Effect of orthostasis on the regulation of skin blood flow in upper and lower extremities in human.

OBJECTIVE: The research is aimed to investigate interactions between cardiovascular signals and to assess contributions of central and local mechanisms to skin blood flow regulation in upper and lower extremities at rest and under orthostasis. METHODS: Heart rate variability, respiration, forearm, and foot skin blood flow were assessed at rest and during postural test in 25 healthy volunteers. Spectral analysis was performed. Phase synchronization degree of analyzed signals was determined by group phase wavelet coherence function. RESULTS: Skin blood flow was lower on foot at rest and during postural test than on forearm. High-frequency component of heart rate variability was higher at ~0.3 Hz during postural test versus rest. Blood flow oscillation amplitudes on the foot were lower in frequency range including respiratory interval at rest than on forearm. Postural exposure increased amplitude of foot blood flow oscillations in respiratory interval and decreased amplitudes in cardiac interval versus rest. Orthostasis increased group wavelet phase coherence between foot blood flow and heart rate variability or respiration, as well as between forearm and foot blood flow at 0.3 Hz corresponding to respiration. CONCLUSIONS: The contribution of central mechanisms associated with respiration to blood flow regulation increased in lower extremities during orthostasis.

Oscillations of Skin Microvascular Blood Flow in Patients with Asthma.

OBJECTIVE: This research is aimed at studying the features of skin blood flow oscillations in patients with severe persistent atopic BA during a period of fine control over symptoms. METHODS: The study of microcirculation was carried out by LDF at rest and in response to a transient ischemia in 20 patients. The time-amplitude adaptive wavelet analysis of the blood flow oscillations was conducted to elucidate the peculiarities of microcirculatory regulation system functioning. RESULTS: No significant changes were revealed for SBP and the oscillation amplitudes in the cardiac (0.6-2 Hz) and respiratory (0.145-0.6 Hz) intervals, both at rest and in response to transient ischemia, in patients compared to the control group. A consistent twofold decrease in the oscillation amplitudes was found in the neurogenic (0.021-0.052 Hz) interval at rest, as well as in the myogenic (0.052-0.145 Hz) and NO-dependent endothelial (0.0095-0.021 Hz) intervals both at rest and during the postocclusive reactive hyperemia in patients with lung obstruction (FEV1 < 80%) in comparison with a control group. CONCLUSIONS: The amplitudes of skin blood flow oscillations in the myogenic, neurogenic and NO-dependent endothelial intervals in patients with obstruction are different from those in patients without obstruction.

To Break or to Brake Neuronal Network Accelerated by Ammonium Ions?

PURPOSE: The aim of present study was to investigate the effects of ammonium ions on in vitro neuronal network activity and to search alternative methods of acute ammonia neurotoxicity prevention. METHODS: Rat hippocampal neuronal and astrocytes co-cultures in vitro, fluorescent microscopy and perforated patch clamp were used to monitor the changes in intracellular Ca2+- and membrane potential produced by ammonium ions and various modulators in the cells implicated in neural networks. RESULTS: Low concentrations of NH4Cl (0.1-4 mM) produce short temporal effects on network activity. Application of 5-8 mM NH4Cl: invariably transforms diverse network firing regimen to identical burst patterns, characterized by substantial neuronal membrane depolarization at plateau phase of potential and high-amplitude Ca2+-oscillations; raises frequency and average for period of oscillations Ca2+-level in all cells implicated in network; results in the appearance of group of «run out¼ cells with high intracellular Ca2+ and steadily diminished amplitudes of oscillations; increases astrocyte Ca2+-signalling, characterized by the appearance of groups of cells with increased intracellular Ca2+-level and/or chaotic Ca2+-oscillations. Accelerated network activity may be suppressed by the blockade of NMDA or AMPA/kainate-receptors or by overactivation of AMPA/kainite-receptors. Ammonia still activate neuronal firing in the presence of GABA(A) receptors antagonist bicuculline, indicating that «disinhibition phenomenon¼ is not implicated in the mechanisms of networks acceleration. Network activity may also be slowed down by glycine, agonists of metabotropic inhibitory receptors, betaine, L-carnitine, L-arginine, etc. CONCLUSIONS: Obtained results demonstrate that ammonium ions accelerate neuronal networks firing, implicating ionotropic glutamate receptors, having preserved the activities of group of inhibitory ionotropic and metabotropic receptors. This may mean, that ammonia neurotoxicity might be prevented by the activation of various inhibitory receptors (i.e. by the reinforcement of negative feedback control), instead of application of various enzyme inhibitors and receptor antagonists (breaking of neural, metabolic and signaling systems).

