Device for Measuring Isotonic or Isometric Contractions of Heart Muscle
William J. Whalen, Orville H. Weddle · Review of Scientific Instruments · 1958
The device converts the motion of isotonic contraction into an electrical signal which can be recorded with the same equipment used to record the output of an isometric strain gauge. The isotonic gauge is essentially a straight wire potentiometer which moves freely through mercury contacts. The muscle is attached to one end of a lever and the resistance wire with a suitable weight (usually 0.5 g) attached to the other end. As shortening of the muscle occurs the resistance between the mercury contacts increases. Changes in length of about 0.1 mm can be quite accurately recorded. Turning a screw attached to a strain gauge down on the lever registers the isometric force in the conventional manner. The whole system is mounted on a movable stage.