The effect of transient stimulation of lung irritant receptors on the pattern of breathing in rabbits.

1. 100 ms pulses of inflation and deflation were applied to the lungs of anaesthetized rabbits before and during inactivation of pulmonary stretch receptors. 2. Pulses of either sign given in inspiration often produced augmented breaths, whether or not stretch receptors were inactivated. Inflation pulses were more effective than deflation pulses. 3. After an augmented breath it was impossible to produce another for at least 1 min (refractoriness). 4. Pulses of deflation always shortened expiration. Pulses of inflation early in expiration shortened expiration. Later in expiration they lengthened expiration when stretch receptors were active and shortened expiration when stretch receptors were blocked. No refractoriness was observed for the effects on expiratory time. 5. Pulses in paralysed animals caused a burst of phrenic activity of fixed duration, usually with brief latency. There was no refractoriness. 6. We suggest that the duration of inspiration is governed by the activity of pulmonary stretch receptors, except during an augmented breath, and that the duration of expiration is governed by a balance of stretch and irritant receptor activity.