Les variations de Na⁺, Ca⁺⁺, K⁺ et [H⁺] du sang chez l'homme

Summary

Interindividual variability of plasma sodium, calcium and potassium is fairly high. Their reliability is low and intraindividual variability is so important that we cannot reasonably estimate, by the results of the first analysis, the results of the second one, even if the interval between taking blood samples does not exceed two days. The constancy of blood pH, usually quoted in order to illustrate the fixity of the internal environment, is a mathematical artefact, as the variability is practically suppressed by the logarithm introduced in the pH formula. If instead of pH we take the hydrogen ions concentration, we find in venous and arterial blood a relative interindividual variation which cannot be neglected. Like some previously published data, these findings show that the traditional idea of the ‘practically constant’ internal environment is misleading.