Tissue and Capillary Force Changes During the Formation of Intra-Alveolar Edema

Abstract

The Starling forces, capillary pressure (P_c) plasma colloid osmotic pressure (Л_c), tissue colloid osmotic pressure (Л_t) and tissue fluid pressure (P_t) are related to the volume movement (J_V) across any capillary system by the relationship:

$$J_v = K_{FC} \left[ {\left( {P_c - P_t } \right) - \sigma _c \left( {\pi _c - \pi _t } \right)} \right]$$

where K_{F, C} is the filtration coefficient of the capillary bed (ml/min-mm Hg-100 gm) and σ is the Staverman reflection coefficient of the plasma proteins (σ of the protein is equal to 1 if the membrane is impermeable to the protein and is equal to 0 if the protein is as permeable as water in the membrane i.e. velocity of solute/velocity of water = 1). Obviously there is not just one σ but a σ for each of the various protein fractions in the body fluids (α₁, α_2. and β globulins, albumin and γ globulins); however, for practical purposes we can assume that σ =1 for all plasma proteins and calculate total ΔЛ by the use of the Landis and Pappenheimer equation (1,2).