Portable pulse oximeter ring with a bluetooth low energy connection for use in physical exertion conditions and for all skin tones

Abstract

The present invention relates to a portable pulse oximeter ring with a Bluetooth low energy connection for use in physical exertion conditions and for all skin tones. The ring is structurally configured as a bridge-shaped surrounding body that can be fitted on the human finger and includes three printed circuit boards (PCB) connected to each other by flexible connections, two being peripheral on the sides, with four light emitting diodes (LED) and two photodiodes (PD) facing one another through the finger by way of a transmission oximeter, and a main board integrating the microprocessor with Bluetooth low energy (BLE), the LED and PD controller and other secondary peripherals. These LED, PD, BLE and controller components have specific features for the desired operation, with an algorithm to more reliably calculate heart rate. An optional temperature sensor is mounted on the main PCB in contact with the skin of the finger.

Description

[0001] DESCRIPTION

[0002] Portable pulse oximeter ring with low-energy Bluetooth connection for use during physical exertion and for all skin tones.

[0003] The claimed invention is a miniaturized prototype of a portable pulse oximeter ring with low-energy Bluetooth connection, with features that make it suitable for use by athletes of different skin tones as a means of monitoring heart rate and oxygen saturation under conditions of exertion, in a precise, continuous and instantaneous manner, with the possibility of also including a thermometer.

[0004] This device is structurally configured as a bridge-shaped, wrap-around body that adapts to the human finger. It integrates optoelectronic hardware whose main components are three PCBs (printed circuit boards) connected by flexible junctions: two peripheral boards on the sides, each containing four light-emitting LEDs and two photoreceptor PDs (digital detectors), positioned facing each other across the finger in transmission oximeter mode; and a main board that integrates the microprocessor with Bluetooth Low Energy (BLE), the LED and PD controller, and other secondary peripherals. These components—LEDs, PDs, BLE, and controllers—have specific characteristics for the desired operation, including a more reliable heart rate calculation algorithm. The optional temperature sensor is mounted on the main PCB in a specific position, in contact with the finger's skin.

[0005] This system offers competitive advantages over other known oximeter rings for use during physical exercise, as it provides greater accuracy and can be used under conditions of maximum exertion, at high heart rates and at saturation values ​​below 80%, for any skin color.

[0006] TECHNICAL FIELD. -

[0007] The technical field in which the present invention falls, within the diagnostic devices in medicine for measuring pulse, heart rate, blood flow and blood oxygen saturation, is that of pulse oximeters or pulse oximeters based on spectral photometry, which use optical sensors for measurement, and more particularly, that of finger pulse oximeters, in which the sensors are attached around the tip of one of the fingers of the hand.

[0008] STATE OF THE ART.

[0009] A pulse oximeter (Internet - Google, Wikipedia) is a medical instrument that indirectly and non-invasively monitors a patient's blood oxygen saturation level by measuring the optical absorbance of light at two or more wavelengths in a specific area of ​​the patient's body. More specifically, it displays the percentage of oxygen-carrying hemoglobin in the blood. It also indicates the patient's heart rate and pulse.

[0010] A typical pulse oximeter uses a microprocessor with a pair of small light-emitting diodes (LEDs) focused on a photodiode. The LEDs send out a series of pulses that pass through a translucent part of the patient's body, usually a finger or earlobe. One LED emits a wavelength of 660 nm (red), and the other emits a wavelength of 940 nm (infrared). The absorption of light at these wavelengths differs significantly between oxygen-laden and deoxygenated hemoglobin: oxygenated hemoglobin absorbs more infrared radiation and allows more red light to pass through, while deoxygenated hemoglobin absorbs more red light and allows more infrared radiation to pass through.The ratio between the intensities of red light and infrared light is calculated, which represents the proportion of oxygenated hemoglobin to deoxygenated hemoglobin, and this ratio is converted by the processor into an SpO2 level using a lookup table obtained empirically by each manufacturer.

