However, this association has not been confirmed. 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. Wheezes can be classified as either high pitched or low pitched wheezes. 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. They result as a collapsed airway lumen gradually opens during inspiration or gradually closes during expiration. Wheezes are continuous musical tones that are most commonly heard at end inspiration or early expiration. They are significant as they imply either accumulation of fluid secretions or exudate within airways or inflammation and edema in the pulmonary tissue. Crackles are heard more commonly during inspiration than expiration. 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. 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. 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. Increased intensity may be associated with pulmonary consolidation.Ĭrackles are discontinuous, explosive, "popping" sounds that originate within the airways. They are highly variable in intensity depending on the species, ventilation, and body condition. These sounds may be absent or silent in the periphery of normal resting animals. 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. They are heard over the periphery of the lung field. Vesicular breath sounds consist of a quiet, wispy inspiratory phase followed by a short, almost silent expiratory phase. Increased intensity of bronchovesicular sounds is most often associated with increased ventilation or pulmonary consolidation. However, in sheep, goats, llamas, and alpacas, they may be heard throughout the full lung field and are often louder than tracheal breath sounds. They are normally heard over the hilar region in most resting animals and should be quieter than the tracheal breath sounds. 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.īronchovesicular breath sounds consist of a full inspiratory phase with a shortened and softer expiratory phase. Otherwise, bronchial sounds heard over the thorax suggest lung consolidation and pulmonary disease. They may be heard over the hilar region in normal animals that are breathing hard (i.e. Bronchial sounds are not normally heard over the thorax in resting animals. They are normally heard over the trachea and larynx. Thus, the sounds that are heard at the periphery of the lung are produced in more central (hilar) regions and are altered in intensity and tonal quality as they pass through pulmonary tissue to the periphery.īronchial breath sounds consist of a full inspiratory and expiratory phase with the inspiratory phase usually being louder. However, terminal airway and alveolar disease does modify the breath sounds heard at the surface by either increasing or decreasing the sound transmission through the diseased tissue. This is incorrect as the air velocity at this level is too slow (very large total cross sectional area) to produce significant turbulence and sound waves. It is a common misconception that air moving through terminal bronchioles (airways with a diameter <2 mm) and alveoli also contribute to breath sounds. Air flow velocity is primarily determined by pulmonary ventilation (*minute volume ® * velocity) and TOTAL cross sectional airway area (¯ area ® * velocity) at any given level in the lungs. Normal breath sound production is directly related to air flow velocity and airway lumen architecture. These vibrations are then transmitted through the lung tissue and thoracic wall to the surface where they may be heard readily with the aid of a stethescope. Breath sounds originate in the large airways where air velocity and turbulence induce vibrations in the airway walls. Breath sounds can be classified into two categories, either NORMAL or ABNORMAL (adventitious).
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