Nitrogen dead space in heavy smokers aged 44-58 years.

Functional and alveolar dead spaces for nitrogen (VDF and VDalv) were calculated in a population of 20 male and 20 female heavy smokers and compared to data from static and forced spirometry (functional residual capacity [FRC], residual volume [RV], lung clearance index [LCI] and volume of trapped gas [VTG]) obtained with the same multiple-breath nitrogen wash-out as the dead spaces, and to variables considered sensitive to small airways disease measured with a single-breath nitrogen elimination (closing volume in per cent of vital capacity [CV%], closing capacity in per cent of total lung capacity [CC%] and slope index [SI]). Both nitrogen dead spaces increased with tidal volume in smokers as well as in healthy non-smokers. The majority of smokers were outside the predicted mean +2 SD for VTG (75%), CC and VDalv (70%) and SI (65%). The following variables were less sensitive for disclosing abnormality: CV (55%), RV (53%), LCI (38%) and forced expired volume in the first second (FEV1, 33%). If high sensitivity is considered preferable in epidemiological studies, the nitrogen dead spaces are equally as sensitive as the better of earlier described tests, and significantly superior to LCI and FEV1. Being tests that measure alveolar distribution of inhaled gas, they are probably sensitive to small airways disease.