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Doppler Velocimetry (doppler + velocimetry)
Kinds of Doppler Velocimetry Selected AbstractsMeasurements by Laser Doppler Velocimetry in the Casing/Impeller Clearance Gap of a Biocentrifugal Ventricular Assist Device ModelARTIFICIAL ORGANS, Issue 4 2009Leok Poh Chua Abstract:, The velocity distributions in the clearance gap of the Kyoto-NTN biocentrifugal ventricular assist device model were measured by laser Doppler velocimetry (LDV) at three inlet flow conditions, namely operating, fully opened, and fully closed conditions. The results obtained have a similar trend as in the earlier measurements using air as medium and the hot-wire probe, a washout mechanism that is a segment of fluids in the gap situated from , = 60° to 220°, has a larger radial velocity component flowing toward the eye of the pump, as compared to other regions in the gap where the tangential velocity component is dominant. It is essential to have a good washout for the leakage flow through the clearance gap between the stationary casing and the impeller of the pump so that the blood will not keep on circulating in the gap but is washed out to the eye in order to reduce the chances of being destroyed. Although the detailed velocity distributions are not the same, this should be due to the minor fabrication differences between two pump models. The current noninvasive LDV measurements should have a better representation of the actual flow field than the earlier studies due to the blood analog being used as the flow medium. Furthermore, as compared to the methods used in the earlier studies, there is basically no modification of the pump geometry in the present measurement. [source] Laser Doppler Velocimetry and Flow Visualization Studies in the Regurgitant Leakage Flow Region of Three Mechanical Mitral ValvesARTIFICIAL ORGANS, Issue 4 2001Richard S. Meyer Abstract: Streak line flow visualization and laser Doppler velocimetry (LDV) were conducted in the regurgitant leakage flow region of 3 mechanical heart valve types: CarboMedics, Medtronic Hall, and St. Jude Medical. Streak line flow visualization identified regions of high regurgitant flow, and LDV measurements were focused on those locations. Maximum regurgitant flow velocities after valve closure ranged from 0.7 to 2.6 m/s, and maximum Reynolds shear stress after valve closure ranged from 450 to 3,600 dyne/cm2. These data indicate that leakage flows can generate turbulent jets with elevated Reynolds stresses even in bileaflet valves. [source] Abnormal fetal aortic velocity waveform and postnatal growthACTA PAEDIATRICA, Issue 11 2000D Ley Postnatal growth from birth up to 7 y of age was evaluated in 151 children with varying degrees of intrauterine growth retardation who were previously examined in their intrauterine life with Doppler velocimetry of the thoracic descending aorta. The children with abnormal fetal aortic blood flow class (BFC), of which 39/46 (85%) had a birthweight 2 SD below the mean of the population, were lean at birth and had a high rate of catch-up growth in weight and length during the first 3 and 6 mo, respectively. After the initial phases of rapid catch-up in weight and length, mean values of SD scores for weight and height remained relatively unchanged up until 2 y of age, thereafter increasing gradually up to 7 y of age, leaving 4/46 (8%) and 4/46 (8%) below ,2 SD for weight and height, respectively. The pattern of changes in length/height and weight over time did not differ between those infants with abnormal BFC and those with normal BFC. The abnormal fetal aortic waveform was not related to rate of early catch-up growth or to height or weight at 7 y of age after adjustment for deviation in growth at birth. The magnitude of deficit in weight and length at birth was more predictive of subsequent growth. [source] High prevalence of vasomotor reflex impairment in newly diagnosed leprosy patientsEUROPEAN JOURNAL OF CLINICAL INVESTIGATION, Issue 10 2005X. Illarramendi Abstract Background, Initial nerve damage in leprosy occurs in small myelinated and unmyelinated nerve fibers. Early detection of leprosy in the peripheral nervous system is challenging as extensive nerve damage may take place before clinical signs of leprosy become apparent. Patients and methods, In order to