[Photoplethysmography and laser Doppler velocimetry in the study of cutaneous vasomotility at high altitudes].

During the second French scientific medical expedition to the Himalaya (ARPE, Annapurna IV, 1985), modifications of cutaneous circulation in hypoxia were studied. Two techniques were used for the first time to evaluate cutaneous vasoactivity under such conditions: laser Doppler velocimetry and photoplethysmography. Measurements were performed on the pulp of the third and fourth fingers of the right hand in 6 subjects native of sea-level countries: first at sea level, then in hypoxia after 15 days at 4,800 m before and after ingestion of a vasodilator drug (nicardipine 20 mg). Cutaneous circulation was explored under three thermal conditions: baseline (ambient temperature); after vasodilation obtained by immersion of the hand in hot water (40 degrees C), and after immersion of the hand in cold water (12 degrees C). In prolonged hypoxia a reduction in vasoconstriction at 12 degrees C was observed with both techniques. No significant change was observed at 40 degrees C. After dosing with nicardipine, the results differed according to the exploratory technique: a slight increase of the laser Doppler signal (NS) and a decrease of the photoplethysmographic signal were recorded. Acclimatization to cold and to hypoxia may concur to determine this response of cutaneous circulation. The action of vasodilating agents on cutaneous microcirculation in prolonged hypoxia is not clear and deserves further investigation. These drugs must be used with caution in the prevention and treatment of frostbite.