Changes in arterioles, arteries, and local perfusion of the brain
stem during hemorrhagic hypotension.
Toyoda, Kazunori, Kenichiro Fujii, Setsuro Ibayashi, Seizo Sadoshima,
and Masatoshi Fujishima.
Second Department of Internal Medicine, Faculty of Medicine, Kyushu
University, Fukuoka, Japan 812-82
APStracts 2:0466H, 1995.
Cerebral arterioles have been regarded as the primary sites of
autoregulatory responses, whereas the role of large arteries in the
cerebral autoregulation is poorly understood. The goal of this study
was to determine in vivo whether the basilar artery and its primary
branches act as resistance vessels under hypotensive conditions by
simultaneously measuring their diameters and local brain stem blood
flow with laser-Doppler flowmetry. In ten anesthetized rats, blood
flow to the brain stem was well maintained during stepwise
hemorrhagic hypotension when mean arterial blood pressure fell from
116+/-3 mmHg to 50 mmHg and decreased gradually between 50 and 30
mmHg. Diameter of the basilar artery (n=10) and its large branches
(n=22), measured through an open cranial window, increased by 10 %
from the baseline value at 50 mmHg and reached their maximum at 30
mmHg (314+/-9 [mu]m from 244+/-6 [mu]m, and 149+/-4 [mu]m from 117+/
-3 [mu]m, respectively). Small branches (n=15) dilated to a larger
extent compared to the larger arteries throughout hypotension and
reached the maximum at 30 mmHg (69+/-3 [mu]m from 48+/-2 [mu]m).
Below 30 mmHg, there was a steep fall in blood flow and reduction in
diameter of all sized arteries. Thus, small vessels contribute to
reductions in cerebrovascular resistance throughout the entire
autoregulatory range in the brain stem circulation. Large arteries,
such as the basilar artery and its branches, also contribute to
reductions in cerebrovascular resistance around the lower limits of
cerebral blood flow autoregulation and thus may play a significant
role in maintaining blood flow to the brain stem during severe
systemic hypotension.
Received 29 September 1995; accepted in final form 29 September
1995.
APS Manuscript Number H248-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 6 November 95