determine the prevalence of, and factors associated with, peripheral autonomic nerve dysfunction in newly diagnosed leprosy patients, 76 Brazilian patients were evaluated prior to treatment. Skin vasomotor reflex was tested by means of laser Doppler velocimetry. Blood perfusion and reflex vasoconstriction following an inspiratory gasp were registered on the second and fifth fingers. Results, Vasomotor reflex was impaired in at least one finger in 33/76 (43%) patients. The fifth fingers were more frequently impaired and suffered more frequent bilateral alterations than the second fingers. Multivariate regression analysis showed that leprosy reaction (adjusted odds ratio = 8·11, 95% confidence interval: 1·4,48·2) was associated with overall impaired vasomotor reflex (average of the four fingers). In addition, palmar erythrocyanosis and an abnormal upper limb sensory score were associated with vasomotor reflex impairment in the second fingers, whereas anti-phenolic glycolipid-I antibodies, ulnar somatic neuropathy and a low finger skin temperature were associated with impairment in the fifth fingers. Conclusions, A high prevalence of peripheral autonomic dysfunction as measured by laser Doppler velocimetry was observed in newly diagnosed leprosy patients, which is clinically evident late in the disease. Autonomic nerve lesion was more frequent than somatic lesions and was strongly related to the immune-inflammatory reaction against M. leprae. [source] Free fatty acids exert a greater effect on ocular and skin blood flow than triglycerides in healthy subjectsEUROPEAN JOURNAL OF CLINICAL INVESTIGATION, Issue 8 2004M. Bayerle-Eder Abstract Background, Free fatty acids (FFAs) and triglycerides (TGs) can cause vascular dysfunction and arteriosclerosis. Acute elevation of plasma FFA and TG concentration strongly increase ocular and skin blood flow. This study was designed to discriminate whether FFA or TG independently induce hyperperfusion by measuring regional and systemic haemodynamics. Methods, In a balanced, randomized, placebo-controlled, double-blind, three-way, crossover study nine healthy subjects received either Intralipid® (Pharmacia and Upjohn, Vienna, Austria) with heparin, Intralipid® alone or placebo control. Pulsatile choroidal blood flow was measured with laser interferometry, retinal blood flow and retinal red blood cell velocity with laser Doppler velocimetry, and skin blood flow with laser Doppler flowmetry during an euglycaemic insulin clamp. Results, A sevenfold increase of FFA during Intralipid®/heparin infusion was paralleled by enhanced choriodal, retinal, and skin blood flow by 17 ± 4%, 26 ± 5% (P < 0·001), and 47 ± 19% (P = 0·03) from baseline, respectively. In contrast, a mere threefold increase of FFA by infusion of Intralipid® alone did not affect outcome parameters, despite the presence of plasma TG levels of 250,700 mg dL,1; similar to those obtained during combined Intralipid®/heparin infusion. Systemic haemodynamics were not affected by drug infusion. Conclusions, Present findings demonstrate a concentration-dependent increase in ocular and skin blood flow by FFA independently of elevated TG plasma concentrations. As vasodilation of resistance vessels occur rapidly, FFA may play a role in the development of continued regional hyperperfusion and deteriorate microvascular function. [source] Doppler velocimetry of maternal renal circulation in pregnancy-induced hypertensionJOURNAL OF CLINICAL ULTRASOUND, Issue 8 2001Hidehiko Miyake MD Abstract Purpose The purpose of this study was to evaluate whether the Doppler waveforms of the maternal main renal, segmental, and interlobar arteries are altered in women with pregnancy-induced hypertension (PIH) compared with healthy pregnant women. Methods Flow waveforms of the maternal main renal, segmental, and interlobar arteries were obtained from 42 healthy pregnant women between 24 and 41 weeks of gestation and 21 women with PIH between 28 and 40 weeks of gestation using pulsed Doppler sonography. We used spectral analysis to measure the peak systolic and end-diastolic velocities and the acceleration time. The presence or absence of the normal early systolic compliance peak-reflective-wave complex (ESP) was assessed in only the main renal artery. Results The acceleration times of the segmental and interlobar