chapter
PHOTOPLETHYSMOGRAPHY
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Photoplethysmography measures small changes in the volume of blood beneath the skin surface. The technique involves shining light into the skin. This light is reflected depending on the amount of blood present in the vessels immediately deep to the skin surface. The probe is placed on the lower part of the leg just above the medial malleolus and the patient is asked to flex the ankle 10 times. Blood will be pumped out of the surface vessels, resulting in a measurable change in light reflection. When the patient stops moving the ankle, there is a slow refilling. The normal refilling is in excess of 15 seconds. If a patient has varicose veins, the refilling can occur not only by the arterial system (normal), but also by reflux through the veins (abnormal). This test provides a useful quick screening method for varicose veins and simple venous disease. The application of rubber bands above or below the knee in the presence of varicose veins and superficial vein reflux will correct these abnormalities, in the absence of deep vein problems.