Localization of the bronchodilatory effects of isoproterenol and aminophylline in patients with bronchial asthma: an investigation using selective alveolobronchography.

The effect of isoproterenol (isoprenaline) and aminophylline on airway calibre in 18 adult patients with bronchial asthma was measured directly using selective alveolobronchography. Isoproterenol caused a significant dilation in the maximal calibre of the central airway from bifurcation numbers 1-5 (P < 0.05) and number 6 (P < 0.01). There was no change in bifurcation number 0 (trachea). Aminophylline caused a significant dilatation in bifurcation numbers 3 and 4 (P < 0.01), with no change in bifurcation numbers 0-2 and 5-6. In the minimal calibre of the central airway, both drugs displayed a significant dilatory effect only at bifurcation number 3 (P < 0.05). These results indicate that the central airway is the main site of the dilatory effects of these drugs. Although their precise mechanisms of action are not known, these results suggest that mechanisms of action of the two drugs are different. Isoproterenol acts on the whole region of the central airway, while the action of aminophylline tends to be limited to bifurcation numbers 3 and 4.