Diffusional and Metabolic Components of Nitrogen Elimination through the Lungs: Effect of Pressure

Abstract : The contribution of cutaneous diffusion of atmospheric nitrogen to pulmonary nitrogen elimination was determined by mass spectrometric analysis. In short-term experiments, subjects were enclosed in gas-tight bags containing helium, O2, N2 or air while breathing room air. Moreover, 24-hour studies of nitrogen elimination were carried out in a pressure chamber in which the ambient gas composition as well as the total pressure was varied. A linear relationship between ambient PN2 and nitrogen elimination through the lungs was established. At zero PN2 ambient elimination was present after 18 hours and amounted to 0.5 m1/mn. This is considered the metabolic component of gaseous nitrogen excretion. Although this amount appears very small, it can account for the frequency found deficit between nitrogen intake in food and nitrogen elimination via urine and faeces. Mass spectrometric analysis of ambient and expired air samples collected during three saturation-excursion diving experiments showed in all seven subjects cyclic variations in the ratio of expired/inspired nitrogen while the simultaneously measured respiratory quotient remained constant. Whether these delayed nitrogen excretions are due to release of nitrogen from pools in poorly perfused tissues or altered metabolic processes cannot be stated at this time.