Vesicular breath sounds (VBS) are the soft, low-pitched sounds heard over the majority of a healthy person’s lung fields during breathing. These sounds represent the normal acoustic baseline for healthy respiration in the peripheral lung tissue. When a healthcare provider uses a stethoscope to listen to the chest, VBS are the most common and widespread sounds detected. Their presence confirms that air is moving freely and quietly into the small, air-filled structures of the lung periphery.
The Physiological Origin of Vesicular Sounds
The sound that becomes the vesicular breath sound actually originates in the larger, more central airways, such as the lobar and segmental bronchi. Airflow in these larger tubes is turbulent, which is the physical condition necessary to generate an audible sound. The air then moves into the smaller terminal bronchioles and eventually into the alveoli, which are the tiny air sacs responsible for gas exchange.
As this sound travels from the central bronchi to the outer chest wall, it passes through a significant amount of healthy, air-filled lung tissue. This dense but porous tissue acts as a natural acoustic filter, dampening and softening the turbulent sound created higher up in the respiratory tree. The laminar, or smooth, flow of air within the alveoli themselves does not produce any sound, which is why the sound reaching the stethoscope is so quiet and diffuse.
The inspiratory component of the sound is generated by the turbulent entry of air into the lobar and segmental airways. The expiratory sound, which is much fainter, originates from the air moving back out of the more central airways. Because expiration is a passive process during quiet breathing, the airflow turbulence is significantly reduced, causing the sound to rapidly fade.
Defining the Acoustic Characteristics
Vesicular breath sounds are distinctively soft and low-pitched, often described as having a gentle rustling or breezy quality. Their frequency is typically below 200 Hertz, classifying them as low-pitched compared to sounds heard over the central chest. The most distinguishing feature of a VBS is the timing difference between the inspiratory and expiratory phases.
The inspiratory phase is noticeably longer and louder than the expiratory phase, often exhibiting an approximate duration ratio of 3:1 or 4:1. Inspiration is the active process of drawing air in, which creates a more forceful and audible sound. The expiratory phase is much shorter, softer, and fades quickly, sometimes only being heard for the first third of the exhalation.
Crucially, there is typically no distinct pause or gap between the end of the inspiratory sound and the beginning of the expiratory sound. The transition is smooth and continuous, reflecting the uninterrupted flow of air throughout the respiratory cycle in the small airways.
Comparing Vesicular Sounds to Other Normal Breath Sounds
Vesicular sounds are one of three types of normal breath sounds, providing a contrast to bronchial and bronchovesicular sounds. Bronchial sounds are the loudest and highest-pitched of the three, possessing a harsh, hollow quality. Unlike VBS, bronchial sounds have an expiratory phase that is equal to or longer than the inspiratory phase, and there is a short but noticeable silent gap between the two phases.
Bronchial sounds are normally heard only over the trachea and the larynx, areas where the stethoscope is directly placed over the largest airways with minimal filtering lung tissue. Bronchovesicular sounds represent an intermediate sound quality, a blend between the soft VBS and the harsh bronchial sounds. These intermediate sounds have a mid-range pitch and intensity, with the inspiratory and expiratory phases being roughly equal in duration.
Bronchovesicular sounds are typically heard over the mainstem bronchi, such as centrally between the shoulder blades or near the upper sternum. Vesicular sounds, by contrast, are the expected sound everywhere else, covering the vast peripheral fields of the lungs.