[Microwave volumetry of the extremities: a technical measuring alternative to the noninvasive venous occlusion test].

Venous occlusion plethysmography is a well-established noninvasive procedure for the investigation of venous outflow disorders. Various different sensor systems are available for the purpose, e.g. photoplethysmography, strain-gauge plethysmography and impedance plethysmography. The technique of microwave volumetry described in this paper is based on the interaction of the electromagnetic fields within the loss medium, tissue, and uses an air-filled resonant cavity as a sensor. As in the case of a microwave oven, this is excited by a high-frequency generator, but involves the use of far less power. As the volume of the measured objects (foot, arm) increases, the losses in the resonator also increase and can be analysed in a computer. The results can be represented in the form of a classical venous occlusion curve.