an Entity references as follows:
Hamman's sign (rarely, Hammond's sign or Hammond's crunch) is a crunching, rasping sound, synchronous with the heartbeat, heard over the precordium in spontaneous mediastinal emphysema. It is felt to result from the heart beating against air-filled tissues. It is named after Johns Hopkins clinician Louis Hamman, M.D. This sound is heard best over the left lateral position. It has been described as a series of precordial crackles that correlate with the heart beat rather than respiration.