Nonlinear Control of a Hybrid Pneumo-Hydraulic Mock Circuit of the
Objective: Hybrid cardiovascular mock circuits (HMC),
designed for dynamic testing of Ventricular Assist Devices (VAD), offer
physiologic accuracy by sequestering model complexity in silico
and ease of construction by reducing number of model elements in
vitro. Despite superior response time and precision, pneumatic
actuation is avoided in HMCs due to nonlinear dynamics and noise. We
tested the hypothesis that a HMC consisting of a variable
elastance-driven numerical circuit coupled to a pneumo-hydraulic
physical circuit can be controlled without linearizing system dynamics.
Methods: Reference left ventricular and aortic pressures
generated in silico were tracked, respectively, in in
vitro preload and afterload reservoirs by controlling non-linear
pneumatic dynamics using the Lyapunov stability criterion. A centrifugal
pump, the speed (i.e. flow) of which was adjusted using PID control, was
interposed between the reservoirs and mimicked the VAD under evaluation.
The flow of a recirculating gear pump was controlled by the backstepping
method to equalize reservoir fluid volumes by rejecting pressure and
flow disturbances. Sensor noise was reduced with discrete-time Kalman
filtering. Results: Our results showed that normal,
failing and assisted cardiovascular physiologies were numerically
simulated and tracked at physical VAD terminals with high accuracy.
Reservoir volumes remained stable at various combinations of heart rate,
pressure, and VAD flow. Conclusion: The HMC described
here offers a stable performance testing platform for VAD prototypes.
Significance : This is the first proof that
hybrid systems using pneumatic actuation at hydraulic interfaces can
optimally be regulated with nonlinear controllers to achieve precise
reference tracking and robust disturbance rejection.