Search

This work aimed to investigate the effect of blood flow pulsation in patients with pulsatile tinnitus (PT). Nine blood flow patterns with different pulsations were designed on the basis of the blood flow data of a patient with PT (control group; cases with blood flow pulsation indexes that had decreased by 20%, 40%, 60%, and 80%; and cases with blood flow pulsation indexes that had increased by 20%, 40%, 60%, and 80%). The transient-state multiphysics coupling method was used to clarify the biomechanical and acoustic changes that had occurred under different blood flow pulsations. Results showed that blood flow impacted directly the vessel wall in the sigmoid sinus wall dehiscence (SSWD) area. The impact velocity of the blood flow slowed with the decrement in blood flow pulsation index but increased with the increase in blood flow pulsation index. With the reduction in blood flow pulsation index, the average pressure of the SSWD area decreased by 1.84, 3.93, 6.23, and 8.31 Pa; the average displacement of the vessel wall in the SSWD area decreased by 0.11, 0.23, 0.36, and 0.48 µm; and the average sound pressure level at the tympanum decreased by 2.2, 4.16, 7.14, and 12.97 dB. By contrast, with the increase in blood flow pulsation index, the average pressure increased by 2.46, 4.21, 6.28, and 8.56; the average displacement increased by 0.14, 0.2, 0.36, and 0.49 µm; and the average sound pressure level increased by 1.32, 2.87, 4.15, and 5.19 dB. Statistical analysis revealed that the pathological induction of PT had a strong quadratic correlation with the pulsation of blood flow. The degree of PT could be attenuated by reducing blood flow pulsation. Such an approach would aid clinical treatment. The conclusion obtained in this work would present a theoretical basis for the treatment of patients with PT.

While coronary revascularization strategies guided by instantaneous wave-free ratio (iFR) are, in general, noninferior to those guided by fractional flow reserve (FFR) with respect to the rate of major adverse cardiac events at one-year follow-up in patients with stable angina or an acute coronary syndrome, the overall accuracy of diagnosis with iFR in large patient cohorts is about 80% compared with the diagnosis with FFR. So far, it remains incompletely understood what factors contribute to the discordant diagnosis between iFR and FFR. In this study, a computational method was used to systemically investigate the respective effects of various cardiovascular factors on FFR and iFR. The results showed that deterioration in aortic valve disease (e.g., regurgitation or stenosis) led to a marked decrease in iFR and a mild increase in FFR given fixed severity of coronary artery stenosis and that increasing coronary microvascular resistance caused a considerable increase in both iFR and FFR, but the degree of increase in iFR was lower than that in FFR. These findings suggest that there is a high probability of discordant diagnosis between iFR and FFR in patients with severe aortic valve disease or coronary microcirculation dysfunction.

Renal denervation transmits radiofrequency (RF) energy through an electrode to treat resistant hypertension (RH), applying ablation in the renal artery. Several experimental studies have shown that this treatment has been used effectively to treat RH. The aim of this paper is to investigate the effect of ablation parameters (i.e., electrode length, applied voltage, ablation time, and blood flow) on the temperature distribution using a balloon-based array electrodes system. A simplified three-dimensional model including four electrodes and a balloon was established. The balloon diameter was 3 mm and placed in a 5 mm diameter renal artery for forming intra-arterial occlusion. Four electrodes were mounted on the balloon and distributed in the same plane to mimic circumferential RF ablation. Computer simulations were conducted to investigate the thermal performances of the device by setting different electrode configurations, treatment protocols, and physiological factors. The thermal performances including the thermal distribution, maximum lesion depth, length, and area were analyzed. The lesion shape of the array RF electrodes was approximately a sphere with a 100% circumference coverage rate of the renal artery. The lesion depth and length increase with each factor except for blood velocity. Increasing the electrode length from 2 to 4 mm or 2 to 6 mm, the lesion depth increases by 1.15 mm and 0.54 mm at 60 s. The corresponding lesion length increases by 2.65 mm and 2.34 mm, respectively. The range of effective lesion depth is 1.90-4.90 mm, at a voltage of 15-30 V. But the peak temperature at the arterial outer wall exceeded 100 °C when the voltage is above 25 V. In tissue, the degree of thermal injury in the 2 mm area reached 100%, but in blood was not more than 5%. There was no significant difference at different flow conditions because the difference value in lesion depth was not exceeded 0.5 mm. The results showed that the balloon-based four electrodes system is expected to overcome the difficulty of incomplete ablation. In clinical application, 2 mm-electrode is recommended to avoid long wall damage as much as possible and control the voltage below 25 V. This treatment has little thermal injury on the blood, which means it may avoid coagulation formation. Moreover, the application of this device does not need to consider the difference in individual blood velocity.

The treatment benefits of enhanced external counterpulsation (EECP) heavily depends on hemodynamics. Global hemodynamics of EECP can cause blood flow redistribution in the circulatory system whereas local hemodynamic effects act on vascular endothelial cells (VECs). Local hemodynamic effects of EECP on VECs are important in the treatment of atherosclerosis, but currently cannot be not evaluated. Herein we aim to establish evaluation models of local hemodynamic effects based on the global hemodynamic indicators.We established 0D/3D geometric multi-scale hemodynamic models of the coronary and cerebral artery of two healthy individuals to calculate the global hemodynamic indicators and the local hemodynamic effects. Clinical EECP trials were performed to verify the accuracy of the multi-scale hemodynamic model. The global hemodynamic indicators included diastolic blood pressure/systolic blood pressure (Q = D/S), mean arterial pressure (MAP), internal carotid artery flow (ICAF) and cerebral blood flow (CBF), whereas local hemodynamic effects focused on time-averaged wall shear stress (TAWSS). The correlation between these indicators was analyzed via Pearson correlation coefficient. Significantly related indicators were selected for curve-fitting to establish evaluation models of the coronary and cerebral artery. Moreover, clinical data of a coronary heart disease patient and a cerebral ischemic stroke patient were collected to verify the effectiveness of the application of the established evaluation models to real patients.For coronary artery, TAWSS was correlated to Q = D/S and ICAF (P 0.05), whereas for cerebral artery, TAWSS was correlated to MAP and CBF (P 0.05). The mean square error (MSE) between the evaluated values using evaluation model and the calculated values using 0D/3D model of TAWSS of the coronary and cerebral artery were 5.4% and 1.0%, respectively. The MSE of evaluation model applied to real patients was greater than that applied to healthy individuals, but within an acceptable range.The presented error demonstrated validity and accuracy of the evaluation models in clinical patients. Based on the evaluation models, global hemodynamic indicators could be used to evaluate the local hemodynamic effects under the current counterpulsation mode. With TAWSS range of 4-7 Pa as the target range, EECP strategies can further be optimized.

This study aimed to examine whether the ratio of vessel-specific coronary arterial lumen volume to the fraction of myocardial mass (VR/MR) affects myocardial ischemia. We proposed a calculation method for VR/MR, and compared the ratio of total epicardial coronary arterial lumen volume to left ventricular myocardial mass (V/M) with VR/MR in predicting myocardial ischemia. VR/MR and V/M were computed using data from 205 patients with 241 stenosis vessel who underwent coronary computed tomography angiography (CTA), quantitative coronary angiography, and fractional flow reserve. The vessel-specific coronary arterial lumen volume (VR) was obtained from CTA by segmenting the coronary arterial lumen volume, while the vessel-specific fraction of myocardial mass (MR) was obtained by allometric scaling. The VR/MR was then calculated. The cut-off values of V/M (23.55 mm3/g) and VR/MR (12.98 mm3/g) were used to define equal groups of ischemic and non-ischemic patients, respectively. Using these cut-off values, the accuracy, specificity, sensitivity, positive predictive value, and negative predictive value of V/M were 60%, 76%, 45%, 57%, and 66%, and of VR/MR were 87%, 92%, 77%, 89%, and 83%, respectively. Patients have different VR/MR values in different stenotic coronary arteries. Clinically, VR/MR is a quantitative indicator of the risk of myocardial ischemia.

