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Description
Background: Heart Rate Asymmetry (HRA) represents a specialized domain of Heart Rate Variability (HRV) analysis, quantifying the unequal contribution of accelerations and decelerations to the overall heart rate variations. While HRA provides unique insight into the nonlinear dynamics of autonomic control, its assessment has traditionally relied on high-resolution Electrocardiography (ECG). With the expansion of wearable technology, there is a critical need to validate whether Pulse-to-Pulse (PP) intervals derived from Photoplethysmography (PPG) can serve as a reliable surrogate for RR intervals in complex HRV analysis.
Methods: Data were obtained from the Autonomic Aging database (PhysioNet), specifically selecting 617 healthy volunteers recorded with the Task Force Monitor system. This subset provided simultaneous recordings of dual-channel ECG (1000 Hz) and continuous non-invasive blood pressure via finger photoplethysmograph (100 Hz upsampled to 1000 Hz). Two sets of RR intervals were extracted from lead I and II ECG, while PP intervals were derived from the blood pressure signal. The analysis focused specifically on comparative assessment of HRA indices: Guzik's Index (GI), Porta's Index (PI), Ehlers' Index (EI), and Deceleration Input (DI). Additionally standard spectral HRV metrics were compared.
Preliminary analysis utilized Pearson’s correlation. To address the limitations of simple correlation, the final study will employ Bland-Altman plots, Linear Mixed Effects Models and Principal Component Analysis (PCA).
Results: Initial findings indicate a high degree correspondence between PPG and ECG derived HRA metrics. Notably, for Guzik’s Index, the correlation between PPG and ECG1 signals (R=0.865; p<0.0001) exceeded the simultaneous ECG inter-lead ECG1 vs ECG2 correlation (R=0.835; p<0.0001). This suggests that PPG signals may possess sufficient precision to capture subtle dynamics in heart rate.
Conclusion: Preliminary results support the utility of using PPG for advanced nonlinear HRV analysis. Our study aims to confirm whether consumer-grade optical sensors can provide medical-grade insights into HRA.
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