arteries were significantly prolonged in the PIH group compared with those in the healthy pregnant women. Of the 21 women with PIH, 3 showed loss of the ESP in the renal artery, but these changes were not significant. Conclusions Decreased systolic acceleration and the absence of ESP, the hemodynamic indicators for significant proximal stenosis, suggest that severe stenosis or continuous vasospasm in the proximal arteries, such as the main renal or segmental artery, may be implicated in the pathogenesis of PIH. © 2001 John Wiley & Sons, Inc. J Clin Ultrasound 29:449,455, 2001. [source] Estimation of agitator flow shear rateAICHE JOURNAL, Issue 7 2006Jie Wu Abstract Laboratory laser Doppler velocimetry (LDV) measurements were conducted to measure the shear rate coefficient KS of a range of impellers. Equations correlating KS with NQ (flow number) are provided for axial flow and radial flow impellers. Theoretical formulations based on the classic boundary layer theory are developed to estimate the shear rate at the blade surface. Calculations show that the shear rates at the blade surface are many orders of magnitude higher than those in the flow at the impeller outlet. The software code XFOIL was used to illustrate typical distributions of the shear rates along the blade surfaces. Effects of viscosity, non-Newtonian shear-thinning index, agitator design, and scale-up on shear rates are illustrated. © 2006 American Institute of Chemical Engineers AIChE J, 2006 [source] Comparative velocity investigations in cerebral arteries and aneurysms: 3D phase-contrast MR angiography, laser Doppler velocimetry and computational fluid dynamicsNMR IN BIOMEDICINE, Issue 8 2009Dorothea I. Hollnagel Abstract In western populations, cerebral aneurysms develop in approximately 4% of humans and they involve the risk of rupture. Blood flow patterns are of interest for understanding the pathogenesis of the lesions and may eventually contribute to deciding on the most efficient treatment procedure for a specific patient. Velocity mapping with phase-contrast magnetic resonance angiography (PC-MRA) is a non-invasive method for performing in vivo measurements on blood velocity. Several hemodynamic properties can either be derived directly from these measurements or a flow field with all its parameters can be simulated on the basis of the measurements. For both approaches, the accuracy of the PC-MRA data and subsequent modeling must be validated. Therefore, a realistic transient flow field in a well-defined patient-specific silicone phantom was investigated. Velocity investigations with PC-MRA in a 3,Tesla MR scanner, laser Doppler velocimetry (LDV) and computational fluid dynamics (CFD) were performed in the same model under equal flow conditions and compared to each other. The results showed that PC-MRA was qualitatively similar to LDV and CFD, but showed notable quantitative differences, while LDV and CFD agreed well. The accuracy of velocity quantification by PC-MRA was best in straight artery regions with the measurement plane being perpendicular to the primary flow direction. The accuracy decreased in regions with disturbed flow and in cases where the measurement plane was not perpendicular to the primary flow. Due to these findings, it is appropriate to use PC-MRA as the inlet and outlet conditions for numerical simulations to calculate velocities and shear stresses in disturbed regions like aneurysms, rather than derive these values directly from the full PC-MRA measured velocity field. Copyright © 2009 John Wiley & Sons, Ltd. [source] Aortic isthmus Doppler velocimetry: role in assessment of preterm fetal growth restrictionPRENATAL DIAGNOSIS, Issue 5 2010M. M. Kennelly Abstract Intrauterine fetal growth restriction (IUGR) is an important pregnancy complication associated with significant adverse clinical outcome, stillbirth, perinatal morbidity and cerebral palsy. To date, no uniformly accepted management protocol of Doppler surveillance that reduces mortality and cognitive morbidity has emerged. Aortic isthmus (AoI) evaluation has been proposed as a potential monitoring tool for IUGR fetuses. In this review, the current knowledge of the relationship between AoI Doppler velocimetry and preterm fetal growth restriction is reviewed. Relevant technical aspects and reproducibility data are reviewed