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Charles E Riva - One of the best experts on this subject based on the ideXlab platform.
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ocular blood flow assessment using continuous Laser Doppler Flowmetry
Acta Ophthalmologica, 2010Co-Authors: Charles E Riva, Martial Geiser, Benno L PetrigAbstract:This article describes the technique of continuous Laser Doppler Flowmetry (LDF) as applied to the measurement of the flux of red blood cells in the optic nerve head, iris and subfoveal choroid. Starting with the exposition of the physical principles underlying LDF, we first describe the various devices developed to perform LDF in these vascular beds. We then discuss the clinical protocols, blood flow parameters, calibration procedures, reproducibility and limitations of the LDF technique. Various problems still need to be solved in order to bring to light the full potential of LDF in the assessment of microcirculatory haemodynamics.
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Laser Doppler Flowmetry and optic nerve head blood flow
American Journal of Ophthalmology, 1999Co-Authors: Benno L Petrig, Charles E Riva, Sohan Singh HayrehAbstract:Abstract Purpose: Ischemic disorders of the optic nerve head constitute an important cause of visual loss. The optic nerve head is supplied by two main sources of blood flow: the superficial layers by the central retinal artery and the deeper layers by the posterior ciliary arteries. This study was conducted in rhesus monkey eyes to obtain a better understanding of which part of the optic nerve head circulation is measured by Laser Doppler Flowmetry. Methods: By means of a fundus camera–based Laser Doppler Flowmetry technique to measure blood flow in the optic nerve head tissue, Laser Doppler Flowmetry measurements were taken at baseline and then after experimental occlusion of central retinal artery (12 eyes), posterior ciliary arteries (nine eyes), and combined occlusion of central retinal artery and posterior ciliary arteries (nine eyes). Optic nerve head, choroidal, and retinal circulations were investigated by fluorescein fundus angiography after the various arterial occlusions. Reseults: Average Laser Doppler Flowmetry flow during central retinal artery occlusion alone was significantly decreased ( P P P > .20). After posterior ciliary artery occlusion alone, however, measurements showed a nonsignificant increase in Laser Doppler Flowmetry flow of 17% ± 37%. Conclusions: The findings of this study suggest that the standard Laser Doppler Flowmetry technique is predominantly sensitive to blood flow changes in the superficial layers of the optic nerve head and less sensitive to those in the prelaminar and deeper regions, and their relative proportions are not known. In this Laser Doppler Flowmetry technique, the weaker Doppler signal from the deep layers cannot be separated from the dominant signal from the superficial layers to exclusively study the circulation in the deep layers; the latter circulation is of interest in optic nerve head ischemic disorders, including glaucoma. Emerging new optical modalities of the Laser Doppler Flowmetry technique may help in selectively measuring blood flow in the deeper layers.
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local choroidal blood flow in the cat by Laser Doppler Flowmetry
Investigative Ophthalmology & Visual Science, 1994Co-Authors: Charles E Riva, Stephen D Cranstoun, R M Mann, G E BarnesAbstract:Purpose. To develop a procedure using a noninvasive technique that will allow the investigation of choroidal blood flow (ChBF) regulation in discrete regions of the cat eye. Validation of this procedure will provide a method to study intrinsic, neural, and pharmacologic factors that regulate regional ChBF. Methods. The technique to measure ChBF is based on Laser Doppler Flowmetry. However, in contrast to conventional Laser Doppler Flowmetry, which uses fiber-optic probes in direct contact with the tissue to deliver the Laser beam and detect the scattered light, with this technique the beam is delivered through a fundus camera and the scattered light is detected in the retinal image plane of the camera. Measurements were made in 34 anesthetized cats under conditions that would ensure that the flow measured represented ChBF in the choriocapillaris: the Laser beam was aimed at retinal intervascular sites in the tapetal region of the fundus; the Doppler shift power spectrum of the light scattered by the red blood cells had the shape and frequency range typical for a microvascular bed; and the recorded flow did not decrease by more than 5% when the cat was given 100% O2 to breathe for 4 minutes. The responses to various physiologic and pharmacologic stimuli were tested and compared with those obtained from retinal vessels. Results. Intravenous infusions of acetylcholine increased ChBF in a dose-response fashion, whereas sympathetic nerve stimulation at various frequencies decreased ChBF as predicted by previous studies. By comparison, retinal blood flow was negligibly affected by these two stimuli. In contrast to retinal blood flow, ChBF was unaffected by diffuse luminance flicker. ChBF was found to be pulsatile. The mean of the pulsatile component of ChBF represented approximately 34% of mean ChBF, a value similar to those derived from ChBF measurements in minipigs and retinal blood flow in the cat. Conclusions. This study demonstrates that Laser Doppler Flowmetry is a valid technique for obtaining local, noninvasive, and continuous recordings of relative ChBF. Tested under steady-state conditions for blood pressure, heart rate, and acid-base balance, ChBF is stable for long periods of time, allowing the investigation of the effect of various physiologic stimuli and pharmacologic agents on this flow. Invest Ophthalmol Vis Sci. 1994;35:608-618.
