BackgroundIn type 2 diabetes mellitus both insulin resistance and hyperglycemia are considered responsible for autonomic dysfunction. The relation between the autonomic activity, impaired fasting glycemia and impaired glucose tolerance is, however, unclear. The purpose of this study was to evaluate and compare the circadian autonomic activity expressed as heart rate variability (HRV) measured by 24-hours ECG recording in insulin resistant subjects (IR) with characteristics as follow: IR subjects with normal oral glucose tolerance test results, IR subjects with impaired fasting glucose, IR subjects with impaired glucose tolerance and subjects with type 2 diabetes mellitus.MethodsEighty Caucasian insulin resistant subjects (IR) and twenty five control subjects were recruited for the study. IR subjects were divided into four groups according to the outcoming results of oral glucose tests (OGTTs): IR subjects with normal glucose regulation (NGR), IR subjects with impaired fasting glycemia (IFG), IR subjects with impaired glucose tolerance (IGT) and subjects with type 2 diabetes mellitus (DM). Autonomic nervous activity was studied by 24-hours ECG recording. Heart rate variability analysis was performed in time and frequency domains: SDNN, RMS-SD, low frequency (LF) and high frequency (HF) were calculated.ResultsThe total SDNN showed statistically significant reduction in all four groups with insulin resistant subjects (IR) when compared to the control group (p <0,001). During night LF normalized units (n.u.) were found to be higher in all four groups including IR subjects than in the control group (all p < 0,001) and subjects with normal glucose regulation (NGR), with impaired fasting glycemia (IFG) and with impaired glucose tolerance (IGT) were found to have higher LF n.u. than those in the type 2 diabetes mellitus group. The linear regression model demonstrated direct association between LF values and the homeostasis model assessment-index (HOMA-I), in the insulin resistant group (r = 0,715, p <0,0001).ConclusionThe results of our study suggest that insulin resistance might cause global autonomic dysfunction which increases along with worsening glucose metabolic impairment. The analysis of sympathetic and parasympathetic components and the sympathovagal balance demonstrated an association between insulin resistance and sympathetic over-activity, especially during night. The results indicated that the sympathetic over-activity is directly correlated to the grade of insulin resistance calculated according to the HOMA-I. Since increased sympathetic activity is related to major cardiovascular accidents, early diagnosis of all insulin resistant patients should be contemplated.

Autonomic nervous system activity is involved in body weight regulation. We assessed whether the body mass index (BMI) is related to the autonomic nervous system activity as assessed by heart rate variability (HRV). Twenty-five adult normotensive, euglycemic healthy males (M) and females (F) were studied (M/F ¼ 13/12). BMI was assessed in each individual. HRV was assessed and the domains of low frequencies (LF, index of the sympathetic modulation) and high frequencies (HF, index of the parasympathetic modulation) were measured. Data were statistically analyzed and are presented as mean±s.d. Mean BMI did not correlate with either HF or LF. It inversely related to HF (r ¼ À0.50, Po0.01), whereas its relationship with LF was marginally significant (r ¼ À0.39, P ¼ 0.05). The HF in individuals with BMI o20 kg/m 2 was significantly higher from those measured in the remaining subjects (Po0.05). The results support the role of parasympathetic activity in influencing BMI through likely modulation of body weight.

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The use of the 24-h HRV method can provide more accurate and reproducible data than other conventional cardiovascular tests.