Device for monitoring physiological signals
By combining a flexible substrate and a floating optical sensor with pressure-sensitive materials and algorithms, the problem of inaccurate measurement of PPG devices when under motion or contact pressure changes has been solved, thereby improving the stability and accuracy of the signal and making it suitable for physiological signal monitoring in wearable devices.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-10-17
- Publication Date
- 2026-05-15
AI Technical Summary
Existing photoplethysmography (PPG) devices suffer from decreased measurement accuracy during movement or changes in contact pressure, leading to increased signal noise, baseline drift, and inaccurate heart rate measurements, particularly in long-term monitoring such as sleep studies.
By employing a flexible substrate and floating or elastically supported optical sensors, combined with pressure-sensitive materials and algorithms, the contact pressure is adjusted in real time to control vasoconstriction, reduce motion artifacts, and optimize signal quality.
It improves the accuracy and stability of PPG signals, reduces baseline drift and motion artifacts, and enhances the measurement accuracy of parameters such as blood oxygen saturation and heart rate. It is suitable for wearable devices such as smartwatches and forehead-worn devices.
Smart Images
Figure CN122055095A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to an apparatus for acquiring electrophysiological signals related to physiological processes, and more particularly to an apparatus for measuring hemoglobin oxygen saturation (SpO2). Background Technology
[0002] Photoplethysmography (PPG) is a non-invasive technique used to transcutaneously measure the oxygen saturation (SpO2) of hemoglobin in arterial blood and to extract valuable information such as heart rate, respiratory rate and respiration rate derived from PPG, arterial tone, and pulse wave volume. This non-invasive technique relies on two light-emitting diodes (LEDs): a red LED and a near-infrared (N-IR) LED, and a photodetector.
[0003] The main principle behind measuring SpO2 using photoplethysmography (PPG) signals lies in the significant difference in the absorption of red and near-infrared light between oxyhemoglobin (HbO2) and deoxyhemoglobin (Hb). Compared to HbO2, Hb absorbs more red light and less near-infrared (N-IR) light. In other words, Hb reflects less red light and more near-infrared light compared to HbO2. Based on this characteristic, two types of pulse oximeters have been developed: (i) transmissive pulse oximeters and (ii) reflective pulse oximeters.
[0004] In transmissive pulse oximeters, the photodiode and detector are positioned on opposite sides of the measurement site, such as the fingertip, and the receiver detects the amount of light transmitted through the tissue. In reflective pulse oximeters, the light source and detector are both positioned on the same side of the measurement site, and measurement is performed by capturing the amount of light reflected back from the tissue. In both cases, the amount of absorbed or reflected light fluctuates due to the following reasons: (i) Arterial blood volume changes during the systolic and diastolic phases of the cardiac cycle; and (ii) Changes in blood oxygen concentration.
[0005] By comparing the relative proportions of red light and near-infrared light absorption, we can distinguish between changes caused by the cardiac cycle and changes caused by changes in blood oxygen concentration.
[0006] The measurement accuracy of transmissive and reflective PPG devices is easily affected by movement and changes in contact pressure between the sensor and the skin. Stable contact pressure is required for reliable PPG device operation, but this is not easily achieved because pressure can change when the patient moves, especially with significant movement. Insufficient contact pressure leads to severe light leakage, resulting in a weak and noisy PPG signal. Conversely, excessive pressure causes vasoconstriction, temporarily reducing or blocking blood perfusion and altering the morphology of the PPG signal.
[0007] In both of these scenarios, suboptimal contact pressure alters the morphology of the PPG signals (i.e., red and infrared signals) and the relative intensity of red and near-infrared light absorption / reflection, significantly reducing the accuracy of all PPG-driven signals (including but not limited to SpO2) and causing baseline shift. This problem is particularly pronounced when continuous monitoring over extended periods, such as during overnight sleep studies, as contact pressure can change due to positional variations during sleep. This can introduce bias in the diagnosis of certain medical conditions, such as cardiopulmonary complications, sleep apnea, chronic obstructive pulmonary disease (COPD), and heart failure. Suboptimal contact pressure also leads to more severe motion artifact contamination of the PPG signal, reduced signal-to-noise ratio, PPG baseline drift, and unreliable or erroneous heart rate measurements.
