A Closed-Loop Cardiovascular Model of the Supine-To-Stand Manoeuvre: Implications for Falls.

The risk of falling increases with age and orthostatic hypotension (OH) is a common cardiovascular contributor. Current OH diagnostics rely on intermittent blood pressure measurements, which may not adequately characterise haemodynamic responses during orthostatic stress. We developed a closed-loop cardiovascular lumped-parameter model and fitting pipeline for continuous beat-to-beat blood pressure and heart rate data during a supine-to-stand manoeuvre, enabling model-based evaluation of orthostatic haemodynamic responses in older adults. Our 23-compartment lumped model included baroreflex and cardiopulmonary reflex regulation and was calibrated using Finapres data from older adults (Nijmegen Radboud University PROHEALTH study). Using a stochastic ranking evolutionary strategy, we fitted 31 parameters to averaged cohort data, classifying participants as with or without a history of falls (≥ 1 fall in the previous year). The model reproduced systolic and diastolic blood pressure and heart rate responses at the population level, with normalised root mean squared errors of 10.6% and 9.6% for participants with and without a history of falls, respectively. Four model parameters differed significantly between the two population-average fits: baroreflex reference heart rate, a baroreflex transfer function parameter, transient external muscle pressure during standing, and total blood volume. These results demonstrate that a physiologically structured cardiovascular model can reproduce population-level orthostatic responses in older adults and highlight model-based parameter differences associated with fall history.