as we discuss AoI Doppler and its place within the existing repertoire of Doppler assessments in placental insufficiency. The AoI is a link between the right and left ventricles which perfuse the lower and upper body, respectively. The clinical use of AoI waveforms for monitoring fetal deterioration in IUGR has been limited, but preliminary work suggests that abnormal AoI impedance indices are an intermediate step between placental insufficiency-hypoxemia and cardiac decompensation. Further prospective studies correlating AoI indices with arterial and venous Doppler indices and perinatal outcome are required before encorporating this index into clinical practice. Copyright © 2010 John Wiley & Sons, Ltd. [source] Comparison, Combination and Validation of Measuring Techniques for Local Flow and Turbulence Analysis in Bubble Columns and Airlift ReactorsTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3-4 2003Christophe Vial Abstract The applicability of velocimetry techniques based on the Doppler effect , such as laser and ultrasound Doppler velocimetry , for investigating local hydrodynamics in bubble columns and airlift reactors have been extended to non-coalescing media. Their limitations are highlighted, especially as a function of gas sparger and reactor type. The ultrasound technique was shown to be able to measure either bubble or liquid velocity. Differences in local hydrodynamics due to coalescence behaviour were used to support the analysis. Data validation was carried out both by mass balance and by comparison with other techniques, such as electrochemical probes, Pavlov tubes and optical probes. L'applicabilité des techniques de vélocimétrie laser Doppler et de vélocimétrie ultrasonore pour décrire l'hydrodynamique locale dans les colonnes à bulles et les airlifts est étendue aux milieux non-coalescents. On étudie leurs limitations, notamment en fonction du type de distributeur et de réacteur. On montre que la technique ultrasonore permet à la fois la mesure de la vitesse locale des bulles et du liquide. Les différences dues à l'aptitude à la coalescence du milieu sont démontrées. Les résultats sont validés par des bilans et par la comparaison avec d'autres techniques (sonde électrochimique, tube de Pavlov et sonde optique). [source] Measurements by Laser Doppler Velocimetry in the Casing/Impeller Clearance Gap of a Biocentrifugal Ventricular Assist Device ModelARTIFICIAL ORGANS, Issue 4 2009Leok Poh Chua Abstract:, The velocity distributions in the clearance gap of the Kyoto-NTN biocentrifugal ventricular assist device model were measured by laser Doppler velocimetry (LDV) at three inlet flow conditions, namely operating, fully opened, and fully closed conditions. The results obtained have a similar trend as in the earlier measurements using air as medium and the hot-wire probe, a washout mechanism that is a segment of fluids in the gap situated from , = 60° to 220°, has a larger radial velocity component flowing toward the eye of the pump, as compared to other regions in the gap where the tangential velocity component is dominant. It is essential to have a good washout for the leakage flow through the clearance gap between the stationary casing and the impeller of the pump so that the blood will not keep on circulating in the gap but is washed out to the eye in order to reduce the chances of being destroyed. Although the detailed velocity distributions are not the same, this should be due to the minor fabrication differences between two pump models. The current noninvasive LDV measurements should have a better representation of the actual flow field than the earlier studies due to the blood analog being used as the flow medium. Furthermore, as compared to the methods used in the earlier studies, there is basically no modification of the pump geometry in the present measurement. [source] Laser Doppler Velocimetry and Flow Visualization Studies in the Regurgitant Leakage Flow Region of Three Mechanical Mitral ValvesARTIFICIAL ORGANS, Issue 4 2001Richard S. Meyer Abstract: Streak line flow visualization and laser Doppler velocimetry (LDV) were conducted in the regurgitant leakage flow region of 3 mechanical heart valve types: CarboMedics, Medtronic Hall, and St. Jude Medical. Streak line flow visualization identified regions of high regurgitant flow, and LDV