Devices like iheart and the Oura ring claim to measure PWV, and even blood pressure, but they don’t. They can’t. They derive PWV from a PPG signal, typically using pulse oxymetrie at one single measurement point. To measure speed you need two points in space and know the distance between them. A single-point measurement will never give you a reliable indication of speed.

The PPG signal is recorded at the arteriolar/capillary level of the vasculature. Then the wave is mathematically deconstructed to derive the PWV on the upstream arterial level. While it is conceivably possible to do this for a given individual after calibrating the device against an actual PWV measurement, I doubt very much that such calibration data are applicable across user populations.

The PPG signal is very sensitive to personal and environmental disturbances and idiosyncrasies. That’s why I doubt its reliability.

Even if these problems can be overcome, you’d only be able to derive the PWV of the closest upstream vascular path (brachial-radial) but not the central PWV. And brachial-radial PWV is a poor indicator of vascular health.

All this conspires against the usability of the ring for the purpose of measuring PWV reliably.

I can also find no validation studies for iheart’s or Oura’s PWV measurements.

What it probably can do is monitoring heart rate, HRV and possibly identify Afib episodes (see my post about the iWatch). That’s because the PPG signal corresponds with heart beats.

I have been involved in developing a medical-grade device that measures central PWV and central BP using very-high-resolution oscillometric signal acquisition at the upper arm. It is possible to deconstruct those waves and calibrate a device across several health conditions. But doing so using a more distant signal, like at the wrist or finger, has proven futile.