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1Pneumologia-Fisiopatologia Respiratoria and 2Riabilitazione Cardiorespiratoria, Azienda Ospedaliera S. Luigi, Orbassano, Torino, Italy; 3Fisiopatologia Respiratoria, Dipartimento di Medicina Interna, Università di Genova, Genova, Italy; 4Department of Physiology and Biophysics and Internal Medicine, Mayo Clinic and Mayo Foundation, Rochester, Minnesota; and 5Centro di Fisiopatologia Respiratoria e di Studio della Dispnea, Azienda Ospedaliera S. Croce e Carle, Cuneo, Italy
Submitted 4 April 2005 ; accepted in final form 21 February 2006
We examined the effects of chest wall strapping (CWS) on the response to inhaled methacholine (MCh) and the effects of deep inspiration (DI). Eight subjects were studied on 1 day with MCh inhaled without CWS (CTRL), 1 day with MCh inhaled during CWS (CWSon/on), and 1 day with MCh inhaled during temporary removal of CWS (CWSoff/on). On the CWSon/on day, MCh caused greater increases in pulmonary resistance, upstream resistance, dynamic elastance, residual volume, and greater decreases in maximal expiratory flow than on the CTRL day. On the CWSoff/on day, the changes in these parameters with MCh were not different from the CTRL day. Six of the subjects were again studied using the same protocol on CTRL and CWSon/on days, except that, on a third day, MCh was given after applying the CWS, but the measurements before and after the inhalation were made without CWS (CWSon/off). The latter sequence was associated with more severe airflow obstruction than during CTRL, but less than with CWSon/on. The bronchodilator effects of a DI were blunted when CWS was applied during measurements (CWSon/on and CWSoff/on) but not after it was removed (CWSon/off). We conclude that CWS is capable of increasing airway responsiveness only when it is applied during the inhalation of the constrictor agent. We speculate that breathing at low lung volumes induced by CWS enhances airway narrowing because the airway smooth muscle is adapted at a length at which the contractile apparatus is able to generate a force greater than normal.
bronchial challenge; mechanics of breathing; lung volumes; airway caliber; deep inhalation; airway smooth muscle
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