Informational dynamics of vasomotion in microvascular networks: a review

Abstract

Vasomotion refers to spontaneous oscillation of small vessels observed in many microvascular beds. It is an intrinsic phenomenon unrelated to cardiac rhythm or neural and hormonal regulation. Vasomotion is found to be particularly prominent under conditions of metabolic stress. In spite of a significant existent literature on vasomotion, its physiological and pathophysiological roles are not clear. It is thought that modulation of vasomotion by vasoactive substances released by metabolizing tissue plays a role in ensuring optimal delivery of nutrients to the tissue. Vasomotion rhythms exhibit a great variety of temporal patterns from regular oscillations to chaos. The nature of vasomotion rhythm is believed to be significant to its function, with chaotic vasomotion offering several physiological advantages over regular, periodic vasomotion. In this article, we emphasize that vasomotion is best understood as a network phenomenon. When there is a local metabolic demand in tissue, an ideal vascular response should extend beyond local microvasculature, with coordinated changes over multiple vascular segments. Mechanisms of information transfer over a vessel network have been discussed in the literature. The microvascular system may be regarded as a network of dynamic elements, interacting, either over the vascular anatomical network via gap junctions, or physiologically by exchange of vasoactive substances. Drawing analogies with spatiotemporal patterns in neuronal networks of central nervous system, we ask if properties like synchronization/desynchronization of vasomotors have special significance to microcirculation. Thus the contemporary literature throws up a novel view of microcirculation as a network that exhibits complex, spatiotemporal and informational dynamics.

Physiological Mechanisms Mediating the Coupling between Heart Period and Arterial Pressure in Response to Postural Changes in Humans

“…These results suggest that the control of limb vascular resistance exerted by the cardiopulmonary and arterial baroreflexes is modulated by local mechanisms induced by gravitational effects (Kitano et al, 2005). Local vascular factors in skeletal muscles may also impact on SAP-LFSD, because spontaneous arteriolar vasomotion occurs in the LF range (Bertuglia et al, 1996) and is affected by perfusion pressure (Meyer et al, 1988) and tissue metabolism (Pradhan and Chakravarthy, 2011), both of which may change in the leg skeletal muscles in the upright position.…”

Laser speckle contrast imaging reveals large-scale synchronization of cortical autoregulation dynamics influenced by nitric oxide

“…Both mechanisms control the diameter of the afferent arteriole to change preglomerular vascular resistance, and both contribute to gain of autoregulation (18,24,51). Although autoregulation is mostly considered in the context of each individual nephron and its afferent arteriole responding to changes in blood pressure (BP) (16), this view is being superseded by the increasing recognition that the microcirculation in many beds operates as a set of distributed networks (4,26,32,33). In such a network, all vessel segments contribute to determining flow in any one vessel; restated, this says that regulation of flow requires coordination of resistance changes along multiple segments in any given pathway (33).…”

An association between vasomotion and oxygen extraction

“…However, the complexity and the transient nature of vasomotion has constrained our ability to observe this phenomenon and has therefore limited our understanding (1). Although a recent review concludes that little is known about the consequences of such oscillations, particularly in microcirculatory function (38), there is some evidence indicating a possible role of vasomotion in tissue oxygenation (15,35,46,47,60). Theoretical modeling of vasomotion has also suggested that these oscillations might ensure adequate oxygen delivery to all tissues (24,60), with the largest effect seen for low frequencies Ͻ0.05 Hz related specifically to endothelial and sympathetic activity (15).…”

“…Vasomotion has also been demonstrated indirectly in vivo by the techniques of laser Doppler fluximetry (LDF), optical reflectance spectroscopy (ORS), near infrared spectroscopy, cell velocity measurements, and capillary pressure measurements (18,26,45,51,59). Although vasomotion is strictly a local phenomenon, the regulation of contractile activity of vascular smooth muscle cells is dependent on the complex interplay between vasodilator and vasoconstrictor stimuli from circulating hormones, neurotransmitters, endothelial-derived factors, and blood pressure (38). However, the complexity and the transient nature of vasomotion has constrained our ability to observe this phenomenon and has therefore limited our understanding (1).…”