Flow Separation Dynamics in Three-Dimensional Asymmetric Diffusers

The mean and instantaneous flow separation of two different three-dimensional asymmetric diffusers is analysed using the data of large-eddy simulations. The geometry of both diffusers under investigation is based on the experimental configuration of Cherry et al. (Int J Heat Fluid Flow 29(3):803–811, 2008). The two diffusers feature similar area ratios of $$\mathrm{AR}=4.8$$ AR = 4.8 and $$\mathrm{AR}=4.5$$ AR = 4.5 while exhibiting differing asymmetric expansion ratios of $$\mathrm{AER}=4.5$$ AER = 4.5 or $$\mathrm{AER}=2.0$$ AER = 2.0 , respectively. The Reynolds number based on the averaged inlet velocity and height of the inlet duct is approximately $${\textit{Re}}=10{,}000$$ Re = 10 , 000 . The time-averaged flow in both diffusers in terms of streamwise velocity profiles or the size and location of the mean backflow region are validated using experimental data. In general good agreement of simulated results with the experimental data is found. Further quantification of the flow separation behaviour and unsteadiness using the backflow coefficient reveals the volume portion in which the instantaneous reversal flow evolves. This new approach investigates the cumulative fractional volume occupied by the instantaneous backflow throughout the simulation, a power density spectra analysis of their time series reveals the periodicity of the growth and reduction phases of the flow separation within the diffusers. The dominating turbulent events responsible for the formation of the energy-containing motions including ejection and sweep are examined using the quadrant analysis at various locations. Finally, isourfaces of the Q-criterion visualise the instantaneous flow and the origin and fate of coherent structures in both diffusers.

RANS-based design of experimental flow model for investigation of complex curved turbulent wakes subjected to adverse pressure gradient

Results are presented of a series of RANS computations aimed at creating a new experimental flow model of a curved turbulent wake evolving under adverse pressure gradient. In the course of the computations, key geometric parameters of the model (the angle of attack of a flat plate generating the wake and the shape and the angles of attack of liner foils creating the pressure gradient) were varied in a wide range. The purpose was to find the parameters ensuring desirable features of the flow, namely, a considerable wake curvature and its strong deceleration leading to formation of a large stagnation or even a reversal flow region, on the one hand, and no flow separation either from the flat plate or from the surfaces of the liner foils, on the other hand. As a result, the design satisfying all these demands has been found. This design will be implemented and studied in the framework of recently launched joint German-Russian project “Complex Wake Flows” which presents a continuation of an earlier similar project devoted to symmetric wakes.

Mechanical thrombectomy and carotid artery stenting for stenosis of the internal carotid artery with free-floating thrombosis: illustrative case

BACKGROUND The authors report a case in which mechanical thrombectomy and carotid artery stenting (CAS) were performed for acute cerebral infarction with free-floating thrombosis (FFT) in left internal carotid artery (ICA) stenosis. Good results were obtained. OBSERVATIONS A 63-year-old man developed sudden disturbance of consciousness and right hemiplegia. He was transported to the authors’ hospital by an emergency vehicle. Head magnetic resonance imaging showed acute cerebral infarction in the left middle cerebral artery region, and magnetic resonance angiography showed poor vascular flow beyond the left ICA. Emergency angiography revealed severe stenosis at the origin of the left ICA and a free-floating thrombus attached to the stenosis and extending to the peripheral side. Percutaneous transluminal angioplasty (PTA) was performed on the stenosis with proximal protection, the thrombus was aspirated under reversal flow, and CAS was performed without exacerbation of clinical symptoms. LESSONS PTA, thrombus aspiration, and CAS under reversal flow may be effective treatments for FFT caused by ICA stenosis.

Reversal Flow in the Left Anterior Descending Artery After Internal Thoracic Artery Grafting

Background: The flow capacity of the in situ internal thoracic artery (ITA) is not necessarily sufficient and can be a cause of hypoperfusion syndrome. We present a catastrophic case of in situ ITA grafting for an isolated left main trunk obstruction 13 years after modified Bentall operation. Case presentation: A 33-year-old woman had previously undergone a modified Bentall operation. Coronary angiography showed a critical stenosis in the left coronary artery. The patient underwent emergent off-pump CABG with the left internal thoracic artery (ITA) to the left anterior descending artery (LAD). On the seventh day, the patient had severe dyspnoea and hypotension. Catheter angiography showed that the ITA was patent, but blood flow from the in situ ITA was delayed, and reversal flow from the apex to the proximal LAD was found. The patient underwent implantation of a left ventricular assist device. Conclusions: In conclusion, concomitant aortocoronary bypass to the circumflex branch will minimise the risk of hypoperfusion, especially for a young patient without atherosclerotic disease.

