Lung Sound Biography
(Source google.com)
Lung sounds, breath sounds, or
Respiratory sounds refer to the specific sounds generated by the movement of
air through the respiratory system. These may be easily audible or identified
through auscultation of the respiratory system through the lung fields. with a
stethoscope. These include normal breath sounds and adventitious or
"added" sounds such as crackles, wheezes, pleural friction rubs,
stertor and stridor. Pectoriloquy, egophony and
bronchophony are a tests of auscultation. For example, in whispered
pectoriloquy the patient is asked to whisper - typically a two syllable number
as the clinician listens over the lung fields. The whisper is not normally
heard over the lungs, but if heard may be indicative of pulmonary consolidation
in that area. This is because sound travels differently through denser (fluid
or solid) media than the air that should normally be predominant in lung
tissue. Description and classification of the sounds usually involves
auscultation of the inspiratory and expiratory phases of the breath cycle,
noting both the pitch (typically described as low, medium or high) and
intensity (soft, medium, loud or very loud) of the sounds heard.
"Rhonchi" and "rales" are obsolete terminology whose use in
the literature has been variable. The terms wheeze and crepitation have
replaced them.
Breath sounds can be classified
into two categories, either NORMAL or ABNORMAL (adventitious). Breath sounds originate in the large airways
where air velocity and turbulence induce vibrations in the airway walls. 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.
Normal breath sound production is directly related to air flow velocity
and airway lumen architecture. Air flow
velocity is primarily determined by pulmonary ventilation and TOTAL cross sectional airway area at any given
level in the lungs. It is a common
misconception that air moving through terminal bronchioles (airways with a diameter
<2 mm) and alveoli also contribute to breath sounds. 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.
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.
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.
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 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 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.
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