Acid-base disorders are currently analyzed and treated using a bicarbonate-centered approach, derived from blood studies prior to the advent of digital computers, which could solve computer models capable of quantifying the complex physicochemical nature governing distribution of water and ions between fluid compartments. An alternative is the Stewart approach, which can predict pH of a simple mixture of ions and electrically charged proteins, hence the role of extravascular fluids has been largely ignored. The present study uses a new, comprehensive computer model of four major fluid compartments, based on a recent blood model, which included ion binding to proteins, electroneutrality constraints and other essential physicochemical laws. The present model predicts quantitative, respiratory, acid-base buffering behavior in the whole body, as well as determining roles of each compartment and their species, particularly, compartmental, electrically-charged proteins, largely responsible for buffering. The model tested an early theory that H+ was conserved in the body fluids, hence, when changing PCO2 states, intracellular buffering could be predicted by net changes in bicarbonate and protein electrical charge in the remaining fluids. Even though H+ is not model conserved, the theory held in simulated respiratory disorders. Model results also agreed with a second part of the theory, that ion movements between cells and interstitial fluid were linked with H+ buffering, but by electroneutrality constraints, not necessarily by some membrane-related mechanisms and that strong-ion difference (SID), an amalgamation of ionic electrical charges, was approximately conserved when going between equilibrium states, caused by PCO2 changes, in the body-fluid system.
Keywords: acid-base; electroneutrality constraint; mathematical model; respiratory buffering; whole body.