An apparatus for measuring microvascular dysfunction in an organ or limb having a vessel and microvasculature connected to the vessel, the apparatus comprising: an infusion catheter (830, 930) comprising a plurality of expandable structures connected to one or more lumens of the catheter (830, 930) to remotely control expansion and contraction of the expandable structures and at least one infusion lumen for delivery of infusate to the catheter (830, 930) proximal the expandable structures; a pressure sensor (941, 942) coupled to the infusion catheter (830, 930) and configured to sense a pressure in the vessel; an infusion pump (820, 920) in communication with the infusion lumen of the infusion catheter (830, 930); a plurality of separate solutions (811, 812, 813, 909, 912, 913) in separate reservoirs in communication with the infusion pump, and a computerized controller (810, 910) configured to communicate with the pressure sensor (941, 942) and the infusion pump (820, 920) and to control operation of the infusion pump (820, 920) to perform controlled flow infusion of at least a first solution of the plurality of solutions (811, 812, 813, 909, 912, 913) to the infusion lumen of the catheter (830, 930) and a second solution of the plurality of solutions to the infusion lumen of the catheter (830, 930), characterized in that the flow infusion of the first solution is associated with assessment of microvascular function and the flow infusion of the second solution is associated with changes to microvascular function, and wherein the microvascular function is assessed using a dynamic microvascular resistance according to the formula R(t) = dP(t)/dQ(t) + R 0, where R 0 is the zero flow resistance, P(t) is the measured distal pressure and Q(t) is the time dependent pump flow. an infusion catheter (830, 930) comprising a plurality of expandable structures connected to one or more lumens of the catheter (830, 930) to remotely control expansion and contraction of the expandable structures and at least one infusion lumen for delivery of infusate to the catheter (830, 930) proximal the expandable structures; a pressure sensor (941, 942) coupled to the infusion catheter (830, 930) and configured to sense a pressure in the vessel; an infusion pump (820, 920) in communication with the infusion lumen of the infusion catheter (830, 930); a plurality of separate solutions (811, 812, 813, 909, 912, 913) in separate reservoirs in communication with the infusion pump, and a computerized controller (810, 910) configured to communicate with the pressure sensor (941, 942) and the infusion pump (820, 920) and to control operation of the infusion pump (820, 920) to perform controlled flow infusion of at least a first solution of the plurality of solutions (811, 812, 813, 909, 912, 913) to the infusion lumen of the catheter (830, 930) and a second solution of the plurality of solutions to the infusion lumen of the catheter (830, 930), characterized in that the flow infusion of the first solution is associated with assessment of microvascular function and the flow infusion of the second solution is associated with changes to microvascular function, and wherein the microvascular function is assessed using a dynamic microvascular resistance according to the formula R(t) = dP(t)/dQ(t) + R 0, where R 0 is the zero flow resistance, P(t) is the measured distal pressure and Q(t) is the time dependent pump flow.