measurements were focused on those locations. Maximum regurgitant flow velocities after valve closure ranged from 0.7 to 2.6 m/s, and maximum Reynolds shear stress after valve closure ranged from 450 to 3,600 dyne/cm2. These data indicate that leakage flows can generate turbulent jets with elevated Reynolds stresses even in bileaflet valves. [source] Effects of Oral L-Arginine on the Foetal Condition and Neonatal Outcome in Preeclampsia: A Preliminary ReportBASIC AND CLINICAL PHARMACOLOGY & TOXICOLOGY, Issue 2 2006Krzysztof Rytlewski Randomized, placebo-controlled, double-blind, clinical trial. Oral therapy with 3 g of L-arginine daily or placebo as a supplement to standard therapy. Eighty-three preeclamptic women, randomly assigned to the L-arginine (n=42) or placebo (n=41) groups; [n=30 (L-arginine) and n=31 (placebo) ended the study, respectively]. Foetal gain chances due to ultrasound biometry, biophysical profile, Doppler velocimetry of pulsatility indices of umbilical and middle cerebral arteries, cerebro-placental ratio, as well as differences in duration of pregnancy and clinical data of newborn. L-arginine treatment transitory accelerated foetal gain and improved biophysical profile. Starting from 3rd week of therapy, the umbilical artery pulsatility indices values were significantly lower in L-arginine than in placebo group. Moreover, treatment with L-arginine caused significant increase of middle cerebral artery pulsatility indices and cerbro-placental ratio values. Latency was longer in L-arginine group. Neonates delivered in the L-arginine group revealed higher Apgar score. Supplementary treatment with oral L-arginine seems to be promising in improving foetal well-being and neonatal outcome as well as in prolonging pregnancy complicated with preeclampsia. However, these benefits require confirmation in more-powered, larger studies. [source] Maternal carriership of factor V Leiden associated with pathological uterine artery Doppler measurements during pregnancyBJOG : AN INTERNATIONAL JOURNAL OF OBSTETRICS & GYNAECOLOGY, Issue 10 2001Pelle G. Lindqvist To determine whether increased vascular resistance in the uterine artery is associated with carriership of factor V Leiden, a retrospective study was undertaken of 231 pregnant women who were monitored with Doppler velocimetry of the uterine arteries. These women had been part of a prospective study of 2480 pregnant women in whom factor V Leiden had been analysed. When compared with non-carriers of factor V Leiden, carriers had a tendency towards an increased proportion of pathological Doppler measurements, including a significant increase in bilateral uterine artery notches (7/33 vs 16/198, relative risk 3.1; 95% CI 1.2,8.1). This suggests an increased vascular resistance in the uteroplacental circulation among carriers of factor V Leiden. [source] Twelve-hour reproducibility of retinal and optic nerve blood flow parameters in healthy individualsACTA OPHTHALMOLOGICA, Issue 8 2009Alexandra Luksch Abstract. Purpose:, The aim of the present study was to investigate the reproducibility and potential diurnal variation of optic nerve head and retinal blood flow parameters in healthy individuals over a period of 12 hr. Methods:, We measured optic nerve head and retinal blood flow parameters in 16 healthy male non-smoking individuals at five time-points during the day (08:00, 11:00, 14:00, 17:00 and 20:00 hr). Outcome parameters were perimacular white blood cell flux (as assessed with the blue field entoptic technique), blood velocities in retinal veins (as assessed with bi-directional laser Doppler velocimetry), retinal arterial and venous diameters (as assessed with the retinal vessel analyser), optic nerve head blood flow, volume and velocity (as assessed with single point and scanning laser Doppler flowmetry) and blood velocities in the central retinal artery (as assessed with colour Doppler imaging). The coefficient of variation and the maximum change from baseline in an individual were calculated for each outcome parameter. Results:, No diurnal variation in optic nerve head or retinal blood flow was observed with any of the techniques employed. Coefficients of variation were between 1.6% and 18.5% for all outcome parameters. The maximum change from baseline in an individual was much higher, ranging from 3.7% to 