which case the electromagnetic radiation is green light.

[0009] The pulse pressure, i.e. the difference between systolic and diastolic blood pressure, increases from the brachial artery located in the upper arm to the radial artery located in the wrist and the transverse palmar arch artery located in the fingertip. Upon entering the arterioles and finally the capillaries, the mean arterial pressure "MAP" and the pulse pressure drop considerably. It has been found that the diastolic pressure in the fingertip artery is approximately equal to the systolic pressure in the fingertip arteriole. Therefore, the above described device can be used to estimate the diastolic pressure in the artery as well as to measure the MAP in the arteriole and the systolic pressure in the arteriole. The measurement procedure can include, for example but not necessarily, increasing and decreasing the mechanical pressure applied to the fingertip and recording the output signal of the PPG sensor. The output signal of the PPG sensor is indicative of the electromagnetic radiation reflected from the fingertip arteriole. The MAP corresponds to the value of the mechanical pressure when the envelope of the reflected electromagnetic radiation reaches a maximum value. The systolic pressure in the arteriole and the diastolic pressure in the artery correspond to values ​​of mechanical pressure at which the envelope of the reflected electromagnetic radiation is a predefined percentage of the maximum value, e.g. 50%, at mechanical pressures greater than the MAP. Increasing or decreasing the mechanical pressure can include, for example, pressing a finger beyond the systolic pressure so that blood flow is blocked, and then gradually reducing the pressure. It is also possible to increase the mechanical pressure from zero to a pressure at which blood flow is blocked. The envelope of the reflected electromagnetic radiation can be formed, for example, by band-pass filtering the output signal of the PPG sensor and constructing an envelope curve of the band-pass filtered output signal.

[0010] As another example, the above device can be used to measure endothelial function. The measurement procedure can include, for example but not necessarily, increasing the mechanical pressure applied to the fingertip until the envelope of the reflected electromagnetic radiation is approximately zero, and then keeping the mechanical pressure constant. In case of proper endothelial function, an increase in the envelope of the reflected electromagnetic radiation can be seen when the mechanical pressure is kept constant. In case of endothelial dysfunction, no increase of the above kind occurs.

[0011] In an example, non-limiting embodiment of the apparatus, the PPG sensor comprises means for emitting to the arterial system, in addition to the first electromagnetic radiation having a wavelength in the range of 475 nm to 600 nm, a second electromagnetic radiation having a wavelength in the range of 620 nm to 900 nm, and means for receiving a portion of the first and second electromagnetic radiation reflected from the arterial system.

[0012] The wavelength range of the second electromagnetic radiation from 620 nm to 900 nm is selected such that the second electromagnetic radiation reaches the artery located in the subcutaneous tissue. The second electromagnetic radiation can then be used to measure the MAP in the artery and the systolic blood pressure in the artery as well as the diastolic blood pressure in the artery. The diastolic blood pressure in the artery can then be measured with both the first and the second electromagnetic radiation, thus improving the accuracy and reliability of the measurement. The measurement procedure can include, for example but not necessarily, increasing and decreasing the mechanical pressure applied to the fingertip and recording first and second output signals from the PPG sensor corresponding to the first and second electromagnetic radiation reflected from the arterial system of the fingertip. As another example, the second electromagnetic radiation can be used to determine the pressure reached when the mechanical pressure applied to the fingertip is increased when measuring endothelial function. In this measurement, the mechanical pressure is increased until the envelope of the reflected second electromagnetic radiation reaches its maximum value. The wavelength of the second electro-magnetic radiation may be, for example, but not necessarily, about 660 nm, in which case the second electro-magnetic radiation is red light, or about 880 nm, in which case the second electro-magnetic radiation is infrared (IR) radiation.

[0013] According to the present invention, a new method for measuring the functionality of an individual's arterial system is provided. The method according to the present invention comprises: emitting electromagnetic radiation having a wavelength in the range of 475 nm to 600 nm to the arterial system; receiving a portion of the electromagnetic radiation reflected from the arterial system; Varying a mechanical pressure applied to the arterial system when electromagnetic radiation is emitted to the arterial system and reflected electromagnetic radiation is received from the arterial system; generating information indicative of functionality of the arterial system based on the received electromagnetic radiation.

[0014] According to the invention there is also provided a new computer program for measuring the functionality of an individual's arterial system. The computer program according to the invention comprises a programmable processing system, the program comprising: controlling the photoplethysmography sensor to emit electromagnetic radiation having a wavelength in the range of 475 nm to 600 nm toward the arterial system and to receive a portion of the electromagnetic radiation reflected from the arterial system; The pressure device comprises computer executable instructions for controlling the pressure device to manage mechanical pressure applied to the arterial system when the photoplethysmographic sensor emits electromagnetic radiation to and receives electromagnetic radiation from the arterial system.

[0015] According to the present invention there is also provided a novel computer program product comprising a non-volatile computer readable medium, for example a compact disc "CD", encoded with a computer program according to the present invention.

[0016] Exemplary, non-limiting embodiments are set forth in the accompanying dependent claims.

[0017] Various example non-limiting embodiments, both as to construction and method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific example embodiments when read in conjunction with the accompanying drawings.

[0018] In this document, the verbs "comprise" and "include" are used as open limitations that do not exclude or require the presence of features not recited. Features recited in the accompanying dependent claims are mutually freely combinable unless expressly stated otherwise. Furthermore, it is to be understood that the use of "a", "an", or "the" does not exclude a plurality throughout this document.