[0011] This is the "transmission" mode, as opposed to the alternative of placing the emitters and the sensor on the same side of the tissue, in "reflection" mode, in which diffuse reflection within the tissue allows measuring the optical absorbance at a certain depth within the tissue.

[0012] There are several types of pulse oximeters depending on the possible locations of the sensors on the patient's body, such as the earlobe, forehead, wrist, etc. However, as a general measure of blood oxygen saturation and heart rate, the most common are finger pulse oximeters, used on the fingertips because they are easily accessible parts of the body with good arterial blood flow and appropriate thickness. The finger pulse oximeter as we know it today was primarily developed in the 1970s. Robert Shaw, an electrical engineer, was one of the pioneers in this area. Working at Stanford University, he developed the first finger pulse oximeter in collaboration with Dr. William New, an anesthesiologist. Their device used light absorption to measure blood oxygen saturation.

[0013] Throughout the 1980s, improvements were made to fingertip pulse oximeter technology, allowing these devices to become more compact, portable, and accurate. Companies like Nellcor, founded in 1981, played a significant role in the marketing and development of more advanced pulse oximeters.

[0014] During the 1990s, further advances were made in fingertip pulse oximeter technology. Signal processing algorithms were improved, and the size of the devices was further reduced, making them more accessible and widely used in medical settings.

[0015] In the decades following 2000, fingertip pulse oximeter technology has continued to evolve into the devices used today: even smaller and more portable devices, incorporating digital displays to show real-time readings, including simple and affordable models for home use, to allow people to monitor their health at home.

[0016] Currently, a finger pulse oximeter is a portable, pocket-sized device that is placed on the finger using a clamp or clip system. It works by means of two light-emitting LEDs on one side of the finger and a measuring photoreceptor on the other side. It has a small computer with a screen and is wireless, as it is powered by batteries or a rechargeable battery.

[0017] These finger pulse oximeters currently used in hospitals or at home have a significant limitation: they are ineffective when the person is moving. In fact, for the oxygenation data to be reliable, the clip device must be securely attached to the finger and the person must be at rest. Furthermore, in the case of people with dark skin, they tend to overestimate oxygen saturation levels. As explained in the discussion of the prior art in European patent ES2747822-T3, which describes a pulse oximeter ring for use by a person exercising, the signal detected by a finger pulse oximeter is weak and easily affected by movement.The measurement is highly susceptible to errors resulting from, for example, selecting an inappropriately sized clip, improper clip placement, and any small patient movements that may alter the position of the optical sensor arrangement within the clip relative to the finger. This has led to the development of devices that incorporate an accelerometer to detect patient movement, so that data is only captured when the patient is stationary and ignored when the patient is in motion.

[0018] Therefore, current finger-type pulse oximeters, even though they are portable devices that can be carried by a person in motion, do not serve as devices for measuring the degree of exercise-induced oxygen desaturation, which is a key parameter for determining a person's tolerance to physical activity or the capacity of a high-level athlete.

[0019] To address this deficiency, in recent years finger pulse oximeter models have been developed in which sensitivity to user movement has been reduced by adapting the sensor design to the shape of a ring or bandage wrapped around the finger, both in reflective and transmissive oximeters. However, in the case of transmissive oximeters, to which the prototype of the present invention corresponds, the electronics and signal processing of the sensor in the form of a ring or bandage is essentially the same as in clip-on devices, based on LED diodes in the same red and infrared emission ranges as conventional clip-on finger rings. This does not completely solve the problems of accuracy in its use, rendering it practically useless under conditions of maximum effort.Furthermore, these oximeter rings do not offer the possibility of a Bluetooth connection, although some are wireless and do not have a wired connection to a wristband interface or external band.

