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Laser Doppler (laser + doppler)

Distribution by Scientific Domains
Medical Sciences75%

Terms modified by Laser Doppler

  • laser doppler flowmetry
  • laser doppler imaging
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  • laser doppler perfusion imaging
  • laser doppler velocimetry
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    Selected Abstracts

    Does dopexamine influence regional vascular tone and oxygenation during intestinal hypotension?

    ACTA ANAESTHESIOLOGICA SCANDINAVICA, Issue 10 2002
    S. Lehtipalo
    Background: Local effects of dopexamine on intestinal vascular tone and oxygenation were investigated during intestinal hypotension. To this end, we employed an experimental model, in which the superior mesenteric arterial pressure (PSMA) was controlled by an adjustable perivascular clamp. This approach enabled us to keep the intestinal perfusion pressure (IPP) constant in the face of any systemic circulatory alterations. Methods: In 11 barbiturate-anesthetized pigs, we instrumented the superior mesenteric circulation for assessments of vascular resistance (RMES), IPP, jejunal mucosal perfusion (Laser Doppler) and intestinal tissue oxygenation (microoximetry). Measurements were carried out before and during dopexamine infusions (0.5 and 1.0 µg·kg,1·min,1) at a freely variable PSMA (i.e. the perivascular clamp fully open) and at a PSMA of 50 mmHg and 30 mmHg. Results: At a constant PSMA of 50 mmHg, dopexamine had no significant intestinal vascular effects. However, at a constant PSMA of 30 mmHg, both doses of dopexamine were associated with decreases in RMES. Effects of dopexamine on intestinal oxygen delivery and extraction were minimal during these procedures, while a minor decrease in intestinal tissue oxygen tension was observed during dopexamine administration at the lowest IPP level. Conclusion: At very low intestinal perfusion pressures (approximately 30 mmHg) dopexamine produces intestinal vasodilation in excess of what is produced by intrinsic autoregulation. This suggests that there is a vasodilatory reserve in the intestine under such conditions and that a pharmacological vasodilator like dopexamine may improve intestinal circulation during regional severe hypotension. [source]

    Non-invasive assessment of endothelial function , relation between vasodilatory responses in skin microcirculation and brachial artery

    CLINICAL PHYSIOLOGY AND FUNCTIONAL IMAGING, Issue 6 2004
    Jimmy Hansell
    Summary Objective:, To compare different non-invasive methods for determination of human endothelial function in peripheral circulation. Design:, Observational, cross-sectional study in 39 healthy subjects (21 females, age 17,56 years). Setting:, Vascular research laboratory at university hospital. Methods:, Laser Doppler (LD) flowmetry was used to compare skin microvascular perfusion changes during postocclusive reactive hyperaemia with those induced by iontophoretic administration of acetylcholine (ACh), an endothelial-dependent vasodilator. LD measurements were compared with ultrasonographic measurements of postocclusive flow-mediated dilatation (FMD) in the brachial artery (n = 21). Results:, Local ACh induced a larger and more sustained skin perfusion increase than reactive hyperaemia after 4 min of regional arterial occlusion (P<0·001). A significant correlation was found between the magnitude of ACh-induced vasodilatation and peak reactive hyperaemia, both in absolute (r = 0·62, P<0·001) and relative terms (r = 0·58, P<0·001). A correlation was also found between brachial artery FMD and the magnitude of ACh-induced skin perfusion increase (r = 0·43, P<0·05) but not between FMD and reactive hyperaemia. Conclusion:, Endothelial function, an early marker of cardiovascular risk, can be non-invasively assessed and graded by LD and FMD-measurements and despite inherent differences, both methods do correlate. [source]

    Single doses of local betamethasone do not suppress allergic patch test reactions to nickel sulfate

