Doppler CO2-test in patients with vertebrobasilar ischemia

The pathogenesis of vertebrobasilar ischemia (VBI) is still uncertain. Embolism and systemic hypotension have been discussed as possible causes. We evaluated the basilar arteries of 35 VBI-patients by transcranial Doppler-sonography at rest and under hypercapnic conditions and compared these findings with the basilar flow velocities in 10 healthy volunteers matched by age. We found no difference between the controls and the VBI-patients for the basilar flow velocities at rest. Under hypercapnia (end-tidal CO2-concentration 8.5%), the basilar blood flow velocities in the healthy controls increased by an average of 53.0% but only by 32.3% in the VBI-patients (p less than 0.005). The reduction of CO2 dependent vasomotor reactivity was observed in all VBI-patients, except in patients with infarction in the posterior cerebral artery area, possibly indicating a different pathogenic mechanism of stroke. The results in all other patients revealed no obvious correlation to the clinical course or angiographic or dopplersonographic findings. As CO2 dependent vasomotor reactivity and brain perfusion pressure dependent cerebral autoregulation have similar mechanisms, we conclude that systemic hypotension might play an important part in VBI.