Relationship of cerebral blood flow regulation to acute mountain sickness

Acute mountain sickness (AMS) is a prevalent illness seen in humans exposed to high altitudes. An increase in cerebral blood flow as a result of cerebrovasodilatation is felt by many to be responsible for its occurrence. Using the recently developed transcranial Doppler (TCD), it has become possible to detect and quantify flow velocity in the large cerebral vessels. By this method, intracranial arterial blood flow velocities and vasodilatation were measured at high altitude and correlated with clinical symptoms. Mean middle cerebral artery velocity (MCA-V) showed a significant increase from 55 +/- 7 cm/s at sea level to 71 +/- 13 cm/s at 13,500 feet. The pulsatility index (PI) and vasomotor reactivity (VMR) both decreased (.71 +/- .11 at sea level to .53 +/- .12 at 13,500 and 45 +/- 17% sea level to 23 +/- 15% at 8,000 feet, respectively). These preliminary studies indicated that TCD technique is a viable tool for measurement of cerebral blood flow velocities and cerebral arterial vasodilatation at altitude.