Devices, systems, and methods for determining oxygen saturation of a subject

Abstract

The present invention relates to an apparatus (100), system (500), and method for determining the SpO2 (160) of a subject. Two types of PPG measurements, wide-field PPG with uniform illumination and / or a speckle pattern, and radial PPG with speckle illumination, are used to quantify the difference in penetration depth for electromagnetic radiation in the red spectral range and the infrared spectral range. This difference in penetration depth is then used to find a more stable ratio (RR) of the ratios, thereby finding a more accurate SpO2 (160).

Description

Technical Field

[0001] The present invention relates to devices, systems and methods for determining the oxygen saturation of a subject. Background Art

[0002] Pulse oximeters, which continuously and noninvasively measure arterial oxygen saturation (SpO2), are now routinely used in many clinical settings. Furthermore, pulse oximeters are widely used in all aspects of general healthcare, including neonatal care, where artificial oxygenation is common.

[0003] Pulse oximetry is often inaccurate for premature infants, often those in the neonatal intensive care unit (NICU), where the safest clinical saturation level is considered to be around 95%, rather than 100% for adults. As studied by A. Hellstrom et al., "Retinopathy of prematurity" (Lancet 382(9902), 2013) and O.D. Saugstad and D. Aune, "Optimal Oxygenation of Extremely Low Birth Weight Infants: A Meta-Analysis and Systematic Review of the Oxygen Saturation Target Studies" (Neonatal 105, 2014), newborns need to strike a very delicate balance between supplying too much oxygen (risking retinopathy of prematurity (ROP)) and too little oxygen (potentially leading to brain damage or death).

[0004] Due in part to the relative inaccuracy of pulse oximeters, the actual target saturation level is not precise, and a large number of international studies have been conducted to determine this. There is an overall urgent need for pulse oximeters with higher accuracy.

[0005] The fundamental problem with prior art pulse oximetry is the implicit assumption that the wavelengths used "see" the same pulsating arteriolar vessels and that the relative photoplethysmographic (PPG) amplitude reflects the saturation of the blood therein. If red and near-infrared light have different penetration depths (e.g., due to absorption by non-pulsating venous blood), differences in the resulting relative PPG amplitudes can be erroneously interpreted as resulting from different SpO2 levels.

[0006] US 2017 / 188919 A1 discloses a patient monitor having a plurality of sensors adapted to be attached to a tissue site of a living subject, wherein the sensors generate sensor signals responsive to optical radiation of at least two wavelengths after being attenuated by pulsating blood within the tissue site.

[0007] Further devices and methods for obtaining vital signs of a subject (e.g., SpO2) can be found in US 2019 / 167124 A1, US 2019 / 286233 A1, and US 2013 / 006074 A1. Summary of the Invention

[0008] It is an object of the present invention to provide a more accurate device, method and system for determining SpO2 of a subject.

[0009] In a first aspect of the present invention, a device for determining SpO2 of a subject is proposed, the device comprising a processing unit configured to:

[0010] obtaining a first detection signal and a second detection signal derived from detected electromagnetic radiation at different wavelengths in the visible spectral range or the infrared spectral range transmitted through or reflected from the skin area of ​​the subject illuminated by the spot illumination;

[0011] obtaining a third detection signal and a fourth detection signal, the third detection signal and the fourth detection signal being derived from detected electromagnetic radiation at the different wavelengths transmitted through or reflected from the skin area of ​​the object illuminated by the uniform illumination and / or the spot illumination pattern, wherein the third detection signal is derived from detected electromagnetic radiation at the same wavelength as the wavelength of the first detection signal and the fourth detection signal is derived from detected electromagnetic radiation at the same wavelength as the wavelength of the second detection signal, wherein in the case of the spot illumination pattern the third detection signal (103) and the fourth detection signal (104) are derived by spatial integration of the electromagnetic radiation (90) transmitted through or reflected from the skin area (12);

[0012] determining a first ratio (RR1) of the ratios based on the first detection signal and the second detection signal, and determining a second ratio (RR2) of the ratios based on the third detection signal and the fourth detection signal;

[0013] determining a first normalized signal by calculating a ratio of the first detection signal to the third detection signal, and determining a second normalized signal by calculating a ratio of the second detection signal to the fourth detection signal;

[0014] determining a penetration depth ratio (PDR) by calculating a ratio of the first normalized signal to the second normalized signal;

[0015] Correcting the RR1 and the RR2 using the PDR to compensate for the difference in penetration depth between the different wavelengths; and

[0016] The SpO2 is determined based on the corrected RR1 and / or the corrected RR2.

[0017] According to another aspect of the present invention, a system for determining the SpO2 of an object is proposed, which, in addition to the above-mentioned device, also includes: an illumination unit configured to emit a narrow beam of electromagnetic radiation to illuminate the skin area of ​​the object by spot illumination; a light diffuser that can be selectively arranged within or outside the path of the emitted light of the illumination unit, wherein the light diffuser is configured to diffuse the electromagnetic radiation emitted by the illumination unit to illuminate the skin area of ​​the object uniformly and / or by a spot pattern; and a detection unit configured to: detect the electromagnetic radiation in the visible spectral range or the infrared spectral range that is transmitted through the skin area of ​​the object or reflected from the skin area of ​​the object, and derive a detection signal based on the detected electromagnetic radiation.

[0018] In a further aspect of the present invention, a corresponding method, a computer program and a non-transitory computer-readable recording medium are provided, wherein the computer program comprises program code means for causing the computer to perform the steps of the method disclosed herein when the computer program is executed on a computer, and the non-transitory computer-readable recording medium has a computer program product stored therein, which, when run by a processor, causes the method disclosed herein to be performed.

[0019] Preferred embodiments of the invention are defined in the dependent claims. It should be understood that the claimed method, system, computer program and medium have similar and / or identical preferred embodiments as the claimed device, in particular the embodiments defined in the dependent claims and the embodiments disclosed herein.

[0020] The present invention is based on the idea of ​​combining two types of PPG measurements (widefield PPG and radial PPG) to quantify the difference in penetration depth for electromagnetic radiation in different spectral ranges. This difference can then be used to find a more stable RR, and therefore a more accurate SpO2 level that is largely independent of the aforementioned inaccuracies. To determine SpO2, a standard model is used that exploits the linear relationship between SpO2 and RR. A more detailed explanation is provided below in the description of the figures.

[0021] Wide-field PPG in the context under discussion means a measurement type in which the subject's skin is illuminated uniformly and / or with structured light (a spot pattern of dots, circles, stripes, etc.), whereas radial PPG in the context under discussion means a measurement type in which the subject's skin is illuminated with spot lighting (e.g. with a laser).

[0022] By combining the radial PPG amplitude and the wide-field PPG amplitude for two different wavelengths, a relative penetration index (called PDR) can be obtained, which is then used to calculate the SpO2 level with much higher accuracy than a standard pulse oximeter.

[0023] This also provides a novel way to provide a depth measure for PPG sources that is independent of individual differences caused by cardiac output or arterial stiffness. This approach is crucial for assessing centralization, vasodilation, or constriction during wound healing or before and after vascular surgery.

[0024] As defined above, RR1 is determined based on the first and second detection signals. Therefore, RR1 can also be referred to as radial RR, as both the first and second detection signals are derived from the radial PPG measurement type. RR2 is determined based on the third and fourth detection signals. Therefore, RR2 can also be referred to as widefield RR, as both the third and fourth detection signals are derived from the widefield PPG measurement type.