Fluid–structure interaction in a fully coupled three-dimensional mitral–atrium–pulmonary model

This paper aims to investigate detailed mechanical interactions between the pulmonary haemodynamics and left heart function in pathophysiological situations (e.g. atrial fibrillation and acute mitral regurgitation). This is achieved by developing a complex computational framework for a coupled pulmonary circulation, left atrium and mitral valve model. The left atrium and mitral valve are modelled with physiologically realistic three-dimensional geometries, fibre-reinforced hyperelastic materials and fluid–structure interaction, and the pulmonary vessels are modelled as one-dimensional network ended with structured trees, with specified vessel geometries and wall material properties. This new coupled model reveals some interesting results which could be of diagnostic values. For example, the wave propagation through the pulmonary vasculature can lead to different arrival times for the second systolic flow wave (S2 wave) among the pulmonary veins, forming vortex rings inside the left atrium. In the case of acute mitral regurgitation, the left atrium experiences an increased energy dissipation and pressure elevation. The pulmonary veins can experience increased wave intensities, reversal flow during systole and increased early-diastolic flow wave (D wave), which in turn causes an additional flow wave across the mitral valve (L wave), as well as a reversal flow at the left atrial appendage orifice. In the case of atrial fibrillation, we show that the loss of active contraction is associated with a slower flow inside the left atrial appendage and disappearances of the late-diastole atrial reversal wave (AR wave) and the first systolic wave (S1 wave) in pulmonary veins. The haemodynamic changes along the pulmonary vessel trees on different scales from microscopic vessels to the main pulmonary artery can all be captured in this model. The work promises a potential in quantifying disease progression and medical treatments of various pulmonary diseases such as the pulmonary hypertension due to a left heart dysfunction.

P0201ASSOCIATION OF INTRARENAL VEIN FLOW PATTERNS WITH CARDIAC FUNCTION IN OUTPATIENTS WITH CHRONIC KIDNEY DISEASE AND HEART FAILURE

Background and Aims In patients with chronic kidney disease (CKD) and heart failure (HF), renal venous congestion plays a key role in determining renal dysfunction and a worse prognosis. Αim of this ongoing study is to identify Doppler intrarenal venous flow patterns reflecting renal congestion in patients with CKD and HF and to detect possible associations with cardiac function parameters. Prognostic implications will be evaluated at a next stge. Method We prospectively enroll outpatients affected by CKD stages 3-4 and HF, in stable clinical conditions and in conventional therapy. All patients undergo clinical evaluation, routine biochemistry, transthoracic echocardiogram and renal echo-Doppler. Pulsed Doppler flow recording is performed at the level of the right interlobular renal veins at the end-expiratory phase. The intrarenal venous flow patterns are divided into five types according to the waveforms of the flow. Type A and B are characterized by a continuous flow and considered normal waveforms. Type C is characterized by a short interruption and/or reversal flow during the end-diastolic or protosystolic phase. Type D and E are characterized by a wide interruption and/or reversal flow, respectively. Types C, D and E are considered abnormal and reflect increasing venous pressure within the kidneys. Results Until now, 36 patients (27males / 9 females), 13 (36%) diabetics, aged 69.4±10.6 years old, have been included, and baseline characteristics are presented. Twenty patients (55%) have CKD stage 3, and 16 patients CKD stage 4 (45%). Fifteen (40%) of these patients have HF New York Heart Association (ΝΥΗA) class II, 18 (50%) ΝΥΗΑ class ΙΙΙ and 3 (10%) ΝΥΗΑ class IV. Mean ejection fraction (EF) is 34.5±7.8%, moderately reduced in 9 (25%) and severely reduced in 27 (75%) of these patients. By analyzing the waveforms, we noticed that 27 patients (75%) had venous patterns of continuous flow (type A 18% and type B 57%) and 9 (25%) had venous patterns with not continuous flows (21% type C and 4% type D). The patients with renal venous patterns A and B had higher EF than those with renal venous patterns C and D (36±8% vs. 30±5%, p=0.045). We have also observed that worsening HF according to NYHA classification was significantly associated to more pathological renal venous patterns (rho=0.402, p=0.034) Conclusion In patients with CKD and HF we may observe abnormal intrarenal vein flow patterns, in the context of renal congestion, related to the functional state of the heart. Further studies will indicate the clinical and prognostic significance of these measurements to better characterize patients with cardio-renal syndrome.

