THE PRESSURE-FLOW RELATIONSHIPS OF THE INTRATHORACIC AIRWAY IN MAN*

Abstract
The gas velocity profile of the extrathoracic trachea was defined in five conscious subjects by a modified Pitot tube. The profile was essentially blunt during both inspiration and expiration for flows from 0.5 to 4.5 1 /second. From this information it was possible to separate the lower airway (alveolus to trachea) pressure drop into that related to the frictional losses in the gas and to the convective acceleration (Bernoulli effect) of the gas. In normal man convective acceleration may account for as much as one-third of the measured pressure drop along the lower airway.