Apical hypercontractility mitigates impaired diastolic filling and lower intraventricular haemodynamic forces in human bed rest

Prolonged physical inactivity alters the cardiovascular system, including the heart. Long-term bed rest is known to decrease left ventricular volume and cause diastolic dysfunction; however, the interplay between these changes and their effect on cardiac contractility have been understudied. Here we used novel non-invasive imaging techniques to longitudinally assess changes in regional cardiac contractility and function that can occur prior to the development of overt cardiac changes. Specifically, we performed cardiac magnetic resonance imaging on 24 healthy participants before, during, and after 60 days of strict head-down tilt bed rest (AGBRESA) to measure intracardiac haemodynamic forces and left-ventricular inward displacements via dedicated software. The integrated left ventricular haemodynamic force as well as the ejection force during systole were reduced throughout the bed rest. While maximal diastolic deceleration (at the E-wave) significantly decreased during bed rest, left ventricular diastolic suction and maximal value for the late diastolic deceleration phase were significantly increased. Inward displacement analysis showed that motion of the cardiac base was significantly reduced after bed rest, whereas apical motion was significantly increased. The analysis of haemodynamic forces and regional cardiac inward displacement are novel non-invasive imaging readouts that can provide longitudinal information about cardiac contractility and function. Our study highlights that prolonged bed rest alters regional cardiac motion and haemodynamic forces, with a desynchrony in contractile alterations to maintain cardiac filling during diastole.