In one sentenceIn COPD the chest is quiet and expiration is long. The main task is to know the patient's familiar baseline and to catch any new finding added to it.
- Baseline: diminished breath sounds and prolonged expiration. Expiratory wheezes and early inspiratory crackles may accompany them.
- Part of the quietness is low airflow. Ask the patient to breathe in deeply through an open mouth, then listen again.
- A new pattern (basal crackles, focal bronchial breathing, loss of sound on one side) suggests another process.
Yes. Airways compressed from outside during expiration can vibrate and produce a wheeze. Airways that open at the start of inspiration can produce early crackles.
Yes. Flow is low, so the sound is produced weakly.
Yes. Hyperinflated lung filters the sound more.
Diminished breath sounds, prolonged expiration, expiratory wheeze, early inspiratory crackles.
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?
Breath sounds are diminished on both sides and expiration is prolonged. During an exacerbation, expiratory wheezes are added. A few coarse crackles may be heard right at the start of inspiration.
Why does it sound like this?
The patient breathes with low airflow. Sound grows stronger with airflow, so when airflow falls, the sound falls too. Much of the quiet chest on routine examination is this low airflow.
Early inspiratory crackles come from airways that open at the start of inspiration. These airways reach their opening threshold under different mechanical conditions from the airways that open at the end of inspiration. This is why early crackles are linked to obstructive disease, and late crackles to fibrosis and congestion.
Distinguishing clues
- Check the airflow: If the sound clearly increases with a deep breath, part of the quietness is low airflow.
- Timing: A few early inspiratory crackles fit the COPD baseline. Late inspiratory, bilateral basal and numerous crackles suggest another process.
- Read the whole picture: Assess background intensity, prolonged expiration, wheezes, crackles and regional asymmetry together.
- Previous examination: The most valuable reference is the patient's own earlier findings.
Pitfalls
- Early inspiratory crackles raise the suspicion of COPD but do not establish the diagnosis. Their positive predictive values are low.
- A new finding is easily missed in a quiet chest. At every examination, compare the two sides at symmetrical points.
- In flow-standardised spectra, stable asthma differs clearly at group level. COPD, however, does not separate clearly from healthy lungs. There are no device-independent clinical thresholds yet.
A cohort study (Topaloğlu et al., 2026) included 235 adults and 1,403 posterior chest recordings from healthy people, patients with stable COPD and patients with a COPD exacerbation. Four indices were examined: median respiratory frequency (MRF), long-term energy index (LTEI), subharmonic index (SubH) and harmonicity deviation index (HDI). MRF, SubH and HDI differed significantly between the groups. The multivariable separation was significant but small, and the overlap was marked. This is a proof of concept.
Next step
If a new pattern has appeared, separate it from the patient's known baseline. Bilateral basal crackles with oedema suggest congestion. Focal bronchial breathing with fever suggests pneumonia. Sudden loss of sound on one side suggests a pneumothorax or a mucus plug. For a step-by-step example, see the From sound to differential diagnosis lesson.
Try this pattern in a case
Going deeperresidents · specialists · numbers and sources
How much of the quiet chest is airflow?
In recordings made at standardised airflow, sound intensity in patients with emphysema may show no clear reduction compared with healthy people. This suggests that part of the quiet chest on routine examination is the low airflow itself.
What did computer analysis find?
A systematic review summarised computerised breath sound studies in COPD. The most consistent findings were expiratory wheezes and inspiratory coarse crackles. Methods and recording conditions were heterogeneous. In flow-standardised spectra, stable asthma separated clearly from COPD and from healthy people at group level. The separation between COPD and healthy people was weaker (inspiratory F50: asthma 239 ± 19 Hz, controls 206 ± 14 Hz, COPD 201 ± 21 Hz).
Early crackles: the numbers
A community study examined 3,684 adults aged 40 years or over, and 204 of them met the definition of COPD. Bilateral early inspiratory crackles were much more strongly associated with COPD than bilateral coarse crackles. The adjusted odds ratios for the two observers were 6.88 and 7.63. However, the positive predictive value for COPD was only about 23%. Timing showed better inter-observer agreement than the fine/coarse distinction.
Regional heterogeneity
A study compared 46 men with stable COPD with 40 healthy male smokers. Asynchrony scores measure how far the timing of sound differs between regions. Right–left and upper–lower asynchrony scores were higher in COPD. The scores showed limited relationships with lung function. They were related to the heterogeneity of emphysematous lesions on CT. These scores describe regional heterogeneity. They do not replace spirometry or a measure of emphysema severity.
Mixed patterns
COPD with heart failure can appear as new dependent crackles in a quiet, hyperinflated chest. In combined pulmonary fibrosis and emphysema, late basal crackles can occur alongside reduced sound intensity in the upper zones. In the spectrogram of a real COPD recording selected from the ICBHI database, the wheeze appears as a continuous band.
See the reference list for sources.