[0020] For example, Sokwoo Rhee, Boo-Ho Yang and Haruhiko Harry Asada (Proceedings of the 22nd Annual EMBS International Conference, Chicago IL, July 23-28, 2000

[0021] Rhee_EMBS_2000_Proc 22nd Ann IntConf IEEE_2792-5 v4.pdf), presents a design for artifact-resistant, low-power finger ring photoplethysmographic sensors suitable for wear while moving. The design includes a prototype consisting of a double ring with an LED and a photodiode or receiver. Its configuration suggests a reflective oximeter, meaning the light does not pass through the finger, unlike the proposed type. The doctoral thesis in Mechanical Engineering, presented at the Barker Massachusetts Institute of Technology in June 2000 (https: / / dspace.mit.edU / handle / 1721.1 / 32706), focuses on the design and analysis of artifact-resistant finger ring photoplethysmographic sensors for vital sign monitoring.This thesis shows a ring with two LEDs and a receiver based on a transmission oximeter, but the component arrangement is not the same, with only two emitting LEDs and a lower capacity processing, and a wired connection.

[0022] PShaltis, L Wood, A Reisner and H Asada (Proc, of the 2005 IEEE Engineering in Medicine and Biology 27th Annual Conference, Shanghai, China, Sept. 1-4, 2005

[0023] Proc_2005_01617250_Asada) presents a novel design for a non-invasive, wireless, portable, and rapidly deployable triage sensor. It is based on a transmission pulse oximeter, but uses only two LEDs and a smaller processor. While wireless, the transmission is not Bluetooth. The design consists of a hard plastic ring with a snap-on clip for securing it to the finger.

[0024] J. Sola-Castoldi et al. (Proceedings of the 28th IEEE EMBS Annual International Conference, New York City, USA, Aug 30-Sept 3, 2006, pp. 4295-4298. Conf Proc IEEE EMBS_2006_1_4295-8_04462750_Sola-Castoldi_so-finger ring Fig. 1) present another SpO2 sensor solution integrated into a finger ring, based on a continuous-circumference steel band design, with the advantage of its low weight (less than 5g) and greater comfort. This ring is a transmission oximeter with four LEDs and two receivers: two red LEDs and two infrared LEDs, and a wired connection to the control interface.

[0025] On the other hand, the pulse oximeter ring of the aforementioned European patent ES2747822-T3, for determining the exercise tolerance or exercise capacity of a user or athlete, configured as a wireless elastic digital band with an attached curved rechargeable battery, comprising a pair of circuit boards, one for emission and one for detection, connected through a flexible circuit board, has a different light source and component composition, and does not have a Bluetooth connection.

[0026] Compared to competing ring pulse oximeters, the developed prototype uses a carefully designed combination of four LEDs with different emission ranges, two light sensors, and a higher-capacity LED processor. This results in distinct operating characteristics that improve the accuracy of heart rate and oxygen saturation measurements. It can be used during high-intensity exercises involving elevated heart rates and saturation levels below 80%, and is suitable for all skin tones, as the wavelengths used do not interfere with melanin. Furthermore, this new ring pulse oximeter offers the option of integrating a low-energy Bluetooth connection into the data processor and a thermometer for monitoring body temperature.

[0027] In short, the present invention offers an improved solution to pulse oximetry during physical exercise, and opens up the possibility of using this technique by athletes in situations of maximum effort.

[0028] THE INVENTION.

[0029] The development of the proposed PMV minimum viable prototype of the portable pulse oximeter ring contemplates the development of opto-electronic hardware integrating suitable pre-selected components, and the development of a mechanical enclosure adaptable to the finger, according to a ring-type structure, which collects the hardware assembly in a configuration that allows the system to be validated under real operating conditions.

[0030] The assembly must be encased in a rigid-flexible 3D-printed housing that ergonomically envelops the finger, allowing the hardware components to be housed, essentially consisting of a combination of four emitting LEDs with two PDs light photoreceptors, the microprocessor, and the LED-PDs controller and secondary peripherals.

