Effect of aging on the concentrations of nitrous oxide in exhaled air

Trace gases in exhaled air have been used as a simple means of assessing metabolic reactions. The investigations of trace gases derived from bacteria in human exhalation are usually hydrogen (H2) or methane (CH4). On the other hand, nitrous oxide (N2O) is also derived from microorganisms, especially denitrifying bacteria. Although many kinds of denitrifying bacteria have been isolated on and in the human body, there has been few concerning N2O. We studied 222 healthy people from the age of 5 to 85 years. The analysis of N2O in exhaled air was carried out by a infrared-photoacoustic (IR-PAS) analyzer. It was found that N2O ranged from 0 to 1670 ppbv in exhaled air and that 59% (131) of the subjects were producers of N2O. A highly significant relationship was observed between age and concentrations of N2O (r = 0.40, P < 0.01). The rate of production in young children and in the aged was significantly higher than that in adults aged 20-39 years (P < 0.01), and less than 30% were producers during puberty. The change of normal microflora on and in human body with aging may have caused the significant relationship between age and emissions of N2O.