COUGH REFLEX THRESHOLD IN DIABETES-MELLITUS WITH AND WITHOUT AUTONOMIC NEUROPATHY

The cough reflex, a vagus-mediated respiratory protective reflex, was investigated in diabetics and healthy controls by establishing a cough reflex threshold to increasing concentrations of citric acid aerosol. Diabetics with autonomic neuropathy (n = 20), whether overtly symptom atic (n = 5) or evident only on certain non-invasive cardiovascular au tonomic function tests, were found to have significantly (p < 0.05 by chi(2) test) raised cough reflex threshold (range 1 to >100%, median v alue 50%) in contrast to either the non-neuropathic diabetics (n = 20) or normal controls (n = 20; range 1-10%, median value 2%). This diffe rence suggests vagal (parasympathetic) denervation of the respiratory tract, with possible serious consequences, hitherto little appreciated .