Table 12-1.

Identification and clinical significance of breath sounds

Sounds	Acoustic characteristics	Significance and examples
Normal breath sounds	Soft blowing sounds, longer and louder on inspiration than on expiration, audible over the trachea and lungs.	Normal respiratory tract
Increased audibility of breath sounds	Mild to moderate increase in loudness of breath sounds audible on inspiration and expiration over the trachea and lungs.	Any factor that increases respiratory rate or depth of respirations, including fever, excitement, exercise, high environmental temperatures, lung disease. Harsh loud breath sounds are audible over the lungs with any disease resulting in collapse or filling of alveoli and leaving bronchial lumina open; pulmonary consolidation and atelectasis.
Decreased audibility of breath sounds	Decreased audibility of breath sounds on inspiration and/or expiration over the lungs.	Obese animal, pleural effusion, space-occupying mass of lung or pleural cavity, pneumothorax, diaphragmatic hernia, occlusive (lung) airway disease as in bronchial lumen filled with exudate.
Crackles	Short duration, interrupted, nonmusical breath sounds. Coarse crackles are loud and most commonly heard over large airways in animals with pulmonary disease and may be heard during inspiration and expiration. Fine crackles are of short duration, less intense, and higher pitched.	Coarse crackles are caused by air bubbling through, and causing vibrations in, secretions in large airways. Fine crackles are caused by sudden explosive popping open of a series of airways closed during expiration. May be detected in early or late inspiration. Suggest the presence of secretions and exudate in airways and edematous bronchial mucosa as in exudative bronchopneumonia, tracheobronchitis, aspiration pneumonia, and obstructive pulmonary disease. Loud crackles may be audible in animals with interstitial pulmonary emphysema.
Wheezes	Continuous musical-type squeaking and whistling sounds audible over the lungs.	Narrowing of large airways; expiratory polyphonic wheezing common in equine reactive airway disease bronchopneumonia, any species; inspiratory monophonic wheezing occurs when upper extrathoracic airways are constricted, such as in laryngeal disease.
Pleuritic friction sounds	“Sandpaper-like” sound; grating; sound close to the surface; on inspiration and expiration; tend to be jerky and not influenced by coughing.	Pleuritis; diminish or disappear with pleural effusion.
Stridor	A harsh, high-pitched sound on inspiration audible with or without stethoscope over the larynx and trachea.	Obstruction of upper airways, especially the larynx (as a result of edema, laryngitis, paralysis of vocal cord); prime example is calf diphtheria or retropharyngeal abscessation in strangles in horses or tracheal collapse in horses.
Stertor	Snoring sound (low-pitched, coarse, and raspy) audible without a stethoscope on inspiration and expiration over the pharyngeal and laryngeal areas.	Partial obstruction of the upper respiratory tract, commonly attributable to abnormalities of soft palate and nasopharynx.
Expiratory grunting	Loud grunting on expiration, which is usually forced against a closed glottis with sudden release, audible on auscultation of the thorax, over the trachea, and often audible without the aid of a stethoscope.	Severe diffuse pulmonary emphysema; pleuropneumonia and pericarditis; extensive consolidation; in acute pleurisy and peritonitis; a groan indicating pain may occur.
Transmitted upper respiratory tract breath sounds	Abnormal tracheal breath sounds (crackles and wheezes) audible by auscultation over the extrathoracic trachea during inspiration.	Indicates presence of abnormalities of the upper respiratory tract (larynx, nasopharynx, nasal cavities, and upper trachea), resulting in accumulation of respiratory secretions causing constriction of airways. Laryngitis is an excellent example.
Extraneous sounds heard on auscultation of respiratory tract
Crepitations in subcutaneous tissues	Loud superficial crackling sounds induced by movement of stethoscope over the skin.	Subcutaneous emphysema from pulmonary emphysema in cattle; trauma to any part of respiratory tract that results in penetration of airway, allowing accumulation of air subcutaneously; gas-forming bacteria in subcutaneous tissues.
Peristaltic sounds	Gurgling, grating, rumbling, squishing sounds audible over the lungs.	Gastrointestinal sounds transmitted from the abdomen: ruminal sounds in cattle; stomach and intestinal sounds in horse. Does not indicate diaphragmatic hernia unless other evidence such as an absence of breath sounds is present.