The authors performed TCD study to measure the CO₂ reactivity to the entire basal cerebral arteries in 30 cases of control group and 14 cases of head inury group between the 3rd and the 7th day after insult. All patients were examined by single photon emission computed tomography and their results were compared to CO₂ reactivities at 8 basal cerebral arteries. All of these results were analyzed by statistical analysis system(SAS).

The increase of MBFV(mean blood flow velocity) and decrease of PI(pulsatility index)were noted in the cerebral arteries with decreased CO₂ reactivity. It meant that the arterial walls were dilated. There was no close relationship between region of interest(ROI) index and CO₂ index but CO₂ reactivity was remarkably decreased in the region which showed abnormal regional cerebral blood flow in SPECT(single photon emission computed tomogram)(P=0.04). In the relationship between the variables, ROI increased as the clinical status worsen(r=0.5, P=0.0008), the prognosis of the patients had positive correlation with CO₂ index(r=0.32, P=0.04) or clinical status had negative correlation with ROI index(r=0.40, P=0.0094).

The doppler CO₂ test in patients with head injury provides useful information regarding hemodynamic state, prognosis and determination of beneficial effects of specific therapy, especially during subacute stage. In the various TCD parameters CO₂ index was correlated well with prognosis.