Cerebrovascular transmural pressure and autoregulation |
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Authors: | Elizabeth M Wagner PhD Richard J Traystman |
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Institution: | (1) Department of Environmental Health Sciences and Anesthesiology/Critical Care Medicine, The Johns Hopkins Medical Institutions, Baltimore, Maryland;(2) Dept. of Anesthesiology/Critical Care Medicine, The Johns Hopkins Hospital, Blalock 1408 B, 600 North Wolfe Street, 21205 Baltimore, MD |
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Abstract: | The cerebral blood flow (CBF) response to changes in perfusion pressure mediated through decreases in arterial pressure, increases
in cerebrospinal fluid (CSF) pressure and increases in jugular venous pressure was studied in anesthetized dogs. A preparation
was developed in which each of the three relevant pressures could be controlled and manipulated independently of each other.
In this preparation, the superior vena cava and femoral vein were cannulated and drained into a reservoir. Blood was pumped
from the reservoir into the right atrium. With this system, mean arterial pressure and jugular venous pressure could be independently
controlled. CSF pressure (measured in the lateral ventricle) could be manipulated via a cisternal puncture. Total and regional
CBF responses to alterations in perfusion pressure were studied with the radiolabelled microsphere technique. Each hemisphere
was sectioned into 13 regions: spinal cord, cerebellum, medulla, pons, midbrain, diencephalon, caudate, hippocampus, parahippocampal
gyrus, and occipital, temporal, parietal and frontal lobes. Despite 30 mm Hg reductions in arterial pressure or increases
in jugular venous pressure or CSF pressure, little change in CBF was observed provided the perfusion pressure (arterial pressure
minus jugular venous pressure or CSF pressure depending on which pressure was of greater magnitude) was greater than the lower
limit for cerebral autoregulation (approximately 60 mm Hg). However, when the perfusion pressure was reduced by any of the
three different methods to levels less than 60 mm Hg (average of 48 mm Hg), a comparable reduction (25–35%) in both total
and regional CBF was obtained. Thus comparable changes in the perfusion pressure gradient established by decreasing arterial
pressure, increasing jugular venous pressure and increasing CSF pressure resulted in similar total and regional blood flow
responses. Independent alterations of arterial and CSF pressures, and jugular venous pressure produce opposite changes in
vascular transmural pressure yet result in similar CBF responses. These results show that cerebral autoregulation is a function
of the perfusion pressure gradient and cannot be accounted for predominantly by myogenic mechanisms. |
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Keywords: | Cerebral venous pressure Cerebrospinal fluid pressure Transmural pressure Cerebral perfusion pressure Myogenic mechanism |
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