Purpose: Sympathovagal imbalance is a common underlying disorder in hypertension and diabetes. This study characterized autonomic nervous system function, indicated by heart rate deceleration capacity (DC) and deceleration runs (DRs), in patients with type 2 diabetes mellitus (T2DM), with or without concomitant essential hypertension.
Subjects and methods: We recruited 50 healthy subjects, 50 patients with T2DM, and 95 with T2DM and essential hypertension. DC, DRs (DR2, DR4, and DR8, ie, episodes of 2, 4, or 8 consecutive beat-to-beat heart rate decelerations, respectively), and heart rate variability were determined by dynamic electrocardiogram. Biochemical markers of glucose and lipid metabolism, including glycated hemoglobin (HbA1c) and high-density lipoprotein cholesterol (HDL-C), were measured from blood samples.
Results: Both T2DM groups featured lower DC, SD of all normal-to-normal sinus RR intervals over 24 h (SDNN), root mean square of the successive normal sinus RR interval difference, and all DR values, but higher average heart rate (AHR) and acceleration capacity (AC), than healthy subjects. There were significant associations between the following: DC and HbA1c, systolic blood pressure (SBP), AHR, age, and HDL-C; DR2 and AHR, SBP, and HbA1c; DR4 and HbA1c, age, SBP, and HDL-C; and DR8 and HbA1c, AHR, and age. In both T2DM groups, HbA1c correlated negatively with DC, DR2, and SDNN, and positively with AC and AHR; homeostasis model assessment-insulin resistance index correlated negatively with DC, all DRs, and SDNN, and positively with AC.
Conclusion: Compared with healthy subjects, T2DM patients with or without essential hypertension have lower DC and DRs. DC and DRs correlate negatively with blood glucose and insulin resistance index.
Keywords: autonomic nervous system; deceleration capacity of heart rate; heart rate deceleration runs; hypertension; insulin resistance; type 2 diabetes mellitus.