Preferential impairment of parasympathetic autonomic function in type 2 diabetes

Objective: Cardiovascular autonomic neuropathy is a known complication in type 2 diabetes (T2D). However, the extent of sympathetic dysfunction and its relation to blood pressure (BP) dysregulation is insufficiently studied. We therefore assessed the cardiovascular sympathetic function using a standardized autonomic test-battery. Research design and methods: Forty T2D patients (mean age and duration of diabetes +/- SD, 65.5 +/- 7.3 and 9.5 +/- 4.2 years) and 40 age-and gender-matched controls were examined through autonomic testing, assessing cardiovascular responses to deep breathing, Valsalva maneuver and tilt-table testing. Additionally, 24-hour oscillometric BP and self-reported autonomic symptoms on COMPASS-31 questionnaire was recorded. Results: Patients with T2D had reduced parasympathetic activity with reduced deep breathing inspiratory: expiratory-ratio (median [IQR] T2D 1.11 [1.08-1.18] vs. controls 1.18 [1.11-1.25] (p = 0.01)), and reduced heart rate variability (p < 0.05). We found no differences in cardiovascular sympathetic function measured through BP responses during the Valsalva maneuver (p > 0.05). 24-hour-BP detected reduced night-time systolic BP drop in T2D (9.8 % +/- 8.8 vs. controls 15.8 % +/- 7.7 (p < 0.01)) with more patients having reverse dipping. Patients with T2D reported more symptoms of orthostatic intolerance on the COMPASS-31 (p = 0.04). Conclusions: Patients with T2D showed reduced parasympathetic activity but preserved short-term cardiovascular sympathetic function, compared to controls, indicating autonomic dysfunction with predominantly para-sympathetic impairment. Despite this, T2D patients reported more symptoms of orthostatic intolerance in COMPASS-31 and had reduced nocturnal BP dipping, indicating that these are not a consequence of cardio-vascular sympathetic dysfunction.