Introduction
The vasovagal reflex causes spontaneous dizziness which appears in a standing or sitting position. This reaction is probably caused by the autonomic reflex. It has long been recognized that the plasma adrenaline (Adr.) level elevates during vasovagal attacks. However, the effect of Adr. on cerebral blood flow during vasovagal reflex has not yet been clarified.
Purpose
This study investigated the effect of Adr. on cerebral blood flow during vasovagal reflex in an experimental cat model.
Methods
Ten cats were tracheotomized and restrained in the supine position with its head raised at a 30-degree angle. Upon vagal neurotomy, the nerve fiber on the cardiac side was subjected to electrostimulation for 1 minute. Intravenous Adr. was infused at 0.25 μg/kg for 30 seconds. The regional blood flows in the nucleus vestibularis, nucleus olivaris inferior and nucleus fastigii were measured by the hydrogen clearance method. Changes in heart rate, blood pressure, and regional blood flow were compared among the three groups; Adr. injection alone (Adr. group), electrostimulation alone (electrostimulation group), and Adr. injection+electrostimulation (Adr.+electrostimulation group).
Results
Heart rate and blood pressure increased in the Adr. group (p<0.01), decreased significantly in the electrostimulation group (p<0.01), whereas there were no changes in the Adr. +electrostimulation group. Blood flows increased in the Adr. group (p<0.01), and decreased in electrostimulation and Adr.+electrostimulation groups (p<0.01). However, there was a more significant decrease in the Adr.+electrostimulation group than in the electrostimulation group (nucleus vestibularis: -3.5 vs. -3.9 ml/min/100 g, p<0.01, nucleus olivaris inferior: -9.4 vs. -2.5 ml/min/100 g, p<0.01, and nucleus fastigii: -7.8 vs. -2.8 ml/min/100 g, p<0.01).
Conclusions
Although Adr. increased cerebral blood flow, Adr. combined with vagal stimulation reduced blood flow more than vagal stimulation alone. This could be explained by accentuated antagonism.
View full abstract