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Introduction: Some authors advocate the use of a dedicated formula to predict the Fontan pressure starting from pre-Fontan catheterisation data. This paper aims at testing the predictive value of the mentioned formula through a retrospective clinical study., Methods and Results: Pre-Fontan catheterisation data and Fontan pressure measured at the completion were retrospectively collected. Pre-Fontan data were used to calculate the predicted pressure in the Fontan system. The predicted values were compared to the Fontan pressure measured at the Fontan completion and with the needs for fenestration. One hundred twenty-four Fontan patients were retrospectively enrolled (At Fontan: median age 30.73 [24.70-37.20] months, median weight 12.00 [10.98-14.15] kg). Fontan conduit was fenestrated in 78 patients. A poor correlation (r2 = 0.05128) between the measured and predicted data for non-fenestrated patients was observed. In the case of Fontan-predicted pressure <17.59 mmHg, the formula identified a good short-term clinical outcome with a sensitivity of 92%., Conclusion: The proposed formula showed a poor capability in estimating the actual pressure into the Fontan system and in identifying patients needing fenestration. As the pressure into the Fontan system is determined by multiple factors, the tested formula could be an additional data in a multi-parametric approach.

Our aim was to study the feasibility of implanting the Infant Jarvik 2015 in patients weighing less than 8 kg. The Infant Jarvik 2015 left ventricular assist device (LVAD) was tested in a hybrid simulator of the cardiovascular system reproducing specific patients' hemodynamics for different patient weights (2-7 kg). For each weight, the sensitivity of the pump to different circulatory parameters (peripheral resistance, left ventricular elastance, right ventricular elastance, heart rate, and heart filling characteristics) has been tested repeating for each experiment a pump ramp (10 000-18 000 rpm). The increase in the pump speed causes a decrease (increase) in the left (right) atrial pressure, an increase (decrease) in the arterial systemic (pulmonary) pressure, an increase in the right ventricular pressure, a decrease (increase) in the left (right) ventricular volume, a decrease in the left ventricular cardiac output, an increase in the LVAD output and an increase in the right ventricular cardiac output (total cardiac output). Suction was observed for lower weight patients and for higher pump speed in the case of vasodilation, left ventricular recovery, bradycardia, right ventricular failure, and left ventricular hypertrophy. Backflow was observed in the case of left ventricular recovery at lower pump speed. In the hybrid simulator, the Infant Jarvik 2015 could be suitable for the implantation in patients lower than 8 kg because of the stability of the device respect to the cardio/circulatory changes (low frequency of suction and backflow) and because of the capability of the device to maintain adequate patient hemodynamics., (© 2018 International Center for Artificial Organs and Transplantation and Wiley Periodicals, Inc.)

The aim of this work is to study pediatric pneumatic ventricle (PVAD) performance, versus VAD rate (VADR) and native heart rate (HR) ratio Rr (VADR/HR). The study uses a hybrid model of the cardiovascular system (HCS). HCS consists of a computational part (a lumped parameter model including left and right ventricles, systemic and pulmonary arterial and venous circulation) interfaced to a physical part. This permits the connection of a VAD (15 mL PVAD). Echocardiographic and hemodynamic data of a pediatric patient (average weight 14.3 kg, HR 100 bpm, systemic pressure 75/44 mm Hg, CO 1.5 L/min) assisted apically with asynchronous PVAD were used to set up a basal condition in the model. After model tuning, the assistance was started, setting VAD parameters (ejection and filling pressures, systole duration) to completely fill and empty the PVAD. The study was conducted with constant HR and variable VADR (50-120, step 10, bpm). Experiments were repeated for two additional patients' HRs, 90 and 110 bpm and for two values of systemic arterial resistance (R as ) and E max . Experimental data were collected and stored on disk. Analyzed data include average left and right ventricular volumes (LVV, RVV), left ventricular flow (LVF), VAD flow (VADF), and total cardiac output (COt). Data were analyzed versus Rr. LVV and RVV are sensitive to Rr and a left ventricular unloading corresponds in general to a right ventricular loading. In the case of asynchronous assistance, frequency beats are always present and the beat rate is equal to the difference between HR and VADR. In the case of pulsatile asynchronous LVAD assistance, VADR should be chosen to minimize frequency beat effects and right ventricular loading and to maximize left ventricular unloading., (© 2017 International Center for Artificial Organs and Transplantation and Wiley Periodicals, Inc.)

