Biosignal monitoring device

Abstract

To reduce motion artifacts, avoid false and non-physiological baseline shifts, and improve signal quality and the accuracy of metrics derived from PPG in both reflective and transmissive photoplethysmography (PPG) devices. [Solution] The biosignal monitoring device according to the present invention comprises a flexible substrate for application to the skin of a subject, at least one sensor for monitoring physiological signals, a sensor for measuring blood oxygen concentration, and a floating or spring-biased optical sensor for mechanically adjusting contact pressure. The present invention incorporates the ability to measure, track, and / or compensate for fluctuations or absolute values ​​of applied pressure between the sensor and the body surface of a biological subject.

Description

Technical Field

[0001] The present invention relates to an acquisition apparatus related to electrophysiological signals associated with physiological processes, and in particular to measurement of blood hemoglobin oxygen saturation (SpO2).

Background Art

[0002] Photoplethysmography (PPG) is a non-invasive technique for transcutaneously measuring hemoglobin oxygen saturation (SpO2) in arterial blood, and enables acquisition of useful information such as heart rate, PPG-driven respiration and respiratory rate, arterial tone, and arterial pulse wave volume. This technology is a non-invasive technique that uses one red light emitting diode (LED), one near-infrared (N-IR) light emitting diode, and a photodetector.

[0003] The main principle of SpO2 measurement by photoplethysmogram is based on the fact that the amounts of red light and near-infrared light absorbed by oxyhemoglobin (HbO2) and deoxygenated hemoglobin (Hb) are significantly different. Hb absorbs more red light and less N-IR light compared to HbO2. In other words, Hb has a smaller reflection amount of red light and a larger reflection amount of N-IR light compared to HbO2. This property is utilized as the basis for the development of two types of oximeters, known as i) transmission type and ii) reflection type. In a transmission oximeter, the photodiode and the detector are arranged on opposite surfaces of a measurement site such as a fingertip, and the amount of light transmitted through the tissue is detected by the receiver. On the other hand, in a reflection oximeter, both the light source and the detector are arranged on the same surface of the measurement site, and the amount of light reflected from the tissue is captured. In either method, the amount of absorbed / reflected light varies due to i) changes in arterial blood volume during the systole and diastole of the cardiac cycle, and ii) fluctuations in blood oxygen concentration. The absorption ratio of red light and N-IR light is used to distinguish between cardiac cycle fluctuations and blood oxygen concentration changes.

[0004] The measurement accuracy of transmissive and reflective PPG devices is susceptible to changes in body movement and contact pressure between the sensor and skin. Stable contact pressure is necessary for stable operation of PPG devices, but maintaining this pressure is difficult due to changes in pressure caused by patient movement, especially with significant movement. Insufficient contact pressure results in significant light leakage, making the PPG signal weak and noisy. Conversely, excessive pressure causes vasoconstriction, temporarily reducing or blocking blood perfusion and altering the morphology of the PPG signal. In either case, suboptimal contact pressure alters the morphology of the PPG signal (both red and IR light) and the relative intensity of absorbed / reflected red light versus N-IR light, significantly reducing the accuracy and baseline of all PPG-driven signals, including SpO2. This is particularly problematic in long-term continuous monitoring, such as overnight sleep studies. Changes in body position during sleep can cause fluctuations in contact pressure, potentially biasing the diagnosis of medical conditions such as cardiopulmonary complications, sleep apnea, chronic obstructive pulmonary disease (COPD), and heart failure. Furthermore, suboptimal contact pressure can lead to increased PPG contamination due to motion artifacts, a decrease in the signal-to-noise ratio (S / N ratio), baseline shift, and unreliable, inaccurate heart rate measurements. Better design of PPG devices is needed to minimize these problems and provide improved measurement signals. [Overview of the project] [Problems that the invention aims to solve]

[0005] The measurement accuracy of transmissive and reflective PPG devices is susceptible to body movement and changes in contact pressure between the sensor and skin. If stable contact pressure is not maintained, the accuracy and baseline of all PPG drive signals, including SpO2, will be significantly reduced. In particular, in long-term continuous monitoring such as overnight sleep studies, fluctuations in contact pressure due to changes in body position during sleep can bias the diagnosis of cardiopulmonary complications, sleep apnea, chronic obstructive pulmonary disease (COPD), and heart failure. Better design of PPG devices is needed to minimize these problems and provide improved measurement signals. [Means for solving the problem]

[0006] The present invention provides an apparatus for performing improved measurement of a subject's biological signals, particularly photoplethysmography (PPG) signals. In one embodiment, the present invention provides an apparatus for monitoring a subject's physiological signals.

