PAIN PERCEPTION UNDER CHRONIC HIGH-ALTITUDE HYPOXIA

Following studies of respiratory sensory functions during high-altitud e adaptation, pain perception investigations were carried out on Europ ean lowlanders during an expedition on the Bhrikuti peak, Himalaya (fi rst 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 subject s' reports of pain. The tests were performed in the field under normox ic conditions, before and after ascent, and under hypoxic conditions a t altitudes of 3500 and 5600 m. The tests were also performed in a con trol group under normoxic conditions and similar ambient temperatures. Under normoxic conditions, the expedition group differed from the con trol group and demonstrated a more stoic attitude and a lower pain thr eshold. At high altitudes, pain thresholds decreased through improved sensory discrimination performances. Hypoxia is supposed to be the mai n 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 dis crimination in pain perception may be a component of a general improve ment in sensory processing during the early stages of altitude acclima tization.