[0019] Exemplary non-limiting embodiments and their advantages are described in more detail below with reference to the accompanying drawings. [Brief description of the drawings]

[0020] [Figure 1a] FIG. 1a illustrates an apparatus according to an exemplary, non-limiting embodiment for measuring the functionality of the arterial system. [Figure 1b] FIG. 1b shows an example graph illustrating electromagnetic radiation reflected from the arterial system of a fingertip as a function of time. [Figure 1c] FIG. 1c shows a mobile device equipped with the apparatus illustrated in FIG. 1a. [Figure 2a] FIG. 2a illustrates an apparatus according to an exemplary, non-limiting embodiment for measuring the functionality of the arterial system. [Figure 2b] FIG. 2b shows an example graph illustrating electromagnetic radiation having different wavelengths reflected from the arterial system of a fingertip as a function of time. [Diagram 3] FIG. 3 illustrates an apparatus according to an exemplary, non-limiting embodiment for measuring the functionality of the arterial system. [Figure 4a] FIG. 4a illustrates an apparatus according to an exemplary, non-limiting embodiment for measuring the functionality of the arterial system. [Figure 4b] FIG. 4b shows an example graph illustrating electromagnetic radiation having different wavelengths reflected from the arterial system of a fingertip as a function of time. [Diagram 5] FIG. 5 shows a flow chart of a method according to an exemplary, non-limiting embodiment for measuring the functionality of the arterial system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Specific examples provided in the following description should not be construed as limiting the scope and / or applicability of the appended claims. Lists and groups of examples provided in the description are not exhaustive unless expressly stated otherwise.

[0022] FIG. 1a shows a schematic diagram of an apparatus for measuring the functionality of the arterial system according to an exemplary non-limiting embodiment. The apparatus comprises a photoplethysmography (PPG) sensor 101 for emitting electromagnetic radiation having a wavelength in the range of 475 nm to 600 nm to an individual's fingertip 108 and for receiving a portion of the electromagnetic radiation reflected from the arterial system of the fingertip 108. In an exemplary non-limiting embodiment, the wavelength is in the range of 480 nm to 600 nm. In an exemplary non-limiting embodiment, the wavelength is in the range of 500 nm to 600 nm. In an exemplary non-limiting embodiment, the wavelength is in the range of 500 nm to 575 nm. In an exemplary non-limiting embodiment, the wavelength is in the range of 500 nm to 550 nm. The wavelength may be, for example, but not necessarily, about 537 nm, in which case the electromagnetic radiation is green light. The PPG sensor 101 comprises a radiation emitter 109 and a photodetector 110. The radiation emitter 109 may be, for example, a light emitting diode "LED" and the photodetector 110 may be, for example, a photodiode or a phototransistor. Fig. 1a also shows an enlarged schematic cross-sectional view 130 of a fingertip. The cross-section is parallel to the yz-plane of the coordinate system 199. In the cross-sectional view 130, the emitted and reflected radiation is indicated by the broken line 117. As illustrated in the cross-sectional view 130, the electromagnetic radiation 117 does not reach the artery 111 located in the subcutaneous tissue 114, but can only reach the arteriole 112 located in the reticular dermis 115. In the cross-sectional view 130, the capillaries are indicated by the reference numeral 113 and the epidermis of the skin of the fingertip is indicated by the reference numeral 116.

[0023] The device further comprises a pressure device 102 for managing the mechanical pressure applied to the arterial system when the photoplethysmographic sensor 101 emits and receives electromagnetic radiation. In this example case, the pressure device 102 comprises a pressure sensor for measuring the mechanical pressure P directed by the fingertip 108 towards the pressure sensor.

[0024] FIG. 1b shows a curve 119 illustrating the reflected electromagnetic radiation in an example situation where the device is used to estimate the mean arterial pressure "MAP" in the arteriole 112 and the systolic pressure "SYS" in the arteriole, as well as the diastolic pressure "DIA" in the artery 111. In this example case, the fingertip 108 is first pressed against the pressure device 102, so that the mechanical pressure P exceeds the systolic pressure, and thus the blood flow is blocked. The pressure is then gradually released, so that the mechanical pressure P decreases as a function of time, as shown by the curve 122 shown in FIG. 1b. The curve 119 can represent, for example, a bandpass filtered output signal of the PPG sensor 101. The passband of the bandpass filtering can be, for example, 1 Hz to 10 Hz. In this example case, the bandpass filtered signal is Hilbert transformed to form the envelope of the bandpass filtered signal. In FIG. 1 b , the Hilbert transformed, filtered signal is shown by curve 120 and its envelope is shown by curve 121 .

[0025] An estimate of the MAP in the arteriole 112 is the value of the mechanical pressure P when said envelope 121 of the reflected electromagnetic radiation reaches its maximum value. The MAP in the arteriole can therefore be estimated by the envelope curve 121 and the mechanical pressure curve 122 as shown in FIG. 1b. An estimate of the systolic blood pressure "SYS" in the arteriole 112 is the value of the mechanical pressure P that is greater than the estimated MAP in the arteriole 112 when the envelope of the reflected electromagnetic radiation is a predefined percentage of the maximum value of the envelope, typically 50%. The SYS in the arteriole can therefore be estimated by the envelope curve 121 and the mechanical pressure curve 122 as shown in FIG. 1b. The estimate of the SYS in the arteriole is also an estimate of the diastolic blood pressure "DIA" in the arteriole 111.

