maxwell–fricke equation maxwell–fricke equation the maxwell–fricke equation relates the resistivity of blood to hematocrit. this relationship has been shown to hold for humans, and a variety on non-human warm-blooded species, including canines. equation the maxwell–fricke equation is written as: ρ 1 ρ − 1 ρ 1 ρ + 2 = φ ρ 1 ρ 2 − 1 ρ 1 ρ 2 + 2 -1}+2}}=\varphi -1}+2}}} where ρ is the resistivity of blood, ρ1 is the resistivity of plasma, ρ2 is the resistivity of blood cells and φ is the hematocrit.