Various autonomic function tests were performed before and after intravenous administration of atropine to determine whether the parasympathetic nerves were damaged earlier than the cardiac sympathetic nerves in the reflex control of heart rate in diabetics.
Fifteen diabetic patients without symptoms of autonomic neuropathy (DM group, 49±9 years) and 9 healthy subjects (N group, 44±10 years) were studied. The autonomic function tests included the baroreceptor sensitivity (BS), Valsalva ratio (VR), beat-to-beat variation in heart rate with deep respiration (DR), and heart rate response to sustained handgrip (HG) and 60° passive tilt (Tilt).
BS and DR were abolished by atropine in both groups. However, HG and Tilt were partially decreased by atropine (48% and 71% respectively). Before atropine, BS, DR and VR were each significantly lower in the DM group than the N group (p<0.01, p<0.001, and p<0.01 respectively), but HG and Tilt were not significantly different between both groups. After atropine, each test showed no significant difference between the groups.
These results suggest that the parasympathetic nerves are affected earlier than the cardiac sympathetic nerves.