Aortic Vessel Wall Properties during 60 Days Strict Head down Tilt Bedrest
Authors: Moestl Stefan , Rabineau Jeremy , Hoffmann Fabian , Caiani Enrico , Migeotte Pierre-Francois , Bachler Martin , Hametner Bernhard , Wassertheurer Siegfried , Jordan Jens , Tank Jens 
Published: April 2020

BackgroundChanges in large artery properties including increased arterial compliance and increased carotid artery stiffness have been described after space flight. Altered vascular structure, which heralds cardiovascular risk, and reversible changes in vascular function could contribute to the response. Compared with previous bedrest studies, which did not reproduce these findings, the artificial gravity bedrest study (AGBRESA) applied strict ‐6° head‐down tilt bedrest (HDT) for 60 days mimicking chronic cephalad fluid shifts in space. We assessed aortic vessel wall properties using state‐of‐the art imaging methods and pulse wave analysis and tested for possible protective effects of artificial gravity training.Material and MethodsThe AGBRESA Study is a joint project between NASA, ESA and DLR and is conducted in line with the declaration of Helsinki and the federal regulations of the U.S. Government. After the first of two AGBRESA campaigns, we present data from 12 healthy subjects (8 men, 4 women) obtained during baseline data collection 9–6 days before bedrest (BDC, supine position) and towards the end of two months head down tilt bedrest (MRI on day 56 and echocardiography on day 60 of HDT). Subjects were assigned to 30 minutes per day continuous short arm centrifugation (cAG), 6 times for 5 minutes interval short arm centrifugation, iAG), or a control group (ctr). We assessed aortic pulse wave velocity (PWV) using oscillometric upper arm and thigh cuffs (PWV‐2C, CardioCube, AIT, Vienna, Austria) and 4D‐flow cardiac velocity encoded phase contrast magnetic resonance imaging (PWV‐4D‐MRI). We also measured area, area changes, and distensibility (AoD) of the ascending aorta by 2D‐phase contrast cardiac MRI and arterial compliance (Ca) using transthoracic echocardiography.ResultsMean aortic area increased in all subjects after 60 days head down tilt bedrest (5.3±0.7 vs. 5.8±0.7 cm2, p<0.05). Stroke volume decreased from 94±13 to 84±10 ml (p<0.05) and pulse pressure from 56±11 to 46±9 mmHg (p<0.05) in part through reductions in stroke volume. The figure
illustrates individual data on aortic properties: Differences (end of HDT – BDC) in PWV measured with 2 cuffs (A) and with 4D‐Flow MRI (B), changes in AoD (C) and Ca (D) from BDC to the end of HDT (red diamonds = women). In contrast to the more consistent changes in aortic area, stroke volume, and pulse pressure, aortic distensibility, arterial compliance, and PWV responses show substantial inter‐individual variability.ConclusionThe important finding of our study is that 60 days strict head down bedrest elicit consistent changes in ascending aortic area, pulse pressure, and stroke volume. The resulting changes in vascular loading conditions likely confound vascular function measurements, both, in head down tilt bedrest studies and in space.Support or Funding InformationThe study was funded by the German Aerospace Center, the European Space Agency (contract number 4000113871/15/NL/PG) and the National Aeronautics and Space Administration (contract number 80JSC018P0078).Figure 1