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      Bronchoconstriction Triggered by Breathing Hot Humid Air in Patients with Asthma : Role of Cholinergic Reflex

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          Abstract

          Rationale: Hyperventilation of hot humid air induces transient bronchoconstriction in patients with asthma; the underlying mechanism is not known. Recent studies showed that an increase in temperature activates vagal bronchopulmonary C-fiber sensory nerves, which upon activation can elicit reflex bronchoconstriction.

          Objectives: This study was designed to test the hypothesis that the bronchoconstriction induced by increasing airway temperature in patients with asthma is mediated through cholinergic reflex resulting from activation of these airway sensory nerves.

          Methods: Specific airway resistance (SR aw) and pulmonary function were measured to determine the airway responses to isocapnic hyperventilation of humidified air at hot (49°C; HA) and room temperature (20–22°C; RA) for 4 minutes in six patients with mild asthma and six healthy subjects. A double-blind design was used to compare the effects between pretreatments with ipratropium bromide and placebo aerosols on the airway responses to HA challenge in these patients.

          Measurements and Main Results: SR aw increased by 112% immediately after hyperventilation of HA and by only 38% after RA in patients with asthma. Breathing HA, but not RA, triggered coughs in these patients. In contrast, hyperventilation of HA did not cause cough and increased SR aw by only 22% in healthy subjects; there was no difference between their SR aw responses to HA and RA challenges. More importantly, pretreatment with ipratropium completely prevented the HA-induced bronchoconstriction in patients with asthma.

          Conclusions: Bronchoconstriction induced by increasing airway temperature in patients with asthma is mediated through the cholinergic reflex pathway. The concomitant increase in cough response further indicates an involvement of airway sensory nerves, presumably the thermosensitive C-fiber afferents.

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          Author and article information

          Journal
          Am J Respir Crit Care Med
          Am. J. Respir. Crit. Care Med
          ajrccm
          ajrccm
          American Journal of Respiratory and Critical Care Medicine
          American Thoracic Society
          1073-449X
          1535-4970
          1 June 2012
          1 June 2012
          1 June 2012
          : 185
          : 11
          : 1190-1196
          Affiliations
          [1 ]Department of Pediatrics
          [2 ]Department of Internal Medicine
          [3 ]Department of Surgery
          [4 ]Pulmonary Function Laboratory, and
          [5 ]Department of Physiology, University of Kentucky Medical Center, Lexington, Kentucky
          Author notes
          Correspondence and requests for reprints should be addressed to Lu-Yuan Lee, Ph.D., Department of Physiology, University of Kentucky Medical Center, 800 Rose Street, Lexington, KY 40536. E-mail: lylee@ 123456uky.edu
          [*]

          Current address: Departments of Pediatrics and Internal Medicine, Ohio State University, Columbus, Ohio.

          Article
          PMC3373066 PMC3373066 3373066 201201-0088OC
          10.1164/rccm.201201-0088OC
          3373066
          22505744
          bb9197e4-486f-4cd9-a419-2a3382fb85bf
          Copyright © 2012 by the American Thoracic Society
          History
          : 17 January 2012
          : 24 March 2012
          Categories
          Articles
          A. Asthma and Allergy

          TRPV1,ipratropium,bronchoconstriction,cough,asthma
          TRPV1, ipratropium, bronchoconstriction, cough, asthma

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