Bronchial breathing causes much confusion because the essential feature of bronchial breathing, the quality of the sound, is difficult or impossible to put into words. Traditionally, it is described by its timing as occurring in both inspiration and expiration with a gap in between. The diagram of bronchial breath sounds is:
In this way it is contrasted with vesicular breathing. These features are undoubtedly true but lead to the confusion in the mind of the student that if anything is heard in middle or late expiration it must be bronchia] breathing. Many normal people and individuals with airways obstruction have prolonged expiratory component to the breath sounds (this is sometimes designated “bronchovesicular” but this term increases the confusion rather than diminishing it). It is best to forget about the timing and concentrate on the essential feature, the quality of the sound. It can be mimicked to some extent by listening over the trachea with the stethoscope, although a better imitation can be obtained by putting the tip of your tongue on to roof of your mouth and breathing in and out through the open mouth. Bronchial breathing is heard when sound generated in the Central airways is transmitted more or less unchanged through the lung substance. This occurs when the lung substance itself is solid as in consolidation but the air passages remain open. Sound is conducted normally to the small airways but then instead of being modified by air in the alveoli, the solid lung conducts the sound better to the lung surface and, hence, to the stethoscope. If the central airways are obstructed by say a carcinoma, then no transmission of sound will take place and no bronchial breathing will occur even though the lung may be solid. An exception is seen in the upper lobes. Here, if the bronchi to either lobe are blocked, sounds from the central airways can still be transmitted directly from die trachea through the solid lung to the chest wall.
The main cause of bronchial breathing is consolidation particularly from pneumonia, so much so that in the minds of most clinicians the three terms are synonymous. Lung abscess, if near the chest wall, can cause bronchial breathing probably because of the consolidation around it. Dense fibrosis is an occasional cause. Breath sounds over an effusion will be diminished but bronchial breathing may be heard over its upper level perhaps because the effusion compresses the lung. Bronchial breathing is only heard over a collapsed lung if the airway is patent. This is rare as the collapse is usually caused by an obstructing carcinoma. Nevertheless, there is an exception with the upper lobes (see above). Bronchial breathing has been divided into tubular, cavernous and amphoric but attempts to score points on ward rounds by using these terms are best left to others.
Date: 2015-02-03; view: 2126