Acute effect of insulin on autonomic regulation of the cardiovascular system: a study by heart rate spectral analysis

Insulin is suggested to have direct effects on the cardiovascular system but these are not well described. We assessed the possible influence of insulin on autonomic control of heart function. A 2-h hyperinsulinaemic euglycaemic clamp was performed in 10 healthy women (mean age 21.7 +/- 1.3 years), at two different insulin infusion rates: 80 mU m-2 and 400 mU m-2 min-1, in 7 and 3 subjects, respectively. Saline alone was infused in 4 controls. Power spectral analysis (PSA) of heart rate was recorded before and after 90-120 min of insulin infusion, as were blood pressure and heart rate. Although there were no significant changes in heart rate or blood pressure, PSA showed marked reductions of high frequency (HF) bands after insulin (2.60 +/- 0.12 vs 2.09 +/- 0.16 log ms2, p < 0.005), as at both low and high infusion rates (2.46 +/- 0.13 to 2.14 +/- 0.23 log ms2, p < 0.05, and 2.92 +/- 0.18 to 1.98 +/- 0.06 log ms2, p < 0.01, respectively). There were no significant changes of low frequency (LF) bands. Densities at LF and HF did not change significantly in control studies. As HF and LF are considered to reflect parasympathetic and mainly sympathetic control respectively, our observation of an increased LF/HF ratio (0.13 +/- 0.10 vs 0.63 +/- 0.13, p < 0.005) may be considered an index of relative sympathetic predominance induced by insulin infusion. We conclude that insulin affects the cardiovascular system, reducing vagal influence on the heart and inducing a relative hypersympathetic tone

Effect of moderate aerobic exercise on sympatho-vagal balance in type 2 diabetic patients.

Aims The purpose of the study was to determine long-term cardiovascular autonomic adaptation to moderate endurance aerobic exercise in people with Type 2 diabetes in order to test the hypothesis of an enhanced vagal drive. Methods We analysed the power spectral density of heart rate cyclic variations at rest, while lying, and while standing in 12 sedentary, non-smoking, Type 2 diabetic individuals. Testing was performed before and after a 6-month, supervised, progressive, aerobic training programme, twice weekly. Heart rate variability was assessed by autoregressive power spectral analysis (PSA); this method allows reliable quantification of low-frequency (LF) and high-frequency (HF) components, which are considered to be under mainly sympathetic and purely parasympathetic control, respectively. Results In 10-min electrocardiogram recordings, mean RR intervals values lying and standing were similar before and after physical exercise. Likewise, total heart rate variability, expressed as total power spectral density (PSD), was not altered by exercise. In contrast, on standing, the HF component, expressed in normalized units, was significantly higher (20.1 +/- 4 vs. 30.4 +/- 5, P < 0.01), whereas the LF component was significantly lower (68.1 +/- 7 vs. 49.8 +/- 8, P < 0.01) after exercise; hence, on standing, the LF/HF ratio, reflecting the sympathetic vs. parasympathetic balance, was markedly lower (16.2 +/- 11 vs. 5.2 +/- 3.2, P = 0.003). No significant exercise-related changes in these PSA components were observed on lying. Conclusions A twice-weekly, 6-month, moderate, aerobic exercise programme, without a concomitant weight loss diet, is associated with significant improvements in cardiovascular autonomic function in overweight, non-smoking, Type 2 diabetic individuals

Effects of aerobic or resistance exercise training on cardiovascular autonomic function of subjects with type 2 diabetes: A pilot study

Background and Aims: Both aerobic (AER) and resistance (RES) training improve metabolic control in patients with type 2 diabetes (T2DM). However, information on the effects of these training modalities on cardiovascular autonomic control is limited. Our aim was to compare the effects of AER and RES training on cardiovascular autonomic function in these subjects. Methods and Results: Cardiovascular autonomic control was assessed by Power Spectral Analysis (PSA) of Heart Rate Variability (HRV) and baroreceptors function indexes in 30 subjects with T2DM, randomly assigned to aerobic or resistance training for 4 months. In particular, PSA of HRV measured the Low Frequency (LF) and High Frequency (HF) bands of RR variations, expression of prevalent sympathetic and parasympathetic drive, respectively. Furthermore, we measured the correlation occurring between systolic blood pressure and heart rate during a standardized Valsalva maneuver using two indexes, b2 and b4, considered an expression of baroreceptor sensitivity and peripheral vasoactive adaptations during predominant sympathetic and parasympathetic drive, respectively. After training, the LF/HF ratio, which summarizes the sympatho-vagal balance in HRV control, was similarly decreased in the AER and RES groups. After AER, b2 and b4 significantly improved. After RES, changes of b2 were of borderline significance, whereas changes of b4 did not reach statistical significance. However, comparison of changes in baroreceptor sensitivity indexes between groups did not show statistically significant differences. Conclusion: Both aerobic and resistance training improve several indices of the autonomic control of the cardiovascular system in patients with T2DM. Although these improvements seem to occur to a similar extent in both training modalities, some differences cannot be ruled out

Plasma clearance rate of 51 Cr-EDTA provides precise and convenient technique for measurement of glomerular filtration rate in diabetic humans.

IF 6.64