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

Abstract

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.

Characteristics of augmented breaths provoked by almitrine bismesylate in cats

“…It seems probable that an injection of almitrine with such long latency of response after ablating the vagi might have provoked the augmented breath. Moreover, as we have previously reported (Szereda-Przestaszewska et al 1990), interruption of the vagal pathways while not eliminating the respiratory responses to almitrine, nevertheless reduced the magnitude and duration of the effect.…”

“…The rate of occurrence of these breaths was not strictly coupled with the almitrine-evoked increase in breathing frequency. The latter was statistically significant 10 min after almitrine injection in our cats (Szereda-Przestaszewska et al 1990). The early stimulation of breathing due to almitrine consisted of the increased ventilatory flow rates and the appearance of the augmented breath.…”

“…Various chemical substances which affect the peripheral chemoreceptors and vagal afferents provoke augmented breaths. We have recently reported experiments in which a chemoreceptor stimulant -almitrine bismesylate -enlarged the laryngeal lumen in both phases of the respiratory cycle (Szereda-Przestaszewska, Jakus & Stransky, 1990). The increase in laryngeal patency was preceded and/or interrupted by the occurrence of augmented breaths.…”