[0031] More specifically, the structural enclosure of this new device is a ring-bridge shaped casing adaptable to the shape of the finger, with a central platform and two flexible side tabs. The opto-electronic hardware integrated into this casing is supported by three independent PCBs (printed circuit boards) connected to each other by flexible connecting cables. These PCBs consist of a main PCB on the central platform, an emission PCB on one of the side tabs, and a detection PCB on the other side tab. These side PCBs are positioned at 90° with respect to the main PCB and face each other through the finger once the device is attached to it.The emission PCB has mounted a series of four light-emitting LEDs (8) in the wavelength ranges of 600-670 nm for LED 1, 740-800 for LED 2, 800-870 for LED 3 and 940-950 for LED 4, with LED 2 and LED 3 arranged at the ends of the board, and LED 1 and LED 4 in the middle.

[0032] The detection PCB has two PD photodiodes mounted on it, detecting light in the wavelength range of 600-1000 nm.

[0033] Three slightly different opto-mechanical designs have been proposed to position the LEDs and PDs at different heights relative to the finger, so that the LED light beams pass through the blood vessels. This was achieved by considering the numerical apertures of the selected LEDs and the relative position of the blood vessels with respect to the bone, resulting in PCB emission angles with respect to the transverse plane of the finger's blood vessels between 20° and 40°. The objective is to validate the optimal PCB configuration based on the PMV illumination angle.

[0034] The main PCB incorporates an LED+PD Driver, an analog / digital controller of the LED emitters and PD detectors, capable of controlling up to eight LEDs and eight PDs, and with a time controller; a microprocessor CPU with the capacity to store raw data series in internal memory, perform basic processing of that data and transmit it to a mobile device, and receive firmware updates for proper maintenance; an external memory for data storage; an RGB red-green-blue lighting status indicator; and a wired DC / DC power supply.

[0035] The device basically consists of a central PCB, which contains all the communication and processing electronics, and two PCBs adjacent at 90° to the central one, which contain the LEDs on one side and the photodiodes on the other, all mounted in a rigid-flexible, bridge-shaped casing adaptable to the shape of the finger.

[0036] A command-line interface has been developed as the user interface, allowing configuration of various parameters (LED currents, PD acquisition times, etc.) and data acquisition. The implemented data processing algorithm for calculating heart rate, adapted to the morphology of a photoplethysmography (PPG) waveform, exhibits significantly greater reliability than any of the previously mentioned devices of this type, especially under conditions of maximum exertion, when problems traditionally arise with high heart rates and the presence of strong motion artifacts and / or inaccurate values. This is because Fourier Transform techniques are applied to improve the accuracy of pulse values ​​at high heart rates.

[0037] Although the minimum viable product (MVP) prototype uses a wired solution for both power and data transmission, components have been selected to facilitate future wireless integration via Bluetooth Low Energy (BLE) and the addition of a thermometer. The goal is to leverage the development of this first prototype to its fullest potential in a future integrated prototype.

[0038] In these particular implementations, the main PCB has an integrated Bluetooth BLE version 5.0 communication module for low energy data transmission, with a microchip for over-the-air firmware updates, and a contact temperature sensor, which is mounted on two layers of thermal conductors: an electrical insulator and a metallic insert to create the thermal bridge in contact with the skin of the finger.

[0039] The competitive advantages of this new portable ring pulse oximeter compared to other similar state-of-the-art devices are as follows:

[0040] - Improved accuracy in measurements at low oxygen saturations.

[0041] - Improved accuracy in measurements at high heart rates, up to 150 beats per minute (bpm).

[0042] - Improved accuracy in measurements with intense movements, including exercises performed while running at speeds over 16 km / h.

[0043] - Improved accuracy in measurements with darker skin tones, where oxygen saturation values ​​are clearly overestimated due to interference from skin melanin.

[0044] Continuous measurement during physical exercise to detect potentially sudden drops in oxygen saturation. - Bluetooth Low Energy (BLE) connection, avoiding movement limitations caused by wired connections or other data acquisition systems (probes).

