Model of structural and functional adaptation of small conductance vesselsto arterial hypotension

Vascular networks adapt structurally in response to local pressure and flow and functionally in response to the changing needs of tissue. Whereas most research has either focused on adaptation of the macrocirculation, which p rimarily transports blood, or the microcirculation, which primarily control s flow, the present work addresses adaptation of the small conductance vess els in between, which both conduct blood and resist flow. A simple hemodyna mic model is introduced consisting of three parts: 1) bifurcating arterial and venous trees, 2) an empirical description of the microvasculature, and 3) a target shear stress depending on pressure. This simple model has the m inimum requirements to explain qualitatively the observed structure in norm otensive conditions. It illustrates that flow regulation in the microvascul ature makes adaptation in the larger conductance vessels stable. Furthermor e, it suggests that structural changes in response to hypotension can accou nt for the observed decrease in the lower limit of autoregulation in chroni cally hypotensive vasculature. Independent adaptation to local conditions t hus yields a coordinated set of structural changes that ultimately adapts s upply to demand.