In order to gain insights into microgravity-induced ophthalmic changes (Microgravity Ocular Syndrome), we investigated the effect of acute hypercapnia following 10-d bed rest and hypoxia on posterior eye structures. Female subjects (N=7) completed three 10-day experimental interventions: i) normoxic bedrest (NBR; PIO2=132.9+0.3 mmHg) ii) hypoxic ambulatory confinement (HAMB; PIO2=90.4+0.3mmHg), and iii) hypoxic bedrest (HBR; n=12; PIO2=90.4+0.3mmHg). Before, and on the last day of each intervention, optical coherence tomography (OCT) of the optic disc was performed and the thicknesses of the retinal nerve fibre layer (RNFL), retina and choroid were measured. OCT examinations were conducted with the subjects breathing the prevailing normocapnic breathing mixture (either normoxic or hypoxic) and then following a 10-min period of breathing the same breathing mixture, but with the addition of 1% CO2. Choroidal thickness was greater during both bedrest conditions (NBR and HBR) compared the ambulatory (HAMB) condition (ANOVA, p<0.001). Increases in RNFL thickness compared to baseline were observed in the hypoxic trials (HBR, p<0.001; and HAMB, p=0.021), but not the normoxic trial (NBR). A further increase in RNFL thickness (p=0.019) was observed after the 10-min hypercapnic trial in the NBR condition only. The fact that choroidal thickness was not affected by PO2 and PCO2, but increased by bedrest, suggests a hydrostatic rather than a vasoactive effect. The increements in RNFL thickness were most likely associated with local hypoxia and hypercapnia-induced dilatation of the retinal blood vessels.
- Space Life Sciences
- planetary habitats
- Copyright © 2015, Journal of Applied Physiology