Egophony

Excerpt

In the era of technological advances, a thorough examination of the respiratory system retains its importance in diagnosing disorders of the respiratory system. Auscultation of the chest is among the oldest bedside diagnostic techniques used to assess airflow through airways. It is an easy, safe, non-invasive and cost-effective diagnostic technique. The majority of the manifestations of respiratory disease present with abnormalities of chest examination. Egophony is increased resonance of voice sounds heard when auscultating the lungs. When spoken voices are auscultated over the chest, a nasal quality is imparted to the sound which resembles the bleating of a goat. Egophony (also known as “E” to “A” change) is an auscultatory finding due to a change in the quality (timbre) of the voice. A solid (consolidated), fluid-filled, or compressed lung decreases the amplitude and only allows select frequencies to pass through. This changes the sound of the vowel “E” to "A."

Pathophysiology

Over the years there have been various theories explaining the mechanism of egophony. In 1894, Dr. Frederick Taylor described egophony as a musical discord. Transmission of sound vibrations from the larynx and tracheobronchial tree to the chest wall depends on the state of the underlying lung tissue and surrounding pleural space. In the lung of a typical individual, air-filled spaces are surrounded by solid parenchymal tissue. Egophony is commonly seen in pneumonia (consolidation) and pleural effusion.

Mechanism of egophony in consolidation

The sound of the vowel "E" has a low frequency in the range of 100 to 200 Hz as compared to the low frequency of "A" which may reach up to 600 Hz. The sound "E" consists of a high frequency in the range of 2000 to 3500 Hz. Consolidation creates a dense medium that facilitates the transmission of lower frequencies. Hence in a patient with an underlying consolidation, an "E" is transformed into an "A."

Mechanism of egophony in pleural effusion

In the case of pleural effusion, fluid accumulates in the pleural space. This fluid compresses the overlying lung parenchyma, making it more solid than usual. Due to this change, there is an alteration in the lung acoustics that preferentially transmits higher sound frequencies and gives rise to an egophony. Egophony in pleural effusion is characteristically heard at the upper border of the effusion.