Intraocular pressure and cardiovascular alterations investigated in artificial gravity as a countermeasure to spaceflight associated neuro-ocular syndrome

Abstract

Artificial gravity (AG) has been proposed as a countermeasure to spaceflight-associated neuro-ocular syndrome (SANS). The etiology of SANS is unknown but mimicking gravitational loading through AG may mitigate these negative adaptations. Seventeen subjects (nine men, eight women; 18–32 yr) were analyzed in four experimental conditions: 1) standing, 2) supine, 3) AG with the center of rotation at the eye (AGEC), and 4) AG with 2 Gs at the feet (AG2G). In both AG conditions, subjects were spun to produce 1 G at their center of mass. Data included self-administered intraocular pressure (IOP, Tono-pen AVIA, Depew, NY), heart rate (HR), and mean arterial blood pressure (MAP, Omron Series 10, Omron Healthcare, Kyoto, Japan). Data were analyzed with repeated measures ANOVAs with Tukey-Kramer corrections for multiple pairwise comparisons. IOP was 15.7 ± 1.4 mmHg (mean ± 95% confidence interval) standing, 18.8 ± 1.3 mmHg supine, 18.5 ± 1.7 mmHg in AGEC, and 17.5 ± 1.5 mmHg in AG2G. Postures showed a main effect [F(3,48) = 11.0, P < 0.0005], with standing significantly lower than supine ( P = 0.0009), AGEC ( P = 0.002), and AG2G (0.036). Supine, AGEC, and AG2G were not statistically different. HR and MAP were lower in supine compared with all other postures ( P = 0.002 to P < 0.0005), but there were no differences between standing, AGEC, and AG2G. IOP in supine and standing was consistent with previous studies, but contrary to our hypothesis, remained elevated in both AG conditions. Cardiovascular parameters and hydrostatic gradients determine IOP, which remain unchanged compared with standing. These results suggest additional influence on IOP from previously unconsidered factors. NEW & NOTEWORTHY This is the first study, to the authors’ knowledge, to measure intraocular pressure in short-radius centrifuge artificial gravity (AG), which has been proposed as a countermeasure to the spaceflight-associated neuro-ocular syndrome (SANS). If the etiology of SANS is related to intraocular pressure, these results have implications for whether or not short-radius AG can be used to prevent ocular changes relevant to it. Our results indicate this proposed countermeasure merits further investigation.