Experimental Impact of Increasing Circuit Resistance in the Artificial Womb.

Objective: To determine the impact of controlled incremental changes in circuit blood flow resistance to the oxygenator on hemodynamics in the fetal lamb supported by the EXTrauterine Environment for Neonatal Development (EXTEND) system.

Methods: A prospective study of oxygenator circuit clamping was conducted on 7 lambs on EXTEND. Echocardiography was performed at four levels of circuit flow (250, 225, 200 and 300 mL/kg/min). Hemodynamic parameters including cardiac output, velocities and pulsatility indexes (PI) were measured, and physiological parameters were documented.

Results: As circuit resistance increases, combined cardiac output (CCO) declines significantly, with reduction most profoundly evident in the right ventricle with left ventricle flow preserved until reaching the lowest circuit flow level of 200 mL/kg/min. Umbilical artery (UA), umbilical vein (UV), and inferior vena cava (IVC) velocities decrease while middle cerebral artery (MCA) velocities increase. UA PI values change commensurately with changes in circuit resistance; however, MCA PI values did not change. Blood pressure and oxygen extraction elevate with increased circuit resistance, while heart rate and oxygen consumption remain unchanged.

Conclusions: Fetal sheep supported by the EXTEND system undergo hemodynamic and physiological changes in response to alterations in circuit flow, reflecting physiological adaptations to maintain circulatory homeostasis.