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effect of probe design on the suitability of Laser Doppler Flowmetry in vitality testing of human teeth
Dental Traumatology, 1993Co-Authors: Aegir Rafn Ingolfsson, Leif Tronstad, Elliot V Hersh, Charles E RivaAbstract:The aim of this investigation was to study the influence of probe design on the signal output from the dental pulp in experiments with Laser Doppler Flowmetry (LDF). Eighteen patients 14 to 39 years of age were examined. Recordings were made from a maxillary and a mandibular central incisor and a maxillary canine with an infrared Laser Doppler Flowmetry. The radiographic appearance of the tested teeth was within normal limits and all teeth responded normally to electric pulp testing (EFT). Five configurations of probes were used. Each probe had 3 fibers arranged in a triangle. One fiber carried the Laser light to the pulp tissue and 2 fibers carried the backscattered light to the detector giving the signal output. The diameter of each of the 3 fibers in the probe was 200 μm except in 1 probe where the diameter of the fibers was 125 μm. The distance between the 3 fibers in the triangular arrangement in each probe was 250, 500, 800, 1000, and 1500 μm. A special rubber base splint was used to hold the probe in place on the buccal surface of the tested teeth. The output signals from the LDF were fed into an analog printer and a lap top computer where all calculations were done. The probe with the largest separation of the fibers produced significantly higher output signals from the maxillary and mandibular incisors than the other probes. The same probe also produced significantly higher output signals than the smaller probes from the maxillary canine with the exception of the 200/800 probe. The output signals were significantly higher from the mandibular incisor than from the maxillary incisor and canine. Consecutive recordings with the LDF from the maxillary incisor in 5 patients within 1 hour gave coefficient of variation from 7.9% to 10.3% in output signals. The results of this study showed that all 5 experimental probes gave output signals indicative of blood flow in the dental pulp and the probe with the largest separation of fibers seemed to be the most suitable one under the experimental conditions used. It appeared to be possible to make reproducible recordings from the pulp of the teeth under the experimental conditions used.
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Laser Doppler Flowmetry in the optic nerve
Experimental Eye Research, 1992Co-Authors: Charles E Riva, Benno L Petrig, S Harino, Ross D ShonatAbstract:Laser Doppler Flowmetry (LDF) is a technique that measures relative average velocity, number and flux (number times velocity) of red blood cells in a tissue. In this paper, we demonstrate its application in the optic nerve head tissue, describe the Laser delivery and light scattering detection schemes and investigate the effect of the distance between the sites of illumination and detection. We also provide evidence that the flow measured by LDF varies linearly with actual blood flow in the optic nerve and examine the question of the depth of the sampled volume. Experiments in anesthetized cats illustrate potential applications which make use of the high temporal resolution of LDF. These include the response of blood flow to changes in the composition of the breathing gases and changes induced by neuronal stimulation with multiple and single flashes.
Benno L Petrig - One of the best experts on this subject based on the ideXlab platform.
