Mathematical modeling of gravitational effects on the circulation: importance of the time course of venous pooling and blood volume changes in the lungs

American Journal of Physiology. Heart and Circulatory Physiology
K van HeusdenJohn M Karemaker

Abstract

A dip in blood pressure (BP) in response to head-up tilt (HUT) or active standing might be due to rapid pooling in the veins below the heart (preload) or muscle activation-induced drop in systemic vascular resistance (afterload). We hypothesized that, in the cardiovascular response to passive HUT, where, in contrast to active standing, little BP dip is observed, features affecting the preload play a key role. We developed a baroreflex model combined with a lumped-parameter model of the circulation, including viscoelastic stress-relaxation of the systemic veins. Cardiac contraction is modeled using the varying-elastance concept. Gravity affects not only the systemic, but also the pulmonary, circulation. In accordance with the experimental results, model simulations do not show a BP dip on HUT; the tilt-back response is also realistic. If it is assumed that venous capacities are steady-state values, the introduction of stress-relaxation initially reduces venous pooling. The resulting time course of venous pooling is comparable to measured impedance changes. When venous pressure-volume dynamics are neglected, rapid (completed within 30 s) venous pooling leads to a drop in BP. The direct effect of gravity on the pulmonary circulati...Continue Reading

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Citations

Feb 10, 2009·Medical & Biological Engineering & Computing·Fuyou LiangHao Liu
Dec 17, 2008·American Journal of Physiology. Heart and Circulatory Physiology·Qi FuBenjamin D Levine
Nov 10, 2013·PloS One·Einly LimNigel H Lovell
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Jun 27, 2009·Vascular and Endovascular Surgery·Prabhu Nanjundeshwar NesargikarAndrew Houghton
Jul 26, 2019·Journal of Applied Physiology·Ana Diaz-ArtilesLaurence R Young
Jun 4, 2019·Journal of Mathematical Biology·Nakeya D WilliamsMette S Olufsen
Jul 27, 2014·American Journal of Physiology. Heart and Circulatory Physiology·Fuyou LiangHao Liu
Jan 2, 2021·Autonomic Neuroscience : Basic & Clinical·Mark P M HarmsWouter Wieling
May 8, 2021·Computer Methods and Programs in Biomedicine·Dong Ah Shin, Jung Chan Lee
Apr 30, 2021·Journal of Applied Physiology·Richard S Whittle, Ana Diaz-Artiles

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