Cardiac adaptations to 60 day head-down-tilt bed rest deconditioning. Findings from the AGBRESA study

Aims Reduced physical activity increases the risk of heart failure; however, non-invasive methodologies detecting subclinical changes in myocardial function are not available. We hypothesized that myocardial, left ventricular, systolic strain measurements could capture subtle abnormalities in myocardial function secondary to physical inactivity. Methods and results In the AGBRESA study, which assessed artificial gravity through centrifugation as potential countermeasure for space travel, 24 healthy persons (eight women) were submitted to 60 day strict -6 degrees head-down-tilt bed rest. Participants were assigned to three groups of eight subjects: a control group, continuous artificial gravity training on a short-arm centrifuge (30 min/day), or intermittent centrifugation (6 x 5 min/day). We assessed cardiac morphology, function, strain, and haemodynamics by cardiac magnetic resonance imaging (MRI) and echocardiography. We observed no differences between groups and, therefore, conducted a pooled analysis. Consistent with deconditioning, resting heart rate (Delta 8.3 +/- 6.3 b. p.m., P < 0.0001), orthostatic heart rate responses (Delta 22.8 +/- 19.7 b.p.m., P < 0.0001), and diastolic blood pressure (Delta 8.8 +/- 6.6 mmHg, P < 0.0001) increased, whereas cardiac output (Delta-0.56 +/- 0.94 L/min, P = 0.0096) decreased during bed rest. Left ventricular mass index obtained by MRI did not change. Echocardiographic left ventricular, systolic, global longitudinal strain (Delta 1.8 +/- 1.83%, P < 0.0001) decreased, whereas left ventricular, systolic, global MRI circumferential strain increased not significantly (Delta-0.68 +/- 1.85%, P = 0.0843). MRI values rapidly returned to baseline during recovery. Conclusion Prolonged head-down-tilt bed rest provokes changes in cardiac function, particularly strain measurements, that appear functional rather than mediated through cardiac remodelling. Thus, strain measurements are of limited utility in assessing influences of physical deconditioning or exercise interventions on cardiac function.

Automated summary

This study examined the effects of prolonged head-down-tilt bed rest on cardiac function, with a focus on strain measurements. The results showed that changes in cardiac function, particularly in strain measurements, appeared to be functional rather than due to cardiac remodeling. Therefore, strain measurements may have limited utility in assessing the impact of physical inactivity or exercise interventions on cardiac function.