ABSTRACT
The intracranial effects of acetazolamide on flow velocities can be monitored noninvasively by transcranial Doppler (TCD) sonography. Extracranial volume flow changes can now reliably be measured with color duplex M-mode systems. The authors tested the volumetric effects of acetazolamide in patients with high-grade unilateral carotid disease to quantify the amount of flow changes. Patients in group 1 had a high-grade > 70% internal carotid artery (ICA) stenosis, without collateral flow through the ophthalmic artery (OA). Patients with occluded ICA were included in group 2 (patent OA collateralization) or group 3 (no OA collateralization) (n = 6 per group). In group 1, common carotid artery (CCA) volume flow in the stenotic (normal contralateral) side increased from 271 (388) ml/min by 52 (54%) with 1 g aceta-zolamide intravenously. Simultaneously, middle cerebral artery (MCA) flow velocities increased from 54 (56) cm/s by 47 (53%). In group 2, extracranial volume flow increased from 166 (444) ml/min by 19 (52)%. MCA flow velocities increased from 43 (65) cm/s by 13 (30)%. In group 3, volume flow increased from 159 (467) ml/min by 2 (46)%. Intracranial flow velocities rose from 49 (54) cm/s by 27 (41)%. Volume flow data showed the expected decline in patients with high-grade ICA stenosis and even more pronounced in patients with occlusion of the vessel. Cerebral reserve capacity was less sufficient in patients with a patent OA, despite an additional supply of 30 ml/min, indicating a hemodynamically critical situation.
Subject(s)
Acetazolamide/pharmacology , Blood Flow Velocity , Blood Volume , Carotid Stenosis/physiopathology , Cerebrovascular Circulation/drug effects , Vasodilator Agents/pharmacology , Aged , Blood Flow Velocity/drug effects , Blood Volume/drug effects , Carbonic Anhydrase Inhibitors/pharmacology , Carotid Artery, Common/diagnostic imaging , Carotid Artery, Common/physiopathology , Carotid Artery, Internal , Carotid Stenosis/diagnostic imaging , Carotid Stenosis/drug therapy , Collateral Circulation , Humans , Middle Aged , Middle Cerebral Artery/diagnostic imaging , Middle Cerebral Artery/physiopathology , Ophthalmic Artery/diagnostic imaging , Ophthalmic Artery/physiopathology , Ultrasonography, Doppler, TranscranialABSTRACT
BACKGROUND AND PURPOSE: The vasomotor response can be tested by means of transcranial Doppler sonography. If a constant vessel diameter is assumed, the flow velocity changes will reflect blood flow volume changes. This hypothesis is difficult to verify. Simultaneous assessment of intracranial flow velocity and extracranial flow volume changes may solve this problem. METHODS: We tested vasomotor response in 32 volunteers (age, 42+/-18 years) with 5% CO2. Acetazolamide (1 g) was tested in 15 volunteers (age, 28+/-8 years). To evaluate drug-dependent flow changes in the external carotid artery territory, acetazolamide was administered in 7 patients with unilateral occlusion of the internal carotid artery without evidence of collateralization through the ophthalmic artery (age, 67+/-12 years). Simultaneous recording included measurements of flow volume in the common carotid arteries (M-mode color duplex system) and flow velocity in the middle cerebral arteries. RESULTS: With CO2 and acetazolamide, intracranial flow velocity increased by 31% and 39%, respectively, with a simultaneous increase of common carotid artery flow volume of 47% and 50%, respectively. No change in extracranial flow volume was observed in patients with an occluded internal carotid artery. CONCLUSIONS: These data show not only the expected increase of flow velocity in the middle cerebral artery but also suggest an increase in cross-sectional vessel diameter of 6% and 4% with CO2 and acetazolamide, respectively. It remains unresolved whether this observation is due to a direct effect of the drug on the vessel walls or is simply pressure dependent.
