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(Stroke. 2009;40:2062.)
© 2009 American Heart Association, Inc.

Original Contributions

Autoregulation in the Posterior Circulation Is Altered by the Metabolic State of the Visual Cortex

Kazuma Nakagawa, MD; Jorge M. Serrador, PhD; Sarah L. LaRose, BA; Fatemeh Moslehi, MD; Lewis A. Lipsitz, MD Farzaneh A. Sorond, MD, PhD

From Department of Neurology (K.N., J.M.S., S.L.L., F.M., F.A.S.), Stroke Division, Brigham and Women’s Hospital, Harvard Medical School, Boston, Mass; Beth Israel Deaconess Medical Center (J.M.S., L.A.L.), Harvard Medical School, Boston, Mass; Research and Training Institute (L.A.L., F.A.S.), Hebrew Rehabilitation Center for Aged, Boston, Mass.

Correspondence to Kazuma Nakagawa, MD, University of California San Francisco, Neurovascular Service, 505 Parnassus Avenue, M-830, San Francisco, CA 94143-0114. E-mail kazuma.nakagawa{at}ucsfmedctr.org

Background and Purpose— Previous studies suggest that dynamic autoregulation in the posterior cerebral artery (PCA) is less efficient compared to the middle cerebral artery (MCA). We examined the role of cerebral vasodilation caused by metabolic activation (ie, visual stimulus) on autoregulatory characteristics in the 2 vascular territories.

Methods— Blood flow velocity in the PCA and MCA and mean arterial pressure were measured continuously in 45 healthy volunteers (62±3 years) while seated with eyes open. Additional 20 subjects (60±5 years) were examined with eyes closed and open. Autoregulation was assessed using transfer function gains in both the PCA and MCA territories in the low (0.03–0.07 Hz), high (0.07–0.15 Hz), and cardiac (1 Hz) frequency ranges.

Results— With eyes open, gains were significantly higher in the PCA compared to the MCA in the low (PCA: 1.41±0.09 vs MCA: 1.18±0.07; P=0.003) and high (PCA: 2.06±0.12 vs MCA: 1.61±0.08; P=0.0001) frequencies. Opening eyes increased blood flow velocity and reduced cerebrovascular resistance index in the PCA but not in MCA. This vasodilation in the PCA was associated with increased gain in the low (autoregulatory) frequency, whereas MCA gain did not change (PCA: 0.89±0.14 vs 1.31±0.17, MCA: 1.24±0.16 vs 1.16±0.11; P=0.02).

Conclusions— Dilation of the PCA territory during visual cortex activation resulted in increased PCA transfer function gain without changing MCA gain. Thus, impaired autoregulation in the PCA reported in previous literature is likely the result of metabolic vasodilation and not an inherent difference in the autoregulatory characteristics of the posterior circulation.

Key Words: cerebral autoregulation • cerebral blood flow • posterior cerebral artery