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ocular blood flow assessment using continuous Laser Doppler Flowmetry
Acta Ophthalmologica, 2010Co-Authors: Charles E Riva, Martial Geiser, Benno L PetrigAbstract:This article describes the technique of continuous Laser Doppler Flowmetry (LDF) as applied to the measurement of the flux of red blood cells in the optic nerve head, iris and subfoveal choroid. Starting with the exposition of the physical principles underlying LDF, we first describe the various devices developed to perform LDF in these vascular beds. We then discuss the clinical protocols, blood flow parameters, calibration procedures, reproducibility and limitations of the LDF technique. Various problems still need to be solved in order to bring to light the full potential of LDF in the assessment of microcirculatory haemodynamics.
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Laser Doppler Flowmetry and optic nerve head blood flow
American Journal of Ophthalmology, 1999Co-Authors: Benno L Petrig, Charles E Riva, Sohan Singh HayrehAbstract:Abstract Purpose: Ischemic disorders of the optic nerve head constitute an important cause of visual loss. The optic nerve head is supplied by two main sources of blood flow: the superficial layers by the central retinal artery and the deeper layers by the posterior ciliary arteries. This study was conducted in rhesus monkey eyes to obtain a better understanding of which part of the optic nerve head circulation is measured by Laser Doppler Flowmetry. Methods: By means of a fundus camera–based Laser Doppler Flowmetry technique to measure blood flow in the optic nerve head tissue, Laser Doppler Flowmetry measurements were taken at baseline and then after experimental occlusion of central retinal artery (12 eyes), posterior ciliary arteries (nine eyes), and combined occlusion of central retinal artery and posterior ciliary arteries (nine eyes). Optic nerve head, choroidal, and retinal circulations were investigated by fluorescein fundus angiography after the various arterial occlusions. Reseults: Average Laser Doppler Flowmetry flow during central retinal artery occlusion alone was significantly decreased ( P P P > .20). After posterior ciliary artery occlusion alone, however, measurements showed a nonsignificant increase in Laser Doppler Flowmetry flow of 17% ± 37%. Conclusions: The findings of this study suggest that the standard Laser Doppler Flowmetry technique is predominantly sensitive to blood flow changes in the superficial layers of the optic nerve head and less sensitive to those in the prelaminar and deeper regions, and their relative proportions are not known. In this Laser Doppler Flowmetry technique, the weaker Doppler signal from the deep layers cannot be separated from the dominant signal from the superficial layers to exclusively study the circulation in the deep layers; the latter circulation is of interest in optic nerve head ischemic disorders, including glaucoma. Emerging new optical modalities of the Laser Doppler Flowmetry technique may help in selectively measuring blood flow in the deeper layers.
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Laser Doppler Flowmetry in the optic nerve
Experimental Eye Research, 1992Co-Authors: Charles E Riva, Benno L Petrig, S Harino, Ross D ShonatAbstract:Laser Doppler Flowmetry (LDF) is a technique that measures relative average velocity, number and flux (number times velocity) of red blood cells in a tissue. In this paper, we demonstrate its application in the optic nerve head tissue, describe the Laser delivery and light scattering detection schemes and investigate the effect of the distance between the sites of illumination and detection. We also provide evidence that the flow measured by LDF varies linearly with actual blood flow in the optic nerve and examine the question of the depth of the sampled volume. Experiments in anesthetized cats illustrate potential applications which make use of the high temporal resolution of LDF. These include the response of blood flow to changes in the composition of the breathing gases and changes induced by neuronal stimulation with multiple and single flashes.
Guillaume Mahe - One of the best experts on this subject based on the ideXlab platform.
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blood perfusion values of Laser speckle contrast imaging and Laser Doppler Flowmetry is a direct comparison possible
IEEE Transactions on Biomedical Engineering, 2013Co-Authors: Tiziano Binzoni, Pierre Abraham, Anne Humeauheurtier, Guillaume MaheAbstract:Laser Doppler Flowmetry (LDF) and Laser speckle contrast imaging (LSCI) allow the monitoring of microvascular blood perfusion. The relationship between the measurements obtained by these two techniques remains unclear. In the present contribution, we demonstrate, experimentally and theoretically, that skin blood flow measurements obtained by LDF and LSCI techniques cannot be compared directly even after “classical” normalization procedure. This technical problem is generated by the nonlinear relationship existing between LDF and LSCI flow data. The experiments have been performed on five healthy voluntary subjects (forearm) by using repeated ischemia/reperfusion cycles to induce the necessary skin blood flow changes. LDF and LSCI data were simultaneously acquired on the same region of interest. Considering the importance of this problem from the clinical point of view, it is concluded that the definition of new corrected algorithms for LSCI is probably a mandatory step that must be taken into account if LDF and LSCI blood flow have to be compared.
