Submitted on November 16, 2006
Accepted on July 2, 2007
DETERMINANTS OF BLOOD OXYGENATION DURING PREGNANCY IN ANDEAN AND EUROPEAN RESIDENTS OF HIGH ALTITUDE
Marco Vargas1, Enrique Vargas1, Colleen G Julian2, J. Fernando Armaza1, Armando Rodriguez1, Wilma Tellez1, Susan Niermeyer3, Megan J Wilson4, Esteban Parra5, Mark Shriver5, and Lorna G. Moore6*
1 Instituto Boliviano de Biologia de la Altura, Universidad Mayor de San Andres, La Paz, Bolivia
2 Department of Health and Behavioral Sciences, University of Colorado at Denver and Health Sciences Center, Denver, Colorado, United States
3 Colorado Center for Altitude Medicine and Physiology, University of Colorado at Denver and Health Sciences Center, Denver, Colorado, United States
4 Denver, Colorado, United States; Department of Health and Behavioral Sciences, University of Colorado at Denver and Health Sciences Center, Denver, Colorado, United States
5 Department of Anthropology, Genetics Laboratory, Pennsylvania State University, State College, Pennsylvania, United States
6 Colorado Center for Altitude Medicine and Physiology and Department of Health and Behavioral Sciences, University of Colorado at Denver and Health Sciences Center, Denver, Colorado, United States
* To whom correspondence should be addressed. E-mail: lorna.g.moore{at}uchsc.edu.
High altitude decreases birth weight but this effect is diminished in long vs. short-resident high-altitude populations. We asked whether women from long vs. short-resident high-altitude populations had higher arterial oxygenation levels by comparing 42 Andean and 26 European residents of La Paz, Bolivia (3600 m) serially during pregnancy (weeks 20, 30, 36) and again 4 mo postpartum. Pregnancy raised hypoxic ventilatory sensitivity 3-fold, resting ventilation (VE), and arterial O2 saturation (SaO2) in both groups. Ancestry, as identified using 81 genetic markers, correlated with respiratory pattern such that greater Andean ancestry was associated with higher respiratory frequency and lower tidal volume. Pregnancy increased total blood and plasma volume ~40% in both groups without changing red cell mass relative to body weight; hence, hemoglobin fell. The hemoglobin decline was compensated for by the rise in VE and SaO2 with the result that arterial O2 content (CaO2) was maintained near nonpregnant levels in both groups. Birth weights were similar for all Andean and European babies but after adjusting for variation in gestational age, maternal height and parity, Andeans weighed 209 gm more than Europeans. Babies with heavier birth weights and greater ponderal indices were born to Andean women with higher VE during pregnancy. We concluded that while maternal VE and arterial oxygenation were important, some factor other than higher CaO2 was responsible for protecting Andeans from altitude-associated reductions in fetal growth.
