Continuous Adventitious Lung Sounds: Site and Method of Production and Significance

Continuous adventitious lung sounds are rarely called such, mainly because the term is both too cumbersome and too general. Rather, a physician will speak of stridor, crowing, wheezes, and rhonchi. The more fastidious will carefully observe such sounds and then add several qualifying terms to denote their loudness, complexity, and pitch, as well as the phase of respiration in which they are heard. Because these sounds are associated with airway obstruction, the purpose of careful notation of their characteristics is to deduce the level and nature of the obstruction within the airway and the number of airways involved—one, few, or many. There follows from such observations a frequently subconscious series of logical steps by which the physician may conclude, for example, that sounds of this type and with these characteristics involve several airways and are related to a combination of bronchospasm and mucus hypersecretion. The way is thus cleared for additional diagnostic steps or even a therapeutic trial. This analysis will begin by defining continuous adventitious lung sounds, next discuss the pathophysiology and acoustics presumably involved in their formation, and then relate certain refining characteristics of these sounds to several diseases in which they have been observed (Table 1). Finally, it will attempt a classification of continuous adventitious lung sounds based on their observable characteristics (Table 2). All continuous adventitious lung sounds have one chief identifying characteristic—an instantly recognizable musical quality. Breath sounds, comprising sounds of many frequencies, lack a clearly dominant pitch, A continuous adventitious lung sound is clinically identified when a musical tone or a mixture of such tones is heard at the mouth, trachea, or chest wall regardless of whether a stethoscope is required or not. The term "continuous" separates such sounds from the other adventitious sounds, the unmusical, "discontinuous," crackling, bubbling, or snapping noises discussed in the following article. The duration of a continuous adventitious lung sound can extend from the fraction of a second required to recognize a musical tone, perhaps 200 msec, to several seconds and can range in pitch from 60 to more than 2000 Hz. Visually, such sounds have a clear pattern of smooth waves whose length is related to pitch and whose height is related to loudness (Fig. 1). On spectral display, they usually show a fundamental frequency with one or more harmonics (Fig. 2). Nomenclature in this area, as in others involving pulmonary auscultation, has been confused. Traditionally, the term "wheeze" has been used for sounds heard at the mouth and "rhonchus," for those heard at the chest wall. In 1967 Forgacs argued convincingly that "wheeze" adequately covers these sounds heard at any observation site. "Rhonchus" has become ambiguous, since the term is variably used by physicians for both musical and unmusical adventitious sounds, of which the latter would not be considered continuous adventitious lung sounds. Nevertheless, some object to the term "wheeze" and continue to espouse "rhonchus" when describing a very low-pitched rumbling continuous adventitious lung sound on the grounds that "wheeze" onomatopoetically suggests a high-pitched sound. In 1975 the Joint Committee on Pulmonary Nomenclature of the American College of Chest Physicians and the American Thoracic Society suggested that "wheeze" and "rhonchus" could be used interchangeably. The Committee indicated also that these sounds could vary in pitch, quality, and in-