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

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