CARDIORESPIRATORY RESPONSES TO ACUTE HYPOXEMIA IN THE CHRONICALLY CATHETERIZED FETAL LLAMA AT 0.7-0.9 OF GESTATION

The adult llama (Lama glama) has several compensatory mechanisms that allow it to successfully survive at high altitude. Llama fetuses at 0. 6-0.7 of gestation, and near-term llama fetuses studied close to surge ry, did not increase cerebral blood flow and decreased cerebral oxygen delivery during acute hypoxemia. It is not known whether these respon ses were the result of immaturity or surgical stress. The aim of this study was to determine whether the lack of increase in cerebral blood flow and the decrease in cerebral oxygen delivery during hypoxemia in the fetal llama is characteristic of this high-altitude species near t erm, and under nonstressed conditions. We chronically catheterized 7 l lamas and their fetuses near to term, at 0.7-0.9 of gestation. Fetal c ardiac output, cerebral and regional blood flows, systemic blood press ure, heart rate, pH, and blood gases, organ vascular resistances and o rgan oxygen deliveries were determined at least Br days after surgery, both during the basal state and after 1 hr of acute fetal hypoxemia. During hypoxemia the llama fetus did not increase cerebral blood flow and markedly decreased its cerebral oxygen delivery. There was also a marked decrease in kidney blood flow and oxygen delivery. These result s indicate that, in contrast to fetuses of lowland species, the fetal llama does not increase the cerebral blood flow during hypoxemia, sugg esting specific cellular mechanisms to preserve brain integrity during oxygen limitation. (C) 1998 Elsevier Science Inc.