[Respiratory functions of the upper airway with special reference to physiological implications of respiratory...

The upper airway is not a simple solid conduit for respiratory airflow. It is also concerned with digestive and defense functions and vocalization. Therefore, it can be recognized as a complex organ to regulate these complex functions. There are three valve-like structures in the upper airway, i.e., the nasal cavity, pharynx and vocal cord. Therefore, airflow is controlled and sometimes obstructed in these particular regions, a phenomenon called airway collapse. In order to maintain the patency of the upper airway during inspiration, it is mandatory to elicit simultaneous activation of both respiratory and upper airway muscles. Even in normal healthy subjects, strong contraction of the respiratory muscles without accompanying activation of the upper airway muscles, such as in hiccups, results in airway collapse. In recent years, a number of physiological and pathophysiological studies have been accomplished to elucidate the mechanisms of the upper airway collapsibility. Particularly, the passive mechanism concept to explain obstructive sleep apnea during REM sleep advocated by Remmers and Guilleminault has substantially contributed to the recent development of research activities in this field. Important new findings related with this topic were presented by Drs. Fukuda, Kitagawa, Hida, Ohi and Kawakami in this symposium. In relation to the swallowing reflex and cough mechanism, interesting discoveries were also reported by Drs. Nishino and Sekizawa.