    CONTACT DERMATITIS, Issue 4 2004
    Gerd Molander
    Topical corticosteroids are usually banned on test areas prior to patch testing. The previous literature on the effect of topical corticosteroids is conflicting. Patients allergic to nickel sulfate were patch tested on 4 sites with nickel on day (D) 0. Intracutaneous betamethasone was injected to test sites on D,1, D0 and D1. NaCl injection on D,1 was control. The patch test reactions were evaluated clinically and with laser Doppler. There were no differences in patch test reaction intensities on sites treated with intracutaneous betamethasone as compared to control. A single local dose of potent corticosteroid does not suppress allergic patch reactions to nickel. The current practice of avoiding topical corticosteroid use prior to patch testing should be re-evaluated. [source]

    Individuals at increased coronary heart disease risk are characterized by an impaired microvascular function in skin

    EUROPEAN JOURNAL OF CLINICAL INVESTIGATION, Issue 7 2003
    R. G. IJzerman
    Abstract Background To investigate whether microvascular function in skin is a valid model to study the relationships between cardiovascular risk factors and microvascular function, we investigated skin microvascular function in individuals with increased coronary heart disease (CHD) risk. Materials and methods Forty-six healthy White individuals aged 30,70 years were studied. Coronary heart disease risk was assessed with the use of the CHD risk score according to the Framingham Heart Study, which is based on the risk factors age, blood pressure, cigarette smoking, total cholesterol, HDL cholesterol and diabetes. Endothelium-dependent and -independent vasodilation in skin were evaluated with laser Doppler after iontophoresis of acetylcholine and sodium nitroprusside. Videomicroscopy was used to measure recruitment of skin capillaries after arterial occlusion. Results Coronary heart disease risk score (i.e. the 10-year probability of CHD) varied from 1,37%. Microvascular function decreased with increasing quartiles of CHD risk (for acetylcholine-mediated vasodilation: 687, 585, 420 and 326%, P = 0·002; for nitroprusside-mediated vasodilation: 776, 582, 513 and 366%, P = 0·02; for capillary recruitment: 49·9, 44·6, 27·2 and 26·7%, P = 0·001). These trends were similar in men and women (P for interaction > 0·2) and independent of body mass index. Conclusions Increased CHD risk is associated with an impaired endothelium-dependent vasodilatation and capillary recruitment in skin, suggesting that microvascular function in skin is a valid model to study the relationships between cardiovascular risk factors and microvascular function. [source]

    Clinical methods for the evaluation of endothelial function , a focus on resistance arteries

    FUNDAMENTAL & CLINICAL PHARMACOLOGY, Issue 3 2006
    Robinson Joannides
    Abstract Endothelial dysfunction is a key event in the pathophysiology of cardiovascular diseases and appears as a strong independent predictor of cardiovascular events. In this context, biological evaluation of endothelial circulating markers can be helpful. However, functional tests using pharmacological stimuli appear more specific for the study of resistance arteries. These methods consist in the evaluation of the endothelium-dependent changes in regional vascular flow in response to local infusion of substances that act through endothelial receptors without modification of systemic arterial pressure and in comparison with a non endothelium-dependent relaxation. Flow is measured by Doppler and intravascular ultrasound in coronary circulation, laser Doppler in skin and by venous occlusion plethysmography in peripheral muscular arteries. Similar studies can be performed ex vivo using isolated resistance arteries obtained from fat subcutaneous biopsies. In addition, other information can be obtained from reactive hyperemia and the study of the flow-mediated dilatation of conduit arteries to enable a selective and comprehensive approach of the heterogeneity of endothelial function in pathophysiology. [source]

