Cholinergic bronchomotor tone and airway caliber in insulin-dependent diabetes mellitus

It has been suggested that the autonomic bronchomotor tone may be altered in diabetes. In the present study, we assessed the cholinergic bronchomotor tone in 34 insulin-dependent diabetic patients and in a control group of 32 healthy subjects (group C). As an index of the intensity of cholinergic tone to the airways, we measured the increase in specific airway conductance (Gaw/VL) induced by aerosol administration of atropine sulfate. In all of the patients and normal individuals the autonomic cardiovascular activity was also evaluated by the tilting test and by the magnitude of the respiratory sinus arrhythmia (RSA). In 19 patients without symptoms of autonomic neuropathy (AN) (group D-1), the autonomic cardiovascular activity was comparable to that of group C. The other 15 patients presented with at least one symptom of AN and a depressed heart rate (HR) control when submitted to the tests of autonomic activity (group D-2). Before atropine administration, Gaw/VL was significantly higher (p less than 0.05) in group D-2 (2.48 +/- 0.12 s-1.kPa-1 [mean +/- SE]) than in group D-1 (2.11 +/- 0.10 s-1.kPa-1). Aerosol atropine caused a significant increase (p less than 0.001) in airway caliber in all three groups; however, the increase in Gaw/VL was significantly lower in group D-2 (0.26 +/- 0.05 s-1.kPa-1) when compared with group D-1 (0.63 +/- 0.09 s-1.kPa-1; p less than 0.01) and group C (0.67 +/- 0.06 s-1.kPa-1; p less than 0.001). A weak but significant (p less than 0.02) correlation was observed between the increases in Gaw/VL provoked by atropine and the magnitude of RSA. Our findings suggest that the reduction in parasympathetic bronchomotor tone may cause an increase in basal airway caliber in diabetic patients with AN, compared to patients without AN.