Affinity pump system: a new peristaltic blood pump for cardiopulmonary bypass

An in vitro study has been carried out to assess the pump performance of a new peristaltic, extracorporeal displacement pump (Affinity) for cardiopulm onary bypass. The pump system consists of a pump rotor (0-110 rpm), a pump chamber, a Venous reservoir with a 5/8 " connecting tube and the Affinity c onsole. The polyurethane chamber is connected to the venous reservoir by a 5/8" tube and fills passively due to the hydrostatic pressure exhibited by the fluid height in the venous reservoir. The implementation of an occlusiv e segment in the pump chamber, which collapses in low filling states, shoul d prevent significant negative pressures. An in vitro circuit was filled wi th bovine blood (37 degrees C, hematocrit 35%) and the pump flow was measur ed by an ultrasonic transit time flow probe with respect to pre-load, diame ter and length of attached tubing in the venous line, pump speed (rpm) and size of the connecting tube (3/8 " and 5/8 "). At 108 rpm and a preload equal to 10 mmHg, the flow was 8.6 +/- 0.42 l/min for an afterload of 80 mmHg. The reduction of the inlet connector to 3/8 " diminished the pump flow significantly to 5.2 +/- 0.31 l/min (p < 0.0001). The pump flow decreased linearly with respect to the length of the attached tube in the venous line and for a 2 m long 5/8 " silicon tube, the rpm-opt imized flow was still 6.0 +/- 0.28 l/min at a preload of 10 mmHg. In case o f low filling slate or too high rpm, the occlusive segment collapsed and no cavitation bubbles could be detected. Our in vitro measurements yield a nomogram for rpm-optimized blood flow wit h respect to the pre-load in the venous reservoir. The delivered 5/8 " conn ecting tube facilitates optimum filling of the pump chamber for high blood flow, but limits the use of venous reservoirs to Affinity products. The pum p yields a high blood flow even when long tubing in the venous line is used . This makes the pump a candidate for a Ventricular assist device. In hypov olemia or high rpm, the occlusive segment collapses and no negative pressur e is generated at the inflow site of the pump chamber.