Microvascular exchange. Kinetic analysis of plasma disappearance curves.

The present paper presents a survey of the kinetic "black box" analysis of plasma disappearance curves obtained after intravascular bolus injection of indicator molecules. Determinations of distribution volumes, capillary permeability, and clearance are based on calculations of mean transit times and mean sojourn times for the system constituents from the entire plasma disappearance curve. The widely used compartmental analysis is criticized, and it is emphasized that more or less arbitrarily chosen "half-life" times are not expressions of meaningful physiological and pharmacological processes.