Hemodynamic Effect of Pulsatile on Blood Flow Distribution with VA ECMO: A Numerical Study.

The pulsatile properties of arterial flow and pressure have been thought to be important. Nevertheless, a gap still exists in the hemodynamic effect of pulsatile flow in improving blood flow distribution of veno-arterial extracorporeal membrane oxygenation (VA ECMO) supported by the circulatory system. The finite-element models, consisting of the aorta, VA ECMO, and intra-aortic balloon pump (IABP) are proposed for fluid-structure interaction calculation of the mechanical response. Group A is cardiogenic shock with 1.5 L/min of cardiac output. Group B is cardiogenic shock with VA ECMO. Group C is added to IABP based on Group B. The sum of the blood flow of cardiac output and VA ECMO remains constant at 4.5 L/min in Group B and Group C. With the recovery of the left ventricular, the flow of VA ECMO declines, and the effective blood of IABP increases. IABP plays the function of balancing blood flow between left arteria femoralis and right arteria femoralis compared with VA ECMO only. The difference of the equivalent energy pressure (dEEP) is crossed at 2.0 L/min to 1.5 L/min of VA ECMO. PPI' (the revised pulse pressure index) with IABP is twice as much as without IABP. The intersection with two opposing blood generates the region of the aortic arch for the VA ECMO (Group B). In contrast to the VA ECMO, the blood intersection appears from the descending aorta to the renal artery with VA ECMO and IABP. The maximum time-averaged wall shear stress (TAWSS) of the renal artery is a significant difference with or not IABP (VA ECMO: 2.02 vs. 1.98 vs. 2.37 vs. 2.61 vs. 2.86 Pa; VA ECMO and IABP: 8.02 vs. 6.99 vs. 6.62 vs. 6.30 vs. 5.83 Pa). In conclusion, with the recovery of the left ventricle, the flow of VA ECMO declines and the effective blood of IABP increases. The difference between the equivalent energy pressure (EEP) and the surplus hemodynamic energy (SHE) indicates the loss of pulsation from the left ventricular to VA ECMO. 2.0 L/min to 1.5 L/min of VA ECMO showing a similar hemodynamic energy loss with the weak influence of IABP.

Identification of Type 2 Diabetes Based on a Ten-Gene Biomarker Prediction Model Constructed Using a Support Vector Machine Algorithm.

Background: Type 2 diabetes is a major health concern worldwide. The present study is aimed at discovering effective biomarkers for an efficient diagnosis of type 2 diabetes. Methods: Differentially expressed genes (DEGs) between type 2 diabetes patients and normal controls were identified by analyses of integrated microarray data obtained from the Gene Expression Omnibus database using the Limma package. Functional analysis of genes was performed using the R software package clusterProfiler. Analyses of protein-protein interaction (PPI) performed using Cytoscape with the CytoHubba plugin were used to determine the most sensitive diagnostic gene biomarkers for type 2 diabetes in our study. The support vector machine (SVM) classification model was used to validate the gene biomarkers used for the diagnosis of type 2 diabetes. Results: GSE164416 dataset analysis revealed 499 genes that were differentially expressed between type 2 diabetes patients and normal controls, and these DEGs were found to be enriched in the regulation of the immune effector pathway, type 1 diabetes mellitus, and fatty acid degradation. PPI analysis data showed that five MCODE clusters could be considered as clinically significant modules and that 10 genes (IL1B, ITGB2, ITGAX, COL1A1, CSF1, CXCL12, SPP1, FN1, C3, and MMP2) were identified as "real" hub genes in the PPI network using algorithms such as Degree, MNC, and Closeness. The sensitivity and specificity of the SVM model for identifying patients with type 2 diabetes were 100%, with an area under the curve of 1 in the training as well as the validation dataset. Conclusion: Our results indicate that the SVM-based model developed by us can facilitate accurate diagnosis of type 2 diabetes.

Fluid shear stress activates YAP to promote epithelial-mesenchymal transition in hepatocellular carcinoma.

