Microvascular adaptation - regulation, coordination and function

Microvascular networks have to adapt continuously in response to changes of the local environment in order to maintain adequate function. This adaptat ion involves reactions to hemodynamic and metabolic stimuli. The present st udy analyzes fundamental requirements for vascular adaptation by combining experimental observations in microvascular networks and mathematical simula tions. Angioarchitecture and flow distribution were analyzed in microvascul ar networks of the rat mesentery by intravital microscopy. In addition, blo od flow and oxygen distribution in these networks were simulated using a ma thematical model. The model was based on experimental information on blood rheology in microvessels. In addition, the diameter adaptation of vessel se gments (n = 300-1000) in the networks to different sets of stimuli was simu lated. The hemodynamic analysis shows that, in the experimentally observed network architecture, average wall shear stress declines consistently with intravascular pressure (from about 100 dyn/cm(2) for pressures of 70 mmHg t o about 10 dyn/cm(2) for pressures of 15 mmHg) indicating the importance of hemodynamic factors for vascular adaptation. However, to obtain stable ada ptation of microvascular networks, additional responses to the metabolic si tuation and information transfer from distal to proximal vessels were neede d. The metabolic stimuli maintain parallel flow pathways and adequate suppl y of distal tissue regions, while the hemodynamic factors optimize network structure and minimize energy expenditure.