[0025] In addition, the first normalized signal is determined by calculating the ratio of the first detection signal to the third detection signal. Both detection signals are derived from electromagnetic radiation having the same wavelength (e.g., exemplary electromagnetic radiation in the near-infrared spectral range). Therefore, the first normalized signal can indicate a normalized signal related to electromagnetic radiation in the near-infrared spectral range. In this context, the first normalized signal is a measure of the penetration depth of electromagnetic radiation in the near-infrared spectral range into the skin of the subject.

[0026] The second normalized signal is determined by calculating the ratio of the second detection signal to the fourth detection signal. Both detection signals are also derived from electromagnetic radiation having the same wavelength, but the wavelength must be different from the underlying wavelength used by the first detection signal and the third detection signal. Therefore, the second detection signal and the fourth detection signal can be derived, for example, from electromagnetic radiation in the red light spectral range. Therefore, the second normalized signal can indicate a normalized signal related to electromagnetic radiation in the red light spectral range. In the context, the second normalized signal is a measure of the penetration depth of electromagnetic radiation in the red light spectral range in the skin of the subject.

[0027] The PDR is determined by calculating the ratio of the first normalized signal to the second normalized signal and is therefore a measure for relative penetration depth.

[0028] The processing unit is configured to derive the third and fourth detection signals by spatially integrating the electromagnetic radiation transmitted through or reflected from the skin area in the case of a spot illumination pattern. Preferably, all electromagnetic radiation transmitted through or reflected from the skin area illuminated by the spot illumination pattern is used for spatial integration to obtain the third and fourth detection signals, respectively. Such a spot illumination pattern can include several illumination spots, but can also include only one illumination spot, for example, a single laser spot. Therefore, the third and fourth detection signals can be obtained, for example, using the spatial integration of all light reflected from a single laser spot. In this case, a single laser configured to emit at least two different wavelengths can be used, or two different lasers configured to emit at corresponding single wavelengths can be used.

[0029] Wide-field PPG is typically measured using a light source that emits electromagnetic radiation uniformly onto an area of ​​the subject's skin. However, structured light (i.e., patterns of dots, stripes, circles, etc.) can also work. In fact, any non-uniform illumination pattern will work, although deconvolution works well.

[0030] Additionally, even if only spot illumination is used (ie, one laser spot on the subject's skin), determining the spatial integral of all light reflected back from the subject's skin is suitable for providing wide-field PPG.

[0031] Compared to using uniform illumination, using a structured pattern or just one illumination spot may offer the advantage of obtaining a larger signal strength in a small number of pixels, which may be suitable for obtaining a more accurate PPG signal.

[0032] Therefore, using a combination of uniform illumination and spot illumination or illumination by structured light may also be a viable option. This may be interesting if the processing unit is also used for PPG imaging, since uniform illumination again provides better spatial resolution than spot illumination or illumination by structured light.

[0033] According to one embodiment, the processing unit is configured to use a reference ratio RR of the ratios ref and reference penetration depth ratio PDR ref To correct the RR1 and / or the RR2.

[0034] These reference ratios can be determined by models, numerical simulations, or by empirical measurements of a large number of individuals. Preferably, the determined RR1 or RR2 and the corresponding determined PDR are both consistent with the RR ref and PDR ref A comparison was made.

[0035] In addition, it should be understood that RR ref The reference ratio is preferably divided into ratios for RR1 and RR2 respectively because the ratios among the ratios determined from the radial PPG and the ratios among the ratios determined from the wide-field PPG are generally different.

[0036] According to another embodiment, the processing unit is configured to compare the RR1 and / or the RR2 and the PDR with a reference ratio RR in the ratio ref and reference penetration depth ratio PDR ref Preferably, the lookup table is divided into a lookup table for a reference ratio of RR1 (radial RR) and a lookup table for a reference ratio of RR2 (widefield RR).

[0037] According to another embodiment, the processing unit is configured to use a reference ratio RR describing the ratio for different SpO2 values ref and reference penetration depth ratio PDR ref A calibration curve showing the relationship between the PDR and the RR1 and / or the RR2 is used to compare the PDR and the RR1 and / or the RR2 with the calibration curve.

[0038] These calibration curves are preferably based on the RR values ​​stored in the corresponding lookup tables for RR1 (radial RR) and RR2 (widefield RR). ref and PDR ref Therefore, these lookup tables may include three columns, where the first column includes RR ref , the second column includes PDR ref, and the third column includes the correct SpO2 value. Based on these lookup tables, the calibration curve can be determined manually by the user or automatically by the processing unit. The calibration curve is then preferably visualized in a graph having an ordinate axis and an abscissa axis, wherein the ordinate axis illustrates the RR ref , and the horizontal axis illustrates PDR ref The various calibration curves for different SpO2 values ​​can then be visualized in one graph. A more detailed explanation will be given later with reference to the description of the accompanying drawings.

[0039] According to another embodiment, the processing unit is configured to select a matching calibration curve to obtain a PDR equal to 1 by extrapolating the matching curve to ref and set the RR1 and / or RR2 to the corresponding RR ref To correct the RR1 and / or the RR2.

[0040] Therefore, the determined RR1 or the determined RR2 and the corresponding PDR are compared with a plurality of calibration curves and a matching calibration curve is selected by the processing unit. This can be done by selecting the matching curve which, when the determined RR1 or the determined RR2 and the corresponding PDR are visualized as a data point in the graph, is closest to the data point obtained in the above-mentioned graph. By selecting the matching curve and extrapolating the curve to a PDR equal to 1 ref And set RR1 or RR2 to the corresponding RR ref As corrected RR1 or corrected RR2 , the ratio of the ratios is corrected for unequal penetration depths of the electromagnetic radiation in the red spectral range and in the infrared spectral range.

[0041] The claimed system is not limited to the use of one illumination unit or one detection unit. Nevertheless, at least one illumination unit must be a spot illumination source (e.g. a laser) to provide the possibility to perform radial PPG measurements.

[0042] The above-described embodiment of the system offers the advantage of requiring only a single illumination unit. Because the light diffuser can be selectively positioned within or outside the path of the illumination unit's emitted light, wide-field PPG or radial PPG measurements can be performed. This provides a compact system for accurate SpO2 measurement. The narrow electromagnetic radiation beam allows for the acquisition of discrete spots on the subject's skin, which can be dots, circles, lines, etc.

[0043] Preferably, the illumination unit is further configured to emit electromagnetic radiation at at least two different wavelengths and / or to alternately emit red and infrared light. Thus, the first measurement can be performed by measuring radial PPG with red light, while the second measurement can be performed by measuring radial PPG with infrared light. A light diffuser can then be arranged within the path of the emitted light to diffuse the light, thereby obtaining a structured illumination pattern and / or uniform illumination on the subject's skin. The third measurement can then be performed by measuring wide-field PPG with red light, and the fourth measurement can be performed by measuring wide-field PPG with infrared light. It should be noted that in applications where visible light is undesirable (e.g., in sleep monitoring where visible light might disturb a person's sleep), two or more infrared wavelengths can be selected in addition to red and infrared light. Nevertheless, red light is generally preferred because the SpO2 contrast at this wavelength is greater than the SpO2 contrast at a combination of infrared wavelengths.

[0044] According to another embodiment, the illumination unit and the detection unit are either both in direct physical contact with the subject's skin or neither is in direct physical contact with the subject's skin.

[0045] It will therefore be appreciated that the system is not limited to use as a remote PPG setup, as it can also be used as a contact PPG, where the illumination unit and the detection unit are attached directly to the subject's skin (e.g. as a finger clip).

[0046] Furthermore, it will also be appreciated that the widefield PPG signal may be replaced by a signal with a very small radial (source-detector) distance, since this signal is very similar (as a widefield PPG signal) in the sense that it primarily probes the upper layers of the skin.

