Unbound MEDLINE

Bronchoconstriction triggered by breathing hot humid air in patients with asthma: role of cholinergic reflex.

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.

Links

  • PMC Free PDF
  • Publisher Full Text
  • Authors

    Hayes D, Collins PB, Khosravi M, Lin RL, Lee LY

    Institution

    Department of Physiology, University of Kentucky Medical Center, 800 Rose Street, Lexington, KY 40536, USA.

    Source

    American journal of respiratory and critical care medicine 185:11 2012 Jun 1 pg 1190-6

    MeSH

    Administration, Inhalation
    Adult
    Airway Resistance
    Analysis of Variance
    Asthma
    Bronchoconstriction
    Cholinergic Antagonists
    Cholinergic Fibers
    Double-Blind Method
    Female
    Follow-Up Studies
    Forced Expiratory Volume
    Hot Temperature
    Humans
    Humidity
    Hyperventilation
    Ipratropium
    Male
    Middle Aged
    Reference Values
    Reflex
    Reflex, Abnormal
    Respiratory Function Tests
    Risk Assessment
    Treatment Outcome
    Young Adult

    Pub Type(s)

    Comparative Study
    Journal Article
    Randomized Controlled Trial
    Research Support, N.I.H., Extramural
    Research Support, Non-U.S. Gov't
    Research Support, U.S. Gov't, Non-P.H.S.

    Language

    eng

    PubMed ID

    22505744