Airway responses to deep inspiration in diabetic autonomic neuropathy

The role of vagal mechanisms in the reversal of pharmacologically-induced bronchoconstriction by deep inspiration is unclear. We examined the effect of lung inflation on methacholine-induced bronchoconstriction in six patients with severe diabetic autonomic neuropathy compared with five patients with diabetes mellitus and normal tests of autonomic function. The effect of deep inspiration on bronchomotor tone was expressed as the ratio of maximal flow rates at 70% of expiratory vital capacity (V30) calculated from complete (V30(c)) and partial (V30(p)) flow-volume curves (V30(c)/V30(p)). In patients with autonomic neuropathy the mean (range) of this ratio was 1.31 (1.19-1.47) and was not significantly different from the control patients with a mean ratio of 1.69 (1.28-2.13). These results suggest that the reversal of methacholine-induced bronchoconstriction by a deep inspiration is not mediated via vagal nerves.