[0047] According to another aspect, the system described above can be modified so that the system includes not only a first lighting unit configured to emit a narrow beam of electromagnetic radiation to illuminate the subject's skin area by spot lighting, but also a second lighting unit configured to emit a uniform illumination profile of electromagnetic radiation and / or structured light to illuminate the subject's skin area uniformly and / or by structured light. Structured light in this context refers to a pattern of electromagnetic radiation, i.e., a pattern of dots, circles, stripes, etc.

[0048] According to this aspect, a light diffuser is not required because radial PPG measurement can be performed by using the first illumination unit and wide-field PPG measurement can be performed by using the second illumination unit.

[0049] It will be appreciated that the modified system may have the same embodiments as discussed with reference to the system having only one lighting unit.

[0050] According to another embodiment, the detection unit is an optical sensor and comprises a plurality of detection elements, in particular an array of photodiodes, a CCD array or a CMOS array. If the detection unit is in contact with the subject's skin as a contact device, wide-field PPG measurement also requires the use of an array of detection units rather than just one detector unit.

[0051] Further advantages are obtained from the description and the drawings. It is understood that the features mentioned above and below can be used not only in the combination indicated but also in other combinations or as a whole without departing from the scope of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter. In the accompanying drawings:

[0053] Figure 1 showing a graph illustrating a subject's blood absorption coefficient in dependence on the wavelength of electromagnetic radiation transmitted through or reflected from the subject's skin;

[0054] Figure 2 shows a graph illustrating reference SpO2 values ​​of a subject depending on RR;

[0055] Figure 3A and Figure 3B A schematic diagram illustrating two default assumptions in pulse oximetry is shown;

[0056] Figure 4A and Figure 4B shows a schematic diagram illustrating the effect of increased venous blood on the penetration depth of red electromagnetic radiation and infrared electromagnetic radiation;

[0057] Figure 5A and Figure 5B shows a schematic diagram illustrating the effect of equal penetration depth of red electromagnetic radiation and infrared electromagnetic radiation on SpO2 measurement;

[0058] Figure 6A and Figure 6B shows a schematic diagram illustrating the effect of unequal penetration depths of red and infrared radiation on SpO2 measurements;

[0059] Figure 7A and Figure 7B shows a schematic diagram illustrating the path of electromagnetic radiation through the skin of a subject for wide-field PPG and radial PPG;

[0060] Figure 8A and Figure 8B shows a schematic diagram illustrating detected reflected light of a wide-field PPG and a radial PPG;

[0061] Figure 9 Schematic diagram showing a Monte Carlo simulation of the path of photons through the skin of a subject for radial PPG;

[0062] Figure 10A and Figure 10B A schematic diagram of a system for determining SpO2 of a subject according to the present invention is shown;

[0063] Figure 11 shows a schematic diagram illustrating a method executed by a device for determining SpO2 of a subject according to the present invention;

[0064] Figure 12 shows a schematic diagram illustrating a first processing step of a detection signal obtained by the device;

[0065] Figure 13A and Figure 13B shows a schematic diagram illustrating the influence of different skin layers on the measured signal;

[0066] Figure 14 shows a graph illustrating the PDR in dependence on radial distance;

[0067] Figure 15 A diagram illustrating the dependence of RR1 on PDR is shown;

[0068] Figure 16 A graph illustrating the dependence of RR2 on PDR is shown;

[0069] Figure 17 shows a graph illustrating RR1 dependence on PDR for various parameters;

[0070] Figure 18 shows a graph illustrating RR2 dependence on PDR for various parameters;

[0071] FIG. 19 shows a graph illustrating an example of correction for RR1 ( Figure 19A ) and the lookup table ( Figure 19B );

[0072] Figure 20 A graph showing a constant corrected RR1 is shown;

[0073] Figure 21 A graph illustrating an example of correction for RR2 is shown;

[0074] Figure 22 shows a graph showing a constant corrected RR2; and

[0075] Figure 23 A-23D shows a graph illustrating the relationship between the determined SpO2 and RR. DETAILED DESCRIPTION

[0076] Figure 1 A graph illustrating the dependence of a subject's blood absorption coefficient on the wavelength of electromagnetic radiation transmitted through or reflected from the subject's skin is shown. The vertical axis 511 represents the blood absorption coefficient, while the horizontal axis 512 represents the wavelength of the electromagnetic radiation in the spectral range from 500 nm to 1100 nm (visible to the near-infrared spectrum). A first curve 513 illustrates the absorption of hemoglobin (Hb), while a second curve 514 illustrates the absorption of oxygenates (HbO2). Both components are part of the blood contained in the blood vessels of the skin.

[0077] The principle of pulse oximetry is simple, namely, HbO2 and Hb absorb electromagnetic radiation in the red and infrared spectral ranges differently, e.g. Figure 1 The different curves 513 and 514 in FIG. The ability of pulse oximetry to detect SpO2 of only arterial blood is based on the principle that the amount of absorbed red light (λ1) and infrared light (λ2) fluctuates with the cardiac cycle because arterial blood volume increases during systole and decreases during diastole. The ratio of ratios (RR) is derived from the resulting modulated light intensity (called PPG) using the following formula:

[0078]

[0079] Here, the ratio of the pulsating signal (AC) to the non-pulsating signal (DC) of a specific wavelength λ1 is normalized to the ratio of the pulsating signal to the non-pulsating signal of another wavelength λ2.

[0080] The RR can be considered to have a nearly linear relationship with the subject's SpO2:

[0081] SpO2=C1-C2RR (2)

[0082] Where C1 and C2 are the coefficients of the linear equation. Thus, SpO2 can be obtained by measuring RR. This is the standard model for determining the SpO2 value of a subject, and it is used here as well. The linear relationship (2) is the simplest form of describing the relationship between SpO2 and RR. Different relationships (e.g., quadratic or higher order polynomials) can also be used, or even a lookup table can be used.

[0083] Figure 2 The reference SpO2 (SpO2) of the subject is shown in dependence on the RR value. 2,ref) values. Here, the vertical axis 521 represents the SpO2 value expressed as a percentage (%), and the horizontal axis 522 represents the RR. The linear dependence of the SpO2 value on the RR value is clearly visible. A linear regression 525 is performed using only the filtered measured data 523, represented by circles. The dotted line 526 represents the corresponding 99% confidence interval, and also shows the discarded measured data points 524 that were not used in the calibration.

[0084] Figure 3A and Figure 3B A schematic diagram illustrating two default assumptions in pulse oximetry is shown. The first assumption is that only arterial blood volume is pulsatile. Figure 3A Illustrated are the epidermis 13 of the subject's skin and the underlying venules 14 and arterioles 16. The pulsatile component of the arterioles 16 is indicated by arrows around the arterioles 16 pointing away from the respective arterioles.

[0085] A second assumption that is always made in pulse oximetry is that the wavelengths λ1 and λ2 used "see" the same vascular structure. Figure 3B The large arrow in the figure shows this situation. Figure 3B Electromagnetic radiation 90a, 90b is indicated in the red spectral range (λ1) and the near infrared spectral range (λ2), wherein the length of the arrows indicates the respective penetration depth 20. This second assumption is particularly problematic in classical pulse oximetry and is addressed by the present invention and further explained with reference to the subsequent figures.

