Learn PPG
Estimating Pulse Wave Velocity from PPG
Pulse Wave Velocity (PWV) is the speed at which the arterial pressure wave travels along a vessel, measured in m/s. It is the gold-standard non-invasive marker of arterial stiffness, a major independent predictor of cardiovascular events. PWV can be estimated from the ratio of vascular path length to PTT.
Carotid-femoral PWV (cf-PWV) measured by applanation tonometry is the reference standard for arterial stiffness assessment. The 2013 ESH/ESC hypertension guidelines (doi:10.1093/eurheartj/eht151) use cf-PWV > 10 m/s as a marker of asymptomatic organ damage.
PPG-based PWV estimation approximates the path length between two measurement sites using body segment models and divides by the measured PTT. Wrist-to-finger or earlobe-to-wrist configurations are common in consumer devices.
Reflective PPG (single-site) can estimate a surrogate of PWV through waveform analysis. The time between the systolic peak and the diastolic inflection point (often called the reflection index or augmentation index proxy) correlates with PWV and arterial stiffness. Single-site PWV proxies are less accurate than two-site transit time measurements but are more practical for consumer wearables.
Go deeper
Frequently Asked Questions
Can a single PPG sensor estimate PWV?
Yes, through waveform morphology analysis. Single-site indices like the stiffness index (SI) and reflection index (RI) from the PPG diastolic peak correlate with PWV but are less accurate than two-site transit time methods.
Is PPG-based PWV clinically validated?
Consumer PPG-based PWV has not achieved clinical validation for independent cardiovascular risk assessment.
How does exercise affect PWV?
Acute exercise transiently decreases PWV through vasodilation despite BP elevation.