Experimental analysis of the influence of stenotic geometry on steady flow.

We studied the flow behavior under steady flow conditions in four models of cylindrical stenoses at Reynolds numbers from 150 to 920. The flow upstream of the constrictions was always fully developed. The constriction ratios of the rigid tubes (D) to the stenoses (d) were d/D = 0.273; 0.505; 0.548; 0.786. The pressure drop at various locations in the stenotic models was measured with water manometers. The flow was visualized with a photoelasticity apparatus using an aqueous birefringent solution. We also studied the flow behavior at pulsatile flow in a dog aorta with a constriction of 71%. The flow through stenotic geometries depends on the Reynolds number of the flow generated in the tube and the constriction ratio d/D. At low d/D ratios, (with the increased constriction), the flow separation zones (recirculation zones, so-called reattachment length) and flow disturbances increased with larger Reynolds numbers. At lower values, eddies were generated. At high Re, eddies were observed in the pre-stenotic regions. The pressure drop is a function of the length and internal diameter of the stenosis, respective ratio of stenosis to the main vessel and the Reynolds numbers. At low Re-numbers and low d/D, distinct recirculation zones were found close to the stenosis. The flow is laminar in the distal areas. Further experiments under steady and unsteady flow conditions in a dog aorta model with a constriction of 71% showed similar effects. High velocity fluctuations downstream of the stenosis were found in the dog aorta. A videotape demonstrates these results.     

The effect of Reynolds number on the propulsive efficiency of a biomorphic pulsed-jet underwater vehicle

The effect of Reynolds number on the propulsive efficiency of pulsed-jet propulsion was studied experimentally on a self-propelled, pulsed-jet underwater vehicle, dubbed Robosquid due to the similarity of its propulsion system with squid. Robosquid was tested for jet slug length-to-diameter ratios (L/D) in the range 2-6 and dimensionless frequency (St(L)) in the range 0.2-0.6 in a glycerin-water mixture. Digital particle image velocimetry was used for measuring the impulse and energy of jet pulses from the velocity and vorticity fields of the jet flow to calculate the pulsed-jet propulsive efficiency, and compare it with an equivalent steady jet system. Robosquid's Reynolds number (Re) based on average vehicle velocity and vehicle diameter ranged between 37 and 60. The current results for propulsive efficiency were compared to the previously published results in water where Re ranged between 1300 and 2700. The results showed that the average propulsive efficiency decreased by 26% as the average Re decreased from 2000 to 50 while the ratio of pulsed-jet to steady jet efficiency (η(P)/η(P, ss)) increased up to 0.15 (26%) as the Re decreased over the same range and for similar pulsing conditions. The improved η(P)/η(P, ss) at lower Re suggests that pulsed-jet propulsion can be used as an efficient propulsion system for millimeter-scale propulsion applications. The Re = 37-60 conditions in the present investigation, showed a reduced dependence of η(P) and η(P)/η(P, ss)on L/D compared to higher Re results. This may be due to the lack of clearly observed vortex ring pinch-off as L/D increased for this Re regime.     

Hemodynamic Changes of the Middle Hepatic Vein in Patients with Pulmonary Hypertension Using Echocardiography

The aim of this study was to analyze the changes of the middle hepatic vein (MHV) spectra in patients with pulmonary hypertension (PH) caused by congenital heart disease (CHD) and determine the proper parameters of MHV to predict PH. Eighty patients with CHD were included, whose pulmonary artery pressure was measured via right heart catheterization, and the MHV spectra were detected via echocardiography. The peak value of velocity (V) and velocity time integral (VTI) of the waves, including S wave, D wave and A wave, were measured at the end of inspiration. The values of the MHV parameters that were predictive of PH were evaluated and their cut-off points were determined. Compared with the control group, V of S wave (S), VTI of S wave (SVTI), V of D wave (D), VTI of D wave (DVTI) decreased and V of A wave (A), VTI of A wave (AVTI), A/S, AVTI/SVTI, A/(S+D), AVTI/ (SVTI+DVTI) increased in the PH group. These differences were statistically significant (P<0.05). A correlation analysis determined that the ratios of A/S, A/(S+D), AVTI/(SVTI+DVTI) were positively correlated with pulmonary artery mean pressure (r=0.529,0.575,0.438,P<0.001). An ROC curve analysis determined that the diagnostic effect of A/(S+D) was superior to the other two parameters. On the ROC curve, when the ratio of A/(S+D) was 0.30, the sensitivity was 85.37% and specificity was 75.00% for predicting PH. The spectral parameters of MHV, including the ratios of A/S, A/(S+D) and AVTI/(SVTI+DVTI), increased with increasing pulmonary pressure in CHD patients. When the ratio of A/(S+D) was 0.30 in MHV spectra, it had sufficient sensitivity and specificity for diagnosing PH, and this method could be used as a new non-invasive complementary echocardiographic parameter for predicting PH.     