P645 Familial restrictive cardiomyopathy and Noonan"s syndrome: a rare association

Background Noonan syndrome is a rare genetic disorder. Typical cardiac involvement include pulmonary stenosis and hypertrophic cardiomyopathy. We present the association of Noonan syndrome with familial non-hypertrophic cardiomyopathy with haemodynamic features of restrictive physiology. Case description. A 30-year old male patient presented to the outpatient clinic with clinical symptoms of heart failure which was slowly progressive since age 20. He was found to have features of restrictive cardiomyopathy aged 12 years at the time when his mother was diagnosed with Noonan syndrome and restrictive cardiomyopathy. On examination, his 1st and 2nd heart sounds were normal, however 3rd heart sound was present. Pulse was regular, 75 per minute, BP 110/70 mmHg. Chest was clear and saturation 98%. Echocardiography showed small left ventricle (LV) with preserved ejection fraction (EF), borderline LV wall thickness (10-11 mm), restrictive filling pattern with mitral valve E/A ratio 4.2 and deceleration time 68 ms; dilated both atria; and pulmonary artery systolic pressure of 37 mmHg (Figure, panels A-C; F). Prominent late diastolic reversal flow was noted in hepatic veins (Panel D). LV longitudinal strain was borderline in absolute value (-18%) however demonstrated ‘apical sparing’ pattern (Panel E). The right ventricle was small in size with mild hypertrophy and dynamic function, but normal flow through pulmonary valve. Prominent diastolic reversal flow was also noted in superior vena cava. Cardiac magnetic resonance confirmed echocardiographic findings and additionally demonstrated prominent trabeculations and myocardial crypts in the LV, small pericardial effusion; no signs of amyloidosis, myocardial infarction, infiltration or fibrosis. Right heart catheterisation showed borderline pulmonary hypertension with a mean pressure of 25 mmHg, raised pulmonary artery wedge pressure 18 mmHg, normal pulmonary vascular resistance 1.9 WU, and a ‘square root sign’ (Panel G). Patient underwent cardiopulmonary exercise testing, he stopped after 9 mins of Bruce protocol due to fatigue, reaching the Peak VO2 of 21.1ml/kg/min (49% of predicted value). No ST changes or arrhythmic events were noted. Patient was diagnosed with primary (non-infiltrative) familial restrictive cardiomyopathy and discussed at multidisciplinary team meeting with recommendation of close follow-up for timing for heart transplantation. Meanwhile he was encouraged to continue treatment with ramipril and start regular physical activity. Discussion There are only few reports describing familial non-hypertrophic cardiomyopathy in patients with Noonan syndrome and none in their family members. We review typical clinical and diagnostic features of restrictive cardiomyopathy involving both ventricles and raise awareness of clinicians of primary familial restrictive cardiomyopathy as a possible cardiac manifestation in patients with Noonan syndrome and their immediate family members. Abstract P645 Figure.

Downward seepage effects on dynamics of scour depth and migrating dune-like bedforms at tandem piers

The present study focuses on multi-scale statistical characterization of scour depth at tandem piers and migrating dune-like bedforms forming behind the piers in downward seepage affected alluvial channel, using an experimental approach. Experiments were conducted using two circular piers arranged in a tandem manner for no seepage, 10% seepage, and 15% seepage condition. The erosive capacity of reversal flow is hindered with downward seepage, which results in reducing velocity and Reynolds stress near the bed at upstream of piers in case of seepage runs. The bed elevation of the scoured region is decreasing with the increasing seepage percentage and the growth in scour depth is diminishing with time. The celerity of scour depth is decreasing with time as well as decreasing with increasing downward seepage. Probability density function of bedform elevation has positive tail slightly thicker than the Gaussian.