78.2%. Conclusion:, Our data indicate that in healthy individuals the selected techniques provide adequate reproducibility to be used in clinical studies. However, in patients with eye diseases and reduced vision the reproducibility may be considerably worse. [source] Effect of systemic moxaverine on ocular blood flow in humansACTA OPHTHALMOLOGICA, Issue 7 2009Hemma Resch Abstract. Purpose:, A number of common eye diseases are associated with ocular perfusion abnormalities. The present study aimed to investigate whether systemically administered moxaverine improves ocular blood flow. Methods:, Sixteen healthy volunteers were studied in this randomized, double-masked, placebo-controlled, two-way crossover study. Moxaverine in a dose of 150 mg was administered i.v. Ocular haemodynamic parameters were measured before and after drug administration. Retinal arterial and venous diameters were measured with a retinal vessel analyser. Retinal blood velocity was assessed using laser Doppler velocimetry and choroidal and optic nerve head blood flow was measured with laser Doppler flowmetry. Results:, Moxaverine increased choroidal blood flow (22.6 ± 27.9%), an effect which was significant versus placebo (p = 0.015). Red blood cell velocity in retinal veins tended to increase by 13.6 ± 13.3% after infusion of moxaverine, but this effect was not significant compared with placebo (p = 0.25). In the optic nerve head moxaverine also tended to increase blood flow (11.8 ± 12.7%), but, again, this effect was not significant versus placebo (p = 0.12). Neither moxaverine nor placebo had an effect on retinal arterial diameters. In retinal veins moxaverine tended to induce vasodilation (2.6 ± 2.8%) and to increase blood flow (19.6 ± 16.5%), but these effects were not significant (both p = 0.12). Conclusions:, The present study indicates an increase in choroidal blood flow after systemic infusion of a single dose of moxaverine in healthy subjects. Further studies are warranted to investigate whether these effects are also seen after longterm treatment in patients with ocular vascular disease. [source] Most readily usable methods to measure ocular blood flowACTA OPHTHALMOLOGICA, Issue 2009K GUGLETA Purpose SIS Lecture. Methods Literature search. Results Ocular Blood Flow Research Association (OBFRA, recently merged with another organization - ISOCO, into one single Association for Ocular CDirculation - AOC) made a significant contribution to standardization of the blood flow measuring techniques in the field of ophthalmology. A consens was reached on the number of OBF measurements techniques that occured in the past decades. Particular emphasis was placed on the basic technology, specific parameters and interpretation, accuracy and reproducibility, field of clinical applications. Open questions were extensively discussed, limits of each technique clearly postulated. and a consensus statement put together for each of the technique involved. It encompassed techniques like color Doppler imaging, laser Doppler flowmetry (continuous as well as scanning LDF), laser Doppler velocimetry, Retinal Vessel Analyzer, combination of the vessel diameter measurement and the LDV, laser interferometry of the fundus pulsations amplitude, retinal oxymetry, measurements of the pulsatile component of the blood flow, blue field entoptic method and the newest - Doppler OCT. Conclusion There is no overwhelming measuring technique able to cover all the aspects of the research and the daily clinical routine. Various parameters and various vascular beds are involved, which makes the interpretation of the obtained results strenuous. Of particular importance is the capability of OBF measuring techniques to capture one dynamic feature of ocular circulation - its ability to regulate and to response to various challenges. It is widely believed that not the constantly reduced blood flow, but rather the lack of regulation thereof, leads to prevalent ocular diseases. [source] Influence of Ginkgo biloba on ocular blood flowACTA OPHTHALMOLOGICA, Issue 4 2007Barbara Wimpissinger Abstract. Purpose:, To investigate the effect of Ginkgo biloba extract (EGb761) on ocular blood flow. Methods:, This randomized, double-masked, placebo-controlled, two-way crossover study included 15 healthy male volunteers. Measurements were taken with laser