Continuous comparison of cerebral blood flow velocity and volume on hypoxia

Cerebral blood flow velocity (CBFV) in the basilar artery, monitored by Doppler sonography, and cerebral blood flow (CBF) in the parietal cortex, monitored by Laser Doppler flowmetry, were continuously recorded and compared during and after hypoxic loading with nitrogen (N2) or carbon dioxide (CO2). On severe hypoxic loading (10% O2) of N2, CBFV and CBF increased with an increase in blood pressure (BP). On the other hand, with 18% and 15% O2 with CO2, CBFV and CBF increased with BP. However, there was a difference between CBF and CBFV in the recovery stage. CBF continued to be elevated for a long time, while CBFV rapidly normalized after loading. With 10% O2 with CO2, CBFV, CBF and BP decreased at first, and then increased during loading. Also, the difference between CBF and CBFV in the recovery stage being more definite. Thus, on continuous measurement, CBFV shows similar changes to CBF in response to hypoxia. However, CBFV shows different changes from CBF in association with dilatation or constriction of cerebral vessels. Resistance index (RI) shows different changes and have a different significance from CBF and CBFV.