Cerebral CO₂vasoreactivity by transcranial Doppler with rebreathing method, comparison between ischemic stroke and normal control.

Abstract

Background & Objectives : Cerebral vasoreactivity is a index of autoregulation of cerebral perfusion, and can be measured by functional imaging such as Xe CT, SPECT, PET in reponse to hypercapneic stimulus. Recently transcranial Doppler (TCD) study helps evaluation of cerebral CO₂vasoreactivity by breath holding method and CO₂inhalation. But breath holding method has some constrictions in reliability and CO₂inhalation method is not so feasible to apply to routine study. In order to measure cerebral CO₂vasoreactivity in routine TCD study conveniently and reliably, we devised a method of rebreathing into closed volume of reservoir bag as a hypercapneic stimulus, and applied it to normal volunteers and patients with ischemic stroke. Method : We performed cerebral CO₂vasoreactivity study by rebreathing method in 15 normal volunteers and 35 ischemic stroke patients which were age and sex matched. As a hypercapneic stimulus, we applied fitting mask connected with closed reservoir bag for about 90 second, and mean flow velocity (MFV) and pulsatility index (PI) were evaluated at proximal middle cerebral arteries of 50-55 mm depth, before and after the hypercapneic stimulus. Cerebral vasoreactivities as percent increment of MFV in MCA were compaired between two groups. Results : MFV of both normal control and patient group increased continuously during hypercapneic stimulus, but the rate of increment of MFV markedly diminished after about 60 seconds of rebreathing. Mean cerebral vasoreactivity of 61 MCA’s in ischemic stroke patient group (47.0 ± 22.0%) was significantly lower than that of 22 MCA’s in normal control group (60.2 ± 16.0%). But percent decrement of PI showed no significant difference between both groups. Conclusion : We suppose that the rebreathing method is a reliable and convenient technique as a hypercapneic stimulus in determining cerebral CO₂vasoreactivity. Cerebral vasoreactivity measured by rebreathing method is significantly lower in ischemic stroke patient group than in normal control group.