[0086] Figure 4A and Figure 4B Shown is a schematic diagram illustrating the effect of increased venous blood on the penetration depth of red and infrared electromagnetic radiation. Figure 4A 5 shows the ratio of the pulsatile component to the non-pulsatile component of the PPG signal (AC / DC) on the ordinate axis 531 and time on the abscissa axis 532. A first curve 533 illustrates the AC / DC ratio (or the relative amplitude of the PPG signal) for near-infrared radiation, while a second curve 534 illustrates the AC / DC ratio (or the relative amplitude of the PPG signal) for electromagnetic radiation in the red spectral range.

[0087] exist Figure 4A At a certain point in time, illustrated by the vertical dashed line 535, the increase in venous blood (which is static, not pulsating) affects the penetration depth of red radiation and infrared radiation, but to different degrees. Figure 4B The length of the arrow in the figure shows this situation. Figure 4B The arrows in FIG. 1 illustrate the electromagnetic radiation 90a in the red spectral range and the electromagnetic radiation 90b in the infrared spectral range before the increase in venous blood ( Figure 4Bto the left) and after ( Figure 4B It can be seen that the infrared light no longer reaches the deeper pulsating blood vessels at a time point greater than the time point illustrated by the vertical dashed line 535, which causes the following Figure 4A In contrast, by comparing Figure 4B As can be seen from the lengths of the corresponding arrows on the left and right sides of the image, the red PPG amplitude is much less affected.

[0088] If the pulsation intensity of the blood vessels is uniform throughout the depth of the skin, then the problem may be minimal, even if the wavelengths have different penetration depths. However, it may cause problems when the pulsating blood vessels are located in different layers. This is discussed below. Figure 5A 、 Figure 5B and Figure 6A 、 Figure 6B This is explained in .

[0089] Figure 5A and Figure 5B A schematic diagram illustrating the effect of equal penetration depth of red electromagnetic radiation and infrared electromagnetic radiation on SpO2 measurement is shown. The ordinate axes 541, 551 represent relative PPG amplitude, while the abscissa axes 542, 552 represent time (at Figure 5A and Figure 5B on the right side of the ). Figure 5A The first curve 543 and Figure 5B The first curve 553 illustrates the PPG amplitude derived from the red electromagnetic radiation 90a transmitted through or reflected from the skin area 12 of the subject, while Figure 5A The second curve 544 and Figure 5B The second curve 554 illustrates a PPG amplitude derived from infrared electromagnetic radiation 90b transmitted through or reflected from the skin area 12 of the subject.

[0090] according to Figure 5A and Figure 5B The two measurements shown calculate an RR equal to 0.5, which results in an SpO2 of 100%. Figure 5A and Figure 5B The only difference between Figure 5A The pulsation profile 555a shown in the middle column is Figure 5B The pulsation profile 555b shown in FIG is much more uniform, which means that Figure 5A The pulsating blood vessels shown in the middle column are Figure 5BCompared to the pulsating blood vessels shown in the middle column of FIG. , the penetration depth of the electromagnetic radiation 90 is more uniformly distributed along the pulsating blood vessels. However, at the same penetration depth, this does not affect the SpO2 results. Whether the pulsation profiles 555a, 555b are uniform or at discrete depths, SpO2 can be accurately measured.

[0091] This is Figure 6A and Figure 6B Obviously different, Figure 6A and Figure 6B A schematic diagram illustrating the effect of unequal penetration depths of red electromagnetic radiation 90a and infrared electromagnetic radiation 90b on SpO2 measurements is shown.

[0092] The ordinate axes 561 , 571 represent PPG amplitude, while the abscissa axes 562 , 572 again represent time. Figure 6A The first curve 563 and Figure 6B The first curve 573 illustrates the PPG amplitude of red electromagnetic radiation 90a transmitted through or reflected from the subject's skin 12, while Figure 6A The second curve 564 and Figure 6B The second curve 574 illustrates the PPG amplitude of near infrared electromagnetic radiation 90b transmitted through or reflected from the subject's skin 12.

[0093] Figure 6A and Figure 6B The difference between the reference Figure 5A and Figure 5B Same differences as discussed: Figure 6B Compared to the pulsation profile 555b shown in Figure 6A The pulsation profile 555a shown in the middle column is more evenly distributed along the penetration depth of the electromagnetic radiation.

[0094] against Figure 6A The RR of 0.6 calculated for the exemplary scenario illustrated in FIG results in an SpO2 value of 90%, while for Figure 6B The exemplary scenario illustrated in FIG2 shows an RR greater than 0.6 calculated, resulting in an SpO2 greater than 90%. Therefore, if the penetration depths are unequal, errors in SpO2 may occur. This is particularly likely to occur when the pulsation profiles 555a, 555b are significantly different.

[0095] The inventors recognized the problem and hypothesized that the relatively poor accuracy of standard pulse oximeters is at least partially caused by the described unequal / varying penetration depths.

[0096] Figure 7A and Figure 7BA schematic diagram illustrating the path of electromagnetic radiation 90 through a subject's skin area 12 for widefield PPG and radial PPG is shown.

[0097] Widefield PPG is a mode that has been commonly used in camera mode for many years, in which the illumination of electromagnetic radiation 90 is evenly distributed over the skin area 12 and the PPG signal is measured over the same skin area. Figure 7A Electromagnetic radiation 90 travels through a skin area 12 having various venules 14 and arterioles 16 before being detected by a detection unit 300 (e.g., a camera). The detected electromagnetic radiation and the derived PPG signal are the average results of all electromagnetic radiation 90 detected by the camera 300.

[0098] Figure 7B The radial PPG mode is shown. The radial PPG is very similar in principle to a conventional contact probe PPG measurement. The skin area 12 is illuminated by a spot (e.g., circle, stripe, dot, etc.) and the PPG signal is measured a few millimeters away from the illumination spot on the skin area 12. Figure 7B The radial distance 15 between the illumination spot on the skin area 12 and the spot from which the PPG signal is measured is exemplarily illustrated by one reflected beam in FIG. Therefore, the radial PPG signal is generally a signal that depends on the radial distance 15. In other words, electromagnetic radiation reflected from the subject's skin area 12 is reflected back from the skin area 12 by the following process: entering the skin area 12 through the epidermis at the illumination spot of the illumination unit 200, reflecting back from components of the skin area 12, and exiting the skin area 12 through the epidermis 13 at a radial distance 15 from the illumination spot. In other words, the electromagnetic radiation detected by the detection unit 300 is scattered back from the skin area 12, and pulsation information is collected from various venules 14 and arterioles 16 in the skin area 12 located beneath the epidermis 13.

[0099] It will be shown below that the present invention combines the results obtained from these two different measurement modes (radial PPG and wide-field PPG).

[0100] Figure 8A and Figure 8B Schematic diagrams illustrating the detected reflected light of wide-field PPG and radial PPG are shown. Figure 8A and Figure 8B The top schematic diagram is the same as that already mentioned previously. Figure 7A and Figure 7B The schematics discussed are the same.

[0101] Figure 8AA graph illustrating the detected reflected light of a wide-field PPG setup is shown (at the bottom). Here, the ordinate axis 571 represents the detected reflected light, while the abscissa axis 572 represents the measurement time. Curve 573 illustrates the detected reflected light, which includes a DC component 575 and an AC component 574. The AC component 574 represents the pulsatile component originating from optical absorption by pulsating arterial blood, while the DC component 575 represents the non-pulsatile component including contributions from non-pulsating arterial blood, venous blood, and other tissues.