Doppler flowmetry, laser Doppler velocimetry, a retinal vessel analyser, laser interferometry and applanation tonometry, before and up to 3 hours after oral intake of 240 mg EGb761. Results:, At baseline, no significant differences in ocular and systemic haemodynamic parameters were observed between the two study days. Ginkgo biloba significantly decreased retinal venous diameters (p < 0.05 versus baseline), but there was no significant difference between the two groups. Blood pressure, retinal arterial and venous diameters, choroidal blood flow, fundus pulsation amplitude, intraocular pressure and retinal blood flow remained unchanged in both groups and did not differ between groups. Optic nerve head blood flow significantly increased in response to Ginkgo biloba (p < 0.002 versus baseline), but this effect was not significant compared with that of placebo. Conclusions:, The results of this study indicate that a single administration of Ginkgo biloba does not influence ocular blood flow to a relevant degree. Whether the drug may influence ocular blood flow in patients with ocular vascular disease after longterm treatment remains to be investigated in a randomized, placebo-controlled clinical trial. [source] Childhood cardiac function after twin-to-twin transfusion syndrome , a 10-year follow upACTA PAEDIATRICA, Issue 9 2009CP Halvorsen Abstract Aim:, To perform a 10-year follow up of cardiac structure and function after twin-to-twin transfusion syndrome (TTTS) , a severe foetal circulatory complication associated with myocardial hypertrophy in the recipient twin. Methods:, Cardiac dimensions, systolic and diastolic function as assessed by echocardiography including flow and tissue Doppler velocimetry in 22 healthy survivors of TTTS with a mean age of 9.6 (7.2,11.8) years. Results:, The donor and recipient twin did not show any differences in end-diastolic ventricular size, interventricular septum thickness, diameter of right ventricular outflow tract, cardiac valves, coronary arteries or in systolic blood flow velocities. However, compared with the donors, the recipients had significantly lower E/A ratios because of lower E-waves in both mitral (,0.15 ± 0.10, p < 0.01) and tricuspid (,0.09 ± 0.07, p < 0.01) valves, indicating reduced early diastolic ventricular fillings compared with donors. Conclusion:, At school age, twins surviving TTTS had a cardiac structure and function within normal range. There were no differences in heart structure or systolic ventricular function between twins but, compared with the donor twin, we found a reduced early diastolic function in the recipient. [source] Coronary arteries in fetal life: physiology, malformations and the "heart-sparing effect"ACTA PAEDIATRICA, Issue 2004R ChaouiArticle first published online: 2 JAN 200 The present knowledge of coronary arteries in prenatal diagnosis is reviewed with a focus on three aspects: the physiology and visualization of coronary flow, malformations involving the coronary arteries, and the "heart-sparing effect". Visualization of coronary arteries in a healthy human fetus is possible in real-time and colour Doppler during the last 10wk of gestation when ultrasound conditions are excellent. Visualization at an earlier gestational age (up to 13 wk) is feasible mainly in association with malformations and impending hypoxia. The main coronary malformations that can be visualized in utero are the ventriculo-coronary communications in fetuses with pulmonary atresia. In the last few years, interest has been focused on the "heart-sparing effect", defined as the increased perfusion of the coronary arteries in fetuses with severe growth restriction and abnormal Doppler velocimetry in the peripheral vessels. Increased perfusion detectable with colour and pulsed Doppler is a late sign of fetal compromise in hypoxaemia. It confirms animal experiments that have demonstrated dilatory reserves of the fetal coronary arteries under chronic hypoxaemia. The outcome of 21 fetuses showing the "heart-sparing effect" before 32 wk gestation was poor: nine fetuses died in utero and two after birth, the median weight at birth was 630 g. In summary, our knowledge of the coronary arteries in the fetus is based on the diagnostic means used in prenatal diagnosis. New information in this field may also contribute to a better