This is equal to the mean venous pressure in the limb. The closer Pv is to Pi the closer to the threshold for edema. Pi is related to changes in tissue pressure and oncotic pressure. The slope of the slow increase in volume of the limb once rapid venous filling is complete provides an estimate of filtered flow and thus vascular permeability. The linear relation between filtered flow and pressure at each pressure increment defines the hydraulic permeability.
Permeability depends on oncotic pressure, and on pre and post capillary resistances.