Velocity profiles in stenosed tube models using magnetic resonance imaging

A time-of-flight MRI velocity measurement technique is evaluated against corresponding LDV measurements in a constriction tube model over a range of physiologic flow conditions. Results from this study show that MR displacement images can: 1) be obtained within both laminar and turbulent jets (maximum stenotic Re approximately equal to 4,200), 2) measure mean jet velocities up to 172 cm/s, and, 3) detect low forward and reverse stenosis (0 less than or equal to L/D less than or equal to 2). Regions between the jet termination point and re-establishment of laminar flow (Re greater than or equal to 1500, greater than or equal to 1000, and greater than or equal to 110 downstream of 40, 60, and 80 percent stenosis, respectively) cannot presently be detected by this technique.     

肱动脉内皮依赖性舒张功能鉴别左室舒张功能假性正常化的价值

目的:研究冠心病患者左室舒张功能假性正常化与肱动脉内皮依赖性舒张功能的关系。方法:将75例行选择性冠状动脉造影的患者按冠状动脉病变程度分为单/双支病变组和三支病变组两组,选取48例健康志愿者作为对照组。检测左室舒张功能指标二尖瓣口血流频谱E峰、A峰、E/A比值,同时观察休息时肱动脉反应性充血后内径变化率。结果:单/双支病变组(第一组)E峰、E/A比值下降,肱动脉反应性充血后内径变化率低于正常对照组(P<0.05);三支病变组(第二组)E峰、E/A值无明显改变,肱动脉反应性充血后内径变化率明显低于对照组(P<0.01)。结论:肱动脉内皮依赖性舒张功能可作为鉴别冠心病左室舒张功能假性正常的指标。     

Contraction wave in axial direction in free wall of guinea pig left ventricle

Mechanical activation of the normal left ventricle (LV) is not simultaneous; however, the potential consequences of the ejection function of the ventricle are not entirely known. We studied contraction of the LV free wall to determine whether it reveals a contraction wave in the axial direction during ejection. Seven guinea pig hearts in situ were studied via thoracotomy. In each heart, the ventricular and aortic pressures were measured by two microtipped manometers (2-Fr, Millar). Contraction of the LV free wall was assessed with a video system (Dalsa D6-0256 camera and EPIX PIXCI D32 frame grabber; acquisition rate, 500 frames/s), and 15-18 epicardial markers were used to divide the region into 20-25 triangular areas. The area sizes were studied during contraction to locate the position of the contraction wave. For each triangular area, two variables were determined as follows: the time (t(c)) from the end of diastole until the size of the area reached 80% of maximum size reduction (normalized with the duration of systole) and the normalized latitude (L(ax)) of the area (determined at the end of diastole). A relationship between these two variables was determined by regression analysis. We found that the t(c) at which the contraction wave reached a triangular area was in positive correlation with the L(ax) value for that triangular area with a slope of 0.25 +/- 0.09 and a linear correlation coefficient of 0.41 +/- 0.08. Thus contraction in the guinea pig LV free wall occurs progressively from apex to base with successive areas reaching 80% contraction.     

