Impact of signal length and window size on heart rate variability and pulse rate variability metrics

Objective. There is growing interest in the use of physiological signals beyond electrocardiography (ECG), particularly photoplethysmography-based noninvasive arterial blood pressure (nABP), to assess autonomic nervous system (ANS) activity with minimal recording durations. This study compared heart rate variability (HRV) and pulse rate variability (PRV) derived from ECG and nABP, respectively. We investigated how signal shortening and calculation window size affect time-domain, frequency-domain, and nonlinear ANS metrics.Approach. Photoplethysmography was used to measure nABP, whereas ECG was recorded with a 3-lead device in healthy individuals (18-31 years). The HRV and PRV were analyzed using time- and frequency-domain metrics, and nonlinear indices, including entropy metrics and Poincaré plots (SD1, SD2). Agreement between signal lengths of 3 min and 5 min was assessed in 86 nABP and 70 ECG participants using intraclass correlation coefficients (ICCs). To evaluate the effect of window size, 15 min recordings from 16 participants were segmented into windows of 3 min, 5 min, and 15 min. HRV-PRV agreement was evaluated using Bland-Altman analysis.Main results. The time-domain metrics demonstrated excellent reproducibility when the signal length (ICCs ⩾ 0.96) and window size (ICCs ⩾ 0.98) were shortened, but moderate agreement between HRV and PRV. Entropy metrics were most affected by signal shortening (e.g. HRV multiscale entropy ICC (95%CI]): 0.67 (0.47-0.80); PRV approximate entropy: 0.45 (0.15-0.64)). Shorter window sizes affected selected ANS metrics, including reduced SD2 (p= 0.003 for HRV,p< 0.001 for PRV) and increased frequency-domain values (p< 0.001 for HRV and PRV).Significance. Time-domain metrics are more robust to reductions in signal length and calculation window size but demonstrate lower interchangeability between HRV and PRV. Both signal length and window size influence selected ANS metrics and should be considered, particularly when employing entropy-based indices in wearable, remote, and short-duration physiological monitoring.