Assessment of Venous Insufficiency using Photoplethysmography: A Comparison to Strain Gauge Plethysmography

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Abstract
Simultaneous photoplethysmographic (PPG) and strain gauge plethysmo graphic (SPG) recordings were obtained in normal subjects and patients with venous insufficiency. In PPG tracings, a so called "negative segment," which represented a further fall below the baseline after exercising, was often ob served. This negative segment is produced by blood flow from the superficial to the deep veins during relaxation, which indicates that PPG can be used to assess the circulatory hemodynamics in the skin. PPG and SPG tracings from limbs with primary varicosis showed a shorter refilling time after exercise than those from normal limbs at the distal as well as the midcalf levels. The mean refilling time measured at the distal level by PPG was unaffected by tourniquets applied proximal to the transducer, indicating that the PPG tracings determined at the distal level were not always influenced by the reflux of blood through the incom petent saphenous system, but by altered cutaneous circulation. SPG was of greater diagnostic value for deep venous disease than PPG. From these results, it would be concluded that PPG in combination with SPG offers a rational ap proach to the assessment and the understanding of the pathophysiology of ve nous diseases.