Reflex activities of the upper airway muscles during experimental nasal occlusion in anesthetized dogs

Reflex responses of the upper airway muscles during experimental nasal and tracheal occlusions were studied in 21 anesthetized dogs breathing through the nose or a tracheostomy (tracheal cannula). Out of them, five animals were examined for maintained negative and positive pressures applied to the isolated upper airway. When the nose was occluded at end-expiration during three consecutive breathings, the electromyographic (EMG) activity of alae nasi (AN) and posterior cricoarytenoid (PCA) muscle markedly increased. The upper airway was subjected to negative pressure, -2.41 approximately -3.04 kPa (n = 34) by these nasal occlusions. The activity of upper airway muscles was also increased by tracheal occlusions. However, such augmentation of PCA activity was much less in tracheal occlusions than nasal occlusions, whereas there was the smaller difference in AN activity between both occlusions. During nasal occlusions, a prolongation of the inspiratory time (TI) was observed. Furthermore, maintained negative pressure applied to the isolated upper airway provoked an augmentation of PCA activity. Such an augmented EMG activity of PCA and the prolongation of TI were largely diminished by sectioning the superior laryngeal nerves. These results proves that the upper airway muscles play an important role to protect the upper airway from collapsing by nasal occlusions. In addition, it is suggested that a lack of lung volume feedback is substantially concerned with the activation of AN, while negative pressure in the upper airway is essential to stimulate PCA.