Heart Rate Variability Relates To Metabolic Insulin Sensitivity And Vascular Function In Adults With Prediabetes

Low heart rate variability (HRV) is an index of elevated sympathetic nervous system activity and has been associated with reduced insulin sensitivity, vascular dysfunction, and elevated cardiovascular disease (CVD) risk among people with obesity. However, it is less clear if HRV differs among individuals with prediabetes defined by either impaired fasting glucose (IFG) or IFG plus impaired glucose tolerance (IFG + IGT). PURPOSE: To determine if HRV differs between IFG and IFG + IGT and relates to insulin sensitivity and vascular function. METHODS: Adults with prediabetes (ADA criteria) were characterized as having either IFG (n = 17, 13F; 35.4 ± 1.0 kg/m2 ) or IFG + IGT (n = 14, 11F; 37.4 ± 1.5 kg/m2) via a 120 min 75 g oral glucose tolerance test. Resting supine ECG was monitored for 5 min to calculate HRV indices: mean RR, standard deviation of HR (STDHR), and the root mean square of NN interval differences (RMSSD). A 120 min euglycemic clamp (40 mU/m2/min, 90 mg/dl) was used to determine metabolic insulin sensitivity (glucose infusion rate (GIR)). Microvascular flow velocity (MFV) was used to assess capillary flow rates (microbubble infusion), while pulse wave analysis (applanation tonometry) depicted arterial function by augmentation index (AIx75) and pressure (AP), forward (Pf) and backward (Pb) pressures, and reflection magnitude (RM) at 0 and 120 min of the clamp. Body composition (DXA) and aerobic fitness (VO2max) were also assessed. RESULTS: There were no group differences in age (P = 0.43), body fat (P = 0.94), VO2max (P = 0.39), GIR (P = 0.32), RMSSD (P = 0.45), mean RR (P = 0.78), or STDHR (P = 0.17). Overall, however, RMSSD associated with insulin-mediated RM (ρ = -0.48, P = 0.02) and AP (ρ = -0.42, P = 0.04) as well as GIR (ρ = 0.42, P = 0.02). Further, mean RR associated with fasting MFV (ρ = 0.45, P = 0.02) and 120 min Pf (ρ = -0.55, P < 0.01). CONCLUSIONS: People with IFG + IGT had similar HRV to those with IFG. Overall, indices of HRV associated with higher metabolic insulin sensitivity and favorable vascular function. Together, these findings suggest autonomic nervous system dysfunction may relate to increased CVD risk through, in part, alterations in macro and microvascular function as well as metabolic insulin sensitivity. NIH RO1-HL130296 and NSF Award 2125872