Visualizing Relaxation in Wearables: Multi-Domain Feature Fusion of HRV Using Fuzzy Recurrence Plots

Area of Science:

• Physiological monitoring
• Biomedical signal processing
• Wearable technology

Background:

• Traditional relaxation monitoring relies on subjective self-assessment.
• Electrocardiograms (ECG) offer limited one-dimensional insights into cardiovascular activity.
• Objective physiological monitoring is crucial for effective biofeedback and stress management.

Purpose of the Study:

• To introduce a novel visual interpretation framework for heart rate variability (HRV) time series using fuzzy recurrence plots (FRPs).
• To develop a multi-domain feature fusion framework for automated detection of autonomic changes from HRV data, suitable for wearable systems.
• To evaluate the performance of the proposed framework in distinguishing between different relaxation states.

Main Methods:

• Transformed HRV time series data into two-dimensional fuzzy recurrence plots (FRPs).
• Extracted features from five domains: time, frequency, non-linear, geometric, and image-based.
• Employed feature selection techniques (Fisher discriminant ratio, correlation filtering, greedy search) and evaluated six classifiers, with Support Vector Machine (SVM) showing the highest performance.

Main Results:

• Fuzzy recurrence plots (FRPs) provide visually distinct patterns corresponding to autonomic changes, aiding non-expert interpretation.
• The multi-domain feature fusion framework achieved 96.6% accuracy and 100% specificity using only three selected features with an SVM classifier.
• The proposed approach demonstrates high efficacy in objectively monitoring real-time stress levels.

Conclusions:

• Fuzzy recurrence plots (FRPs) offer a promising, human-interpretable method for visualizing physiological changes related to relaxation.
• The automated detection framework using feature fusion and SVM provides accurate and efficient objective monitoring of autonomic status.
• This approach holds significant potential for developing advanced biofeedback systems integrated into wearable devices for real-time stress management.