Impairment of the respiratory system in diabetic autonomic neuropathy.

Diabetic autonomic neuropathy (DAN) may affect up to 30% of the diabetic population. Sometimes DAN becomes clinically manifest causing specific symptoms and signs; more often, however, DAN is responsible for subtle alterations detectable only by functional tests, as in the case of the respiratory system. At first, abnormalities both in the bronchomotor tone and aspecific airway responsiveness to different stimuli were recognised in diabetic patients with DAN, indicating a defective control of mechanisms which regulate the bronchial calibre in these subjects. Subsequently, peculiar changes in breathing pattern and greater ventilatory requirements have been observed during incremental exercise in diabetics with DAN, suggesting an altered control of breathing in stressful conditions. Alterations in either peripheral or central chemosensitivity have been repeatedly shown in these patients, with marked differences related to the severity of DAN, concerning the neuro-muscular and ventilatory responsiveness to CO2. Following anecdotal reports, respiratory disturbances during sleep have been more carefully investigated in diabetic subjects and greater prevalence of sleep apnea, mainly in the obstructive form, has been found in the presence of DAN. The underlying mechanisms of sleep disordered breathing, however, are poorly understood in DAN and further studies are needed to elucidate them.