[0026] In the exemplary case shown in Fig. 1b, the mechanical pressure P is decreased. However, it is also possible to increase the mechanical pressure P in order to estimate the MAP in the arteriole 112, the SYS in the arteriole, and the DIA in the artery 111. In this exemplary case, the envelope of the reflected electromagnetic radiation is a time-reversed version of the envelope 121. Furthermore, it should be noted that the mechanical pressure P does not necessarily follow an ideal straight line as a function of time when decreasing or increasing the mechanical pressure P.

[0027] The apparatus according to the exemplary non-limiting embodiment comprises a processing system 103 configured to determine an estimate of MAP in the arteriole 112. In other words, the processing system 103 is configured to determine a first value of the mechanical pressure P when said envelope 121 of the reflected electromagnetic radiation reaches its maximum value when the mechanical pressure P is decreased or increased from a start value to an end value, where the first value is the estimate of MAP in the arteriole 112. In the apparatus according to the exemplary non-limiting embodiment, the processing system 103 is configured to determine an estimate of SYS in the arteriole 112 and an estimate of DIA in the artery 111. In other words, the processing system 103 is configured to determine a second value of the mechanical pressure P greater than the determined first value when the envelope of the reflected electromagnetic radiation is approximately a predefined percentage, typically 50%, of the maximum value of the envelope, where the determined second value is the estimate of SYS in the arteriole 112 and the estimate of DIA in the artery 111. However, the device according to the example non-limiting embodiment may also comprise a memory for storing the time series of the output signals of the PPG sensor and the pressure sensor and / or a transmitter for transmitting the time series to an external device, in this example case, said estimates representative of the functionality of the arterial system can be formed offline by an external device, for example a personal computer.

[0028] FIG. 1c shows a mobile device 107 comprising the device illustrated in FIG. 1a. The mobile device 107 may be, for example, a mobile phone or a palmtop computer. The pressure sensor and the PPG sensor are on the surface of the mobile device, which allows an individual to press a fingertip 108 against the pressure sensor and the PPG sensor. In this example case, the mobile device 107 is configured to display the band-pass filtered output signal of the PPG sensor and the envelope of the band-pass filtered output signal. Furthermore, the mobile device 107 is configured to display estimates of the SYS in the arteriole, the MAP in the arteriole, and the DIA in the artery, which estimates are formed by the envelope and the time dependence of the mechanical pressure measured by the pressure sensor. The device according to the example embodiment of the present invention can be part of a ring, a bracelet, a wristwatch, or any other wearable device, or a combination thereof, or a combination of a wearable device and a mobile phone or other mobile communication device. For example, the PPG sensor and the pressure sensor can be provided on the inner surface of a ring or a bracelet. In this example case, the user can control the pressure by pressing the ring or bracelet against the surface of the finger or wrist that is surrounded by the ring or bracelet.

[0029] FIG. 2a shows a schematic diagram of an apparatus for measuring the functionality of the arterial system according to an exemplary non-limiting embodiment. The apparatus comprises a photoplethysmography (PPG) sensor 201 for emitting a first electromagnetic radiation having a wavelength in the range of 475 nm to 600 nm and a second electromagnetic radiation having a wavelength in the range of 620 nm to 900 nm to an individual's fingertip 208, and for receiving a portion of the first and second electromagnetic radiation reflected from the arterial system of the fingertip 208. The wavelength of the first electromagnetic radiation may be, for example, but not necessarily, about 537 nm, in which case the first electromagnetic radiation is green light. In the apparatus according to an exemplary non-limiting embodiment, the wavelength of the second electromagnetic radiation is in the range of 650 nm to 890 nm. The wavelength of the second electromagnetic radiation may be, for example, but not necessarily, about 660 nm, in which case the second electromagnetic radiation is red light, or about 880 nm, in which case the second electromagnetic radiation is infrared (IR) radiation. The PPG sensor 201 can also be configured to emit and measure electromagnetic radiation having three or more different wavelengths. The PPG sensor 201 comprises a radiation emitter 209 and a photodetector 210. The radiation emitter 209 can comprise, for example, a light emitting diode "LED" and the photodetector 210 can comprise, for example, a wavelength sensitive photodiode or phototransistor. FIG. 2a also shows an enlarged schematic cross-sectional view 230 of a fingertip. The cross-section is parallel to the yz-plane of the coordinate system 299. In the cross-sectional view 230, the emitted and reflected first electromagnetic radiation is shown by the broken line 217 and the emitted and reflected second electromagnetic radiation is shown by the broken line 218. As illustrated in the cross-sectional view 230, the first electromagnetic radiation 217 does not reach the artery 111 located in the subcutaneous tissue 114 and can only reach the arteriole 112 located in the reticular dermis 115, while the second electromagnetic radiation 218 can reach the artery 111. In cross-section 230, the capillaries are indicated by reference numeral 113 and the epidermis of the skin of the fingertip is indicated by reference numeral 116.

[0030] The device further comprises a pressure device for managing the mechanical pressure applied to the arterial system when the PPG sensor 201 emits and receives said first and second electromagnetic radiation. In this example case, the pressure device comprises a pressure sensor 202a for measuring a mechanical pressure P directed by the fingertip 208 to the pressure sensor, and a pressing means 202b for controllably pressing the fingertip 208 against the PPG sensor 201 and the pressure sensor 202a. In this example device, the pressing means comprises a pressing element 204 and a force generating means 228 for directing a force to the pressing element 204. The force generating means 228 can comprise, for example, an electric stepper motor and a threaded rod.