[0102] Figure 8B In the middle row are shown three graphs illustrating the detected reflected light for a radial PPG setup. To this end, the ordinate axis 581 represents the detected reflected light, while the abscissa axis 582 represents the measurement time. As can be clearly seen from the three curves 583, 584, 585, the longer the time it takes for the light to travel through the subject's skin 12 (and the greater the radial distance 15, see Figure 7B ), the smaller the DC component of the detected reflected light. This is schematically illustrated by the shifts in curves 583, 584, and 585, respectively. This is because if light travels a longer path through the skin, skin area 12 absorbs more light or electromagnetic radiation 90.

[0103] exist Figure 8B This dependence is also illustrated in the bottommost graph at the bottom of the graph. This graph plots the AC or DC component of the detected reflected light on the ordinate axis 591 and the radial distance 15 on the abscissa axis 592. A first curve 593 plots the DC component of the detected reflected light, while a second curve 594 plots the AC / DC ratio of the detected reflected light. The trends already discussed become apparent. Furthermore, it is clear that the greater the radial distance 15, the greater the AC / DC ratio (and the greater the relative pulsating component).

[0104] Figure 9 A schematic diagram of a Monte Carlo simulation of the path of light through a subject's skin 12 for a radial PPG is shown. The light distribution inside the skin 12 is visualized to illustrate different penetration depths 20.

[0105] Figure 10A and Figure 10B A system 500 for determining the SpO2 value of a subject according to the present invention is shown. The system 500 is configured to measure the SpO2 value of a subject by converting the wide-field PPG measurement results (see FIG. Figure 10A ) and radial PPG measurement results (see Figure 10B ) are combined to overcome the problems discussed above.

[0106] like Figure 10AAs shown, the system 500 comprises at least an illumination unit 200, a detection unit 300 and an apparatus 100 for determining the SpO2 of a subject. Figure 11 The apparatus 100 is explained in more detail.

[0107] The lighting unit 200 is configured to emit electromagnetic radiation 90 to illuminate the subject's skin 12. Preferably, the lighting unit 200 is configured to emit a controllable, narrow beam of electromagnetic radiation 90. The electromagnetic radiation 90 preferably lies within the visible and infrared spectral ranges. Thus, the lighting unit 200 can be configured to emit electromagnetic radiation 90 at at least two different wavelengths and / or to alternately emit red light and infrared light as electromagnetic radiation 90.

[0108] according to Figure 10A In the embodiment shown, the system 500 may further include a support 250 for confining the subject's skin area 12 to a restricted skin region to be measured. The support 250 may be as follows: Figure 10A The is shown placed on the subject's skin and is preferably made of a material that is opaque to incident electromagnetic radiation 90. Preferably, the skin area 12 used for measurement is therefore limited to a zone comprising a skin area 12 having a uniform surface along the area to be measured.

[0109] Additionally, the system 500 may further comprise a diffuser 220. The diffuser 220 is configured to diffuse the controllable narrow beam of electromagnetic radiation 90 emitted by the illumination unit 200 to generate a uniform illumination profile and / or structured light on the skin area 12 of the subject.

[0110] The detection unit 300 is preferably a camera configured to detect electromagnetic radiation 90 in the visible spectral range and the infrared spectral range. The camera 300 is positioned such that the field of view 310 covers the area of ​​the skin 12 illuminated by the illumination unit 200.

[0111] It should be noted that not only wide-field PPG can be measured if the subject's skin 12 is uniformly illuminated. It also works properly if the skin 12 is illuminated with structured light, for example, with a speckle pattern (dots, circles, stripes, etc.). In this case, the PPG signal is derived by spatially integrating all electromagnetic radiation 90 transmitted through or reflected from the subject's skin 12. The processing unit 100 can be configured to perform this spatial integration.

[0112] Additionally, it should be noted that generating a uniform illumination profile on the subject's skin area 12 can be achieved not only by using an illumination unit 200 configured to emit a controllable narrow beam (e.g., laser) and a diffuser 220 for diffusing the narrow beam, but also by using one or even more illumination units that directly emit a uniform illumination profile.

[0113] Figure 10B 1 shows a diagram of a system 500 for radial PPG mode as discussed in accordance with the present invention. Figure 10A The embodiment of the system 500 shown is different. Figure 10B The illustrated system 500 does not include the diffuser 220. Thus, the controllable, narrow beam of electromagnetic radiation 90 emitted by the lighting unit 220 is directed directly toward the subject's skin 12 without being diffused. To this end, the diffuser 220 can be configured so that it can be optionally placed into the path of the electromagnetic radiation 90 emitted by the lighting unit 200 to switch between radial PPG mode and widefield PPG mode.

[0114] Figure 10A and Figure 10B The inlet in FIG shows a wide-field PPG on the subject's skin area 12 ( Figure 10A ) and radial PPG( Figure 10B ) image of the lighting profile.

[0115] It should be understood that Figure 10A and Figure 10B The embodiment shown is merely exemplary, as the system 500 comprises only one lighting unit 200 configured to emit a narrow beam of electromagnetic radiation 90. As already discussed above, the present invention is based on the concept of combining the results of wide-field PPG and radial PPG. Thus, according to another aspect of the present invention, the system 500 may include not only one lighting unit configured to emit a narrow beam of radiation, but also another lighting unit configured to emit a uniform illumination profile and / or a structured pattern (i.e., an illumination speckle pattern).

[0116] According to this aspect, there is no need for the light diffuser 220. Thus, the system 500 may include a first lighting unit 200a and a second lighting unit 200b, wherein the lighting units 200a, 200b themselves are configured to generate corresponding lighting profiles (i.e., spot lighting and uniform lighting profiles and / or structured patterns).

[0117] Figure 11 Shown is a schematic diagram illustrating a method according to the present invention performed by a device 100 for determining an SpO2 value of a subject.

[0118] The device 100 comprises a processing unit 110 which obtains in a first step S10 a first detection signal 101 and a second detection signal 102 which are derived from detected electromagnetic radiation 90 at different wavelengths transmitted through or reflected from the skin area 12 of the subject being illuminated by the spot illumination. These detection signals 101, 102 may be obtained from, for example Figure 10B The radial PPG setup shown is derived.

[0119] Furthermore, the processing unit 110 is configured to obtain, in a next step S20, a third detection signal 103 and a fourth detection signal 104, the third detection signal 103 and the fourth detection signal 104 being derived from the detected electromagnetic radiation 90 at the different wavelengths transmitted through or reflected from the skin area 12 of the subject irradiated with the uniformly illuminated and / or structured light, wherein the third detection signal 103 is derived from the detected electromagnetic radiation at the same wavelength as the first detection signal 101, and the fourth detection signal 104 is derived from the detected electromagnetic radiation at the same wavelength as the second detection signal 102. The detection signals 103, 104 may be derived from, for example Figure 10B 1 and 2. The first detection signal 101 and the third detection signal 103 may be derived from electromagnetic radiation in the infrared spectral range, while the second detection signal 102 and the fourth detection signal 103 may be derived from electromagnetic radiation in the red spectral range.

[0120] In the next step S30, the processing unit 110 is configured to determine a first ratio (RR1) 121 of the ratios based on the first detection signal 101 and the second detection signal 102, and to determine a second ratio (RR2) 122 of the ratios based on the third detection signal 103 and the fourth detection signal 104. The manner of determining the ratios 121 and 122 of the ratios has been explained in the above formula (1).

[0121] In a next step S40, the processing unit 110 determines a first normalized signal 131 by calculating the ratio of the first detection signal 101 to the third detection signal 103, and determines a second normalized signal 132 by calculating the ratio of the second detection signal 102 to the fourth detection signal 104. These normalized signals 131, 132 are a measure of the penetration depth 20 for the corresponding wavelength (of electromagnetic radiation in the infrared spectral range and of electromagnetic radiation in the red spectral range).

