Development of an Anatomy-Mimicking, Wave Transport-Preserving Mock Circulation Loop for Evaluating Pulsatile Hemodynamics as Supported by Cardiovascular Assist Devices

Figures

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  Fig. 1. Schematic of the anatomic-mimicking mock circulation loop. Names and station/segment numbers of constituent components are provided in Table. 1. Silicone artificial arteries (orange) and smaller Tygon tubing arteries (blue) form the tree-like arterial system. Lumped pulmonary and venous components are interconnected with the arterial system by larger Tygon tubing (blue). LV, left ventricle; RV, right ventricle; CoW, Circle of Willis; P1–P3, pinch valve resistors; R1–R31, terminal resistors; C1–C10, compliance chambers; S1–S5, settling chambers; MC1, MC2, myocardial compression chambers; Red dots, pressure measurement sites

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  Fig. 2. Picture of the anatomy-mimicking mock circulation loop. The numbers marked on the parts are defined in Table 1

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  Fig. 3. Cardiac simulator design. Ventricular contraction and relaxation are realized using a computer-controlled pneumatic driving system. A flexible blood sac is housed in a rigid-walled acrylic chamber in communication with a piston/cylinder actuator driven by a pneumatic regulator and air supply system. The inlet and outlet ports of the sac space (ventricle) are installed with two silicon tri-leaflet valves, respectively. A illustrated the schematic of the cardiac simulator design and the pneumatic ventricular actuator motion at systole and diastole. B depicts the control block diagram of pneumatic supply/regulation, driving flow and the commands sent from the control unit to actuate the ventricles. C shows the picture of the mechanical parts of the cardiac simulator

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  Fig. 4. Schematic representation of the arterial tree replicas used on the present mock circulation loop. The segment numbers, names, and geometrical parameters are documented in Table 1. Spinal and intercostal circulations are simplified into lumped tubing parts as illustrated in the schematic. The lumped spinal/intercostal circulation parts are connected with the systemic arterial and venous subsystems to provide the afferent and efferent flows in the Circle of Willis as well as in the spinal circulation. AKA, artery of Adamkiewicz; ASA, anterior spinal artery

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  Fig. 5. Triple-layered left coronary vasculature model (A) and the electric circuit analogue (B). Intramyocardial compression is imitated using collapsible silicon tubes housed in two air chambers (dash boxes), respectively. Driving pressures in the two air chambers are synchronized with the left ventricular driving system with regulated pressure drops to simulate the transmural muscular compression/relaxation effect. Resistances R13–R18 (see Table 1) are parameters used for the tuning of coronary flow distributions in the triple-layered myocardium model

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  Fig. 6. Flow chart showing the parameter tuning process of the present mock circulation loop

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  Fig. 7. Comparison of the MCL-generated pressure and flowrate waveforms to those computational (Reymond et al. [23]) and clinically observed (Mills et al. [28]) results

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  Fig. 8. Phasic coronary flow and wave characteristics analyzed using Wave Intensity Analysis (WIA); MCL (A) vs. animal experiment (B) results. Characteristic coronary waves labeled with numbers can be found in Davies [30]. Wave 2 is the dominant forward-traveling pushing wave resulting from early ventricular contraction. Wave 5 represent the dominant backward-traveling “suction” wave, which is the major coronary perfusion mechanism attributed to vasculature sudden expansion during early diastolic phase

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  Fig. 9. Hemodynamic simulation of healthy, heart failure, and heart failure supported by rotary pump left ventricular assist device (LVAD). A shows the left ventricular pressure-volume loops of a heart with and without LVAD support. B–E illustrate the pressures, flow and wave intensities corresponding to a healthy heart (B); a heart failure control (C); a heart failure supported by rotary pump with support level barely allowing aortic valve opening (D), and a heart failure having full rotary pump support with aortic valve closed

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  Fig. 10. Simulation of heart failure (CO = 3.3 LPM, MAP = 90 mmHg, HR = 85 BPM) supported by intra-aortic balloon pump (IABP). A shows the pressure and flow waveforms at representative end organs and arteries under counterpulsatile IABP support (assist ratio 1:1, full augmentation). The time traces show IABP-standby and IABP-assisted waveforms separated by a line of start. The time-averaged pressure and flow enhancements are expressed as baseline/assisted (% increment). Units of flow and pressure are ml/min and mmHg, respectively. B illustrates the pressures and flows measured in the ascending aorta as well as in the coronary triple-layered (subepi-, subendo- and endo-myocardium layers) myocardial model. The time-varying resistance, resistor and compliance parameters are those adopted in Fig. 5.