[0031] FIG. 2b shows a curve 219 illustrating a reflected first electromagnetic radiation and a curve 223 illustrating a reflected second electromagnetic radiation in an example situation in which the device is used to estimate the mean arterial blood pressure "MAP1" in the artery 112, the mean arterial blood pressure "MAP2" in the artery 111, the systolic blood pressure "SYS1" in the artery, the systolic blood pressure "SYS2" in the artery, and the diastolic blood pressure "DIA2" in the artery. In this example case, the fingertip 208 is first pressed against the pressure sensor 202a, such that the mechanical pressure P exceeds the systolic blood pressure and thus the blood flow is blocked. The pressure is then gradually released, such that the mechanical pressure P decreases as a function of time, as shown by the curve 222 shown in FIG. 2b. The curves 219 and 223 can represent, for example, band-pass filtered output signals of the PPG sensor 201. The passband of the band-pass filtering can be, for example, 1 Hz to 10 Hz. In this example case, the bandpass filtered signal is Hilbert transformed to form the envelope of the bandpass filtered signal. In Fig. 2b the Hilbert transformed filtered signal is shown by the dashed curves. The envelope of the reflected first electromagnetic radiation is shown by curve 221 and the envelope of the reflected second electromagnetic radiation is shown by curve 224.

[0032] 2b, the estimate of MAP1 is the value of the mechanical pressure P when the envelope 221 reaches its maximum value, the estimate of MAP2 is the value of the mechanical pressure P when the envelope 224 reaches its maximum value, the estimate of SYS1 is the value of the mechanical pressure P greater than MAP1 when the envelope 221 is at 50% of its maximum value, the estimate of SYS2 is the value of the mechanical pressure P greater than MAP2 when the envelope 224 is at 50% of its maximum value, and the estimate of DIA2 is the value of the mechanical pressure P less than MAP2 when the envelope 224 is at 80% of its maximum value. Since the systolic pressure SYS1 in the arteriole is approximately equal to the diastolic pressure DIA2 in the artery, the estimate of SYS1 behaves as another estimate for the diastolic pressure in the artery. The final estimate for the diastolic pressure in the artery may be, for example, a weighted average of the estimate based on envelope 224 and the estimate based on envelope 221 .

[0033] The device according to an exemplary, non-limiting embodiment comprises a processing system 203 configured to control the force generating means 228 such that the mechanical pressure P has a desired behavior as a function of time, for example as shown by the curve 222 in Fig. 2b. Furthermore, the processing system 203 can be configured to form said estimate using the output signal of the PPG sensor 201 and the output signal of the pressure sensor 202b.

[0034] FIG. 3 shows a schematic diagram of an apparatus according to an exemplary, non-limiting embodiment for measuring the functionality of the arterial system. The apparatus comprises a photoplethysmography "PPG" sensor 301 for emitting electromagnetic radiation having a wavelength in the range of 475 nm to 600 nm to the arterial system and for receiving a portion of the electromagnetic radiation reflected from the arterial system. The wavelength may be, for example, about 515 nm. The apparatus comprises a pressure device 302 for managing a mechanical pressure applied to the arterial system when the photoplethysmography sensor 301 emits electromagnetic radiation to the arterial system and receives electromagnetic radiation from the arterial system. In this exemplary case, the pressure device 302 comprises a pressing device 305 for directing a controllable mechanical pressure to the brachial artery. The pressing device 305 may be, for example, a cuff and the apparatus may comprise a pump system 306 for controlling the pressure of a gas, for example air, inside the cuff to direct a controllable mechanical pressure to the brachial artery. However, it is also possible that the pressing device comprises, for example, a flexible belt that is tightened around the upper arm. The PPG sensor 301 is located on the surface of the pressing device 305, so that the PPG sensor 301 can be placed on top of the brachial artery. The brachial artery can be found, for example, by palpation. Experiments have shown that the output signal of the PPG sensor 301 does not show a pulsatile waveform when the mechanical pressure exceeds the diastolic blood pressure, and the output signal of the PPG sensor 301 starts to show a pulsatile waveform when the mechanical pressure falls below the diastolic blood pressure. Therefore, the device can be used for direct measurement of the diastolic blood pressure.

[0035] The device according to the example non-limiting embodiment comprises a processing system 303 configured to control the pressing device 305 such that the mechanical pressure has a desired behavior as a function of time. In the example case shown in Fig. 3, the processing system 303 is configured to control the pump system 306 such that the mechanical pressure generated by the cuff has a desired behavior as a function of time. Furthermore, the processing system 303 can be configured to determine the value of the mechanical pressure when the output signal of the PPG sensor 301 starts to show a pulsatile waveform.

[0036] 4a shows a schematic diagram of an apparatus according to an example, non-limiting embodiment for measuring the functionality of the arterial system. The apparatus comprises a photoplethysmography "PPG" sensor 401 for emitting a first electromagnetic radiation having a wavelength in the range of 475 nm to 600 nm and a second electromagnetic radiation having a wavelength in the range of 620 nm to 900 nm to an individual's fingertip 408, and for receiving a portion of the first and second electromagnetic radiation reflected from the arterial system of the fingertip 408. The wavelength of the first electromagnetic radiation may be, for example, but not necessarily, about 537 nm, in which case the first electromagnetic radiation is green light. The wavelength of the second electromagnetic radiation may be, for example, but not necessarily, about 660 nm, in which case the second electromagnetic radiation is red light, or about 880 nm, in which case the second electromagnetic radiation is infrared "IR" radiation. The PPG sensor 401 comprises a radiation emitter 409 and a photodetector 410.

