[Effect of prolonged beta-adrenergic treatment on the ventilatory response to sympathomimetics]

Ventilatory adrenergic responsiveness induced by long-term beta-mimetic treatment over three years were analysed in a study carried out in two groups of asthmatics. In group I, 11 patients received theophylline and oral beta-2-agonists; in group II, 7 patients received the same drugs and corticosteroids. Pulmonary function tests were serially performed with a body plethysmograph (Jaeger). The effect of beta adrenergic stimulation with 400 micrograms fenoterol was measured using variations of flow-volume curves. The mean increase of FEV1 after fenoterol was: in group I, 0.680 +/- 0.200 1 before treatment and 0.500 +/- 0.340 1 after beta adrenergic therapy; in group II, it was 0.550 +/- 0.340 1 before treatment and 0.510 +/- 0.350 1 after treatment (difference not statistically significant). For each patient, FEV1 variations were expressed in percent of optimum improvement. In most cases, there was a significant correlation between the two parameters (0.38 less than r less than 0.59), but the slopes of the regression curves differed from one patient to another. Intra-individual variation coefficient of the improvement of FEV1 has been calculated and showed large variations of the adrenergic pulmonary responses: from 34% to 98% of the mean improvement. Four patients only exhibited a significant and definitive decrease of their adrenergic response, which could be due to tachyphylaxis. But a transient loss of responsiveness to adrenergic stimulation has been found in all patients. Those cases were related to viral infections or allergen inhalations.