Heart rate variability modifications following exercise training in type 2 diabetic patients with definite cardiac autonomic neuropathy

Abstract

Objectives: Cardiac autonomic neuropathy (CAN), as a result of diabetic autonomic neuropathy, is positively related with poor prognosis in diabetic patients. Heart rate variability (HRV) measurement consists a remarkable index of cardiac autonomic dysfunction. The aim of the study was to examine the effects of long-term exercise training on HRV in type 2 diabetic patients with definite CAN.

Methods: Seventeen type 2 diabetic patients with definite CAN (Group A – aged 56.2±5.8 yrs old) and fifteen without CAN (Group B – aged 55.8±5.6 yrs old) participated in the study. All patients followed a six-month aerobic exercise training program, three times per week, at an intensity of 70-85% of heart rate reserved. At the beginning and at the end of the study all subjects underwent graded maximal exercise testing with spiroergometry for the evaluation of their aerobic capacity (VO2peak). Moreover, both time- and frequency domain indices of HRV were measured from 24 hrs ambulatory continuous ECG Holter recordings.

Results: At baseline all measurements of HRV indices were significantly reduced in group A compared with B (p<0.05). Moreover, group A reached significantly lower VO2peak by 14.8% compared with group B (p<0.05). Following exercise training program, the SDNN was increased by 18.8% (p<0.05) and 13.8% (p<0.05), rMSSd was increased by 35% (p<0.05) and 15.2% (p<0.05) and pNN50 was increased by 400% (p<0.05) and 67.9% (p<0.05) in groups A and B, respectively. Regarding the frequency domain indices, only the HF was found to be significantly increased in group A. At the end of the exercise training program SDNN, rMSSd and LF were significantly lower by 24.3% (p<0.05), 20.3% (p<0.05) and 40% (p<0.05), respectively, in group A compared with group B. Also, VO2peak increased by 17.8% (p<0.05) in group A and by 11% (p<0.05) in B. Furthermore, the exercise training program had significant effects on blood lipids, glucose levels and HbA1c in both groups.

Conclusions: Our results indicate that 6-month aerobic exercise training improves the cardiac autonomic nervous system function in type 2 diabetic patients. However more favorable effects are found in type 2 diabetic patients with definite CAN.