a device for measuring the fluctuations in volume of a bodily organ or part, such as those caused by variations in the amount of blood it contains
Word origin
C19: from Greek plēthusmos enlargement + graphein to write
plethysmograph in American English
(pləˈθɪzməˌgræf)
noun
any of several instruments for measuring and recording various body functions, as the velocity or volume of blood flow, heart rate or breathing rate, changes in the size of organs or limbs, etc.