Sympathetic control of the cerebral vasculature in humans.
OBJECTIVE
The role of the sympathetic nervous system in cerebral autoregulation remains poorly characterized. We examined cerebral blood flow responses to augmented arterial pressure oscillations with and without sympathetic blockade and compared them with responses in the forearm circulation.


METHODS
An oscillatory lower body negative pressure of 40 mm Hg was used at 6 frequencies from 0.03 to 0.08 Hz in 11 healthy subjects with and without alpha-adrenergic blockade by phentolamine.


RESULTS
Sympathetic blockade resulted in unchanged mean pressure and cerebral flow. The transfer function relationship to arterial pressure at frequencies >0.05 Hz was significantly increased in both the cerebral and brachial circulations, but the coherence of the relation remained weak at the lowest frequencies in the cerebral circulation.


CONCLUSIONS
Our data demonstrate a strong, frequency-dependent role for sympathetic regulation of blood flow in both cerebral and brachial circulations. However, marked differences in the response to blockade suggest the control of the cerebral circulation at longer time scales is characterized by important nonlinearities and relies on regulatory mechanisms other than the sympathetic system.
Hamner
J W
JW
Cardiovascular Research Laboratory, Spaulding Rehabilitation Hospital, 125 Nashua Street, Boston, MA 02114, USA.
Tan
Can Ozan
CO
Lee
Kichang
K
Cohen
Michael A
MA
Taylor
J Andrew
JA
D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000328:Adult; D002560:Cerebrovascular Circulation / Q000187:drug effects / Q000502:physiology*; D005260:Female; D006706:Homeostasis / Q000187:drug effects / Q000502:physiology; D006801:Humans; D008297:Male; D013564:Sympathetic Nervous System / Q000187:drug effects / Q000502:physiology*; D017585:Ultrasonography, Doppler, Transcranial / Q000379:methods; D055815:Young Adult
D000317:Adrenergic alpha-Antagonists