On the glottal activity of experimental hiccup.

In cats, rats and rabbits under light barbiturate anesthesia, glottal activity during spontaneous or evoked hiccups was studied. By measuring laryngeal pressure or resistance to flow to a constant current of air, and controlling several sources of error, it was found that glottal closure is an important component of this complex phenomenon. Adductor activity of the vocal cords seemed more labile to the anesthetic action and, under this condition, showed a weaker force of contraction than the abductor one. It is suggested that this can be due to the correlation of glottal adduction with expiratory premotoneurons that are more depressed by anesthesia than the inspiratory ones. In hiccup, both adductor and abductor muscles would act simultaneously but in different proportions. The results add evidence to the idea of considering hiccup as due to a specific complex mechanism integrated at specific networks of the breathing generator.