[0045] - Possibility of controlling body temperature during exercise and preventing skin overheating due to the continuous application of LEDs.

[0046] FIGURES AND GRAPHS. -

[0047] For a better understanding of the proposed pulse oximeter ring for sports use, a series of figures with images, drawings, graphics and diagrams of the device and its operation are included at the end of this descriptive memorandum.

[0048] Figure 1 shows a perspective view of the wraparound housing assembly developed to support the system hardware and allow it to be attached to the finger.

[0049] Figure 2 is another perspective view of the enclosing housing, in which the metal insert for thermal bridge is separated from the temperature sensor.

[0050] Figure 3 is a plan view of the opto-electronic hardware of the developed minimum viable prototype PMV, with the three PCBs connected by flexible junctions in the deployed position, with its main components.

[0051] Figure 4 is a schematic of the overall system architecture, in cross-section of the finger.

[0052] Figure 5 is a schematic of the position of the lateral PCBs around a finger as a function of the device's illumination angle relative to the blood vessel plane.

[0053] Figure 6 is a front perspective view of the emission PCB, with the chips of the four light-emitting LEDs.

[0054] Figure 7 is a conceptual diagram of the adaptation of the opto-electronic hardware to the finger, in cross-section, showing the temperature sensor and its couplings.

[0055] Figure 8 is a perspective view of the PMV optoelectronic hardware shown in Figure 3, with the three PCBs positioned for coupling into the enclosure, while Figure 9 shows a perspective view of the enclosure with said hardware integrated.

[0056] Figure 10 is a graph showing the configurable parameters in the implementation of the measurement and operation firmware of the PMV device.

[0057] Figure 11 is an illustrative graphic of the PMV's operating mode.

[0058] Finally, Figures 12 and 13 are graphs showing the preliminary readings in the functional verification of the PMV, with two different combinations of LEDs

[0059] METHOD OF IMPLEMENTATION. -

[0060] As described in the compendium of the invention, the new portable pulse oximeter ring developed, specially designed for athletes, with wireless control by Bluetooth, is configured in a mechanical envelope adaptable to the finger that supports opto-electronic hardware based on four LED emitters and two light sensors, and components specific to its function.

[0061] Figures 1 and 2 show the mechanical housing designed to contain the system's electronics and adapt to the shape of the user's finger. It consists of a ring-bridge-shaped casing (1) with a central platform (3) and two flexible lateral tabs (4) to ensure a perfect fit on the finger (2). Figure 2 includes the metal insert for the thermal bridge with the contact temperature sensor.

[0062] Figure 3 clearly shows the optoelectronic hardware of the PMV, the developed minimum viable prototype, supported on three independent PCBs or printed circuit boards connected by flexible connecting cables: the emission PCB (6) on one side, with the four light-emitting LEDs (8); the detection PCB (7) on the other side, with the two light-detecting photodiodes (PDs) (9); and the main PCB (5) in the center, where the LED+PD Driver (10), the analog / digital controller of the LED emitters and PD detectors, the RGB red-green-blue lighting status indicator (11), the Bluetooth Low Energy (BLE) communication module (13), and the contact temperature sensor (14) are clearly visible. All this electronics, which appear unfolded in the image, are then mounted in the ring-shaped enclosure.The arrangement of the four light-emitting LED chips (8) on the emission PCB is shown in detail in Figure 6, which represents a front perspective view of this board.

[0063] In the component diagrams of Figures 4, 5, and 7, where the system is represented in cross-section around a finger (2), the electronic hardware components are shown, including the Bluetooth CPU+BLE microprocessor and wired power supply (12), and how they are adapted around the finger thanks to the flexible connections between boards. The diagram in Figure 7 also shows the coupling elements of the temperature sensor on the finger, using electrical insulation (15) and metal inserts (16) for thermal bridging. Figure 5 shows the position of the PCBs as a function of the PMV illumination angle relative to the plane of the blood vessels (18), below the bone (17).

