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SOME EFFECTS OF MATERNAL HYPEROXIA AND HYPOXIA ON THE BLOOD GAS TENSIONS AND VASCULAR PRESSURES IN THE FOETAL SHEEP
Author(s) -
Parker H. R.,
Purves M. J.
Publication year - 1967
Publication title -
quarterly journal of experimental physiology and cognate medical sciences
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.925
H-Index - 101
eISSN - 1469-445X
pISSN - 0033-5541
DOI - 10.1113/expphysiol.1967.sp001903
Subject(s) - ductus arteriosus , umbilical artery , pulmonary artery , umbilical vein , oxygen tension , fetus , venous blood , aorta , medicine , oxygen , blood pressure , cardiology , anesthesia , hypoxia (environmental) , hyperoxia , anatomy , chemistry , pregnancy , lung , biology , biochemistry , organic chemistry , in vitro , genetics
Blood gas tensions, pH and intravascular pressures have been measured at various sites in 22 foetal sheep of gestational age 110–147 days. Umbilical venous oxygen tension did not change significantly with age. The mean pulmonary artery pressure always exceeded that in the aorta and this pressure gradient did not change with age. By contrast the umbilical arterio‐venous pressure gradient increased with age. When the ewe breathed room air, the oxygen difference between uterine artery and umbilical vein was 43–62 mm. Hg. When the ewe breathed 100 per cent 0 2 umbilical venous P 02 rose by 4–15 mm. Hg and umbilical venous pH fell by 0·04–0·07 pH units. There were no consistent changes in foetal heart rate or blood pressures. When the ewe breathed 10 per cent O 2 in N 2 , umbilical venous P 02 . fell by 7–14 mm. Hg, mean pressures in pulmonary artery and aorta and the pulmonary artery/aortic pressure gradient increased as did the size of the right to left shunt across the ductus arteriosus. Heart rate invariably increased. The oxygen saturation difference between ascending and descending aorta was maintained or increased. These results suggest (1) that factors other than a diffusion barrier to oxygen are responsible for the maternal/foetal oxygen gradient and (2) that, with maternal hypoxia, there is a redistribution of blood flow in the foetus so that as high a tissue P 02 as possible is maintained in coronary and cerebral circulations.