1. Forced expiratory flow rates and specific airways conductance were measured before and after the inhalation of the atropine-like drug ipratropium bromide in 11 diabetic patients with autonomic neuropathy and a control group of 11 diabetic patients without autonomic neuropathy. Respiratory muscle function was assessed by recording maximal inspiratory and expiratory mouth pressures.
2. There was no difference between the two groups of diabetic patients in airway calibre before ipratropium bromide or in maximal mouth pressures.
3. Bronchodilatation after ipratropium bromide was greater in the control group than in the autonomic neuropathy group of patients.
4. It is concluded that, despite the lack of clinical evidence of respiratory involvement, patients with diabetic autonomic neuropathy have reduced airway vagal tone.