[0064] The development of the device began by selecting the electronic components of the system, based on the technical specifications of the invention; its architecture and conceptual design were defined; the electronic PCB was designed and its correct operation verified; the Minimum Viable Prototype “MVP” was developed, integrating the electronic hardware into the mechanical enclosure; the firmware for the control of the LED-PDs and the heart rate detection algorithm was implemented; and finally, the functional verification of the device (MVP) was performed, all as described below.

[0065] 1. Electronic components.

[0066] The components for the configuration of the opto-electronic system of the developed device, as a consolidated embodiment, have been selected based on the technical characteristics specified for compliance with the main requirements.

[0067] In the case of LED emitters, two possible alternatives have been selected for each of the preset wavelength ranges, in order to be able to test different alternatives in case the first option did not give good results.

[0068] Light-emitting diodes (LEDs):

[0069] • Range 1 of 600-670 nm: WURTH ELEKTRONIK 156120AS82500 (609nm) /

[0070] BIVAR SM1206NAC-IL (610nm) • 740-800nm ​​Range 2: OSA OPTO LIGHT OIS-330 740 (740nm) /

[0071] OSA OPTO LIGHT OIS-330 770 (770nm)

[0072] • Range 3 of 800-870 nm: WURTH ELEKTRONIK 15412085A3060 (850nm) /

[0073] OSA OPTO LIGHT OIS-330 IT855 (855nm)

[0074] • 940-950 nm range 4: HARVATEK B15V1 IR-A1C00015 (940nm) /

[0075] BRIGHT LED ELECTRONICS BIR-HMC33K-TRB (940nm)

[0076] PD photodiodes light detectors in the 600-1000 nm range:

[0077] • 2 OSRAM BPW34S photodiodes

[0078] LED+PD Driver with capacity for eight LEDs and eight PDs:

[0079] • Analog Devices ADPD4100

[0080] CPU microprocessor with internal memory and the ability to process and transmit data to a mobile device, and to receive firmware updates:

[0081] • Laird BL653p module with Nordic nRF52833 microcontroller, incorporating 512KB Flash memory and 128KB RAM

[0082] BLE Bluetooth version 5.0 for low energy data transmission and OTA firmware updates:

[0083] • Laird BL653p module, which allows remote firmware updates via Bluetooth connectivity

[0084] Temperature sensor:

[0085] • PANASONIC “PGS” Graphite Sheet.

[0086] 2. System architecture and conceptual design.

[0087] The basic architecture of the device is detailed in the diagram in Figure 4, which shows the main PCB (5) that integrates the CPU microprocessor with Bluetooth BLE communication module, the LED and PD controller and other secondary peripherals; and the two side PCBs, the emission board (6) with the LEDs, and the detection board (7) with the PDs photodetectors, facing each other through the finger.

[0088] The development of a rigid-flex electronics design has been proposed, such that the three PCBs are actually a single PCB, eliminating the need for additional connectors. Flexible connections between the PCBs will allow the emitter diodes and detectors to be positioned facing each other through the finger (2), as shown in the schematic in Figure 3. This diagram also illustrates the integration of the temperature sensor (14) and the thermal bridge using a metal insert (16) and a flexible, thermally conductive material (15).

[0089] The overall system architecture consists of three interconnected, independent PCBs. The main PCB, “TEK077,” will house the microprocessor, the LED and PD controller, the power supplies, and other secondary peripherals (temperature sensor, etc.). The peripheral PCBs, “TEK078” and “TEK079,” will house the LED emitters and PD detectors, respectively.

[0090] 3. Electronic Hardware Design.

[0091] Based on the defined architecture and the selected component elements, the electronic PCB design has been carried out, first at the schematic level and then at the routing level.

[0092] Figure 8 shows the rigid-flexible PCB design that allows the LEDs and PDs to be positioned at 90° with respect to the main PCB and facing each other through the finger.