Epithelial-mesenchymal transition (EMT) mediated by fluid shear stress (FSS) in the tumor microenvironment plays an important role in driving metastasis of the malignant tumor. As a mechanotransducer, Yes-associated protein (YAP) is known to translocate into the nucleus to initiate transcription of genes involved in cell proliferation upon extracellular biophysical stimuli. Here, we showed that FSS facilitated cytoskeleton rearrangement in hepatocellular carcinoma cells, which led to the release of YAP from its binding partner, integrin ß subunit, in the cytomembrane. Moreover, we found that upregulation of guanine nucleotide exchange factor (GEF)-H1, a microtubule-associated Rho GEF, is a critical step in the FSS-induced translocation of YAP. Nuclear YAP activated the expression of the EMT-regulating transcription factor SNAI1, but suppressed the expression of N6-methyladenosine (m6 A) modulators; together, this promoted the expression of EMT-related genes. We also observed that FSS-treated HepG2 cells showed markedly increased tumorigenesis and metastasis in vivo. Collectively, our findings unravel the underlying molecular processes by which FSS induces translocation of YAP from the cytomembrane to the nucleus, contributes to EMT and enhances metastasis in hepatocellular carcinoma.

Computational numerical analysis of different cannulation methods during cardiopulmonary bypass of type A aortic dissection model based on computational fluid dynamics.

BACKGROUND: The aim of the present study was to use a numerical simulation based on computational fluid dynamics (CFD) to analyze the difference of different cannulation methods on hemodynamics characteristic in a type A aortic dissection (TAAD) model. METHODS: A finite-element analysis based on the CFD model of a TAAD patient was used, and axillary artery cannulation (AAC), innominate artery cannulation (IAC), and femoral artery cannulation (FAC) were analyzed under different situations, including a cardiac output (CO) of 2.5 L/min and cardiopulmonary bypass (CPB) of 2.5 L/min (partial CPB before cross-clamping aorta, defined as condition A), and a CO of 0 L/min and CPB of 5 L/min (aortic cross-clamping phase, defined as condition B). The insertion of an 8-mm cannula into the different models was simulated. Hemodynamic characteristics, including wall shear stress, wall stress, blood flow, and velocity were analyzed. RESULTS: In condition A, the total flow of branches of the aortic arch was 2,009.5 mL/min (AAC), 1,855.47 mL/min (IAC), and 1,648.03 mL/min (FAC). All cannulation methods improved left renal blood perfusion. However, in relation to blood flow in the right renal artery, FAC showed the highest blood flow (105 mL/min). The results in condition B were similar to those of condition A. The velocity, shear stress, and stress of entry tear via AAC and IAC decreased in condition B compared with condition A. The velocity, shear stress, stress of tear via AAC was lower than that of IAC. CONCLUSIONS: Different cannulation modes have an effect on the hemodynamic characteristic of the tear, but this effect is related to different states of CPB. AAC was found to superior to IAC, especially in reducing velocity, stress, and shear stress of site of tear. However, IAC and AAC are more conductive to blood supply than FAC in branch vessels of the aortic arch without being affected by the CPB state.

A patient-specific modelling method of blood circulatory system for the numerical simulation of enhanced external counterpulsation.

Lumped parameter model (LPM) is a common numerical model for hemodynamic simulation of human's blood circulatory system. The numerical simulation of enhanced external counterpulsation (EECP) is a typical biomechanical simulation process based on the LPM of blood circulatory system. In order to simulate patient-specific hemodynamic effects of EECP and develop best treatment strategy for each individual, this study developed an optimization algorithm to individualize LPM elements. Physiological data from 30 volunteers including approximate aortic pressure, cardiac output, ankle pressure and carotid artery flow were clinically collected as optimization objectives. A closed-loop LPM was established for the simulation of blood circulatory system. Aiming at clinical data, a sensitivity analysis for each element was conducted to identify the significant ones. We improved the traditional simulated annealing algorithm to iteratively optimize the sensitive elements. To verify the accuracy of the patient-specific model, 30 samples of simulated data were compared with clinical measurements. In addition, an EECP experiment was conducted on a volunteer to verify the applicability of the optimized model for the simulation of EECP. For these 30 samples, the optimization results show a slight difference between clinical data and simulated data. The average relative root mean square error is lower than 5%. For the subject of EECP experiment, the relative error of hemodynamic responses during EECP is lower than 10%. This slight error demonstrated a good state of optimization. The optimized modeling algorithm can effectively individualize the LPM for blood circulatory system, which is significant to the numerical simulation of patient-specific hemodynamics.

