An Automatic Pressure Regulator for Extracorporeal Circulation

An automatic pressure regulator for controlling venous pressure during extracorporeal heart operations is described. The controller is used in procedures where a pressure is maintained in the venae cavae; i.e., where gravity flow is not used to drain the venous blood. A differential pressure transducer produces an error signal which controls the field current in a dc shunt motor and, consequently, the rate of pumping. The sensitivity of the controller can be varied in eight steps; on the most sensitive range, an error of less than 0.20 mm Hg can be detected and corrected. The total change in motor speed and hence pumping rate is ± 20 per cent.