Traditional enhanced external counterpulsation (EECP) used for the clinical treatment of patients with coronary heart disease only assesses diastolic/systolic blood pressure (Q = D/S > 1.2). However, improvement of the hemodynamic environment surrounding vascular endothelial cells of coronary arteries after long-term application of EECP is the basis of the treatment. Currently, the quantitative hemodynamic mechanism is not well understood. In this study, a standard 0D/3D geometric multi-scale model of the coronary artery was established to simulate the hemodynamic effects of different counterpulsation modes on the vascular endothelium. In this model, the neural regulation caused by counterpulsation was thoroughly considered. Two clinical trials were carried out to verify the numerical calculation model. The results demonstrated that the increase in counterpulsation pressure amplitude and pressurization duration increased coronary blood perfusion and wall shear stress (WSS) and reduced the oscillatory shear index (OSI) of the vascular wall. However, the impact of pressurization duration was the predominant factor. The results of the standard model and the two real individual models indicated that a long pressurization duration would cause more hemodynamic risk areas by resulting in excessive WSS, which could not be reflected by the change in the Q value. Therefore, long-term pressurization during each cardiac cycle therapy is not recommended for patients with coronary heart disease and clinical treatment should not just pay attention to the change in the Q value. Additional physiological indicators can be used to evaluate the effects of counterpulsation treatment.

Background and objectives Fractional flow reserve (FFR) is considered to be the "gold standard" for the clinical diagnosis of functional myocardial ischemia. With the development of medical imaging and computational fluid dynamics (CFD), noninvasive computation of FFR has been developed. The most representative calculation method is the noninvasive FFR derived from coronary CT angiography (FFRCT), but it cannot thoroughly simulate the real physiological structure of the cardiovascular system. In this study, we propose a noninvasive closed-loop FFR derived from coronary CT angiography (FFRCCT). Methods The closed-loop multi-scale model includes three parts: the heart module, the coronary artery module with microcirculation structure and the systemic circulation module. The proposed structure was formed by coupling a lumped parameter model (0D) with a 3D model, such that the 0D model provides the boundary conditions for the 3D model. We enrolled 100 patients through a prospective multi-center clinical trial and calculated their FFRCCT. Then, we extracted the pressure and flow waveforms of the coronary stenosis vessels through closed-loop geometric multi-scale CFD calculations. We evaluated the accuracy of FFRCCT in diagnosing myocardial ischemia using the clinical measurement of FFR as the standard. Results The results of FFRCCT calculation in all patients showed a good correlation between FFRCCT and FFR (r = 0.64, p Conclusions The closed-loop multi-scale model proposed in this study can simulate the physiological cycle in a more realistic way. FFRCCT is a reliable diagnostic index for myocardial ischemia.

Clinically, fractional flow reserve (FFR)-guided coronary artery bypass grafting (CABG) is more effective than CABG guided by coronary angiography alone. However, no scholars have explained the mechanism from the perspective of hemodynamics. Two patients were clinically selected; their angiography showed 70% coronary stenosis, and the FFRs were 0.7 (patient 1) and 0.95 (patient 2). The FFR non-invasive computational model of the two patients was constructed by a 0–3D coupled multiscaled model, in order to verify that the model can accurately calculate the FFR results. Virtual bypass surgery was performed on these two stenoses, and a CABG multiscaled model was constructed. The flow rate of the graft and the stenosis coronary artery, as well as the wall shear stress (WSS) and the oscillatory shear index (OSI) in the graft were calculated. The non-invasive calculation results of FFR are 0.67 and 0.91, which are close to the clinical results, which proves that our model is accurate. According to the CABG model, the flow ratios of the stenosis coronary artery to the graft of patient 1 and patient 2 were 0.12 and 0.42, respectively. The time-average wall shear stress (TAWSS) results of patient 1 and patient 2 grafts were 2.09 and 2.16 Pa, respectively, and WSS showed uniform distribution on the grafts. The OSI results of patients 1 and 2 grafts were 0.0375 and 0.1264, respectively, and a significantly high OSI region appeared at the anastomosis of patient 2. The FFR value of the stenosis should be considered when performing bypass surgery. When the stenosis of high FFR values is grafted, a high OSI region is created at the graft, especially at the anastomosis. In the long term, this can cause anastomotic blockage and graft failure.

Coronary artery bypass grafts (CABGs), including saphenous vein grafts (SVGs) or left internal mammary artery (LIMA) grafts, are recently applied to treat coronary artery aneurysm (CAA). Surgical outcomes are considered to be related to surgical strategies (types of the bypass graft and whether CAA ligated or not) and the size of the CAA (usually characterized by diameter). However, the understanding of the relationship between the surgical outcomes and the abovementioned factors is limited. Previous studies related to CABG treatments have shown hemodynamic studies could help evaluate surgical outcomes through graft mass flow rate, wall shear stress (WSS), and oscillatory shear index (OSI). It is believed that the hemodynamic study of applying CABGs to CAA, which is not studied yet, could help us understand the different CABG surgeries. The aim of the study was to evaluate the hemodynamic differences among different surgical methods. To do this, eight three-dimensional models were constructed, representing application of SVGs and LIMA grafts to CAAs (whether ligated or not) with diameters two, three, and five times the normal diameter, to perform computational fluid dynamics (CFD) simulation. The lumped-parameter model (LPM) was coupled to the boundary of the 3D models which increase the complexity of the simulation, but it can ensure the stability of the simulation boundary conditions. The results show that SVG (no matter whether ligated or not) hemodynamic characteristics are positive, with an average high graft mass flow rate of 70 ml/min, an average WSS of 0.479 Pa, and a low OSI of 0.001. LIMA with CAA ligation has the same characteristics with higher WSS (average 1.701 Pa). The hemodynamic characteristics of LIMA without CAA ligation are negative, including high reverse mass flow rate and high OSI (0.367). The results indicate that the surgical outcomes of LIMA with CAA ligation are likely to be the best among these models. The surgical outcomes of LIMA without CAA ligation seem to be undesirable due to the high reverse mass flow and high OSI. The CAA diameter may not have a significant effect on surgical outcomes.

Traditional clinical mode of enhanced external counterpulsation is not targeted for different diseases. Specialized strategies in the treatment of enhanced external counterpulsation for coronary heart disease and cerebral ischemic stroke are supposed to be distinguished. The goal of treatment for coronary heart disease is diastolic blood pressure/systolic blood pressure = Q ≥ 1.2 after counterpulsation, while the goal of treatment for cerebral ischemic stroke is the improvement of mean arterial pressure. A computational lumped parameter model was established for the simulation of hemodynamic effect of enhanced external counterpulsation on two diseases. Vessel collapse was considered during the simulation of counterpulsation. Based on different pressurized and decompressed rate, pressurized moment, pressure duration, and pressure amplitude, different counterpulsation modes were applied to the model and the immediate hemodynamic effects were compared. Results showed that the pressure duration and pressure amplitude had most influence on two diseases. For cerebral ischemic stroke, the longer pressure duration and the higher pressure amplitude of thighs, the higher mean arterial pressure; while for coronary heart disease, the value of Q was highest when the pressure end moment was 0.6 s during a 0.88-s cardiac cycle, and Q had a linear increase in the pressure amplitude of buttocks, but little change with the increase of calves and thighs pressure amplitude. For patients with coronary heart disease, the pressure duration was not supposed to be too long to avoid the increase of systolic blood pressure, and the improvement of pressure amplitude of buttocks could promise a positive treatment effect for coronary heart disease. While for patients with cerebral ischemic stroke, both the long pressure duration of each part and the high pressure amplitude of thighs could result in the systolic blood pressure and diastolic blood pressure have a certain increase, thus promoting the maximum mean arterial pressure and a best treatment. Graphical abstract The specialized treatment strategies of EECP for cardiovascular and cerebrovascular disease.