[0007] The device comprises a flexible substrate for application to the subject's skin, the flexible substrate being engaged with at least one sensor for monitoring the subject's physiological signals, a sensor for measuring blood oxygen concentration, and a floating or spring-loaded optical sensor for mechanically adjusting contact pressure to constantly control, limit, and / or minimize vasoconstriction caused by the application of the sensor.

[0008] The present invention advantageously provides a mechanism for measuring pressure on the skin, or on the limbs or other body surface areas of a flexible substrate. Preferably, the flexible substrate is made of a flexible pressure-sensitive material. Preferably, the present invention incorporates an algorithm that automatically optimizes the signal in real time and adjusts the derivation index in response to the measured contact pressure.

[0009] Preferably, the present invention incorporates the ability to measure and / or track and / or compensate for fluctuations or absolute values ​​of applied pressure between a sensor and the subject's body surface, and includes all sensors or associated probes. Preferably, one or more application sensors or probes can be deployed to achieve the above functions.

[0010] Preferably, the measurement or output from the sensor can be modified, adapted, compensated, or calculated in any way that takes into account the "applied pressure between the sensor and the subject's body surface" as part of the relevant algorithm or any relevant calculation. [Effects of the Invention]

[0011] According to the present invention, it is most advantageous to introduce a mechanism in which the pulse oximeter continuously monitors the contact pressure between the sensor and the skin and adjusts / optimizes the signal in accordance with the contact pressure. The present invention incorporates a floating or spring-biased optical sensor and mechanically adjusts the contact pressure to constantly control, limit and / or minimize vasoconstriction caused by the application of the sensor. The present invention incorporates the ability to measure and / or track and / or compensate for fluctuations or absolute values ​​of the applied pressure between the sensor and the subject's body surface, and includes all sensors or associated probes.

[0012] The present invention can help distinguish between naturally low perfusion and blood flow restriction (vasoconstriction) due to increased contact pressure. Advantageously, the present invention can help distinguish between a true low SpO2 baseline (resulting from diseases such as chronic obstructive pulmonary disease) and an artificially low baseline due to suboptimal contact pressure between the skin and the sensor.

[0013] The present invention includes applications beyond translucent body parts such as fingers, toes, and earlobes, where only transmissive optical sensors can be used. The invention expands the range of measurement sites and broadens opportunities for developing wearable devices such as smartwatches and forehead and chest-worn PPG monitors with clinical-grade accuracy. [Brief explanation of the drawing]

[0014] [Figure 1] This is a side view of an embodiment of the invention incorporating a reflective pulse oximeter of the present invention equipped with a pressure-sensitive material or sensor. [Figure 2] This is a side view of an embodiment of the invention incorporating a transmissive finger clip probe pulse oximeter of the present invention equipped with a pressure-sensitive material or sensor, showing a finger inserted into the clip. [Modes for carrying out the invention]

[0015] This invention relates to design improvements for both reflective and transmissive photoelectric pulse wave measurement (PPG) devices, reducing motion artifacts, avoiding false and non-physiological baseline shifts in the signal, and improving the signal quality and accuracy of indices derived from PPG. The invention improves the estimation accuracy of all PPG-driven parameters, including blood oxygen saturation (SpO2), heart rate, heart rate variability, respiratory rate, blood pressure, and continuous measurement of arterial pulse wave volume (peripheral arterial pressure pulse wave analysis (PAT)).

[0016] The present invention incorporates the ability to measure and / or track and / or compensate for fluctuations or absolute values ​​of applied pressure between a sensor and the body surface of a biological subject, and includes all sensors or associated probes.

[0017] The present invention most advantageously introduces a mechanism in which a pulse oximeter continuously monitors the contact pressure between a sensor and the skin and adjusts / optimizes the signal in accordance with the contact pressure. The present invention incorporates a floating or spring-biased optical sensor and mechanically adjusts the contact pressure to constantly control, limit, and / or minimize vasoconstriction caused by the application of the sensor. The present invention advantageously provides a mechanism for measuring pressure on the skin or limbs or other body surface areas of a flexible substrate. The present invention may incorporate an algorithm that automatically optimizes the signal in real time and adjusts the derived index in accordance with the measured contact pressure.

[0018] The present invention may include the ability to modify, adapt, compensate for, or calculate a measurement or output from a sensor in any way that takes into account the "applied pressure between the sensor and the body surface of a biological subject" as part of a related algorithm or any related calculation.

