Low-pitched wheeze (CORSA) · sonorous rhonchus
In one sentenceA low-pitched continuous sound. In the CORSA definition it is below 300 Hz and longer than 100 ms. It is associated with secretions or narrowing in large airways.
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?
A low-pitched, continuous sound. When it is heard as a regular tone, it comes close to a low-pitched wheeze. When secretions are present, it sounds rougher and more irregular, and it may change after a cough.
Where is it heard?
Over the large airways, regional or widespread.
What causes it?
A rhonchus does not depend on a single mechanism. A regular, low-pitched rhonchus may arise from oscillation of the wall of a large or central airway. It belongs to the same family as the low-pitched wheeze. A rougher, more irregular sound suggests an airway with mobile secretions in its lumen. A change with coughing shows a mobile component, but it does not prove the mechanism on its own.
Quantitative criteria
- CORSA definition: a low-pitched wheeze containing rapidly damping periodic waveforms, longer than 100 ms and below 300 Hz (Sovijärvi et al., 2000).
- On the spectrogram, a low-frequency fundamental tone appears with strong, evenly spaced harmonic lines above it. In this site's example, the pitch falls from about 150 Hz to 105 Hz through expiration. The strong harmonics set a rhonchus apart from a low-pitched wheeze, whose waveform is close to a sine wave. In sound from secretions, the lines are more irregular. Older English texts call this low-pitched musical sound a sonorous rhonchus, and the high-pitched one (the wheeze) a sibilant rhonchus.
- The 2016 ERS task force listed low-pitched wheezes and rhonchi among the categories with poor inter-observer agreement. It stressed that the rhonchus should not be reduced to a wheeze defined by frequency.
Clinical meaning
A rhonchus is most useful as a sign of a changeable large airway process. It is common in diseases rich in secretions, such as bronchiectasis. A change with coughing or airway clearance supports mobile secretions or a change in large airway calibre. If it persists at the same site, think of a fixed narrowing or another fixed source. The term has been used inconsistently in the past, so do not write only "rhonchus" in your notes. Also record the pitch, phase, site and response to coughing.
Sounds it can be confused with
A low-pitched wheeze and a rhonchus belong to the same family, and the boundary between them is not sharp. Next to the name of the sound, record the pitch and the response to coughing.
Coarse crackles are separate bursts. A rhonchus is continuous.
When you hear a rhonchus, ask the patient to cough and listen again at the same point. This simple manoeuvre can change the meaning of the finding.
See the reference list for sources.