Sensitivity of the cough reflex in young and elderly subjects

To compare the sensitivity of the cough reflex--which is said to be normal in elderly people--in elderly and young subjects.

20 elderly (14 female) subjects, mean (SEM) age 83 (1) years and 20 young (nine female) subjects, mean (SEM) age 27 (1) years, who were all non-smokers. None of the subjects was taking antitussive drugs and none suffered from clinically evident lung, cardiac or neurological disease. Five elderly subjects were unable to perform adequate spirometry and were excluded from analysis.

Each subject inhaled 10 ml of nebulized distilled water and isotonic saline (as placebo) for 30 s, 10 min apart in a randomized double-blind crossover fashion. The cough frequency induced with each treatment was recorded on a click counter.

Cough frequency on inhaling distilled water was significantly lower in the elderly group than in the younger group, with a difference of 9.53 (95% confidence intervals: 3.63, 15.4; P < 0.001). None of the subjects coughed when inhaling placebo solution, resulting in significant differences in cough frequencies between distilled water and placebo of 5.87 (2.82, 8.92; P < 0.05) for the elderly group and 15.4 (11.0, 19.8; P < 0.0005) for the younger group.

The sensitivity of the cough reflex appears to be significantly reduced in elderly subjects. This may increase the risk of aspiration and bronchopulmonary infection in old age, even in the absence of respiratory disease.