[The effect of ageing on airway responsiveness]

In order to evaluate the significance of airway responsiveness in the elderly: 1. Airway responsiveness in the healthy elderly was evaluated and compared with that of the healthy young adults. Methacholine dose response curve was constructed by measuring total respiratory resistance using the modified partial airway occlusion method which provides a simple, convenient, and non-invasive assessment of the resistance of the total respiratory system. Although the responders were fewer and the average threshold values were higher in the elderly, there was no significant differences in the methacholine dose response curve. 2. In vivo and in vitro methacholine dose response relationship was measured in the old guinea pigs (20 to 25 months old) and was compared with that of the young adult guinea pigs. Although no significant differences in the threshold values was observed, the in vivo airway response to the methacholine dose of 1 mg/ml was significantly lower in the old guinea pigs than in the young. The old guinea pig showed small but significant right side shift in the in vitro methacholine dose response relationship. 3. The intra-tracheal instillation of hydrochloric acid to the guinea pig was used as an animal model of aspiration pneumonia. The airway responsiveness was evaluated before and after the instillation. The acid instillation caused the acute and transient bronchoconstriction and the airway responsiveness was markedly increased one hour after the instillation. We conclude that the airway responsiveness may be unchanged or somewhat decreased in the elderly and that the increased airway responsiveness may play a role in the phathologic state such as an aspiration pneumonia.