In vitro flow characteristics of a new pump with a high inherent sensitivity to venous return.

A new type of pump, the differential displacement pump, has recently been developed. The new pump and a conventional pneumatic displacement pump were evaluated with respect to pump flow, filling pressures, stroke frequency, and inflow pattern under equivalent test conditions. The pumps were connected via inlet and outlet cannulas to a Donovan hydraulic circulation analogue. The differential displacement pump showed a high sensitivity to filling pressure in the range of 2.3-9.6 L/min/mmHg, and a high efficiency as long as the stroke volume was submaximal. The inflow was continuous and pulsatile with a maximal forward flow velocity during systole as long as the maximal stroke volume was not employed. In contrast, the conventional displacement pump showed low sensitivity to filling pressures, a discontinuous inflow, with a maximal inlet cannula forward flow during diastole and a substantial flow reversal during systole. These results indicate that the differential displacement pump is a better concept with respect to sensitivity to venous return, and that it provides an inflow pattern and regulation of pump flow similar to that of the biologic heart.