Measurement of heart rate variations: influencing factors, normal values and diagnostic impact on diabetic autonomic neuropathy.

Different methods of heart rate variation (HRV) measurement are recommended to assess disturbances of cardiovascular reflexes in autonomic polyneuropathies. Influencing factors on the E/I-ratio, HRV variations during Valsalva's maneuver, and change of position from lying down to standing up, as well as age, gender, time of day and satiety were investigated in healthy volunteers. Normal values were then calculated and a total of 100 diabetics with clinically manifest neuropathy of different stages (N0 = 8, N1 = 15, N2a = 24, N2b = 28, N3 = 25), 26 of whom were insulin-dependent and 74 non-insulin-dependent, were examined. Apart from clinical examination, nerve conduction velocity (NCV) measurement of five nerves as well as amplitude measurement of evoked sensory and motor action potentials was performed. No significant influence of the time of day the test was performed could be found. Test reproducibility was good, day-to-day differences did not reach a significant level. This was also true for the test results before and after food intake. Gender-correlated test result differences could not be proven. Statistical analysis showed significant differences between the overall group of diabetics and controls. The difference was most accentuated in the E/I ratio. The further developed the clinical picture of neuropathy, the more pathological were the results obtained in different tests. The results suggest that most changes leading to pathological values of NCV and HRV occur in a clinical stage in which no, or only very slight, clinical signs give evidence of diabetic neuropathy (N0-N1). Therefore, these examinations should, especially, be performed in diabetics with no, or only slight, clinical signs of neuropathy in order to reveal those patients with neuropathic disturbances at an initial stage.