Prediction of maximal expiratory flow in excised human lungs

Abstract

Predictions of the wave-speed theory of flow limitation were tested against measured values of maximal expiratory flow (.ovrhdot.Vmax) in 9 normal excised human lungs. Static pressure-volume curves and deflation pressure-area (PA) curves of the first 3-4 airway generations were obtained. The pressure drop from the alveolus to the flow limitation site was assumed to consist of a peripheral frictional loss (estimated from a catheter upstream from the flow limitation site) and a convective acceleration pressure drop. Predicted .ovrhdot.Vmax was determined graphically by finding the lowest flow for which the Bernoulli PA curve was tangent to one of the bronchial PA curves. At the point of tangency local flow speed equals local wave speed. At low lung volumes a point of tangency with the PA curves of the 1st few generations did not exist, and the flow limitation site was assumed to be the minimal bronchial area at zero transpulmonary pressure. There was good agreement between measured and predicted .ovrhdot.Vmax. Measured .ovrhdot.Vmax was not different from .ovrhdot.Vmax predicted from normal living man. The wave speed theory predicted flow over much of the vital capacity, but other mechanisms may limit flow at low lung volumes.