A Plethysmographic Method for Measuring the Systolic and Diastolic Blood Pressure in Newborn Infants

The principles of plethysmography and technical details in the use of this method on infants have already been described elsewhere (4). Fig. 1 shows the underlying principles when observations on blood flow are used to determine the blood pressure. It is quite obvious that, i f a sphygmomanometer cuff is inflated a t a suprasystolic pressure, the circulation to the limb will be arrested. An arterial inflow will start the very moment the effective cuff pressure falls below the intravascular systolic peaks. This is the basis of the “flush method”, suggested by Glirtner (7) already in 1899, but clinically applied only recently (8). The flush method has a sound theoretical background but it is crude and largely subjective. I f the rate of blood flow is measured repeatedly a t a large variety of occluding pressures in the sphygmomanometer cuff, the effects of the cuff pressure on the rate of arterial inflow