IP: 91.200.81.25 On: Fri, 01 Feb 2019 07:21:22 Copyright: Aerospace Medical Association Delivered by Ingenta AEROSPACE MEDICINE AND HUMAN PERFORMANCE Vol. 87, No. 12 December 2016 1045 TECHNICAL NOTE N ormally, while breathing, the partial pressure of inhaled nitrogen (P I N 2 ) is the same as in the tissues, where it exists in a dissolved state. When the P I N 2 increases, as during diving, pulmonary N 2 uptake occurs and tissue PN 2 increases until a new steady state is reached. Te opposite hap- pens when P I N 2 decreases. If there is a fast and large enough reduction in ambient pressure, the N 2 dissolved in the tissues may form gas bubbles. Tis is generally accepted as the initiat- ing step in decompression sickness. Te rate of N 2 uptake or wash-out secondary to a given change in P I N 2 is afected by sev- eral factors such as temperature, physical exercise, and body position. 2,10 It has also been suggested that bubble formation per se afects inert gas elimination during decompression. 4,6 N 2 elimination has been measured previously, typically dur- ing normobaric conditions, using hyperoxic gas or alterna- tively using argon or helium enriched gas. 2,3,6 N 2 elimination has also been measured in hyperbaric conditions, 1,7 but to our knowledge there exists only a single report on direct measure- ment of N 2 absorption at pressure. 9 N 2 absorption has instead been investigated indirectly by assessing the elimination, afer diving for example. In addition, only a few reports exist regard- ing actual measurements of direct elimination of nitrogen dur- ing hypobaric conditions. 5 We developed a method, using a similar approach as Dick et al., 4 where N 2 volume in a closed rebreathing system is From the Department of Environmental Physiology, Swedish Aerospace Physiology Centre, School of Technology and Health, KTH Royal Institute of Technology, Stockholm, Sweden; and the Department of Mechanical Engineering, Blekinge Institute of Technology, Karlskrona, Sweden. Tis manuscript was received for review in May 2016. It was accepted for publication in August 2016. Address correspondence to: Patrik Sundblad, Department of Environmental Physiology, KTH, Berzelius v. 13, 171 77 Solna, Sweden; patsu@kth.se. Reprint & Copyright © by the Aerospace Medical Association, Alexandria, VA. DOI: 10.3357/AMHP.4680.2016 Measuring Uptake and Elimination of Nitrogen in Humans at Diferent Ambient Pressures Patrik Sundblad; Oskar Frånberg; Christoph Siebenmann; Mikael Gennser BACKGROUND: To measure nitrogen (N 2 ) 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 N 2 turnover in humans which can be used at diferent ambient pressures. METHODS: A modifed close-circuit electronic rebreather was used to assess N 2 turnover. Changes in N 2 volume within the rebreathing circuit, refecting N 2 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 N 2 volume curves was performed of-line using dedicated computer software. RESULTS: Four subjects participated in the proof-of-concept tests. At steady state, the drift in calculated N 2 volume in the rebreathing circuit over a 1-h duration was minimal. Three of the subjects participated in additional N 2 steady-state measurements where 1019 mL (BTPD) of N 2 was injected into the rebreathing circuit over 20 min and the measured volume increase was 1006 6 32 mL. Lastly, N 2 elimination was assessed during decompression to 0.5 atm and while breathing hyperoxic gas. N 2 uptake was measured during compression to 1.8 atm. The elimination and uptake curves were deemed to be realistic. DISCUSSION: A method for assessing N 2 turnover in humans has been developed and a frst evaluation has been performed. It is easy to work with operationally and can be used at diferent ambient pressures. More research is needed in order to further validate it as a method for assessing N 2 turnover in humans. KEYWORDS: decompression, nitrogen elimination, pressure, diving. Sundblad P, Frånberg O, Siebenmann C, Gennser M. Measuring uptake and elimination of nitrogen in humans at diferent ambient pressures. Aerosp Med Hum Perform. 2016; 87(12):1045–1050.