SMALLER ALVEOLAR-ARTERIAL O-2 GRADIENTS IN TIBETAN THAN HAN RESIDENTSOF LHASA (3658 M)

Previous studies have indicated that native Tibetans have a larger lun g capacity and better maintain arterial O-2 saturation during exercise than Han (''Chinese'') acclimatized lowlanders. To test if difference s in ventilation or alveolar-arterial O-2 gradient (A-aD(O2)) were res ponsible, we compared 10 lifelong Tibetan and 9 Han acclimatized newco mer residents of Lhasa (3658 m) at rest and during progressive exercis e. Resting blood gas tensions and arterial O-2 saturation in the two g roups were similar. During exercise the Tibetans had lower total venti lation and higher arterial CO2 tensions than the Han (both P < 0.01) a nd markedly lower A-aD(O2) (7 +/- 1 vs. 11 +/- 1, 13 +/- 1 vs. 18 +/- 1, and 14 +/- 1 vs. 20 +/- 1 mmHg at light, medium, and heavy workload s respectively, all P < 0.01). The Tibetans' narrower A-aD(O2) compens ated for their lower exercise ventilation such that arterial O-2 tensi on and saturation were raised above acclimatized newcomer values and b etter maintained during exercise. We concluded that the Tibetans exhib ited more efficient pulmonary gas exchange which compensated for reduc ed ventilation and lessened respiratory effort.