[0037] The device further comprises a pressure device 402 for managing the mechanical pressure applied to the arterial system when the PPG sensor 401 emits the first and second electromagnetic radiation to and receives the first and second electromagnetic radiation from the fingertip 408. In this example case, the pressure device 402 comprises a pressing element 404 for pressing against the fingertip 408 and a force generating means 428 for directing a force to the pressing element 404.

[0038] FIG. 4b shows a curve 425 illustrating the reflected first electromagnetic radiation and a curve 426 illustrating the reflected second electromagnetic radiation in an exemplary situation where the pressure device 402 first increases the mechanical pressure and then keeps the mechanical pressure approximately constant. The curves 425 and 426 can, for example, represent band-pass filtered output signals of the PPG sensor 401. The passband of the band-pass filtering can be, for example, 1 Hz to 10 Hz. The mechanical pressure as a function of time is shown by the curve 427 shown in FIG. 4b. As shown in FIG. 4b, the mechanical pressure is increased to a pressure at which the pulsating waveform of the reflected first electromagnetic radiation drops to approximately zero and the pulsating waveform of the reflected second electromagnetic radiation reaches its maximum value. The small pulsating waveform of the reflected first electromagnetic radiation indicates a near occlusion of the arteriole, which is indicative of a near systolic arteriolar pressure. The tangential stress caused by the small flow induces the release of oxygen mononitride (NO) in the endothelial cells, which causes vasodilation in the arterioles allowing more blood to flow through the endothelium. If the applied mechanical pressure is held constant, the pulsatile waveform of the reflected first electromagnetic radiation increases as illustrated by curve 425. This increase in the pulsatile waveform of the reflected first electromagnetic radiation is indicative of normal endothelial function, while the absence of an increase is indicative of endothelial dysfunction.

[0039] The apparatus according to the exemplary non-limiting embodiment includes a processing system 403 for controlling the pressure device 402 to increase the mechanical pressure until the envelope of the reflected first electro-magnetic radiation drops to approximately zero, and then to keep the mechanical pressure constant. In another exemplary non-limiting embodiment, the processing system 403 is configured to control the pressure device 402 to increase the mechanical pressure until the envelope of the reflected second electro-magnetic radiation reaches its maximum value, and then to keep the mechanical pressure constant. The force generating means 428 can include, for example, a threaded rod and an electric stepper motor controlled by the processing system 403. The mechanical pressure can be increased by activating the electric stepper motor in an appropriate rotational direction, and the mechanical pressure can be kept constant by keeping the electric stepper motor stationary. In the exemplary non-limiting embodiment, the processing system 403 is configured to detect whether the envelope of the reflected first electro-magnetic radiation increases when the mechanical pressure is kept constant.

[0040] Each of the processing systems 103, 203, 303, and 403 shown in Figures 1a, 2a, 3, and 4a may be implemented, for example, with one or more processor circuits, which may be programmable processor circuits provided with appropriate software, or may be dedicated hardware processors, such as, for example, application specific integrated circuits "ASICs," or configurable hardware processors, such as, for example, field programmable gate arrays "FPGAs." Each of the processing systems 103, 203, 303, and 403 may further include memory, for example, implemented with one or more memory circuits, which may be, for example, random access memory "RAM" devices.

[0041] 5 shows a flow chart of a method according to an exemplary, non-limiting embodiment for measuring the functionality of an individual's arterial system. The method comprises the following operations: - action 501: emitting electromagnetic radiation having a wavelength in the range of 475 nm to 600 nm to the arterial system; Action 502: receiving a portion of electromagnetic radiation reflected from the arterial system; - operation 503; modifying a mechanical pressure applied to the arterial system when electromagnetic radiation is emitted to the arterial system and reflected electromagnetic radiation is received from the arterial system; Action 504: The method comprises generating information indicative of functionality of the arterial system based on the received electromagnetic radiation.

[0042] In a method according to an example non-limiting embodiment, the wavelength of the electromagnetic radiation ranges from 480 nm to 600 nm.

[0043] In a method according to an example non-limiting embodiment, the wavelength of the electromagnetic radiation is in the range of 500 nm to 600 nm.

[0044] In a method according to an example non-limiting embodiment, the wavelength of the electromagnetic radiation ranges from 500 nm to 575 nm.

[0045] In a method according to an example non-limiting embodiment, the wavelength of the electromagnetic radiation is in the range of 500 nm to 550 nm.

[0046] According to an example non-limiting embodiment, the method comprises determining a first value of the mechanical pressure at which the envelope of the reflected electromagnetic radiation reaches its maximum value as the mechanical pressure is decreased or increased from a start value to an end value, the determined first value being indicative of a mean arterial blood pressure "MAP" of an arteriole of the arterial system.

[0047] According to an example non-limiting embodiment, the method comprises determining a second value of the mechanical pressure greater than the first determined value when the envelope of the reflected electromagnetic radiation is approximately a predetermined percentage, e.g., 50%, of a maximum value of the envelope. The second determined value is indicative of the systolic pressure "SYS" of the arterioles of the arterial system as well as the diastolic pressure "DIA" of the arteries of the arterial system.

