Association between functional capacity and heart rate variability in patients with uncomplicated type 2 diabetes

Objective: We sought to investigate functional capacity, heart rate variability (HRV), as well as their relationship in the patients with uncomplicated type 2 diabetes. Methods: This cross-sectional observational study included 62 controls and 53 uncomplicated diabetic patients. Included subjects underwent laboratory analysis, 24-h ECG Holter monitoring and cardiopulmonary exercise testing. Results: All parameters of time and frequency domain of HRV were decreased in the diabetic patients. Oxygen uptake at ventilatory threshold (18.3 ± 3.9 vs. 14.6 ± 3.6 mL/kg/min, p <.001), peak oxygen uptake (peak VO2) (27.8 ± 4.1 vs. 19.5 ± 4.3, mL/kg/min, p <.001) and oxygen pulse were significantly lower in the diabetic group, whereas ventilation/carbon dioxide ratio and ventilation/carbon dioxide slope (25.4 ± 2.5 vs. 28.6 ± 3.9, p <.001) were significantly higher in this group. Furthermore, heart rate recovery in the first minute was significantly lower in the diabetic group (26 ± 5 vs. 23 ± 5 beats/min, p =.003). In the whole study population HbA1c and SDNN were independently of other clinical and HRV parameters associated with peak VO2, ventilation/carbon dioxide slope and heart rate recovery in the first minute. Conclusions: Our investigation showed that both functional capacity and HRV were significantly impaired in uncomplicated diabetic patients. HbA1c, an important parameter of glucose regulation, was independently associated with HRV parameters and functional capacity in the whole study population. This reveals a potentially important role of determination of functional capacity and cardiac autonomic function as important markers of preclinical damage in diabetic population.