    Near Wall Studies of Pulp Suspension Flow Using LDA

    THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 4 2006
    A. Johan Pettersson
    Abstract A detailed study of the flow behaviour in the near wall region of pulp suspensions up to 4.7% have been performed using Laser Doppler Anemometry (LDA) in pipe flow. Axial mean velocity profiles show a distinct plug flow and an increase of the plug region as the flow rate decreases and fibre concentration increases. An attempt is made to relate the LDA data-rate to fibre concentration, which indicates a dilution region at 1-2 mm from the wall that is larger than the annulus region. The dilution region increases with increasing flow rate, decreasing concentration and when using longer pulp fibres. On a réalisé une étude détaillée du comportement d'un écoulement dans la région proche de la paroi de suspensions de pâte jusqu'à 4,7 %, en utilisant l'anémométrie laser Doppler (LDA) dans une conduite. Les profils de vitesse axiale moyens montrent un écoulement piston distinct et une augmentation de la région piston lorsque le débit diminue et la concentration de fibres augmente. Une tentative est faite pour relier les données de vitesse LDA à la concentration de fibres, qui indique une région de dilution à 1-2 mm de la paroi plus grande que l'espace annulaire. La région de dilution augmente avec l'augmentation du débit, la diminution de la concentration et l'utilisation de fibres de pâtes plus longues. [source]

    Local Bubble Dynamics and Macroscopic Flow Structure in Bubble Columns with Different Scales

    THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 6 2003
    Wei Chen
    Abstract Local bubble behaviours were investigated in three bubble columns with different diameters of 200, 400 and 800 mm. By means of a novel single-tip optical fibre probe employing laser Doppler technique, the local gas holdup, bubble frequency, bubble size and velocity were measured simultaneously at different locations of the columns. Measurements were performed in air-water system at superficial gas velocities up to 90 mm/s. The averaged profiles and instantaneous measurements were analyzed and compared for different columns. The presence of a coherent gross circulation structure spanning the entire column diameter in the larger column rather than a pair of symmetrical circulation cells observed in the smaller columns has been confirmed. Les comportements locaux des bulles ont été étudiés dans trois colonnes à bulles de diamètres différents, soient 200, 400 et 800 mm. Au moyen d'une nouvelle sonde à fibre optique à embout unique employant la technique laser Doppler, des mesures locales de la rétention de gaz, de la fréquence des bulles, de la taille des bulles et de la vitesse ont été effectuées simultanément à différents endroits dans les colonnes. Ces mesures ont été effectuées pour un système air-eau à des vitesses de gaz superficielles atteignant 90 mm/s. Les profils moyennés et les mesures instantanées ont été analysés puis comparés pour différentes colonnes. La présence d'une structure de circulation unique cohérente occupant tout le diamètre de la colonne dans la colonne la plus large plutôt qu'une paire de cellules de circulation symétriques observées dans les colonnes plus petites est confirmée. [source]

    The influence of local heating on skin microcirculation in pressure ulcers, monitored by a combined laser Doppler and transcutaneous oxygen tension probe

    CLINICAL PHYSIOLOGY AND FUNCTIONAL IMAGING, Issue 6 2000
    Vivianne Schubert
    In a prospective, controlled study the skin microcirculation and transcutaneous oxygen tension were evaluated in 28 elderly patients (85 ± 0·8 years) with grade 2 and 3 pressure ulcer. Laser Doppler fluxmetry and transcutaneous oxymetry techniques were used together in a combined probe to simultaneously evaluate the influence of heat stress at 44°C, at the same time and in the same area of the ulcer edge. Total skin microcirculation was already increased at rest before heating, and increased even more during a fast and then a more gradually heat-induced hyperaemia response compared with undamaged skin. The increase showed a biphasic manner. On the other hand, the oxygen diffusibility from the capillaries to the skin surface was significantly reduced, compared with undamaged skin. One hypothesis may be that in ageing skin the main part of the increased skin microcirculation in a pressure ulcer were passing through thermoregulatory vessels in subpapillary tissue layers. Interactions between the increased blood flow and metabolic activity at the ulcer edge might be oxygen-consuming, leading to reduced oxygen content passing through the capillaries and contributing to tissue ischaemia. Disturbances of the local skin microcirculation and tissue oxygenation will influence the ulcer healing rate and may affect the healing progress. [source]