Modification of the intensity of the expiration reflex during short-term inflation of the lungs in rabbits.

Too little is known of the mechanisms participating in the regulation of defence reflexes of the organs of respiration. The activity of respiratory tract--in particular lung stretch and cough receptors--may play an important role. In the present study the authors investigated the effect of short-term inflation of the lungs, during which lung stretch receptors are mainly stimulated, on the expiration reflex, which is one of the respiratory defence reflexes. The experiments were carried out on 18 rabbits (2.5-2.8 kg) under general anaesthesia (Pentobarbital Spofa, 30 mg.kg-1 i.v.). The VT, V', Ppl and systemic BP were recorded. The expiration reflex was elicited by stimulating the vocal folds with a silon fibre loop during resting respiration and during inflation of the lungs with pressures of 0.49, 0.98 and 1.47 kPa. The criterion of the intensity of the expiration reflex was the Ppl expressed in kPa. The authors found that the intensity of the expiration reflex during resting respiration was 0.29 +/- 0.02 kPa (S.E.M.). An inflation pressure of 0.49 kPa raised it to 0.69 +/- 0.06 kPa, a pressure of 0.98 kPa raised it still further to 1.12 +/- 0.06 kPa and a pressure of 1.47 kPa raised it yet again to 1.59 +/- 0.08 kPa. In the authors' opinion, the increase in the intensity of the reflex is due to augmented activity of lung stretch receptors.