[0008] Therefore, an improved PPG device design is needed to minimize the aforementioned problems and provide better measurement signals. Summary of the Invention
[0009] This invention provides an apparatus for improving the measurement of biological signals (especially photoplethysmography signals) of a subject. In one aspect, the invention provides an apparatus for monitoring physiological signals of a subject, the apparatus comprising: a flexible substrate for attachment to the subject's skin; at least one sensor for monitoring the subject's physiological signals; a sensor for measuring blood oxygen concentration; and a floating or elastically supported optical sensor for mechanically adjusting contact pressure and ensuring that vasoconstriction caused by the application of the sensor is always controlled, limited, and / or minimized.
[0010] This invention advantageously provides a mechanism for measuring the pressure exerted by a flexible substrate relative to skin, limbs, or other body surfaces. Preferably, the flexible substrate comprises a flexible pressure-sensitive material. Preferably, the invention incorporates an algorithm for automatically and in real-time optimizing the signal based on the measured contact pressure and adjusting the resulting indices. Preferably, the invention also incorporates the ability to measure and / or track and / or compensate for changes in pressure or its absolute value between a sensor and a subject's surface, applicable to all sensors or associated probes. Preferably, one or more applied sensors or probes can be deployed to achieve the above functionality. Preferably, the measurement results or outputs from the sensors can be modified, adjusted, compensated, or calculated in the associated algorithm or any form of associated calculation, using the "pressure exerted between the sensor and the subject's surface" as a parameter. Attached Figure Description
[0011] Figure 1 This is a side view of an embodiment of the present invention, which includes a reflective pulse oximeter equipped with a pressure-sensitive material or pressure sensor.
[0012] Figure 2 This is a side view of an embodiment of the present invention, which includes a transmissive finger clip pulse oximeter equipped with a pressure-sensitive material or pressure sensor. The figure shows a finger inserted into the finger clip. Detailed Implementation
[0013] This invention relates to improvements in the design of reflective and transmissive photoplethysmography (PPG) devices to reduce motion artifacts, avoid spurious and non-physiological baseline drift in the signal, and improve signal quality and the accuracy of parameters derived from PPG. This invention improves the accuracy of estimations of all PPG-driven parameters, such as continuous measurements of blood oxygen saturation (SpO2), heart rate, heart rate variability, respiratory rate, blood pressure, and arterial pulse wave volume (i.e., peripheral arterial tension measurement and arterial pulse tension measurement).
[0014] The invention also incorporates the ability to measure and / or track and / or compensate for changes in or the absolute value of pressure applied between the sensor and the surface of a biological subject, applicable to all sensors or related probes.
[0015] This invention particularly advantageously introduces a mechanism for pulse oximeters to continuously monitor the contact pressure between the skin and the sensor, and to adjust / optimize the signal based on this contact pressure. The invention employs a floating or elastically supported optical sensor to mechanically regulate the contact pressure and ensure that vasoconstriction caused by the application of the sensor is always controlled, limited, and / or minimized.
[0016] Furthermore, the present invention advantageously provides a mechanism for measuring the pressure exerted by a flexible substrate relative to skin, limbs, or other body surfaces. The invention can also incorporate an algorithm for automatically and in real-time optimizing the signal based on the measured contact pressure and adjusting the resulting indices.
[0017] The present invention can also modify, adjust, compensate, or calculate the pressure applied between the sensor and the surface of the biological subject as a parameter in related algorithms or any form of related calculations, based on the measurement results or outputs from the sensor.
[0018] This invention can also help distinguish between cases of natural hypoperfusion and cases of blood flow restriction (i.e., vasoconstriction) caused by increased contact pressure. Furthermore, this invention is beneficial in differentiating between a true low SpO2 baseline (e.g., caused by conditions such as chronic obstructive pulmonary disease) and a spurious low baseline caused by suboptimal contact pressure between the skin and the sensor.
