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Design Innovation Papers

Implementation of an Automated Peripheral Resistance Device in a Mock Circulatory Loop With Characterization of Performance Values Using Simulink Simscape and Parameter Estimation

[+] Author and Article Information
Charles E. Taylor

Department of Biomedical Engineering,
Virginia Commonwealth University,
401 West Main Street RM1229,
Richmond, VA 23220
e-mail: taylorce@mymail.vcu.edu

Gerald E. Miller

Department of Biomedical Engineering,
Virginia Commonwealth University,
401 West Main Street RM1229,
Richmond, VA 23220
e-mail: gemiller@vcu.edu

Manuscript received January 6, 2012; final manuscript received August 7, 2012; published online October 11, 2012. Assoc. Editor: Paul A. Iaizzo.

J. Med. Devices 6(4), 045001 (Oct 11, 2012) (7 pages) doi:10.1115/1.4007458 History: Received January 06, 2012; Revised August 07, 2012

Accurate peripheral resistance simulation in a mock circulatory loop is critical to the evaluation of ventricular assist devices and heart valves. Implementation of an automated device that is capable of accurate resistance settings and precise reproduction of cardiovascular parameters allows for improved construction of experimental conditions within a mock circulatory loop. A mock circulatory loop resistor that employs a proportional valve design is proposed; a piston extending into the flow path to produce a resistance to flow. Real-time position feedback of the piston is used to determine orifice size, providing resolution in the change of resistance over time. Characterization of the physical system with The MathWorks SIMULINKSIMSCAPE™ block set allowed the determination of objective device parameters; the discharge coefficient and critical Reynolds number. The determination of these values was achieved utilizing the SIMULINK™ Parameter Estimation™ tool, experimental data, and a computational plant model of the experimental setup. With this information, an accurate computational model of the resistance device is presented for use in determining resistance settings in silico prior to implementation in the mock circulatory loop. Experimental in vitro trials verified the repeatability of the automated resistor performance by means of a staircase testing of piston position during several different continuous flow rates of a glycerin/water solution.

FIGURES IN THIS ARTICLE
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References

Figures

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Fig. 1

A manually actuated clamp employed as a resistance mechanism by Legendre et al. [6] (left). An example of a Hass (New York, NY) proportional pinch valve as an automated solution to resistance actuation by Timms et al. [5] (right).

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Fig. 2

Cutaway view of the CAD model for the resistor assembly. Components of the device are as follows: (a) linear actuator lead screw, (b) stepper motor, (c) resistor motor frame, (d) rotation constraint bar, (e) piston, (f) O-rings, (g) threaded flow outlet, and (h) resistor block. This depiction is analogous to the annotated photograph of the assembly displayed as Fig. 3.

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Fig. 3

Resistor as installed in the mock circulatory loop. The elements of the design are as follows: (1) vertical optical rail, (2) linear actuator lead screw, (3) stepper motor, (4) resistor motor frame, (5) rotation constraint bar, (6) piston, (7) flow inlet, (8) 1 of 4 mounting holes for optical rail attachment, (9) flow outlet, (10) potentiometer, and (11) connector with cable leading to driver board (11).

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Fig. 4

LabVIEW interface used to control the resistor and collect data. The slider allows for a position to be selected and the radix below it enables a particular set point to be entered. The read back is the intermittently updated position read back from the position controller. The button at the bottom communicates the new set point to the controller, initiating the movement of the resistor. This panel can be inserted into other LabVIEW interfaces when constructing control panels for mock circulatory loops, where this device would be a subsystem.

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Fig. 5

Modified mock circulatory loop used in this analysis; the black arrow counter clockwise from pump indicates flow direction. The order of the pump, compliance chamber, resistor, and venous reservoir is consistent with a mock circulatory loop design. The purpose of pressure sensors downstream of the compliance chamber and resistor is to acquire differential pressure across the resistor. The flowmeter has been repositioned downstream of the resistor for better acuity in flow rate measurement for this segment of the loop. The upstream and downstream throttling valves provide fluid flow regulation and backpressure control, respectively [10].

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Fig. 6

SIMULINK model of the experimental system utilizing simscape blocks to model the physical components of the mock circulatory loop. The simulated flow is from left to right, with components similar to those described in the experimental setup and in Fig. 2. The experimental flow sensor data is permuted as a flow source in the computational model; the model needs a volume source. The downstream pressure sensor experimental data is represented as a pressure source in the model, since there needs to be an exit condition for the simulated flow.

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Fig. 7

The top graph depicts the tuning dataset with the result of the model using the tuned values to that of the experimental dataset for the upstream resistor. The flow rate graph (middle graph) indicates that an approximately constant flow was maintained through the resistor movement (bottom graph).

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Fig. 8

Performance of the tuned SIMULINK model using input data with different conditions to that of the tuning data. The model simulation at the lower flow rate showed signs of sensitivity to the fluctuations in flow, which was also seen in the tuning data. The similarity of the simulation to the experimental data provides verification that the parameter estimation was a success.

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