狭窄血管远心端低密度脂蛋白浓度极化促进动脉粥样硬化形成

低密度脂蛋白（low density lipoprotein,LDL）浓度极化可能是动脉粥样硬化局灶性的重要原因,本文以狭窄血管远心端为研究对象,探讨LDL浓度极化对动脉粥样硬化发生、发展的影响。用数值计算模拟狭窄血管远心端LDL的壁面浓度分布,用激光扫描共聚焦显微镜测定狭窄血管远心端LDL沿z轴的浓度分布;用外科手术方法建立颈总动脉局部狭窄的实验模型,从整体动物水平观察LDL浓度极化对动脉粥样硬化形成的影响。数值计算和激光扫描共聚焦显微镜测定的结果表明,狭窄血管远心端存在显著的LDL浓度极化现象,且LDL壁面浓度与入口液流速度和狭窄程度有关：在相同的速率下,LDL壁面浓度在狭窄度为40％的圆管内最大;在狭窄程度相同的情况下,雷诺数（Re）为250时测得的LDL壁面浓度高于Re为500时测得的壁面浓度。整体动物实验表明,在狭窄血管远心端LDL浓度极化显著的区域形成明显的动脉粥样硬化病变,并且有大量的脂质沉积。以上结果提示,LDL浓度极化可能是导致动脉粥样硬化局灶性的重要因素。     

Morphometry and hemodynamics of posterior communicating artery aneurysms: Ruptured versus unruptured

Posterior communicating artery (PCoA) aneurysms frequently rupture in small size (<7 mm). The aim of the study is to demonstrate morphometric and hemodynamic analyses in ruptured and unruptured PCoA aneurysms to improve predictive accuracy for rupture. Geometrical models were reconstructed from rotational DSA images of 57 ruptured and 22 unruptured side-wall PCoA aneurysms, which were classified into four two-dimensional (2D) groups by a combination of H/D and H/S ratios (H: dome height, D: dome diameter, and S: semi-axis height). Surface area ratio (SAR) of low time-averaged wall shear stress (TAWSS, ≤4 dynes cm⁻²) and high oscillatory shear index (OSI, ≥0.15) were computed in aneurysms. We hypothesized that a two-step analysis method, i.e., one-dimensionally morphometric and hemodynamic analyses in each 2D group, can enhance accuracy of PCoA aneurysm rupture evaluation. There was the highest incidence of H/D > 1 and H/S ≤ 2 with the largest surface area and SAR-TAWSS, but the lowest incidence of H/D ≤ 1 and H/S > 2 with the smallest surface area and SAR-TAWSS in ruptured PCoA aneurysms. PCoA aneurysms of H/D > 1 and H/S ≤ 2 with surface area > 70 mm², H/D ≤ 1 and H/S > 2 with neck diameter > 2.3 mm, H/D ≤ 1 and H/S ≤ 2 with aneurysmal height/parent diameter ratio > 1.0, and H/D > 1 and H/S > 2 with aneurysmal angle > 115° need special attention for clinical diagnosis and treatment. The study highlighted the importance of the two-step analysis method for clinical evaluation of PCoA aneurysm rupture.     

Some characteristics of laminar flow velocity spectra detected by a 20 MHz pulsed ultrasound Doppler

For the purpose of improving accuracy of noninvasive flow measurements in small (1–2 mm diameter) blood vessels, an existing 20 MHz pulsed ultrasound Doppler velocimeter (PUDVM) has been augmented to allow fast Fourier transformation (FFT) of its Doppler shift signal. The modified instrument was used to collect velocity spectra for a benchtop test section delivering precise Poiseuille flows at velocities in the range of physiological interest. The velocity spectra demonstrated a substantial degree of broadening, much of which was attributable to the geometry of the finite sample volume size. Several spectral indices were studied as a function of flow field variables. Results showed that the intensity-weighted mean Doppler shift frequency, when converted to its corresponding velocity v_M, agreed very closely with the theoretically predicted local fluid velocity. Measurement linearity and repeatability were evaluated for a number of system variables, indicating that FFT performance was essentially unaffected by several parameters capable of causing major degradation of (phasic) Doppler shift signals produced by conventional zero-crossing-counter circuitry. As presently configured, the augmented PUDVM instrument is fully capable of detailed flow field mapping in small subcutaneous vessels such as human digital arteries.     

Two-layered blood flow in stenosed tubes for different diseases

A two-fluid model for blood flow through a stenosed tube has been developed. The model consists of a core (suspension of RBCs) and peripheral plasma layer. The core is assumed to be represented by a polar fluid and the plasma layer by a Newtonian fluid. The flow is assumed to be steady and laminar, and the fluids incompressible. The flow variables are computed for normal blood and for the cases of polycythemia, plasma cell dyscrasias and for Hb SS diseases. Resistance to flow has been computed for different stenosis length and for different stenosis height. Shear stress distribution along the axial distance has been computed for different stenosis height. The impact of size effects (particle size to tube diameter) on blood diseases is discussed.     