Introduction: To develop and test a lumped parameter model to simulate and compare the effects of the simultaneous use of continuous flow (CF) and pulsatile flow (PF) ventricular assist devices (VADs) to assist biventricular circulation vs. single ventricle circulation in pediatrics., Methods: Baseline data of 5 patients with biventricular circulation eligible for LVAD and of 5 patients with Fontan physiology were retrospectively collected and used to simulate patient baselines. Then, for each patient the following simulations were performed: (a) CF VAD to assist the left ventricle (single ventricle) + a PF VAD to assist the right ventricle (cavo-pulmonary connection) (LCF + RPF); (b) PF VAD to assist the left ventricle (single ventricle) + a CF VAD to assist the right ventricle (cavo-pulmonary connection) (RCF + LPF)., Results: In biventricular circulation, the following results were found: cardiac output (17% RCF + LPF, 21% LCF + RPF), artero-ventricular coupling (-36% for the left ventricle and -21.6% for the right ventricle), pulsatility index (+6.4% RCF + LPF, p = 0.02; -8.5% LCF + RPF, p = 0.00009). Right (left) atrial pressure and right (left) ventricular volumes are decreased by the RCF + LPF (by RPF + LCF). Pulmonary arterial pressure decreases in the LCF + RPF configuration. In Fontan physiology: cardiac output (LCF + RPF 35% vs. 8% in RCF + LPF), ventricular preload (+4% RCF + LPF, -10% LCF + RPF), Fontan conduit pressure (-5% RCF + LPF, +7% LCF + RPF), artero-ventricular coupling (-14% RCF + LPF vs. -41% LCF + RPF) and pulsatility (+13% RCF + LPF, - 8% LCF + RPF)., Conclusions: A numerical model supports clinicians in defining and innovating the VAD implantation strategy to maximize the hemodynamic benefits. Results suggest that the hemodynamic benefits are maximized by the LCF + RPF configuration.

The aim of this work is to develop and test a lumped parameter model of the cardiovascular system to simulate the concurrent use of pulsatile (PVAD) and continuous flow (CVAD) ventricular assist device (VAD) on Fontan patients. Echocardiographic and hemodynamic data of five Fontan patients were retrospectively collected and used to simulate the patients' baseline hemodynamics. Then, for each patient, the following assistance modality was simulated for the cavopulmonary and the single ventricle (SV): (a) CVAD for cavopulmonary assistance (RCF) and PVAD assisting the SV (LCF) (RPF + LCF), (b) CVAD assisting SV and PVAD for cavopulmonary assistance (LPF + RCF). The numerical model can well reproduce patients' baseline. The cardiac output increases more importantly in the LCF + RPF configuration (35 vs. 8%). Ventricular volume decreases more evidently in the configuration LCF + RPF (28 vs. 6%), atrial pressure decreases in the LCF + RPF modality (10%), while it slightly increases in the RCF + LPF modality. The pulmonary arterial pressure slightly decreases (increases) in the configuration RCF + LPF (LCF + RPF). Ventricular external work increases in both configurations because of the total increment of the cardiac output. However, artero-ventricular coupling improves in both configurations: RCF + LPF-14%, LCF + RPF-41%. The pulsatility index decreases (increases) by 8% (13.8%) in the configuration LCF + RPF (RCF + LPF). A model could permit us to simulate extreme physiological conditions of the implantation of both CF and PF VAD on the Fontan patient and could permit to choose the proper VAD on the base of patients' condition. The configuration LCF + RPF seems to maximize the hemodynamic benefits., (© 2016 International Center for Artificial Organs and Transplantation and Wiley Periodicals, Inc.)

