Assessment of baroreflex sensitivity by the closed-loop blood pressure to interbeat interval transfer function

Noninvasive baroreflex sensitivity (BRS) measurements in humans - by computation of the transfer function from systolic blood pressure to inter-beat interval - are basically assessments, because they are made under closed-loop blood pressure control. Our study aims to compare such closed-loop BRS assessments with true open-loop BRS values by means of a simulation model of the human blood-pressure control system. Simulations were done with B.J. TenVoorde et al.´s (2000) model, modified by removing respiration and by adding a pressure probe, adjustable autonomic and haemodynamic conditions and a switch to open/close the loop. True open-loop BRS values ranged from 1 to 23 ms/mmHg. Closed-loop BRS assessments differed between -5 to +4.0% from the open-loop values. Our results demonstrate that, under physiological and pathological conditions, non-invasive closed-loop BRS measurements assess true open-loop BRS with virtually no bias