Hydrodynamic features of pulmonary air embolism: a model study.

To elucidate the hydrodynamic events during pulmonary air embolism, experiments were conducted in a branching-tube apparatus and in small vessels. It was found that, as long as there existed an elevation differential between the two branches of a bifurcation, the vast majority of air bubbles always entered the higher branch. This finding is explained in terms of buoyancy, shear forces, and liquid flow velocity and is consistent with the in vivo finding of increased blood perfusion in the dependent lung regions during air embolization (J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 51: 211-217, 1981). The pressures required to drive air bubbles through various small vessels were determined using three aqueous solutions of different surface tensions. Based on these measurements and a theoretical analysis, the diameter of air bubbles that could not pass through the pulmonary vessels was calculated to be 20-30 micrometers, agreeing well with a recent in vivo measurement (J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 47: 537-543, 1979).