Control of a total artificial heart using mixed venous oxygen saturation.

We developed a control of the total artificial heart (TAH) using mixed venous oxygen saturation (SvO(2)). With this method, the TAH output was controlled by automatically adjusting drive parameters in response to changes in measured SvO(2). The feasibility and validity of this method were evaluated in a series of treadmill exercise tests using a calf implanted with a pneumatic TAH. The cardiac output (CO) and SvO(2) were measured with an ultrasonic flowmeter and an oximetric catheter, respectively. The calf performed graded exercise under a fixed drive control mode (fixed mode), in which the drive parameters were unchanged throughout the treadmill test and under the SvO(2) based control mode (SvO(2) mode). The calf could go to Stage 6 in both modes, but the maximal oxygen consumption in the SvO(2) mode was 1.5 times as large as that of the fixed mode. Compared with the fixed mode, CO was increased effectively in the SvO(2) mode, and the capacity for exercise was augmented. When considering the relationship between oxygen consumption and oxygen delivery, it was revealed that the CO in the SvO(2) mode responded more adequately to the recipient's oxygen demand than that in the fixed mode. We conclude that this SvO(2) based control method is feasible and physiologically effective.