Oculomotor and Pupillary Reflexes During Acclimatization to Altitude (4300 m)

Abstract

Abstract : To identify soldiers with a possible health risk when deployed rapidly to moderate altitude, oculometrics were investigated as an objective index of the hypoxic effect on the CNS. The authors previously described the effects of a 4-hour exposure to real and simulated 4,300 m altitude on the pupillary light reflex as measured by the initial pupil diameter (PD), constriction amplitude (CA), and constriction latency (CL). Saccadic Velocity (SV) was measured as an index of extraocular motor function. Within 1 hour of exposure PD was reduced 5% and CL 2%. After 24 hours the reductions progressed to 12% and 5%, respectively. These effects were due to hypoxia per se, readily reversible, not gender related, and independent of eye dominance. SV was not acutely affected. To determine whether oculomotor reflexes could serve as an acclimatization variable and an index of AMS severity, data were collected during the long-term phase of the field study conducted at Pikes Peak, CO (4,300 m). After sea-level, baseline (SLB) measurements were taken, 18 men 19-to-33 years old were transported to Pikes Peak, where they remained for 14 days. The same oculometric variables were measured on days 1-4, 6, 7, 9, 10, and 12 in addition to several classical measures of altitude acclimatization: environmental symptoms questionnaire (ESQ), heart rate (HR), pulse oximetry (SpO2), end-tidal PO2 and PCO2, and 24-hour urinary epinephrine and norepinephrine concentrations. PD and CL decreased from SLB for days 1-4 and returned toward SLB, paralleling changes in ventilatory and circulatory variables. CA decreased on days 1-2 and remained decreased for 12 days. SV increased over the first 6 days and then returned toward SLB with continued exposure, similar to changes in urinary catecholamines. With acclimatization, CL correlated with HR and SpO2; SV correlated with PCO2, HR, and SpO2. AMS severity peaked during days 2-4, returned toward SLB over the next 10 days, and correlated only with CL (p=0.047