[0048] A method according to an exemplary non-limiting embodiment includes increasing the mechanical pressure until the envelope of the reflected electromagnetic radiation drops to approximately zero, and subsequently holding the mechanical pressure constant. The method according to this exemplary non-limiting embodiment further includes detecting whether the envelope of the reflected electromagnetic radiation increases when the mechanical pressure is held constant. An increase in the envelope indicates normal endothelial function of the arterial system, while no increase indicates endothelial dysfunction.

[0049] A method according to an example non-limiting embodiment comprises directing mechanical pressure to an individual's fingertip as electromagnetic radiation is emitted to the fingertip and electromagnetic radiation is received from the fingertip.

[0050] A method according to an example, non-limiting embodiment includes measuring pressure directed at a fingertip as electromagnetic radiation is emitted to the fingertip and electromagnetic radiation is received from the fingertip.

[0051] A method according to an example non-limiting embodiment comprises controlling a pressure of gas within a cuff surrounding an individual's upper arm to direct mechanical pressure to the individual's brachial artery when electromagnetic radiation is emitted to and received from an area of ​​the upper arm above the brachial artery.

[0052] In a method according to an example, non-limiting embodiment, the electromagnetic radiation having a wavelength in the range of 475 nm to 600 nm is the first electromagnetic radiation, and the method according to this example, non-limiting embodiment, comprises: - emitting a second electromagnetic radiation having a wavelength in the range of 620 nm to 900 nm to the arterial system; and receiving a portion of the second electromagnetic radiation reflected from the arterial system.

[0053] In a method according to an example non-limiting embodiment, the wavelength of the second electro-magnetic radiation ranges from 650 nm to 890 nm.

[0054] According to an example non-limiting embodiment, the method comprises determining a third value of the mechanical pressure at which the envelope of the reflected second electromagnetic radiation reaches its maximum value as the mechanical pressure is decreased or increased from a start value to an end value, the determined third value being indicative of a mean arterial blood pressure "MAP" of an artery of the arterial system.

[0055] According to an example non-limiting embodiment, the method comprises determining a fourth value of the mechanical pressure that is greater than the determined third value when the envelope of the reflected second electro-magnetic radiation is approximately a first predetermined percentage, e.g., 50%, of a maximum value of the envelope of the reflected second electro-magnetic radiation, the determined fourth value being indicative of the systolic blood pressure "SYS" of the arteries of the arterial system.

[0056] According to an example non-limiting embodiment, the method comprises determining a fifth value of the mechanical pressure less than the determined third value when the envelope of the reflected second electromagnetic radiation is approximately a second predetermined percentage, e.g., 80%, of a maximum value of the envelope of the reflected second electromagnetic radiation, the determined fifth value being indicative of a diastolic pressure "DIA" of the arteries of the arterial system.

[0057] A method according to an exemplary non-limiting embodiment includes increasing the mechanical pressure until the envelope of the reflected second electromagnetic radiation reaches its maximum value, and subsequently holding the mechanical pressure constant. The method according to this exemplary non-limiting embodiment further includes detecting whether the envelope of the reflected first electromagnetic radiation increases when the mechanical pressure is held constant. An increase in the envelope of the reflected first electromagnetic radiation is indicative of normal endothelial function of the arterial system.

[0058] A computer program according to the example non-limiting embodiments comprises computer executable instructions for controlling a programmable processing system to perform operations related to the methods according to any of the example non-limiting embodiments above.

[0059] A computer program according to an exemplary, non-limiting embodiment comprises a software module for measuring the functionality of an individual's arterial system, the software module being configured to be implemented by a programmable processing system, the programmable processing system comprising: controlling a photoplethysmography (PPG) sensor to emit electromagnetic radiation having a wavelength in the range of 475 nm to 600 nm toward the arterial system and to receive a portion of the electromagnetic radiation reflected from the arterial system; - comprising computer executable instructions for controlling a pressure device to manage mechanical pressure applied to the arterial system when the PPG sensor emits electromagnetic radiation to and receives electromagnetic radiation from the arterial system.

[0060] A software module may be, for example, a subroutine or a function that is implemented by suitable programming tools on a programmable processing device.

[0061] In an example, non-limiting embodiment of a computer program, a software module includes computer executable instructions for controlling a programmable processing system to control a pressure device to modify the mechanical pressure applied to the arterial system when the PPG sensor emits electromagnetic radiation to and receives electromagnetic radiation from the arterial system.

[0062] A computer program product according to an example, non-limiting embodiment comprises a computer readable medium, such as a compact disc "CD", encoded with a computer program according to an example embodiment.

[0063] A signal in accordance with the example, non-limiting embodiments is encoded to carry information that defines a computer program in accordance with the example embodiments.

[0064] A computer program according to the example non-limiting embodiment may for example form part of the software of a mobile device, such as for example a smartphone or a wearable device.

