Tidal expiratory flow patterns in airflow obstruction.

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Abstract
Tidal expiratory flow pattern was analyzed in 99 subjects to assessing it as a quantitative measurement of airflow obstruction. Normal volunteers [15], 9 patients with dyspnea referred for investigation in whom airway resistance was within normal limits, 24 patients with restrictive lung disorders and 51 patients wit airway obstruction were studied. Expiratory flow pattern vs. time had a quadrilateral configuration in airway obstruction, which differed from the more sinusoidal form in subjects without airflow obstruction. The rapid rise to tidal peak flow was analyzed in 2 ways; percentage of volume expired at tidal pea flow (.DELTA.V/V) and percentage of expiratory time to tidal peak flow (.DELTA.t/t). Both these indices correlated significantlywith conventional measurements of airway obstruction. Expiratory flow pattern in airflow obstruction during quiet breathing resembles that of a forced expiratory maneuver at similar lung volumes. In some cases this may be caused by dynamic compression occurring during tidal breathing. In others the pattern may result from the static recoil of the lung being permitted to drive flow freely in expiration, rather than being braked by postinspiratory contraction of inspiratory musculature.