Failure of Laser Doppler Signal to Correlate with Total Flow in Muscle: Is This a Question of Vessel Architecture?

Clark, Michael G.; Clark, Andrew; Rattigan, Stephen

doi:10.1006/mvre.2000.2273

Cited by 13 publications

(13 citation statements)

References 12 publications

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“…Independence has been assumed but not directly shown previously. Thus the CEU/ microbubble technique contrasts with laser Doppler flowmetry where the signal predominantly reflects non-vectorial motion rather than particle number (Clark et al, 2000) and measurements of capillary recruitment by laser Doppler flowmetry can only be made when bulk blood flow does not change.…”

Section: Discussionmentioning

confidence: 99%

Contrast-enhanced ultrasound measurement of microvascular perfusion relevant to nutrient and hormone delivery in skeletal muscle: A model study in vitro

Ross

Downey

Newman

et al. 2008

Microvascular Research

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Contrast-enhanced ultrasound (CEU) has been used to measure muscle microvascular perfusion in vivo in response to exercise and insulin. In the present study we address whether CEU measurement of capillary volume is influenced by bulk flow and if measured capillary filling rate allows discrimination of different flow pattern changes within muscle. Three in vitro models were used: (i) bulk flow rate was varied within a single length of capillary tubing; (ii) at constant bulk flow, capillary volume was increased 3-fold by joining lengths of capillary in series, and compared to a single length; and (iii) at constant bulk flow, capillary volume was increased by sharing flow between a number of lengths of identical capillaries in parallel. The contrast medium for CEU was gas-filled albumin microbubbles. Pulsing interval (time) versus acoustic-intensity curves were constructed and from these, capillary volume and capillary filling rate were calculated. CEU estimates of capillary volume were not affected by changes in bulk flow. Furthermore, as CEU estimates of capillary volume increased, measures of capillary filling rate decreased, regardless of whether capillaries were connected in series or parallel. Therefore, CEU can detect a change in filling rate of the microvascular volume under measurement, but it can not be used to discriminate between different flow patterns within muscle that might account for capillary recruitment in vivo.

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Section: Discussionmentioning

confidence: 99%

Contrast-enhanced ultrasound measurement of microvascular perfusion relevant to nutrient and hormone delivery in skeletal muscle: A model study in vitro

Ross

Downey

Newman

et al. 2008

Microvascular Research

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“…Using various constructed models of fine tubing, we showed that the reflected LDF signal arose predominantly from red blood cell movement (nonvectorial speed) and less so from cell number (25), emphasizing that any change in LDF signal, obtained from tissue measurements, should be treated with caution. One way to avoid this potentially confounding issue is to use experimental conditions where bulk flow does not change (e.g., low concentrations of insulin or low levels of exercise).…”

Section: Insulin-mediated Increases In Microvascular Perfusionmentioning

confidence: 97%

“…Second, the increase in laser Doppler signal from iontophoresed insulin on the skin of the wrist may not necessarily reflect capillary recruitment. This is because LDF appears to be more sensitive to changes in nonvectorial speed resulting from increased blood flow rate than an increase in cell number from an increase in the number of perfused capillaries (25). Thus an increase in LDF signal during iontophoresis could arise from a vasodilatory action of insulin to increase local blood flow rate in vessels already perfused rather than a vasodilatory action of insulin at branch points of the terminal arterioles to increase the number of capillaries perfused.…”

Section: Insulin-mediated Increases In Microvascular Perfusionmentioning

confidence: 99%

Impaired microvascular perfusion: a consequence of vascular dysfunction and a potential cause of insulin resistance in muscle

Clark

2008

American Journal of Physiology-Endocrinology and Metabolism

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Insulin has an exercise-like action to increase microvascular perfusion of skeletal muscle and thereby enhance delivery of hormone and nutrient to the myocytes. With insulin resistance, insulin's action to increase microvascular perfusion is markedly impaired. This review examines the present status of these observations and techniques available to measure such changes as well as the possible underpinning mechanisms. Low physiological doses of insulin and light exercise have been shown to increase microvascular perfusion without increasing bulk blood flow. In these circumstances, blood flow is proposed to be redirected from the nonnutritive route to the nutritive route with flow becoming dominant in the nonnutritive route when insulin resistance has developed. Increased vasomotion controlled by vascular smooth muscle may be part of the explanation by which insulin mediates an increase in microvascular perfusion, as seen from the effects of insulin on both muscle and skin microvascular blood flow. In addition, vascular dysfunction appears to be an early development in the onset of insulin resistance, with the consequence that impaired glucose delivery, more so than insulin delivery, accounts for the diminished glucose uptake by insulin-resistant muscle. Regular exercise may prevent and ameliorate insulin resistance by increasing "vascular fitness" and thereby recovering insulin-mediated capillary recruitment.

