Effect of inspired volume on airway closure in relation to age.

Closing volume (CV) was measured in 64 healthy subjects aged 18--76 years, in supine position, with a bolus (helium) technique in two ways: following a maximal (CV100) and a submaximal (=50% VC; CV50) inspiration from residual volume. With increasing age CV50 increased less than CV100 according to the equation CV100(%VC)-CV50(%VC)=0.13Xage-0.6(r=0.46, P less than 0.001), e.g. at 70 years of age CV100=32(%VC) and CV50=24(%VC). Therefore, during normal breathing elderly subjects to not presumably close airways at as high a lung volume as predicted from conventional CV-measurements. A strong correlation between CV50 and CV100 was found, CV50(%VC)=0.55XCV100(%VC)+5.3(r=0.90; P less than 0.001), thus allowing a more accurate prediction of CV50 from CV100 than from age. Neither smoking habits nor body position affected the decrease of CV with reduced inspired volume.