Failing single-ventricle (SV) patients might benefit from ventricular assist devices (VADs) as a bridge to heart transplantation. Considering the complex physiopathology of SV patients and the lack of established experience, the aim of this work was to realize and test a lumped parameter model of the cardiovascular system, able to simulate SV hemodynamics and VAD implantation effects. Data of 30 SV patients (10 Norwood, 10 Glenn, and 10 Fontan) were retrospectively collected and used to simulate patients' baseline. Then, the effects of VAD implantation were simulated. Additionally, both the effects of ventricular assistance and cavopulmonary assistance were simulated in different pathologic conditions on Fontan patients, including systolic dysfunction, diastolic dysfunction, and pulmonary vascular resistance increment. The model can reproduce patients' baseline well. Simulation results suggest that the implantation of VAD: (i) increases the cardiac output (CO) in all the three palliation conditions (Norwood 77.2%, Glenn 38.6%, and Fontan 17.2%); (ii) decreases the SV external work (SVEW) (Norwood 55%, Glenn 35.6%, and Fontan 41%); (iii) increases the mean pulmonary arterial pressure (Pap) (Norwood 39.7%, Glenn 12.1%, and Fontan 3%). In Fontan circulation, with systolic dysfunction, the left VAD (LVAD) increases CO (35%), while the right VAD (RVAD) determines a decrement of inferior vena cava pressure (Pvci) (39%) with 34% increment of CO. With diastolic dysfunction, the LVAD increases CO (42%) and the RVAD decreases the Pvci. With pulmonary vascular resistance increment, the RVAD allows the highest CO (50%) increment with the highest decrement of Pvci (53%). The single ventricular external work (SVEW) increases (decreases) increasing the VAD speed in cavopulmonary (ventricular) assistance. Numeric models could be helpful in this challenging and innovative field to support patients and VAD selection to optimize the clinical outcome and personalize the therapy., (Copyright © 2015 International Center for Artificial Organs and Transplantation and Wiley Periodicals, Inc.)

The growing population of failing single-ventricle (SV) patients might benefit from ventricular assist device (VAD) support as a bridge to heart transplantation. However, the documented experience is limited to isolated case reports. Considering the complex and different physiopathology of Norwood, Glenn, and Fontan patients and the lack of established experience, the aim of this work is to realize and test a lumped parameter model of the cardiovascular system able to simulate SV hemodynamics and VAD implantation effects to support clinical decision. Hemodynamic and echocardiographic data of 30 SV patients (10 Norwood, 10 Glenn, and 10 Fontan) were retrospectively collected and used to simulate patients' baseline. Then, the effects of VAD implantation were simulated. Simulation results suggest that the implantation of VAD: (i) increases the cardiac output and the mean arterial systemic pressure in all the three palliation conditions (Norwood 77.2 and 19.7%, Glenn 38.6 and 32.2%, and Fontan 17.2 and 14.2%); (ii) decreases the SV external work (Norwood 55%, Glenn 35.6%, and Fontan 41%); (iii) decreases the pressure pulsatility index (Norwood 65.2%, Glenn 81.3%, and Fontan 64.8%); (iv) increases the pulmonary arterial pressure in particular in the Norwood circulation (Norwood 39.7%, Glenn 12.1% and Fontan 3%); and (v) decreases the atrial pressure (Norwood 2%, Glenn 10.6%, and Fontan 8.6%). Finally, the VAD work is lower in the Norwood circulation (30.4 mL·mm Hg) in comparison with Fontan (40.3 mL·mm Hg) and to Glenn (64.5 mL·mm Hg) circulations. The use of VAD in SV physiology could be helpful to bridge patients to heart transplantations by increasing the CO and unloading the SV with a decrement of the atrial pressure and the SV external work. The regulation of the pulmonary flow is challenging because the Pap is increased by the presence of VAD. The hemodynamic changes are different in the different SV palliation step. The use of numerical models could be helpful to support patient and VAD selection to optimize the clinical outcome., (Copyright © 2015 International Center for Artificial Organs and Transplantation and Wiley Periodicals, Inc.)

