ASSESSING SKIN MICROCIRCULATION IN PATIENTS AT CARDIOVASCULAR RISK BY USING LASER SPECKLE CONTRAST IMAGING. A NARRATIVE REVIEW

Skin tissue holds a prominent role in microcirculatory research as an easily accessible vascular bed for the non-invasive evaluation of microvascular function. Skin microvascular changes have been associated to alterations in distinct target organs and vascular beds, reinforcing the hypothesis that skin microcirculation can be used as a model of generalized microvascular function. In addition, skin microvascular dysfunction has been documented in cardiovascular disease and patients of increased cardiovascular risk where it has been associated with multiple cardiovascular risk factors, rendering it a candidate surrogate marker of vascular damage. Laser Speckle Contrast Imaging (LSCI) is a non-invasive, dynamic laser technique that allows assessment of skin microvascular function (SMF) by obtaining two-dimensional maps of the skin perfusion in real time with high spatial and temporal resolution and, most importantly, with the highest reproducibility as compared to other laser methods. An ever-increasing number of studies using LSCI is confirming evidence of impaired SMF in several cardiovascular risk groups, therefore expanding its application in microvascular research and showing its potential clinical utility. This review attempts to present the growing importance of SMF in cardiovascular research and the emergence of LSCI technique as a robust imaging modality with a promising role to explore skin microvascular physiology. After a short description of the relevant technique and its main principle of function, we have also opted to present the most up to date studies using LSCI for the investigation of SMF in patients with cardiovascular disease as well as various groups of increased cardiovascular risk. This article is protected by copyright. All rights reserved.

Microvascular Dysfunction in Patients with Critical Covid-19, a Pilot Study

BACKGROUND

Endothelial and microvascular dysfunction may be a key pathogenic feature of severe COVID-19. The aim of this study was to investigate endothelial-dependent and endothelial-independent skin microvascular reactivity in patients with critical COVID-19.

METHODS

Twelve patients with COVID-19 treated with non-invasive or invasive mechanical ventilation were included in the study. We investigated skin microvascular reactivity on 2 separate days during hospitalization (study day 1 and 2) and at least 3 months after disease onset (study day 3). Twelve controls with no confirmed or suspected COVID-19 infection during 2020 were also examined. Skin perfusion was investigated through Laser Speckle Contrast Imaging before and after iontophoresis of acetylcholine (ACh) and sodium nitroprusside (SNP) to determine the endothelial-dependent and the endothelial-independent vasodilation, respectively.

RESULTS

Compared to controls, patients with critical COVID-19 had higher basal skin perfusion and reduced responses to endothelial-dependent (ACh, P = 0.002) and endothelial-independent (SNP, P = 0.01) vasodilator drugs on study day 1. In addition, the ACh/SNP ratio was significantly reduced in patients (0.50 ± 0.36 vs. 0.91 ± 0.49 in controls, P = 0.02). Three months after disease onset, surviving patients tended to have reduced ACh-mediated vasodilation compared to controls (P = 0.08).

CONCLUSIONS

This small-sized pilot study demonstrates that critical COVID-19 infection is associated with microvascular impairment and, in particular, a markedly reduced endothelial function. Our results also suggest that microvascular function may not be fully recovered 3 months after disease onset.

Skin microvascular reactivity correlates to clinical microangiopathy in type 1 diabetes: A pilot study

AIM

The aim of this study was to investigate the correlation between skin microvascular reactivity and clinical microangiopathy in patients with type 1 diabetes.

METHODS

We included 61 patients with type 1 diabetes, that is, 31 patients with and 30 without clinical microangiopathy, and 31 healthy controls. A microangiopathy scoring system was introduced for comparison of data between patients with microangiopathy. Responses to iontophoresis of acetylcholine and sodium nitroprusside were assessed by laser Doppler imaging.

RESULTS

Patients with microangiopathy had reduced acetylcholine- and sodium nitroprusside-mediated flux in forearm skin microcirculation compared to healthy controls (p = 0.03 and p < 0.001, respectively, repeated measures analysis of variance), whereas no significant differences were found between patients without microangiopathy and controls. Skin reactivity was reduced in patients with microangiopathy compared to patients without microangiopathy: 1.43 ± 0.38 versus 1.59 ± 0.39 arbitrary units for acetylcholine-mediated peak flux and 1.44 ± 0.46 versus 1.74 ± 0.34 arbitrary units for sodium nitroprusside-mediated peak flux (p < 0.05 for both). A tendency of gradual decrease in acetylcholine and sodium nitroprusside responses was found in patients with increasing microangiopathy scores.

CONCLUSION

We conclude that skin microvascular reactivity is associated with clinical microangiopathy in patients with type 1 diabetes. Impaired skin microvascular function in type 1 diabetes seems to be multifactorial and involves both endothelial-dependent and endothelial-independent pathways. We introduce a novel microangiopathy score that could easily be used in a clinical setting for comparison of patients with various degrees of microangiopathy.

Application of cmOCT and continuous wavelet transform analysis to the assessment of skin microcirculation dynamics

Correlation mapping optical coherence tomography (cmOCT) is a powerful technique for the imaging of skin microvessels structure, based on the discrimination of the static and dynamic regions of the tissue. Although the suitability of cmOCT to visualize the microcirculation has been proved in humans and animal models, less evidence has been provided about its application to examine functional dynamics. Therefore, the goal of this research was validating the cmOCT method for the investigation into microvascular function and vasomotion. A spectral domain optical coherence tomography (SD-OCT) device was employed to image 90 sequential three-dimensional (3-D) OCT volumes from the forearm of 12 volunteers during a 25-min postocclusive reactive hyperemia (PORH) test. The volumes were processed using cmOCT to generate blood flow maps at selected cutaneous depths. The maps clearly trace flow variations during the PORH response for both capillaries and arterioles/venules microvascular layers. Continuous blood flow signals were reconstructed from cmOCT maps to study vasomotion by applying wavelet transform spectral analysis, which revealed fluctuations of flow during PORH, reflecting the regulation of microvascular tone mediated by endothelial cells and sympathetic nerves. The results clearly demonstrate that cmOCT allows the generation of functional information that may be used for diagnostic applications.