[0122] Then, in a further step S50, the processing unit 110 determines a penetration depth ratio (PDR) 140 by calculating the ratio of the first normalized signal 131 to the second normalized signal 132. The PDR reflects the difference in penetration depth of electromagnetic radiation in the red spectral range and in the infrared spectral range. The PDR is generally not only a value but also a curve PDR(r), where r is the radial distance 15 between the spot on the skin from which the radial PPG signal is measured and the illuminated spot on the skin (see Figure 7B The radial distance in 15). As will become apparent from the description with reference to the following figures, the curve PDR(r) is quite flat and can therefore be assumed to be one value.

[0123] In the next step S60 , the processing unit 110 corrects RR1 121 and RR2 122 by compensating for the difference in penetration depth 20 between the different wavelengths using the PDR 140 .

[0124] At the final step S70, the processing unit determines SpO2 160 based on the corrected RR1 151 and / or the corrected RR2 152. Figure 1 The manner in which SpO2 160 is determined from the ratio of the corrected ratios is explained.

[0125] Steps S10 - S70 executed by the processing unit 110 of the device 100 are explained in detail with reference to the following drawings.

[0126] Figure 12 Shown is a schematic diagram illustrating a first processing step of the detection signal obtained by the device 100 by illustrating the step of determining S40 a first normalized signal 131 and a second normalized signal 132 . Figure 12 The diagram on the left side of FIG illustrates the detection signals 101, 102, 103, 104 as a function of the radial distance 15 (see Figure 7B To further explain the radial distance 15).

[0127] A first detection signal 101 is derived from electromagnetic radiation in the infrared spectral range that is transmitted through or reflected from a skin area of ​​a subject illuminated with spot illumination (radial PPG). A second detection signal 102 is derived from electromagnetic radiation in the red spectral range that is transmitted through or reflected from a skin area of ​​a subject illuminated with spot illumination (radial PPG). A third detection signal 103 is derived from electromagnetic radiation in the infrared spectral range that is transmitted through or reflected from a skin area of ​​a subject illuminated with uniform illumination and / or structured light (widefield PPG). A fourth detection signal 104 is derived from electromagnetic radiation in the red spectral range that is transmitted through or reflected from a skin area of ​​a subject illuminated with uniform illumination and / or structured light (widefield PPG).

[0128] The third detection signal 103 and the fourth detection signal 104 derived from the wide-field PPG are constant and independent of the radial distance 15 , whereas the first detection signal 101 and the second detection signal 102 are functions that are dependent on the radial distance 15 .

[0129] As explained above, the processing unit 110 determines the first normalized signal 131 by calculating the ratio of the first detection signal 101 to the third detection signal 103 in step S40, and determines the second normalized signal 132 by calculating the ratio of the second detection signal 102 to the fourth detection signal 104. Therefore, Figure 12 The right graph illustrates the relationship between the first normalized signal 131 derived from electromagnetic radiation in the infrared spectral range and the second detection signal 132 derived from electromagnetic radiation in the red spectral range and the radial distance 15.

[0130] Figure 12 The illustrated graph and the graphs shown in subsequent Figures 13-23 are preferably all visualized on a monitor connected to apparatus 100 for determining SpO2 of a subject.

[0131] Figure 13A and Figure 13B A schematic diagram illustrating the influence of different skin layers 631 - 636 on the measured signal is shown. Figure 13B The schematic diagram shows skin layers 631-636 with one, two or three pulsating layers 611 and one epidermal layer 13. The six different skin layers 631-636 are further indicated by six different color codes 623 having different colors or shades of gray. These shades of gray are also used for Figure 13AThe corresponding curve in .

[0132] Figure 13A In the first row, radial PPG curves (radial PPG(r)) for six different skin geometries are shown. Where appropriate, "r" will be used hereinafter to denote the radial distance 15. Figure 13A The unit of radial distance 15 is centimeters.

[0133] Figure 13A The left-hand graph in the first row shows the second detection signal 102, and the right-hand graph shows the first detection signal 101 for six different skin layers 631-636. As is apparent from the left-hand graph, the curves have no clear relationship to the PPG skin geometry. The highest curve belongs to the fifth skin layer 635 because this skin layer is modeled for three pulsating layers 611, rather than just one or two. Therefore, this curve has the highest intensity.

[0134] It can also be seen that the curves are very strongly dependent on the optical depth of the PPG source. The curves show that the values ​​associated with the skin geometry of the third skin layer 633 are much larger than those associated with the skin geometry of the first skin layer 631. Furthermore, the curves for electromagnetic radiation in the infrared spectral range show slightly larger values ​​than the curves for electromagnetic radiation in the red spectral range. This can be explained by the fact that infrared light penetrates the skin slightly less deeply than red light. Therefore, the pulsation layer 611 is deeper for infrared light than for red light.

[0135] The infrared values ​​shown in the first row of the right-hand graph are approximately twice the red values, reflecting the larger absorption coefficient of pulsating blood in the infrared spectral range.

[0136] exist Figure 13A The left graph in the second row of FIG shows the second normalized signals 132 for six different skin layers 631-636, and the right graph shows the first normalized signals 131 for the six different skin layers 631-636. These graphs show that the values ​​are larger when the physical depth of the pulsating layer 611 is greater. This can be seen by comparing the highest curve belonging to the third skin layer 633 with the lowest curve belonging to the first skin layer 631.

[0137] The optical depth index (ODI) can be defined by taking the value of the first normalized signal 131 and the value of the second normalized signal 132 when r=1 cm. The ODI is not a true physical depth, but an expression of the relative optical depth of the source of the PPG: one or more pulsating layers (see Figure 13BThe word “relative” implies that ODI can be used to compare optical depths at different wavelengths, but ODI can also be used to compare relative optical depths at different anatomical locations.

[0138] The larger ODI value of infrared compared to red (see Figure 13A The difference in the values ​​of first and second normalized signals 131 and 132 at r = 1 cm is clearly due to the different penetration depths of these wavelengths. The actual physical depth of the pulsating layer is the same for both wavelengths. For infrared light, it simply "appears" deeper (larger ODI) because infrared light has a lower penetration depth. Penetration depth is inversely proportional to ODI.

[0139] As referenced above Figure 11 As explained, the processing unit 110 is further configured to determine S50 a penetration depth ratio (PDR) 140 by calculating the ratio of the first normalized signal 131 to the second normalized signal 132. The PDR 140 reflects the difference in penetration depth of electromagnetic radiation in the red spectral range and in the infrared spectral range. Knowing that the normalized signals 131, 132 are a measure of the penetration depth of the wavelength, these normalized signals 131, 132 are therefore used to obtain a measure of relative penetration depth: the PDR 140. Figure 14 The diagram illustrates this situation.

[0140] Figure 14 The PDR 140 is shown as a function of radial distance 15. The PDR 140 is again calculated for six different skin layers 631-636. It is clear that the PDR(r) 140 is always less than 1, indicating that red light "sees" deeper than infrared light. This difference in penetration depth between red light and infrared radiation is believed to be the cause of the inaccuracy of SpO2 in pulse oximetry measurements of the prior art (see above). Figure 6A and Figure 6B ), so it is used here to obtain a more accurate SpO2 value, which will be explained in more detail below.

[0141] like Figure 14 As shown, PDR(r) 140 is a curve that is a function of the radial distance 15 (the radial distance 15 between the illumination spot on the skin area 12 and the spot from which the PPG signal is measured; see reference 140). Figure 7B for more details). However, in Figure 14 As can be seen in Figure 1, the curve PDR(r) 140 is quite flat for all skin geometries. Therefore, it is assumed below that the PDR 140 is a constant value. This can be done by taking only the median value of the PDR(r) 140, or simply by using the ratio of the ODI values ​​(PDI = ODI(λ1) / ODI(λ2)).

