Autoregulation in the posterior circulation is altered by the metabolic state of the visual cortex.
OBJECTIVE
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 (approximately 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.
Department of Neurology, Stroke Division, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA. kazuma.nakagawa@ucsfmedctr.org
Kazuma
K
Nakagawa
Jorge M
JM
Serrador
Sarah L
SL
Larose
Fatemeh
F
Moslehi
Lewis A
LA
Lipsitz
Farzaneh A
FA
Sorond
D000368:Aged; D001794:Blood Pressure / Q000502:physiology; D002560:Cerebrovascular Circulation / Q000502:physiology*; D003627:Data Interpretation, Statistical; D004562:Electrocardiography; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006706:Homeostasis / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D020768:Middle Cerebral Artery / Q000502:physiology; D020769:Posterior Cerebral Artery / Q000502:physiology*; D014655:Vascular Resistance; D014664:Vasodilation / Q000502:physiology; D014785:Vision, Ocular / Q000502:physiology; D014793:Visual Cortex / Q000378:metabolism*