Oxygen transport in Tibetan women during pregnancy at 3,658 m

High-altitude reduces infant birth weight as a result of intrauterine growt h restriction (IUGR) and is associated with increased neonatal mortality. W e hypothesized that babies born to Tibetan compared to Han (Chinese) high-a ltitude residents were protected from IUGR as the result of increased mater nal O-2 transport due, in turn, to increased uterine artery (UA) blood flow . We studied 68 nonpregnant or pregnant Tibetan or Han residents of Lhasa, Tibet Autonomous Region, China (3,658 m). The pregnant women had higher hyp oxic ventilatory responses (HVR A) and resting ventilations (V-E) than thei r nonpregnant counterparts (Tib HVR = 134 +/- 16 (SEM) vs. 30 +/- 8, Han HV R = 134 +/- 16 vs. 66 +/- 18 A units; Tib V-E = 11.8 +/- 0.3 vs. 10.1 +/- 0 .5, Han V-E = 10.7 +/- 0.5 vs. 9.4 +/- 0.51 BTPs/min; all P < 0.05). Pregna ncy did not change hemoglobin concentration in the Han but lowered values m ore than 2 g/dl in the Tibetans, serving to reduce arterial O-2 content bel ow Han values (15.4 +/- 0.3 vs. 17.4 +/- 0.5 ml O-2/100 ml whole blood, P < 0.05). Compared with the Han, the pregnant Tibetans had higher UA blood fl ow velocity (58.5 +/- 2.9 vs. 49.1 +/- 3.2, P < 0.05) and distributed a hig her portion of common iliac (CI) blood flow to the UA (4.8 +/- 0.4 vs. 3.3 +/- 0.3, P < 0.05). Birth weights averaged 635 g greater in the Tibetan tha n Han high-altitude residents (3,280 +/- 78 vs. 2,645 +/- 96 g, P < 0.01), or 694 g more when adjusted for maternal age, parity, height, and near-term body weight. Heavier birth weight babies were born to women with higher V, (r = 0.62, P < 0.01) and greater distribution of CI blood flow to the UA ( r = 0.42, P < 0.05). We conclude that increased UA blood flow, and not high er arterial O-2 content, permits Tibetan women to increase uteroplacental O -2 delivery and protect their infants from altitude-associated IUGR. (C) 20 01 Wiley-Liss, Inc.