Of the many complicated problems in the field of the mechanism of the physical signs of the respiratory system, perhaps none has been so admittedly puzzling, particularly in adults, as that of the normal or increased vocal resonance sometimes encountered in cases of pleural effusion. Skoda thought he had solved the riddle by attributing the phenomenon to what he calls consonance, but his explanation is untenable. The literature on the subject is, for the most part, rather suggestive than really helpful. Walshe's statement is : "Sometimes explicable by solid adhesions conveying the vibrations from the lung to the chest wall; in other instances the anomaly does not admit of explanation."
In trying to obtain any explanation — and only one will be offered here — for the occurrence of normal or increased vocal resonance in cases of pleural effusion, it is necessary first of all to have
MONTGOMERY CM, ECKHARDT EA. FACTORS INVOLVED IN SOME CASES OF PLEURAL FLUID ASSOCIATED WITH NORMAL OR INCREASED VOCAL RESONANCE. Arch Intern Med (Chic). 1915;XV(6):1040–1045. doi:10.1001/archinte.1915.00070250101006