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“…The MI depends on the average velocity of blood and erythrocyte concentration in a volume of tissue [1,2]. It has been estimated in in vitro experiments using polymer tubes with different diameters that the MI depends mainly on the blood cell velocity and less on the cell count [3].The main limitation of MI application in tissue perfusion research is an unstable linear correlation and differences from blood flow values assayed by other methods, in particular, with labeled microspheres. It has been demonstrated in experiments with rat skeletal muscles that the formula for vascular resistance R (mm Hg/PU)…”

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Evaluation of the parameters of total, nutritive, and shunt blood flows in the skin microvasculature using laser Doppler flowmetry

Крупаткин

2005

Hum Physiol

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Laser Doppler flowmetry (LDF) has been applied widely in tissue microcirculation research. Annually, more than 100 studies using the method are published in the Russian literature and more than 500 studies, worldwide. The method is based on the optical probing of tissue and analysis of the signal scattered by moving blood cells, mainly erythrocytes, in a studied volume (1-2 mm 3 ). The LDF results are expressed in perfusion units (PU). The depth of probing in the skin is limited by the subpapillary plexus, in particular, small (terminal) arterioles and collecting venules. Tissue microcirculation is characterized by the microcirculation index (MI; in PU), which reflects the mean perfusion value in the given area. The MI depends on the average velocity of blood and erythrocyte concentration in a volume of tissue [1,2]. It has been estimated in in vitro experiments using polymer tubes with different diameters that the MI depends mainly on the blood cell velocity and less on the cell count [3].The main limitation of MI application in tissue perfusion research is an unstable linear correlation and differences from blood flow values assayed by other methods, in particular, with labeled microspheres. It has been demonstrated in experiments with rat skeletal muscles that the formula for vascular resistance R (mm Hg/PU)where P m is the mean arterial pressure, may fail to reflect true alterations of R [2]. Consequently, the skin vascular conduction parameter (SVCP, mm Hg/PU) estimated as SVCP = MI/ P m is not physiologically valid [4].Another limitation is that the MI characterizes the total microvascular perfusion rather than just the transcapillary nutritive flow. This restricts the application of LDF and makes interpretation of its results difficult in clinical physiological studies in humans.Microvascular blood flow is unstable and variable. LDF-accessible changes of erythrocyte flow are termed flux motions, flow motions, or oscillations. The contributions of particular regulatory mechanisms to the LDF pattern can be evaluated by computer spectral amplitude-frequency analysis. Each rhythm is characterized by frequency ( F , in Hz or oscillations per minute) and amplitude ( A , in PU) [1,5]. The frequency is more inert than the amplitude under external modulation. The genesis of very low frequency rhythms (0.095-0.02 Hz) is still unclear, but they are presumably related with endothelium secretion of nitric oxide [6]. Neurogenic rhythms (0.02-0.06 Hz) are caused by sympathetic adrenergic influences on myocytes of arterioles and arteriovenous anastomoses [5,7,8]; myogenic rhythms (0.06-0.15 Hz) are determined by the activity of myocytes of precapillary sphincters and precapillary metarterioles [5]. I previously suggested a method for separate evaluation of the neurogenic and myogenic tones, which are inversely proportional to the amplitudes of the neurogenic and myogenic rhythms in microvessels [8,9]. Respiratory and cardiac rhythms are synchroAbstract -Examination of 28 healthy subjects and 66 patients was performed usin...

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Failure of Laser Doppler Signal to Correlate with Total Flow in Muscle: Is This a Question of Vessel Architecture?

Cited by 13 publications

References 12 publications

Contrast-enhanced ultrasound measurement of microvascular perfusion relevant to nutrient and hormone delivery in skeletal muscle: A model study in vitro

Contrast-enhanced ultrasound measurement of microvascular perfusion relevant to nutrient and hormone delivery in skeletal muscle: A model study in vitro

Impaired microvascular perfusion: a consequence of vascular dysfunction and a potential cause of insulin resistance in muscle

Evaluation of the parameters of total, nutritive, and shunt blood flows in the skin microvasculature using laser Doppler flowmetry

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