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reproducibility of non invasive assessment of skin endothelial function using Laser Doppler Flowmetry and Laser speckle contrast imaging
PLOS ONE, 2013Co-Authors: Cyril Puissant, Pierre Abraham, Sylvain Durand, Anne Humeauheurtier, Sebastien Faure, Georges Leftheriotis, Pascal Rousseau, Guillaume MaheAbstract:Background Endothelial dysfunction precedes atherosclerosis. Vasodilation induced by acetylcholine (ACh) is a specific test of endothelial function. Reproducibility of Laser techniques such as Laser-Doppler-Flowmetry (LDF) and Laser-speckle-contrast-imaging (LSCI) to detect ACh vasodilation is debated and results expressions lack standardization. We aimed to study at a 7-day interval (i) the inter-subject reproducibility, (ii) the intra-subjects reproducibility, and (iii) the effect of the results expressions over variability.
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skin perfusion evaluation between Laser speckle contrast imaging and Laser Doppler Flowmetry
Optics Communications, 2013Co-Authors: Anne Humeauheurtier, Sylvain Durand, Guillaume Mahe, Pierre AbrahamAbstract:Abstract In the biomedical field, Laser Doppler Flowmetry (LDF) and Laser speckle contrast imaging (LSCI) are two optical techniques aiming at monitoring – non-invasively – the microvascular blood perfusion. LDF has been used for nearly 40 years whereas LSCI is a recent technique that overcomes some drawbacks of LDF. Both LDF and LSCI give perfusion assessments in arbitrary units. However, the possible relationship existing between perfusions given by LDF and by LSCI over large blood flow values has not been completely studied yet. We therefore herein evaluate the relationship between the LDF and LSCI perfusion values across a broad range of skin blood flows. For this purpose, LDF and LSCI data were acquired simultaneously on the forearm of 12 healthy subjects, at rest, during different durations of vascular occlusion and during reactive hyperemia. For the range of skin blood flows studied, the power function fits the data better than the linear function: powers for individual subjects go from 1.2 to 1.7 and the power is close to 1.3 when all the subjects are studied together. We thus suggest distinguishing perfusion values given by the two optical systems.
Pierre Abraham - One of the best experts on this subject based on the ideXlab platform.
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blood perfusion values of Laser speckle contrast imaging and Laser Doppler Flowmetry is a direct comparison possible
IEEE Transactions on Biomedical Engineering, 2013Co-Authors: Tiziano Binzoni, Pierre Abraham, Anne Humeauheurtier, Guillaume MaheAbstract:Laser Doppler Flowmetry (LDF) and Laser speckle contrast imaging (LSCI) allow the monitoring of microvascular blood perfusion. The relationship between the measurements obtained by these two techniques remains unclear. In the present contribution, we demonstrate, experimentally and theoretically, that skin blood flow measurements obtained by LDF and LSCI techniques cannot be compared directly even after “classical” normalization procedure. This technical problem is generated by the nonlinear relationship existing between LDF and LSCI flow data. The experiments have been performed on five healthy voluntary subjects (forearm) by using repeated ischemia/reperfusion cycles to induce the necessary skin blood flow changes. LDF and LSCI data were simultaneously acquired on the same region of interest. Considering the importance of this problem from the clinical point of view, it is concluded that the definition of new corrected algorithms for LSCI is probably a mandatory step that must be taken into account if LDF and LSCI blood flow have to be compared.
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reproducibility of non invasive assessment of skin endothelial function using Laser Doppler Flowmetry and Laser speckle contrast imaging
PLOS ONE, 2013Co-Authors: Cyril Puissant, Pierre Abraham, Sylvain Durand, Anne Humeauheurtier, Sebastien Faure, Georges Leftheriotis, Pascal Rousseau, Guillaume MaheAbstract:Background Endothelial dysfunction precedes atherosclerosis. Vasodilation induced by acetylcholine (ACh) is a specific test of endothelial function. Reproducibility of Laser techniques such as Laser-Doppler-Flowmetry (LDF) and Laser-speckle-contrast-imaging (LSCI) to detect ACh vasodilation is debated and results expressions lack standardization. We aimed to study at a 7-day interval (i) the inter-subject reproducibility, (ii) the intra-subjects reproducibility, and (iii) the effect of the results expressions over variability.
