Published ahead of print on December 1, 2005, doi:10.1164/rccm.200509-1455OC Am. J. Respir. Crit. Care Med., Volume 173, Number 5, March 2006, 506-511 A more recent version of this article appeared on March 1, 2006
Submitted on September 19, 2005 Acute Sustained Hypoxia Suppresses the Cough Reflex in Healthy SubjectsDanny J Eckert1*,1 Adelaide Institute for Sleep Health, Repatriation General Hospital, Daw Park, South Australia, Australia; School of Molecular and Biomedical Science, Discipline of Physiology, University of Adelaide, Adelaide, South Australia, Australia, 2 Adelaide Institute for Sleep Health, Repatriation General Hospital, Daw Park, South Australia, Australia, 3 Adelaide Institute for Sleep Health, Repatriation General Hospital, Daw Park, South Australia, Australia; Department of Medicine, Flinders University, Bedford Park, South Australia, Australia * To whom correspondence should be addressed. E-mail: danny.eckert{at}rgh.sa.gov.au.
Rationale: An intact cough reflex is important to protect the lung from injurious substances and to clear excess secretions. A blunted cough reflex may be harmful or even fatal in respiratory disease. Hypoxia is common in respiratory disorders and has been shown to have depressant effects on respiratory sensation and ventilation. We hypothesized that it might also suppress the cough reflex. Objectives: To determine if acute hypoxia increases cough threshold and cough tachyphylaxis to inhaled capsaicin. Methods: On two separate occasions, 16-healthy subjects inhaled a saline control followed by doubling doses of capsaicin aerosol (range 0.49- 500 µM) every minute for 15-sec during controlled ventilation (~190% baseline) with isocapnic hypoxia (SpO2~80%) or isocapnic normoxia, in random order. Upon reaching 5 or more coughs to one dose the next doubling dose of capsaicin was administered continuously for 60-sec to assess acute tachyphylaxis. Main Results: The capsaicin concentration required to elicit 5 coughs (C5) was significantly higher during isocapnic hypoxia compared to normoxia (37.3± 17.0 vs. 31.6 ± 17.0µM, p=0.01). During continuous capsaicin inhalation significantly more coughs were evoked in the first 10-sec compared to the last (1.3 ± 0.3 vs. 2.3 ± 0.3, p<0.01) indicating cough tachyphylaxis. However, the decrease was the same during hypoxia and normoxia (-1.3 ± 0.4 vs. -0.9 ± 0.6, p=0.54). Conclusions: Acute isocapnic hypoxia suppresses cough reflex sensitivity to inhaled capsaicin. This finding raises the possibility that the cough reflex may be impaired during acute exacerbations of hypoxic-respiratory disorders. Key words: tachyphylaxis, capsaicin, cough reflex
This article has been cited by other articles:
|
|
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