The Effect of Different Types of Mechanical Circulatory Support on Mortality of Patients after Adult Cardiac Surgery: A Systematic Review and Meta-Analysis.

OBJECTIVES: Sample size may limit the ability of individual studies to detect differences in clinical outcomes between extracorporeal membrane oxygenation (ECMO) alone and ECMO plus intra-aortic balloon pump (IABP) after adult cardiac surgery. Therefore, we undertook a meta-analysis of the best evidence available on the comparison of clinical outcomes of ECMO alone and ECMO plus IABP after adult cardiac surgery. METHODS: PubMed, EMBASE, Web of Science, and Cochrane Center Registry of Controlled Trials were searched for studies comparing the use of ECMO alone and ECMO plus IABP after adult cardiac surgery. A meta-analysis and a sensitivity analysis were conducted. RESULTS: Among the 472 screened articles, 24 studies (1302 cases of ECMO plus IABP and 1603 cases of ECMO) were included. A significant relationship between patient risk profile and benefits from IABP plus ECMO was found in terms of the 30-day mortality (odds ratio [OR] 0.75; 95% confidence interval [CI] 0.62 to 0.91; P = .004) with postcardiotomy shock (PCS). However, ECMO alone was associated with lower in-hospital mortality (OR 1.75; 95% CI 1.06 to 3.01; Z = 2.19; P = .03) compared with ECMO plus IABP without PCS. CONCLUSIONS: Pooled data show that patients receiving IABP plus ECMO with PCS have lower 30-day mortality than those receiving ECMO also, which in turn show higher 30-day mortality in patients with IABP plus ECMO without PCS. Further randomized studies are warranted to corroborate these observational data.

Short-term outcomes of on- vs off-pump coronary artery bypass grafting in patients with left ventricular dysfunction: a systematic review and meta-analysis.

OBJECTIVES: Does the manipulation of the off-pump CABG (OPCAB) in patient with depressed left ventricular function is better than on-pump CABG (ONCAB) approach in in-hospital mortality and morbidities? Here we undertook a meta-analysis of the best evidence available on the comparison of primary and second clinical outcomes of the off-pump and on-pump CABG. DESIGN: Systematic literature reviewer and meta-analysis. DATA SOURCES: PubMed, EMBASE, Web of science and Cochrane Center Registry of Controlled Trials were searched the studies which comparing the use of the off-pump CABG(OPCAB) and on-pump CABG (ONCAB) for patients with LVD during January 1990.1 to January 2018. ELIGIBILITY CRITERIA: All observation studies and randomized controlled trials comparing on-pump and off-pump as main technique for multi-vessel coronary artery disease (defined as severe stenosis (>70%) in at least 2 major diseased coronary arteries) with left ventricular dysfunction(defined as ejection fraction (EF) 40% or less) were included. DATA EXTRACTION AND SYNTHESIS: Authors will screen and select the studies extract the following data, first author, year of publication, trial characters, study design, inclusion and exclusion criteria, graft type, clinical outcome, assess the risk of bias and heterogeneity. Study-specific estimates will pool through the modification of the Newcastle-Ottawa scale for the quality of study and while leave-one-out analysis will be used to detect the impact of individual studies on the robustness of outcomes. RESULTS: Among the 987 screened articles, a total of 16 studies (32,354 patients) were included. A significant relationship between patient risk profile and benefits from OPCAB was found in terms of the 30-day mortality (odds ratio [OR], 0.84; 95% confidence interval [CI], 0.73-0.97; P = 0.02), stroke (OR, 0.69; 95% CI, 0.55-0.86; P = 0.00), myocardial infarction (MI) (OR, 0.71; 95% CI, 0.53-0.96; P = 0.02), renal failure (OR, 0.71; 95% CI, 0.55-0.93; P = 0.01), pulmonary complication (OR, 0.68; 95% CI, 0.52-0.90; P = 0.01), infection (OR, 0.67; 95% CI, 0.49-0.91; P = 0.00),postoperative transfusion (OR, 0.25; 95% CI, 0.08-0.84; P = 0.02) and reoperation for bleeding (OR, 0.56; 95% CI, 0.41-0.75; P = 0.00). There was no significant difference in atrial fibrillation (AF) (OR, 0.96;95%; CI, 0.78-1.41; P = 0.56) and neurological dysfunction (OR, 0.88; 95% CI, 0.49-1.57; P = 0.65). CONCLUSIONS: Compared with the on-pump CABG with LVD, using the off-pump CABG is a better choice for patients with lower mortality, stroke, MI, RF, pulmonary complication, infection, postoperative transfusion and reoperation for bleeding. Further randomized studies are warranted to corroborate these observational data.

