Exergy analysis of the cardiovascular system

Abstract

© 2017 IMEKOIn the past few years, different scientific papers have proposed the use of an exergy perspective to analyze some physiological systems of the human body under different physical and environmental conditions. Such perspective, focused on the exergy transformations and the efficiency of the biological processes, which may aid the medical field in its assessment of a patient’s physical health. Following this concept, this paper proposes a model of the human cardiovascular system in order to calculate the exergy transfers and its destruction from the intrasystemic and intersystemic interactions, taking into account all significant energy conversion processes that involve the heart and the blood vessels as blood circulates in both the systemic and the pulmonary circulations. With this model, a 7.86 W exergy destruction was obtained for a person under basal conditions. As a follow-up, a statistical model was developed to describe the evolution of the transvalvular pressure gradient in the aortic valve as a valve stenosis becomes more severe. This model was created using physiological data from 40 patients available in the literature, as well as 32 operating points from different Bileaflet aortic valve prosthesis. A final logarithmic regression resulted in a 14.6 kPa (109.7 mmHg) pressure gradient in the most severe case, evolving from 0.9 kPa (6.5 mmHg) from the healthy scenario. Finally, the pressure gradients were analysed using the base model, arriving at an extreme value of 1.04 W of destroyed exergy in the aortic valve and 9.64 W for the entire system, an increase of 22.6% when comparing with the result for the healthy condition.

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