When would a therapist expect to hear tympanic sounds during percussion?

Tympanic sounds during percussion are typically heard over the stomach when it is filled with air. This sound is produced when the percussion tap resonates against gas within the hollow organs of the abdomen, resulting in a high-pitched, drum-like sound. The stomach, being an air-filled organ, is the most common location where tympanic percussion notes are expected. This is consistent with normal anatomical structures in which air is present and the resonance can be effectively sound.

Other options relate to different anatomical contexts: fluid-filled organs would produce dull sounds, as fluids dampen the resonance; lung tissue would typically yield a resonance note that is duller than tympanic because of the denser tissue and air-saturated alveoli; and the sternum, being a solid bone structure, would also produce a dull sound. Hence, the presence of tympanic sounds is specifically associated with air-filled spaces like the stomach.