Pattern of breathing and laryngeal patency following almitrine bismesylate in anesthetized cats

The effects of almitrine bismesylate on the pattern of breathing and laryngeal caliber were investigated in anesthetized, spontaneously breathing cats. Breathing occurred via a tracheostomy, while the laryngeal resistance to airflow was measured with the larynx isolated in situ. Almitrine bismesylate in a dose of 0.5 mg/kg of body weight was injected intravenously three times: in the intact animals, following bilateral vagotomy (sparing the right recurrent laryngeal nerve), and after a sensory denervation of the larynx. In each condition, almitrine stimulated ventilation by significantly increasing inspiratory airflow, by increasing the respiratory rate in the 10th and the 20th minutes following injection, and by reducing laryngeal resistance to airflow in both the inspiratory and expiratory phases. The stimulatory effects of almitrine were most apparent in the intact animals. Following vagotomy, these significant changes in the pattern of breathing as well as the enlarged laryngeal caliber persisted. However, these latter effects were short-lived and were followed by narrowing of the laryngeal lumen. Laryngeal afferents were not essential for the response to almitrine.