[0065] The specific examples provided in the above description should not be construed as limiting the scope and / or applicability of the appended claims. The lists and groupings of examples provided in the above description are not exhaustive unless expressly stated otherwise. The above-described embodiment can also be described as follows, but is not limited to the following. [Configuration 1] 1. A device for measuring the functionality of an individual's arterial system, comprising: The apparatus comprises a photoplethysmography sensor (101, 201, 301, 401) for emitting electromagnetic radiation having a wavelength in the range of 475 nm to 600 nm to the arterial system and for receiving a portion of the electromagnetic radiation reflected from the arterial system, the apparatus further comprising a pressure device (102, 202a, 202b, 302, 402) for managing a mechanical pressure applied to the arterial system when the photoplethysmography sensor emits the electromagnetic radiation to the arterial system and receives the electromagnetic radiation from the arterial system. [Configuration 2] The apparatus of configuration 1, characterized in that the pressure device (202a, 202b, 302, 402) is suitable for modifying the mechanical pressure applied to the arterial system when the photoplethysmography sensor emits the electromagnetic radiation to the arterial system and receives the electromagnetic radiation from the arterial system. [Configuration 3] The apparatus of configuration 2, characterized in that the pressure device (202b, 402) comprises a pressing element (204, 404) for directing the mechanical pressure to the individual's fingertip and modifying the mechanical pressure when the photoplethysmography sensor emits the electromagnetic radiation to the arterial system and receives the electromagnetic radiation from the arterial system. [Configuration 4] 4. The apparatus according to any one of configurations 1 to 3, further comprising a processing system (103, 203, 303) for determining a first value of the mechanical pressure at which an envelope of the reflected electromagnetic radiation reaches a maximum value as the mechanical pressure is increased or decreased from a start value to an end value, characterized in that the determined first value is indicative of a mean arterial blood pressure in an arteriole of the arterial system. [Configuration 5] 5. The apparatus of claim 4, wherein the processing system is configured to determine a second value of the mechanical pressure that is greater than the determined first value when the envelope of the reflected electromagnetic radiation is approximately a predetermined percentage of the maximum value, the determined second value being indicative of a diastolic blood pressure of an artery of the arterial system together with a systolic blood pressure of an arteriole of the arterial system. [Configuration 6] 4. The apparatus of claim 2 or 3, further comprising a processing system (403) for controlling the pressure device to increase the mechanical pressure until the envelope of the reflected electromagnetic radiation drops to approximately zero, and thereafter to keep the mechanical pressure constant. [Configuration 7] 7. The apparatus of claim 6, wherein the processing system is configured to detect whether the envelope of the reflected electromagnetic radiation increases when the mechanical pressure is held constant, an increase in the envelope being indicative of normal endothelial function of the artery. [Configuration 8] 8. The apparatus of any of configurations 1 to 7, characterized in that the pressure device (102, 202a) comprises a pressure sensor for measuring pressure directed by the fingertip of the individual towards the pressure sensor when the photoplethysmography sensor emits the electromagnetic radiation to the fingertip and receives the electromagnetic radiation from the fingertip. [Configuration 9] 9. The apparatus of claim 8, wherein the apparatus is part of a mobile device (107) and the pressure sensor and the photoplethysmography sensor are on a surface of the mobile device. [Configuration 10] 10. Apparatus according to any of the preceding claims, characterized in that the wavelength of the electromagnetic radiation is in the range of 500nm to 600nm. [Configuration 11] 11. Apparatus according to any of the preceding claims, characterized in that the wavelength of the electromagnetic radiation is in the range of 500 nm to 550 nm. [Configuration 12] 12. The apparatus of any one of configurations 1 to 11, characterized in that the electromagnetic radiation having the wavelength in the range of 475 nm to 600 nm is a first electromagnetic radiation, and the photoplethysmography sensor (201, 401) is configured to emit a second electromagnetic radiation having a wavelength in the range of 620 nm to 900 nm to the arterial system and to receive a portion of the second electromagnetic radiation reflected from the arterial system. [Configuration 13] 13. The apparatus of claim 12, further comprising a processing system (203) for determining a third value of the mechanical pressure at which an envelope of the reflected second electromagnetic radiation reaches a maximum value as the mechanical pressure is increased or decreased from a start value to an end value, the determined third value being indicative of a mean arterial blood pressure in an artery of the arterial system. [Configuration 14] 14. The apparatus of claim 13, wherein the processing system is configured to determine a fourth value of the mechanical pressure that is greater than the determined third value when the envelope of the reflected second electromagnetic radiation is approximately a first predetermined percentage of the maximum value of the envelope of the reflected second electromagnetic radiation, the determined fourth value being indicative of a systolic blood pressure of an artery of the arterial system. [Configuration 15] 13. The apparatus of claim 12, further comprising a processing system (403) for controlling the pressure device to increase the mechanical pressure until a maximum value of the envelope of the reflected second electromagnetic radiation is reached, and thereafter to keep the mechanical pressure constant. [Configuration 16] 3. The apparatus of claim 2, wherein the pressure device (302) comprises a pressing device (305) for directing the mechanical pressure to the brachial artery of the individual, and the photoplethysmography sensor (301) is located on a surface of the pressing device that is intended to be above the brachial artery. [Configuration 17] 17. The apparatus of claim 16, wherein the pressure device (305) is a cuff, the pressure device comprising a pump system (306) for controlling the pressure of gas inside the cuff to direct the mechanical pressure to the brachial artery, and the photoplethysmography sensor (301) is located on an inner surface of the cuff. [Configuration 18] 1. A method for measuring the functionality of an individual's arterial system, comprising: emitting electromagnetic radiation having a wavelength in the range of 475 nm to 600 nm to the arterial system (501); receiving (502) a portion of the electromagnetic radiation reflected from the arterial system; generating (503) information indicative of the functionality of the arterial system based on the received electromagnetic radiation; The method further comprises modifying (504) a mechanical pressure applied to the arterial system when the electromagnetic radiation is emitted to the arterial system and the reflected electromagnetic radiation is received from the arterial system. [Configuration 19] A computer program comprising: a programmable processing system; comprising computer executable instructions for controlling a photoplethysmography sensor to emit electromagnetic radiation having a wavelength in a range of 475 nm to 600 nm into the arterial system and to receive a portion of the electromagnetic radiation reflected from the arterial system; The computer program further comprises computer executable instructions for the programmable processing system to control a pressure device to manage the mechanical pressure applied to the arterial system when the photoplethysmographic sensor emits the electromagnetic radiation to and receives the electromagnetic radiation from the arterial system. [Configuration 20] 20. The computer program of claim 19, wherein the computer program comprises computer executable instructions for the programmable processing system to control the pressure device to modify the mechanical pressure applied to the arterial system when the photoplethysmographic sensor emits the electromagnetic radiation to and receives the electromagnetic radiation from the arterial system. [Configuration 21] 21. A computer program product comprising a non-transitory computer-readable medium encoded with the computer program of any one of claims 19 to 20.

