Introduction: Pathology driven alterations in the geometric shape of the heart have been found to result in regional changes in ventricular wall stress and a remodeling of the myocardium. If reductions in the gravitational forces acting on the heart produce similar changes in the overall contour of the ventricles, this modification might also induce adaptations in the cardiac structure during long-term spaceflight. In this study we examined the changes in left ventricle (LV) shape in spaceflight and during parabolic flights.
Methods: The diastole dimensions of the human LV were assessed with echocardiography during spaceflight and in parabolic flights which replicated the gravity of the Moon, Mars, and spaceflight and were compared to findings in Earth's gravity. LV dimensions were translated into circularity indices and geometric aspect ratios and correlated with their corresponding gravitational conditions.
Results: During parabolic flight, a linear relationship (r = 0.99) was found between both the circularity index and geometric aspect ratio values and the respective gravitational fields in which they were measured. During spaceflight (N = 4) and parabolic flights (N = 3), there was an average 4.1 and 4.4% higher circularity index and a 5.3 and 8.1% lower geometric aspect ratio, respectively.
Conclusions: A correlative trend was found between the degree of LV sphericity and the amount of gravitational force directed caudal to the longitudinal orientation of the body. The importance of this finding is uncertain, but may have implications regarding physiologic adaptations in the myocardial structure secondary to changes in LV wall stress upon prolonged exposure to microgravity.