Subject index inhalation

In initial studies in which substance P was administered to subjects by intravenous infusion, no effect on airway caliber could be demonstrated. It is possible that potent cardiovascular side effects resulted in homeostatic reflexes with secondary effects on the airways that masked the effects of substance P (Fuller et al., 1987). However, when changes in the partial flow volume curve, a highly sensitive index of airway caliber, were used as the index of airway obstruction, inhaled NkA - and, to a lesser extent, inhaled substance P - caused airway obstruction in healthy people (Joos et al., 1987). NkA is approximately 10-100 times more potent as a bronchocon-strictor in asthmatic than in non-asthmatic subjects (Cheung et al., 1992, 1993) this ratio of potency is similar to that observed for other agonists. 

There have been a number of reports that surfactants and emusifying agents affect the spray characteristics particularly the size of droplets formed and the distribution of droplet sizes. A particularly important droplet index is the proportion of droplets with a diameter less than 100 urn since such droplets represent the upper limit of sizes subject to respiratory inhalation. When the proportion of such droplets is high hazards arise because breathing in spray mist causes intoxication. Furthermore, sprays with these characteristics are prone to drift and action on non-target areas is more difficult to control. 

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