A system for the continuous generation of simulated human breath supplemented with trace gases

Abstract

A system was developed to simulate the relative humidity (RH) and temperature characteristics of human breath at a constant human volume flow rate. The system was also designed to allow supplementation of the artificial breath with known concentrations of a trace gas; in this case, ammonia. The system was assembled from several components including an air pump, respiratory humidifier, mass flow controllers and additional valves and sensors to monitor and verify the system variables. Flow rates were measured as maximum voluntary ventilation (MVV) and could be set to standards within human levels. The desired temperature (i.e. 32 to 37 °C) and relative humidity (i.e. 91 to 96%) ranges could be achieved over defined operational periods. Good agreement for the concentration of ammonia in the simulated breath matrix was obtained between the theoretically calculated concentration and with photoacoustic spectroscopy in the clinically relevant range of 18 to 2993 ppb (r2 = 0.9978). The system can be used for the calibration of sensors being developed for breath monitoring applications.