18 Phase Coherence of Finger Skin Blood Flow …
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activity oscillations [15]. A tight relation between breathing and sympathetic nerve
activity is known. In particular, the sympathetic activity increases during inhalation and becomes maximal at the last stage of inhalation and at the beginning of
exhalation [7, 13, 23]. The cutaneous blood flow is regulated with vasoconstriction induced by a sympathetic nervous system. Moreover, the peripheral blood flow
depends on the sympathetic activity because the arteriovenular anastomoses located
in the acral parts have high sympathetic innervation. So the respiratory activity influences the peripheral blood flow indirectly, whereas the sympathetic activity induces
vasoconstriction independently from the mechanical manifestation of the respiratory
cycle [16]. We suggest that the described mechanisms are involved in the formation of respiratory-related oscillations in peripheral blood flow registered by LDF
technique. The prevalence of the mechanism regulating blood flow is caused by
the impact of an arterio-venous component on the total signal and by the regional
differences in vascular sympathetic innervation. The palmar finger skin has a large
number of arterio-venuous anastomoses, the tone of which is not affected by baroreceptors and is regulated exclusively by sympathetic innervation [10, 11]. Therefore, the respiratory-related skin blood flow oscillations are mainly influenced by
respiratory-modulated sympathetic vasoconstriction. An addition, one of the possible
mechanisms for synchronization of blood flow oscillations might rest upon the reaction of the muscular layer of the vascular wall on the pressure change - myogenic
response. It is known that a decrease of arterial blood pressure results in a transient artery dilatation, while its increase leads to a constriction due to the reaction
from the vascular muscle layer, the so-called Bayliss effect [4]. Thus, perhaps the
pressure wave is well propagated to the periphery, as myogenic is defined as a reaction to a pressure wave. Not only may the myogenic response be involved in the
synchronization of cardiovascular oscillations, but also respiratory sinus arrhythmia
(RSA). RSA is heart rate variability in synchrony with respiration, associated with an
increase in heart rate during inspiration and a decrease during expiration [2, 20]. RSA
is a physiologic phenomenon reflecting respiratory-circulatory interactions universally observed among vertebrates. We suggest that these two mechanisms can also
influence phase interactions in microvasculature. But this assumption needs further
investigations.
It should be mentioned that only young females participated in the study. Apparently, the results may be different for other participants, for instance, for women
of another age or for men. However, studying gender- and age-related features of
phase coherence of skin blood flow oscillations is beyond the scope of this study and
requires additional research.
18.5 Conclusion
In the study we present the results of investigation of phase interactions between blood
flow oscillations of left and right forefinger-pad skin under breathing controlled on
both rate and depth. It was obtained that controlled breathing leads to the significant
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activity oscillations [15]. A tight relation between breathing and sympathetic nerve
activity is known. In particular, the sympathetic activity increases during inhalation and becomes maximal at the last stage of inhalation and at the beginning of
exhalation [7, 13, 23]. The cutaneous blood flow is regulated with vasoconstriction induced by a sympathetic nervous system. Moreover, the peripheral blood flow
depends on the sympathetic activity because the arteriovenular anastomoses located
in the acral parts have high sympathetic innervation. So the respiratory activity influences the peripheral blood flow indirectly, whereas the sympathetic activity induces
vasoconstriction independently from the mechanical manifestation of the respiratory
cycle [16]. We suggest that the described mechanisms are involved in the formation of respiratory-related oscillations in peripheral blood flow registered by LDF
technique. The prevalence of the mechanism regulating blood flow is caused by
the impact of an arterio-venous component on the total signal and by the regional
differences in vascular sympathetic innervation. The palmar finger skin has a large
number of arterio-venuous anastomoses, the tone of which is not affected by baroreceptors and is regulated exclusively by sympathetic innervation [10, 11]. Therefore, the respiratory-related skin blood flow oscillations are mainly influenced by
respiratory-modulated sympathetic vasoconstriction. An addition, one of the possible
mechanisms for synchronization of blood flow oscillations might rest upon the reaction of the muscular layer of the vascular wall on the pressure change - myogenic
response. It is known that a decrease of arterial blood pressure results in a transient artery dilatation, while its increase leads to a constriction due to the reaction
from the vascular muscle layer, the so-called Bayliss effect [4]. Thus, perhaps the
pressure wave is well propagated to the periphery, as myogenic is defined as a reaction to a pressure wave. Not only may the myogenic response be involved in the
synchronization of cardiovascular oscillations, but also respiratory sinus arrhythmia
(RSA). RSA is heart rate variability in synchrony with respiration, associated with an
increase in heart rate during inspiration and a decrease during expiration [2, 20]. RSA
is a physiologic phenomenon reflecting respiratory-circulatory interactions universally observed among vertebrates. We suggest that these two mechanisms can also
influence phase interactions in microvasculature. But this assumption needs further
investigations.
It should be mentioned that only young females participated in the study. Apparently, the results may be different for other participants, for instance, for women
of another age or for men. However, studying gender- and age-related features of
phase coherence of skin blood flow oscillations is beyond the scope of this study and
requires additional research.
18.5 Conclusion
In the study we present the results of investigation of phase interactions between blood
flow oscillations of left and right forefinger-pad skin under breathing controlled on
both rate and depth. It was obtained that controlled breathing leads to the significant