This article has multiple pages.
Basics
- A quiet environment is desirable as it makes it easier to listen to respiratory sounds.
- The patient should be in the proper position. Preferably in a sitting position, so that all the areas of chest are accessible for examination. However, the anterior areas can be examined even when the patient is lying down.
- Stethoscope should be preferably touching the patient’s bare skin. Auscultation through clothes should be avoided as far as possible. This is to avoid friction sounds that may cause confusion. If the patient's chest is hairy, then moistening that chest with warm water might be helpful.
- Always ensure patient comfort. Auscultation can easily be carried out 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 a 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!
- Is the intensity of breath sounds increased, normal, or decreased?
- Is the character of breath sounds normal or abnormal?
- Are there any abnormal or adventitious sounds?
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 sounds are produced in the alveoli. But they are not. The velocity of air in the alveoli is not significant enough to produce turbulance and audible sounds.
What is the character of the breath sound that is produced?
You will know if you have auscultated at the trachea. It is bronchial breath sound. But aren't we told that the 'normal' breath sound is vesicular? YES!
- The breath sound normally produced at the trachea is bronchial.
- The breath sound normally heard on the chest wall, respiratory areas, is vesicular.
The bronchial breath sounds produced at the major airways have to travel all across the tissues (through air in the bronchi, bronchioles, alveolar walls, etc) to reach the body surface from where they are auscultated.
While they are being transmitted through these tissues, some (high) frequencies of sound are absorbed (attenuated) and the character of the sound changes. This changed (attenuated) sound is termed vesicular breath sound.
If you remember this basic concept, we shall discuss about the genesis of abnormal sounds in each condition in subsequent pages of this article.
Normal Breath Sounds
Vesicular Breath Sounds
This is the normal breath sound and is heard over most of the lungs. 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.
It is compared in character to the rustling of dry leaves.
Listen to this audio of vesicular breath sounds:
The term vesicular breath sound was coined by Laennec, the inventor of the stethoscope. He named it so due to his belief that they were produced by air flowing through the alveoli. But it is not so. as we have learnt before in the previous page.
The mp3 audio clips used in this article can be downloaded from our downloads section. Please remember that these are for teaching-learning purposes only.
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