Investigations on the neural control of respiration in experimental constriction of the upper airways.

The adaptation of the work of the respiratory centers to suddenly arising respiratory resistance has been the object of interest of numerous investigators. Some of them believed that in this condition an essential role is played by the vagus nerves. Others considered that neurocontrol is mainly dependent on the respiratory muscles. The present study was undertaken to establish which of these two systems is the preponderantly responsible one. Experiments were made with anesthetized intact and vagotomized rabbits. Constriction of the airways was achieved by connecting narrowed glass tube to the trachea. The activity of the respiratory centers was evaluated on the basis of their main two "outputs", the activity of phrenic neurons and of the respiratory motoneurons of the vagus nerve. In intact animals as a response to constriction a decrease of the respiratory frequency and an immediate increase of neural activity were observed. An increased activity of motoneurons was also noted in vagotomized animals, however, after a latency period lasting about 15 sec. The respiratory frequency in these animals changed in the opposite direction becoming higher after 15 sec. Results indicate that the vagus nerves play an essential role in the adaptation of the respiratory centers to constriction. All other sources and ways of information may compensate respiratory resistance by intensifying the work of the respiratory muscles only after the lapse of a certain time, moreover, they are incapable of adjusting an optimal rhythm. The possible sources of information in these conditions are discussed.