[A two-stage regulatory system for pressure-constant perfusion of coronary vessels]

This paper describes a double-loop servo-controlled pump system for the constant-pressure perfusion of a coronary artery. Due to the transient nature of changes in coronary vasomotor tone, such a perfusion system must have a fast regulatory response. In the first stage, a servo-controlled pump primes a windkessel having a volume of 35 ml with blood. The pumping rate is electronically controlled to maintain a constant pressure within the windkessel max. 700 mmHg. The maximal flow rate is 300 ml/min. To reduce the high pressure in the windkessel to the desired coronary perfusion pressure, a variable flow resistance, comprising a clamped thin-walled silicone tube, is provided in the output line of the system. A fast servo-motor drives the clamp and is controlled by an electronic regulator, using a second feedback loop from the pressure signal measured at the tip of the perfusion cannula. The system stabilizes the coronary perfusion pressure within 300 ms. An additional modulation of the setpoint signal in synchrony with the cardiac cycle improves the phasic pattern of the blood flow, and thus prevents changes in transmural blood flow distribution. The dead volume of the overall system is about 60 ml. Hemolysis caused by this system during five hours of perfusion in vivo is negligible.