In one sentenceAsthma causes widespread and variable airway narrowing. This is why wheezes come from many sites and change over time and with treatment.
- Typical finding: bilateral wheezes, mostly expiratory and often polyphonic.
- Variability is the most important clue. In a patient whose asthma is controlled, the chest may be clear.
- In a severe attack, loss of wheeze may not mean improvement. A silent chest is an alarm sign.
Yes. Narrowed bronchi vibrate with the flow and a new musical sound arises.
Yes, in a severe attack. Flow falls so far that even the wheeze goes quiet.
No clear change. Air trapping can make the sound a little weaker.
Widespread, expiratory, polyphonic wheezes. In a severe attack, a silent chest.
For the reasoning: Where does sound come from? · How does sound reach the chest wall? · How do adventitious sounds arise? · From sound to differential diagnosis
What do you hear?
During an attack you hear wheezes on both sides, mostly in expiration. Expiration is prolonged. If you hear several tones of different pitch at the same time, the wheeze is called polyphonic.
The finding does not stay the same. It changes during the day, with the depth of breathing and with treatment. In a patient whose asthma is controlled, the chest may be completely clear.
Why does it sound like this?
Smooth muscle contraction, mucosal oedema and inflammatory secretions narrow the bronchial lumen. The narrowed, flexible wall starts to vibrate as fast airflow passes through it. In expiration, the pressure inside the chest also compresses the airways from outside. This is why wheezes are heard mostly in expiration.
The narrowing is widespread, so many airways vibrate at the same time. This is why polyphony is common.
Distinguishing clues
- Variability: Wheezes that clear between attacks and shorten with treatment support asthma.
- Distribution: In asthma, wheezes are widespread. A monophonic wheeze that always stays at the same spot suggests a local obstruction (focal wheeze).
- Neck: If the sound is much louder over the neck than over the chest, and prominent in inspiration, think of the upper airway (stridor).
Pitfalls
- Loss of wheeze does not always mean improvement. In a patient who cannot speak and has increased work of breathing, a silent chest indicates severe obstruction.
- The intensity and pitch of a wheeze do not rise in direct proportion to the degree of obstruction.
- A clear chest does not exclude asthma. In controlled disease the examination may be normal.
A study of 120 adults included patients with controlled asthma and healthy controls (Topaloğlu et al., 2025). Digital stethoscope recordings showed measurable differences, even though conventional auscultation was normal and spirometry showed no obstruction. Classification performance was very high in the development cohort. It was lower in two external datasets but remained strong. Multicentre validation across devices and populations is needed before routine use.
Next step
In a stable patient, perform spirometry with a reversibility test. In a severe attack, first assess oxygenation, the ability to speak and the work of breathing. Listen again after treatment. Shorter wheezes support improved airflow. For a side-by-side reading, see the Asthma, COPD and local obstruction lesson.
Try this pattern in a case
Going deeperresidents · specialists · numbers and sources
How much of the cycle does the wheeze occupy?
The proportion of the respiratory cycle occupied by wheeze (Tw/Ttot) is a more consistent measure than pitch or intensity. In 20 patients with acute asthma, bronchodilator treatment lowered Tw/Ttot from a mean of 86% to 31%, and FEV₁ improved. In a monitoring study of 12 patients with wheeze, Tw/Ttot calculated from repeated sound segments was related to FEV₁ (r = 0.893). Even so, this relationship is not strong enough to predict an individual patient's FEV₁ precisely.
Changes the ear does not hear
F50 is the median frequency of the sound spectrum. In flow-standardised recordings, inspiratory chest wall F50 was 239 ± 19 Hz in stable asthma, 206 ± 14 Hz in healthy controls and 201 ± 21 Hz in COPD. During histamine challenge, the spectral changes differed by recording site and phase. Expiratory tracheal F50 showed a strong relationship with the spirometric change. Bronchial challenge can shift the spectrum before the change becomes clear to the ear.
What does polyphony count?
A polyphonic wheeze is consistent with more than one active source. However, the chest mixes sounds that come from different sites. Do not read the number of tones you hear as a count of vibrating airways. Read it as a clue that there are many sources.
Digital monitoring
A systematic review summarised candidate acoustic biomarkers in asthma. A study based on speech sounds reported associations with the change in FEV₁ during methacholine challenge. In the emergency department, wheeze was associated with a higher oxygen requirement. An AI-assisted home stethoscope was evaluated for monitoring attacks at home.
The role of a measure depends on its purpose. In a patient with known asthma, the night-time wheeze burden can be used for monitoring. For the same measure to work as a diagnostic test, it must be tested in patients whose wheeze has other causes.
See the reference list for sources.