[0142] Since the processing unit 110 is preferably connected to a monitor (not shown), the monitor can monitor the Figure 12-23 The graph shown is visualized, so if the PDR 140 is not within the predetermined range, the processing unit 110 can be configured to generate a warning signal for visualization on the monitor. This will indicate to the user that the wavelength used does not appear to be probing the same depth and associated vascular system. In addition, it indicates that the typical uncorrected SpO2 based on the ratio 121, 122 in the uncorrected ratio may not give an accurate SpO2.

[0143] As reference Figure 11 As explained, the processing unit 110 further determines, in step S30, a first ratio (RR1) 121 of the ratios based on the first detection signal 101 and the second detection signal 102, and determines a second ratio (RR2) 122 of the ratios based on the third detection signal 103 and the fourth detection signal 104. The manner of determining the ratios 121 and 122 of the ratios has been explained above in formula (2).

[0144] Figure 15 A graph illustrating the relationship of RR1 121 to PDR 140 is shown. Figure 16 A graph illustrating the relationship between RR2 122 and PDR 140 is shown. PDR 140 is extracted for all six different skin layers 631-636 by taking a constant value for each PDR(r) curve (see Figure 14 ).

[0145] exist Figure 15 and Figure 16 As can be seen in the graph, the variation of radial PPG (RR1=0.54-0.57) is much smaller than the variation of widefield PPG (RR2=0.63-0.82). It can also be seen that both RR1 and RR2 have a certain linear relationship with PDR 140, indicating a good opportunity to use PDR 140.

[0146] Figure 17 and Figure 18 An additional graph illustrating the relationship of RR1 121 and RR2 122 to PDR 140 is shown. Figure 15 and Figure 16 The data points shown are opposite, Figure 17 and Figure 18 More results are shown for a wider range of skin properties, simulating different individuals and different physiological states. Different degrees of venous oxygenation (e.g., 0.02 to 0.08 in the non-pulsating layer) and scattering coefficients (150 and 250 cm -1) and various combinations of anisotropy factors (0.7 and 0.74). By comparison Figure 17 and Figure 18 It can be seen that the relationship between RR1 (radial RR) 121 and PDR 140 shows much less correlation with PDR 140 than the relationship between RR2 (widefield RR) 122 and PDR 140. This is due to the much smaller variation of RR1 (see also Figure 15 and Figure 16 ). This means that the SpO2 160 derived from RR1 may be more accurate than the SpO2 160 derived from RR2. Figure 16 and Figure 18 Shows huge changes.

[0147] Hereinafter, it will be described how to use the relationship between RR1 121 and / or RR2 122 and PDR 140 shown in the last figure to obtain corrected RR1 151 and / or corrected RR2 152, thereby allowing SpO2 160 of a subject to be determined with higher accuracy.

[0148] FIG. 19 shows a graph illustrating an example of correction for RR1 ( Figure 19A ) and lookup table 135 ( Figure 19B ). The relationship between RR1 121 and PDR 140 is shown. The reference ratio (RR) in the description ratio is shown for different SpO2 and different RR values. ref )125 and reference penetration depth (PDR ref ) 145. These calibration curves 136 can be based on the relationship between Figure 19B The RR stored in the lookup table 135 is shown as ref 125 and PDR ref 145. Figure 19A The curves shown in were generated using Monte Carlo simulations using values ​​for skin component concentrations and optical properties within a realistic range.

[0149] The processing unit 110 is configured to select the matching calibration curve 136 to obtain a PDR by extrapolating the matching curve to 1. ref And set RR1 121 to the corresponding RR ref 125 to correct RR1 121. Therefore, by extracting the matching calibration curve 136 with Figure 19A The corrected RR1 is obtained by comparing the RR1 value at the intersection of the vertical lines 611 shown. The matching calibration curve 136 is preferably selected by selecting a curve that is closest to the value at which the determined RR1 121 and the determined PDR 140 would appear if they were visualized in a graph. Figure 19AThe data points obtained in .

[0150] Figure 20 A corresponding graph showing the constant corrected RR1 151 is shown. The constant corrected RR1 151 is obtained by referring to the above Figure 19A Obtained by the explained process.

[0151] Figure 21 and Figure 22 The same correction process for obtaining the corrected RR2 152 is shown for RR2 122. Preferably, RR2 122 is also corrected by comparing it with RR ref 125 and PDR ref 145 and compared with the lookup table 135 (not shown) and through the same extrapolation process (already referred to for RR1) Figure 19A and Figure 20 is explained) to complete the calibration process.

[0152] Figure 23 AD show graphs illustrating the relationship between the determined SpO2 and RR. Figure 23 A and Figure 23 B shows a graph illustrating SpO2 160 determined from RR1 121 and RR2 122 . Figure 23 C and Figure 23 D shows a graph illustrating SpO2 160 determined from corrected RR1 151 and corrected RR2 152 .

[0153] As can be seen, the corrected RR1 151 and corrected RR2 show less scatter than the (uncorrected) RR1 121 and RR2 122. This results in a tighter SpO2 calibration curve. This means that using the corrected RR1 151 and corrected RR2 152 allows for more accurate SpO2, especially compared to the relatively inaccurate RR2 (wide-field RR) commonly used in various stand-up pulse oximeters.

[0154] Various RR ref The relationship between 125 and SpO2 160 can be determined through models, numerical simulations, or through empirical measurements of a large number of individuals, different anatomical locations, and a variety of actual SpO2 levels.

[0155] Similar to the normal pulse oximetry process, a series of wide field RR (RR2), radial RR (RR1) and SpO2 can be acquired from the blood gas analysis to determine the relationship. This calibration process provides a reference data RR ref 125 and PDR ref 145.

[0156] As with current calibration procedures, multiple volunteers are asked to breathe mixtures with varying O2 concentrations, which can cause SpO2 values ​​(e.g., 70-95%) to be lower than normal (95-100%). Both wide-field PPG and radial PPG are measured using red and infrared electromagnetic radiation (90°), rather than just one measurement using a pulse oximeter. For each measurement, a corresponding PDR (140°) is calculated.

[0157] Once such a calibration curve 136 or calibration lookup table 135 is created, the pulse oximeter device 100 can measure in continuous radial PPG mode, occasionally taking wide-field PPG measurements to update the PDR mode. Alternatively, the pulse oximeter device 100 can also measure continuous wide-field PPG, occasionally taking radial PPG measurements.

[0158] Either way, the final SpO2 output will be based on the corrected RR1 151 and / or the corrected RR2, rather than RR1 121 and / or RR2, resulting in a more accurate SpO2 value for the subject.

[0159] Although the present invention has been illustrated and described in detail in the drawings and the foregoing description, such illustration and description should be considered illustrative or exemplary rather than restrictive; the present invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention by studying the drawings, the disclosure, and the claims.

[0160] In the claims, the word "comprising" does not exclude other elements or steps, and the word "a" or "an" does not exclude a plurality. A single element or other unit may fulfill the functions of several items recited in the claims. The fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0161] The computer program may be stored / distributed on suitable non-transitory media, such as optical storage media or solid-state media supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems.

[0162] Any reference signs in the claims should not be construed as limiting the scope.