Physiological flow analysis in significant human coronary artery stenoses

To evaluate the local hemodynamics in flow limiting coronary lesions, computational hemodynamics was applied to a group of patients previously reported by Wilson et al. (1988) with representative pre-angioplasty stenosis geometry (minimal lesion size d(m)=0.95 mm; 68% mean diameter stenosis) and with measured values of coronary flow reserve (CFR) in the abnormal range (2.3+/-0.1). The computations were at mean flow rates (Q) of 50, 75 and 100 ml/min (the limit of our converged calculations). Computed mean pressure drops Deltap were approximately 9 mmHg for basal flow (50 ml/min), approximately 27 mmHg for elevated flow (100 ml/min) and increased to an extrapolated value of approximately 34 mmHg for hyperemic flow (115 ml/min), which led to a distal mean coronary pressure p(rh) of approximately 55 mmHg, a level known to cause ischemia in the subendocardium (Brown et al., 1984), and consistent with the occurrence of angina in the patients. Relatively high levels of wall shear stress were computed in the narrow throat region and ranged from about 600 to 1500 dyn/cm(2), with periodic (phase shifted) peak systolic values of about 3500 dyn/cm(2). In the distal vessel, the interaction between the separated shear layer wave, convected downstream by the core flow, and the wall shear layer flow, led to the formation of vortical flow cells along the distal vessel wall during the systolic phase where Reynolds numbers Re(e)(t) were higher. During the phasic vortical mode observed at both basal and elevated mean flow rates, wide variations in distal wall shear stress occurred, distal transmural pressures were depressed below throat levels, and pressure recovery was larger farther along the distal vessel. Along the constriction (convergent) and throat segments of the lesion the pulsatile flow field was principally quasi-steady before flow separation occurred. The flow regimes were complex in the narrow mean flow Reynolds number range Re(e)=100-230 and a frequency parameter of alphae=2.25. The shear layer flow disturbances diminished in strength due to viscous damping along the distal vessel at these relatively low values of Re(e), typical of flow through diseased epicardial coronary vessels. The distal hyperemic flow field was likely to be in an early stage of turbulent flow development during the peak systolic phase.     

Vibrational equilibration in absorption difference spectra of chlorophyll a.

We describe Franck-Condon simulations of vibrational cooling effects on absorption difference spectra in chlorophyll a (Chl a). The relative contributions of vibrational equilibration in the electronic ground and excited states depend on the pump and probe wavelengths. For Franck-Condon-active vibrational modes exhibiting small Huang-Rhys factors (S < 0.1, characteristic in Chl a pigments), vibrational thermalization causes essentially no spectral changes when the origin band is excited. Significant spectral evolution does occur for S < 0.1 when the 0-1 and 1.0 (hot) vibronic bands are excited. However, vibrational equilibration in these cases causes no spectral shifting in the empirical photobleaching/stimulated emission band maximum. This result bears on the interpretation of time-resolved absorption difference spectra of Chl a-containing antennae such as the Chl a/b light-harvesting peripheral antenna of photosystem II.     

超声心动图评价左室舒张性心力衰竭患者左心形态及舒张功能的应用价值

目的:研究超声心动图对左室舒张性心力衰竭(LVDHF)患者左心形态及舒张功能的评估价值。方法:选择2014年3月至2016年3月我院收治的LVDHF患者78例记为观察组,另选择同期健康志愿者80例记为对照组,两组受试者均进行血压、心率检查,并利用超声心动图技术检测两组受试者的心脏相关指标。结果:观察组的舒张压(DBP)、收缩压(SBP)、心率(HR)、左房内径(LAD)、室间隔厚度(IVST)、左室后壁厚度(LVPWT)、综合指标(E/Ea)及反向血流速度(Ar)水平均明显高于对照组,而早、晚期的运动速度比(Ea/Aa)、血流传播速度(Vp)及峰速比(S/D)水平明显低于对照组,差异均有统计学意义(P0.05)。结论:超声心动图能准确地反应LVDHF患者的左心形态以及舒张功能,可在临床进行推广。     

