Autonomic neural control of dynamic cerebral autoregulation in humans.
BACKGROUND
The purpose of the present study was to determine the role of autonomic neural control of dynamic cerebral autoregulation in humans.


RESULTS
We measured arterial pressure and cerebral blood flow (CBF) velocity in 12 healthy subjects (aged 29+/-6 years) before and after ganglion blockade with trimethaphan. CBF velocity was measured in the middle cerebral artery using transcranial Doppler. The magnitude of spontaneous changes in mean blood pressure and CBF velocity were quantified by spectral analysis. The transfer function gain, phase, and coherence between these variables were estimated to quantify dynamic cerebral autoregulation. After ganglion blockade, systolic and pulse pressure decreased significantly by 13% and 26%, respectively. CBF velocity decreased by 6% (P<0.05). In the very low frequency range (0.02 to 0.07 Hz), mean blood pressure variability decreased significantly (by 82%), while CBF velocity variability persisted. Thus, transfer function gain increased by 81%. In addition, the phase lead of CBF velocity to arterial pressure diminished. These changes in transfer function gain and phase persisted despite restoration of arterial pressure by infusion of phenylephrine and normalization of mean blood pressure variability by oscillatory lower body negative pressure.


CONCLUSIONS
These data suggest that dynamic cerebral autoregulation is altered by ganglion blockade. We speculate that autonomic neural control of the cerebral circulation is tonically active and likely plays a significant role in the regulation of beat-to-beat CBF in humans.
D000328:Adult; D001341:Autonomic Nervous System / Q000502:physiology*; D001783:Blood Flow Velocity / Q000187:drug effects; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology; D001921:Brain / Q000098:blood supply* / Q000502:physiology*; D002560:Cerebrovascular Circulation / Q000502:physiology*; D005260:Female; D005730:Ganglionic Blockers / Q000494:pharmacology; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology; D006801:Humans; D008150:Lower Body Negative Pressure; D008297:Male; D020768:Middle Cerebral Artery / Q000000981:diagnostic imaging / Q000502:physiology; D010656:Phenylephrine / Q000494:pharmacology; D012016:Reference Values; D014294:Trimethaphan / Q000494:pharmacology; D017585:Ultrasonography, Doppler, Transcranial; D014662:Vasoconstrictor Agents / Q000494:pharmacology
D005730:Ganglionic Blockers; D014662:Vasoconstrictor Agents; D010656:Phenylephrine; D014294:Trimethaphan
NASA Discipline Cardiopulmonary; Non-NASA Center