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Tijs Louwies, Polona Jaki Mekjavic, Bianca Cox, Ola Eiken, Igor B. Mekjavic, Stylianos Kounalakis, Patrick De Boever; Separate and Combined Effects of Hypoxia and Horizontal Bed Rest on Retinal Blood Vessel Diameters. Invest. Ophthalmol. Vis. Sci. 2016;57(11):4927-4932. doi: 10.1167/iovs.16-19968.
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© ARVO (1962-2015); The Authors (2016-present)
To assess the separate and combined effects of exposure to prolonged and sustained recumbency (bed rest) and hypoxia on retinal microcirculation.
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.
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.
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.
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