ABSTRACT
Plethysmography is a term for a set of NI techniques for measuring volume changes in parts of the body, or even the whole body. The two main techniques used today for plethysmography are volume displacement using air or water outside the body, and the measurement of the electrical impedance or admittance of the body part. Volume changes can also be estimated by ultrasonic and x-ray imaging. A major application of impedance plethysmography (IP) is in occlusive impedance phlebography (OIP). This procedure is used to detect venous blood clots in deep leg veins. IP can also be used to detect blood clots in the lungs. IP is also used to monitor breathing (and also heart beats) in intensive care and neonatal applications. Impedance pneumograph-cardiotachometers used for neonatal and ICU applications have an alarm system that measures a sudden increase in measured impedance such as would be caused by electrodes drying out, coming detached, or falling off the chest.
