Normal breath sound
In one sentenceThe soft, non-musical, broadband background sound over the peripheral lung fields.
Listen to the same sound in another patient. Breathing rate, chest wall, the pitch of the sound and the number of adventitious sounds vary within realistic limits.
What does it sound like?
Heard throughout inspiration. Only the first part of expiration is heard, and it fades quickly. Low-pitched, with a rustling quality.
Where is it heard?
Most of the peripheral areas of the chest wall.
What causes it?
The sound arises in the fast, irregular flow of the large airways. As it passes through aerated lung, its high-pitched parts are filtered out. A soft, low-pitched rustle reaches the chest wall. The small airways add almost nothing to this sound.
Quantitative criteria
- Under controlled flow, the inspiratory chest wall sound is about twice the expiratory sound (1.99–2.43 times). In the tracheal sound this phase difference is not marked.
- In healthy adults, the high-frequency slope is about 13–15 dB/octave during inspiration.
- Intensity rises with flow. In one study, the mean exponent of the flow–sound relationship was 1.66.
Clinical meaning
This is the reference sound. Its intensity depends strongly on flow. In a patient who breathes shallowly, "diminished sounds" may not mean disease. Compare right and left at symmetrical points, with breaths of similar depth.
Sounds it can be confused with
Shallow breathing, a thick chest wall or poor stethoscope contact weakens the vesicular sound. Ask the patient to breathe deeply and listen again.
If expiration is clearly prolonged and the high-frequency content of the sound has increased, think of a bronchovesicular quality.
Ask the patient to breathe through an open mouth, a little more deeply than normal. As flow rises, the sound becomes louder.
See the reference list for sources.