Llanos A, Riquelme R, Sanhueza E, Gaete C, Cabello G, Parer J
Laboratorio de Fisiología y Fisiopatología, Facultad de Medicina, Universidad de Chile, Santiago, Chile.
Comp Biochem Physiol A Mol Integr Physiol. 1998 Mar;119(3):705-9. doi: 10.1016/s1095-6433(98)01008-3.
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 surgery, did not increase cerebral blood flow and decreased cerebral oxygen delivery during acute hypoxemia. It is not known whether these responses 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 term, and under nonstressed conditions. We chronically catheterized 7 llamas and their fetuses near to term, at 0.7-0.9 of gestation. Fetal cardiac output, cerebral and regional blood flows, systemic blood pressure, heart rate, pH, and blood gases, organ vascular resistances and organ oxygen deliveries were determined at least 4 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 results indicate that, in contrast to fetuses of lowland species, the fetal llama does not increase the cerebral blood flow during hypoxemia, suggesting specific cellular mechanisms to preserve brain integrity during oxygen limitation.
成年美洲驼（小羊驼）具有多种代偿机制，使其能够在高海拔地区成功生存。处于妊娠0.6 - 0.7阶段的美洲驼胎儿，以及在手术临近时研究的足月美洲驼胎儿，在急性低氧血症期间并未增加脑血流量，且脑氧输送量降低。尚不清楚这些反应是未成熟还是手术应激的结果。本研究的目的是确定在无应激条件下，足月的美洲驼胎儿在低氧血症期间脑血流量不增加以及脑氧输送量降低是否是这种高海拔物种的特征。我们对7只妊娠0.7 - 0.9阶段、临近足月的美洲驼及其胎儿进行了长期导管插入术。在手术后至少4天，分别于基础状态和急性胎儿低氧血症1小时后，测定胎儿的心输出量、脑和局部血流量、全身血压、心率、pH值以及血气、器官血管阻力和器官氧输送量。在低氧血症期间，美洲驼胎儿并未增加脑血流量，且脑氧输送量显著降低。肾血流量和氧输送量也显著减少。这些结果表明，与低地物种的胎儿不同，美洲驼胎儿在低氧血症期间不会增加脑血流量，这表明在氧限制期间存在特定的细胞机制来维持脑的完整性。