Background: Right ventricular failure (RVF) is one of the major complications during LVAD. Apart from drug therapy, the most reliable option is the implantation of RVAD. However, BIVAD have a poor prognosis and increased complications. Experiments have been conducted on alternative approaches, such as the creation of an atrial septal defect (ASD), a cavo-aortic shunt (CAS) including the LVAD and a cavo-pulmonary connection (CPC). This work aims at realizing a lumped parameter model (LPM) to compare the acute hemodynamic effects of ASD, CPC, CAS, RVAD in LVAD pediatric patients with RVF., Methods: Data of 5 pediatric patients undergoing LVAD were retrospectively collected to reproduce patients baseline hemodynamics with the LPM. The effects of continuous flow LVAD implantation complicated by RVF was simulated and then the effects of ASD, CPC, CAS and RVAD treatments were simulated for each patient., Results: The model successfully reproduced patients' baseline and the hemodynamic effects of the surgical strategies. Simulating the different surgical strategies, an unloading of the right ventricle and an increment of left ventricular preload were observed with an improvement of the hemodynamics (total cardiac output: ASD +15%, CPC +10%, CAS +70% RVAD +20%; right ventricular external work: ASD -19%, CPC -46%, CAS -76%, RVAD -32%; left ventricular external work: ASD +12%, CPC +28%, RVAD +64%)., Conclusions: The use of numerical model could offer an additional support for clinical decision-making, also potentially reducing animal experiments, to compare the outcome of different surgical strategies to treat RVF in LVAD.

Considering the lack of donors, ventricular assist devices (VADs) could be an alternative to heart transplantation for failing Fontan patients, in spite of the lack of experience and the complex anatomy and physiopathology of these patients. Considering the high number of variables that play an important role such as type of Fontan failure, type of VAD connection, and setting (right VAD [RVAD], left VAD [LVAD], or biventricular VAD [BIVAD]), a numerical model could be useful to support clinical decisions. The aim of this article is to develop and test a lumped parameter model of the cardiovascular system simulating and comparing the VAD effects on failing Fontan. Hemodynamic and echocardiographic data of 10 Fontan patients were used to simulate the baseline patients' condition using a dedicated lumped parameter model. Starting from the simulated baseline and for each patient, a systolic dysfunction, a diastolic dysfunction, and an increment of the pulmonary vascular resistance were simulated. Then, for each patient and for each pathology, the RVAD, LVAD, and BIVAD implantations were simulated. The model can reproduce patients' baseline well. In the case of systolic dysfunction, the LVAD unloads the single ventricle and increases the cardiac output (CO) (35%) and the arterial systemic pressure (Pas) (25%). With RVAD, a decrement of inferior vena cava pressure (Pvci) (39%) was observed with 34% increment of CO, but an increment of the single ventricle external work (SVEW). With the BIVAD, an increment of Pas (29%) and CO (37%) was observed. In the case of diastolic dysfunction, the LVAD increases CO (42%) and the RVAD decreases the Pvci, while both increase the SVEW. In the case of pulmonary vascular resistance increment, the highest CO (50%) and Pas (28%) increment is obtained with an RVAD with the highest decrement of Pvci (53%) and an increment of the SVEW but with the lowest VAD power consumption. The use of numerical models could be helpful in this innovative field to evaluate the effect of VAD implantation on Fontan patients to support patient and VAD type selection personalizing the assistance., (Copyright © 2015 International Center for Artificial Organs and Transplantation and Wiley Periodicals, Inc.)

The aim of this work is to develop a tool to study the effect of sodium nitroprusside (SNP) on hemodynamics in conjunction with baroreflex and mechanical circulatory assistance. To this aim, a numerical model of the pharmacodynamic effect of SNP was developed and inserted into a cardiovascular circulatory model integrated with baroreflex and LVAD (continuous flow pump with atrio-aortic connection) sub-models.The experiments were carried out in two steps. In the first step the model was verified comparing simulations with experimental data acquired from mongrel dogs on mean arterial pressure (MAP), cardiac output (CO), heart rate (HR), peripheral resistance, and left ventricular properties.In the second step, the combined action of SNP and mechanical circulatory assistance was studied. Data were measured at pump off and at pump on (20000 rpm and 24000 rpm). At pump off, with a 2.5 µg/kg per min SNP infusion in heart failure condition, the MAP was reduced by approximately 8%, CO and HR increased by about 16% and 18%, respectively. In contrast, during assistance (24000 rpm) the changes in MAP, CO and HR were around -9%, +12%, and +20%, respectively. Furthermore, the effects of the drug on hemodynamic parameters at different heart conditions were significantly different. Thus, the model provides insight into the complex interactions between baroreflex, drug infusion, and LVAD and could be a support for clinical decision-making in cardiovascular pathologies.

