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Laser Doppler Velocimetry (laser + 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] 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] 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] 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] 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] 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] 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] | ||||||||||