Numerical modelling of simulated blood flow in idealized composite arterial coronary grafts: transient flow.

In composite arterial coronary grafts (CACGs), transport phenomena and geometry may considerably alter blood flow dynamics. CACGs aim at revascularizing pathological arteries according to the human anatomy. However, the exact mechanisms causing the failure of coronary bypass grafting are not yet well elucidated. In the present study, computational fluid dynamics (CFD) techniques are applied for the simulation of multi-branched CACGs under physiologically realistic inflow waveforms. The numerical solution is obtained by a finite-volume method formulated in non-orthogonal, curvilinear coordinates and a multi-grid approach. The geometrical models, consisting of idealized and rigid vessels, include the typical T- and a rather new pi-graft configuration. The stenotic effect is also investigated by comparing computational results for three different degrees of area constriction, namely 25%, 50% and 75%, as well as the case without stenosis. Different grafting distances and various inflow rate ratios are imposed, to give an insight into haemodynamical alterations of CACGs and to study the process of restenosis. The results focus on the interaction between the grafts and coronary flows in terms of spatial and temporal variations of velocity and wall shear stress (WSS) distribution. Prominent variations among the different geometries, concerning the velocity profiles and secondary flow motion, are shown. Moreover, the residual flow emerging from different degrees of area constriction shows that low and oscillating shear stresses may arise for even moderate stenotic fields.

Numerical modeling of simulated blood flow in idealized composite arterial coronary grafts: steady state simulations.

This paper presents a comparative study of simulated blood flow in different configurations of simplified composite arterial coronary grafts (CACGs). Even though the composite arterial grafting is increasingly used in cardiac surgery, it is still questionable whether or not the blood flow in such grafts can adequately meet the demands of the native myocardial circulation. A computational fluid dynamics (CFD) model was developed to conduct computer-based studies of simulated blood flow in four different geometric configurations of CACGs, corresponding to routinely used networks in cardiac surgery coronary grafts (T, Y, Pi and sequential). The flow was assumed three-dimensional, laminar and steady and the fluid as Newtonian, while the vessel walls were considered as inelastic and impermeable. It was concluded that local haemodynamics, practically described by velocity, pressure drop, wall shear stress (WSS) and flow rates, may be strongly influenced by the local geometry, especially at the anastomotic sites. The computations were made at mean flow rates of 37.5, 75 and 150ml/min. The side-branch outflow rates, computed for each bypass graft, showed noticeable differences. The results, which were found both qualitatively and quantitatively consistent with other studies, indicate that the Pi-graft exhibits significantly less uniform distribution of outflow rates than the other geometric configurations. Moreover, prominent variations in WSS and velocity distribution among the assessed CACGs were predicted, showing remarkable flow interactions among the arterial branches. The lowest shear stress regions were found on the lateral walls of bifurcations, which are predominantly susceptible to the occurrence of coronary artery disease (CAD). In contrast, the highest WSS were observed at the turn of the arterial branches.

Applications of Fourier transform-infrared spectroscopy to edible oils.

Recent developments in Fourier transform infrared (FT-IR) spectroscopy instrumentation extend the application of this technique to the field of food research, facilitating particularly the studies on edible oils and fats. In this work, FT-IR spectroscopy is used as an effective analytical tool in order: (a) to determine extra virgin olive oil adulteration with lower priced vegetable oils (sunflower oil, soyabean oil, sesame oil, corn oil) and (b) to monitor the oxidation process of corn oil samples undergone during heating or/and exposure to ultraviolet radiation. A band shift observed at 3009 cm(-1) assigned to the C_H stretching vibration of the cis-double bond, allows the determination of extra virgin olive oil adulteration. Changes in the 3050-2800 and 1745 cm(-1) spectral region appear after heating at elevated temperatures and aid the oxidation process monitoring. In addition, an analytical technique for the measurement of carbonylic compounds in oils, produced after heating, is applied. The possible antioxidant effect of oregano is also discussed.

Usefulness of reperfusion ventricular arrhythmias in non-invasive prediction of early reperfusion and sustained coronary artery patency in acute myocardial infarction.

