Respiratory Rate Detection via PPG Sub-signal Analysis
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Solution Overview
Problem
Existing methods for detecting respiratory rate are not suitable for continuous monitoring, especially for ambulatory patients or sports applications, due to limitations such as the need for invasive electrodes, sensitivity to external noise, and discomfort from wearing masks or electrodes.
Innovation Solution
A method and device that utilize peripheral pulse wave data from sensors like pulse oximeters to extract and analyze sub-signals, combining time and frequency domain analysis for reliable estimation of respiratory rate, while removing noise and outliers, allowing for continuous and non-invasive monitoring.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If capnography is used to detect respiratory rate, then measurement precision is improved, but ease of operation deteriorates due to requiring mask wearing
Solution Approach 1:
The patent replaces the mechanical/acoustic capnography system with an optical detection system using photoplethysmography (PPG). Instead of using a mask to capture breath sounds and airflow, the system uses light absorption changes in peripheral blood vessels to detect respiratory rate, eliminating the need for mask wearing while maintaining measurement capability.
Solution Approach 2:
The patent introduces an intermediary relationship between respiratory activity and PPG signal modulation. Respiratory movements cause changes in intrathoracic pressure that affect venous return and peripheral blood flow, which in turn modulate the PPG signal. This intermediary mechanism allows indirect detection of respiratory rate through easily obtainable peripheral pulse wave data.
2Ease of operation
If microphone-based technologies are used to detect respiratory rate, then ease of operation is improved, but reliability deteriorates due to sensitivity to external noise
Solution Approach 1:
The patent replaces the acoustic microphone-based detection system with an optical PPG-based system. Instead of capturing sound waves that are susceptible to environmental noise, the system uses optical absorption changes in blood vessels, which are inherently isolated from external acoustic interference, thereby improving signal reliability.
3Measurement precision
If impedance tomography is used to detect respiratory rate, then measurement precision is improved, but device complexity increases due to electrode placement requirements
Solution Approach 1:
The patent replaces the electrical impedance tomography system with an optical PPG system. Instead of requiring multiple electrodes to be placed on the chest to measure impedance changes, the system uses a single or few optical sensors placed on peripheral sites like the wrist or finger, dramatically simplifying the device while maintaining measurement accuracy.
4Ease of operation
If physical examination is used to detect respiratory rate, then ease of operation is improved, but productivity deteriorates due to inability to perform continuous monitoring
Solution Approach 1:
The patent transforms the discontinuous manual physical examination into a continuous automated monitoring system. The PPG sensor continuously captures peripheral pulse wave data, and the processing system continuously analyzes the signal to extract respiratory rate, enabling uninterrupted monitoring while maintaining the simplicity of the measurement approach.
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
Enables reliable, continuous, and non-invasive estimation of respiratory rate with improved robustness against environmental noise, using multiple sensors and providing accurate results for long-term monitoring.
Implementation Method 1
The PPG signal is windowed in overlapping windows of typically 30 seconds' length... The invention relates to a method for estimating respiratory rate comprises steps of: gathering data, such as spectrum data, related to peripheral pulse wave in an electrical form
Data Source
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AI summary
A method for estimating respiratory rate comprises gathering data related to pulse wave in an electrical form, extracting a good quality beat series with proper noise removal and interpolated beats for missing beats, extracting four primary sub-signals and two derived sub-signals from the beat series, performing both time and frequency domain analysis independently for each of the aforementioned six sub-signals and combining the results of the time and frequency domain analysis independently for each sub-signal thus obtaining a group of estimates (2 x 6) for the respiratory rate. The estimating of the respiratory rate is then calculated by removing sub-signal estimates with poor signal-to-noise ratio and those that are statistical outliers.