Hemodynamic effects of pulsatile unloading of left ventricular assist devices (LVAD) on intraventricular flow and ventricular stress.

The role of pulsatile unloading in hemodynamic changes in intraventricular flow and ventricular wall stress remains unknown. In this study, a finite element model of the left ventricle (LV) is proposed to calculate the mechanical response. The constitutive model of the LV is composed of a quasi-incompressible transversely isotropic model and an active contraction of the myocardium model. Pulsatile unloading is provided by the left ventricular assist device (LVAD), which is implanted between the aortic root and aortic arch. Support models (constant speed and co-pulse) were utilized to study the effect of pulsatile unloading on intraventricular flow and ventricular stress. The result indicates that the formation time of the vortex increases under pulsatile unloading. The area rate of high time-averaged wall shear stress (TAWSS) increased after pulsatile unloading. The area of the high oscillatory shear index (OSI) region (OSI > 0.375) was calculated for heart failure, constant speed, and co-pulse (9.9 cm2, 9.6 cm2, and 9.2 cm2, respectively). The maximum value of the stress that reflects the level of stretch declined after pulsatile unloading (66.4 kPa, 30.9 kPa, and 21.3 kPa, respectively). Besides, pulsatile unloading impacts the maximum value of thickness at the ventricular wall (-0.75 mm, -1 mm, and -1.25 mm, respectively). The change ratios of the thickness are 10%, 14%, and 17%, respectively. In conclusion, pulsatile unloading contributes to the distribution of intraventricular flow and the formation time of the vortex. Co-pulse support significantly reduces the maximum value of the ventricular wall stress and the area of high stress on the ventricular wall.

Numerical analysis of aortic hemodynamics under the support of venoarterial extracorporeal membrane oxygenation and intra-aortic balloon pump.

BACKGROUND AND OBJECTIVE: A gap still exists in the hemodynamic effect of intra-aortic balloon pump (IABP), venoarterial extracorporeal membrane oxygenation (VA-ECMO), and VA-ECMO plus IABP on the blood perfusion of the coronary artery, brain, and lower limb; the relation between heart flow and ECMO flow; and the wall stress of vessels. METHODS: A finite-element model of the aorta, ECMO, and IABP was proposed to calculate the mechanical response via fluid-structure interaction. Heart failure (HF), IABP, ECMO, and ECMO plus IABP were utilized to study the effect of support models. RESULTS: For the pressure curve, VA-ECMO weakened the dicrotic notch of pressure compared with HF and the pulsatile index (0.494 vs. 0.706 vs. 0.471 vs. 0.613). IABP, ECMO, and ECMO plus IABP increased the perfusion of the coronary, brain, and renal artery compared with HF. However, ECMO and ECMO plus IABP clearly reduced the blood flow of the left arteria femoralis compared to that of the right arteria femoralis (ECMO: 194.04 vs. 730.80 mL/min; ECMO plus IABP: 342.15 vs. 947.22 mL/min). In addition, the flow of ECMO accessed the renal artery more than the left ventricular flow. Greater ventricular flow perfused to the renal artery at a diastolic period for ECMO plus IABP, especially at the time points of 2.192 s and 2.304 s. Compared to the velocity distribution with ECMO, the flow of the right arteria femoralis was increased in the process of IABP-on. According to these four cases, the stress of the vascular wall was increased for ECMO support at the systolic period. The peak wall stress of ECMO is increased by 20% at 1.68 s. CONCLUSIONS: ECMO plus IABP is more conducive to the blood supply than other cases from the result of numerical simulation. The location of blood intersection was generated in the region of the renal artery, which is estimated carefully.

