PPG Respiration Monitoring Using DC Signal Isolation
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Solution Overview
Problem
There is a critical unmet need for non-invasive, real-time monitoring of respiration in spontaneously breathing patients, as existing methods fail to reliably extract respiratory information from photoplethysmography (PPG) signals due to small respiratory components and interference from motion and noise, especially in non-intubated patients.
Innovation Solution
The method involves obtaining a raw PPG signal stream, isolating DC and AC component signal streams, calculating waveform parameters, and analyzing these parameters over time to monitor respiration, using band-pass filters and confidence metrics to enhance accuracy, and combining with secondary respiration sensors for validation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional PPG signal processing methods (Fourier Transforms, wavelets) are used to extract respiratory information, then frequency-based component separation is achieved, but the respiratory component remains difficult to extract due to small signal amplitude and interference from motion and noise
Solution Approach 1:
The patent segments the PPG signal into multiple frequency components using Fourier Transforms and wavelet analysis, separating the respiratory signal from cardiac and noise components. By dividing the complex signal into frequency bands, the method isolates the respiratory component (0.1-0.5 Hz) from higher frequency cardiac signals and motion artifacts, enabling precise extraction despite small signal amplitude.
Solution Approach 2:
The patent introduces an intermediary processing stage that uses template matching and correlation analysis between the PPG signal and expected respiratory waveforms. This intermediary step acts as a filter that enhances the respiratory component by comparing it against known physiological patterns, thereby improving extraction accuracy in the presence of motion interference and noise.
2Reliability
If time window averaging is applied to determine respiration rate, then some smoothing of respiratory data is achieved, but real-time tracking of respiratory events is lost with delays of 45 seconds to several minutes
Solution Approach 1:
The patent implements a dynamic processing approach where the time window for averaging is adaptively adjusted based on the stability of the respiratory signal. When the signal is stable, a longer window provides reliable averaging; when rapid changes occur, the window shortens to enable real-time detection. This dynamic adjustment allows the system to maintain measurement stability while reducing time delays for respiratory event tracking.
Solution Approach 2:
The patent incorporates feedback mechanisms that continuously monitor the quality and stability of the extracted respiratory signal. Based on this feedback, the processing algorithm adjusts the averaging window length and filtering parameters in real-time. This feedback loop enables the system to maintain reliable measurements during stable breathing while quickly detecting and reporting respiratory events when they occur, thereby reducing the 45-second to several-minute delays associated with fixed time-window methods.
3Ease of operation
If PPG signals are obtained from peripheral body sites (fingers, toes, ears), then the measurement locations are easily accessible, but the respiratory component signal is relatively small and difficult to extract
Solution Approach 1:
The patent changes the measurement parameter by selecting the nasal alar site instead of traditional peripheral sites. The nasal alar provides a stronger respiratory component signal due to its unique physiological characteristics (proximity to the respiratory tract, vascular anatomy). This parameter change (measurement site selection) maintains ease of operation while significantly improving the amplitude and extractability of the respiratory component signal.
4Measurement precision
If comprehensive respiratory monitoring is provided for intubated patients using capnometry and pressure transducers, then precise measurement of respiratory parameters is achieved, but non-invasive monitoring for non-intubated patients is not available
Solution Approach 1:
The patent makes the PPG sensor multi-functional by enabling it to extract multiple respiratory parameters (respiratory rate, tidal volume, respiratory effort) from a single non-invasive measurement. The same sensor that traditionally only measured heart rate and oxygen saturation is now configured to also provide comprehensive respiratory monitoring through advanced signal processing, thereby achieving intubation-level monitoring capability without the invasiveness of intubation or multiple specialized sensors.
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 real-time detection of respiratory events with improved accuracy by isolating and analyzing PPG signal components, reducing noise interference, and validating with secondary sensors, facilitating reliable monitoring of respiration in spontaneously breathing patients.
Implementation Method 1
Photoplethysmography, or 'PPG,' is an optical technique for detecting blood volume changes in a tissue. In this technique, one or more emitters are used to direct light at a tissue and one or more detectors are used to detect the light that is transmitted through the tissue ('transmissive PPG') or reflected by the tissue ('reflectance PPG'). The volume of blood, or perfusion, of the tissue affects the amount of light that is transmitted or reflected.
Data Source
AI summary
Provided according to embodiments of the invention are methods, devices and systems for monitoring respiration. Methods described herein include isolating an isolated DC component signal stream, and optionally an isolated AC component signal stream, from the raw PPG signal; calculating a waveform parameter using at least a portion of the isolated DC component signal stream, and optionally, a corresponding portion of the raw PPG signal stream and/or the isolated AC component signal stream; and monitoring respiration in the individual by analyzing the waveform parameter over time.