Physical examnination: Vesicular breath sounds

Vesicular breath sound production

Classically the lung sounds were thought to be produced by the vibrations of the vocal cords and the proximal airways set in by the inspiratory movement of air, which is attenuated and conducted to the chest wall and the auscultating stethoscope by the normal air filled sacs called alveoli/acinus. The normal breath sounds were initially thought to be produced in the terminal air filled alveoli, and was called Vesicular sounds (Vesicle = small vessels). Present view is that the terminal airways including acinus are silent due to the laminar flow and low velocity of airflow,and breath sounds are solely producd by the vibrations of the proximal airways. As the vibrations of taut vocal cord can produce harmonics of both high and low pitches, and the normal vesicular breath sound is low pitched with a frequency of 16-200HZ, further supports the earlier proposed mechanism of attenuation and conduction of sounds by the terminal air spaces.

Definition of vesicular breath sounds

ATS definition of vesicular breath sound -- VBS is a low pitched rustling sound with a high intensity inspiratory phase which is continuous with a less intense and shorter expiratory phase, which normally extends to less than one third of inspiratory phase.

Now look at the first part of the diagram for the possible site of origin of each component of vesicular breath sound.

Look at the second part of the diagram for diagrammatic representation of normal vesicular breath sound (inverted and mirror image for better understanding).

Causes for decreased intensity of normal vescular breath sound.
1. Pleural effusion (Separation of conducting units from chest wall)
2. Pleural thickening (-do-)
3. Collapsed lung with occluded bronchus (Loss of conducting pathways)
4. Emphysema (Loss of laminar flow and low velocity airflow due to distended acinus)
5. Bronchial asthma (occlusion of conducting airways)
6. Thick chest wall (eg;Obesity)(separation of steth from the area of activity” lung”).

References

1. Kraman,SS: Vesicular(normal) lung sounds:How are they made,where do they come from,and what do they man?; Semi. In Resp Med 6:183,1985.
2. Forgacs,P: The functional basis of pulmonary sounds, Chest 73:399,1978.