Deterioration of baroreflex by transient global cerebral ischemia: Its correlation with the degree of ischemia or post-ischemic hypoperfusion in the medulla oblongata.

Abstract

Abstract-In a canine model of transient global cerebral ischemia, the correlation between the decrease in baroreflex sensitivity (BRS) following 5-min ischemia and the degree of ischemia or post-ischemic hypoperfusion was investigated. Although the medulla oblongata and the cerebral cortex suffered a similar degree of ischemia, the extent of post-ischemic decrease in BRS was inversely correlated with the re sidual blood flow during ischemia in the medulla, but not with that in the cerebral cortex. A similar degree of post-ischemic hypoperfusion occurred in the medulla and the cerebral cortex.However, the extent of decrease in BRS was not correlated with the degree of hypoperfusion, and the cortical EEG was not significantly affected. These results suggest that the decrease in BRS may be due to the functional damage in the medulla and that the selective decrease in BRS without concomitant impair ment of the EEG cannot be ascribed to the regional difference in the degree of isch emia or post-ischemic hypoperfusion.

Difference between Halothane and Barbiturate Anesthesia in the Influence of Cerebral Ischemia on the Vagal Baroreflex in Dogs.

“…The calculated mean re sidual blood flow during 5-min ischemia was 36.5 ± 5.9% (n = 10), and this value was similar to that reported under pentobarbital anesthesia (2).…”

“…The percent ratios of delta (1 to 3.5 Hz), theta (4 to 7.5 Hz), alpha (8 to 12.5 Hz) and beta (13 to 32 Hz) components of the EEG power spectrum to the total power were 24.2 ± 2.0, 40.7 ± 1.5, 26.3 ± 1.5 and 8.8± 1.5% (n = 10), respectively. This pattern of the EEG power spectrum was similar to that obtained under pentobarbital anesthesia (1,2).…”

“…However, the extent of the decrease in BRS in the present study (about 20% de crease) was less than that under pentobarbital anesthesia (about 50% decrease, see refer ences 1 and 2), and the change in the absolute value of BRS was not statistically significant. Furthermore, in contrast to the results under pentobarbital anesthesia (2), no significant re duction of rCBF in the medulla oblongata was observed during the period of 60 to 180 min of reperfusion (Table 1). Additionally, there was no significant change in EEG pattern during the reperfusion period.…”

“…The blood flow level immediately prior to ischemia was regarded as 100%, and zero flow was obtained by killing the animal with saturated KCl at the end of each experiment. Mean residual blood flow during ischemia was calculated as described in the previous report (2) to assess the severity of ischemia. Furthermore, a platinum elec trode was inserted contralaterally to the ther mocouple electrode to a depth of 1 to 2 mm, and the absolute value of rCBF was measured by the hydrogen clearance method (9).…”

“…We have reported that transient global cere bral ischemia of longer than 5 min produced a marked dysfunction of the central pathway of the vagal baroreflex in dogs (1,2). Since these experiments have been performed under pen tobarbital anesthesia, a possibility exists that the influence of ischemia might be underesti mated due to a cerebroprotective effect of barbiturates (3).…”