Wavelet phase coherence analysis of the skin blood flow oscillations in human.

The wavelet phase coherence of oscillations in the peripheral blood flow of contralateral skin sites was studied in 20 healthy subjects. Skin perfusion was registered simultaneously on similar regions of the outer sides of the right and left forearms by the laser Doppler flowmetry technique. To estimate the reliability of the obtained wavelet phase coherence values we applied the comparative method using amplitude-adjusted Fourier transform surrogates. High median values (0.63 and 0.59) of the wavelet phase coherence were obtained for the frequency intervals of respiratory (0.145-0.6Hz) and cardiac (0.6-2Hz) rhythms in 18 and 20 participants, respectively. In all the 20 participants we detected high and reliable values (Ме=0.72) of the wavelet phase coherence for skin blood flow oscillations in the myogenic interval (0.052-0.145Hz). Additionally, we demonstrated high wavelet phase coherence in the neurogenic (0.021-0.052Hz) and endothelial (0.0095-0.021Hz) intervals in 8 and 7 participants, respectively. The corresponding medians of the reliable wavelet phase coherence values for these intervals were 0.74 and 0.82. The obtained results suggest that the microvascular blood flow possesses not only the local mechanisms of generating low-frequency blood flow oscillations, but also a central mechanism, which is likely to synchronize low-frequency oscillations throughout the whole cardiovascular system.

Age-related changes of skin blood flow during postocclusive reactive hyperemia in human.

BACKGROUND/PURPOSE: The objective was to study age-related alterations in the time-amplitude characteristics of the oscillatory components of peripheral blood flow in healthy humans during postocclusive reactive hyperemia. METHODS: Forearm blood skin perfusion was studied by the method of laser Doppler flowmetry in 120 healthy volunteers, who were divided into two age groups: young (19-30 years old; n = 82) and middle-age (30-60 years old; n = 38). The forearm occlusion approach was used to reveal the reaction of the microvascular bed to transient ischemia. To estimate the age-related changes of separate oscillatory components of LDF signals during postocclusive reactive hyperemia, we applied adaptive time-amplitude wavelet analysis. RESULTS: A statistically significant increase in the skin blood perfusion after occlusion removal was revealed: 4-fold in the 1st and 3.5-fold in the 2nd group respectively. Both the amplitude of blood flow oscillations at rest and the postocclusive growth of the amplitude showed an age-related decline in the frequency intervals associated with the myogenic (0.052-0.145 Hz), sympathetic (0.021-0.052 Hz) and endothelial (0.0095-0.021 Hz) activity. CONCLUSION: The time-amplitude characteristics of the oscillatory components of peripheral blood flow depend on age, with the dependence becoming more evident after a transient ischemia.

Analysis of heart rate variability and skin blood flow oscillations under deep controlled breathing.

The effect of deep breathing controlled in both rate (0.25, 0.16, 0.1, 0.07, 0.05 and 0.03 Hz) and amplitude on the heart rate variability (HRV) and respiration-dependent oscillations of forearm/finger skin blood flow (SBF) has been studied in 29 young healthy volunteers. The influence of sympathovagal balance on the respiratory sinus arrhythmia (RSA) amplitude and respiratory SBF oscillations has been studied. The subjects with predominant parasympathetic tonus had statistically significant higher RSA amplitudes in the breathing rate region of 0.03-0.07 Hz than the subjects with predominant sympathetic tonus. In the finger-cushion zone, having a well-developed sympathetic vascular innervations, the amplitudes of respiratory SBF oscillations at breathing rates 0.05 and 0.07 Hz were higher in the group of subjects with predominant parasympathetic tonus. In the forearm skin, where the density of sympathetic innervations is low comparatively to that in the finger skin, no statistically significant differences in the amplitude of respiratory SBF oscillations were found concerning the two groups of subjects.

