The concentration of hydrogen peroxide in exhaled air depends on expiratory flow rate

Hydrogen peroxide (H2O2) is known to be detectable in exhaled air. The pres ent study aimed to determine whether the concentration of exhaled H2O2 depe nds on expiratory flow rate in order to make inferences on the site of its production within the lung. Breath condensate was collected in cooled Teflon tubes, at three different expiratory flow rates, in 15 healthy or mild asthmatic subjects. Tests were repeated 2-5 times to assess reproducibility. Mean+/-SEM concentrations of H2O2 at now rates of 140, 69 and 48 mL.s(-1) w ere 0.12+/-0.02, 0.19+/-0.02 and 0.32+/-0.03 muM, respectively. These value s differed significantly from each other (p<0.001). For comparison, average coefficients of variability within repeated measurements at each of the th ree flow rates were 68, 62 and 82%, respectively. These data demonstrate that the concentration of exhaled hydrogen peroxide depends on expiratory now rate. Since flow dependence is an indicator of pr oduction within the airways, this result suggests that, to a large extent, the exhaled hydrogen peroxide originates within the airways. However, even under strictly controlled conditions, a high degree of variability persists , which may limit the usefulness of exhaled hydrogen peroxide as a marker o f airway inflammation.