A volume-displacement plethysmograph to measure limb blood flow in the newborn infant.

An instrument is described that measures limb blood flow in newborn infants by venous occlusion plethysmography. The plethysmograph is filled with air and a pneumotachygraph measures the volume displaced during venous occlusion. The response of the system is linear for flows over the range 1 to 100 ml/min and the frequency response to a square wave pressure change is 22 Hz with a 95% response time of 0.5 second. The average flow in the forearm of 10 normal newborn infants was 5.9 ml/min per 100 ml of tissue.