Effect of changes in sympathovagal balance on the accuracy of heart rate variability obtained from photoplethysmography

Heart rate variability (HRV) obtained using photoplethysmography (PPG), which is also known as pulse rate variability (PRY), has already been used in clinical practice. However, it is uncertain whether PRY reflects changes in autonomic nervous function accurately. The aim of the present study was to evaluate quantitatively the effect of alterations in the sympathovagal balance on the agreement between PRY and HRV from electrocardiographs (ECG). Healthy subjects (male, 26; female, 7; age, 22-25 years old) participated in the present study. Paced respiration with 15 breathes/min and breath holding (apnea) were performed to alter the autonomic nervous states of patients. The changes in the low-to-high frequency power ratio (LF/HF) of HRV indicated that there was a sympathovagal balance shift toward vagal predominance during paced respiration, but toward sympathetic predominance during apnea. The results demonstrated that, during paced respiration, all indices had an acceptable agreement [Bland-Altman ratio (BAr)<0.2] between PRY and HRV, with the exception of LF/HF that had an insufficient agreement (BAr=0.25). All indices had very strong correlations [Pearson's correlation coefficients (CC)>0.99] and PRY had a minor but highly significant (P<0.001) increase for the majority of the variability indices, when compared with HRV. During apnea, the discrepancy of the short-term variability indices between PRY and HRV became sizeable with a BAr>0.3 and a minimum CC of 0.96. In conclusion, a decrease of LF/HF caused a marginal inaccuracy of PRY in the indication of sympathovagal balance, while sympathetic activation increased differences in short-term variability between PRV and HRV.