[Lung sound analysis and pulmonary function studies].

Because of technical difficulties, the study of lung sounds has been neglected for the last 200 years since the age of Laennec. However, recent advances in signal processing and in technology have made it possible to record lung sounds routinely at the bedside or in clinical laboratories. Lung sound analysis has many advantages because it is safe, non-invasive, low-cost, and repeatable. Normal lung sounds can be classified into tracheal, bronchial, and alveolar (vesicular) sounds. They are all common in that the origin of the sound is the turbulence in the airways. The most important and convenient way of distinguishing them is the place where they are heard and the difference in intensity in relation to breathing cycle. Alveolar sounds are heard at the bases and are definitely larger during inspiration, while bronchial sounds are heard at the apex, over the sternum and inter-scapular area, and are equal or louder during expiration. The abnormal, or adventitious lung sounds are classified into continuous and discontinuous. Wheezes are most common continuous sounds. However, in patients with stenosis of trachea or major bronchus large continuous sounds often referred to as rhonchi are heard. They are easily heard over the neck and are important clinical signs which nurses and laboratory technicians must be aware of. By the use of adaptive digital filters we can reduce contaminating noises without the use of sound proof rooms. Because of many advantages, the lung sound analysis has a promising future as a method to supplement other pulmonary function studies.