In one sentenceIn pneumonia, the most distinctive clue is bronchial breathing and increased voice transmission over the same region as the crackles.
- Consolidation transmits sound better: bronchial breathing, bronchophony, whispered pectoriloquy, egophony.
- Crackles are often focal or asymmetrical. Their number and timing change during the course of the illness.
- Secretion sounds may change after coughing. Bronchial breathing over consolidated lung usually persists.
Yes. Air spaces and airways filled with exudate produce crackles as they open.
Not the main change.
Yes. If the bronchus is open, solid lung carries sound without filtering it.
Bronchial breathing, crackles and increased voice transmission.
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?
You hear crackles over one region. Over the same region, the breath sound is higher-pitched and expiration is more prominent. This is bronchial breathing. When the patient speaks or whispers, the words are heard more clearly over that region.
Why does it sound like this?
Pneumonia changes two things at once. Crackles form as the affected peripheral airways and air spaces open. This is a change in the source. When inflammatory material replaces the air in the alveoli, transmission changes too. The high-pitched parts of tracheobronchial sound, and speech, reach the chest wall more easily.
Consolidated lung does not produce a new sound. As long as the bronchus stays open, it carries the existing central sound better.
Distinguishing clues
- Same site: Bronchial breathing and increased voice transmission carry diagnostic weight when they are over the same region as the crackles.
- Cough: Secretion sounds may change after coughing. Bronchial breathing usually persists.
- Symmetry: In a patient with signs of congestion, bilateral symmetrical basal crackles support a cardiac explanation. A focal cluster of crackles with bronchial breathing supports a local pulmonary process.
- Bronchial patency: If the bronchus of the consolidated region is blocked, you may hear reduced sound instead of bronchial breathing.
Pitfalls
- Crackles are neither constant nor specific to infection.
- If an effusion accompanies the pneumonia, you may find increased transmission over the consolidated lung and marked loss of sound over the fluid below it.
- Auscultation finds the abnormal region. Imaging and the clinical course determine the cause.
Next step
Arrange a chest X-ray or lung ultrasound, with clinical and laboratory assessment. Listen to the same region again during treatment. For the technique of the voice tests, see the Voice transmission tests and percussion lesson.
Try this pattern in a case
Going deeperresidents · specialists · numbers and sources
Crackles through the course of illness
In pneumonia, the number and timing of crackles change during the clinical course. Automated systems have measured the number and distribution of crackles in pneumonia. In 79% of patients with pneumonia, heart failure and interstitial fibrosis, crackle pitch rose through inspiration. The rise at each stage was about 40 Hz.
Spatial pattern
Multi-sensor images of breath sound distribution showed group differences between 20 patients with pneumonia, 20 patients with pleural effusion and healthy controls. This shows that the images hold spatial information linked to disease. The clinical context, however, decides what a single map means. Increased high-frequency content over consolidation does not identify pneumonia on its own.
Relation to ultrasound
In acute respiratory failure, lung ultrasound can show pleural fluid, consolidation, interstitial syndrome and pneumothorax with high accuracy. In critically ill patients, it may be better than auscultation for some structural abnormalities. The two methods answer different questions. Ultrasound reflects pleural and subpleural structure. Acoustic recording reflects airflow, airway calibre and transmission.
Squawks and childhood
Squawks have also been reported in pneumonia. In community-acquired pneumonia in children, a wireless stethoscope system was tested in a multicentre study across four hospitals.
See the reference list for sources.