(1) Background: Arrhythmia, which is an umbrella term for various types of abnormal rhythms of heartbeat, has a high prevalence in both the general population and patients with coronary artery disease. So far, it remains unclear how different types of arrhythmia would affect myocardial perfusion and the risk/severity of myocardial ischemia. (2) Methods: A computational model of the coronary circulation coupled to the global cardiovascular system was employed to quantify the impacts of arrhythmia and its combination with coronary artery disease on myocardial perfusion. Furthermore, a myocardial supply–demand balance index (MSDBx) was proposed to quantitatively evaluate the severity of myocardial ischemia under various arrhythmic conditions. (3) Results: Tachycardia and severe irregularity of heart rates (HRs) depressed myocardial perfusion and increased the risk of subendocardial ischemia (evaluated by MSDBx), whereas lowering HR improved myocardial perfusion. The presence of a moderate to severe coronary artery stenosis considerably augmented the sensitivity of MSDBx to arrhythmia. Further data analyses revealed that arrhythmia induced myocardial ischemia mainly via reducing the amount of coronary artery blood flow in each individual cardiac cycle rather than increasing the metabolic demand of the myocardium (measured by the left ventricular pressure-volume area). (4) Conclusions: Both tachycardia and irregular heartbeat tend to increase the risk of myocardial ischemia, especially in the subendocardium, and the effects can be further enhanced by concomitant existence of coronary artery disease. In contrast, properly lowering HR using drugs like β-blockers may improve myocardial perfusion, thereby preventing or relieving myocardial ischemia in patients with coronary artery disease.

Coronary artery aneurysms (CAAs) have been reported to associate with an increased risk for thrombosis. Distinct to the brain aneurysm, which can cause a rupture, CAA’s threat is more about its potential to induce thrombosis, leading to myocardial infarction. Case reports suggest that thrombosis risk varied with the different CAA diameters and hemodynamics effects (usually wall shear stress (WSS), oscillatory shear index (OSI), and relative residence time (RRT)) may relate to the thrombosis risk. However, currently, due to the rareness of the disease, there is limited knowledge of the hemodynamics effects of CAA. The aim of the study was to estimate the relationship between hemodynamic effects and different diameters of CAAs. Computational fluid dynamics (CFD) provides a noninvasive means of hemodynamic research. Four three-dimensional models were constructed, representing coronary arteries with a normal diameter (1x) and CAAs with diameters two (2x), three (3x), and five times (5x) that of the normal diameter. A lumped parameter model (LPM) which can capture the feature of coronary blood flow supplied the boundary conditions. WSS in the aneurysm decreased 97.7% apparently from 3.51 Pa (1x) to 0.08 Pa (5x). OSI and RRT in the aneurysm were increased apparently by two orders of magnitude from 0.01 (1x) to 0.30 (5x), and from 0.38 Pa−1 (1x) to 51.59 Pa−1 (5x), separately. Changes in the local volume of the CAA resulted in dramatic changes in local hemodynamic parameters. The findings demonstrated that thrombosis risk increased with increasing diameter and was strongly exacerbated at larger diameters of CAA. The 2x model exhibited the lowest thrombosis risk among the models, suggesting the low-damage (medication) treatment may work. High-damage (surgery) treatment may need to be considered when CAA diameter is 3 times or higher. This diameter classification method may be a good example for constructing a more complex hemodynamic-based risk stratification method and could support clinical decision-making in the assessment of CAA.

Sigmoid sinus wall anomalies (SSWA) are a common pathophysiology of pulsatile tinnitus (PT) and usually treated by sigmoid sinus wall dehiscence (SSWD) resurfacing surgery. However, symptoms of tinnitus remain unrelieved after surgery in some patients with PT, and even new tinnitus appears. The cause of the difference in therapeutic effects is unclear. In this study, eight patient-specific SSWA geometric models were reconstructed on the basis of computed tomography angiography, including four cases of postoperative rehabilitation (group 1, 1–4 cases) and four cases of non-rehabilitation (group 2, 5–8 cases). Transient-state computational fluid dynamics (CFD) was performed to clarify the SS blood flow pattern and hemodynamic states. The wall pressure distribution on SSWA area, pressure difference, and flow pattern in SS were calculated to evaluate the hemodynamic changes of rehabilitation and non-rehabilitation patients before and after surgery. The difference of hemodynamics between these patients was statistically analyzed. The accuracy of CFD simulation was evaluated by cross validating the numerical and particle image velocimetry experimental results. Results showed that the SSWA area in patients with PT was loaded with high pressure. No difference was found in the hemodynamic characteristics between the two groups pre- and postoperation. When the average pressure (Pavg) and time-average Pavg (TAPavg) on the SSWA area were studied, the TAPavg difference pre- and postoperation between the two groups was found significant (p = 0.0021). The TAPavg difference had a negative change in postoperative rehabilitation patients (case 1, -44.49 Pa vs. case 2, -15.85 Pa vs. case 3, -25.88 Pa vs. case 4, -16.58 Pa). The postoperative TAPavg of non-rehabilitation patients was higher than the preoperative one (case 5, 24.70 Pa vs. case 6, 28.56 Pa vs. case 7, 5.81 Pa vs. case 8, 13.04 Pa). The velocity streamlines in the SS with rehabilitation became smoother and more regular than that without rehabilitation. By contrast, the velocity streamlines in SS without rehabilitation showed increased twisting and curling. No difference was found in time-average volume-averaged vorticity (TAVavgV) between the two groups. Therefore, the high pressure of the vessel wall on SSWA area was one of the causes of PT. The variation of SSWA wall pressure difference before and after PT was the cause of the difference in therapeutic effects after SSWD resurfacing surgery. In patients with SSWA, disordered blood flow in SS was another cause of PT. SSWD repair may relieve tinnitus to some extent, but blood flow disorders may still arise.

Although fractional flow reserve (FFR) and coronary flow reserve (CFR) are both frequently used to assess the functional severity of coronary artery stenosis, discordant results of diagnosis between FFR and CFR in some patient cohorts have been reported. In the present study, a computational model was employed to quantify the impacts of various pathophysiological factors on FFR and CFR. In addition, a hyperemic myocardial ischemic index (HMIx) was proposed as a reference for comparing the diagnostic performances of FFR and CFR. Obtained results showed that CFR was more susceptible than FFR to the influence of many pathophysiological factors unrelated to coronary artery stenosis. In particular, the numerical study proved that increasing hyperemic coronary microvascular resistance significantly elevated FFR while reducing CFR despite fixed severity of coronary artery stenosis, whereas introducing aortic valve disease only caused a significant decrease in CFR with little influence on FFR. These results provided theoretical evidence for explaining some clinical observations, such as the increased risk of discordant diagnostic results between FFR and CFR in patients with increased hyperemic microvascular resistance, and significant increase in CFR after surgical relief of severe aortic valve disease. When evaluated with respect to the predictive value for hyperemic myocardial ischemia, the performance of FFR was found to be considerably compromised in the presence of severe coronary vasodilation dysfunction or aortic valve disease, whereas the relationship between CFR and HMIx remained relatively stable, suggesting that CFR may be a more reliable indicator of myocardial ischemia under complex pathophysiological conditions.