Minimally Invasive CABG or Hybrid Coronary Revascularization for Multivessel Coronary Diseases: Which Is Best? A Systematic Review and Metaanalysis.

OBJECTIVES: Minimally invasive coronary revascularization (MICR) involves minimally invasive direct coronary artery bypass grafting (MIDCAB) and robotic-assisted coronary artery bypass grafting (RCABG), and hybrid coronary revascularization (HCR) aims to combine MICR/RCABG on left anterior descending (LAD) and percutaneous coronary interventions (PCI) on non-LAD lesions. We performed a systematic review and metaanalysis to compare clinical outcome after MICR and HCR. METHODS: A metaanalysis was carried out through searching PubMed, EMBASE, Web of Science, and Medline for comparative studies evaluating the primary and secondary clinical end points. RESULTS: A systematic literature search identified 8 observational studies that satisfied our inclusion criteria, including being suitable for metaanalysis; the studies were between 1990 and 2018 and included 1084 cases of HCR and 2349 cases of MICR. Metaanalysis of these studies showed that HCR was associated with a reduced need for ICU LOS (WMD -11.46 hours, 95% CI, -18.76 ~ -4.25, P = .02), to hospital time (WMD -1.34 hours, 95% CI, -2.42 to 0.26, P < .01), and blood transfusion (OR 0.43, 95% CI, 0.31-0.59, P < .00001) than MICR. Comparisons of individual components showed no significant difference in terms of in-hospital mortality, MACCE, shock, myocardial infarction (MI), long-term survival, total variable cost, and surgical complications (including renal failure, chest drainage, bleeding). CONCLUSIONS: HCR was noninferior to MICR in terms of in-hospital mortality, MACCE, shock, MI, long-term survival, total variable cost, and surgical complications (including renal failure, chest drainage, bleeding), whereas HCR was associated with a reduced need for ICU LOS, hospital time, and blood transfusion than MICR and less infection than MICR. Further randomized studies are warranted to corroborate these observational data.

Computational analysis of the hemodynamic characteristics under interaction influence of ß-blocker and LVAD.

BACKGROUND: Hemodynamic characteristics of the interaction influence among support level and model of LVAD, and coupling ß-blocker has not been reported. METHODS: In this study, the effect of support level and model of LVAD on cardiovascular hemodynamic characteristics is investigated. In addition, the effect of ß-blocker on unloading with LVAD is analyzed to elucidate the mechanism of LVAD coupling ß-blocker. A multi-scale model from cell level to system level is proposed. Moreover, LVAD coupling ß-blocker has been researching to explain the hemodynamics of cardiovascular system. RESULTS: Myocardial force was decreased along with the increase of support level of LVAD, and co-pulse mode was the lowest among the three support modes. Additionally, the ß-blocker combined with LVAD significantly reduced the left ventricular volume compared with LVAD support without ß-blocker. However, the left ventricular pressure under both cases has no significant difference. External work of right ventricular was increased along with the growth of support level of only LVAD. The LVAD under co-pulse mode achieved the lowest right-ventricular EW among the three support modes. CONCLUSIONS: Co-pulse mode with ß-blocker could be an optimal strategy for promoting cardiac structure and function recovery.

Hemodynamic effects of perfusion level of peripheral ECMO on cardiovascular system.

