Monitoring of cerebral vasodilatory capacity with transcranial Doppler carbon dioxide inhalation in patients with severe carotid artery disease.
OBJECTIVE
Cerebral vasodilatory capacity (CVC) testing with transcranial Doppler has been shown to be useful in the assessment of stroke risk in patients with symptomatic and asymptomatic internal carotid artery (ICA) stenosis and occlusion, but whether hemodynamic status improves, deteriorates, or remains the same over time is uncertain.


METHODS
Thirty-five patients with >or=80% carotid artery stenosis or complete occlusion underwent CVC testing at baseline and 6 months later. CVC was assessed by measuring the increase in ipsilateral middle cerebral artery mean flow velocity in response to 5% inhaled CO2. Continuous tracings of left and right middle cerebral artery flow velocity, heart rate, respiratory rate, and Pco2 were recorded and then analyzed offline. One-way analysis of variance was used to compare baseline CVC in symptomatic and asymptomatic patients with control subjects. A paired t test was used to compare CVC before and after revascularization. Also, chi2 analysis was used to compare rates of cerebrovascular events in patients with low compared with normal CVC over the 6-month period and in 14 patients whose ICAs were revascularized.


RESULTS
Patients with high-grade stenosis or occlusion of the ICA who had ICA disease had an average CVC of 2.4+/-1.9%/mm Hg Pco2; control subjects averaged 4.2+/-1.1%/mm Hg Pco2. (P=0.01). In the revascularization group, CVC increased from an average of 1.4+/-1.7%/mm Hg Pco2 at baseline to an average of 2.8+/-1.0%/mm Hg Pco2 after revascularization, significantly different from the spontaneous change in the natural history group over 6 months (P=0.003). Over the 6-month follow-up period, in the natural history group and in the treatment group after revascularization, 4 ischemic events occurred, all in patients with abnormal CVCs; abnormal CVC was associated with ischemic events (Fisher's exact test, P=0.03).


CONCLUSIONS
In a timeframe pertinent to clinical decision making and clinical trial outcomes, cerebral hemodynamic status may not be constant. A higher ischemic risk may be present in patients with severe carotid artery disease whose CVC is poor at baseline, becomes poor over 6 months, or fails to normalize after revascularization.
Marshall
Randolph S
RS
The Neurological Institute, Columbia University, College of Physicians and Surgeons, New York, NY 10032, USA. rsm2@columbia.edu
Rundek
Tanja
T
Sproule
Douglas M
DM
Fitzsimmons
Brian-Fred M
BF
Schwartz
Shauna
S
Lazar
Ronald M
RM
D000280:Administration, Inhalation; D000328:Adult; D000368:Aged; D001783:Blood Flow Velocity; D002545:Brain Ischemia / Q000453:epidemiology; D002245:Carbon Dioxide / Q000008:administration & dosage; D016893:Carotid Stenosis / Q000175:diagnosis / Q000000981:diagnostic imaging / Q000503:physiopathology*; D002548:Cerebral Revascularization; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D020768:Middle Cerebral Artery / Q000000981:diagnostic imaging / Q000503:physiopathology*; D011446:Prospective Studies; D017585:Ultrasonography, Doppler, Transcranial / Q000379:methods*; D014664:Vasodilation; D014665:Vasodilator Agents / Q000008:administration & dosage
D014665:Vasodilator Agents; D002245:Carbon Dioxide