Time-amplitude analysis of skin blood flow oscillations during the post-occlusive reactive hyperemia in human.

The perfusion of forearm skin with blood was studied by the method of laser Doppler flowmetry (LDF) in 94 healthy volunteers. We studied the reaction of the microvascular bed to the transient ischemia, which was initiated by the forearm occlusion. After occlusion, we registered, on average, a 4-fold increase of skin blood perfusion as compared to the level of this parameter at rest. In the study, we also analyzed changes of the oscillatory components of LDF signals during post-occlusive reactive hyperemia; these components were revealed with the adaptive time-amplitude wavelet analysis. It was found that the time needed for oscillations to reach their maximal amplitude is different for each of the frequency intervals examined. After occlusion, a statistically significant rise of the amplitude of blood flow oscillations was revealed-for the frequency intervals corresponding to the cardiac (0.6-2 Hz), respiratory (0.145-0.6 Hz), myogenic (0.052-0.145 Hz), sympathetic (0.021-0.052 Hz), and endothelial (0.0095-0.021 Hz) activity (a more than 11-, 8-, 6-, 3-, and 6-fold increase, respectively, as compared to the state of rest). The method applied here for the analysis of oscillatory components of LDF signals can, therefore, be used to study the dynamics of oscillations of peripheral blood flow under various functional tests.

A method of adaptive wavelet filtering of the peripheral blood flow oscillations under stationary and non-stationary conditions.

The paper describes an original method for analysis of the peripheral blood flow oscillations measured with the laser Doppler flowmetry (LDF) technique. The method is based on the continuous wavelet transform and adaptive wavelet theory and applies an adaptive wavelet filtering to the LDF data. The method developed allows one to examine the dynamics of amplitude oscillations in a wide frequency range (from 0.007 to 2 Hz) and to process both stationary and non-stationary short (6 min) signals. The capabilities of the method have been demonstrated by analyzing LDF signals registered in the state of rest and upon humeral occlusion. The paper shows the main advantage of the method proposed, which is the significant reduction of 'border effects', as compared to the traditional wavelet analysis. It was found that the low-frequency amplitudes obtained by adaptive wavelets are significantly higher than those obtained by non-adaptive ones. The method suggested would be useful for the analysis of low-frequency components of the short-living transitional processes under the conditions of functional tests. The method of adaptive wavelet filtering can be used to process stationary and non-stationary biomedical signals (cardiograms, encephalograms, myograms, etc), as well as signals studied in the other fields of science and engineering.

DNA damage in frog erythrocytes after in vitro exposure to a high peak-power pulsed electromagnetic field.

Till the present time, the genotoxic effects of high peak-power pulsed electromagnetic fields (HPPP EMF) on cultured cells have not been studied. We investigated possible genotoxic effects of HPPP EMF (8.8 GHz, 180 ns pulse width, peak power 65 kW, repetition rate 50 Hz) on erythrocytes of the frog Xenopus laevis. We used the alkaline comet assay, which is a highly sensitive method to assess DNA single-strand breaks and alkali-labile lesions. Blood samples were exposed to HPPP EMF for 40 min in rectangular wave guide. The specific absorption rate (SAR) calculated from temperature kinetics was about 1.6 kW/kg (peak SAR was about 300 MW/kg). The temperature rise in the blood samples at steady state was 3.5 +/- 0.1 degrees C. The data show that the increase in DNA damage after exposure of erythrocytes to HPPP EMF was induced by the rise in temperature in the exposed cell suspension. This was confirmed in experiments in which cells were incubated for 40 min under the corresponding temperature conditions. The results allow us to conclude that HPPP EMF-exposure at the given modality did not cause any a-thermal genotoxic effect on frog erythrocytes in vitro.