The current 3D CABG model is time consuming, a lumped parameter CABG model may solve this problem. A coronary lumped parameter model without stenosis and graft was constructed. The stenosis resistance was calculated and graft model was constructed. After calculation, the graft flow results of CABG lumped parameter model fit well with 3D CABG model results.

Background Enhanced external counterpulsation (EECP) is an effective method for treating patients with cerebral ischemic stroke, while hemodynamics is the major contributing factor in the treatment of EECP. Different counterpulsation modes have the potential to lead to different acute and long-term hemodynamic changes, resulting in different treatment effects. However, various questions about appropriate counterpulsation modes for optimizing hemodynamic effects remain unanswered in clinical treatment. Methods A zero-dimensional/three-dimensional (0D/3D) geometric multiscale model of the cerebral artery was established to obtain acute hemodynamic indicators, including mean arterial pressure (MAP) and cerebral blood flow (CBF), as well as localized hemodynamic details for the cerebral artery, which includes wall shear stress (WSS) and oscillatory shear index (OSI). Counterpulsation was achieved by applying pressure on calf, thigh and buttock modules in the 0D model. Different counterpulsation modes including various pressure amplitudes and pressurization durations were applied to investigate hemodynamic responses, which impact acute and long-term treatment effects. Both vascular collapse and cerebral autoregulation were considered during counterpulsation. Results Variations of pressure amplitude and pressurization duration have different impacts on hemodynamic effects during EECP treatment. There were small differences in the hemodynamics when similar or different pressure amplitudes were applied to calves, thighs and buttocks. When increasing pressure amplitude was applied to the three body parts, MAP and CBF improved slightly. When pressure amplitude exceeded 200 mmHg, hemodynamic indicators almost never changed, demonstrating consistency with clinical data. However, hemodynamic indicators improved significantly with increasing pressurization duration. For pressurization durations of 0.5, 0.6 and 0.7 s, percentage increases for MAP during counterpulsation were 1.5%, 23.5% and 39.0%, for CBF were 1.2%, 23.4% and 41.6% and for time-averaged WSS were 0.2%, 43.5% and 85.0%, respectively. Conclusions When EECP was applied to patients with cerebral ischemic stroke, pressure amplitude applied to the three parts may remain the same. Patients may not gain much more benefit from EECP treatment by excessively increasing pressure amplitude above 200 mmHg. However, during clinical procedures, pressurization duration could be increased to 0.7 s during the cardiac circle to optimize the hemodynamics for possible superior treatment outcomes.

Enhanced external counterpulsation (EECP) is a noninvasive treatment method for coronary artery atherosclerosis that acts on the vascular endothelial cells. The intracoronary hemodynamic parameters that influence long-term treatment effect are the fundamental factors for the inhibition of intimal hyperplasia, which cannot be measured in real time. In order to optimize the long-term treatment effect of coronary heart disease, it is necessary to establish a method for quantified calculation of intracoronary hemodynamic parameters during counterpulsation to research the long-term hemodynamic mechanism of EECP. A geometric multiscale model coupled by the zero-dimensional (0D) lumped parameter model and the three-dimensional (3D) model of narrow coronary artery was established for the simulation of intracoronary hemodynamic environment. The 3D model was used to calculate the hemodynamic parameters such as wall shear stress (WSS) and oscillatory shear index (OSI), while the 0D model was used to simulate the blood circulatory system. Sequential pressure was applied to calves, thighs, and buttocks module in 0D model with the consideration of vessel collapse. Hemodynamic performance was compared with clinical reports to verify the effectiveness of the method. There were significant increases of the diastolic blood pressure (DBP), coronary flow, and the area-averaged WSS during application of EECP, while OSI behind stenosis has some decrease. The waveforms of coronary flow has good similarity with the clinical measured waveforms, and the differences between calculated mean arterial pressures (MAPs) and clinical measurements were within 1%. The fundamental factor in the cure of coronary heart disease by EECP is the improvement of WSS and the decrease of OSI. Comparing with the clinical reports, the immediate hemodynamic changes demonstrate the effectiveness of model. Intracoronary hemodynamic parameters during EECP could be acquired and the method could be used to simulate the long-term treatment effect of EECP. Graphical abstract.

Background: The fractional flow reserve (FFR) is the gold standard used to diagnose whether coronary stenosis triggers myocardial ischemia. Myocardial ischemia is not only related to the degree of coronary artery disease but also to hemodynamic parameters such as mean arterial pressure, flow, and so on. This paper will explore the effects of hemodynamic parameters on FFR. Methods: Construct an ideal vascular model of moderately stenosis lesions (40–70%) with different hemodynamic environments. A pressure waveform was set as the inlet boundary, a microcirculation resistance in the hyperemia state was set as the outlet boundary, and different hemodynamic environments were constructed by changing the mean arterial pressure and flow at rest. The microcirculation resistance in the resting state was determined by the mean arterial pressure and flow, and the microcirculation resistance in the hyperemia state was 0.24 times than in the resting state. Results:Flow at rest was found to have the greatest impact on FFR, followed by arterial pressure. Both a decrease in flow and an increase in mean arterial pressure caused an increase in the FFR value. Conclusion:Based on the degree of stenosis of the diseased blood vessel, systolic pressure, diastolic blood pressure, and blood flow through the diseased blood vessel in the resting state, a preliminary judgment can be directly made as to whether the stenosis causes myocardial ischemia.

Background: When the coronary artery expands more than two times its diameter, it will form a coronary artery aneurysm (CAA). CAA can lead to myocardial ischemia. In this paper, the mechanism of myocardial ischemia induced by CAA was studied by geometric multiscale method. Methods: Four kinds of three-dimensional models of CAA with different dilation diameters were established on the basis of normal three-dimensional models. The dilation diameters were 2, 3, 5 and 7 times, capacitance was added after the CAA to simulate the elasticity of the vascular wall. Results:A large number of eddies exist in CAA. 2–7 times model: 1.1–14.4% reduction of blood flow downstream of CAA and 5, 7 times model showed upstream diastolic backward flow, the backward flow rate was 1.1% and 5.6%, respectively. The aveWSS at the CAA was 1.76–0.35[Formula: see text]Pa; the relative retention time was 1.1–14.6[Formula: see text]Pa[Formula: see text]; the average vorticity was 0.0085–231.7[Formula: see text]s[Formula: see text]. Conclusion:CAA can store blood, and the elasticity of the wall of CAA results in the flow of blood upstream. These two reasons make the downstream flow of CAA decrease and easily form intratumoral thrombosis, which may lead to myocardial ischemia.

Background: In coronary artery bypass grafting (CABG), the patency of venous sequential graft remains controversial. Hemodynamic factors have been proved to be the important factors influencing graft patency. The objective of this study is to compare the patency of sequential grafts and normal grafts by hemodynamic environment. Methods: This study used a patient’s clinical data to construct a 0D/3D coupled multi-scale model, and used this model to calculate graft’s hemodynamics under two grafting methods. Meanwhile, CABG ideal models were constructed based on grafts’ flow data of 60 patients (63 normal grafts, 19 sequential grafts) to calculate grafts’ hemodynamics. Results: Based on the multi-scale model, it was found that the sequential graft flow and time average wall shear stress (TAWSS) were higher than normal graft, which was good for graft patency. But there were a flow separation region, some regions of high oscillatory shear index (OSI) and relative residence time (RRT) in sequential graft, which could lead to intimal hyperplasia. Based on ideal CABG models, it was known that failure rate of sequential and normal grafts were 36.8% and 36.5%, and there were significant differences between them in flow rate, TAWSS and OSI (sequential versus normal: flow rate (ml/min): [Formula: see text] versus [Formula: see text], TAWSS (Pa): [Formula: see text] versus [Formula: see text], OSI: 0.[Formula: see text] versus [Formula: see text]). Conclusion: For saphenous venous graft (SVG), although the normal graft has similar patency with the sequential graft, the hemodynamic mechanism behind it is different. In flow rate and WSS, sequential grafts have an advantage over normal grafts. But there are high OSI and RRT regions in sequential grafts.

