AJP - Heart and Circulatory Physiology, Vol 242, Issue 5 862-H866, Copyright © 1982 by American Physiological Society
Response of cerebral blood flow to changes in PCO2 in fetal, newborn, and adult sheep
A. A. Rosenberg, M. D. Jones Jr, R. J. Traystman, M. A. Simmons and R. A. Molteni
Developmental effects on the response of cerebral blood flow (Qc) and
cerebral O2 consumption (CMRO2) to changes in CO2 tension were assessed in
unanesthetized fetal, newborn, and adult sheep. Blood flow was measured
using the radioactive microsphere technique. CMRO2 was calculated as the
product of Qc and the difference in O2 content between arterial and
sagittal sinus blood (CaO2 -- CVO2). The response of Qc to changes in
arterial CO2 tension increased from fetus [3.53 +/- 0.56 ml.100
g-1.min-1.mmHg PaCO2(-1) (SE)] to newborn (5.16 +/- 0.59) to adult (6.20
+/- 0.63). Only the fetal-adult difference was significant (P less than
0.05). It has been suggested that developmental differences in CO2
responsiveness of cerebral blood flow are the result of differences in
CMRO2. We corrected for differences in CMRO2 by looking at the response to
CO2 of the variable 1/(CaO2--CVO2). According to the Fick principle
1/(CaO2--CVO2) = Qc/CMRO2, i.e., blood flow per unit O2 consumption. The
fetal response was not significantly different from the newborn, but the
adult was significantly different from both (P less than 0.05). Thus the
difference in CO2 response of cerebral blood flow between fetus and adult
cannot be explained by differences in CMRO2.
