Spatial heterogeneity of cutaneous blood flow respiratory-related oscillations quantified via laser speckle contrast imaging

LSCI technique provides experimental data which can be considered in the context of spatial blood flow coherency. Analysis of vascular tone oscillations gives additional information to ensure a better understanding of the mechanisms affecting microvascular physiology. The oscillations with different frequencies are due to different physiological mechanisms. The reasons for the generation of peripheral blood flow oscillations in the 0.14–0.6 Hz frequency band are as follows: cardio-respiratory interactions, pressure variations in the venous part of the circulatory system, and the effect of the sympathetic nervous system on the vascular tone. Earlier, we described the spatial heterogeneity of around 0.3 Hz oscillations and this motivated us to continue the research to find the conditions for the occurrence of spatial phase synchronization. For this purpose, a number of physiological tests (controlled respiration, breath holder, and venous occlusion tests) which influence the blood flow oscillations of 0.14–0.6 Hz were considered, an appropriate measurement system and the required data processing algorithms were developed. At spontaneous respiration, the oscillations with frequencies around 0.3 Hz were stochastic, whereas all the performed tests induced an increase in spatial coherence. The protocols and methods proposed here can help to clarify whether the heterogeneity of respiratory-related blood flow oscillations exists on the skin surface.

Spectral analysis of blood flow oscillations to assess the plantar skin blood flow regulation in response to preconditioning local vibrations

BACKGROUND: Local vibration has been shown promise in improving skin blood flow and wound healing. However, the underlying mechanism of local vibration as a preconditioning intervention to alter plantar skin blood flow after walking is unclear. OBJECTIVE: The objective was to use wavelet analysis of skin blood flow oscillations to investigate the effect of preconditioning local vibration on plantar tissues after walking. METHODS: A double-blind, repeated measures design was tested in 10 healthy participants. The protocol included 10-min baseline, 10-min local vibrations (100Hz or sham), 10-min walking, and 10-min recovery periods. Skin blood flow was measured over the first metatarsal head of the right foot during the baseline and recovery periods. Wavelet amplitudes after walking were expressed as the ratio of the wavelet amplitude before walking. RESULTS: The results showed the significant difference in the metabolic (vibration 10.06 ± 1.97, sham 5.78 ± 1.53, p < 0.01) and neurogenic (vibration 7.45 ± 1.54, sham 4.78 ± 1.22, p < 0.01) controls. There were no significant differences in the myogenic, respiratory and cardiac controls between the preconditioning local vibration and sham conditions. CONCLUSIONS: Our results showed that preconditioning local vibration altered the normalization rates of plantar skin blood flow after walking by stimulating the metabolic and neurogenic controls.

Accidental hypothermia as a factor of microcirculatory disorders

Aim. To study the dynamics of indicators of microcirculation during a single episode of hypothermia of moderate degree in rats, both immediately after cessation of cooling, and in different periods of posthypothermia. Methods. The study was performed on 25 Wistar rats. The animals were subjected to a single immersion cooling in water at a temperature of 5 °C until reaching a rectal temperature of 27-30 °C. Analysis of the microvasculature was carried out immediately upon reaching a moderate degree of hypothermia, 2, 5, 10 and 14 days after the cooling. The microcirculation parameters were estimated using a laser analyzer of capillary circulation LAKK-02 (SMO «Lazma», Russia) at a wavelength of 0.63 μm. The main parameters of microcirculation were recorded, and the amplitude-frequency spectrum of blood flow oscillations was analyzed. Results. Immediately after reaching a moderate degree of hypothermia, vasospasm was recorded, which was confirmed by a decrease in the rate of perfusion and wave amplitudes of all frequency ranges. 2 days after stopping the cooling perfusion index returned to baseline, a decrease in amplitude of endothelial, vasomotor and respiratory waves was observed with an increase in pulse waves. On day 5, perfusion increased by 5 times was observed along with decreased amplitudes of the waves of all ranges. By day 10, the level of blood flow returned to its original values, and the wave amplitudes of all frequency ranges remained at the same low level. By day 14, a progressive decrease of the factors of bloodflow modulation was associated by the decrease of perfusion. Conclusion. Single cooling to a moderate degree of hypothermia leads to a progressive decrease of tissue perfusion and deep inhibition of active and passive factors of bloodflow modulation.

Acute Brain Injury Is Associated With Prolonged Suppression of Cerebral Blood Flow Oscillations

INTRODUCTION Low-frequency oscillations (LFOs, < 0.1 Hz) in cerebral blood flow (CBF) reflect changes in the coordinated activity of neuronal assemblies. Synchronized LFOs across multiple brain regions can be identified using magnetic resonance imaging to reveal functionally connected networks; however, how LFOs are altered by brain injury is largely unknown. METHODS We quantified changes in LFO magnitude over time in brain-injured patients where CBF was recorded continuously using invasive thermal diffusion flowmetry. Intracranial pressure (ICP), brain tissue oxygen (PbO2), and arterial blood pressure (ABP) were recorded concurrently in all patients. For each epoch of uninterrupted CBF data, the power spectral density within the 0.05 to 0.1 Hz frequency band was calculated. Periods of LFO suppression were defined as occurring when equal to 10% of the total power across all frequencies occurred in the 0.05 to 1 Hz frequency band. Average values of CBF, ICP, PbO2, and ABP were compared between suppressed and nonsuppressed epochs across all patients. RESULTS Twenty-five patients were included in this retrospective observational study. LFO suppression was associated with a lower average CBF (11.3 mL/100 g/min suppressed vs 31.6 mL/100 g/min unsuppressed, P < .0001) and lower average PbO2 (21.6 mm Hg suppressed vs 31.0 mm Hg unsuppressed, P < .0001). In a subset of patients, LFO suppression was associated with intracranial hypertension (ICP 25-60 mm Hg). Patients that regained consciousness and were discharged to acute rehab had a lower median fraction of time spent in the suppressed state (0.03 rehab vs 0.67 death/nursing home, P = .053). CONCLUSION Brain injury is associated with the suppression of low-frequency CBF fluctuations. LFO suppression is associated with periods of physiological distress and may provide a sensitive marker of disrupted brain function. The degree of LFO suppression may have a prognostic significance, and the re-emergence of LFOs after a period of suppression may provide a marker of return of consciousness after coma.