BACKGROUND: Peripheral ECMO is an effective cardiopulmonary support in clinical. The perfusion level could directly influence the performances and complications. However, there are few studies on the effects of the perfusion level on hemodynamics of peripheral ECMO. METHODS: The geometric model of cardiovascular system with peripheral ECMO was established. The blood assist index was used to classify the perfusion level of the ECMO. The flow pattern from the aorta to the femoral artery and their branches, blood flow rate from aorta to brain and limbs, flow interface, harmonic index of blood flow, wall shear stress and oscillatory shear index were chosen to evaluate the hemodynamic effects of peripheral ECMO. RESULTS: The results demonstrated that the flow rate of aorta outlets increased and perfusion condition had been improved. And the average flow to the upper limbs and brain has a positive correlation with BAI (r = 0.037, p < 0.05), while there is a negative correlation with lower limbs (r = - 0.054, p < 0.05). The HI has negative correlation with BAI (p < 0.05, r < 0). The blood interface is further from the heart with the BAI decrease. And the average WSS has negative correlation with BAI (p < 0.05, r = - 0.983) at the bifurcation of femoral aorta and has positive correlation with BAI (p < 0.05, r = 0.99) at the inner aorta. The OSI under different BAI is higher (reaching 0.4) at the inner wall of the aortic arch, the descending aorta and the femoral access. CONCLUSIONS: The pathogenesis of peripheral ECMO with different perfusion levels varies; its further research will be thorough and extensive.

Pulsatile Support Mode of BJUT-II Ventricular Assist Device (VAD) has Better Hemodynamic Effects on the Aorta than Constant Speed Mode: A Primary Numerical Study.

BACKGROUND BJUT-II VAD is a novel left ventricular assist device (LVADs), directly implanted into the ascending aorta. The pulsatile support mode is proposed to achieve better unloading performance than constant speed mode. However, the hemodynamic effects of this support mode on the aorta are still unclear. The aim of this study was to clarify the hemodynamic effects BJUT-II VAD under pulsatile support mode on the aorta. MATERIAL AND METHODS Computational fluid dynamics (CFD) studies, based on a patient-specific aortic geometric model, were conducted. Wall shear stress (WSS), averaged WSS (avWSS), oscillatory shear index (OSI), and averaged helicity density (Ha) were calculated to compare the differences in hemodynamic effects between pulsatile support mode and constant speed mode. RESULTS The results show that avWSS under pulsatile support mode is significantly higher than that under constant speed mode (0.955Pa vs. 0.675Pa). Similarly, the OSI value under pulsatile mode is higher than that under constant speed mode (0.104 vs. 0.057). In addition, Ha under pulsatile mode for all selected cross-sections is larger than that under constant mode. CONCLUSIONS BJUT-II VAD, under pulsatile control mode, may prevent atherosclerosis lesions and aortic remodeling. The precise effects of pulsatile support mode on atherosclerosis and aortic remodeling need to be further studied in animal experiments.

Hemodynamic Differences Between Central ECMO and Peripheral ECMO: A Primary CFD Study.

BACKGROUND Veno-arterial extracorporeal membrane oxygenation (VAECMO), including central ECMO (cECMO) and peripheral ECMO (pECMO), is widely used in cardiopulmonary surgery. The outcomes and complications of both types of ECMO are quite different from each other. The hemodynamic differences among them are hypothesized as a key factor. Hence, a numerical study was conducted to test this hypothesis. MATERIAL AND METHODS Ideal cardiovascular models with pECMO and cECMO were established. The aortic pressure and flow rate were chosen as boundary conditions. The flow pattern, blood flow distributions, flow junction, harmonic index (HI) of blood flow, wall shear stress (WSS), and the oscillatory shear index (OSI) were calculated to evaluate the hemodynamic states. RESULTS pECMO could achieve better upper limb and brain perfusion (0.05458 vs. 0.05062 kg/s), and worse lower limb perfusion (0.03067 vs. 0.03401 kg/s). There exist low WSS (<0.4 pa) regions at the inner and posterior wall of the aorta, and high WSS (>2 pa) region at the access of the femoral artery. These regions also have relatively high OSI value (reaching 0.45). In contrast, for cECMO, there exist high WSS at the posterior wall of the aortic arch. CONCLUSIONS The hemodynamic performances of various types of ECMO are different from each other, which maybe the key reasons for the differences in the outcomes and complications. Therefore, for pEMCO, the lower-extremity ischemia is a complication that must be considered. The type, support level, and duration of ECMO should also be carefully regulated according to the patients' condition, as they are the important factors related to vascular complications.

