plethysmograph

‖n. [ Gr. &unr_; an enlargement + -graph. ] (Physiol.) An instrument for determining and registering the variations in the size or volume of a limb, as the arm or leg, and hence the variations in the amount of blood in the limb. [ 1913 Webster ]

-- Pleth`ys*mo*graph"ic a. [1913 Webster]