Proceedings of the Society for Experimental Biology and Medicine. Society for Experimental Biology and Medicine (New York, N.Y.)
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Proc. Soc. Exp. Biol. Med. · Feb 1994
Cerebral vascular response to hemorrhagic hypotension in newborn lambs: the influence of developing anemia.
The ability of newborn animals to autoregulate cerebral blood flow (CBF) has been documented. Most studies of the cerebral vascular response to hypotension utilize hemorrhage, generally confounded with anemia. We studied the cerebral blood flow and metabolic response of chloralose and urethane anesthetized newborn lambs to regulated hypotension. ⋯ Calculated oxygen consumption was maintained in the AH group but increased (approximately 50%) in the NH group at 50 and 40 mm Hg. The ratio of oxygen uptake to oxygen delivery (fractional oxygen extraction) increased linearly in both groups as arterial pressure decreased. The major findings of these experiments are (i) The anesthetized newborn lamb can maintain CBF when perfusion pressure falls to 25 mm Hg and this autoregulatory capacity (classically defined) is not dependent on a change in hematocrit and, presumably, viscosity; (ii) Cerebral hypotension, anemic or not, appears to be accompanied by an increase in fractional extraction of oxygen.