Sympathetic neural traffic in older patients with type 2 diabetes mellitus

Abstract

Introduction: Mechanistic studies suggested that excess sympathetic activity promotes arterial hypertension while worsening insulin sensitivity. The finding raised interest in interventions targeting the sympathetic nervous system. Older patients with type 2 diabetes are at particularly high cardiovascular and metabolic risk. However, data on sympathetic activity in this population is scarce. Material and Methods: We recruited patients with type 2 diabetes mellitus for at least 2 years, an age of 50-80 years, an HbA1c of 6.5-10.0%, and a BMI of 25-40 kg/m2. They had to be treated with stable doses of metformin only. In the supine position, we recorded ECG, brachial blood pressure, and muscle sympathetic nerve activity (MSNA). We quantified MSNA as burst frequency, burst incidence, and burst area. Results: We included 37 patients (14 women, 63±1 years, 32.8±0.8 kg/m2; 23 men, 64±1 years, 30.3±0.7 kg/m2). Blood pressure was 127±4/74±3 mmHg in women and 126±3/77±2 mmHg in men (p=0.92/0.42). Heart rate was 68±3 bpm in women and 62±1 bpm in men (p=0.03). Overall, MSNA ranged between 15 and 72 bursts/min. MSNA was 39.5±3.5 bursts/min in women and 38.5±2.3 bpm in men (p=0.80). Similarly, MSNA burst incidence and burst area did not differ between women and men. In the pooled analysis, MSNA was not correlated with systolic blood pressure, diastolic blood pressure, body mass index, or HbA1c (r2 0.30 for all). Conclusions: In older patients with type 2 diabetes mellitus, MSNA appears to be not or only weakly related to gender, blood pressure, body mass index, or glycemic control. The findings suggest that sympathetic contributions to blood pressure and glucose metabolism are highly variable in this population, which may have implications for therapeutic interventions targeting the sympathetic nervous system.