The blood flow in tubed skin pedicles calibration for the photoelectric plethysmograph

possible to calibrate this equipment, so that the blood flow past a particular point on a tubed pedicle can be expressed as a rate of flow in cubic centimetres per minute. Principle of the Measuring Technique.--The photoelectric measuring technique depends on shining a beam of light on to the skin surface of a tubed pedicle and using a photoelectric cell placed on the opposite side of the pedicle to measure the light transmitted through the tube of skin. The haemoglobin in the blood absorbs the light and acts as a filter. The amount of light transmitted depends on the amount of blood present in the tubed pedicle. Thus, if a tube is exsanguinated and then blood is allowed to flow in from one end, the change in the light intensity falling on the photoelectric cell will be proportional to the amount of haemoglobin that has entered the pedicle at this point.