Impact of 60 days of head-down bed rest on large arteries

The long-term cardiovascular consequences of microgravity on large arteries are a threat for long-term space missions. We hypothesized that changes in arterial properties differ according to the arterial territory (upper or lower body), and arterial structure (elastic vs. muscular arteries), in response to 60-day head-down bed rest (HDBR).

Twenty healthy male volunteers were included and received a daily multivitamin supplementation in a double-blind fashion. At baseline, 29 and 52 days during strict HDBR, then 12 and 30 days after HDBR, aortic stiffness was measured using carotid-to-femoral pulse wave velocity (cf-PWV) and aortic MRI. Carotid, femoral, brachial and popliteal arteries were studied by ultrasound echo tracking, central blood pressure (BP) by tonometry and endothelial function by flow-mediated dilatation.

Cf-PWV increased during HDBR (+0.8 and +1.1m/s, at D29 and D52, respectively, P = 0.004), corresponding to an increase in vascular age up to +11 years (P = 0.003). Changes were similar to those observed on MRI (+0.8 m/s at D52, P < 0.01) and were independent of BP and heart rate changes. After HDBR, cf-PWV showed a substantial recovery at R12 but still remained higher than baseline at R30 (+0.8 m/s, P = 0.018), corresponding to +6.5 years of vascular aging (P = 0.018). Thoracic aorta diameter increased significantly (+6%, P = 0.0008). During HDBR, femoral and popliteal arteries showed dimensional changes, leading to femoral inward hypotrophic remodeling (femoral diameter: -12%, P < 0.05; wall cross-sectional area: -25%, P = 0.014) and popliteal inward eutrophic remodeling (popliteal diameter: -25%, P < 0.05; wall cross-sectional area: -3%, P = 0.51). After HDBR, both arterial territories of the leg recovered. We did not observe any significant changes for carotid arteries nor for endothelial function during and after HDBR. Multivitamin supplementation did not affect vascular changes. HDBR was associated with an important increase in aortic stiffness, which did not completely recover 1 month after the end of HDBR. The thoracic aorta and the lower body muscular arteries underwent significant changes in dimensions whereas the common carotid arteries were preserved.

These results should raise caution for those exposed to microgravity, real or simulated.