Auscultation of breath sounds is one of the most essential and useful clinical techniques for evaluating a patient’s respiratory pathology. You will find the description of various respiratory auscultation findings with audio examples in this article.
Please explore all the audio examples included in this page. Please use headphones for a stethoscope-like experience.
I have used a Littmann 3200 electronic stethoscope for recording most of the breath sounds.
Let us start by looking at some requirements for effective auscultation:
- A quiet environment is desirable as it makes it easier to listen to breath sounds.
- The patient should be in the proper position during auscultation. Preferably in a sitting position, so that all the areas of the chest are accessible for examination. However, we can examine the anterior regions even when the patient is lying down.
- The stethoscope should be preferably touching the patient’s bare skin. We should avoid auscultation through clothes as far as possible. This avoidance is to prevent friction sounds that may confuse. If the patient’s chest is hairy, then moistening that chest with warm water might be helpful.
- Always ensure patient comfort. We can easily carry out auscultation while the patient is breathing normally. Requests for deep breathing should be as infrequent as possible, as they can tire the patient. Remember that we tend to examine the respiratory system of a patient in great detail only when we suspect that he has a respiratory disease. It will be a paradox if we expect that patient to breathe harder for a long time!
While performing auscultation, we need to answer THREE simple questions:
- Is the intensity of breath sounds high, normal, or low?
- Is the character of breath sounds normal or abnormal?
- Are there any abnormal or adventitious sounds?
Mechanism of Breath Sounds Production
How are the breath sounds produced?
Breath sounds are produced in the major airways – trachea and major bronchi.
It is a common misconception that these alveoli produce these sounds. But they do not. The velocity of air in the alveoli is not significant enough to create turbulence and audible sounds on auscultation.
What is the character of the produced breath sound?
You will know if you have auscultated at the trachea. It is most certainly bronchial breath sound. But aren’t we told that the ‘normal’ breath sound is vesicular? Yes, we are.
- The breath sound normally produced at the trachea is bronchial.
- The breath sound normally heard on the chest wall, over the respiratory areas, is vesicular.
Now, here is the explanation –
The bronchial breath sounds produced at the major airways have to travel all across the tissues (through the air in the bronchi, bronchioles, alveolar walls, etc.) to reach the body surface from where we auscultate them.
While they are conducting through these tissues, some (high) frequencies of sound are absorbed (attenuated) and the character of the sound changes. We call this changed (attenuated) sound – vesicular breath sound.
If you remember this basic concept, we shall discuss the genesis of abnormal sounds in each condition in the subsequent sections of this article.
Normal Breath Sounds
Vesicular Breath Sounds
Vesicular breath sound is the normal breath sound, heard over most of the lung fields during auscultation. It is soft and low-pitched (low frequency), and the expiratory phase is shorter than the inspiratory phase. The expiratory phase is shorter because the breath sounds produced in the latter 2/3 of expiration are mainly composed of high-pitched sounds which are filtered out.
Vesicular breath sounds are similar in character to the rustling of dry leaves.
Laennec, the inventor of the stethoscope, coined the term vesicular breath sound. He named it so due to his belief that the air flowing through the alveoli produced these sounds. This term, however, is a misnomer, as we have discussed above.
Abnormal Breath Sounds
Absent or Decreased Breath Sounds
Here are some common causes of absent or decreased breath sounds:
- Asthma: decreased breath sounds.
- Atelectasis (collapse): If the bronchial obstruction persists, breath sounds will become absent. However, in atelectasis of the upper lobes, sounds produced in the trachea may be audible as the trachea is pulled towards the side of atelectasis.
- Fibrosis: decreased breath sounds, unless fibrosis occurs in upper lobes when adjacent tracheal sounds may be audible.
- Emphysema: decreased breath sounds.
- Pleural Effusion: reduced or absent breath sounds. We hear bronchial breath sounds at the upper level of fluid if the effusion is large.
- Pneumothorax: decreased or absent breath sounds.
- ARDS: decreased breath sounds in the late stages.
Vesicular breath sounds may also be softer if the patient is
- very muscular
Listen to the audio of a diminished vesicular breath sound above.
Harsh Vesicular Breath Sounds
Vesicular breath sounds may be harsher and slightly longer if there is
- rapid deep ventilation (e.g. post-exercise)
- in persons with thinner chest walls.
Listen to the audio of harsh vesicular breath sound above.
Bronchovesicular Breath Sounds
These are breath sounds of moderate intensity and pitch.
The inspiratory and expiratory sounds are equal in length.
They are best heard during auscultation
- in the 1st and 2nd intercostal space (anterior chest)
- between the scapulae (posterior chest) – i.e., over the mainstem bronchi.
Listen to the audio of bronchovesicular breath sound:
Bronchial Breath Sounds
Bronchial breath sounds are usually loud, high-pitched and sound close to the stethoscope.
The character of the sound is HOLLOW. There is a gap between the inspiratory and expiratory phases of respiration, and the expiratory sounds are equal in length to inspiratory sounds.
If these sounds are heard anywhere other than over the manubrium, they indicate an abnormality (we can also hear these sounds over the trachea, but trachea is NOT a standard area for auscultation).
- The upper level of pleural effusion
- Upper lobe fibrosis
- Upper lobe collapse
- bronchopleural fistula
NOTE: The best way to recognise bronchial breathing while performing auscultation is to look for the hollow character of the sound. Then, confirm that it is indeed bronchial breathing by looking for the gap between inspiration and expiration, and the equality of these two phases of respiration.
