(Stroke. 1999;30:2197-2205.)
© 1999 American Heart Association, Inc.
Original Contributions |
From the Harvard-MIT Division of Health Sciences and Technology (G.Z., B.R.R.), Harvard Medical School, Boston, and Massachusetts Institute of Technology, Cambridge; the Department of Radiology (J.B.M., B.R.R.), Massachusetts General Hospital Nuclear Magnetic Resonance (MGH-NMR) Center (2301); the Center for Molecular Imaging Research (A.A.B., R.W.); and the Department of Anesthesia and Critical Care (J.J.A.M.), Massachusetts General Hospital, Boston, Mass.
Correspondence to Greg Zaharchuk, PhD, MGH-NMR Center (2301), 149 13th St, Charlestown, MA 02129. E-mail gregz{at}nmr.mgh.harvard.edu
Background and PurposeTo determine how cerebral blood flow (CBF), total and microvascular cerebral blood volume (CBV), and blood oxygenation leveldependent (BOLD) contrast change during autoregulation and hypotension using hemodynamic MRI.
MethodsUsing arterial spin labeling and steady-state susceptibility contrast, we measured CBF and changes in both total and microvascular CBV during hemorrhagic hypotension in the rat (n=9).
ResultsWe observed CBF autoregulation for mean arterial blood pressure (MABP) between 50 and 140 mm Hg, at which average CBF was 1.27±0.44 mL · g-1 · min-1 (mean±SD). During autoregulation, total and microvascular CBV changes were small and not significantly different from CBF changes. Consistent with this, no significant BOLD changes were observed. For MABP between 10 and 40 mm Hg, total CBV in the striatum increased slightly (+7±12%, P<0.05) whereas microvascular CBV decreased (-15±17%, P<0.01); on the cortical surface, total CBV increases were larger (+21±18%, P<0.01) and microvascular CBV was unchanged (3±22%, P>0.05). With severe hypotension, both total and microvascular CBV decreased significantly. Over the entire range of graded global hypoperfusion, there were increases in the CBV/CBF ratio.
ConclusionsParenchymal CBV changes are smaller than those of previous reports but are consistent with the small arteriolar fraction of total blood volume. Such measurements allow a framework for understanding effective compensatory vasodilation during autoregulation and volume-flow relationships during hypoperfusion.
Laboratory of Cerebrovascular Biology and Stroke, Department of Neurology, Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota
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