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The predictors of airway hyperresponsiveness differ between old and young asthmatics.

Chest. 2011 Mar 31 Hardaker KM, Downie SR, Kermode JA, Farah CS, Brown NJ, Berend N, King GG, Salome CM. 1 Woolcock Institute of Medical Research, Glebe, NSW, Australia.

BACKGROUND: Age-related increases in morbidity and mortality due to asthma may be due to changes in pathophysiology as asthmatics get older. There is limited knowledge about the effects of age on the predictors of airway hyperresponsiveness, a key feature of asthma. The aim of this study was to determine if the pathophysiological predictors of airway hyperresponsiveness, including inflammation, ventilation heterogeneity and airway closure, differed between young and old asthmatics. Methods 61 young (18-46 years) and 43 old (50-80 years) asthmatics had lung function, lung volumes, exhaled nitric oxide, ventilation heterogeneity, and airway responsiveness to methacholine measured. Airway response to methacholine was measured by the dose response slope, as the percent fall in FEV(1) per micromole of methacholine. Indices of ventilation heterogeneity were calculated for convection-dependent and diffusion-dependent airways.

RESULTS: In young asthmatics, the independent predictors of airway hyperresponsiveness were convection-dependent ventilation heterogeneity, exhaled nitric oxide and % predicted FEV(1)/FVC (model r(2)=0.51, p<0.0001). In old asthmatics, the independent predictors of airway responsiveness were % predicted residual volume, diffusion-dependent ventilation heterogeneity and % predicted FEV(1) (model r(2)=0.57, p<0.0001).

CONCLUSION: In old asthmatics, airway hyperresponsiveness is predicted by gas trapping and ventilation heterogeneity in peripheral, diffusion-dependant airways. In the young, it is predicted by ventilation heterogeneity in less peripheral conducting airways and by inflammation. These findings suggest that there are differences in the pathophysiological determinants of AHR between young and old asthmatics.

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