Hierarchical characterization of complex networks

While the majority of approaches to the characterization of complex networks has relied on measurements considering only the immediate neighborhood of each network node, valuable information about the network topological properties can be obtained by considering further neighborhoods. The current work discusses on how the concepts of hierarchical node degree and hierarchical clustering coefficient (introduced in cond-mat/0408076), complemented by new hierarchical measurements, can be used in order to obtain a powerful set of topological features of complex networks. The interpretation of such measurements is discussed, including an analytical study of the hierarchical node degree for random networks, and the potential of the suggested measurements for the characterization of complex networks is illustrated with respect to simulations of random, scale-free and regular network models as well as real data (airports, proteins and word associations). The enhanced characterization of the connectivity provided by the set of hierarchical measurements also allows the use of agglomerative clustering methods in order to obtain taxonomies of relationships between nodes in a network, a possibility which is also illustrated in the current article.Comment: 19 pages, 23 figure

Coronary microvascular dysfunction in cardiovascular disease:Lessons from large animal models

The coronary microvasculature is responsible for maintaining local matching of myocardial blood flow to myocardial demand of oxygen and nutrients. Long term adjustment of myocardial blood flow involves structural changes in microvascular density and diameter while fine-tuning of flow is achieved via adaptations in vascular smooth muscle tone in the coronary microvasculature.In the past several decades, considerable research efforts have been directed at understanding structural and functional microvascular adaptations involved in matching myocardial oxygen supply and demand and how these mechanisms are affected by various diseases. In this review we will discuss our current understanding of the mechanisms underlying the regulation of coronary microvascular tone under healthy physiological conditions, and the role of microvascular dysfunction in obstructive and non-obstructive coronary artery disease, as studied in large animal (particularly swine) models and confirmed in human studies. Future studies should be directed at further unraveling the mechanisms of coronary microvascular dysfunction in different disease entities in order to, and ultimately directed at improving microvascular function as a therapeutic target in patients with ischemic heart disease