Claims

1. A device (100) for determining an oxygen saturation SpO2 (160) of a subject, the device (100) comprising a processing unit (110) configured to: obtaining (S10) a first detection signal (101) and a second detection signal (102), the first detection signal and the second detection signal being derived from detected electromagnetic radiation (90) at different wavelengths in the visible spectral range or the infrared spectral range transmitted through or reflected from the skin area (12) of the subject illuminated by the spot illumination; Obtaining (S20) a third detection signal (103) and a fourth detection signal (104), the third detection signal and the fourth detection signal being derived from the detected electromagnetic radiation (90) at the different wavelengths transmitted through or reflected from the skin area (12) of the subject illuminated by the uniform illumination and / or the spot illumination pattern, wherein the third detection signal (103) being derived from electromagnetic radiation detected at the same wavelength as the first detection signal (101), and the fourth detection signal (104) being derived from electromagnetic radiation detected at the same wavelength as the second detection signal (102), wherein, in the case of a spot illumination pattern, the third detection signal (103) and the fourth detection signal (104) are derived by spatial integration of the electromagnetic radiation (90) transmitted through or reflected from the skin area (12); determining (S30) a first ratio RR1 (121) of the ratios based on the first detection signal (101) and the second detection signal (102), and determining a second ratio RR2 (122) of the ratios based on the third detection signal (103) and the fourth detection signal (104); determining (S40) a first normalized signal (131) by calculating a ratio of the first detection signal (101) to the third detection signal (103), and determining a second normalized signal (132) by calculating a ratio of the second detection signal (102) to the fourth detection signal (104); determining (S50) a penetration depth ratio PDR (140) by calculating a ratio of the first normalized signal (131) to the second normalized signal (132); Correcting (S60) the RR1 (121) and the RR2 (122) by compensating for the difference in penetration depth (20) between the different wavelengths using the PDR (140); and The SpO2 (160) is determined (S70) based on the corrected RR1 (151) and / or the corrected RR2 (152).

2. The device (100) according to claim 1, in, The processing unit (110) is configured to use a reference ratio RR in the ratio ref (125) and reference penetration depth ratio PDR ref (145) to correct the RR1 (121) and / or the RR2 (122).

3. The device (100) according to claim 1 or 2, in, The processing unit (110) is configured to compare the RR1 (121) and / or the RR2 (122) and the PDR (140) with a reference ratio RR in the ratio ref (125) and reference penetration depth ratio PDR ref The lookup table (135) of (145) is compared to correct the RR1 (121) and / or the RR2 (122).

4. The device (100) according to claim 1 or 2, in, The processing unit (110) is configured to use a reference ratio RR describing a ratio for different SpO2 values ​​(160) ref (125) and reference penetration depth ratio PDR ref (145) to compare the PDR (140) and the RR1 (121) and / or the RR2 (122) with the calibration curve (136).

5. The device (100) according to claim 4, in, The processing unit (110) is configured to select a matching calibration curve to obtain a PDR equal to 1 by extrapolating the matching calibration curve to ref (145) and set the RR1 (121) and / or the RR2 (122) to the corresponding RR ref (125) to correct the RR1 (121) and / or the RR2 (122).

6. The device according to claim 4, in, The processing unit (110) is configured to calibrate the RR1 (121) and / or the RR2 (122) using different calibration curves (136).

7. A system (500) for determining oxygen saturation SpO2 (160) of a subject, the system (500) comprising: an illumination unit (200) configured to emit a narrow radiation beam of electromagnetic radiation to illuminate a skin area (12) of the subject by spot illumination; a light diffuser (220) that can be selectively arranged within or outside a path of emitted light from the lighting unit (200), wherein the light diffuser (220) is configured to diffuse the electromagnetic radiation (90) emitted by the lighting unit (200) to illuminate the skin area (12) of the subject uniformly and / or with a speckled pattern; a detection unit (300) configured to detect the electromagnetic radiation (90) in the visible spectral range or the infrared spectral range transmitted through or reflected from the skin area (12) of the subject, and to derive a detection signal (101, 102, 103, 104) based on the detected electromagnetic radiation (90); and The device (100) according to any one of the preceding claims, for determining the SpO2 (160) of the subject based on the detection signal (101, 102, 103, 104).

8. The system (500) according to claim 7, in, The lighting unit (200) is configured to emit electromagnetic radiation (90) at at least two different wavelengths and / or to emit red light and infrared light alternately as the electromagnetic radiation (90).

9. The system according to claim 7 or 8, in, The lighting unit (200) and the detection unit (300) are either both in direct physical contact with the subject's skin (12) or neither is in direct physical contact with the subject's skin (12).

10. The system according to claim 7 or 8, in, The detection unit (300) is an optical sensor and comprises a plurality of detection elements, in particular an array of photodiodes, a CCD array or a CMOS array.

11. A system (500) for determining oxygen saturation SpO2 (160) of a subject, the system (500) comprising: a first lighting unit (200a) configured to emit a narrow radiation beam of electromagnetic radiation to illuminate a skin area (12) of the subject by spot lighting; a second lighting unit (200b) configured to emit a uniform lighting profile and / or a spot pattern of electromagnetic radiation to illuminate the skin area (12) of the subject uniformly and / or with a spot pattern; a detection unit (300) configured to detect the electromagnetic radiation (90) in the visible spectral range or the infrared spectral range transmitted through or reflected from the skin area (12) of the subject, and to derive a detection signal (101, 102, 103, 104) based on the detected electromagnetic radiation (90); and The device (100) according to any one of the preceding claims, for determining the SpO2 (160) of the subject based on the detection signal (101, 102, 103, 104).

12. The system according to claim 11, in, The detection unit (300) is an optical sensor and comprises a plurality of detection elements, in particular an array of photodiodes, a CCD array or a CMOS array.

13. A method for determining the oxygen saturation SpO2 (160) of a subject, the method comprising the steps of: obtaining (S10) a first detection signal (101) and a second detection signal (102), the first detection signal and the second detection signal being derived from detected electromagnetic radiation (90) at different wavelengths in the visible spectral range or the infrared spectral range transmitted through or reflected from the skin area (12) of the subject illuminated by the spot illumination; obtaining (S20) a third detection signal (103) and a fourth detection signal (104), said third detection signal and said fourth detection signal being derived from detected electromagnetic radiation (90) at said different wavelengths transmitted through or reflected from said skin area of ​​said subject illuminated by uniform illumination and / or spot illumination, wherein said third detection signal (103) is derived from detected electromagnetic radiation at the same wavelength as the wavelength of said first detection signal (101), and said fourth detection signal (104) is derived from detected electromagnetic radiation at the same wavelength as the wavelength of said second detection signal (102), wherein, in case of a spot illumination pattern, said third detection signal (103) and said fourth detection signal (104) are derived by spatial integration of said electromagnetic radiation (90) transmitted through or reflected from said skin area (12); determining (S30) a first ratio RR1 (121) of the ratios based on the first detection signal (101) and the second detection signal (102), and determining a second ratio RR2 (122) of the ratios based on the third detection signal (103) and the fourth detection signal (104); determining (S40) a first normalized signal (131) by calculating a ratio of the first detection signal (101) to the third detection signal (103), and determining a second normalized signal (132) by calculating a ratio of the second detection signal (102) to the fourth detection signal (104); determining (S50) a penetration depth ratio PDR (140) by calculating a ratio of the first normalized signal (131) to the second normalized signal (132); Correcting (S60) the RR1 (121) and the RR2 (122) by compensating for the difference in penetration depth (20) between the different wavelengths using the PDR (140); and The SpO2 (160) is determined (S70) based on the corrected RR1 (151) and / or the corrected RR2 (152).

14. A computer program product comprising program code means for causing a computer to perform the steps of the method according to claim 13, when the program code means are executed on the computer.

Images