Measuring caffeine-induced changes in middle cerebral artery blood velocity using transcranial Doppler in patients recovering from ischaemic stroke.

Acute ingestion of caffeine is known to reduce cerebral blood flow in normal volunteers and in certain patient groups. There is no evidence that this causes problems in the normal population. However, there may be implications if a similar reduction occurs in patients recovering from an ischaemic stroke, in whom local blood flow has already been reduced. Transcranial Doppler provides a non-invasive method for measuring changes in middle cerebral artery (mca) blood velocity. A method for obtaining consistent. reliable measurements was developed and used in a double blind, randomized, crossover study on 20 patients (18 M, 2 F; mean age 70) recovering from ischaemic stroke in the mca territory. Middle cerebral artery blood velocity was measured bilaterally using transcranial Doppler before and after 250 mg caffeine (equivalent to about two cups of filter coffee) or matched placebo. Caffeine caused an average 12% reduction in blood velocity compared to placebo in the hemisphere affected by the stroke (95%c CI 8%-16%, p < 0.00001), and a 12% reduction in the non-affected hemisphere (95% CI 6%-18%, p < 0.001). The clinical implications are unclear at present, and imaging techniques will be required to establish whether caffeine does reduce flow to hypo-perfused regions.