Fetal sheep central hemodynamics and cardiac function during ascending aorta occlusion

Abstract

Fetal aortic isthmus (AoI) allows communication between left (LV) and right (RV) ventricular outputs and represents arterial watershed between the brachiocephalic (brain) and subdiaphragmatic (placenta) circulations. To understand the capability of AoI to maintain the balance between upper and lower body circulations, we performed a complete fetal ascending aorta occlusion in 9 chronically instrumented sheep at near term gestation. We hypothesized that the occlusion would significantly decrease LV output and concomitantly increase RV output in order to maintain adequate systemic cardiac output and perfusion pressure to the fetal brain circulation through retrograde filling of the AoI. Fetal cardiac function and hemodynamics were assessed by pulsed and tissue Doppler at baseline, 15 and 60 minutes after ascending aorta occlusion, and 15 minutes after occlusion was released. Carotid artery and jugular vein pressures were monitored. Ascending aorta occlusion increased (P < 0.002) RV output from 684(369) to 907(414) ml/min, and decreased (P < 0.0001) LV output from 440(136) to 40(16) ml/min. Combined cardiac output fell (P < 0.02) from 1125(494) to 946(417) ml min⁻¹. During occlusion carotid artery mean pressure fell from 32(7) to 12(7) mmHg (P < 0.0001). Systemic venous pressure was unaffected. LV systolic and diastolic function deteriorated during occlusion. RV systolic function improved, while diastolic dysfunction developed. Fetal carotid artery perfusion pressure fell significantly during ascending aorta occlusion demonstrating that AoI failed to redirect blood flow and pressure from the ductus arteriosus to the aortic arch. Our finding suggests that at near term gestation aortic AoI cannot provide unrestrictive communication between LV and RV circulations.

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