Pusher-plate type TAH system operated in the left and right free-running variable rate mode.

A TAH system utilizing two pusher-plate type pumps was developed and tested in two calves for 45 and 108 days with excellent results. A Hall effect sensor was utilized to operate each pump with a full stroke at variable rates (VR); each pump was then allowed to run independently at different rates depending on its own preload and afterload. With this system, the animals' atrial pressures were kept to near-normal levels (less than 10 mmHg). However, significant differences in the left and right pump flows were observed (left higher than right) and they ranged from 5 to 30% of the left flow with a mean of 15%. These flow differences may be due to the bronchial circulation and related shunts. Right pump flows averaged 70 to 95 ml/min-kg and circulating blood volume ranged from 67 to 95 ml/kg. When various control modes including fixed rate and master-slave type simultaneously or alternatively ejecting VR modes were applied in the same animals and both pump flows were forced to be equal, unphysiological atrial pressures resulted. This result indicates that perhaps left and right flow differences are necessary physiological conditions to regulate the atrial pressures within normal ranges. Metabolic data also indicated that under simultaneously and alternately ejecting modes, A-V O2 content differences were increased due to decreased right pump flow as compared with those of the free-running VR mode. The left and right free-running VR mode of operation imposed minimal constraints on the animals' cardiovascular system and therefore yielded excellent hemodynamic and metabolic results.