AJP - Heart and Circulatory Physiology, Vol 270, Issue 4 1441-H1445, Copyright © 1996 by American Physiological Society
Parallel changes of blood flow and heterogeneity of capillary plasma perfusion in rat brains during hypocapnia
J. Vogel, R. Abounader, H. Schrock, K. Zeller, R. Duelli and W. Kuschinsky
Department of Physiology, University of Heidelberg, Germany.
Plasma perfusion patterns were investigated in brain capillaries during
decreased cerebral blood flow induced by hyperventilation. Anesthetized
rats were decapitated 3-4 s after being given an intravenous bolus
injection of Evans blue dye. the measured steep increase of the arterial
dye concentration at this moment ensures that different capillary plasma
transit times are reflected in different intracapillary dye concentrations.
The observed heterogeneity of capillary plasma transit time was expressed
as the coefficient of variation (means +/- SD) of the intracapillary dye
concentrations. For comparison, cerebral blood flow was determined at
comparable PCO2 values in a second experimental group. At arterial PCO2
values between 40 and 25 mmHg, the cerebral blood flow and the coefficient
of variation of the intracapillary dye concentration decreased with
decreasing PCO2, whereas at PCO2 values <25 mmHg cerebral blood flow and
coefficient of variation did not correlate with the arterial PCO2. However,
it cannot be excluded that the coefficient of variation of the
intracapillary dye concentration increases between 25 and 14 mmHg and
decreases between 14 and 10 mmHg. It is concluded that the reduction of
cerebral blood flow measured during moderate hypocapnia is paralleled by a
decreased heterogeneity of the brain capillary perfusion. During severe
hypocapnia this relationship is lost, indicating a potential disturbance of
the cerebral microcirculation.
