Exercise based assessment of cardiac autonomic function in type 1 versus type 2 diabetes mellitus

BACKGROUND: Cardiac autonomic neuropathy (CAN) is a complication of diabetes mellitus (DM) that is associated with increased mortality. Exercise-based assessment of autonomic function has identified diminished parasympathetic reactivation after exercise in type 2 DM. It is postulated herein, that this would be more prominent among those with type 1 DM. METHODS: Sixteen subjects with type 1 DM (age 32.9 ± 10.1 years), 18 subjects with type 2 DM (55.4 ± 8.0 years) and 30 controls (44.0 ± 11.6 years) underwent exercise-based assessment of autonomic function. Two 16-min submaximal bicycle tests were performed followed by 45 min of recovery. On the second test, atropine (0.04 mg/kg) was administered near end-exercise so that all of the recovery occurred under parasympathetic blockade. Plasma epinephrine and norepinephrine levels were measured at rest, during exercise, and during recovery. RESULTS: There were no differences in resting or end-exercise heart rates in the three groups. Parasympathetic effect on RR-intervals during recovery (p < 0.03) and heart rate recovery (p = 0.02) were blunted in type 2 DM. Type 1 DM had higher baseline epinephrine and norepinephrine levels (p < 0.03), and exhibited persistent sympathoexcitation during recovery. CONCLUSIONS: Despite a longer duration of DM in the study patients with type 1 versus type 2 DM, diminished parasympathetic reactivation was not noted in type 1 DM. Instead, elevation in resting plasma catecholamines was noted compared to type 2 DM and controls. The variable pathophysiology for exercise-induced autonomic abnormalities in type 1 versus type 2 DM may impact prognosis.