Plethysmograph

Plethysmograph
Plethysmograph or "body box" used in lung measurements
MeSHD010991
MedlinePlus003771
A man undergoing whole body plethysmography.
A modern body plethysmograph using ultrasound

A plethysmograph is an instrument for measuring changes in volume within an organ or whole body (usually resulting from fluctuations in the amount of blood or air it contains). The word is derived from the Greek "plethysmos" (increasing, enlarging, becoming full), and "graphein" (to write).[1]