Measuring Uptake and Elimination of Nitrogen in Humans at Different Ambient Pressures

To measure nitrogen (N2) wash-out and uptake requires elaborate set-ups, especially when doing the measurements at increased or decreased ambient pressure. Here we present a transportable device for quantifying N2 turnover in humans which can be used at different ambient pressures.

A modified close-circuit electronic rebreather was used to assess N2 turnover. Changes in N2 volume within the rebreathing circuit, reflecting N2 uptake or washout, were derived from the continuously monitored total system volume and the calculated volumes of oxygen and water vapor. The calculation of continuous N2 volume curves was performed off-line using dedicated computer software.

Four subjects participated in the proof-of-concept tests. At steady state, the drift in calculated N2 volume in the rebreathing circuit over a 1-h duration was minimal. Three of the subjects participated in additional N2 steady-state measurements where 1019 mL (BTPD) of N2 was injected into the rebreathing circuit over 20 min and the measured volume increase was 1006 ± 32 mL. Lastly, N2 elimination was assessed during decompression to 0.5 atm and while breathing hyperoxic gas. N2 uptake was measured during compression to 1.8 atm. The elimination and uptake curves were deemed to be realistic.

A method for assessing N2 turnover in humans has been developed and a first evaluation has been performed. It is easy to work with operationally and can be used at different ambient pressures. More research is needed in order to further validate it as a method for assessing N2 turnover in humans.Sundblad P, Frånberg O, Siebenmann C, Gennser M. Measuring uptake and elimination of nitrogen in humans at different ambient pressures. Aerosp Med Hum Perform. 2016; 87(12):1045-1050.