Limitations of electric impedance plethysmography.

Klectrie impedance plethysmography has been offered as a substitute for mechanical plethysmography and would be particularly suitable for regions in which the mechanical method cannot be applied. A comparative investigation of mechanical and impedance plethysmograms, taken simultaneously from a finger or a forearm, revealed that, while the normal pulsations were reproduced reasonably well, electric impedance plethysmography cannot be employed to determine volume changes following venous occlusion. The reasons are discussed.