Effects of chemical drive on the inhibition of respiration produced by laryngeal stimulation in cats.

In 8 anesthetized cats the acute respiratory responses to laryngeal stimulation were studied under various levels of chemical drive. Under air breathing condition with strong stimulation the animals showed either cough or apnea, whereas with relatively weak stimulation the animals showed smooth reduction in respiration due to a decrease in tidal volume and prolongation of both inspiratory and expiratory time. Although the inhibitory effect of laryngeal stimulation on tidal volume was independent of the level of chemical drive, the inhibition of respiration, when analyzed in terms of decrease in the minute ventilation, was greater the higher the chemical drive regardless of the type of chemical stimulus. Although bilateral vagotomy decreased the threshold of stimulus intensity for changes in respiratory pattern, especially under hypoxia, the effects of laryngeal stimulation on respiratory pattern in vagotomized animals were qualitatively similar to those obtained in the intact animals. We concluded that laryngeal stimulation has a direct action on the central respiratory mechanism regulating respiratory duration and that the interaction between laryngeal stimulation and chemical drive causes multiplicative inhibitory effects on ventilation.