[Investigation of the role of acetazolamide-reactive mechanism in autoregulation].
METHODS
The cerebral blood flow (CBF) and mean stump pressure (MSTP) of 25 preoperative patients were measured during a 15 minute test occlusion of the ipsilateral internal carotid artery (ICA). CBF measurements were carried out by the Xenon/CT system adapted to the Toshiba 20A scanner with 4 min wash-in and 6 min wash-out of 30% Xe. Intra-arterial Xe concentration was calculated from endotidal tube-scanning. We selected two areas: the one fed by the middle cerebral artery (MCA), and the other defined as a unilateral cerebral hemisphere on the axial CT slice through the foramen of Monroe, to obtain CBF. We assessed the asymmetry ratio (AR) of CBF (AR = CBF in occlusion side/CBF in contralateral side) and investigated the correlation and regression of MSTP and AR in 25 cases. Furthermore, in 10 of the 25 patients, we measured the CBF with occlusion of the ICA 20 minutes after intravenous administration of acetazolamide. We evaluated the differences between before and after acetazolamide administration in MSTP and AR (paired t test), and investigated the correlation of and regression between MSTP and AR before and after acetazolamide administration again in these 10 patients.


RESULTS
A) In 25 cases; In the cases where MSTP was below 40 mmHg, a straight correlation with significant correlation and regression coefficients (MCA: r = 0.834, P = 0.020; Hemisphere: r = 0.840, P = 0.018) between MSTP and AR recognized. However, this statistical correlation was not seen in the cases where MSTP exceeded 40 mmHg, indicating that relationship could be expressed as horizontal line. B) In 10 cases; (1) AR was found to be significantly decreased after acetazolamide administration (MCA: P = 0.007; Hemisphere: P = 0.004, paired t test), although MSTP remained unchanged. (2) Although the relationship between MSTP and AR could be expressed as horizontal lines without a significant regression coefficient before acetazolamide administration, after that their relationship became a straight correlation with a significant regression coefficient (MCA: r = 0.698, P = 0.025; Hemisphere: r = 0.826, P = 0.003).


CONCLUSIONS
These results suggest that 40 mmHg of MSTP in the cases considered as almost normal is the lower limit of the autoregulatory range. In addition, an acetazolamide reactive mechanism might have a role in autoregulation, and in the lower range down to the lower limit of that the compensated CBF by this mechanism would increase as a progressive reduction of MSTP.
Okudaira
Y
Y
Department of Neurosurgery, Juntendo University School of Medicine, Tokyo, Japan.
Bandoh
K
K
Arai
H
H
Sato
K
K
Iizuka
Y
Y
D000086:Acetazolamide; D000328:Adult; D000368:Aged; D001794:Blood Pressure; D002343:Carotid Artery, Internal / Q000502:physiology; D002404:Catheterization; D002560:Cerebrovascular Circulation; D005260:Female; D006706:Homeostasis / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged
D000086:Acetazolamide