A mathematical hydrodynamic model of human cardiovascular bed has been developed. The model includes a 4- chamber heart, two circles of blood circulation and a multilevel microvasculature. Using model developed we studied the influence of low-intensity noise on blood flow oscillations in microvascular bed. In the study low-intensity noise effects on heart wall tone of left ventricle. Unmodulated noise and noise modulated by a sine with frequencies of 0.02, 0.0625 and 0.1 Hz were used. Unmodulated noise induced the forming of low-frequency oscillations of microvascular blood flow with a peak at the frequency of 0.1 Hz. Modulated noise induced low-frequency oscillations of blood flow with pronounced peaks at the modulation frequencies. The obtained results indicate a detecting property of simulated vascular bed that allows one to define modulating signal. This behavior is a characteristic of the system consisting of nonlinear and filtering components.
Phase interactions between cardiovascular and respiratory systems were analyzed at rest in volunteers. 22 healthy normotensive non-smoking subjects aged from 21 to 45 years participated in the study. The following physiological signals were recorded simultaneously: respiratory rate, heart rate variability (HRV), forearm and foot skin blood flow, tissue blood volume from hand and foot finger pads. The degree of synchronization between phases of analyzed signals was estimated with the value of wavelet phase coherence function. It was found high phase synchronization between respiration and tissue blood volume oscillations of both fingers and low synchronization between respiration and skin blood flow oscillations of both skin sites under study. It was also obtained high phase synchronization between HRV and tissue blood volume oscillations of both fingers as well as low synchronization between HRV and skin blood flow oscillations of both skin sites at the respiration frequency (~ 0.3 Hz). There are similarities of phase interactions of both analyzed signals (blood flow and blood volume) with HRV in the low frequency range from 0.0095 to 0.1 Hz. These results were independent of extremities under study. We assume the results obtained can be used for development of new diagnostic approaches for assessment of state of peripheral vessels in pathologies.
Phase synchronization between breath rate, heart rate variability, blood flow and blood volume oscillations were studied from healthy volunteers at rest. The degree of synchronization between the phases of the analyzed signals was estimated from the value of the wavelet phase coherence. High phase synchronization between blood perfusion and blood volume oscillations in a wide frequency range from 0.0095 to 0.1 Hz and at the frequency of heart rate (~ 1 Hz) was obtained. Significant phase synchronization were demonstrated between heart rate variability both skin blood flow oscillations and blood volume ones at the frequency of endothelial (~ 0.01 Hz) and myogenic (~ 0.1 Hz) activities. It was revealed high phase synchronization at the respiratory frequency (~ 0.3 Hz) for blood volume oscillations and low synchronization for blood flow ones. Also there are differences of phase synchronization of blood volume and blood flow oscillations with respiratory rate at the breath frequency. It was obtained high phase synchronization at this frequency for blood volume oscillations and low synchronization for oscillations of skin microvasculature. We assume that the results obtained can form the basis of new diagnostic criteria for assessing the state of the cardiovascular system in pathologies.
In the framework of our previous hypothesis about the participation of structural and hydrodynamic properties of the vascular bed in the formation of the 0.1-Hz component of blood flow oscillations in the human cardiovascular system and on the basis of the reduced hydrodynamic model, the role of additive stochastic perturbations of the operation of the single-chamber pump that simulates the heart was investigated. It was shown that aperiodic noise modulation of the rigidity of the walls of the pump or its valves generates low-frequency oscillations of pressure of arterial vascular bed with the spectral components at a frequency close to 0.1 Hz.
Phase synchronization between blood flow oscillations of left and right forearm skin sites, heart rate variability (HRV) and breath rate were studied from healthy volunteers at rest. The degree of synchronization between the phases of the analyzed signals was estimated from the value of the wavelet phase coherence. High medians of values of phase wavelet coherence function were obtained for the endothelial, neurogenic, myogenic and cardiac intervals. Significant phase synchronization were demonstrated between HRV and skin blood flow oscillations in both left and right forearms in a wide frequency range from 0.04 to 0.4 Hz. Six participants exhibited low phase synchronization (< 0.5) between the breath rate and HRV, while nine participants had high phase synchronization (> 0.5). This distribution was not affected by the sex or sympathovagal status of volunteers. Participants with low phase synchronization between breath rate and HRV featured low phase synchronization (< 0.5) between breath rate and blood flow oscillations in both forearms. Contrariwise, in subjects with high phase synchronization between respiratory rhythm and HRV both low and high phase synchronization between breath rate and blood flow oscillations in both forearms was observed. The results obtained allow us to suggest that the organism possesses a mechanism mediating the synchronization of blood flow oscillations in the skin microvasculature with all other periodical processes across the cardiovascular system, in particular, with HRV and breath rate over a wide frequency range.
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