Determinants of exhaled particles of a standardized breathing maneuver

Exhaled particles are produced by reopening of closed small airways and contain surfactant. However, the amount of exhaled particles varies by orders of magnitude between subjects. A standardized breathing pattern reduces the variation but it remains large and the reasons are unknown. The aim of the present study has been to assess to what extent sex, age, body size and spirometry results explain the inter-individual variation of exhaled particles of healthy subjects performing a standardized breathing maneuver. Methods: The PExA instrument was used to measure exhaled particles (PEx) in 126 healthy subjects of the European Respiratory Community survey (ERCHS-III). Subjects performed a standardized breathing maneuver involving expiration to residual volume, breath holding for three seconds prior to the measurement in order to maximize the amount of PEx. PEx number concentrations were expressed per exhaled liter. The distribution of PEx was skewed and were thus log transformed as InPEx. Multiple linear regression was used for futher analyses. Results: LnPEx was increased by age (4%/year) and decreased with 1% by weight in kg. Those with increased bronchial tone also had lower number of PEx (-5% per % ΔFEV1). At best 28 percent of the variation was explained. Conclusions: The inter-individual variation of exhaled particles among middle aged healthy subjects performing a standardized breathing maneuver is large and a minor part of the variation is explained by age, weight and spirometry variables. Number of exhaled particles increase with age, probably due to increasing airway closure.