[0093] 4. Development of the Minimum Viable Prototype “MVP” (electronic hardware and mechanical enclosure). -

[0094] Figure 9 shows how the indicated electronic hardware is assembled in the mechanical enclosure designed to adapt the device to the physiognomy of the finger, shown separately in Figure 1, with the LEDs and PDs facing each other.

[0095] Three mechanical enclosures have been designed, based on the prototype in Figure 1, to allow the emission and detection PCBs to be positioned at different relative heights, with a margin of ±1.5 mm from the nominal position. The electronic hardware, however, is unique, with the flexible connections between the main PCB and the peripherals absorbing the mechanical tolerances.

[0096] Following the design phase of the electronic hardware and the mechanical enclosure, the first prototypes have been manufactured.

[0097] The initial fabrications of the mechanical housing were carried out using rapid prototyping (3D printing). These first mechanical prototypes will allow for adjustments to various design parameters to ensure proper fit with the electronics and by touch before final manufacturing.

[0098] 5. Implementation of the device measurement and operation firmware (MPV).-

[0099] After verifying the correct operation of the electronic hardware, the firmware for controlling the measuring elements (LEDs and PDs) was implemented. Figure 10 shows the main configurable measurement parameters; namely:

[0100] - LED current (mA)

[0101] - LED turn-on time (ms)

[0102] - PD integration time (ms)

[0103] The LED on time and PD integration time will be closely linked, and will be offered as a single configurable parameter (pulse width).

[0104] The current for each LED will be limited according to the maximum current levels indicated in Table 1, or, failing that, to the maximum current that the LED driver is capable of supplying per channel (200mA). TABLE 1

[0105] Figure 11 illustrates the device's operating mode. In the first interval (approximately 3 seconds), measurements are taken with LED 1 illuminated to determine the heart rate from its signal. Subsequently, the oxygen saturation (oximetry) measurement is performed. This involves illuminating LED 1 followed by one of the other three LEDs (the LED ID is configurable). The pulse width is determined by the heart rate, such that fifteen measurements are taken with the selected pair of LEDs within the interval of one heartbeat. These LED measurements are repeated for approximately 10 seconds, after which another heart rate measurement is taken to adjust the timing for the next oxygen saturation measurement.

[0106] To calculate the pulses, LED1 (609 nm) is turned on for a minimum time of 3 s and measured with photodiode 1 at a specific sampling frequency (TS-10ms)

[0107] For oximetry calculation, the LEDs are lit in pairs (always LED1 with another combination of LEDs).

[0108] 6. Heart rate detection algorithm.

[0109] Different peak detection algorithms have been evaluated and tested for calculating heart rate.

[0110] Finally, it was decided to implement a peak detection algorithm adapted to the morphology of a photoplethysmography wave through a Fourier transform.

[0111] The chosen and implemented algorithm is an adaptation of the algorithm described in the article “On the development of an efficient, low-complexity and highly reproducible method for systolic peak detection” (Erick Javier Argüello Prada, 2021) (DOI: https: / / doi.Org / 10.1016 / j.bspc.2021.102606). The effectiveness of this algorithm is proportional to the signal quality and noise.

[0112] 7. Functional verification of the device (PMV).- Once the electronic hardware was started and the first version of the measurement firmware and the command line interface were implemented, the operation of the device was verified by taking measurements through the finger.

[0113] The graphs in Figure 12 show the signals obtained for each of the four LEDs selected as the first option for the PMV. As can be seen, with LED 1 (609nm), there is hardly any sensitivity in the measurement, and what is observed is practically noise. As the wavelength of the emitted light increases (LED 2, LED 3, and LED 4), a cleaner signal is obtained (the signal-to-noise ratio increases), and the photoplethysmographic image begins to be clearly visible. For LEDs 2, LED 3, and LED 4, the signal filtered by an FIR filter is also shown.