Coronary heart disease (CHD) is one of the most common forms of heart disease, which means that coronary stenosis can cause insufficient blood supply to the heart and lead to coronary heart disease. Coronary artery bypass grafting (coronary bypass) is often used in the treatment of patients with coronary heart disease. After surgery, because the stenosis of the coronary artery is not completely occluded, the blood flow through it will compete with the blood flow of the graft, making it possible to transplant blood vessels. The blood flow is affected, reducing long-term permeability. When the coronary artery is completely stenotic, the distal blood flow is completely supplied by the graft; when the coronary artery is not completely narrow, the blood flow is supplied by the stenotic coronary artery and the graft vessel, thus creating a competitive relationship, the narrow crown The blood flow in the vein is considered to be a competitive flow, and different stenosis produces a competitive flow of different strengths. A highly competitive flow reduces blood flow in the graft and reduces graft life.On the other hand, at the anastomosis, due to the existence of competitive flow, abnormal blood flow occurs at the anastomosis, which causes local intimal hyperplasia of the blood vessel, leading to restenosis. The degree of stenosis is an important factor affecting the competitive flow.In order to study the influence of competitive flow under different stenosis conditions on the local area of ​​bypass surgery ,the numerical simulation and PIV experiments were used to analyze the effects of competitive flow on grafts and anastomosis.The ideal coronary artery stenosis model was established with 30%, 40%, 50%, 60%, 70%, 80%, 90%, and seven different degrees of stenosis.Numerical simulation uses finite element analysis software to determine the normal physiological boundary conditions for steady state analysis; PIV experiment establishes transparent silica gel model, using water flow as medium, water pressure as boundary condition to simulate competitive flow, and macroscopic flow field inside the bypass surgery site Steady-state flow studies were performed and the effects of competitive flow on bridging blood vessels and stenotic blood flow were analyzed.The ratio of the flow rate QC of the stenotic vessel to the flow rate of the bridge vessel flow QG is an index of the reaction competition.A ratio greater than 1 is considered to be a highly competitive flow.In the numerical simulation, the intensity of the competitive flow is less than 1 when the degree of stenosis is below 50%, indicating that the blood flow in the graft vessel is significantly lower than that in the stenotic coronary artery, which is a highly competitive flow, and the average wall in the entire graft vessel.The shear stress is less than 1 Pa. Many studies have found that wall shear stress is an important factor causing vascular lesions. Wall shear stress below 1 Pa will cause adaptive contraction of blood vessels, which is not conducive to the long-term effectiveness of grafts; the degree of stenosis is 80. At %-90%, eddy currents appear at the anastomosis, which easily causes anastomotic stenosis. In the PIV experiment, the overall flow velocity in the graft vessel increased by 50% with a narrowing degree as a dividing line, less than 50%, and the intensity of the competitive flow was higher at the time of stenosis, and the competition ratio was greater than 1. 70% of the stenosis. The phenomenon of eddy currents also occurs.The velocity flow diagram in the numerical simulation is basically similar to the flow field measured in the PIV experiment. The PIV experiment qualitatively verifies the result of numerical simulation. The 50% stenosis of the coronary artery is a transition point of a competitive flow, and less than 50% of the stenosis will result.Highly competitive flow affects blood flow in the graft vessel, which results in a lower average wall shear stress at the lower end of the graft vessel and is not effective for a long period of time; above 70% stenosis, eddy currents may occur at the anastomosis, which may This leads to stenosis at the anastomosis and restenosis of the stenotic coronary artery.

Coronary atherosclerotic heart disease, or coronary heart disease for short, is a heart disease caused by atherosclerotic lesions of coronary arteries, resulting in stenosis, spasm and live obstruction, leading to myocardial ischemia, hypoxia and even necrosis, and is the most common type of organ lesions caused by atherosclerosis. Coronary computed tomograph angiography (CCTA) has been the most effective method for examining coronary heart disease, but this method can only be judged from the morphology. It has been shown that when the coronary stenosis rate is as high as 70%, only 32% of blood vessels can cause myocardial ischemia. Therefore, there is no direct relationship between coronary stenosis and myocardial ischemia. Long-term clinical studies have shown that the determination of fractional flow reserve (FFR) is the gold standard for the current diagnosis of hemodynamic changes in coronary artery stenosis. FFR is invasive, expensive and technically demanding for operators, which greatly limits clinical use. FFR-CT, which is derived by CCTA and Computational fluid dynamics (CFD), is a new noninvasive method for assessing coronary stenosis. Initially, FFR was calculated by Myo= (pd-pv) /(pa-pv), where Pd (distal pressure) was stenosis, Pa (proximal arterial pressure) was stenosis, and Pv (venous pressure or right atrial pressure, RAP) was right atrial pressure. Since Pv is small, usually 4~8mmHg, a simplified formula can be used for literature expenditure, namely, Myo=Pd/Pa. However, due to the small amount of clinical data, it is impossible to determine whether Pv has an influence on the calculation of FFR. Therefore, an ideal vascular model with a diameter of 3 mm, a stenosis length of 10 mm, and a stenosis degree of 40%, 50%, 60%, and 70%, respectively, was established. This study defines interface conditions and special coupling algorithms for 0D/3D coupling. ANSYS-CFX is used in 3d simulation, and the 0D model is calculated with Fortran subroutine based on CFX Junction Box. Data exchange between the 0D and 3D models is implemented using CFX User CEL Function. A constant pressure of 90mmHg was applied at the model entrance, and a constant resistance Rmicro was provided at the outlet boundary to simulate the microcirculation resistance in the downstream hyperemia state. Pv was given at the resistance end, and the values were respectively 0mmHg, 4mmHg, 6mmHg and 8mmHg. Three cardiac cycles are calculated, and the cardiac cycle is 0.8s.The calculation results of the last period are extracted after the result converges. It was calculated that when the stenosis degree was 40%, Pv was 0 mmHg, FFR=0.913; when Pv was 8 mmHg, FFR=0.921; the rate of change was 0.876%. When the degree of stenosis is 50%, Pv is 0 mmHg, FFR=0.87; when Pv is 8 mmHg, FFR=0.883; the rate of change is 1.49%. When the degree of stenosis is 60%, Pv is 0 mmHg, FFR=0.776; when Pv is 8 mmHg, FFR=0.799; the rate of change is 2.96%. When the degree of stenosis is 70%, Pv is 0 mmHg, FFR=0.579; when Pv is 8 mmHg, FFR=0.623; the rate of change is 7.60%. The results show that with the increase of Pv, the calculated value of FFR also increases; and as the degree of stenosis increases, the degree of influence of Pv deepens. In the actual situation, the patient's right atrial pressure is not 0 mmHg, so in order to improve the accuracy of FFR calculation, Pv should be taken into consideration, and the calculation formula should not be simplified.

In the existing patency prediction model of coronary artery bypass grafting (CABG), the characteristics are based on graft flow, but no researchers selected hemodynamic factors as the characteristics. The purpose of this paper is to study whether the introduction of hemodynamic factors will affect the performance of the prediction model. Transit time flow-meter (TTFM) waveforms and 1-year postoperative patency results were obtained from 50 internal mammary arterial grafts (LIMA) and 82 saphenous venous grafts (SVG) in 60 patients. Taking TTFM waveforms as the boundary conditions, the CABG ideal models were constructed to obtain hemodynamic factors in grafts. Based on clinical characteristics and combination of clinical and hemodynamic characteristics, patency prediction models based on support vector machine (SVM) were constructed respectively. For LIMA, after the introduction of hemodynamic factors, the accuracy, sensitivity and specificity of the prediction model increased from 70.35%, 50% and 74.17% to 78.02%, 70% and 78.89%, respectively. For SVG, the accuracy, sensitivity and specificity of the prediction model increased from 63.24%, 40% and 76.91% to 74.41%, 60.1% and 82.73%, respectively. The performance of the prediction model can be improved by introducing hemodynamic factors into the characteristics of the model. The accuracy, sensitivity and specificity of the prediction results are higher with the addition of hemodynamic characteristics.

