Distribution of common carotid blood flow, measured by Doppler, in man at high altitude.

The aim of the work was to estimate the possible changes induced by high altitude in the distribution of the common carotid arterial blood flow towards the internal and external carotid arteries. Common carotid blood flow and internal and external blood velocities were measured in 20 lowlanders at sea level, in 5 of them over a 3-week period at 3800 m and in 20 permanent residents of this high altitude. Internal and external blood velocities were recorded with a continuous Doppler and blood flow was recorded by range-gated Doppler velocimeter. Common carotid blood flow was 15% higher in all subjects exposed to high altitude due to a lowering in downstream vascular resistance since systemic blood pressure did not change at high altitude. The increase of blood flow in the common carotid was the result of a rise mainly in the external carotid blood flow.