ABSTRACT
The diagnosis of disease and the definition of clinical class are based on clinical evaluation, while noninvasive testing is used to identify pathophysiological changes in individual anatomical segments of the venous system, and, in some cases, to define etiology. Indirect noninvasive tests, such as the various forms of plethysmography, are alternatives. The indirect noninvasive tests most often used in the evaluation of patients with chronic venous disease are air plethysmography and strain-gauge plethysmography. Photoplethysmography and light reflection rheography calculate changes in tissue blood density by measuring the intensity of reflected light. When venous obstruction is suspected, but not identified by duplex scan, plethysmography can help to overcome the low sensitivity of the ultrasound for the detection of venous obstruction. Identification and assessment of venous obstruction by plethysmography is based on the estimation of the following two parameters: venous capacitance and venous resistance.