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skin perfusion evaluation between Laser speckle contrast imaging and Laser Doppler Flowmetry
Optics Communications, 2013Co-Authors: Anne Humeauheurtier, Sylvain Durand, Guillaume Mahe, Pierre AbrahamAbstract:Abstract In the biomedical field, Laser Doppler Flowmetry (LDF) and Laser speckle contrast imaging (LSCI) are two optical techniques aiming at monitoring – non-invasively – the microvascular blood perfusion. LDF has been used for nearly 40 years whereas LSCI is a recent technique that overcomes some drawbacks of LDF. Both LDF and LSCI give perfusion assessments in arbitrary units. However, the possible relationship existing between perfusions given by LDF and by LSCI over large blood flow values has not been completely studied yet. We therefore herein evaluate the relationship between the LDF and LSCI perfusion values across a broad range of skin blood flows. For this purpose, LDF and LSCI data were acquired simultaneously on the forearm of 12 healthy subjects, at rest, during different durations of vascular occlusion and during reactive hyperemia. For the range of skin blood flows studied, the power function fits the data better than the linear function: powers for individual subjects go from 1.2 to 1.7 and the power is close to 1.3 when all the subjects are studied together. We thus suggest distinguishing perfusion values given by the two optical systems.
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multifractality in the peripheral cardiovascular system from pointwise holder exponents of Laser Doppler Flowmetry signals
Biophysical Journal, 2007Co-Authors: Anne Humeau, M. Tartas, Francois Chapeaublondeau, D Rousseau, Berengere Fromy, Pierre AbrahamAbstract:We study the dynamics of skin Laser Doppler Flowmetry signals giving a peripheral view of the cardiovascular system. The analysis of Holder exponents reveals that the experimental signals are weakly multifractal for young healthy subjects at rest. We implement the same analysis on data generated by a standard theoretical model of the cardiovascular system based on nonlinear coupled oscillators with linear couplings and fluctuations. We show that the theoretical model, although it captures basic features of the dynamics, is not complex enough to reflect the multifractal irregularities of microvascular mechanisms.
Bruce J Martin - One of the best experts on this subject based on the ideXlab platform.
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Laser Doppler Flowmetry measurement of changes in human optic nerve head blood flow in response to blood gas perturbations
Journal of Glaucoma, 1996Co-Authors: Alon Harris, Douglas R Anderson, Lutz E Pillunat, Karen M Joos, Robert W Knighton, Larry Kagemann, Bruce J MartinAbstract:PURPOSE The objective of this study was to establish the ability of Laser Doppler Flowmetry to detect relative changes in human optic nerve head hemodynamics caused by physiologic blood gas perturbations. METHODS Laser Doppler Flowmetry permits the noninvasive assessment of relative blood velocity, volume, and flow (flux) in a sample volume of the nerve head. Such measurements were performed in two groups of healthy subjects. The first group (n = 11) was tested during normal room air breathing and then while breathing 100% oxygen (isocapnic hyperoxia). The second group (n = 10) was also tested under normal conditions as well as during isoxic hypercapnia (+ 15% end-tidal carbon dioxide). Results were analyzed by paired t tests. RESULTS Hyperoxia created a significant 25% (p = 0.002) decrease in optic nerve head blood flow, with blood volume decreased by 9% (p = 0.095) and blood velocity reduced by 13% (p = 0.154) compared to the room air condition. During hypercapnia, optic nerve head blood flow was increased by 28% (p = 0.012), with blood volume increased by 22% (p = 0.017) and blood velocity increased by 9% (p = 0.218) as compared to the normal room air condition. CONCLUSION Blood flow in the optic nerve head capillaries changes in response to hyperoxia and hypercapnia as demonstrated in the brain and retina. Laser Doppler Flowmetry permits the noninvasive assessment of these responses in humans under conditions within the physiologic range.
