Validity Of Photoplethysmography-derived Heart Rate Variability Data During Slow-paced Breathing

Chronic low resting heart rate variability (HRV) has been associated with poorer mental health and higher cardiovascular morbidity and mortality. HRV biofeedback and slow-paced breathing protocols have been utilized to increase HRV. Photoplethysmography (PPG) devices paired with smartphone applications provide more feasible methods of field-based HRV data collection, but these PPG devices must be validated during non-spontaneous breathing conditions. PURPOSE: To determine the concurrent validity of PPG-derived HRV metrics in relation to electrocardiography (ECG)-derived HRV metrics during slow-paced breathing in the seated and supine positions. METHODS: 5 minutes of R-R interval, heart rate (HR), and natural log of root mean square of the successive differences (lnRMSSD) data from 18 participants (10 males, 8 females) were simultaneously collected by PPG and ECG devices in the seated and then supine positions with breathing frequency controlled at 6 breaths per minute. RESULTS: A trivial (g = 0.20), but statistically significant (p < 0.05) difference between PPG-derived and ECG-derived HR data was observed in the supine position only. All other differences were non-statistically significant (p > 0.05) and trivial-to-small (g = 0.03 – 0.38) in nature. In addition, a strong relationship (r = 0.67) and large agreement (CCC = 0.62) between PPG-derived and ECG-derived lnRMSSD data was observed in the supine position, but near-perfect relationships (r = 0.95 – 1.00) and agreement (CCC = 0.87 – 1.00) were observed in all other conditions. Lastly, all percentage errors were under the clinically acceptable threshold (< 30%) in all conditions. CONCLUSIONS: Adequate validity of PPG-derived HRV data was observed during slow-paced breathing in both the seated and supine positions, with a slight attenuation in the supine position. As a result, practitioners and researchers can confidently utilize PPG-derived HRV data under slow-paced breathing conditions.