During surgery, an anesthesiologist watches a screen where pressure and pulse curves run. But behind these lines hide several other quantities: how much the vessels constrict, how fast the blood flows, how elastic the artery walls are. Precise instruments for measuring them are only used in the most severe cases because it's risky — a needle in the artery, a catheter in the heart.

Researchers proposed the HIPNO system, which reconstructs hidden blood flow parameters from ordinary signals — pulse, arm pressure, ECG. The difficulty is that different combinations of flow, resistance, and vessel elasticity can produce the same pressure. It's like hearing the same melody played on different instruments. HIPNO learns to distinguish these instruments by relying on the physics of circulation. It finds three key coordinates: how quickly blood decays in the vessels, the ratio of flow to elasticity, and the characteristic impedance of the arteries.

On data from nearly a million measurements in 2562 patients, HIPNO predicted the decay rate of the pulse wave 32% more accurately than simple methods, and without losing accuracy in estimating mean pressure. Moreover, if you mentally change one parameter, say increase vascular resistance, the system responds as expected in 90% of cases — meaning it truly separated the hidden factors rather than just memorizing the curves. This separation opens the way to non-invasive assessment of cardiac output and other important indicators.