Despite 50 years of research to assess the intra-aortic balloon pump (IABP) effects on patients' hemodynamics, some issues related to the effects of this therapy are still not fully understood. One of these issues is the effect of IABP, its inflation timing and duration on peripheral circulation autonomic controls. This work provides a systematic analysis of IABP effects on baroreflex using a cardiovascular hybrid model, which consists of computational and hydraulic submodels. The work also included a baroreflex computational model that was connected to a hydraulic model with a 40-cm(3) balloon. The IABP was operated at different inflation trigger timings (-0.14 to 0.31 s) and inflation durations (0.05-0.45 s), with time of the dicrotic notch being taken as t = 0. Baroreflex-dependent parameters-afferent and efferent pathway activity, heart rate, peripheral resistance, and venous tone-were evaluated at each of the inflation trigger times and durations considered. Balloon early inflation (0.09 s before the dicrotic notch) with inflation duration of 0.25 s generated a maximum net increment of afferent pathway activity of 10%, thus leading to a decrement of efferent sympathetic activity by 15.3% compared with baseline values. These times also resulted in a reduction in peripheral resistance and heart rate by 4 and 4.3% compared with baseline value. We conclude that optimum IABP triggering time results in positive effects on peripheral circulation autonomic controls. Conversely, if the balloon is not properly timed, peripheral resistance and heart rate may even increase, which could lead to detrimental outcomes., (© 2012, Copyright the Authors. Artificial Organs © 2012, International Center for Artificial Organs and Transplantation and Wiley Periodicals, Inc.)

We investigated the effects of the intra-aortic balloon pump (IABP) on endocardial viability ratio (EVR), cardiac output (CO), end-systolic (V(es)) and end-diastolic (V(ed)) ventricular volumes, total coronary blood flow (TCBF), and ventricular energetics (external work [EW], pressure-volume area [PVA]) under different ventricular (E(max) and diastolic stiffness) and circulatory (arterial compliance) parameters. We derived a hybrid model from a computational model, which is based on merging computational and hydraulic submodels. The lumped parameter computational submodel consists of left and right hearts and systemic, pulmonary, and coronary circulations. The hydraulic submodel includes part of the systemic arterial circulation, essentially a silicone rubber tube representing the aorta, which contains a 40-mL IAB. EVR, CO, V(es), and V(ed), TCBF and ventricular energetics (EW, PVA) were analyzed against the ranges of left ventricular E(max) (0.3-0.5-1 mm Hg/cm(3)) and diastolic stiffness V(stiffness) (≈0.08 and ≈0.3 mm Hg/cm(3), obtained by changing diastolic stiffness constant) and systemic arterial compliance (1.8-2.5 cm(3)/mm Hg). All experiments were performed comparing the selected variables before and during IABP assistance. Increasing E(maxl) from 0.5 to 2 mm Hg/cm(3) resulted in IABP assistance producing lower percentage changes in the selected variables. The changes in ventricular diastolic stiffness strongly influence both absolute value of EVR and its variations during IABP (71 and 65% for lower and higher arterial compliance, respectively). V(ed) and V(es) changes are rather small but higher for lower E(max) and higher V(stiffness). Lower E(max) and higher V(stiffness) resulted in higher TCBF and CO during IABP assistance (∼35 and 10%, respectively). The use of this hybrid model allows for testing real devices in realistic, stable, and repeatable circulatory conditions. Specifically, the presented results show that IABP performance is dependent, at least in part, on left ventricular filling, ejection characteristics, and arterial compliance. It is possible in this way to simulate patient-specific conditions and predict the IABP performance at different values of the circulatory or ventricular parameters. Further work is required to study the conditions for heart recovery modeling, baroreceptor controls, and physiological feedbacks., (© 2011, Copyright the Authors. Artificial Organs © 2011, International Center for Artificial Organs and Transplantation and Wiley Periodicals, Inc.)

