Non invasive recording of CO2 cerebrovascular reactivity in normal subjects and patients with unilateral internal carotid artery stenosis.

CO2 cerebrovascular reactivity has been recorded in 12 healthy volunteers and 10 patients with unilateral > 70% extracranial internal carotid artery (ICA) stenosis, using non invasive techniques. The relative changes of middle cerebral artery blood flow velocity (VMCA) and velocity waveform pulsatility (PIMCA) after that hypocapnia was induced by spontaneous hyperventilation were recorded. 35.5% average VMCA reduction and 63% PIMCA increment of basal values was produced in healthy subjects after hyperventilation. The percentage variation of CO2 Reactivity Index (RI), expressed in terms of VMCA (V-RI) and PIMCA (PI-RI), per mmHg change in pCO2, presents a good right-left side correlation (r = 0.82 and r = 0.83 respectively) in healthy subjects, while a dissociation between V-RI and PI-RI was found in our patients. A significant reduction of PI-RI was also recorded in the group of patients on the side of ICA stenosis. From our data CO2 reactivity index recorded in terms of PI seems to allow a better separation between pathology and normality, without the need to assume a close relationship between velocity and blood flow under the condition considered. Furthermore, PI-RI seems to be a valid index in the evaluation of some attribute pertaining to the distal vascular bed.