The effect of lung reflexes on the pattern of breathing in cats.

Tidal volume (VT), and inspiratory (tI) AND EXPIRATORY (TE) durations have been measured in anaesthetized cats on stimulation of alveolar type J (nociceptive) and lung irritant receptors by intravenous injections of phenyl diguanide and of histamine acid phosphate respectively. The reflexes were studied during eupnoea, hypercapnic and hypoxic hyperpnoea, during rebreathing from hyperventilation apnoea and at different body temperatures. In all conditions the drugs caused rapid shallow breathing with reduction in VT, tI and tE. The VT/tI relationship for injection of the drugs was different from that caused by hypercapnic stimulation of breathing, but the tI/tE relationship was proportionally similar for all conditions. Recording single unit activity from phrenic motor fibres showed that the lung reflexes had little action on the initial frequency of discharge of the fibres, but cut short the discharge earlier than for the controls. The results are interpreted in terms of the ways in which lung reflexes can modify the pattern of breathing.