How is a measuring method tested scientifically?

The test begins at the reference, not at the sensor

Continuous blood pressure measurement for wearables is usually presented as a sensor question: a better component, better optics, a better result. But the difficulty starts earlier.

Before anything can be calibrated, it has to be shown that a non-invasive method captures the same pressure course as the invasive measurement. Only when both see the same changes is the data usable for a calibration.

The central question is therefore not which sensor is used. It is whether the non-invasive measurement reproduces the same physiological reality as the reference.

Why the site of the reference decides

Even an invasive measurement is not equally informative everywhere. Close to the vessel wall, local influences take effect: wall tension, reflections of the pressure wave, haemodynamic effects at the measuring point.

Measuring in the middle of the aorta, by contrast, gives the central reference pressure and removes a large part of these error sources. Testing against a badly placed reference produces deviations that say nothing about the method being tested.

What was tested in Paper 1

The BPER rests on the second-order blood pressure fluctuation — not on a static single value, but on the breath-driven dynamics of the circulation, which look different in every person.

It is exactly this foundation that was tested, for the first time, directly against invasive aortic pressure. That is the content of Paper 1: not another calibration method, but the precondition for stress-free blood pressure measurement to work correctly at all.

Calibration here is not the blood pressure value itself. It is the demonstrated relationship between a measured signal and the actual pressure. The data from wearables stays the same — the open question is how the calibration is done.