Hemodynamic and metabolic responses to moderate asphyxia in brain and skeletal muscle of late-gestation fetal sheep

The purpose of this study was to investigate metabolic and hemodynamic resp onses in two fetal tissues, hindlimb muscle and brain, to an episode of acu te moderate asphyxia. Near-infrared spectroscopy was used to measure change s in total hemoglobin concentration ([tHb]) and the redox state of cytochro me oxidase (COX) simultaneously in the brain and hindlimb of near-term unan esthetized fetal sheep in utero. Oxygen delivery (DO2) to, and consumption ((V) over dot O-2) by each tissue was derived from the arteriovenous differ ence in oxygen content and blood flow, measured by implanted flow probes. O ne hour of moderate asphyxia (n = II), caused by occlusion of the maternal common internal iliac artery, led to a significant fall in Dot to both tiss ues and to a significant drop in (V) over dot O-2 by the head. This was ass ociated with an initial fall in redox state COX in the leg but an increase in the brain. [tHb], and therefore blood volume, fell in the leg and increa sed in the brain. These data suggest the presence of a fetal metabolic resp onse to hypoxia, which, in the brain, occurs rapidly and could be neuroprot ective.