Effects of physical training on heart rate variability in diabetic patients with various degrees of cardiovascular autonomic neuropathy.

OBJECTIVE To investigate the effects of regularly performed endurance training on heart rate variability in diabetic patients with different degrees of cardiovascular autonomic neuropathy (CAN). METHODS Bicycle ergometer training (12 weeks, 2 x 30 min/week, with 65% of maximal performance) was performed by 22 insulin-requiring diabetic patients (age 49.5 +/- 8.7 years; diabetes duration 18.6 +/- 10.6 years; BMI 25.1 +/- 3.4 kg/m2): i.e., by 8 subjects with no CAN, 8 with early CAN and by 6 patients with definite/severe CAN. A standard battery of cardiovascular reflex tests was used for grading of CAN, a short-term spectral analysis of heart rate variability for follow-up monitoring of training-induced effects. RESULTS While the training-free interval induced no changes in spectral indices, the 12-week training period increased the cumulative spectral power of the total frequency band (P = 0.04) but to a different extent (P = 0.039) in different degrees of neuropathy. In patients with no CAN the spectral power in the high-frequency (HF) band (0.15-0.50 Hz) increased from 6.2 +/- 0.3 to 6.6 +/- 0.4 In [ms2]; P = 0.016, and in the low-frequency (LF) band (0.06-0.13 Hz) from 7.1 +/- 0.1 to 7.6 +/- 0.3 in [ms2]; P = 0.08 which resulted in an increase of total spectral power (0.06-0.50 Hz) from 7.5 +/- 0.1 to 8.0 +/- 0.3 in [ms2] (P = 0.05). Patients with the early form of CAN showed an increase of spectral power in HF (5.1 +/- 0.2 to 5.8 +/- 0.1 in [ms2], P = 0.05) and LF bands (5.6 +/- 0.1 to 6.3 +/- 0.1 in [ms2], P = 0.008), resulting in an increase of total power from 6.1 +/- 0.1 to 6.6 +/- 0.1 in [ms2] (P = 0.04), whereas those with definite/severe CAN showed no changes after the training period. Training improved fitness in the whole patient cohort. The increased autonomic tone as assessed by spectral indices disappeared after a training withdrawal period of 6 weeks. CONCLUSIONS In diabetic patients with no or early CAN, regularly performed endurance training increased heart rate variability due to improved sympathetic and parasympathetic supply, whereas in subjects with definite/severe CAN no effect on heart rate variability could be demonstrated after this kind of training.