Variability of the circadian heart rate in diabetes mellitus-related autonomic neuropathy

For assessing the alterations of circadian heart rate variability 66 diabetic patients (age: 52.9 +/- 1.0 years; x +/- SEM) and 23 control subjects (age: 52.7 +/- 1.7 years) were investigated using 24 hours Holter monitoring. Autonomic neuropathy (AN) was evaluated by tests for cardiovascular reflexes and patients were classified as being without AN (n = 26), having mild (n = 25) or definitive (n = 15) signs of AN. Minimal heart rates were significantly higher while maximal heart rates were considerably lower in patients with than without AN (60 +/- 2 min-1 versus 54 +/- 1, min-1, p < 0.05 and 125 +/- 4 min-1 versus 146 +/- 4 min-1, p < 0.01). Diabetic groups were comparable regarding values of averaged heart rates. The difference between the mean waking and sleeping averaged heart rates was the smallest in diabetic patients with definitive signs of AN (9 +/- 2 min-1) differing from those of control subjects (17 +/- 1 min-1, p < 0.01) and diabetic patients without (17 +/- 1 min-1, p < 0.001) or with mild (15 +/- 1 min-1, p < 0.05) signs of AN. Characteristic alteration, i.e. a reduction in circadian heart rate variability could be found in diabetic patients with signs of AN. This phenomenon has primarily been a consequence of more frequent sleeping heart rates due to dominant impairment in cardiac parasympathetic innervation.