Transcranial Doppler: clinical and experimental uses.

Blood flow velocity in the basal intracranial arteries can be reliably recorded using transcranial Doppler (TCD) ultrasonography. The utility of Doppler ultrasound in detecting stenosis of arteries has therefore been extended to include the intracranial basal arteries. This has been useful in detecting intracranial stenosis from a variety of causes including atherosclerosis and vasospasm induced by subarachnoid hemorrhage. Changes in cerebral hemodynamics during significantly increased intracranial pressure have also been detected, and have been useful in warning of compromise of the cerebral circulation in head injury. The assessment of the final hemodynamic effects of occlusive disease on the middle cerebral artery can be studied using the CO2 reactivity test. This offers additional diagnostic information in these patients. The direct detection of intracranial microemboli using TCD is also now possible and this has implications in the management of patients with stroke and transient ischemic attacks. Continuous monitoring of the middle cerebral artery velocity has been useful in indicating relative blood flow changes through this artery under certain specific circumstances. By providing continuous information on relative blood flow changes, the dynamics of the cerebral circulation can be studied in more detail. This has allowed the assessment of cerebral autoregulation, as well as blood flow changes, due to changes in cortical activity induced by visual stimulation. Further research on the dynamics of the human cerebral circulation will be possible using this technology.