Effect of Exercise on Coronary Hemodynamics Under the Earth's Gravity and Microgravity Conditions: A CFD Study

Exposure to microgravity affects the cardiovascular system and fluid distribution in the vasculature system of the human body depending on the short term or long term exposure. Literature suggests that in the initial few days in the microgravity environment, a short term exposure, the cardiac output and plasma volume are altered. Gradually, after about a week of long exposure to the microgravity environment, these parameters return to the same levels as those under the Earth's gravity. In this computational fluid dynamics (CFD) study, we investigate the effect of microgravity environment on coronary hemodynamics in a patient-specific coronary artery, for long exposure when the cardiac output and plasma volume are the same as under Earth's gravity assuming the vessels to be rigid. The CFD analysis suggests that redistribution of blood happens with the blood flow decreasing in the arteries at the lower elevation and increasing in those at higher elevation when compared with that in the Earth's gravity. From the qualitative and quantitative analysis of wall shear stress based hemodynamic biomarkers, it is found that the regions with low time-averaged wall shear stress (< 0.4 Pa) and high relative residence time (> 8 Pa^-1) increase in the microgravity environment. Further, the effect of exercise conditions is modelled by increasing the heart rate and the cardiac output and the regions with low time-averaged wall shear stress and high relative residence time are found to decrease. The flow is observed to be helical in nature in several arterial segments and the strength of helical flow increases under exercise conditions.