A COMPARATIVE STUDY OF HEART RATE VARIABILITY IN DIABETIC SUBJECTS AND NORMAL SUBJECTS

Aim: The main objective of this study is to enlighten medical faculty and diabetic patients about neurological and cardiovascular complications in Diabetes and to compare heart rate variability in normal individuals and diabetic patients. Materials and Method: This research study was case-control study using Niviqure data acquisition system to record 5-minutes E.C.G. in 400 individuals who consisted of the cases group comprised of 200 diabetic patients and controls group consisted of 200 healthy individuals.5-minutes E.C.G. data gathered was subjected to frequency domain analysis of Heart Rate Variability and from which various parameter depicting parasympathetic activity and sympathetic activity were analyzed. HbA1c levels were estimated by high performance liquid chromatography. Statistical analysis was done using MS office excel 2007 software. Results: In the present study it was observed that parameters of heart rate variability are reduced (power of High Frequency-H.F., power of Low Frequency-L.F., total power-T.P. and L.F. /H.F. ratio) and parameters of heart rate variability depicting parasympathetic modulation of heart (H.F.) are more reduced when compared to parameters of heart rate variability depicting sympathetic modulation (L.F.) in diabetics compared to normal individuals. It was also found that there is a negative correlation between HbA1c values of subjects and parameters of HRV. Conclusion: These results may be attributed to early parasympathetic damage due to axonal degeneration of longer vagal fibers .This axonal degeneration is mostly caused due to chronically elevated levels of blood glucose.


Introduction
Current interest centers on the development of a new generation of tests of autonomic nerve function that are simple, non-invasive, reproducible and allow precision in diagnosis and accurate quantization. Most of them are based on cardiovascular reflexes and abnormality in them is assumed to reflect autonomic damage elsewhere. 10 Measurement of Heart Rate Variability (HRV) is the best non-invasive method to measure the working of the heart, as it measures many aspects of cardiac functioning, including autonomic nerve functioning. 1, 8,18. The new method can replace the traditional manual method for evaluating cardiovascular responses with the advantages of speed and objectivity. 8 Analysis of 5 minutes measurements of heart rate variability (HRV) has been shown to be a good predictor of physiological distress and mortality, especially for cardiovascular disease. 5,12,16,21,24,25 Diabetes is an ICEBERG disease. According to WHO report the prevalence of diabetes in adults worldwide has risen and the number will rise from 135 million in 1995 to 300 million by the year 2025. Epidemiological data in India shows the same upward trend according to the World Health Organization estimates, that India had 32 million diabetic subjects in the year 2000 and this number would increase to 80 million by the year 2030. Neuropathy is one of the most common complications of diabetes. 13 Silent myocardial infarct is more common in diabetics due to involvement of cardiac autonomic nerves. At an early stage autonomic dysfunction may be asymptomatic or mildly symptomatic. Symptomatic autonomic neuropathy carries worst prognosis, so early diagnosis is essential for maximum benefit more so in diabetes. 15 Heart rate variability monitoring plays a vital role in prevention and early diagnosis of cardiac autonomic neuropathic complications. Data are expressed as mean ± SD. The procedure of testing the hypothesis was concluded by accepting the hypothesis or rejecting it. Data between the study group and control group were compared using z-test. When the statistic z value is computed, we found p value corresponding to it from the tables If p value is < 0.001 it is considered highly significant and if it is <0.05 it is considered significant, and it is >0.05, then we concluded that the parameters under study are not significantly related.
In case of correlation study, Pearson's correlation coefficient was used. Correlation value (r) lies in between -1 and +1. If the r value is -1≤ r <0-both parameters are negatively correlated If the r value is 0 < r ≤ 1 -both parameters are positively correlated if the r value is 0, no relation exists between the parameters.

Discussion
In the present study it was observed that parameters of heart rate variability are reduced and parameters of heart rate variability depicting parasympathetic modulation of heart are more reduced when compared to parameters of heart rate variability depicting sympathetic modulation in diabetics compared to normal individuals. High frequency (H.  19 These recommendations suggest that these parameters are sensitive measure of HRV and that these measures would primarily reflect parasympathetic mediated activity.

Parameters depicting parasympathetic activity:
In The most significant factor correlating with incidence and progression of diabetic neuropathy is the status of Glycemic control (HBA1C). HBA1C reflects the status of glycaemia. In diabetes, presence of hyperglycemia is the basis for pathogenesis and progression of autonomic neuropathy. In this study HbA1C levels in diabetic individuals are significantly raised. Colhoun, et al 11 in their study they concluded that reduced heart rate variability parameters may be a very early feature of insulin resistance and loss of glycemic control. In this study HbA1c is negatively correlated (but not significant) with all parameters of heart rate variability (L.F., H.F. and T.P.) except L.F. /H.F. ratio. It is positively correlated to L.F. /H.F. ratio. This is consistent with study done by Faulkner MS, et al 14

Conclusion
Our study suggests that there is both sympathetic dysfunction and parasympathetic dysfunction, but from increased values of L.F. /H.F. ratios it is inferred that there is more parasympathetic damage than sympathetic nerve damage. Parasympathetic modulation is mediated via vagus nerve which itself is long nerve and it is well known fact that long nerves are prone for neuropathy in diabetes mellitus. 6 This may be accounted for early parasympathetic damage due to axonal degeneration of longer vagal fibers .This axonal degeneration is mostly caused due to chronically elevated levels of blood glucose.Reduced parasympathetic activity lowers the threshold for ventricular fibrillation, which is one of the important causes for sudden death. Hence, the best way to prevent sudden death caused by cardiac autonomic neuropathy is by:-1. Regularly monitoring HRV. 2. Maintaining good glycemic control.

3.
Doing regular exercise increases parasympathetic tone. 4. Practicing yoga improves parasympathetic tone which reduces morbidity and mortality caused due cardiac autonomic neuropathy.