[Changes in sound transmissibility through the canine thorax due to the experimental pleural effusion]

The authors studied the effects of pleural effusion on sound transmissibility through the canine thorax. In the supine position, dogs received sound ranging from 100 to 1000 Hz at the tracheostoma. Using the microphones attached to the dorsal and ventral part of the chest wall, the relative level of the transmitted sound wave was determined in reference to the amplitude of the sound wave at a tracheostom. Measurements of sound transmissibility were performed before and after injecting saline into the bilateral pleural space which was intended to be experimental pleural effusion. In the dorsal part, the experimental pleural effusion decreased sound transmissibility in the frequency range between 100 and 300 Hz. At 100 Hz, the pleural effusion of 5, 10, and 15 ml/kg/hemithorax caused a decrease in sound transmissibility by 3.7 +/- 3.7, 6.6 +/- 4.9, and 10.0 +/- 5.7 dB, respectively. In the ventral part, the reduction in sound transmissibility in the low frequency range due to the pleural effusion was small. In contrast, introduction of pleural effusion caused an increase in sound transmissibility by 5 to 9 dB in the frequency range above 500 Hz. We consider that these changes in sound transmission are implicated in the physical findings such as "aegophony" and reduction in vocal fremitus or vocal ausculation.