Pulmonary pressure-flow curves measured by a data-averaging circuit

We measured pulmonary pressure-flow curves in nine normal nonsmoking subjects using a data-averaging circuit. With this method we obtained mean pressure flow curves of 20 consecutive breaths free of cardiac artifacts. Within-observer and within-subject-within-day reproducibility were good especially for the inspiratory limb of the curve. Within-subject-between-day variability in curvilinearity was substantial. In most subjects there was a continuous increase in resistance throughout the course of expiration even though the airways did not become dynamically compressed. This resulted in a mean value of expiratory resistance that was greater than during inspiration. Resistance early in expiration, however, was identical to that during inspiration. The data-averaging circuit allows for a more accurate assessment of the slope and the curvilinearity of pulmonary pressure-flow curves than other methods described before.