A closed-circuit rebreather for the characterization of denitrogenation

The denitrogenation methods currently used to characterize the washout kinetics of body nitrogen require costly devices that are not easily transportable for measurements in real conditions. An original and simple system to measure the denitrogenation kinetics of the human body at rest and at ambient pressure is presented here.

The nitrogen content accumulated in the loop of a closed-circuit rebreather supplied by pure oxygen was determined using galvanic oxygen sensors and a small size data logger for pressure, temperature, and relative humidity measurements. The method was applied to three subjects through a preliminary validation phase. The collected data, after processing, were compared: 1) to the results found in previous papers for similar experiments using other methods; and 2) to the results of a physiological gas exchanges model.

Denitrogenation curves for 60-min and 120-min durations were obtained for the three subjects, with an interindividual variability being in agreement with their body fat percentage (560 +/- 140 ml for the subject with less body fat and 880 +/- 70 ml for the subject with more body fat) after 60 min. Both the experimental results found in the literature and the simulation results were compared to the present results.

From a preliminary analysis, the proposed denitrogenation procedure proved to be adequate compared to other methods. An investigation of the method demonstrated that the system accuracy can be improved. A validation phase using more subjects may support the use of this new technology.