Clinical Vignette
A 12-year-old castrated male West Highland white terrier was presented with the chief complaint of a harsh cough of 3-months duration, which occurred after exertion. Physical examination revealed a body condition score of 4 out of 5, a rectal temperature of 102.0°F, heart rate of 80–124 bpm, respiratory rate of 16 rpm, a grade II/VI systolic heart murmur at the level of the left apex, normal sinus arrhythmia, and inspiratory crackles on thoracic auscultation. Owner reported no systemic symptoms of illness.
Problem Definition and Recognition
Breath sounds are broadly classified as normal; normal but with increased intensity; and abnormal, or adventitious. Care should be taken to avoid confusing abnormal breath sounds from sounds produced by the movement of the stethoscope over the patient’s hair coat.
Pathophysiology
Breath sounds are produced by oscillations of solid respiratory tissues with rapid fluctuations in gas pressure. Breath sounds heard best over the central lung regions are described as bronchial; those heard best over the peripheral lung regions, as vesicular; and those heard best over the peripheral lung regions during increased ventilation or airway disease, as bronchovesicular. Due to laminar airflow in the terminal bronchioles and alveoli, air movement in these regions is inaudible.
Breath sounds that are normal but increased in intensity are associated with an increased rate and depth of breathing (Chapter 21) or from less attenuation of sound due to a thin thoracic wall (small and/or very thin animals).
Abnormal or adventitious breath sounds include crackles, wheezes, stridor, and stertor (Table 23-1). Crackles are discontinuous sounds of small airways (≤2 mm in diameter) heard best during inspiration. Although two different mechanisms are responsible for crackles (compression or collapse), clinically it is often difficult to differentiate these. Closure of these small airways occurs secondary to compression by interstitial pulmonary edema, pleural effusion, or with pulmonary fibrosis. Collapse occurs secondary to complete obstruction of these small airways. Fine crackles are produced by the sudden opening of multiple small airways (<2 mm in diameter). Coarse crackles are caused by air bubbling through fluid in larger small airways (>2 to <5 mm in diameter) such as occurs with bronchopneumonia, hemorrhage, or with severe pulmonary edema with flooding of the smaller airways. Wheezes, which are continuous sounds, are secondary to narrowing or partial obstruction of larger airways (> 5 mm in diameter and are usually heard best during expiration). Common causes of airway narrowing and obstruction are bronchitis with exudation and chronic obstructive pulmonary disease with airway collapse on expiration. An exception to this rule is wheezes or stridor associated with an extrathoracic obstructive pattern and an increased inspiratory effort (i.e., laryngeal paralysis). Stridor is generally produced by a narrowed larynx and is most often heard on inspiration or sometimes during forced expiration, while stertorous sounds are produced by the soft palate during inspiration when there is partial obstruction of the nasal and/or oral pharynx. “Friction rubs” are heard on inspiration and expiration when inflamed pleura exists; but these are rarely recognized in the veterinary patient.
TABLE 23-1. Classification of normal and abnormal breath sounds
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