[0114] Due to the noise level observed with LED 1, it was decided to replace the original LED (WURTH ELEKTRONIK 156120AS82500; 609nm) with the alternative proposed for the same wavelength range (BIVAR SM1206NAC-IL; 610nm). The results with the new LED are shown in Figure 13. For comparison, the signal obtained with LED 2 (740nm) and the signal obtained with LED 1 (610nm) measured only through the fingertip are included.

[0115] The signal in this case is somewhat cleaner than in the previous case, but there is still little signal and quite a lot of noise, so the photoplethysmographic image is not clearly visible.

[0116] Measuring only through the fingertip clearly reveals the photoplethysmographic image. The penetrating power of light is proportional to its wavelength, therefore it is concluded that light is not able to pass through the entire finger with wavelengths as short as 610 nm.

[0117] Given this, it was decided to test other LED ranges closer to the second LED, to obtain a cleaner signal and allow comparative readings with the other LEDs, in order to obtain an adequate reading of both the heart rate, and subsequently obtain / rescale the oxygen saturation measurements.

[0118] In the end, the preferred LED configuration for the PMV was the four LEDs defined with the following wavelengths:

[0119] • LED 1: 610 nm

[0120] • LED 2: 740 nm

[0121] • LED 3: 850 nm

[0122] • LED 4: 940 nm

[0123] 8. Communication between device and PC.-

[0124] Serial communication is used via USB. When the device is connected, the PC will detect a serial port with the following characteristics:

[0125] • 115200 baudrate

[0126] • 8 data bits

[0127] • Stop bit 1

[0128] • Parity None

[0129] This port is used to download data to the computer.

[0130] 9. Configuration. -

[0131] The device is configured and transmits data via the Command Line Interface (CLI). Upon opening the serial terminal and establishing a connection, pressing the Enter button will display the CLI prompt.

[0132] To operate the device, there are a series of commands that can be viewed by pressing the tab key.

Claims

CLAIMS 1. A portable pulse oximeter ring, of the type of pulse oximeters or pulse oximeters that operate based on spectral transmission photometry and are attached to the fingertip, characterized by a ring-bridge-shaped enveloping housing structure (1) adaptable to the shape of the finger (2), with a central platform (3) and two flexible lateral tabs (4), which integrates optoelectronic hardware consisting of three independent printed circuit boards (PCBs) connected to each other by cables or flexible links, consisting of a main PCB (5) on the central platform, an emission PCB (6) on one of the lateral tabs, and a detection PCB (7) on the other lateral tab, these PCBs being positioned at 90° with respect to the main PCB and facing each other through the finger, such that: - the emission PCB (6) has mounted a series of four light-emitting LEDs (8) in the wavelength ranges of 600-670 nm LED 1, 740-800 nm LED 2, 800-870 nm LED 3 and 940-950 nm LED 4, with LED 2 and LED 3 arranged at the ends of the board, and LED 1 and LED 4 in the middle, with opening angles with respect to the transverse plane of the finger blood vessels between 20°-40°; - the detection PCB (7) has two PD photodiodes mounted on it, detecting light (9) in the wavelength range of 600-1000 nm; and - The main PCB (5) has mounted an LED+PD Driver (10) analog / digital controller of the LED emitters and PD detectors, with the capacity to control up to eight LEDs and eight PDs, and with a time controller; a microprocessor CPU with the capacity to store raw data series in internal memory, to perform basic processing of that data and to transmit it to a mobile device, and to receive firmware updates; an external memory for data storage; an RGB Red-Green-Blue Lighting Status Indicator (11), and a wired DC / DC power supply (12).

2. Portable pulse oximeter ring, according to claim 1, characterized in that the main PCB has an integrated Bluetooth Low Energy BLE communication module (13) version 5.0 for low energy data transmission, with a micro for over-the-air firmware OTA updates.

3. Portable pulse oximeter ring, according to claim 1, characterized in that the main PCB has an integrated contact temperature sensor (14), mounted on two layers of thermal conductors: an electrical insulator (15) and a metallic insert (16) for thermal bridge in contact with the skin of the finger.

Images