Instantaneous wave-free ratio (iFR), an invasive index of coronary artery tree, can evaluate the functional performance of vascular stenosis without pharmacological vasodilators. The noninvasive assessment of diameter stenosis (DS) obtained from coronary computed tomography angiography (CTA) has high false positive rate in contrast to iFR. The aim of this study was to develop a numerical simulation method that predicts the iFR and noninvasively assess the myocardial ischemia. Based on the CTA images, a patient-specific three-dimensional model of the aorta and coronary arteries were reconstructed. A stenosis was created in the left anterior descending artery (LAD) by reducing the DS of geometric model (40%, 50%, 60%, 75% and 90%). The patient-specific LPM boundary condition were set up to compute iFRct value during the wave-free period at the resting condition. The computed pressure and flow of coronary artery were realistic as compared to literature data. In contrast to invasive iFR, the iFRct can make a cost-benefit balance in terms of clinical cost and patient’s health.

A method which can personalize the lumped parameter model of coronary artery and cardiovascular system based on the non-invasive physiological parameters has been developed. The parameters of system were determined by different physiological parameters. The heart module was determined by aortic pressure and heart rate; the systemic circulation module was determined by cardiac output, height and cardio-ankle vascular index (CAVI), while the CAVI was determined by age and aortic pressure; the coronary module was determined by the target waveforms of coronary flow rate predicted from cardiac output. The considerable results proved that this method could be applied to each patient.

In coronary artery bypass grafting (CABG), competitive flow usually happens when the native coronary has a moderate stenosis. But whether the competitive flow could be affected by the length of this moderate stenosis is still a problem. This study constructs a series of CABG models with different stenosis lengths and uses multi-scale modeling method for numerical simulations. The results contain graft flow, the magnitude of competitive flow, wall shear stress (WSS) and oscillating shear index (OSI). According to the results, it is known that the effect of competitive flow will decrease with the increase of stenosis length. But when the length reaches 15[Formula: see text]mm, the competitive flow will hardly change anymore.

Intra-aorta pump is a novel rotary ventricular assist device. Because of the special structure and connection with the native heart, the hemodynamic effect of support mode of this pump on the cardiovascular system is not clear. In this work, three support modes, including "constant speed" mode, "co-pulse" mode, and "counter-pulse" mode, have been designed for the intra-aorta pump to evaluate the hemodynamic effect of different support modes on the cardiovascular system. Simulation results demonstrate that that both "co-pulse" mode and "counter-pulse" mode can achieve better unloading performance than "constant speed" mode. The intra-aorta pump controlled by "co-pulse" mode is beneficial for improving coronary flow. Moreover, the external work, which is defined as the product of left ventricular pressure and cardiac output, under "co-pulse" mode is the minimum of the three support modes (0.783 w vs. 0.615 w vs. 0.702 w). The pulsatility ratio, defined as the ratio of the peak-to-peak value of arterial pressure (AP) to the mean arterial pressure value, under "co-pulse" mode is the maximum of the three modes (24% vs. 32.8% vs. 23.7%). The equivalent afterload value, which is the ratio of pulsatile pressure at the pump inflow and pulsatile pump flow, is larger than other support modes (0.596 mm Hg.s/mL vs. 0.9704 mm Hg.s/mL vs. 0.55 mm Hg.s/mL). In brief, the intra-aorta pump under "co-pulse" mode support is beneficial for improving myocardial perfusion and restoring pulsatility of AP, while "counter-pulse" mode is beneficial to the perfusion of vital organs.

Background Sequential and single grafting are two surgical procedures of coronary artery bypass grafting. However, it remains unclear if the sequential graft can be used between the right and left coronary artery system. The purpose of this paper is to clarify the possibility of right coronary artery system anastomosis to left coronary system. Methods A patient-specific 3D model was first reconstructed based on coronary computed tomography angiography (CCTA) images. Two different grafts, the normal multi-graft (Model 1) and the novel multi-graft (Model 2), were then implemented on this patient-specific model using virtual surgery techniques. In Model 1, the single graft was anastomosed to right coronary artery (RCA) and the sequential graft was adopted to anastomose left anterior descending (LAD) and left circumflex artery (LCX). While in Model 2, the single graft was anastomosed to LAD and the sequential graft was adopted to anastomose RCA and LCX. A zero-dimensional/three-dimensional (0D/3D) coupling method was used to realize the multi-scale simulation of both the pre-operative and two post-operative models. Results Flow rates in the coronary artery and grafts were obtained. The hemodynamic parameters were also showed, including wall shear stress (WSS) and oscillatory shear index (OSI). The area of low WSS and OSI in Model 1 was much less than that in Model 2. Conclusions Model 1 shows optimistic hemodynamic modifications which may enhance the long-term patency of grafts. The anterior segments of sequential graft have better long-term patency than the posterior segments. With rational spatial position of the heart vessels, the last anastomosis of sequential graft should be connected to the main branch.

The intraaorta pump is a novel left ventricular assist device (LVAD) whose hemodynamic effects on the circulatory system is unknown. This article aims to evaluate the different effects on the circulatory system supported by the intraaorta pump. In this article, the pump is controlled by three control strategies, including the continuous flow method, the constant rotational speed, and the constant pressure head. A cardiovascular pump system, which includes cardiovascular circulation, intraaorta pump, and regulating mechanisms of systemic circulation, has been proposed. Left ventricle pressure (LVP), end-diastolic volume (EDV), and left ventricular external work (LVEW) were used to evaluate the degree of ventricular unloading. The pulsatile index (PI), which is defined as a ratio of pulse pressure and mean arterial pressure (MAP), was used to evaluate the effect of the vessel response by three control strategies. The comparison results showed that LVP and EDV were lower than those measured before the intraaorta pump was implanted. For LVEW, the constant pressure head strategy provided a superior ventricular unloading compared with other strategies. Support of the pump led to the lower pulsatility by the three models. However, the PI of the constant pressure head was the most at 0.37. In conclusion, these results indicate that the intraaorta pump controlled by constant pressure head strategy provides superior ventricular unloading and pulsatility of the vessel.

SUMMARY The extracardiac Fontan connection (EFC) is an effective treatment for congenital single ventricle heart defects. Numerous studies have sought to optimize the EFC design. However, the optimal design of EFC remains uncertain. This study aims to examine the influence of bypass angles between the inferior vena cava (IVC) and right pulmonary artery (RPA), and the angles between the IVC and superior vena cava (SVC), on hemodynamics. Furthermore, this study demonstrates a methodology for cardiovascular surgical planning. First, a three-dimensional anatomical geometry was reconstructed from the medical images of a patient with single ventricle heart defects. Second, based on haptic deformations, six computational models were virtually generated. Third, numerical simulations were conducted using computational fluid dynamics through the finite volume method. Finally, hemodynamic parameters were obtained and evaluated. The hemodynamic parameters, including the flow patterns, streamlines, and swirling flow, were obtained. Meanwhile, the energy loss and flow distributions of vena cava blood were calculated. First, the hepatic artery blood distribution to two lungs and the flow ratio of the left pulmonary artery to RPA are sensitive to the angle between the IVC and RPA and not to that between the IVC and SVC. Second, energy dissipation is mainly sensitive to the angle between the IVC and SVC and not to that between the IVC and RPA. Third, an appropriate increase in the angle between the IVC and RPA or that between the IVC and SVC may lead to optimal options. This study is useful for surgeons in evaluating optimal Fontan options. Copyright © 2012 John Wiley & Sons, Ltd.

