Plethysmography is a technique of measuring volume changes of an organ, the volume may be due to blood, water or air. It is of many types like Photo electric Plethysmography, Pneumo ( Body or Chamber ) Plethysmography, Inductive Plethysmography, Impedance Plethysmography, Magnetic Susceptibility Plethysmography, Body Plethysmography, Strain Gauge Plethysmography2-5. We are mainly concerned with IMPEDANCE PLETHYSMOGRAPHY that measures volume changes of blood in chest, calf or any other region of the body by sensing electrical resistance changes in respective area.