Applications
PPG-Based Sleep Apnea Detection
PPG enables wearable sleep apnea screening by detecting the characteristic oxygen desaturation events (SpO2 dips below 90%), heart rate surges following apnea termination, and sympathetic nervous system activation signatures encoded in IBI and pulse amplitude.
How it works
Schematic summary of this guide. Waveforms are illustrative, not measured data.
Obstructive sleep apnea (OSA) produces a stereotyped PPG signature during apneic events: progressive SpO2 decrease, loss of respiratory modulation in the PPG amplitude envelope, followed by abrupt SpO2 recovery and heart rate surge upon apnea termination. The autonomic arousal at apnea termination produces a distinctive sympathetic burst visible in the PPG as a transient vasoconstriction (reduced AC amplitude) followed by vasodilation. These signatures repeat cyclically at the AHI-dependent rate.
The ODI (Oxygen Desaturation Index) — number of SpO2 dips below 3% or 4% per hour — is the primary PPG-derived metric for OSA severity screening. Screening results and their limits against polysomnography are summarized in this evidence review of wearable sleep apnea studies.
Frequently Asked Questions
Can a fitness tracker diagnose sleep apnea?
No. Consumer PPG devices can flag high-risk nights warranting formal polysomnography evaluation but cannot provide diagnostic-grade AHI scores.
How does PPG compare to polysomnography for sleep apnea?
Polysomnography (PSG) with electrodes, respiratory belts, and airflow sensors remains the gold standard.
Does REM sleep affect PPG sleep apnea detection?
Yes. REM-related OSA often involves longer, more complex apneas with greater SpO2 desaturation and larger autonomic surges.