ABC of Vascular Disease
Photoplethysmography (PPG) is a non-invasive measurement of the efficiency of the musculovenous pump of the lower leg. The technique measures the change in skin blood volume using a small light probe that is placed on then surface of the skin just above the ankle. After a period of rest the subject exercises the calf pump by moving the foot up and down at the ankle. The PPG probe measures the reduction in skin blood content that is a result of the pumping action of the calf muscles. After a fixed number of ankle movements (usually 10) the subject is asked to rest and the rate at which the blood returns to the skin is measured. These two measurements are related to the efficiency of the musculovenous pump and the presence of abnormal venous reflux. Patients with problems with the superficial or deep veins usually have poor emptying of the skin and abnormally rapid refilling. The test is repeated with inflatable cuffs placed on the leg below then above the knee. The effect of the cuff on the PPG measurement gives further information about the severity and nature of the venous problem. PPG is a quick, painless, non-invasive test that can be performed in the vascular outpatient clinic in a few minutes.
© S.R.Dodds 2001