Percussion note can reveal a great deal of information regarding the thoracic cavity, but to be proficient in it requires time and experience. The sensation on percussion felt through the finger tips is as important as the sound. A cavity that contains air has a deeply resonant sound and feel, whereas solid tissue or fluid will be dull. Percuss the chest from side to side starting at the apices (including the supraclavicular spaces and axillae when examining anteriorly) and then down the chest. Compare the percussion note side to side but ensure you are choosing points equidistant from the midline. Particularly on the posterior chest wall the note will differ slightly at different distances from the midline. Various disease processes will result in a dull percussion note including pleural thickening or effusion, consolidation of the underlying lung or masses adjacent to the chest wall.
Hyperresonace on percussion can be found in subjects with severe airflow obstruction. It is a more sensitive sign of hyperinflation than is the presence of a barrel chest. However being confident that a chest is hyperresonant requires experience and confidence, the presence of loss of cardiac and liver dullness is probably a good clue to reinforce this impression.