[0019] The application of this invention is not limited to light-transmitting body parts such as fingers, toes, and earlobes, which can only be used with transmissive optical sensors. This invention expands the range of selectable measurement sites, providing more possibilities for developing wearable devices with clinical-grade accuracy, such as smartwatches, forehead-worn, and chest-worn PPG monitoring devices.
[0020] Preferably, the present invention employs a flexible pressure-sensitive material, such as "Velostat" or "Linqstat," and / or an electronic pressure sensor, combined with a spring-loaded optical sensor. The optical sensor is mounted on a spring of known type and specifications, which can be made in any form, such as a helical spring or a folded metal structure, to adjust its contact pressure relative to any part of the body. The inclusion of a pressure sensor (or pressure-sensitive material) in the spring-loaded optical sensor enables real-time measurement of pressure signals related to the integrity of the connection between the skin and the sensor.
[0021] The accompanying drawings illustrate preferred embodiments of the invention. Those skilled in the art will understand that other embodiments may exist within the scope of the claims.
[0022] See now Figure 1This illustrates an embodiment of a reflective PPG device according to the invention, which includes pulse oximetry and is disposed on the skin 1 (i.e., the measurement site). Depending on the location of the measurement site, the device includes a strip structure or adhesive patch 2 to hold the device in place. Both the transmitter 3 and the receiver 10 are mounted on a rigid substrate 15, which is connected to a main rigid substrate 5 via two flexible substrates 9 and 18. These two flexible substrates are used to transmit electrical signals from 15 to 16, and then via a third flexible substrate 19 to the main rigid substrate 5 containing all electronic components 4.
[0023] A pressure-sensitive material or pressure sensor 7 is disposed between two rigid substrates 5 and 16 for detecting contact pressure. A helical spring 6 and a metal rod 12 for housing the spring are disposed between substrates 15 and 16. This structure allows the sensor and lens to move within a plastic housing 8, thereby providing the ability to absorb and release energy, providing cushioning, and facilitating adjustment of the contact force according to the shape of the measurement site.
[0024] The transmitter 3 and receiver 10 are covered by a plastic housing 15, which has two openings above each of the two sensors. These openings are used to mount optical lenses 11 and 17 to conduct light. A U-shaped optical isolator 13 is disposed between them to prevent light leakage between the transmitter 3 and the receiver 10. The isolator has a U-shaped structure to accommodate the metal rod 12 when the spring 6 is compressed.
[0025] See now Figure 2 The figure illustrates another embodiment of the invention, a transmissive PPG finger clip probe, showing a finger 1 inserted into the finger clip. The device includes an upper housing 4 and a lower housing 9, which are interconnected by a spring 7. The lower housing 9 houses a receiver 11 mounted on a rigid substrate 10, which in turn is mounted on a pressure-sensitive material 8. The upper housing 4 houses a transmitter 3 mounted on a rigid substrate 5. All electronic components 2 are mounted on the opposite side of the rigid substrate 5.
[0026] A silicone pad 6 is disposed inside the opening of the device. It conforms to the shape of the finger 1 and helps to adjust the contact force between the finger 1 and the transmitter 3 and receiver 11. The silicone pad also provides optical isolation and prevents light from leaking from the transmitter 3 to the receiver 11.
Claims
1. A device for monitoring physiological signals of a subject, comprising: a) A flexible substrate for attaching to the subject's skin; b) At least one sensor attached to the flexible substrate for monitoring the physiological signals of the subject; c) A sensor coupled to the flexible substrate for measuring the oxygen concentration in blood; as well as d) A floating or elastically supported optical sensor, which is combined with the flexible substrate, for mechanically adjusting the contact pressure and ensuring that vasoconstriction caused by the application of the sensor is always controlled, limited and / or minimized.
2. The device according to claim 1, wherein the flexible substrate comprises a flexible pressure-sensitive material.
3. The apparatus according to claim 1 or 2 further includes a microprocessor programmed with an algorithm for automatically and in real-time optimizing the monitored signal and adjusting the derived parameters based on the measured contact pressure.
4. The apparatus according to any one of claims 1 to 3, further comprising a microprocessor programmed to calculate and / or track and / or compensate for changes or absolute values of pressure applied between the sensor and the subject surface.