understanding of coronary heart disease later in life. [source] Three-dimensional simulation of planar contraction viscoelastic flow by penalty finite element methodINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 7 2010Yue Mu Abstract The planar contraction flow is a benchmark problem for the numerical investigation of viscoelastic flow. The mathematical model of three-dimensional viscoelastic fluids flow is established and the numerical simulation of its planar contraction flow is conducted by using the penalty finite element method with a differential Phan-Thien,Tanner constitutive model. The discrete elastic viscous split stress formulation in cooperating with the inconsistent streamline upwind scheme is employed to improve the computation stability. The distributions of velocity and stress obtained by simulation are compared with that of Quinzani's experimental results detected by laser,doppler velocimetry and flow-induced birefringence technologies. It shows that the numerical results agree well with the experimental results. The numerical methods proposed in the study can be well used to predict complex flow patterns of viscoelastic fluids. Copyright © 2009 John Wiley & Sons, Ltd. [source] Experimental study of the hydraulic operation of an annular centrifugal contactor with various mixing vane geometriesAICHE JOURNAL, Issue 8 2010Kent E. Wardle Abstract The annular centrifugal contactor is a combination mixer/centrifuge that has been developed for solvent extraction processes for recycling used nuclear reactor fuel. The experimental observations presented were part of a simulation-focused research effort aimed at providing a more complete understanding of the fluid flow within these contactors to enable further advancements in design and operation of future units and greater confidence for use of such contactors in a variety of other solvent extraction applications. Laser doppler velocimetry (LDV), particle image velocimetry (PIV), pressure measurements, and high-speed video imaging for a range of flow rates and rotor speeds were performed to characterize the flow of water in the annular mixing region of the contactor using three different mixing vane geometries. It was found that the geometry of the mixing vanes has a significant impact on the annular liquid height and general flow in the contactor mixing zone. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Retinal photocoagulation and oxygenationACTA OPHTHALMOLOGICA, Issue 2009CJ POURNARAS Purpose The clinical role of photocoagulation for the treatment of hypoxia related complications of retinal ischemic microangiopathies is well established. Methods Measurements of the partial pressure of oxygen (PO2) distribution within the the retina in various animal species using oxygen sensitive microelectrodes and evaluation of the retinal vessels reactivity by laser doppler velocimetry gave additional insights concerning photocoagulation mechanisms. Results The PO2 within the vitreo-retinal interface is heterogeneous. Preretinal and trans-retinal PO2 profiles indicate that the preretinal PO2 far away from vessels remain constant in all retinal areas. Intervascular intraretinal PO2 gradually decreases from both the vitreo-retinal interface and the choroid towards the mid-retina. Close to the pigment epithelium, it is significantly higher than at the vitreoretinal interface due to the much higher O2 supply provided by choroidal compaires to retinal circulation. Laser photocoagulation reduces the outer retina O2 consumption and allows O2 diffusion into the inner retina from the choroid raising the PO2 in the inner healthy retinal layers and in the preretinal intervascular normal areas. In this way laser treatment relieves retinal hypoxia in experimental branch vein occlusion (BRVO). In patients with diabetic retinopathy (DR), the retinal PO2 is higher in areas previously treated with laser. Following photocoagulation, the resulting reversal of hypoxia, the retinal vasculature constriction and the improvement of the regulatory response to hyperoxia all affect favorably both the retinal neovascularisation and macular edema. Conclusion Photocoagulation induces an increase of the inner retinal oxygenation reversing the retinal hypoxia and improving the regulatory response of the retinal vessels [source] | |||||||||||||