Model-based assessment of pressure and ¯ow-dependent coronary responses following abrupt pressure drops C. Guiot a, b, *, A. Merletti a , P. Pagliaro a , G. Losano a, b a Dip. Neuroscienze (sez. Fisiologia), dell' Universita Á di Torino, C. Raaello 30, I-10125, Torino, Italy b INFM Bio®sica, UdR dell' Universita Á di Torino, C. Raaello 30, I-10125, Torino, Italy Received 2 June 1999; accepted 2 December 1999 Abstract The response of the coronary vasculature to an experimental manoeuvre of step-like decrease of the perfusion pressure has been investigated with a model. The coronary vasculature was simulated using a `windkessel' scheme. Proximal resistance and compliance were assumed to be pressure-independent. The distal resistance, on the contrary, was controlled by a feed-back loop which accounts for the smooth muscle activation induced by the pressure variation. Three more parameters were introduced, and namely the smooth muscle activation time constant and the pressure-induced and ¯ow-induced gains. The parameter values were assessed by comparing the model predicted coronary ¯ow with the one actually measured in animals. 7 2000 Elsevier Science Ltd. All rights reserved. Keywords: Nitric oxide; Coronary ¯ow; Physical model; Vasomotor tone; Vascular responses 1. Introduction Sudden variations in coronary perfusion pressure can result from traumatic injuries or pathological processes, and studies in animal models showed that blood ¯ow tends to keep constant by a complex autoregulatory response. Such a response includes a contribution from the vascular smooth muscles, known as the `myogenic' response, some aspects of which are investigated in the present paper. Computers in Biology and Medicine 30 (2000) 111±126 0010-4825/00/$ - see front matter 7 2000 Elsevier Science Ltd. All rights reserved. PII: S0010-4825(00)00002-0 www.elsevier.com/locate/compbiomed * Corresponding author. Tel.: +39-11-670-7710; fax: +39-11-670-7708. E-mail address: guiot@medfarm.unito.it (C. Guiot).