Pressure-diameter relationship under passive and active vessel conditions. (A–D) The model predicted vessel diameter, D, normalized by the vessel diameter under zero pressure, D₀, in the passive state (solid line) and under full myogenic state (dashed line), and the diameter reduction under full metabolic activation (dotted line), as functions of the trans-vascular pressure $ΔP¯$⁠, for (A) small arteriole of order 5, (B) intermediate arteriole (I.A.) of order 6, (C) large arteriole (L.A.) of order 6, and (D) small artery of order 7. Corresponding data are the symbols (o, □, and ∆ respectively) from in vitro studies of isolated vessels (Liao and Kuo, 1997).