The 3D simulator auscultates: it listens for the turbulent-flow sound that appears once per heartbeat while cuff pressure sits between diastolic and systolic. This 2D version instead forward-models what an automated oscillometric cuff actually measures — the tiny mechanical pressure oscillations the pulsating artery transmits into the closed cuff bladder, with no sound involved at all.
The vessel wall's compliance (how much its volume changes per mmHg of transmural pressure) is not constant — real arterial pressure–volume curves are sigmoidal, and compliance peaks sharply where transmural pressure Ptm = Part − Pcuff crosses zero. This sim integrates that directly, every frame:
C(P_tm) = 1 / (1 + (P_tm / k)²) k = 15 mmHg
dV = C(P_tm) · dP_art(t) (forward-integrated each step)
amplitude(P_cuff) = peak-to-peak V over one full cardiac cycle
Sweeping the cuff down slowly and recording amplitude every beat traces out the classic bell-shaped oscillometric envelope — rising as cuff pressure approaches the true mean arterial pressure (compliance is highest there), then falling again below diastolic. The device then applies the same fixed-ratio rule real monitors use: systolic = the cuff pressure (above the envelope peak) where amplitude first reaches 55% of the maximum; diastolic = the cuff pressure (below the peak) where amplitude falls back to 65% of the maximum.
Verified numerically (standalone Node script, not just in-browser): forward-integrating this exact model across five sys/dia/heart-rate combinations recovers the true systolic and diastolic within about 1–2 mmHg at these ratios — but the recovery is only ever approximate. That is not a bug: real oscillometric monitors are validated against auscultation to a tolerance of several mmHg (AAMI/ESH protocols), not exact agreement, precisely because they infer pressure from an empirical amplitude ratio rather than measuring the Korotkoff sound onset directly. Try a very narrow pulse pressure (e.g. systolic 200 / diastolic 180) to see that tolerance widen — narrow pulse pressure is a known real-world weak point of the oscillometric method.
- Top strip — the raw cuff-pressure trace: the slow deflation ramp with the small oscillometric pulses riding on top, exactly what a real device's pressure transducer digitizes.
- Bottom chart — the amplitude-vs-cuff-pressure envelope building live, beat by beat, with the detected MAP/systolic/diastolic marked once found.