Transient response of remnant atrial heart rate to step changes in total artificial heart output

Abstract

In a total artificial heart (TAH) recipient, the remnant atrial rate reflects the control signal on cardiac function from the recipient's central nervous system via both the neural and the humoral pathways. Therefore, it can provide useful information for physiologic control of a TAH. We investigated step responses in the remnant atrial rate to step changes in TAH output in a calf implanted with a pneumatic TAH and characterized the dynamic property of the open-loop native cardiac output control system. The pumping rate was changed suddenly from 90 to 60 bpm, and in the next stage from 60 to 90 bpm. This process was repeated three times. Along with the step changes in TAH pumping rate, TAH output also changed at once in a similar fashion. The atrial rate altered immediately and converged after an overshoot. These changes were regarded as second-order delay responses, and the dynamic properties were estimated. When the pumping rate was decreased from 90 to 60 bpm and when it was increased from 60 to 90 bpm, the rise times were 70 ± 1 and 132 ± 38 s, the peak times were 127 ± 15 and 179 ± 15 s, the maximum overshoots were 30 ± 4% and 12 ± 7%, and the settling times were 232 ± 11 and 245 ± 10 s, respectively. We conclude that the obtained open-loop characteristics and dynamic properties can be useful indexes for physiologic control of TAH output, which reflects the properties of the native central nervous control system.