Evaluation of Radar-Based Cardiorespiratory Monitoring Under Different Physiological Conditions.

The use of Frequency-Modulated Continuous Wave (FMCW) radar for contactless monitoring of cardiac and respiratory activity has demonstrated significant potential for clinical applications. However, its performance in nonphysiological frequency ranges remains underexplored. This study evaluated the accuracy of a FMCW radar system operating at 122.5 GHz for monitoring heart rate (HR) and respiratory rate (RR) across physiological and nonphysiological conditions. The estimation of heart and respiration rates, as well as the separation of signals, was conducted using Maximum Likelihood Estimation (MLE) and further optimized through orthogonal projection. Theoretical performance limits were evaluated using the Cramér-Rao Lower Bound (CRLB) and validated through Monte Carlo simulations. The experimental protocol included four distinct scenarios-resting, post-exercise, bradypnea, and tachypnea-designed to evaluate the robustness of the method in different physiological conditions. Six healthy participants (n=6) were monitored using a validated reference device. The results confirmed the feasibility of radar technology for accurate cardiorespiratory monitoring across both physiological and nonphysiological ranges. The algorithm demonstrated improved accuracy for RR estimation compared to HR, aligning with theoretical predictions. The findings highlighted the importance of evaluating radar-based monitoring systems in different frequency ranges to enhance their clinical applicability. Future research should focus on validating this technology in patients with diagnosed conditions.Clinical relevance- The validation of this methodology in nonphysiological frequency ranges is essential for justifying its integration into clinical systems. Demonstrating the ability to accurately detect abnormal respiratory and cardiac patterns will ensure its applicability in diagnosing and monitoring of patients. This will facilitate the introduction of contactless radar technology as a reliable tool for clinical use.