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Pathological alterations of the microcirculatory system can be identified by measuring the temporal and spectral properties of laser Doppler flowmetry (LDF) signals acquired on the skin, and their changes following physiological stimulation. A wide range of stimulation protocols and measurement locations is observed in literature. Researchers often use non-invasive stimulation techniques, such as post-occlusive hyperaemia, cold tests, and local heating. As concerns the stimulation/recording sites, the forearm, fingers, and toes are typically selected to conduct microcirculation studies. However, recent clinical investigations showed that different anatomical sites present dissimilar blood flow patterns. Therefore, studies involving the comparison of LDF data, obtained from various anatomical locations, and thus subjected to the intrinsic heterogeneity of the microcirculation, may be methodologically inaccurate. At the moment, no consensus has been reached upon the optimal measurement location, the stimulation pattern, and the physiological parameters of interest. The aim of this study is to quantitatively characterize the heterogeneity of the peripheral perfusion at different anatomical locations: the index finger, the forearm, and the hallux. The skin microvascular system exhibits a complex vasodilatory response in the temporal domain, upon local heating. This physiological reactive hyperaemia comprises two effects: a fast transient response, correlated to neural activation, named axon reflex, followed by a slower hyperaemic plateau, mediated by the release of nitric oxide. In this work, we compare the vasodilatory reaction to heating at the different sites, based on a parametric representation of the perfusion signal. Moreover, skin blood flow is characterized by several components fluctuating at different time scales. Time-frequency decomposition of LDF signals allows to quantitatively evaluate the relative contribution of known physiological mechanisms to the regulation of the peripheral circulation. For this reason, we analyze the wavelet transform coefficients of LDF signals at baseline, to assess potential spatial heterogeneities of the perfusion power spectra among the aforementioned anatomical locations.

Objectives: To assess laser Doppler-recorded postocclusive reactive hyperemic responses in vibration-induced Raynaud's phenomenon and compare it with primary and secondary to sclerodermy Raynaud's phenomenon., Material and Methods: Thirty patients with vibration-induced Raynaud's phenomenon and 30 healthy controls and patients with primary and secondary to sclerodermy Raynaud's phenomenon were investigated. Fingerpulp skin blood flow was monitored by laser Doppler flowmetry during postocclusive reactive hyperemia test., Results: Lower initial perfusion values were established in all the patients with Raynaud's phenomenon compared to the healthy controls (p < 0.0001). The postocclusive reactive hyperemic peak was lower in all the Raynaud's phenomenon groups compared to the controls (p < 0.0001). The postocclusive and basal perfusions were lower in the secondary Raynaud's phenomenon groups compared to the control and the primary Raynaud's phenomenon groups (p < 0.0001). The velocities to postocclusive hyperemic peak were lower in all the Raynaud's phenomenon patients (p < 0.0001), so were in the vibration-induced (p < 0.002) and the sclerodermy Raynaud's phenomenon (p < 0.004) groups in relation to the primary Raynaud's phenomenon group. The perfusion values and the velocities were significantly influenced by the initial superficial skin temperatures and perfusions, while the velocities were dependent also on gender, and the hyperemic peak on age., Conclusions: Postocclusive reactive hyperemia is abnormal in all Raynaud's phenomenon patients. Laser Doppler-recorded reactive hyperemia test contributes to diagnosing Raynaud's phenomenon and has proved to be valuable for group analysis. The applied method is not sensitive enough to discriminate adequately the type of Raynaud's phenomenon among individual cases., (This work is available in Open Access model and licensed under a CC BY-NC 3.0 PL license.)

The study aimed to investigate the hemorheological parameters in patients with diabetes mellitus type 2 and to estimate their relationship with the cerebral and cutaneous blood flow and their responses to postural changes. The basic hemorheological constituents: hematocrit (Ht), fibrinogen (Fib), whole blood (WBV) and plasma viscosity (PV) were examined in 20 patients with diabetes mellitus type 2 and in 10 healthy age and sex matched controls. Blood flow velocity in the middle cerebral artery (MCA) was measured by transcranial Doppler monitoring at rest and during 5-min head-up tilt. Also laser Doppler-recorded tiptoe skin blood flow was investigated and venoarteriolar reflex perfusion responses to postural impact was monitored. Significant increase of Fib and WBV at shear rates of 0.0237 s(-1) to 128.5 s(-1) in the patients in comparison to controls was found. The postural challenge caused decrease of the cerebral blood flow velocity and increase of the resistance index (RI) in the diabetic patients. The initial mean skin perfusion values of the tiptoes and the venoarteriolar constriction response indices were significantly higher in the diabetes group. In the patients with diabetes mellitus type 2 the increased blood viscosity values were associated with impaired cerebrovascular and peripheral vascular responces.