Airway distensibility in healthy and asthmatic subjects: effect of lung volume history.
Anatomic dead space (VD) is known to increase with end-inspiratory lung volume (EILV), and the gradient of the relationship has been proposed as an index of airway distensibility (DeltaVD). The aims of this study were to apply a rapid method for measuring DeltaVD and to determine whether it was affected by lung volume history. VD of 16 healthy and 16 mildly asthmatic subjects was measured at a number of known EILVs by using a tidal breathing, CO(2)-washout method. The effect of lung volume history was assessed by using three tidal breathing regimens: 1) three discrete EILVs (low/medium/high; LMH); 2) progressively decreasing EILVs from total lung capacity (TLC; TLC-RV); and 3) progressively increasing EILVs from residual volume (RV; RV-TLC). DeltaVD was lower in the asthmatic group for the LMH (25.3 +/- 2.24 vs. 21.2 +/- 1.66 ml/l, means +/- SE) and TLC-RV (24. 3 +/- 1.69 vs. 18.7 +/- 1.16 ml/l) regimens. There was a trend for a lower DeltaVD in the asthmatic group for the RV-TLC regimen (23.3 +/- 2.19 vs. 18.8 +/- 1.68 ml/l). There was no difference in DeltaVD between groups. In conclusion, mild asthmatic subjects have stiffer airways than normal subjects, and this is not obviously affected by lung volume history.
Johns
D P
DP
Department of Respiratory Medicine, The Alfred Hospital and Monash University Medical School, Prahran, Melbourne, Victoria 3181, Australia. d.johns@alfred.org.au
Wilson
J
J
Harding
R
R
Walters
E H
EH
D000328:Adult; D001249:Asthma / Q000503:physiopathology*; D016535:Bronchial Hyperreactivity / Q000503:physiopathology; D001985:Bronchial Provocation Tests; D016085:Bronchoconstrictor Agents / Q000494:pharmacology; D002245:Carbon Dioxide / Q000032:analysis; D005260:Female; D006801:Humans; D008170:Lung Compliance / Q000187:drug effects / Q000502:physiology*; D008176:Lung Volume Measurements; D008297:Male; D016210:Methacholine Chloride / Q000494:pharmacology; D012016:Reference Values; D012044:Regression Analysis; D015203:Reproducibility of Results; D015656:Respiratory Mechanics
D016085:Bronchoconstrictor Agents; D016210:Methacholine Chloride; D002245:Carbon Dioxide