Non‐invasive Assessment of Skin Microvascular Function in Humans: An Insight Into Methods

Abstract

For more than two decades, methods for the non-invasive exploration of cutaneous microcirculation have been mainly based on optical microscopy and laser Doppler techniques. In this review, we discuss the advantages and drawbacks of these techniques. Although optical microscopy-derived techniques, such as nailfold videocapillaroscopy, have found clinical applications, they mainly provide morphological information about the microvessels. Laser Doppler techniques coupled with reactivity tests are widespread in the field of microvascular function research, but many technical issues need to be taken into account when performing these tests. Post-occlusive reactive hyperemia and local thermal hyperemia have been shown to be reliable tests, although their underlying mechanisms are not yet fully understood.Acetylcholine and sodium nitroprusside iontophoresis, despite their wide use as specific tests of endothelium-dependent and -independent function, respectively, show limitations. The influence of the skin site, recording conditions, and the way of expressing data are also reviewed.Finally, we focus on promising tools such as laser speckle contrast imaging.Key words: microcirculation, capillaroscopy, laser Doppler, laser speckle, iontophoresis, local thermal hyperemia, post-occlusive hyperemia WHY AND HOW TO ASSESS SKIN MICROVASCULAR FUNCTION?Since the development of methods allowing the study of microcirculation, microvascular dysfunction has been associated with several vascular diseases as well as in aging [100]. The role of generalized microvascular dysfunction in the pathophysiology or as a consequence of these diseases has also been questioned. Indeed, patients with impaired coronary microvascular function also have evidence of impaired peripheral microvascular function, suggesting a generalized disorder in the regulation of the microvasculature [120]. Similar findings have been reported of correlated abnormalities between cutaneous and retinal microvasculature in diabetic patients [20].As the skin is readily accessible, it provides an appropriate site to assess peripheral microvascular reactivity. Moreover, recent technological advances have provided simple and non-invasive methods to assess skin microvascular function. Therefore, human cutaneous circulation could be used as a surrogate marker of systemic microvascular function in various diseases. However, this raises the issue of how representative the microcirculation in the skin is to the microcirculation in other organs. To date, the skin has been used as a model of microcirculation to investigate vascular mechanisms in a variety of diseases, including

Analysis of Laser Speckle Contrast Images Variability Using a Novel Empirical Mode Decomposition: Comparison of Results With Laser Doppler Flowmetry Signals Variability

“…Different optical techniques have become available to monitor microvascular blood flow. Among them, the laser Doppler flowmetry (LDF) and the laser speckle contrast imaging (LSCI) offer advantages for a continuous and non invasive monitoring of microvascular blood flow ( [8], [9]). LDF was introduced in the 1970s ( [10]) and is now a commonly used technique that provides an index of perfusion, see an example in Fig.…”

The wavelet transform as a tool for the characterization of the vascular response in the human lower limb

“…A pele é facilmente acessível [1] e potencialmente representativa [2] para a avaliação dos mecanismos de função e disfunção da microcirculação periférica [3][4][5] em particular quando são usadas tecnologias não invasivas, como a Fluxometria por Laser Doppler (FLD). A FLD está entre as tecnologias mais amplamente utilizadas para este propósito [6] , fornecendo um sinal complexo que pode ser decomposto em componentes com intervalos de frequência característicos, por meio de ferramentas de análise espectrais, tais como a transformada rápida de Fourier, a modelação autorregressiva e a análise de ôndula [7] . A transformada de ôndula permite o isolamento de uma dada estrutura no espaço físico e no espaço de Fourier.…”

“…The skin is easily accessible [1] and potentially representative [2] for the evaluation of peripheral microcirculation function and dysfunction mechanisms [3][4][5] , in particular when noninvasive technologies such as Laser Doppler Flowmetry (LDF) are used. LDF is among the most widely employed technologies for this purpose [6] , providing a complex signal which can be decomposed into components with characteristic frequency ranges by means of spectral analysis tools, such as the fast Fourier transform, autoregressive modelling and wavelet analysis [7] . A wavelet transform allows the isolation of a given structure in the physical space and in the Fourier space.…”

Laser speckle contrast imaging of the skin: interest in processing the perfusion data

“…Our goal herein is to report on the potentialities of studies dedicated to the processing of LSCI perfusion data. Linear and nonlinear analyses could be of interest to improve the understanding of LSCI images.Keywords Laser speckle contrast imaging Á Microcirculation Á Signal processing Á Image processing Á Laser Doppler flowmetryIn clinical research, the real-time monitoring of skin microvascular blood perfusion can be performed, among others, with laser Doppler flowmetry (LDF) and laser speckle contrast imaging (LSCI) (see, e.g., [7, 13, 18, 26,43,46]). LDF has been proposed in the 1970's [45] to monitor the microvascular blood perfusion in a small volume of tissue (approximately 1 mm 3 in skin when a 780 nm laser wavelength is used).…”

“…In clinical research, the real-time monitoring of skin microvascular blood perfusion can be performed, among others, with laser Doppler flowmetry (LDF) and laser speckle contrast imaging (LSCI) (see, e.g., [7,13,18,26,43,46]). LDF has been proposed in the 1970's [45] to monitor the microvascular blood perfusion in a small volume of tissue (approximately 1 mm 3 in skin when a 780 nm laser wavelength is used).…”