Heart Rate Estimation Using Digital Automatic Gain Control
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Solution Overview
Problem
Existing heart rate estimation methods using photoplethysmography (PPG) face challenges in accurately determining heart rate during motion due to motion artifacts caused by hemodynamic effects, tissue deformation, and sensor movement, which can lead to inaccuracies in PPG signal analysis.
Innovation Solution
The implementation of a heart rate monitor system that filters and motion compensates PPG sample values, computes gain values for individual segments, and applies these gain values to the motion-compensated values, followed by digital automatic gain control (DAGC) and Fast Fourier Transform (FFT) processing to determine the heart rate estimate based on the frequency content of the adjusted values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If motion compensation techniques are applied to remove motion artifacts from PPG signal, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The PPG signal is divided into multiple segments, and individual gain values are computed for each segment. This segmentation approach allows motion artifacts to be addressed locally in each segment rather than requiring complex global processing, thereby improving heart rate estimation accuracy while controlling processing complexity.
Solution Approach 2:
The patent applies digital automatic gain control by computing gain values for individual segments and applying them to adjust the signal amplitude. This parameter change approach equalizes the average power across segments, reducing motion artifact effects and improving measurement precision without requiring complex structural modifications.
2Measurement precision
If digital automatic gain control is applied to equalize average power across segments, then measurement precision is improved, but use of energy increases
Solution Approach 1:
The patent applies gain control selectively to individual segments rather than processing the entire signal uniformly. By computing and applying gain values only where needed to equalize average power across segments, the system improves signal fidelity while minimizing unnecessary computational energy expenditure.
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
This approach enhances the accuracy of heart rate estimation by minimizing the impact of motion artifacts, ensuring that the input to the FFT processing has approximately constant variance, thereby improving the fidelity of heart rate monitoring, especially during patient movement.
Implementation Method 1
A photodiode or other optical sensor generates the PPG signal indicating the measured light absorption (transmission) or reflection
Implementation Method 2
A heart rate estimate value representing the patient heart rate is determined according to the frequency content of the adjusted values
Data Source
AI summary
Disclosed examples include heart rate monitor systems and methods to estimate a patient heart rate, in which a processor filters digital photoplethysmogram (PPG) sample values representing transmission or reflection of a light signal in the patient during a time window, performs motion compensation processing on the filtered values, computes a gain value for individual segments of the time window using the motion compensated values, applies the individual gain values to the motion compensated values of blocks associated with the corresponding segments, and determines a heart rate estimate value representing the patient heart rate according to the frequency content of the adjusted values.