Bilateral severe carotid artery stenosis or occlusion - cerebral autoregulation dynamics and collateral flow patterns.
BACKGROUND
Bilateral severe obstruction of the internal carotid artery is a hemodynamically critical state. We aimed to (1) analyze dynamic cerebral autoregulation (DCA) in affected patients, and (2) to correlate DCA data with different collateral flow patterns.


METHODS
DCA was assessed noninvasively by transfer function analysis (phase shift) of respiratory-induced oscillations at 0.1 Hz of arterial blood pressure (Finapres method) and cerebral blood flow velocity (transcranial Doppler) in 30 patients with severe bilateral carotid stenosis (> or =75%) or occlusion. CO(2)-reactivity was measured via inhalation of 7% CO(2). 30 patients with unilateral stenosis were recruited as controls.


RESULTS
Patients with bilateral 75-89% stenosis had a virtually preserved phase shift. A pronounced reduction was found in bilateral critical stenosis or obstruction (90-100%). Patients with ipsilateral 90-100% and contralateral 75-89% stenosis had a significantly less severe reduction of phase shift on the ipsilateral side. CO(2)-reactivity showed a less marked reduction in patients with bilateral critical stenosis or occlusion. Phase shift was best if "Willisian" collaterals were present. Significantly reduced values were found if only secondary collaterals (ophthalmic artery, leptomeningeal flow) were detected. Poorest values occurred with recruitment of functionally stenosed "Willisian" collaterals. CO(2)-reactivity showed poor values with sole recruitment of secondary collaterals, whereas functionally stenosed primary collaterals did not show values as poor as for phase shift. Clinically symptomatic patients had significantly lower phase shift and CO(2)-reactivity values.


CONCLUSIONS
DCA is severely impaired in bilateral critical carotid stenosis or occlusion. Sole recruitment of secondary collaterals and signs of a functional stenosis in primary ("Willisian") collaterals reflect insufficient collateral supply with a poor hemodynamic status. CO(2)-reactivity assessing the vasodilatory reserve and DCA represent different information for characterizing cerebral hemodynamic impairment. Determining transfer function phase might be a physiologically well supported approach for analysis of cerebral hemodynamic compromise.
Reinhard
M
M
Department of Neurology and Clinical Neurophysiology, University of Freiburg, Freiburg, Germany.
Müller
T
T
Roth
M
M
Guschlbauer
B
B
Timmer
J
J
Hetzel
A
A
D000368:Aged; D001783:Blood Flow Velocity / Q000502:physiology; D001794:Blood Pressure / Q000502:physiology; D001921:Brain / Q000098:blood supply*; D002245:Carbon Dioxide / Q000097:blood; D016893:Carotid Stenosis / Q000000981:diagnostic imaging* / Q000503:physiopathology / Q000601:surgery; D002536:Cerebral Arteries / Q000000981:diagnostic imaging; D002544:Cerebral Infarction / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000601:surgery; D002941:Circle of Willis / Q000000981:diagnostic imaging / Q000503:physiopathology; D003097:Collateral Circulation / Q000502:physiology*; D004292:Dominance, Cerebral / Q000502:physiology*; D005260:Female; D005583:Fourier Analysis; D006706:Homeostasis / Q000502:physiology*; D006801:Humans; D002546:Ischemic Attack, Transient / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000601:surgery; D008297:Male; D008875:Middle Aged; D009991:Oscillometry; D011673:Pulsatile Flow; D012008:Recurrence; D018570:Risk Assessment; D017585:Ultrasonography, Doppler, Transcranial; D014655:Vascular Resistance / Q000502:physiology
D002245:Carbon Dioxide