To research the change in the physiological mechanism between the heart failure (HF) patient and healthy persons, the physiology parameters, which include the myocardial contractility, systemic vascular resistance (SVR), and vascular compliance, were studied. Through clinical data of HF patients, the computing method of the myocardial contractility was proposed; SVR as a function with respect to mean arterial pressure (MAP) was represented; and the vascular compliance was defined as a function with respect to MAP and cardiac output. Based on these parameters, a lumped parameter model of the cardiovascular system was established to reproduce the hemodynamic status of HF patients and verify the validity of the physiological mechanism. The simulation results demonstrate that the proportional error of mean flow, arterial pressure, and systolic blood pressure is 11.9%, 2.3%, and 4.7% compared with the clinical data, respectively. The proportional error of end-diastolic volume, end-systolic volume , and ejection fraction is 13.4%, 3%, and 3.9%, respectively.

Left ventricular assist devices are increasingly used for long-term support in heart failure patients. To promote heart recovery, finding an optimum operating point of the pump that is appropriate for the heart function, and state of the circulatory system is important. Therefore, the baroreflex sensitivity (BRS), which reflect the state of heart function, is used as a control variable. To find the optimum point automatically, an extremum search algorithm (ESA) is designed to find the mean arterial pressure (MAP) that is corresponding to the maximum value of BRS. Then, a MAP controller based on model-free adaptive controller (MFAC) is designed to maintain the measured MAP tracking the desired one. A mathematical model of the cardiovascular system is used to verify the feasibility of the control strategy in the presence of left ventricular (LV) failure, physically active, and a recovery of cardiac function. The simulation shows that the ESA can find the maximum value of BRS automatically. When the peripheral resistance is reduced for simulating a slight physical active, the rotational speed of the pump is automatically increased (6,800 rpm vs. 8,000 rpm). When E(max) is increased from 0.6 to 1.8 mm Hg/ml to mimic a heart recovery, the speed is decreased from 8000 to 7200 rpm, which may avoid the damage of LV contractility. As a key feature, the proposed control strategy finds the optimum operating point of the pump without the need to set reference value of control variable. This feature is benefit for heart recovery.

Competitive flow from native coronary artery is considered as a major factor in the failure of the coronary artery bypass grafts. However, the physiological effects are not very clear. The aim is to research the impact of competitive flow caused by different left anterior descending (LAD) artery stenosis degrees on hemodynamics in internal thoracic artery (ITA) bypass graft. An idealized ITA-LAD model was built in CAD tools. The degree of the competitive flow was divided into five classes according to different LAD stenosis degrees: higher (no stenosis), secondary (30% stenosis), reduced (50% stenosis), lower (75% stenosis) and no competitive flow (fully stenosis). Finite volume method was employed for the numerical simulation. The flow velocity distributions, wall shear stress and oscillatory shear index were analyzed. Results showed that higher competitive flow in the bypass graft would produce unbeneficial wall shear stress distribution associating with endothelial dysfunction and subsequent graft failure. The coronary bypass graft surgery was preferred to be carried out when the LAD stenosis was higher than 75%.

To study the effect of large blood vessels on the temperature field in invasive microwave ablation, a finite element method was applied based on the convective-type boundary condition on the interface between tissues and blood flow. Whether a large blood vessel is outside of or involved in the lesion area will affect the 54 degrees C effective therapeutic area in different critical conditions. This paper drew the function diagraph on the distance between blood vessel and antenna with the diameter of the blood vessel and put forward the concept of effective therapy radius. It can be used to study the influence of large vessels on the external boundary of the coagulation area and can be used as a theoretical basis to help to decide whether to occlude the large vessels before microwave ablation therapy.

The geometry factors have prominent impacts on the flow patterns of bypass graft. In order to clarify the influence of graft diameter on the hemodynamics of femoral bypass graft, the pulsatile blood flows in three bypassing models with different graft diameters were simulated with finite-element method. The temporal–spatial distributions of flow patterns, pressure drops, and wall shear stresses were depicted and compared. The results indicated that femoral artery bypassed with a large graft demonstrates relatively better and more profitable hemodynamic phenomena with large longitudinal velocity, uniform wall shear stress, and small wall shear stress gradient. The large model may be effective in decreasing the probability of the initiation and development of postoperative intimal hyperplasia and restenosis. Copyright © 2007 John Wiley & Sons, Ltd.

Purpose The internal thoracic artery is the choice of graft for coronary artery bypass grafting due to the excellent long-term patency. However internal thoracic artery graft failures still occur due to diffuse narrowing, known as the string phenomenon. Studies suggest that the string phenomenon is caused by competitive flow when the coronary stenosis is not serious, but the hemodynamics of the string phenomenon are still unclear. The purpose of this study is to clarify the hemodynamic characteristics of the string phenomenon. Materials A patient-specific 3-dimensional model of the aortic arch and coronary arteries was reconstructed. A moderate stenosis was applied to the left anterior descending artery. The internal thoracic artery was used to bypass the stenosis. Two further 3D models were built to study the hemodynamics of the string phenomenon. Methods A numerical study was performed by coupling the 3D artery model with 0-dimensional lumped parameter model of the cardiovascular system. Results The graft flow, native coronary flow, wall shear stress and oscillatory shear index were calculated and illustrated. Inverse flow and high oscillatory shear index appeared on the internal thoracic artery graft when the stenosis was moderate. Conclusion High oscillatory shear index might be the major hemodynamic characteristic of the string phenomenon in internal thoracic artery graft. The inverse graft flow and the difference in graft flow caused by clamping the stenosis can be used to evaluate the probability of observing the string phenomenon.

The Coronary Artery Bypass Graft (CABG) yields excellent results and remains the modern standard of care for treatment of occlusive disease in the cardiovascular system. However, the development of anastomotic Intimal Hyperplasia (IH) and restenosis can compromise the medium-and-long term effects of the CABG. This problem can be correlated with the geometric configuration and hemodynamics of the bypass graft. A novel geometric configuration was proposed for the CABG with two symmetrically implanted grafts for the purpose of improving the hemodynamics. Physiological blood flows in two models of bypass grafts were simulated using numerical methods. One model was for the conventional bypass configuration with a single graft (1-way model); the other model was for the proposed bypass configuration with two grafts (2-way model). The temporal and spatial distributions of hemodynamics, such as flow patterns and Wall Shear Stress (WSS) in the vicinity of the distal anastomoses, were analyzed and compared. Calculation results showed that the 2-way model possessed favorable hemodynamics with uniform longitudinal flow patterns and WSS distributions, which could decrease the probability of restenosis and improve the effect of the surgical treatment. Concerning the limitations of the 2-way bypass grafts, it is necessary to perform animal experiments to verify the viability of this novel idea for the CABG.

Interventional therapy is commonly applied to the treatment of arterial aneurysm. Thermal ablation features rapid and minimal invasive treatment. A hypothesis of combining these two techniques was proposed to treat arterial aneurysm. An antenna is delivered with a catheter into the aneurysm sac and heated with microwave or RF, and hence induces instant coagulation and thrombosis of blood flow in the aneurysm sac so that the treatment motivation is achieved. The initiation of this hypothesis is to overcome the disadvantages of biological/mechanical mismatch between the interventional devices and the arteries in the interventional therapy, also utilize the advantages of rapid treatment and minimal invasion in the thermal ablation procedure.