Do not try to identify the bronchial sound by looking for the gap or equality of phases! You will spend a lot of time and also miss bronchial often. Look for the hollow character. You will rarely go wrong.
Crackles are discontinuous, brief sounds heard more commonly on inspiration.
Synonyms: crepitations; rales.
Crackles can be classified as,
- fine (high pitched, very brief) or
- coarse (low pitched, less brief).
Two common mechanisms can produce crackles:
- When previously closed small airways suddenly open. To see how this can happen, gently close your wet lips and open them suddenly. You will hear a ‘plop’. We can hear fine crackles when this occurs in the terminal bronchioles.
- When air bubbles pass through secretions, as in pulmonary oedema and resolving pneumonia.
Listen to the audio of crackles above.
Causes of crackles:
- pulmonary oedema
- chronic bronchitis
- interstitial lung disease
Wheezes are continuous, high pitched, musical sounds usually heard on expiration.
They are produced when air flows through airways narrowed by secretions, foreign bodies, or obstructive lesions. The proportion of the respiratory cycle occupied by the wheeze roughly corresponds to the degree of airway obstruction.
Wheezes resemble the sound of a violin playing.
There are two types of wheezes:
- monophonic (suggesting obstruction of one airway, often a malignant tumour compressing on a bronchiole) or
- polyphonic (indicating generalised obstruction of airways, as in asthma).
Listen to the audio of wheezes above.
- chronic bronchitis
- acute bronchitis
- sometimes in pulmonary oedema
The presence of expiratory wheezing signifies that the patient’s peak expiratory flow rate is less than 50% of normal, and due to dynamic bronchoconstriction as in bronchial asthma.
Wheezing, heard during inspiration, most often signifies a more static bronchoconstriction usually caused by tumours, foreign bodies or fibrosis. These causes are especially likely if they are monophonic wheezes. Monophonic wheezes are generally sinister in their implication. They are usually heard when a single or a small number of bronchioles is/are compressed, typically seen in patients bronchogenic carcinoma.
The location on the chest where the wheezes are heard also hints at the cause. Generalized bronchoconstriction, as in asthma, results in wheezes audible in all respiratory areas, when it is also typically polyphonic.
The term ‘rhonchi’ (singular – rhonchus) is also sometimes used as a synonym for wheezes. But they also have a different description, as below.
Rhonchi are low pitched, continuous sounds that are similar to wheezes. They usually imply obstruction of a slightly larger airway by secretions. They are often also described as the “coarse rattling sound somewhat like snoring, usually caused by secretion in bronchial airways”. Rhonchi is the plural form of the singular word ‘rhonchus’.
However, we also use this term as a synonym for wheezes.
Squawks are short inspiratory wheezes. They are almost always associated with crackles. These are brief “squeaky” sounds that are also sometimes referred to as squeaks.
- hypersensitivity pneumonitis
- interstitial fibrosis
Rales is an obsolete term, used as a synonym for crackles, especially coarse crackles. We pronounce it as ‘raahls’.
Stridor is a noisy inspiratory sound heard loudest over the trachea during inspiration. This sound is indicative of an obstructed trachea or larynx and is, therefore, a medical emergency that demands immediate attention.
Pleural rubs are creaking sounds produced when the pleural surfaces are inflamed or roughened and rub against each other. Friction between the two pleural surfaces produces this sound. They may be discontinuous or continuous sounds. They can usually be localised to a particular place on the chest wall and heard during both the inspiratory and expiratory phases.
- Pleural effusion, sometimes, above the level of the fluid
Abnormal Vocal Sounds (Resonance)
The patient is asked to speak a word, usually ’99’ to produce resonance.
NORMAL: As the vocal sound gets transmitted from the larynx down through the trachea, the bronchi, the alveoli and then to the chest wall, the sound becomes less distinct and much softer than when heard directly.
Bronchophony occurs over areas of the lung in which the alveoli are filled with fluid or replaced by solid tissue. It can be heard in consolidation due to pneumonia, collapse, or tumours. When bronchophony is present, the sound is very clear and loud.
Listen to the audio of bronchophony: Patient is telling ‘ninety-nine’ above.
Egophony (also aegophony) is an increased resonance of voice sounds heard when auscultating the lungs. This is often caused by the compressed lung tissue due to pleural effusion, or consolidation due to pulmonary infection (pneumonia) or a lung tumour.
While performing auscultation on the chest with a stethoscope, the patient is asked to say ‘e’. If we hear it like the sound of ‘a’, then the patient has egophony. The sound here assumes a ‘nasal quality’. To demonstrate this, try closing your nose with your fingers and then say ‘e’. You will hear ‘a’.
It is due to better transmission of high-frequency sounds across the abnormal tissues mentioned above, with lower frequencies being filtered out. It results in a high-pitched nasal or bleating quality in the affected person’s voice when auscultated over the affected area.
Listen to the audio of egophony: Patient is telling ‘eee’ above.
Note the bronchial breath sounds and end-inspiratory crackles in the recording:
Note the fine crackles heard in this recording from a patient with pulmonary oedema.
These sounds represent fluid in the alveoli.
Dr Shashikiran Umakanth (MBBS, MD, FRCP Edin.) is Professor & Head of Internal Medicine at MMMC, Manipal Academy of Higher Education, and has clinical responsibilities at the Department of Medicine, Dr TMA Pai Hospital, Udupi, Karnataka, India.