A Cardiovascular Mathematical Model of Graded Head-Up Tilt

Einly Lim,Gregory S H Chan,Socrates Dokos,Siew C Ng,Stijn Vandenberghe,Nigel H Lovell,Lydia A Latif,Mohan Karunanithi,Mathias Baumert

doi:10.1371/journal.pone.0077357

Abstract

A lumped parameter model of the cardiovascular system has been developed and optimized using experimental data obtained from 13 healthy subjects during graded head-up tilt (HUT) from the supine position to . The model includes descriptions of the left and right heart, direct ventricular interaction through the septum and pericardium, the systemic and pulmonary circulations, nonlinear pressure volume relationship of the lower body compartment, arterial and cardiopulmonary baroreceptors, as well as autoregulatory mechanisms. A number of important features, including the separate effects of arterial and cardiopulmonary baroreflexes, and autoregulation in the lower body, as well as diastolic ventricular interaction through the pericardium have been included and tested for their significance. Furthermore, the individual effect of parameter associated with heart failure, including LV and RV contractility, baseline systemic vascular resistance, pulmonary vascular resistance, total blood volume, LV diastolic stiffness and reflex gain on HUT response have also been investigated. Our fitted model compares favorably with our experimental measurements and published literature at a range of tilt angles, in terms of both global and regional hemodynamic variables. Compared to the normal condition, a simulated congestive heart failure condition produced a blunted response to HUT with regards to the percentage changes in cardiac output, stroke volume, end diastolic volume and effector response (i.e., heart contractility, venous unstressed volume, systemic vascular resistance and heart rate) with progressive tilting.

Highlights

Cardiovascular response to upright posture has been widely studied through numerous experiments and mathematical models
There is a high degree of correlation between the model and experimental data in all variables, including absolute changes in the mean arterial pressure (Psa), as well as percentage changes in the heart rate (HR), stroke volume (SV ), mean cardiac output (CO) and left ventricular (LV) end diastolic volume (LVEDV )
Our simulation results revealed that cardiopulmonary baroreceptors, which are sensitive to slight falls in preload or central venous pressure, contributes to the nonlinearity observed in the cardiac output response to progressive tilting (Fig. 4) through a substantial increase in the systemic vascular resistance at low tilt angles

Summary

Introduction

Cardiovascular response to upright posture has been widely studied through numerous experiments and mathematical models. Melchior et al [11] presented a comprehensive review of the important features involved during orthostatic stress, for example nonlinear blood vessel compliance, fluid filtration, role of extravascular pressures, as well as both reflex control and autoregulation mechanisms. The inclusion of these features in the model depends on the specific phenomenon the model intended to study. Olufsen et al [5,6] included cerebral autoregulation in their model to capture the transient response in pressure and cerebral blood flow velocity which acts to compensate for hypotension during standing

Methods

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Discussion

Conclusion