To monitor the changes in optic nerve sheath diameter (ONSD) induced by acute exposure to hypobaric hypoxia and to investigate factors associated with these changes, including development of acute mountain sickness.Methods:
In this cohort study, neurologic signs and symptoms, cardiovascular parameters, and ultrasonography of ONSD were prospectively assessed in 19 healthy lowlanders at baseline and after ascent to 3,830 m (3 hours, 9 hours, 24 hours, 48 hours, 72 hours, and 8 days) by blinded investigators. Potential confounding factors (e.g., altitude variations, physical effort) were minimized. A multivariate analysis of factors associated with ONSD was performed by means of generalized estimating equations.Results:
ONSD increased with exposure to altitude in all participants (p < 0.001). The increase between 9 and 24 hours was larger in patients who developed acute mountain sickness (p = 0.001). There was no influence of sex, oxygen saturation, or acclimatization on ONSD.Conclusion:
Both physiologic and pathologic responses to hypobaric hypoxia were independently associated with changes in ONSD. Studies on a larger cohort, at a range of altitudes, and with baseline neuroimaging techniques are necessary to further understand the clinical significance of increased ONSD during exposure to hypobaric hypoxia.