Effects of norepinephrine and glyceryl trinitrate on cerebral haemodynamics: transcranial Doppler study in healthy volunteers.
BACKGROUND
The effects of vasoactive substances on cerebral haemodynamics are not fully known. We studied the effects of norepinephrine and glyceryl trinitrate (GTN) on cerebral haemodynamics in healthy volunteers.


METHODS
The effects of norepinephrine (n=10) and GTN (n=10) on the middle cerebral artery flow velocity (MCAFV), cerebral autoregulation, reactivity to carbon dioxide, and estimated cerebral perfusion pressure (eCPP) were studied using transcranial Doppler ultrasound. Established methods were used for calculating zero flow pressure (ZFP). Measurements were made at baseline, and after i.v. infusion of the study drug to the endpoints of 25% increase in mean arterial pressure (MAP) for norepinephrine (0.02-0.1 microg kg(-1) min(-1)), or 15% decrease in MAP for GTN (0.5-2.5 microg kg(-1) min(-1)).


RESULTS
The MCAFV remained unchanged with norepinephrine, but decreased slightly with GTN {from [median (inter-quartile range)] 53 (38, 62) to 48 (33, 52) cm s(-1)}. Cerebrovascular reactivity did not change significantly with either drug. The eCPP did not change significantly with norepinephrine, but increased significantly with GTN [from 49 (32, 54) to 62 (47, 79) mm Hg]. ZFP increased with norepinephrine [from 39 (28, 48) to 56 (46, 62) mm Hg] and decreased with GTN [from 35 (30, 49) to 12 (-7, 20) mm Hg].


CONCLUSIONS
Norepinephrine, despite increasing arterial pressure, did not increase the eCPP. The eCPP increased significantly with GTN, despite decreased MAP. Cerebral vascular tone is an important determinant of CPP during pharmacologically induced changes in arterial pressure.
Moppett
I K
IK
University Department of Anaesthesia and Intensive Care, Queen's Medical Centre, Nottingham, UK. iain.moppett@nottingham.ac.uk
Sherman
R W
RW
Wild
M J
MJ
Latter
J A
JA
Mahajan
R P
RP
D000328:Adult; D001783:Blood Flow Velocity / Q000187:drug effects; D002560:Cerebrovascular Circulation / Q000187:drug effects*; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D006706:Homeostasis / Q000187:drug effects; D006801:Humans; D008297:Male; D020768:Middle Cerebral Artery / Q000000981:diagnostic imaging / Q000187:drug effects / Q000502:physiology; D005996:Nitroglycerin / Q000494:pharmacology*; D009638:Norepinephrine / Q000494:pharmacology*; D017585:Ultrasonography, Doppler, Transcranial; D014662:Vasoconstrictor Agents / Q000494:pharmacology*; D014665:Vasodilator Agents / Q000494:pharmacology*
D014662:Vasoconstrictor Agents; D014665:Vasodilator Agents; D005996:Nitroglycerin; D009638:Norepinephrine