Oscillation characteristics of biofilm streamers in turbulent flowing water as related to drag and pressure drop

Mixed population biofilms consisting of Pseudomonas aeruginosa, P. fluorescens, and Klebsiella pneumoniae were grown in a flow cell under turbulent conditions with a water flow velocity of 18 cm/s (Reynolds number, Re, =1192). After 7 days the biofilms were patchy and consisted of cell clusters and streamers (filamentous structures attached to the downstream edge of the clusters) separated by interstitial channels. The cell clusters ranged in size from 25 to 750 microm in diameter. The largest clusters were approximately 85 microm thick. The streamers, which were up to 3 mm long, oscillated laterally in the flow. The motion of the streamers was recorded at various flow velocities up to 50.5 cm/s (Re 3351) using confocal scanning laser microscopy. The resulting time traces were evaluated by image analysis and fast Fourier transform analysis (FFT). The amplitude of the motion increased with flow velocity in a sigmoidal shaped curve, reaching a plateau at an average fluid flow velocity of approximately 25 cm/s (Re 1656). The motion of the streamers was possibly limited by the flexibility of the biofilm material. FFT indicated that the frequency of oscillation was directly proportional to the average flow velocity (u(ave)) below 9.5 cm/s (Re 629). At u(ave) greater than 9.5 cm/s, oscillation frequencies were above our measurable frequency range (0.12-6.7 Hz). The oscillation frequency was related to the flow velocity by the Strouhal relationship, suggesting that the oscillations were possibly caused by vortex shedding from the upstream biofilm clusters. A loss coefficient (k) was used to assess the influence of biofilm accumulation on pressure drop. The k across the flow cell colonized with biofilm was 2.2 times greater than the k across a clean flow cell.     

Continuous cultivation of the diatom Nitzschia laevis for eicosapentaenoic acid production: physiological study and process optimization

The continuous cultures of the diatom Nitzschia laevis were performed at different dilution rates (D) and feed glucose concentrations (S(0)) to investigate cellular physiological responses and its production potential of eicosapentaenoic acid (EPA). Steady-state cell dry weight, residual glucose concentration, cell growth yield, specific glucose consumption rate, and fatty acid profiles were investigated within the range of D from 0.1 to 1.0 day(-1) (S(0) fixed at 20 g/L) and the range of S(0) from 5 to 35 g/L (D fixed at 0.3 day(-1)), respectively. The highest EPA productivity of 73 mg L(-1) day(-1) was obtained at D = 0.5 day(-1) and S(0) = 20 g/L. However, when the continuous culture achieved high productivities of EPA at certain dilution rates and feed glucose concentrations, glucose in the feed could not be consumed completely. Accordingly, the continuous culture was evaluated in terms of both EPA productivity (P) and glucose assimilation efficiency (E). The parameter eta, defined as the product of P and E, was used as an overall performance index. Since eta is a function of the two independent variables D and S(0), we employed a central composite design to optimize D and S(0) for the highest eta value. Based on the experimental results of the design, a second-order polynomial equation was established to represent the relationship between eta and D and S(0). The optimal values of D and S(0) were subsequently determined as 0.481 day(-1) and 15.56 g/L, respectively by the empirical model. The verification experiment confirmed the validity of the model. Under the optimal conditions, eta value reached 46.5 mg L(-1) day(-1), suggesting a considerably high efficiency of the continuous culture of N. laevis in terms of EPA production and glucose utilization.     

Disorder distal to modeled stenoses in steady and pulsatile flow

Measurements of the velocity and energy spectra were made in the distal region of modeled stenoses in a rigid tube with both steady and pulsatile water flows. Reynolds numbers of 318–2540 and a pulsatile flow frequency parameter of 15 were employed. The effects of the degree of stenosis, the stenosis geometry and the presence or absence of the downstream confining wall on the development of flow disturbances were investigated. Visualization of the distal flow patterns in stenotic and free jets illustrated the existence of complex fields which included vortex shedding, highly turbulent regions, and recirculation zones. Significant flow disorder was created by a mild stenosis in pulsatile, but not in steady, flow. Nondimensionalization employing the stenosis diameter and flow velocity in the throat of the constriction correlates the vortex shedding frequency and energy spectra within a limited postestenotic region.     

