Bronchial Breath Sounds
PRETEST 
1. What happens to normal breath sounds when lung density increases?
2. What are bronchial breath sounds?
3. How does consolidation affect breath sounds?
4. How does atelectasis affect breath sounds?
5. How does fibrosis affect breath sounds?
SOUND PRODUCTION
When lung tissue between the central airways and the chest wall becomes airless because of conditions that increase lung density, transmission of breath sounds from large airways is enhanced. This happens because little high-frequency sound is lost through attenuation or filtration. As lung tissue density increases the impedance between the fluid-filled lung tissue and the pleurae and chest wall, these three media become well-matched, which decreases the normal filtering of high-frequency sounds. Consequently, breath sounds are transmitted more readily to the chest wall surface and are louder and more tubular than normal breath sounds heard over the same chest wall area. Expiration is significantly louder and longer than normal. The inspiratory-expiratory (I:E) ratio changes from the normal 3:1 or 4:1 to 1:1 or 1:2. These sounds, called bronchial breath sounds, are considered abnormal when found anywhere except anteriorly over the large airways.
Related conditions
Conditions associated with bronchial breath sounds include consolidation, atelectasis, and fibrosis, all of which increase lung tissue density because of fluid accumulation, lung collapse, or fibrotic scarring. Bronchial breath sounds are heard over the affected lung area.
Consolidation
The most common cause of lung tissue consolidation (solidification) is pneumonia, a lung inflammation that can be caused by bacteria, viruses, or chemical insults (such as with aspiration). In this condition, fluid, leukocytes, and erythrocytes accumulate in spaces that are normally air-filled, producing a consolidated area. Clinical findings vary, depending on the location of the consolidated area and the causative agent. When classic consolidation is
present, decreased chest wall movement and a dull percussion note are apparent over the affected area. Bronchial breath sounds are heard over a dense, airless upper lobe, even without a patent bronchus (♦Sound 60), because the upper lobe surfaces are in direct contact with the trachea and loud tracheal breath sounds are transmitted directly to the dense, airless upper lobe tissues. In contrast, bronchial breath sounds are heard over a dense, airless lower lobe only when the bronchi are patent, because sound isn’t transmitted directly to the airless lower lobe tissues.
present, decreased chest wall movement and a dull percussion note are apparent over the affected area. Bronchial breath sounds are heard over a dense, airless upper lobe, even without a patent bronchus (♦Sound 60), because the upper lobe surfaces are in direct contact with the trachea and loud tracheal breath sounds are transmitted directly to the dense, airless upper lobe tissues. In contrast, bronchial breath sounds are heard over a dense, airless lower lobe only when the bronchi are patent, because sound isn’t transmitted directly to the airless lower lobe tissues.
Sound characteristics
In a patient with lobar pneumonia with right posterior midlung consolidation, bronchial breath sounds are heard over the right posterior midlung field, located over the seventh and eighth intercostal spaces along the vertebral column. (See Bronchial breath sounds heard over consolidated right posterior midlung, page 138.) These sounds are high-pitched and have the typical hollow, or tubular, quality of normal central airway breath sounds. They remain audible during both expiration and inspiration, but the expiratory sounds are longer and louder when the patient is sitting up; the I:E ratio is 1:2. These sounds may be auscultated using either the bell or diaphragm of the stethoscope. (♦Sound 60)
Atelectasis
Atelectasis, incomplete expansion of a lung area, is typically diagnosed in postoperative or immobile patients and in some patients with bronchiectasis or pneumonia. It’s thought to result from prolonged shallow breathing (hypoventilation) or uncleared secretions that occlude the airway. Because no air enters the distal airways, the segmental or lobar bronchi collapse. If a large airway is occluded, clinical findings include decreased chest wall movement, a dull percussion note, regional changes in lung volume, and bronchial breath sounds over a dense, airless upper airway. (♦Sound 61)
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