Regional brain blood flow and cerebral hemispheric oxygen consumption during acute hypoxaemia in the llama fetus
Unlike fetal animals of lowland species, the llama fetus does not increase its cerebral blood flow during an episode of acute hypoxaemia. This study tested the hypothesis that the fetal llama brain maintains cerebral hemispheric O 2 consumption by increasing cerebral O 2 extraction rather than decre...
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Published in | The Journal of physiology Vol. 538; no. 3; pp. 975 - 983 |
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Main Authors | , , , , , , |
Format | Journal Article |
Language | English |
Published |
Oxford, UK
The Physiological Society
01.02.2002
Blackwell Publishing Ltd Blackwell Science Inc |
Subjects | |
Online Access | Get full text |
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Summary: | Unlike fetal animals of lowland species, the llama fetus does not increase its cerebral blood flow during an episode of acute
hypoxaemia. This study tested the hypothesis that the fetal llama brain maintains cerebral hemispheric O 2 consumption by increasing cerebral O 2 extraction rather than decreasing cerebral oxygen utilisation during acute hypoxaemia. Six llama fetuses were surgically
instrumented under general anaesthesia at 217 days of gestation (term ca 350 days) with vascular and amniotic catheters in order to carry out cardiorespiratory studies. Following a control period
of 1 h, the llama fetuses underwent 3 Ã 20 min episodes of progressive hypoxaemia, induced by maternal inhalational hypoxia.
During basal conditions and during each of the 20 min of hypoxaemia, fetal cerebral blood flow was measured with radioactive
microspheres, cerebral oxygen extraction was calculated, and fetal cerebral hemispheric O 2 consumption was determined by the modified Fick principle. During hypoxaemia, fetal arterial O 2 tension and fetal pH decreased progressively from 24 ± 1 to 20 ± 1 Torr and from 7.36 ± 0.01 to 7.33 ± 0.01, respectively,
during the first 20 min episode, to 16 ± 1 Torr and 7.25 ± 0.05 during the second 20 min episode and to 14 ± 1 Torr and 7.21
± 0.04 during the final 20 min episode. Fetal arterial partial pressure of CO 2 ( P a,C O 2 , 42 ± 2 Torr) remained unaltered from baseline throughout the experiment. Fetal cerebral hemispheric blood flow and cerebral
hemispheric oxygen extraction were unaltered from baseline during progressive hypoxaemia. In contrast, a progressive fall
in fetal cerebral hemispheric oxygen consumption occurred during the hypoxaemic challenge. In conclusion, these data do not
support the hypothesis that the fetal llama brain maintains cerebral hemispheric O 2 consumption by increasing cerebral hemispheric O 2 extraction. Rather, the data show that in the llama fetus, a reduction in cerebral hemispheric metabolism occurs during acute
hypoxaemia. |
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Bibliography: | ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
ISSN: | 0022-3751 1469-7793 |
DOI: | 10.1113/jphysiol.2001.013230 |