AJP - Heart and Circulatory Physiology, Vol 241, Issue 1 78-H84, Copyright © 1981 by American Physiological Society
Cerebral blood flow during elevation of intracranial pressure: role of sympathetic nerves
S. Sadoshima, M. Thames and D. Heistad
This study was performed to examine effects of increased intracranial
pressure on cerebral blood flow (CBF) and to determine if sympathetic
nerves modulate this response. Intracranial pressure was raised by infusion
of artificial cerebrospinal fluid into a lateral ventricle of rabbits.
Increases in intracranial pressure were similar in the lateral ventricles
and cisterna magna. Graded increases in intracranial pressure from base
line of 7 to 96 mmHg produced graded reductions in CBF (measured with
microspheres). Reductions in blood flow were heterogeneous: elevation of
intracranial pressure from 7 +/- 1 to 46 +/- 3 (SE) mmHg reduced blood flow
to the cerebrum by 33 +/- 5% and blood flow to the medulla by only 5 +/- 2%
(P less than 0.05). Reduction of intracranial pressure to normal levels
produced marked reactive hyperemia in all areas of the brain. Although
sympathetic nerve traffic increased fivefold during intracranial
hypertension, superior cervical ganglionectomy did not affect CBF. In other
experiments, electrical stimulation of sympathetic nerves at 4 Hz reduced
blood flow to skeletal muscle by 80% but did not affect CBF; stimulation at
15 Hz produced a modest reduction in CBF. We conclude that 1) during
increases in intracranial pressure, blood flow is better preserved to the
medulla than to the cerebrum despite similar intracranial pressure in the
two areas and 2) intense reflex activation of sympathetic nerves during
intracranial hypertension does not affect CBF.
