Older individuals experience cardiovascular dysfunction during extended bedridden hospital or care home stays. Bed rest is also used as a model to simulate accelerated vascular deconditioning occurring during spaceflight. This study investigates changes in retinal microcirculation during a ten-day bed rest protocol. Ten healthy young males (22.9 ± 4.7 years; body mass index: 23.6 ± 2.5 kg·m-2) participated in a strictly controlled repeated-measures bed rest study lasting ten days. High-resolution images were obtained using a hand-held fundus camera at baseline, daily during the 10 days of bed rest, and 1 day after re-ambulation. Retinal vessel analysis was performed using a semi-automated software system to obtain metrics for retinal arteriolar and venular diameters, central retinal artery equivalent and central retinal vein equivalent, respectively. Data analysis employed a mixed linear model. At the end of the bed rest period, a significant decrease in retinal venular diameter was observed, indicated by a significantly lower central retinal vein equivalent (from 226.1 µm, CI 8.90, to 211.4 µm, CI 8.28, p = .026), while no significant changes in central retinal artery equivalent were noted. Prolonged bed rest confinement resulted in a significant (up to 6.5%) reduction in retinal venular diameter. These findings suggest that the changes in retinal venular diameter during bedrest may be attributed to plasma volume losses and reflect overall (cardio)-vascular deconditioning.

Centre for Environmental Sciences Hasselt University Hasselt Belgium

College of Medicine Mohammed Bin Rashid University of Medicine and Health Sciences Dubai United Arab Emirates

Department 1 of Internal Medicine Centre for Integrated Oncology Aachen Bonn Cologne Düsseldorf University Hospital of Cologne Cologne Germany

Department of Biological and Environmental Sciences Faculty of Health Sciences Walter Sisulu University PBX1 Mthatha 5117 South Africa

Department of Biomedical Sciences University of Padua Padua Italy

Department of Psychiatry University Hospital Münster Münster Germany

Division of Physiology and Pathophysiology Otto Loewi Research Center for Vascular Biology Immunology and Inflammation Medical University of Graz Graz Austria

Faculty of Applied Ecology Agricultural Sciences and Biotechnology Inland Norway University of Applied Sciences Lillehammer Norway

Institute for Kinesiology Research Science and Research Centre Koper Koper Slovenia

Integrative Health Alma Mater Europaea Maribor Maribor Slovenia

Internal Medicine Division of Endocrinology and Diabetology Interdisciplinary Metabolic Medicine Trials Unit Medical University of Graz Graz Austria

Laboratory of Neurobiology and Molecular Psychiatry Department of Biochemistry Faculty of Science Masaryk University Kamenice 753 5 625 00 Brno Czech Republic

Laboratory of Neurobiology and Pathological Physiology Institute of Animal Physiology and Genetics Czech Academy of Sciences Veveří 97 602 00 Brno Czech Republic

Research Unit Gravitational Physiology and Medicine Physiology Otto Loewi Research Center Medical University of Graz Neue Stiftingtalstraße 6 D 05 8010 Graz Austria

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