Physiologic affects of altitude on recreational climbers.

Objectives: Previous analyses of physiologic parameter changes during ascent to altitude have incorporated small numbers of well-trained climbers. The effects of altitude illness are more likely to occur and may come to medical attention more frequently in unacclimatized recreational individuals. We sought to evaluate acute changes in physiologic parameters during ascent to high altitude (14,100 ft) in recreational climbers.

Methods: We performed a prospective naturalistic study of 221 recreational climbers at Mount Shasta (peak altitude of 14,162 ft). Baseline vital signs were recorded at 3500 ft (blood pressure, heart rate, respiratory rate, pulse oximetry, and peak flow). Subsequent measurements were obtained at 6700 ft, 10,400 ft, and at the summit. Mean vital signs and the amount they changed with altitude were estimated using mixed linear models.

Results: One hundred twenty-five climbers (56.6%) reached the summit. Heart rate increased and pulse oximetry decreased with ascent (mean, 71.9, 79, 97, and 102.4 beats/min and 96.9%, 93.9%, 88.8%, and 80.8%, respectively), with estimates at each altitude differing statistically at P < .0001. Mean systolic and diastolic blood pressures varied significantly by altitude (not measured at summit), but the changes were not monotonic. Peak flow progressively declined with ascent, but the difference between 6700 and 10,400 was not statistically significant. Respiratory rate did not change significantly.

Conclusions: Acute compensation for altitude-induced hypoxia involves numerous physiologic changes; this is supported by our data that demonstrate significant changes in blood pressure and stepwise changes in pulse oximetry, peak flow, and heart rate. Consideration of these changes can be incorporated in future studies of the affect of altitude on recreational climbers.