- A dictionary of medical eponyms

Friedreich's sound change

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A lowering of the pitch of the percussion note that occurs over an area of cavitation during inspiration. It is due to the difference in tension in the wall of the cavum on inspiration and expiration – higher on inspiration, lower on expiration.


  • N. Friedreich:
    Über die respiratorischen Änderungen des Perkussionsschalls am Thorax unter normalen und pathologischen Verhältnissen.
    Deutsches Archiv für klinische Medicin, Leipzig, 1880, 26: 24-82.

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