The pulsatile catheter pump (PUCA pump) is a left ventricular assist device that provides additional flow to the left ventricle. It is usually run in order to ensure a counterpulsation effect, as in the case of the intra-aortic balloon pump (IABP). Because of this similarity, a comparison between the PUCA pump and the IABP was conducted from both the hemodynamic and energetic points of view. Numerical models of the two devices were created and connected to the CARDIOSIM cardiovascular simulator. The PUCA and IABP models were then verified using in vivo experimental data and literature data, respectively. Numerical experiments were conducted for different values of left ventricular end systolic elastance (Els) and systemic arterial compliance (Csa). The energetic comparison was conducted taking into account the diastolic pressure time index and the endocardial viability ratio. Hemodynamic results expressed as cardiac output (CO) and mean coronary blood flow (CBF) show that both the IABP and the PUCA pump efficacy decrease with higher values of Els and Csa. The IABP especially shows higher sensitivity to these parameters, to the extent that in some cases CO actually drops and CBF does not increase. On the other hand, for lower values of Csa, IABP performance improves so much that the PUCA pump flow needs to be increased in order to ensure a hemodynamic effect comparable to that of the IABP. Energetic results show a trend similar to the hemodynamic ones. The study will be continued by investigating other energetic variables and the autonomic response of the cardiovascular system.

To assess the interaction between a continuous flow pump (CFP) and the native ventricle (NV) when both pumps are giving a flow contribution. The pumping system, composed of NV and of CFP, is replaced by an equivalent pump (EP) with the same NV filling characteristics and heart rate. It is assumed that EP cardiac output is equal to the sum of NV and CFP flows and that its E max is correlated to the CFP pump speed. Both the pumping system and EP are addressed with a closed loop lumped parameters cardiovascular model connected to a Heart Mate II (HM-II) CFP. The experiments were performed to: 1: verify EP E max correlation with CFP speed. Resulting correlation:∼0.98; 2: verify EP parameters calculation accuracy, in comparison with the pumping system parameters for different values of peripheral resistance, E max_NV , HR and CFP speed (8000–11000 RPM). Resulting average error: less than 4%; 3: show how EP can be used to obtain the desired haemodynamic or energetic conditions, then feeding the results into the pumping system, so as to regulate CFP speed accordingly. EP merges the properties of the pumping system composed of NV and CFP into a single pulsatile pump. The described methodology can be a useful support to optimise both haemodynamic and energetic variables in the pumping system when, with the simultaneous presence of CFP and NV flows, flow distribution between the two pumps becomes a critical issue. [ABSTRACT FROM AUTHOR]

Patients with a Ventricular Assist Device (VAD) are hemodynamically stable but show an impaired exercise capacity. Aim of this work is to identify and to describe the limiting factors of exercise physiology with a VAD. We searched for data concerning exercise in heart failure condition and after VAD implantation from the literature. Data were analyzed by using a cardiorespiratory simulator that worked as a collector of inputs coming from different papers. As a preliminary step the simulator was used to reproduce the evolution of hemodynamics from rest to peak exercise (ergometer cycling) in heart failure condition. Results evidence an increase of cardiac output of +2.8 l/min and a heart rate increase to 67% of the expected value. Then, we simulated the effect of a continuous-flow VAD at both rest and exercise. Total cardiac output increases of +3.0 l/min (+0.9 l/min due to the VAD and +2.1 l/min to the native ventricle). Since the left ventricle works in a non-linear portion of the diastolic stiffness line, we observed a consistent increase of pulmonary capillary wedge pressure (from 14 to 20 mmHg) for a relatively small increase of end-diastolic volume (from 182 to 189 cm3). We finally increased VAD speed during exercise to the maximum possible value and we observed a reduction of wedge pressure (-4.5 mmHg), a slight improvement of cardiac output (8.0 l/min) and a complete unloading of the native ventricle. The VAD can assure a proper hemodynamics at rest, but provides an insufficient unloading of the left ventricle and does not prevent wedge pressure from rising during exercise. Neither the VAD provides major benefits during exercise in terms of total cardiac output, which increases to a similar extend to an unassisted heart failure condition. VAD speed modulation can contribute to better unload the ventricle but the maximal flow reachable with the current devices is below the cardiac output observed in a healthy heart. [ABSTRACT FROM AUTHOR]