Effect of alpha-adrenergic blockade on the cerebrovascular response to increased intracranial pressure after hemorrhage.
OBJECTIVE
In this study the authors tested the hypothesis that hemorrhagic hypotension and high intracranial pressure induce an increase in cerebrovascular resistance that is caused by sympathetic compensatory mechanisms and can be modified by alpha-adrenergic blockade.


METHODS
Continuous measurements of cerebral blood flow were obtained using laser Doppler microprobes placed in the cerebral cortex in anesthetized pigs during induced hemorrhagic hypotension and high cerebrospinal fluid pressure. Eight pigs received 2 mg/kg phentolamine in 10 ml saline, and 13 pigs served as control animals. During high intracranial pressure occurring after blood loss, cerebral perfusion pressure (CPP) (p < 0.01) and cerebral blood flow (p < 0.01) decreased in both groups. Cerebrovascular resistance increased (p < 0.05) in the control group and decreased (p < 0.005) in the phentolamine-treated group. The cerebrovascular resistance was significantly lower in the phentolamine-treated group (p < 0.05) than in the control group. Cerebrovascular resistance increased at lower CPPs in the control group (linear correlation, r = 0.39, p < 0.01) and decreased with decreasing CPP in the phentolamine-treated group (linear correlation, r = 0.76, p < 0.001).


CONCLUSIONS
This study shows that the deleterious effects on cerebral hemodynamics induced by blood loss in combination with high intracranial pressure are inhibited by alpha-adrenergic blockade. This suggests that these responses are caused by alpha-adrenergically mediated cerebral vasoconstriction.
Institute for Surgical Research, The National Hospital, Oslo, Norway.
I R
IR
Rise
O J
OJ
Kirkeby
D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology*; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D002540:Cerebral Cortex / Q000098:blood supply; D002543:Cerebral Hemorrhage / Q000503:physiopathology*; D015170:Cerebrospinal Fluid Pressure / Q000187:drug effects; D002560:Cerebrovascular Circulation / Q000187:drug effects*; D004195:Disease Models, Animal; D005260:Female; D006439:Hemodynamics / Q000187:drug effects; D019586:Intracranial Hypertension / Q000503:physiopathology*; D019585:Intracranial Hypotension / Q000503:physiopathology*; D017078:Laser-Doppler Flowmetry / Q000295:instrumentation; D008297:Male; D008904:Miniaturization; D010646:Phentolamine / Q000494:pharmacology; D011942:Receptors, Adrenergic, alpha / Q000502:physiology; D013552:Swine; D014655:Vascular Resistance / Q000187:drug effects; D014661:Vasoconstriction / Q000187:drug effects
D000317:Adrenergic alpha-Antagonists; D011942:Receptors, Adrenergic, alpha; D010646:Phentolamine