Claims

1. 1. A device for measuring the functionality of an individual's arterial system, comprising: The apparatus comprises a photoplethysmography sensor (101, 201, 301, 401) for emitting electromagnetic radiation having a wavelength in the range of 475 nm to 600 nm to the arterial system and for receiving a portion of the electromagnetic radiation reflected from the arterial system, the apparatus further comprising a pressure device (102, 202a, 202b, 302, 402) for managing a mechanical pressure applied to the arterial system when the photoplethysmography sensor emits the electromagnetic radiation to the arterial system and receives the electromagnetic radiation from the arterial system, the pressure device (202a, 202b, 302, 402) being configured to control ...

13. An apparatus adapted to emit electromagnetic radiation into the arterial system and modify the mechanical pressure applied to the arterial system when receiving said electromagnetic radiation from the arterial system, the apparatus comprising a processing system (403) for controlling the pressure device to increase the mechanical pressure until an envelope of the reflected electromagnetic radiation drops to approximately zero and thereafter to keep the mechanical pressure constant, the processing system being configured to detect whether the envelope of the reflected electromagnetic radiation increases when the mechanical pressure is kept constant, an increase in the envelope being indicative of normal endothelial function of the arterial system.

2. 2. The apparatus of claim 1, wherein the pressure device (202b, 402) comprises a pressing element (204, 404) for directing the mechanical pressure to the individual's fingertip and modifying the mechanical pressure when the photoplethysmography sensor emits the electromagnetic radiation to the arterial system and receives the electromagnetic radiation from the arterial system.

3. 3. The device according to claim 1 or 2, characterized in that the device comprises a processing system (103, 203, 303) for determining a first value of the mechanical pressure at which the envelope of the reflected electromagnetic radiation reaches a maximum value as the mechanical pressure is increased or decreased from a start value to an end value, the determined first value being indicative of the mean arterial blood pressure of the arterioles of the arterial system.

4. 2. The device of claim 1, wherein the pressure device (302) comprises a pressing device (305) for directing the mechanical pressure towards the brachial artery of the individual, and the photoplethysmography sensor (301) is located on a surface of the pressing device that is intended to be above the brachial artery.

5. 5. The device of claim 4, wherein the pressure device (305) is a cuff, the pressure device comprising a pump system (306) for controlling the pressure of gas inside the cuff to direct the mechanical pressure towards the brachial artery, and the photoplethysmography sensor (301) is located on an inner surface of the cuff.

6. 1. A method for measuring the functionality of an individual's arterial system, comprising: emitting electromagnetic radiation having a wavelength in the range of 475 nm to 600 nm to the arterial system (501); receiving (502) a portion of the electromagnetic radiation reflected from the arterial system; generating information indicative of the functionality of the arterial system based on the received electromagnetic radiation (503); Varying (504) the mechanical pressure applied to the arterial system such that when the electromagnetic radiation is emitted to the arterial system and the reflected electromagnetic radiation is received from the arterial system, the mechanical pressure increases until an envelope of the reflected electromagnetic radiation drops to approximately zero; and holding the mechanical pressure constant after the envelope of the reflected electromagnetic radiation drops to approximately zero; The method comprises detecting whether the envelope of the reflected electromagnetic radiation increases when the mechanical pressure is held constant, wherein an increase in the envelope is indicative of normal endothelial function of the arterial system.

7. A computer program comprising: a programmable processing system; controlling the photoplethysmography sensor to emit electromagnetic radiation having a wavelength in the range of 475 nm to 600 nm toward the arterial system and to receive a portion of the electromagnetic radiation reflected from the arterial system; managing the mechanical pressure applied to the arterial system by controlling a pressure device to increase mechanical pressure when the photoplethysmographic sensor emits the electromagnetic radiation into the arterial system and receives the electromagnetic radiation from the arterial system until an envelope of the reflected electromagnetic radiation drops to approximately zero; and computer executable instructions for controlling the mechanical pressure to remain constant after the envelope of the reflected electromagnetic radiation drops to approximately zero; The computer program further comprises computer executable instructions for controlling the programmable processing system to detect whether the envelope of the reflected electromagnetic radiation increases when the mechanical pressure is held constant, an increase in the envelope being indicative of normal endothelial function of the arterial system.

8. 8. The computer program of claim 7, comprising computer executable instructions for the programmable processing system to control the pressure device to modify the mechanical pressure applied to the arterial system when the photoplethysmographic sensor emits the electromagnetic radiation to and receives the electromagnetic radiation from the arterial system.

9. A non-transitory computer readable medium encoded with a computer program according to claim 7 or 8.

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