[0019] The present invention can help distinguish between naturally low perfusion and blood flow restriction (vasoconstriction) due to increased contact pressure. Advantageously, the present invention can help distinguish between a true low SpO2 baseline (resulting from diseases such as chronic obstructive pulmonary disease) and an artificially low baseline due to suboptimal contact pressure between the skin and the sensor.

[0020] The present invention includes applications beyond translucent body parts such as fingers, toes, and earlobes, where only transmissive optical sensors can be used. The invention expands the range of measurement sites and broadens opportunities for developing wearable devices such as smartwatches and forehead and chest-worn PPG monitors with clinical-grade accuracy.

[0021] The present invention preferably incorporates the application of a flexible pressure-sensitive material and / or an electronic pressure sensor, such as "Velostat" or "Linqsatat," and engages it with a spring-biased optical sensor. The optical sensor is mounted on a spring of known types and specifications, which can be manufactured in any shape, such as coiled or folded metal, to adjust the contact pressure against any body part. By adding a pressure sensor (or pressure-sensitive material) to the spring-biased optical sensor, real-time measurement of the pressure signal related to the integrity of the connection between the skin and the sensor becomes possible.

[0022] The drawings illustrate preferred embodiments of the present invention. Other embodiments within the scope of the claims are also possible. Referring to Figure 1, there is shown an embodiment of a reflective PPG device according to the present invention, which incorporates a pulse oximetry function and is presented on the skin 1 (measurement site). Depending on the position of the measurement site, a strap or adhesive patch 2 for securing the device in place is incorporated.

[0023] Both the transmitter 3 and the receiver 10 are mounted on a rigid substrate 15, which is connected to the main rigid substrate 5 via two flexible substrates 9 and 18. These two substrates transmit electrical signals from 15 to 16, and further via a third flexible substrate 19 to 5, which carries all the electronic components 4. The pressure-sensitive material or sensor 7 is arranged between the two rigid substrates 5 and 16 to detect contact pressure.

[0024] The helical spring 6 equipped with a metal rod 12 is arranged between the substrates 15 and 16. This mechanism allows the sensor and the lens to move inside the plastic housing 8. This provides the ability to absorb and release energy, add cushioning properties, and adjust the contact force according to the shape of the measurement site. The transmitter and receiver 3 and 10 are covered by a plastic case 15 with two cutouts located above each sensor.

[0025] These two cutouts hold optical lenses 11 and 17 that form a U-shaped optical path with a U-shaped optical isolator 13 in the center to block light leakage between the transmitter 3 and the receiver 10. This isolator has a U-shape for accommodating the metal rod 12 when the spring 6 is compressed.

[0026] Referring to Figure 2, this drawing shows a further example of an embodiment of the present invention as a transmission-type PPG with a finger clip probe, depicting a finger 1 inserted into the clip. The device has an upper housing 4 and a lower housing 9 interconnected by a spring 7. The lower housing 9 accommodates a receiver 11 mounted on a rigid substrate 10 that is attached onto the pressure-sensitive material 8.

[0027] The upper housing 4 houses the transmitter 3 mounted on a rigid substrate 5. All electronic components 2 are mounted on the opposite side of the rigid substrate 5. Inside the device opening, a silicone cushion 6 is provided to conform to the shape of a finger 1 and to adjust the contact force between the finger 1 and the transmitter / receiver 3 and 11. This cushion also provides optical isolation, preventing light leakage from 3 to 11.

Claims

1. A device for monitoring the physiological signals of a subject, a) A flexible substrate for application to the skin of the subject, b) At least one sensor engaged with a flexible substrate for monitoring the physiological signals of the subject, c) A sensor engaged with a flexible substrate for measuring blood oxygen concentration, d) A floating or spring-biased optical sensor engaged with a flexible substrate to mechanically adjust the contact pressure and constantly control, limit, and / or minimize vasoconstriction caused by the application of the sensor. A device characterized by being equipped with the following features.

2. The flexible substrate is made of a flexible pressure-sensitive material. The apparatus according to claim 1.

3. Further incorporating a microprocessor programmed with an algorithm that automatically calculates and adjusts the derivation index for real-time optimization of the monitoring signal in response to the measured contact pressure. The apparatus according to claim 1 or claim 2.

4. Further incorporate a microprocessor programmed to measure and / or track and / or compensate for fluctuations or absolute values ​​of applied pressure between the sensor and the subject's body surface. The apparatus according to any one of claims 1 to 3.

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