Hemodynamic effects of bradycardia in the fetal lamb.

BRINKMAN, CHARLES R. III, GARY H. JOHNSON, AND N. S. ~SSALI. Hemodynamic effects of bradycardia in the fetal lamb. Am. J. Physiol. 223(6) : 1465-1469. 1972.-The hemodynamic impact of induced cardiac deceleration were studied in near-term fetal lamb. Vagal stimulation resulted in rhythmic or arrhythmic bradycardia, each type having somewhat different effects on arterial pressure, stroke volume, and on ascending aortic, main pulmonary artery, and ductus arteriosus flows. Rhythmic bradycardia was accompanied by reciprocal changes in stroke volume so that the ventricular output was not altered appreciably. During arrhythmic bradycardia, the stroke volume also increased, but the increment was insufficient to prevent a decrease in ventricular output. Rhythmic bradycardia reading 30y0 of control resulted in only 10 7* decrease in effective cardiac output and systemic arterial pressure. With arrhythmic bradycardia of the same degree (307,), the effective cardiac output and arterial pressure both fell by approximately 307& It was concluded that: 1) the cardiac rhythm has a great influence upon the hemodynamic effects of fetal bradycardia, and 2) that the fetal heart appears to follow the FrankStarling relationship.