TOF-Based Vital Sign Sensing for Variable Tissue Light Paths
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Solution Overview
Problem
Conventional vital sign determination methods, such as PPG, assume uniform light paths through tissue, leading to inaccuracies and noise due to varying light paths based on wavelength, physiology, and restricted body site usage, resulting in unreliable vital sign measurements at non-specific sites.
Innovation Solution
Utilizing Time of Flight (TOF) information to determine light path characteristics (LPC) for precise vital sign measurement, allowing flexible monitoring at various body sites by accounting for scattering and penetration differences across wavelengths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional PPG methods assume uniform light paths through tissue, then the measurement process is simple, but the accuracy and reliability of vital sign measurements deteriorates due to varying light paths based on wavelength, physiology, and body site
Solution Approach 1:
The system performs preliminary characterization of light path characteristics (LPC) by emitting light at multiple wavelengths and detecting the light after it travels through the tissue. The LPC are determined before vital sign measurement, accounting for individual anatomical and physiological variations. This preliminary action enables accurate vital sign determination by establishing the specific light path characteristics for each subject and measurement site.
2Adaptability or versatility
If conventional PPG devices are restricted to specific body sites, then the measurement reliability is maintained, but the versatility and convenience of monitoring deteriorates
Solution Approach 1:
The system changes the parameters used for measurement by determining light path characteristics (LPC) that account for individual variations in anatomy and physiology at different body sites. By measuring LPC at multiple wavelengths and adapting the measurement parameters to each specific body site and subject, the system maintains reliable vital sign measurements while enabling flexible monitoring at various locations including wrist, forehead, and other non-conventional sites.
3Adaptability or versatility
If multi-color PPG devices are used to determine additional vital signs, then the capability to measure SpO2 and other parameters is improved, but the complexity of the measurement system increases
Solution Approach 1:
The system achieves multi-functionality by using light path characteristics (LPC) determined from multi-wavelength measurements to enable determination of multiple vital signs including heart rate, oxygen saturation (SpO2), and other physiological parameters. The same LPC measurement framework supports various vital sign measurements, making the system universal and eliminating the need for separate specialized devices for each parameter.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enhances accuracy and reliability of vital sign determination by compensating for inter-person anatomical and physiological variations, enabling flexible and convenient monitoring beyond conventional sites.
Implementation Method 1
determining one or more time of flight, TOF, signals from the one or more obtained detection signals; determining, from the one or more TOF signals, one or more light path characteristics of the light path along which the light has traveled
Implementation Method 2
The underlying principle of PPG is that that blood absorbs light more than surrounding tissue. Therefore, blood volume changes in the blood vessels may be detected by measuring the light absorption
Implementation Method 3
the principle of PPG is based on that the quantity of absorbed blood depends on the oxygen content of the blood. Hemoglobin 'loaded' with oxygen ('oxygenated hemoglobin') and hemoglobin with less oxygen ('deoxygenated hemoglobin') have different absorption spectra
Data Source
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AI summary
The present invention relates to a method, device and system for determining vital sign information (42) of a subject (200). The method comprises controlling a light source (10) to emit light signals at one or more wavelengths into tissue (220) of the subject (200); obtaining one or more detection signals (40) from a light detector (20) configured to detect light after travelling from the light source (10) through the tissue (220) of the subject (200) to the light detector (20) along a light path (44); determining one or more time of flight, TOF, signals from the one or more obtained detection signals (40); determining, from the one or more TOF signals, one or more light path characteristics of the light path (44) along which the light has traveled; and determining vital sign information (42) of the subject (200) from the one or more determined light path characteristics.