Influence of a downstream narrowing on the flow profile in a tube

The distance over which the upstream flow conditions in a tube are disturbed by a stenosis downstream, i.e. the outlet length, was investigated for Reynolds numbers in the range 210-2900. Two methods were used, the Navier-Stokes equations were solved with a computer and a physical model was constructed and maximal velocities were measured with an ultrasound Doppler system. The computer model showed that Re number does not influence the outlet length, varying the stenosis area from 25% to 90% has an effect. However, the outlet length remained small, below 70% of the diameter of the tube. The physical model confirmed for a 75% stenosis that the outlet length is small, this method set the limit at not more than 1.2 times the tube diameter.     

Influence of operating variables on liquid circulation in a 10.5-m(3) jet loop bioreactor

A 10.5-m(3) concentric tube jet loop reactor was used to study the influence of the working liquid volume, mean superficial air velocity, operating pressure, downcomer aeration, liquid jet velocity, and two ratios of draft tube/reactor diameter (D(t)/D) on liquid circulation time (T(c)). The experiments were carried out in a water-air system with the use of the acid pulse method. Results showed that circulation time was independent of the working liquid volume over a certain minimum liquid level, whereas downcomer aeration and D(t)/D ratio appeared as amenable parameters to achieve a high degree of control over liquid circulation and mixing efficiency, and to optimize the overall reactor performance. Increasing the operating pressure caused a reduction of the liquid circulation rate. However, ionger residence times of the air bubbles and the higher mass transfer driving force that result at higher pressures improve oxygen utilization. The relationship between T(c) and air load was independent of the operating pressure, provided the correlation is given as a function of the mean superficial air velocity. Neither liquid circulation nor gas holdup were significantly affected by liquid jet velocity. (c) 1995 John Wiley & Sons, Inc.     

Superior vena caval blood flow velocities in adults: a Doppler echocardiographic study

Superior vena caval blood flow velocity was measured in 30 normal adults (age 20-65, mean 36 yr). The flow velocities were measured by pulsed Doppler echocardiography, using a Duplex system with the transducer at the right supraclavicular fossa, approximating a 0 degrees Doppler angle. Four distinct flow waveforms were found during each cardiac cycle: A, a small retrograde flow during right atrial contraction (peak flow velocity 12.4 +/- 2.2 cm/s); B, a small antegrade flow during right atrial relaxation (15.7 +/- 5.0 cm/s); S, a large antegrade flow during ventricular systole (35.2 +/- 7.3 cm/s); and D, a large antegrade flow during ventricular diastole (23.2 +/- 3.1 cm/s). The wave duration was inversely related to heart rate. The peak flow velocities of the S and D waves were inversely related to the patients' ages. This study provides recognition of the pattern and range of normality essential to extension of this noninvasive technique to the diagnosis of pathological conditions.     

Two-dimensional short-term model of oxygen uptake kinetics

An empirical case is presented for a two-dimensional O2 uptake (VO2) response surface, taking into account both short-term time dependence and the effect of power output. The surface is of the form VO2 = Re + aWt + bW(1-e-kt) where Re is the resting level, 0 less than W less than 2,100 kpm and 0 less than t less than 480 s are the power and time variables, respectively, k is the rate constant for the transient phase of uptake, and a and b are parameters. As a more general test of this expression, VO2 data on six middle-distance runners exercising for 8 min on a cycle ergometer at 1,200, 1,600, 1,850, and 2,100 kpm/min were collected in a respiratory laboratory. Fits of the surface gave coefficients of determination (R2) averaging 0.947, although for one subject a much lower value of 0.807 was obtained. The final fitted equation for the whole group was VO2 = 0.403 + 0.0012Wt + 1.821W(1-e-0.031t) with R2 = 0.857. (VO2 was measured in liters per minute, W in thousands of kilopond-meters per minute and t in seconds). A surface fit to a multirun experiment permits a more comprehensive examination of residuals. In this instance for one subject, such an examination suggests the possibility of a damped cyclic response-control mechanism. Residual variation, however, appears large enough to obscure any possible cycle in the remaining subjects.