The effect of captopril on the performance of the control strategies of BJUT-II VAD.

BACKGROUND: With the development of left ventricular assist device (LVAD), the long-term support has been paid more attention by various researchers. According to previous researches, the combination of LVAD and pharmacological therapy can significantly improve the heart rate recovery and survival rate of patient. However, the effect of pharmacological therapy on the cardiovascular hemodynamic states with LVAD support is still unclear. METHODS: In this study, pharmacokinetic model of captopril is established to describe the relationship between plasma-drug concentration and time. Then, combination model, consisting of pharmacokinetic model of captopril and lumped parameter model of cardiovascular system with BJUT-II VAD support, is established to mimic the effect of pharmacological therapy on cardiovascular hemodynamics. BAI control strategy and HR control strategy for BJUT-II VAD are chosen to evaluate their performance by the combination model. RESULTS: The simulation results demonstrate that the concentration of captopril could affect the pressure and heart rate by changing the peripheral resistance, and then affect the performance of BJUT-II VAD in a short duration. Under the regulation of control strategies of BJUT-II VAD, the hemodynamic states of cardiovascular system returned to the standard value in 10 s. CONCLUSION: This study could provide useful information about how to design coupled strategy of LVAD support and pharmacological therapy.

The study on hemodynamic effect of varied support models of BJUT-II VAD on coronary artery: a primary CFD study.

BJUT-II VAD (Beijing University of Technology ventricular assist device II) is a novel left ventricular assist device. Because of the special connection between the pump and native heart, the hemodynamic effects of BJUT-II VAD on coronary artery are still unclear. Hence, numerical simulations have been conducted to clarify changes in hemodynamic effects of different support modes. A patient-specific left coronary arterial geometric model is reconstructed based on the computed tomography (CT) data. Three support modes, "constant speed mode," "co-pulse mode," and "counter pulse mode," are used in this study. The wall shear stress (WSS), wall shear stress gradient (WSSG), cycle-averaged wall shear stress (avWSS), oscillatory shear index (OSI), and the flow pattern are calculated to evaluate the hemodynamic states of coronary artery. The computational results demonstrate that the hemodynamic states of coronary artery are directly affected by the support modes. The co-pulse modes could achieve the highest blood perfusion (constant speed: 153 ml/min vs. co-pulse: 775 ml/min vs. counter pulse: 140 ml/min) and the highest avWSS (constant speed: 18.1 Pa vs. co-pulse: 42.6 Pa vs. counter pulse: 22.6 Pa). In addition, both the WSS and WSSG at the time of peak blood velocity under the constant speed mode are lower than those under other two support modes. In contrast, the counter pulse mode generates the highest OSI value (constant speed: 0.365 vs. co-pulse: 0.379 vs. counter pulse: 0.426). BJUT-II VAD under co-pulse mode may have benefits for improving coronary perfusion and preventing the development of atherosclerosis; however, the constant speed mode may have benefit for preventing the development of plaque vulnerability.

Hemodynamic effects of various support modes of continuous flow LVADs on the cardiovascular system: a numerical study.

BACKGROUND: The aim of this study was to determine the hemodynamic effects of various support modes of continuous flow left ventricular assist devices (CF-LVADs) on the cardiovascular system using a numerical cardiovascular system model. MATERIAL AND METHODS: Three support modes were selected for controlling the CF-LVAD: constant flow mode, constant speed mode, and constant pressure head mode of CF-LVAD. The CF-LVAD is established between the left ventricular apex and the ascending aorta, and was incorporated into the numerical model. Various parameters were evaluated, including the blood assist index (BAI), the left ventricular external work (LVEW), the energy of blood flow (EBF), pulsatility index (PI), and surplus hemodynamic energy (SHE). RESULTS: The results show that the constant flow mode, when compared to the constant speed mode and the constant pressure head mode, increases LVEW by 31% and 14%, and EBF by 21% and 15%, respectively, indicating that this mode achieved the best ventricular unloading among the 3 support modes. As BAI is increased, PI and SHE are gradually decreased, whereas PI of the constant pressure head reaches the maximum value. CONCLUSIONS: The study demonstrates that the continuous flow control mode of the CF-LVAD may achieve the highest ventricular unloading. In contrast, the constant rotational speed mode permits the optimal blood perfusion. Finally, the constant pressure head strategy, permitting optimal pulsatility, should optimize the vascular function.

