Women at altitude: Blood vessels.

Abstract

The physiological response of women to altitude has received comparatively little study until recently. Of interest is whether women and men differ in their physiological response to high altitude and if so, whether differences are due to circulating ovarian or gonadal hormones or to gender differences unrelated to levels of circulating hormones. It is important to recall that the determination of gender involves considerable evolutionary, genetic and developmental complexity. Studies of acute and chronic response to high altitude provide are useful for examining the general mechanisms and evolutionary significance of the influences of gender and sex hormones on processes of oxygen transport. The period of pregnancy and fetal development is subject to greater mortality risk than any other period during the life cycle. At high altitude, fertility is maintained at or above sea level values but infant birth weight decreases an average of 100 gm per 1000 m altitude gain, principally as a result of fetal growth retardation. An increased frequency of maternal complications of pregnancy also has been reported at high altitude and may, in turn, contribute to the birth weight decline. Pregnancy stimulates several components of maternal O₂ transport, raising ventilation and arterial oxygenation as the result of the combined actions of ovarian hormones and increased mletabolic rate. The magnitude of the rise in maternal ventilation and arterial oxygenation relates to infant birth weight at high altitude. Uteroplacental blood flow also appears to be reduced at high altitude, particularly among women developing preeclampsia. Thus the maternal ventilatory and cardiovascular adjustments by which fetal-placental O₂ and other nutrient delivery is maintained may be crucial in attaining successful adaptation to high altitude.