A Mock Circulation Loop for In Vitro Hemodynamic Evaluation of Aorta: Application in Aortic Dissection

Purpose Aortic dissection (AD) is a catastrophic disease with complex hemodynamic conditions, however, understandings regarding its perfusion characteristics were not sufficient. In this study, a mock circulation loop (MCL) that integrated the Windkessel element and patient-specific silicone aortic phantoms was proposed to reproduce the aortic flow environment in vitro. Materials and Methods Patient-specific normal and dissected aortic phantoms with 12 branching vessels were established and embedded into this MCL. Velocities for aortic branches based on 20 healthy volunteers were regarded as the standardized data for flow division. By altering boundary conditions, the proposed MCL could mimic normal resting and left-sided heart failure (LHF) conditions. Flow rates and pressure status of the aortic branches could be quantified by separate sensors. Results In normal resting condition, the simulated heart rate and systemic flow rate were 60 bpm and 4.85 L/minute, respectively. For the LHF condition, the systolic and diastolic blood pressures were 75.94±0.77 mmHg and 57.65±0.35 mmHg, respectively. By tuning the vascular compliance and peripheral resistance, the flow distribution ratio (FDR) of each aortic branch was validated by the standardized data in the normal aortic phantom (mean difference 2.4%±1.70%). By comparing between the normal and dissected aortic models under resting condition, our results indicated that the AD model presented higher systolic (117.82±0.60 vs 108.75±2.26 mmHg) and diastolic (72.38±0.58 vs 70.46±2.33 mmHg) pressures, the time-average velocity in the true lumen (TL; 36.95 cm/s) was higher than that in the false lumen (FL; 22.95 cm/s), and the blood transport direction between the TL and FL varied in different re-entries. Conclusions The proposed MCL could be applied as a research tool for in vitro hemodynamic analysis of the aorta diseases under various physical conditions.

Aortic flow below and visceral circulation during aortic counterpulsation: Evaluation of an in vitro model

Introduction: This study aimed to test a computer-driven cardiovascular model for the evaluation of the visceral flow during intra-aortic balloon pump (IABP) assistance. Methods: The model includes a systemic and pulmonary circulation as well as a heart contraction model. The straight polyurethane tube aorta had a single visceral while four windkessel components mimicked resistance compliance of the brachiocephalic, renal and sub-mesenteric, pulmonary, and systemic circulation. Twelve flow probes were placed in the circuit to measure pressures and flows with the IABP on and off. Results: With the balloon off, the meantime to reach the steady state was 48 ± 16 s; with the balloon on, this figure was 178 ± 20 s. The stability of pressure and flow signals was obtained after 72 ± 11 min. The number of cycles of stability of the system was 93 [86–103]. Measurements were reliable either with samples of 10 or 20 beats. Bland Altman method demonstrated the reliability of measurements. Finally, all measurements were comparable to published in vivo data. Conclusion: The presented mock circulation was reliable and gave values with high accuracy both at baseline and during mechanical assistance. This system allows evaluation of the mesenteric flow during IABP, under different clinical/hemodynamic conditions. Nonetheless, its translational potential needs to be further evaluated

Left atrial assist device function at various heart rates using a mock circulation loop

We are developing a new left atrial assist device (LAAD) for patients who have heart failure with preserved ejection fraction (HFpEF). This study aimed to assess the hemodynamic effects of the LAAD under both normal heart conditions and various diastolic heart failure (DHF) conditions using a mock circulatory loop. A continuous-flow pump that simulates LAAD, was placed between the left atrial (LA) reservoir and a pneumatic ventricle that simulated a native left ventricle on a pulsatile mock loop. Normal heart (NH) and mild, moderate, and severe DHF conditions were simulated by adjusting the diastolic drive pressures of the pneumatic ventricle. With the LAAD running at 3200 rpm, data were collected at 60, 80, and 120 bpm of the pneumatic ventricle. Cardiac output (CO), mean aortic pressure (AoP), and mean LA pressure (LAP) were compared to evaluate the LAAD performance. With LAAD support, the CO and AoP rose to a sufficient level at all heart rates and DHF conditions (CO; 3.4–3.8 L/min, AoP; 90–105 mm Hg). Each difference in the CO and the AoP among various heart rates was minuscule compared with non-pump support. The LAP decreased from 21–23 to 17–19 mm Hg in all DHF conditions (difference not significant). Furthermore, hemodynamic parameters improved for all DHF conditions, independent of heart rate. The LAAD can provide adequate flow to maintain the circulation status at various heart rates in an in vitro mock circulatory loop.

A mock circulation loop to test extracorporeal CO2 elimination setups

Background Extracorporeal carbon dioxide removal (ECCO2R) is a promising yet limited researched therapy for hypercapnic respiratory failure in acute respiratory distress syndrome and exacerbated chronic obstructive pulmonary disease. Herein, we describe a new mock circuit that enables experimental ECCO2R research without animal models. In a second step, we use this model to investigate three experimental scenarios of ECCO2R: (I) the influence of hemoglobin concentration on CO2 removal. (II) a potentially portable ECCO2R that uses air instead of oxygen, (III) a low-flow ECCO2R that achieves effective CO2 clearance by recirculation and acidification of the limited blood volume of a small dual lumen cannula (such as a dialysis catheter). Results With the presented ECCO2R mock, CO2 removal rates comparable to previous studies were obtained. The mock works with either fresh porcine blood or diluted expired human packed red blood cells. However, fresh porcine blood was preferred because of better handling and availability. In the second step of this work, hemoglobin concentration was identified as an important factor for CO2 removal. In the second scenario, an air-driven ECCO2R setup showed only a slightly lower CO2 wash-out than the same setup with pure oxygen as sweep gas. In the last scenario, the low-flow ECCO2R, the blood flow at the test membrane lung was successfully raised with a recirculation channel without the need to increase cannula flow. Low recirculation ratios resulted in increased efficiency, while high recirculation ratios caused slightly reduced CO2 removal rates. Acidification of the CO2 depleted blood in the recirculation channel caused an increase in CO2 removal rate. Conclusions We demonstrate a simple and cost effective, yet powerful, “in-vitro” ECCO2R model that can be used as an alternative to animal experiments for many research scenarios. Moreover, in our approach parameters such as hemoglobin level can be modified more easily than in animal models.

Analysis of Operating Modes for Left Ventricle Assist Devices via Integrated Models of Blood Circulation

Left ventricular assist devices provide circulatory support to patients with end-stage heart failure. The standard operating conditions of the pump imply limitations on the rotation speed of the rotor. In this work we validate a model for three pumps (Sputnik 1, Sputnik 2, Sputnik D) using a mock circulation facility and known data for the pump HeartMate II. We combine this model with a 1D model of haemodynamics in the aorta and a lumped model of the left heart with valves dynamics. The model without pump is validated with known data in normal conditions. Simulations of left ventricular dilated cardiomyopathy show that none of the pumps are capable of reproducing the normal stroke volume in their operating ranges while complying with all criteria of physiologically feasible operation. We also observe that the paediatric pump Sputnik D can operate in the conditions of adult circulation with the same efficiency as the adult LVADs.