Impaired urge-to-cough in elderly patients with aspiration pneumonia

Background. The down-regulation of the cough reflex in patients with aspiration pneumonia can involve both cortical facilitatory pathways for cough and medullary reflex pathways. In order to study the possible involvement of the supramedullary system in the down-regulation of cough reflex, we evaluated the urge-to-cough in patients with aspiration pneumonia. Methods. Cough reflex sensitivity and the urge-to-cough to inhaled citric acid were evaluated in patients with at least a history of aspiration pneumonia and age-matched healthy elderly people. The cough reflex sensitivities were defined as the lowest concentration of citric acid that elicited two or more coughs (C₂) and five or more coughs (C₅). The urge-to-cough scores at the concentration of C₂and C₅, and at the concentration of two times dilution of C₂(C₂/2) and C₅(C ₅/2) were estimated for each subject. Results. Both C₂and C₅in the control subjects were significantly greater than those for patients with aspiration pneumonia. There were no significant differences in the urge-to-cough at C₂and C₅between control subjects and patients with aspiration pneumonia. However, the urge-to-cough scores at both C₂/2 and C₅/2 in patients with aspiration pneumonia were significantly lower than those in control subjects. The number of coughs at C₅/2 was significantly greater in the control subjects than those in the patients with aspiration pneumonia whereas the number of coughs at C ₂/2 did not show a significant difference between the control subjects and the patients with aspiration pneumonia. Conclusion. The study suggests the involvement of supramedullary dysfunction in the etiology of aspiration pneumonia in the elderly. Therefore, restoration of the cough motivation system could be a new strategy to prevent aspiration pneumonia in the elderly.