for the application in biochemical and physiological studies, we set out to provide accurate equations for gas solubility applicable to a wide range of temperatures. The foundation for quantification and modeling of gas transport depend on the principles that determine gas solubility in liquids and defines gas concentrations in the body. Henry’s law states that gas dissolves in a solvent in proportion to the partial pressure of gas at equilibrium. O2 and CO2 solubilities decrease with increasing temperature and are also diminished by the presence of other solutes, ions, polymers, or proteins (12). Solute concentration, not partial pressure, drives reactions and defines diffusion gradients, so it is quantitatively important to account for changes in gas solubility as temperature increases between the inflow and outflow of heat-producing organs to define reaction rates and binding equilibria. For O2 and CO2, the binding and unbinding reactions with Hb are further complicated by the Bohr and Haldane effects, where increasing Pco2 augments O2 release in tissue and vice versa in the lung (5, 7). Alveolar temperatures are lower than heart, brain, and liver temperatures, and, as arterial blood enters these highly metabolizing organs, the rising temperature depresses gas solubility as the blood warms (1).
General equations that hold over temperatures from 15°C in skin to 44°C are needed for estimating solubilities during bypass operations with hypothermia, during dialysis where hematocrit and protein concentrations oscillate, and during intense exercise with hemoconcentration of 10-15%. The need is for the solubility in the water of solutions containing both small solutes and proteins. Hb binding of O2 and proteins forming carbamino groups with CO2 merely remove the gases from solution by the chemical reaction and are not to be accounted for as solubility, which is unaffected.
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We took data from the literature, assessing it as best we could for accuracy of methods and reproducibility of observations, and especially for large numbers of observations over wide ranges of temperature. We found high-quality data for O2 and CO2 in saline and water. Data in plasma were not of equivalent quality; for example, protein concentrations were rarely measured. The plasma data were sampled from humans, and “normal human” concentrations were assumed to be all the same.
The output of this study is algebraic equations describing the solubilities of O2 and CO2 in pure water, saline, and acidified plasma across a wide range of temperatures. These will aid investigators using temperature-dependent reactions and exchange. In capillary beds, gases and heat exchange between blood and tissue, where the concentrations and temperatures are varied over micrometer distances. For the mathematical modeling of gas transport, it is essential to account for the changes in solubilities and partial pressures continuously. With changing metabolism and consequent osmotic transients, one needs also to account for the effects of changing blood density, as well as temperature, in defining the solubility. Reactions using or producing O2 and CO2 must be accounted for separately but simultaneously.
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