[Regulation of the duration of expiratory phases in decerebrate cats]

The changes of durations of the first (postinspiratory, TPIA) and second (TE2) stages of expiration in hypercapnic hyperpnoea before and after bilateral vagotomy and after subsequent injection of pentabarbitone, were evaluated in 10 decerebrated cats. With vagal nerves intact, the hyperpnoea was accompanied by the diminution of the TPIA with no significant changes of the TE2. Vagotomy increased the TPIA. During the hyperpnoea, the TPIA did not change significantly in vagotomized cats whereas the TE2 increased. Pentobarbitone did not affect the TPIA but increased the TE2. Under these conditions, hypercapnia was accompanied by no significant changes of either the TPIA or TE2. The leading part in the regulation of expiratory duration in decerebrated cats seems to be played by the lung mechanoreceptors whose impulses reduce both the TPIA and TE2 in hyperpnoea. The lung stretch receptors impulses inhibit the postinspiratory activity. The TPIA and TE2 regulation is performed by separate central mechanisms. Postinspiratory activity is relatively resistant to pentabarbitone, although the latter delays the start of the next inspiration and obviously suppresses active expirations.