趙啟明醫生醫務所         Dr Leo Chiu, Central Vascular Clinic 

(Non-invasive studies)  PPG makes use of infrared light to detect blood flow at the surface of the skin. Patients with long-standing diabetes or kidney disease may have rigid arteries that are difficult to compress with the blood pressure cuff.  As toe arteries are rarely rigid, toe pressure may be measured.  Doppler probe is not sensitive enough in detecting blood flow inside a small digit.  Therefore, PPG probe is applied to take toe pressure or used for waveform analysis. How is PPG performed A tiny PPG sensor is placed over the tip of the toe and waveforms recordings will be displayed. In measuring toe pressure, a small blood pressure cuff around the toe is inflated. The pressure inside the cuff is lowered gradually, the pressure at which blood flow started to return as detected by the infrared light sensor is the toe pressure. It is compared with the arm pressure to give a ratio called Toe-Brachial Index (TBI).