Pulmonary auscultation, listening to a patient’s lungs with a stethoscope, is a foundational technique in medical diagnosis. This non-invasive examination provides valuable information about the airways and surrounding lung tissue. Clinicians categorize the sounds heard into distinct types based on their acoustic properties, such as pitch and intensity, and the specific anatomical location where they are heard. Understanding these breath sounds is crucial for distinguishing between a healthy and diseased respiratory system.
Characteristics of Bronchovesicular Sounds
Bronchovesicular (BV) sounds blend the qualities of the hollow, high-pitched bronchial sounds and the softer, lower-pitched vesicular sounds. These sounds possess a moderate intensity and a medium pitch, making them distinct from the very loud sounds over the trachea or the quiet sounds heard over the lung periphery. The most defining feature of BV sounds is the ratio of their inspiratory and expiratory phases.
In a normal BV sound, the duration of inspiration is approximately equal to the duration of expiration, resulting in an Inspiration-to-Expiration (I:E) ratio of about 1:1. The BV sound is continuous, unlike bronchial sounds (prolonged expiration) or vesicular sounds (prolonged inspiration), and lacks a noticeable pause between the two phases. The physiological origin is turbulent airflow moving through the larger airways. The sound waves are partially filtered by the surrounding lung tissue, preventing the sound from being as harsh as a pure bronchial sound, yet keeping it louder than the distant vesicular sound.
Normal Anatomical Placement
Bronchovesicular sounds are considered a normal finding only when heard directly over the central, larger airways. Their typical location is highly specific because they reflect the transitional area where the main bronchi begin to branch into smaller tubes.
Anteriorly, a clinician normally hears these sounds over the mid-chest, specifically in the first and second intercostal spaces adjacent to the sternum. This placement corresponds to the underlying location of the mainstem bronchi. Posteriorly, the normal placement for BV sounds is in the interscapular region, the area situated between the shoulder blades. This posterior location is directly over the upper parts of the primary bronchi.
These sounds are restricted to central zones due to the filtering effect of healthy lung tissue. The air-filled alveoli of the peripheral lungs act as an acoustic dampener, muffling the higher-frequency, louder sounds originating from the central airways. Therefore, the BV sound is only heard where the stethoscope is positioned over larger air passages with a relatively thin layer of surrounding lung tissue. Auscultating outside of these precise areas often indicates a change in lung structure.
Clinical Significance of Abnormal Findings
The presence of bronchovesicular sounds outside of their normal central locations is a significant finding that may indicate an underlying pathology. When these intermediate sounds are heard in the peripheral lung fields, where only soft, low-pitched vesicular sounds should be present, it suggests an alteration in the density of the lung tissue. Normal lung tissue, filled mostly with air, is a poor transmitter of high-frequency sound, which is why the loud, central sounds are filtered out.
Conditions such as lobar pneumonia cause consolidation, replacing the air in the alveoli with fluid and inflammatory cells. This denser tissue transmits the sound vibrations from the central airways more efficiently, allowing the characteristic BV sound to be heard in areas where it should be absent. The same principle applies to atelectasis, or a collapsed lung, where the airless tissue conducts sound more effectively.
Conversely, a diminished or absent sound in any lung field, including the normal BV areas, can also be a sign of disease. For instance, a large pleural effusion (fluid buildup between the lung and the chest wall) or a pneumothorax (air accumulation in the chest cavity) can block sound transmission. Therefore, the character of the breath sound, whether it is present, absent, or misplaced, provides immediate clues about the physical state of the lungs.