Can the ppg cardiac component envelope reflect the respiratory drive?

Abstract Introduction Using a home-based fingertip monitor can decrease the time and cost of screening obstructive sleep apnea (OSA). During OSA events, respiration is partially or totally blocked, which stimulates the compensatory respiratory drive. We discovered a significant cardiac component envelope dynamics induced by the apnea events, particularly a strong surge following most apnea events. We conjecture that it reflects the respiratory drive. Methods We recruited 76 participants with suspected OSA. Each participant attends overnight PSG analysis with the TipTraQ device, which is installed in the fingertip with red, infrared and green photoplethysmography (PPG). Sleep apnea events were labeled by the same sleep experts. The envelope of the cardiac component (EC) and the instantaneous heart rate (IHR) were extracted from each PPG channel. The surge in the EC and IHR near the end of each OSA event was extracted by the spectrum analysis. The lag seconds of the surge after each event, latency between the EC surge and the IHR surge, and maximal shifted correlation coefficient were evaluated. Results During periods of frequent OSA, the EC surge and the IHR surge are well-aligned. The correlation coefficient is over 0.8 with the EC surge shift of about 4 seconds forward. The lag seconds are distributed from 10 to 40 for both channels’ surges, central at 25. The age does not affect distributions. Conclusion The study results show that after OSA events, the EC surges often happen after IHR surges. This suggests that the sympathetic stimulation induced by OSA happens earlier than hemodynamic changes reflecting respiratory efforts, especially when participants enter the frequent OSA periods state, which further suggests that EC encodes respiratory drive. This observation could help better determine whether a patient is suffering a severe apnea from the mobile fingertip devices like TipTraQ. Support (if any)