AJP - Heart and Circulatory Physiology, Vol 243, Issue 1 27-H32, Copyright © 1982 by American Physiological Society
Cerebral circulatory response to carbon monoxide and hypoxic hypoxia in the lamb
R. C. Koehler, M. D. Jones Jr and R. J. Traystman
In 14 unanesthetized newborn lambs the relationship between cerebral blood
flow (measured by radiolabeled microspheres) and arterial O2 saturation
(SaO2) was compared during two types of hypoxia: hypoxic hypoxia and carbon
monoxide (CO) hypoxia. Cerebral venous samples were obtained from the
sagittal sinus. The Increase in blood flow was 47% greater during CO than
during hypoxic hypoxia. Cerebral O2 consumption and O2 delivery were
constant during hypoxic hypoxia. Thus fractional O2 extraction, which
equals O2 consumption/O2 delivery, remained constant with hypoxic hypoxia.
During CO hypoxia, although O2 consumption remained constant, O2 delivery
increased and fractional O2 extraction decreased. This decline in
fractional O2 extraction was correlated with the leftward shift of the
oxyhemoglobin dissociation curve that accompanied CO hypoxia. We suggest
that cerebral blood flow depends on both SaO2 and the position of the
oxyhemoglobin dissociation curve in the newborn lamb. However, this
correlation does not exclude other potential histotoxic effects
contributing to the relative overperfusion with CO hypoxia.
