Determinants of maximal expiratory flow from the lungs.

Abstract

Expiratory isovolume pressure-flow curves were obtained by a new method in 13 normal subjects, 8 men with irreversible airway obstruction, and 14 subjects with reversible airway obstruction. The difference between alveolar and mouth pressures when flow 1st reached maximum ( [DELTA]P[image]), the maximum flow (VEmax), and airway resistance (Ra) in the range of driving pressures below [DELTA] P[image] were studied at different lung volumes. Relationships between VEmax [DELTA]P[image], RA, and lung volume showed 3 different patterns for the 3 groups of subjects studied. When VEmax is reached in an isovolume pressure-flow curve a "waterfall" or Starling resistor effect develops in the airways. Using the waterfall model, simple equations were developed relating the roles of elastic recoil of the lung, airway resistance, and bronchial collapsibility in determining VEmax, [DELTA]P[image], and RA- Analysis using this model suggests that irreversible airway obstruction was characterized by increased resistance of the airway from the alveolus to the point where a waterfall develops, while in reversible airway obstruction the major abnormality was a decrease in driving pressure from alveolus to the waterfall due to increased back pressure from bronchomotor tone.