Uncoupled cerebral blood flow and metabolism after severe global ischemia in rats.
In a rat model of complete global brain ischemia (neck tourniquet) lasting either 3 min or 20 min, we monitored global CBF (sagittal sinus H2 clearance) and CMRO2 for 6 h to test the hypothesis that delayed postischemic hyperemia and uncoupling of CBF and CMRO2 occur depending on the severity of the insult. Early postischemic hyperemia occurred in both the 3-min and 20-min groups (p less than 0.05 vs. baseline values) and resolved by 15 min. Hypoperfusion occurred in the 3-min group between 15 and 60 min postischemia (approximately 23% reduction), and in the 20-min group from 15 to 120 min postischemia (approximately 50% reduction) (p less than 0.05), and then resolved. CMRO2 was not significantly different from baseline at any time after ischemia in the 3-min group. After 20 min of ischemia, however, CMRO2 was decreased (approximately 60%) throughout the postischemic period (p less than 0.05). At 5 min after ischemia, CBF/CMRO2 was increased in both groups but returned to baseline from 60 to 120 min postischemia. In the 3-min group, CBF/CMRO2 remained at baseline throughout the rest of the experiment. However, in the 20-min group, CBF/CMRO2 once again increased (approximately 100%), reaching a significant level at 180 min and remaining so for the rest of the 6-h period (p less than 0.05). These data demonstrate biphasic uncoupling of CBF and CMRO2 after severe (20 min) global ischemia in rats. This relatively early reemergence of CBF/CMRO2 uncoupling after 180 min of reperfusion is similar to that observed after prolonged cardiac arrest and resuscitation in humans.
Singh
N C
NC
Department of Anesthesiology/Critical Care Medicine, University of Pittsburgh, PA.
Kochanek
P M
PM
Schiding
J K
JK
Melick
J A
JA
Nemoto
E M
EM
D000818:Animals; D001921:Brain / Q000378:metabolism* / Q000503:physiopathology; D002545:Brain Ischemia / Q000150:complications / Q000378:metabolism / Q000503:physiopathology*; D002560:Cerebrovascular Circulation / Q000502:physiology*; D006940:Hyperemia / Q000209:etiology / Q000378:metabolism; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D013997:Time Factors