抄録
Since lung sounds are physiological signals which anybody can acquire safe and free without any limitations, it is quite an achievement if one can extract any useful information from them. Auscultation of the lung has been a basic diagnostic tool for a physician, and there are many auscultatory findings which we know, yet the origin of which we do not know. For instance, normal breath sounds heard over the neck are louder in expiration than in inspiration, while those heard over the lower chest are louder in inspiration than in expiration. The former is probably due to the narrowing of glottis during expiration, but the latter is more complicated. The structure of the airways and the direction of the flow could be closely related, but we do not know exactly how. Flow limitation during forced expiration has been one of the hottest issues in respiratory physiology for many years. It is generally agreed that an airway collapse is the cause of flow limitation, but what causes the airway collapse? Is it possible for the vortices or other secondary flows developed rapidly in the airway during forced expiration to cause a significant pressure drops in the airway? We do not know the answer and we would like to know it either way, hopefully in near future.
