Tijs Louwies1, Polona Jaki Mekjavic2, Bianca Cox3, Ola Eiken4, Igor B Mekjavic5, Stylianos Kounalakis6, Patrick De Boever1. 1. Environmental Risk and Health, Flemish Institute for Technological Research (VITO), Mol, Belgium 2Centre for Environmental Sciences, Hasselt University, Hasselt, Belgium. 2. Eye Hospital, University Medical Centre Ljubljana, Ljubljana, Slovenia. 3. Centre for Environmental Sciences, Hasselt University, Hasselt, Belgium. 4. Department of Environmental Physiology, Swedish Aerospace Physiology Centre, Royal Institute of Technology, Kungliga Tekniska Högskolan (KTH), Stockholm, Sweden. 5. Department of Automation, Biocybernetics and Robotics, Jozef Stefan Institute, Ljubljana, Slovenia 6Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, British Columbia, Canada. 6. Human Performance-Rehabilitation Laboratory, Faculty of Physical and Cultural Education, Evelpidon Hellenic Military University, Vari, Greece.
Abstract
PURPOSE: To assess the separate and combined effects of exposure to prolonged and sustained recumbency (bed rest) and hypoxia on retinal microcirculation. METHODS: Eleven healthy male subjects (mean ± SD age = 27 ± 6 years; body mass index [BMI] = 23.7 ± 3.0 kg m-2) participated in a repeated-measures crossover design study comprising three 21-day interventions: normoxic bed rest (NBR; partial pressure of inspired O2, PiO2 = 133.1 ± 0.3 mm Hg); hypoxic ambulation (HAMB; PiO2 = 90.0 ± 0.4 mm Hg), and hypoxic bed rest (HBR; PiO2 = 90.0 ± 0.4 mm Hg). Central retinal arteriolar (CRAE) and venular (CRVE) equivalents were measured at baseline and at regular intervals during each 21-day intervention. RESULTS: Normoxic bed rest caused a progressive reduction in CRAE, with the change in CRAE relative to baseline being highest on day 15 (ΔCRAE = -7.5 μm; 95% confidence interval [CI]: -10.8 to -4.2; P < 0.0001). Hypoxic ambulation resulted in a persistent 21-day increase in CRAE, reaching a maximum on day 4 (ΔCRAE = 9.4 μm; 95% CI: 6.0-12.7; P < 0.0001). During HBR, the increase in CRAE was highest on day 3 (ΔCRAE = 4.5 μm; 95% CI: 1.2-7.8; P = 0.007), but CRAE returned to baseline levels thereafter. Central retinal venular equivalent decreased during NBR and increased during HAMB and HBR. The reduction in CRVE during NBR was highest on day 1 (ΔCRVE = -7.9 μm; 95 CI: -13.3 to -2.5), and the maximum ΔCRVE during HAMB (24.6 μm; 95% CI: 18.9-30.3) and HBR (15.2 μm; 95% CI: 9.8-20.5) was observed on days 10 and 3, respectively. CONCLUSIONS: The diameters of retinal blood vessels exhibited a dynamic response to hypoxia and bed rest, such that retinal vasodilation was smaller during combined bed rest and hypoxia than during hypoxic exposure.
PURPOSE: To assess the separate and combined effects of exposure to prolonged and sustained recumbency (bed rest) and hypoxia on retinal microcirculation. METHODS: Eleven healthy male subjects (mean ± SD age = 27 ± 6 years; body mass index [BMI] = 23.7 ± 3.0 kg m-2) participated in a repeated-measures crossover design study comprising three 21-day interventions: normoxic bed rest (NBR; partial pressure of inspired O2, PiO2 = 133.1 ± 0.3 mm Hg); hypoxic ambulation (HAMB; PiO2 = 90.0 ± 0.4 mm Hg), and hypoxic bed rest (HBR; PiO2 = 90.0 ± 0.4 mm Hg). Central retinal arteriolar (CRAE) and venular (CRVE) equivalents were measured at baseline and at regular intervals during each 21-day intervention. RESULTS: Normoxic bed rest caused a progressive reduction in CRAE, with the change in CRAE relative to baseline being highest on day 15 (ΔCRAE = -7.5 μm; 95% confidence interval [CI]: -10.8 to -4.2; P < 0.0001). Hypoxic ambulation resulted in a persistent 21-day increase in CRAE, reaching a maximum on day 4 (ΔCRAE = 9.4 μm; 95% CI: 6.0-12.7; P < 0.0001). During HBR, the increase in CRAE was highest on day 3 (ΔCRAE = 4.5 μm; 95% CI: 1.2-7.8; P = 0.007), but CRAE returned to baseline levels thereafter. Central retinal venular equivalent decreased during NBR and increased during HAMB and HBR. The reduction in CRVE during NBR was highest on day 1 (ΔCRVE = -7.9 μm; 95 CI: -13.3 to -2.5), and the maximum ΔCRVE during HAMB (24.6 μm; 95% CI: 18.9-30.3) and HBR (15.2 μm; 95% CI: 9.8-20.5) was observed on days 10 and 3, respectively. CONCLUSIONS: The diameters of retinal blood vessels exhibited a dynamic response to hypoxia and bed rest, such that retinal vasodilation was smaller during combined bed rest and hypoxia than during hypoxic exposure.
Authors: Robert Šket; Leon Deutsch; Zala Prevoršek; Igor B Mekjavić; Janez Plavec; Joern Rittweger; Tadej Debevec; Ola Eiken; Blaz Stres Journal: Front Physiol Date: 2020-12-07 Impact factor: 4.566