Investigation of statistical characteristics of interaction between the low-frequency oscillations in heart rate variability and photoplethysmographic waveform variability in healthy subjects and myocardial infarction patients

Objective ― This study compares the statistical characteristics of interaction between 0.1 Hz oscillations in heart rate variability (HRV) and photoplethysmographic waveform variability (PPGV) in healthy subjects and patients with myocardial infarction (MI). Material and Methods ― We studied 23 healthy subjects (20 men and 3 women, aged 26±3 years) and 23 patients (12 men and 11 women, aged 52±4 years) at about one month after MI. The 10-minute signals of simultaneously recorded electrocardiogram (ECG) and photoplethysmogram (PPG) were studied. We calculated the total percentage of phase synchronization between the studied 0.1 Hz oscillations and estimated the distribution functions of duration of synchronous and non-synchronous epochs, the variability of basic frequency of oscillations, and variance of phase noises in 0.1 Hz oscillations in HRV and PPGV. Results ― The total percentage of phase synchronization between 0.1 Hz oscillations is significantly greater in healthy subjects than in MI patients (47±3% and 26±4%, respectively). Significant difference between these two groups in the distribution of duration of synchronous and non-synchronous epochs was not revealed. The MI patients had greater variance between the basic frequencies of 0.1 Hz oscillations in HRV and PPGV than healthy subjects. This phenomenon correlates with the increased level of phase noises in the records of MI patients. Conclusion ― The quality of synchronization between 0.1 Hz oscillations in HRV and PPG is associated with the strength of influence of external factors (noises) and variability of the basic frequency of these oscillations.