Methaemoglobinemia induced by nitric oxide in whole blood. Quantitative relationship

We studied in vitro the effects of nitric oxide (NO) in human and rat blood and in human erythrolysate. Using NO in the tonometric technique allows to predict through an experimental model the amount of methemoglobin formed. At known oxygen and carbon dioxide pressures, methaemoglobinemia is all the more important as NO concentration is great and tonometry duration is long. Moreover methaemoglobin concentration is greater in saturated (P02 congruent to 500 Torr) than in desaturated blood (P02 congruent to O Torr) while only slight changes occur for small P02 variations. Thus the study of the oxygen dissociation curve should be possible in presence of NO. Methaemoglobin is responsible for the drop in the oxygen combining capacity and thus impairs blood oxygen transport. Results are similar in human and in rat blood.