Comparison of the effects of intravenously administered aminophylline and inhaled isoproterenol on normal airways.

Although beta-agonists and anticholinergics have been well documented to alter the resting tone in normal airways, the effects of aminophylline on normal airway function is controversial. We therefore studied the effects of intravenously administered placebo and aminophylline, inhaled isoproterenol, and intravenously administered aminophylline plus inhaled isoproterenol in 8 nonasthmatic subjects using full and partial flow-volume curves, plethysmography, and respiratory resistance as measured by forced oscillation. Isoproterenol, as has been demonstrated previously, caused improvement in FEV1 FEF50, and the flow of a partial flow-volume curve at 75% of the VC (PFEF75). Intravenously administered aminophylline at therapeutic concentrations (17.0 to 22.4 mg/L) resulted in improvement in FEV1, PFEF75, and the total respiratory resistance. Aminophylline and isoproterenol administered together produced additive effects. Thus, contrary to other studies, intravenously administered aminophylline produced a small but significant effect on normal basal airway tone that was less than that seen after an adrenergic agent but proportionally similar to the effects seen in asthmatic subjects.