Background. Single ventricle disease is treated by Glenn surgery. It is generally accompanied by stenosis on a pulmonary artery or its branches, which has great effect on hemodynamics. This study investigated the hemodynamic influence of different pulmonary stenosis degree in Glenn procedure. Materials. Four three-dimensional Glenn models with different left pulmonary artery stenosis rates as, respectively, 0% (model 1), 25% (model 2), 50% (model 3), and 75% (model 4) by the diameter were generated. Method. Geometric multiscale analysis method was used in the numerical simulations by coupling the lumped parameter model (LPM) and three-dimensional model. Results. During one cardiac cycle, the flow ratio between left pulmonary artery and superior vena cava was about 0.49 for models 1, 2, and 3, while the ratio decreased to 0.34 for model 4. On the other hand, hemodynamics parameters like power loss and oscillation shear index show complications of the stenosis to the postoperative development. Conclusion. When the stenosis rate is above 75%, it is suggested to treat stenosis before Glenn procedure, while when the stenosis rate is below 50%, there is no necessity to pay attention to it due to the little effect it makes.

In this challenge, we intended to mimic the patient's cardiovascular system by using 0D-3D connected multiscale model. The purpose of the multiscale analysis is to find out the appropriate boundary conditions of the innominate artery IA, left common carotid artery LCA and left subclavian artery LSA in the local 3D computational fluid dynamics simulation. Firstly, a lumped parameter modelLPM of the patient's circulatory system was established which could mimic both the rest and stress conditions by adjusting parameters like elastance function of the heart and the peripheral resistance, since that administering is oprenaline leads to the patient's heart beat rate and peripheral resistance changes. Secondly, the values of parameters in the LPM were slightly revised to match the following conditions: 1. provided pressure and flow rate curves, 2. provided blood distribution ratio of the AcsAo, IA, LCA and LSA. Finally, we got the outlet conditions of the IA, LCA and LSA, and then connecting the 0D model and the 3D model at each time step. As the results, we got the streamlines, pressure drop through the coarctation, pressure gradient, and some other parameters by coupled multiscale simuation.

Sequential graft was used frequently in clinical studies. In this study, the hemodynamic effect of one kind of sequential graft in two different conditions of the lesion was discussed and some recommendations on the surgical procedures were made. A patient-specific three-dimensional (3D) model of left anterior descending artery (LAD) was reconstructed. A moderate stenosis exist in the trunk of LAD between the first and the second diagonal branch (D1 and D2). Another 3D model without stenosis was also reconstructed based on the patient-specific model. Sequential graft and single graft were applied on these two 3D model. Thus four 3D models were built so that the hemodynamic effect of sequential graft can be discussed. The zero-dimensional (0D)/3D coupling method was used to perform the numerical simulation by coupling the 3D artery model with a 0D lumped parameter model of the cardiovascular system. The flow rates in the branches of LAD and the graft flow were calculated and illustrated in this paper. The wall shear stress (WSS) and oscillatory shear index (OSI) were also calculated and depicted. If the native LAD is stenosis, sequential graft should be applied for the short-term outcomes. Moreover, the long-term patency of the sequential graft applied on the stenosis LAD is good. The long-term patency of the single graft was bad. But the short-term outcomes are almost the same when LAD is not stenosis. If no stenosis exist in the native LAD, a graft with smaller diameter should be applied to improve the long-term patency.

Atrial Fibrillation is the most common sustained cardiac arrhythmia. Minimally invasive ablation using surgical navigation technology gradually becomes the main-stream method in atrial fibrillation surgery. In this paper, a simplified 3D antenna-myocardium-blood numerical model is built and specific absorption rate (SAR) distribution is investigated at the frequency of 2450MHz using the FEM method embodied in Ansoft HFSS. The peak SAR is localized in the tissue at about 26mm along the axis of microwave antenna (with antenna length about 30mm) and very low SAR values is along the antenna length. The electromagnetic numerical results validated that the microwave antenna can deliver localized microwave power and provide acceptable SAR pattern. Also the research does an initial coupled electromagnetic-thermal analysis to obtain the temperature distribution with increasing heating time during microwave ablation.

The intra-aorta pump is a novel continuous flow (CF) left ventricular (LV) device. According to literatures, the pulsatile flow LV device can provide superior LV unloading and circulatory support compared with CF LV assist devices at the same level of ventricular assist device flow. Therefore, a pulsatile control algorithm for the intra-aorta pump is designed. It can regulate the pump to generate pulsatile arterial pressure (AP) and blood flow. A mathematic model of the cardiovascular-pump system is used to verify the feasibility of the control strategy in the presence of LV failure. The surplus hemodynamic energy (SHE), pulsatile ratio (PR), and pulsatile attenuation index (PAI) are used to evaluate the pulsatility of AP and blood flow. The SHE is 8,012.0 ergs/cm(3) by using the pulsatile control strategy (PCS) compared with 5,630.0 ergs/cm(3) by failing heart without support. The PR is 0.302 in the PCS vs. 0.315 in failing heart without support. Meanwhile, the PAI is 85.9% in the PCS compared with 69.7% in failing heart without support. The results demonstrate that the presented control strategy can maintain the pulsatility of AP and blood flow. Moreover, the pulsatile controller provides notably LV unloading. To test the response of the controller to the change of blood demand of patients, another simulation is conducted. In this simulation, the peripheral resistance is reduced to mimic the status of a slight physical active; the Emax is increased to simulate the ventricular contractility recovery. The simulation results demonstrate that the proposed control strategy can automatically regulate the pump in response to the change of the parameters of the circulatory system. To test the dynamic character of the intra-aorta pump, an in vitro experiment is conducted on an in vitro experiment rig. The experimental results demonstrate that the intra-aorta pump can achieve the pulsatile pump speed calculated by the pulsatile controller. The PCS is feasible for the intra-aorta pump. As a key feature, the proposed control strategy provides adequate perfusion in response to the change of blood demands of patients, while restoring the pulsatility of AP and blood flow.

Currently, the cardiovascular diseases threaten almost two in one thousand new borns all around the world. The treatment of these diseases mainly depends on the surgeons' experiences. Surgeons have to choose one of the assumed options for a patient without comparing which is more feasible. In this paper, a cardiovascular surgical planning system was proposed to help the surgeons predict the optimal surgical options using Computational Fluid Dynamics (CFD) and numerical analysis. Three significant stages were included. First, patient-specific three-dimensional anatomical model was reconstructed from CT or MRI data. Second, the reconstructed model was modified into diverse surgical options as the surgeons envisioned. Third, the modified models were imported into ANSYS or CFX for CFD simulations. Hemodynamic characters, for instance, static pressure, flow rate, wall sheer stress, total pressure, flow structure and so on can be obtained. Surgeons are able to predict the post-operation outcomes according to the results of the numerical analysis. This paper studied the Fontan procedure using in the treatment of single ventricle congenital heart defect.

Tetralogy of Fallot (TOF) is one of the most common complex congenital heart diseases of newborns. In the presence of TOF, it is vital that creation of a shunt between the pulmonary and systemic circulations. The objective of this study is to use computational fluid dynamics (CFD) approaches to simulate flow variations in patients of TOF before and after the operation. Knowledge of the flow conditions may be helpful in the clinical management of these patients, whose survival is critically dependent on the blood flow distribution between the pulmonary and systemic circulations.

In order to show the application of computational fluid dynamics in biomedical engineering, some numerical simulations of blood flow in arteries, such as hemodynamics of bypass graft for stenosed arteries, hemodynamics of stented aneurysm at the aortic arch, hemodynamics of bypass treatment for DeBakey III aortic dissection, and influence of blood flow on the thermal characteristics of microwave ablation, which were performed by the authors, were reviewed. These simulations can be a powerful tool for the computer assisted surgery in medical application.