BACKGROUND: Established tenets of occurrence of reperfusion ventricular arrhythmias in acute myocardial infarction (AMI) do not provide insight into the timing of achieving reperfusion or whether coronary artery patency is sustained. We assessed the significance of ventricular arrhythmias in the non-invasive prediction of timely reperfusion and sustained restoration of coronary patency after thrombolysis in patients with AMI. METHODS: 24-hour Holter monitors were placed in 163 patients with an AMI before administration of thrombolytic therapy. Patients were classified into 3 groups of early (within 2 hours) or late reperfusion, or no-reperfusion, according with clinical and continuous ST-segment electrocardiographic criteria. Ventricular fibrillation, ventricular tachycardia (VT) and accelerated idioventricular rhythm (AIVR) were also categorized as having occurred early (within the first 2 hours) or late (after the first 2-hour period). Angiographic confirmation of coronary patency was determined 2 to 6 days after AMI. RESULTS: Early reperfusion was predicted by early sustained AIVR in 86% of patients and early non-sustained AIVR in 62.5% of patients, with sensitivity 38% and 77%, and specificity 96% and 69%, respectively; p<0.0001. Late non-sustained AIVR was commonly seen in early and late reperfused patients (92-97%) as well as in non-reperfused patients (74%). Sustained coronary patency was predicted by early sustained AIVR in 93% of patients, as well as by early non-sustained AIVR in 86% of patients and late non-sustained AIVR in 79% of patients, with sensitivity 22%, 55% and 94%, and specificity 95%, 71% and 18%, respectively; p<0.05. CONCLUSION: Only the occurrence of sustained AIVR, and probably early non-sustained AIVR convey useful information about both early reperfusion and sustained coronary artery patency. The absence of AIVR does not preclude successful thrombolysis.

LDA measurements and numerical prediction of pulsatile laminar flow in a plane 90-degree bifurcation.

An experimental and numerical study of pulsatile laminar flow in a plane 90-degree bifurcation is presented. Detailed LDA velocity measurements of the oscillatory flow field have been carried out. The numerical predictions, which are based on an iterative, finite-difference numerical procedure using primitive dependent variables, are in good agreement with the measurements. The results show that one separation zone is established near the bottom wall of the main duct and another near the upstream wall of the branch. The location and size of the separation zones vary within the cycle and are influenced by the Reynolds number, the flow rate ratio, and the Stokes number.

Measurement and calculations of laminar flow in a ninety degree bifurcation.

Measurements and numericaL calculations of laminar flow in a plane 90 degrees bifurcation are presented. The corresponding two-dimensional steady flow Navier-Stokes equations solved by a finite-difference procedure employing pressure and velocity as dependent variables. The influence of Reynolds number and mass flow ratio on the velocity field, streamlines, local shear stress and pressure drop are quantified and shown to be substantial. The circulation patterns and shear stresses are examined in view of available data regarding the formation of atherotic plaques in the human circulatory system. The calculated velocity profiles are compared with measurements obtained with laser Doppler anemometry and the agreement is shown to be satisfactory. Calculations outside the range of measurements which are of value to biomechanics are also presented.

Effect of wall scattering on SNR in laser Doppler anemometry.

A method, based on geometrical optics and diffraction theory of Gaussian beams, is presented and describes the image formation of scattered light in laser Doppler anemometry. The intensity distributions of the images of scattered light from both the control volume and a nearby transparent wall are given as a function of distance between the control volume and the wall, collecting lens aperture radius, magnification, incident beam radius, and beam angle. The effect of the scattered light from the wall surface on the Doppler SNR is discussed. The minimum distance close to the wall for which a good signal quality can be obtained is defined and quantitatively determined. The results show that this distance is strongly affected by the aperture size of the collecting lens and beam angle.

Observations on the reproductive performance of ewe lambs synchronised for oestrus.

Oestrus induction and synchronisation achieved by means of progesterone implants (Silestrus; Abbott) and one or two injections of 500 in FSH (Gestyl; Organon) at 15-day intervals was followed by natural service in 194 10-month-old ewe lambs, fed on pasture (Group A, of 101 animals) or pasture and concentrates (Group B, of 93 animals) used to study the influence of nutrition and of induction of a second synchronised oestrus on the percentage of oestrus manifestations, conception rate, number of lambings and of lambs born among the above animals.