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>CARDIOLOGY: Assessment of systemic and pulmonary baroreceptor function in intact and unanesthetized fetal and newborn lambs
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CARDIOLOGY: Assessment of systemic and pulmonary baroreceptor function in intact and unanesthetized fetal and newborn lambs
Baroreceptor response have been observed in exteriorized fetal lambs, but ther have been no quantitative studies of changes with maturation in fetuses in utero. In 9 fetal and 3 newborn lambs an inflatable balloon catheter was passed from the femoral artery into the descending aorta. In 7 other fetuses inflatable balloons were placed around the pulmonary artery (PA) or the aortic isthmus. Vinyl catheters were positioned in a brachial or carotid artery, and catheters and ECG leads were exteriorized. Arterial pH, PCO2 and PO2 were normal in all studies. Reflex bradycardia in response to blood pressure elevation by balloon inflation was measured repeatedly for several weeks. Baroreceptor sensitivity was expressed as the regression coefficient of the beat-to-beat relationship between systolic (SP) and pulse (PP) pressure, and the subsequent R-R interval (R-R) or heart rate (HR). In over 100 observations we found: (1) elevation of systemic but not main PA pressure elicits reflex bradycardia; (2) reflex bradycardia could be elicite in all animals but was frequently absent in fetuses less than 120 days gestation; (3) reflex bradycardia was blocked by atropine but not influenced by propranolol; (4) in fetuse the regression coefficients of SP or PP vs. R-R increased with gestational age, but not when SP or PP was correlated with HR because of the lower initial HR in older fetuses; (5) lambs had significantly higher regression coefficients for all correlations than fetuses. We have not yet evaluated if baroreceptor response depend on gestational age and initial HR in combination.
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