The hemodynamic effect of phase differences between the BJUT-II ventricular assist device and native heart on the cardiovascular system.

The BJUT-II VAD (which was previously called the intra-aorta pump) is a novel left ventricular assist device (LVAD) with a special structure and connection with the native heart. The hemodynamic effect of the phase difference of this pump on the cardiovascular system is still unclear. In this work, seven speed waveforms, whose phase differences vary from 0° to 180°, are used to evaluate the hemodynamic effect of change in phase difference on the cardiovascular system. The external work (EW), equivalent afterload (EAL), pulsatile ratio (PR), and mean aortic pressure during diastolic period (MAPD) are chosen to evaluate the hemodynamic state of the circulatory system. Mathematical study results show that the support levels generated by the BJUT-II VAD under various phase differences are comparable. In contrast, EW, EAL, PR, and MAPD are significantly affected by change in phase difference. It is found that EW reaches its maximum value when the phase difference equals 30°. Similarly, EAL declines with increasing phase difference. PR reaches its maximum value when the phase difference is at 60°. In addition, MAPD decreases with increasing phase difference and then achieves its maximum value at 30°. To obtain comprehensive evaluation of the hemodynamic effects of phase difference on the cardiovascular system, a weight detection algorithm (WDA) whose output indicates the hemodynamic state of the circulatory system is also designed, with EW, PR, and MAPD chosen as the inputs. The minimum value of the output of the WDA indicates the optimal hemodynamic state and optimal phase difference for the BJUT-II VAD. According to the output of the WDA, 30° is considered to be the optimal phase difference for the BJUT-II VAD.

Development of ventricular assist devices in China: present status, opportunities and challenges.

The growing number of heart failure patients and the scarcity of organ donors account for the huge need for the development of mechanical circulatory systems, including ventricular assist devices (VADs) and artificial hearts, in China. Several research programmes on blood pumps have been under way for the last three decades. However, unlike in other countries, the development of VADs has been extremely slow, and no system is currently approved and available for clinical application. There are many reasons for this situation. This article provides an overview of the present development of experimental and clinical research on VADs in China. In addition, the challenges for the clinical development of mechanical circulatory support in China are discussed.

Physiological controller of an intra-aorta pump based on baroreflex sensitivity.

Left ventricular assist devices are increasingly used for long-term support in heart failure patients. It is important to find an optimum operating point for the pump that is appropriate for the existing function of the heart and the state of the circulatory system. Therefore, baroreflex sensitivity (BRS), as an indicator of heart function, is chosen as the control variable. In order to find an optimum point automatically, an extremum search algorithm (ESA) is designed to find an optimal mean arterial pressure (MAP), for which the BRS is maximum. Then, a MAP controller based on model-free adaptive control is designed to ensure that the measured MAP tracks the desired one. In order to test the feasibility of the control strategy, numerical simulations and simplified in vitro experiments were conducted. A mathematic model of the cardiovascular system simulating left ventricular failure, physical activity, and recovery of cardiac function is used in the simulation. The numerical simulations show that the maximum value of BRS can be found automatically by using ESA. The rotational speed of the pump is automatically increased (from 6500 rpm to 7000 rpm), and peripheral resistance is decreased to simulate slight physical activity. When E(max) is increased from 0.6 mm Hg/mL to 1.8 mm Hg/mL to mimic heart recovery, the speed is decreased from 7000 rpm to 6300 rpm in response. The optimum operating point for the pump can be detected by the proposed control strategy without the need to set a reference value for the control variable by operators.