This study was designed to evaluate the involvement of airways innervation during diabetic autonomic neuropathy. Bronchial response to methacholine was assessed by inhalation of serially doubling doses in 22 insulin-dependent diabetes mellitus (IDDM) patients and 11 nondiabetic control subjects selected for their nonsmoking habits. Cardiovascular autonomic control was studied by four standardized tests, i.e., blood pressure and heart-rate variations during orthostatism, heart-rate variation during Valsalva maneuver, and deep breathing. Magnitude and time-course of response to methacholine were similar in nondiabetic subjects and IDDM patients without any abnormal result on cardiovascular tests. Conversely, bronchial response to methacholine was markedly reduced in IDDM patients with one or more abnormal results by cardiovascular assessment of autonomic control. In the IDDM patients, bronchial response to methacholine was significantly correlated to indexes of cardiovascular autonomic control. These results suggest that, during diabetic neuropathy, innervation of the airways likewise involves cardiac autonomic control and leads to impairment of defense reflexes of the airways.

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