[The effect of physical stress on the blood flow velocity in the middle cerebral artery. A transcranial Doppler sonographic study].

Changes in blood flow velocity of the middle cerebral artery (MCA) were measured by transcranial Doppler Sonography in 10 healthy subjects during a 10-minute period of moderate bicycle exercise. During physical exercise, a marked increase in heart rate (+63%) und ventilation rate (+48%) and a moderate increase in mean arterial blood pressure (+16%) were found. The end tidal carbon dioxide partial pressure rose in all cases by a mean value of 6.7 mmHg. The MCA flow velocity increased from 62 cm/s to 75 cm/s by 13 cm/s or 21% (mean values). When corrected to a standard pCO2 of 40 mmHg no significant changes in flow velocities (-1 cm/s) were found. Our Doppler sonographic findings indicate that during moderate physical exercises the MCA flow velocity - and the cerebral circulation - are regulated by the carbon dioxide partial pressure and not by cardiac output.