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The single-breath N2-test and spirometry in healthy non-smoking males.

Healthy males (aged 30-70), who had never smoked, were studied. The 178 subjects were selected by systematic sampling from an urban population. Using the single-breath N2-washout test we measured the closing volume (CV) and the slope of the alveolar plateau (delta N2). A prediction equation for CV was produced by simple regression on age. delta N2 showed an accelerated increase with age above the age of 50. A curvilinear equation was established: delta N2 (%/1) = 0.85 + e0.0929 x A( yrs ) -6.302. Reference equations were also established for vital capacity (VC), forced expiratory volume in one second (FEV1) and FEV1 in per cent VC (FEV%) by means of linear multiple regression on age and height. The distribution of delta N2 was not homogenous throughout the age-range. As an upper limit of the reference range, we suggest 180% of the predicted value.