Pain perception under chronic high-altitude hypoxia.

Following studies of respiratory sensory functions during high-altitude adaptation, pain perception investigations were carried out on European lowlanders during an expedition on the Bhrikuti peak, Himalaya (first ascent). Perception thresholds and discrimination performances of electrical stimuli applied to the skin were determined with a constant stimulus method. Additionally, Clark's Situational Pain Questionnaire was used to measure discriminability and response bias of the subjects' reports of pain. The tests were performed in the field under normoxic conditions, before and after ascent, and under hypoxic conditions at altitudes of 3500 and 5600 m. The tests were also performed in a control group under normoxic conditions and similar ambient temperatures. Under normoxic conditions, the expedition group differed from the control group and demonstrated a more stoic attitude and a lower pain threshold. At high altitudes, pain thresholds decreased through improved sensory discrimination performances. Hypoxia is supposed to be the main cause of this sensory adaptive reaction to altitude as psychological attitude remained unchanged and a decrease in ambient temperature was without effect on pain perception in the control group. Increased discrimination in pain perception may be a component of a general improvement in sensory processing during the early stages of altitude acclimatization.