Aspiration pneumonia is a common and serious complication, especially among elderly patients. By using randomized concentrations of ammonia gas as an irritant, the threshold of the protective airway reflex was determined in 103 subjects. The end-point was a brief stop in the inspiration as recorded on a metabolic spirometer. The median threshold was found to increase sixfold from the second to the eighth and ninth decades of life. This decrease in sensitivity explains, in part, why silent tracheal aspiration seems to occur oftener in older people. The protective airway reflex can be further depressed by injudicious use of depressant drugs in elderly patients. The effects of various drugs on the reflex can be determined readily by applying the method here described.
Henning Pontoppidan, Henry K. Beecher. Progressive Loss of Protective Reflexes in the Airway with the Advance of Age. JAMA. 1960;174(18):2209–2213. doi:10.1001/jama.1960.03030180029007
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