Figure 11-15 Hydraulic model analogy of three-compartment pharmacokinetic model. The height, h_i (t), represents the water level in each compartment. Each bucket is characterized by a cylindrical area, CA_i , and the pipes connecting the buckets to each other or to the outside world are characterized by a conductance, G_i . Water enters bucket 1 at the rate r(t) and leaks irreversibly through G₁ . (From Hughes MA, Glass PS, Jacobs JR: Context-sensitive half-time in multicompartment pharmacokinetic models for intravenous anesthetic drugs. Anesthesiology 76:334–341, 1992.)