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 (0.06-0.15 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.
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