Normal Breath Sounds
Bronchial Sounds
Bronchial breath sounds consist of a full inspiratory and expiratory phase with the inspiratory phase usually being louder. They are normally heard over the trachea and larynx. Bronchial sounds are not normally heard over the thorax in resting animals. They may be heard over the hilar region in normal animals that are breathing hard (i.e. after exercise). Otherwise, bronchial sounds heard over the thorax suggest lung consolidation and pulmonary disease. Pulmonary consolidation results in improved transmission of breath sounds originating in the trachea and primary bronchi that are then heard at increased intensity over the thorax.
Bronchovesicular Sounds
Bronchovesicular breath sounds consist of a full inspiratory phase with a shortened and softer expiratory phase. They are normally heard over the hilar region in most resting animals and should be quieter than the tracheal breath sounds. However, in sheep, goats, llamas, and alpacas, they may be heard throughout the full lung field and are often louder than tracheal breath sounds. Increased intensity of bronchovesicular sounds is most often associated with increased ventilation or pulmonary consolidation.
Vesicular Sounds
Vesicular breath sounds consist of a quiet, wispy inspiratory phase followed by a short, almost silent expiratory phase. They are heard over the periphery of the lung field. As stated earlier, these sounds are NOT produced by air moving through the terminal bronchioles and alveoli but rather are the result of attenuation of breath sounds produced in the bronchi at the hilar region of the lungs. These sounds may be absent or silent in the periphery of normal resting animals. They are highly variable in intensity depending on the species, ventilation, and body condition. Increased intensity may be associated with pulmonary consolidation.
Abnormal Breath Sounds
Crackles
Crackles are discontinuous, explosive, "popping" sounds that originate within the airways. They are heard when an obstructed airway suddenly opens and the pressures on either side of the obstruction suddenly equilibrates resulting in transient, distinct vibrations in the airway wall. The dynamic airway obstruction can be caused by either accumulation of secretions within the airway lumen or by airway collapse caused by pressure from inflammation or edema in surrounding pulmonary tissue. Crackles can be heard during inspiration when intrathoracic negative pressure results in opening of the airways or on expiration when thoracic positive pressure forces collapsed or blocked airways open. Crackles are heard more commonly during inspiration than expiration. They are significant as they imply either accumulation of fluid secretions or exudate within airways or inflammation and edema in the pulmonary tissue.
Wheezes
Wheezes are continuous musical tones that are most commonly heard at end inspiration or early expiration. They result as a collapsed airway lumen gradually opens during inspiration or gradually closes during expiration. As the airway lumen becomes smaller, the air flow velocity increases resulting in harmonic vibration of the airway wall and thus the musical tonal quality. Wheezes can be classified as either high pitched or low pitched wheezes. It is often inferred that high pitch wheezes are associated with disease of the small airways and low pitch wheezes are associated with disease of larger airways. However, this association has not been confirmed. Wheezes may be monophonic (a single pitch and tonal quality heard over an isolated area) or polyphonic (multiple pitches and tones heard over a variable area of the lung). Wheezes are significant as they imply decreased airway lumen diameter either due to thickening of reactive airway walls or collapse of airways due to pressure from surrounding pulmonary disease.
Stridor
Stridor are intense continuous monophonic wheezes heard loudest over extrathoracic airways. They tend to be accentuated during inspiration when extrathoracic airways collapse due to lower internal lumen pressure. They can often be heard without the aid of a stethoscope. Careful auscultation with a stethoscope can usually identify an area of maximum intensity that is associated with the airway obstruction. This is typically either at the larynx or at the thoracic inlet. These extrathoracic sounds are often referred down the airways and can often be heard over the thorax and are often mistaken as pulmonary wheezes. Stridor is significant and indicates upper airway obstruction.
Stertor
Stertor is a poorly defined and inconsistently used term to describe harsh discontinuous crackling sounds heard over the larynx or trachea. It is also described as a sonorous snoring sound heard over extrathoracic airways. Stertor does not have the musical quality of stridor. Stertor is significant as it is suggestive of accumulation of secretions within extrathoracic airways.
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