Airway hyperresponsiveness with chest strapping: A matter of heterogeneity or reduced lung volume?

Chest wall strapping has been recently shown to be associated with an increase in airway responsiveness to methacholine. To investigate whether this is the result of the decreased lung volume or an increased heterogeneity due to chest wall distortion, ten healthy volunteers underwent a methacholine challenge at control conditions and after selective strapping of the rib cage, the abdomen or the whole chest wall resulting in similar decrements of functional residual capacity and total lung capacity but causing different distribution of the bronchoconstrictor. Methacholine during strapping reduced forced expiratory flow, dynamic compliance, and reactance at 5Hz and increased pulmonary resistance and respiratory resistance at 5Hz that were significantly greater than at control and associated with a blunted bronchodilator effect of the deep breath. However, no significant differences were observed between selective and total chest wall strapping, suggesting that the major mechanism for increasing airway responsiveness with chest wall strapping is the breathing at low lung volume rather than regional heterogeneities.