Abstract
We studied the effects of parasympathetic blockade on the cardiovascular response to hypoxemia in 4 fetal lambs, of 125-130 days gestation. Catheters were placed in fetal and maternal vessels, an electromagnetic flowprobe was placed on the fetal aorta, and the animals recovered over 5 days. Fetal and maternal arterial pressure, O2 content, and pH were measured repeatedly during the control state and while the ewe breathed 6-10% O2 and 3% CO2. Cardiac output (CO) and its distribution were measured with labelled microspheres during the control state, parasympathetic blockade with atropine (0.2 mg/kg), and during fetal hypoxemia with blockade. During hypoxemia with atropine blockade, fetal heart rate (FHR) increased 43%, arterial pressure rose 11%. Descending aortic blood flow fell by 25%, and CO decreased by 40% despite the elevated FHR (mean 235). Umbilical blood flow was maintained, and the percentage of CO to the placenta increased from 42% to 65%. The fall in CO, the maintenance of umbilical blood flow, and the redistribution of CO found in these studies were comparable to those previously reported for hypoxemia without blockade. Since changes in fetal CO have been shown to vary directly with FHR other factors must be responsible for the fall in CO which we measured. It is possible that the direct effect of oxygen lack on the myocardium may be significant.
Supported in part by the John A. Hartford Foundation, Inc.N.Y.
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Cohn, H., Plasecki, G. & Jackson, B. EFFECTS OF PARASYMPATHETIC BLOCKADE ON THE CARDIOVASCULAR RESPONSE TO HYPOXEMIA IN UNANESTHETIZED FETAL LAMBS. Pediatr Res 8, 348 (1974). https://doi.org/10.1203/00006450-197404000-00047
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DOI: https://doi.org/10.1203/00006450-197404000-00047