What percussion note replaces resonance when fluid replaces air-containing lung tissue?

When fluid replaces air in lung tissue, the percussion note changes from the resonance typically found in normal, air-filled lungs to dullness. This occurs because fluid does not transmit sound in the same way that air does, leading to a more muted sound when percussing over the affected area. Dullness indicates the presence of denser material—like fluid or solid mass—whereas resonance is associated with air.

In contrast, hyperresonance would be heard with an increase of air, such as in conditions like pneumothorax, and flatness is typically characterized by very dense structures like muscle or bone, which produce a completely different sound, much duller than that of fluid-filled spaces. Tympanic sounds are commonly associated with air-filled structures such as the stomach or intestines, which is also not applicable to fluid-filled lung tissue. Thus, recognizing the sound of dullness is crucial for assessing conditions such as pleural effusion or pneumonia where fluid accumulation occurs in the lungs.