Cardiovascular autonomic dysfunction in Type II diabetics diagnosed within six months
N Kaveer, AK Das, Aparna Agrawal, Madanmohan, N Veena
Jawaharlal Institute of Post Graduate Medical Education and Research, Pondicherry, India
Jawaharlal Institute of Post Graduate Medical Education and Research, Pondicherry
|How to cite this article:|
Kaveer N, Das A K, Agrawal A, Madanmohan, Veena N. Cardiovascular autonomic dysfunction in Type II diabetics diagnosed within six months.J Postgrad Med 2004;50:233-234
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Kaveer N, Das A K, Agrawal A, Madanmohan, Veena N. Cardiovascular autonomic dysfunction in Type II diabetics diagnosed within six months. J Postgrad Med [serial online] 2004 [cited 2019 Aug 25 ];50:233-234
Available from: http://www.jpgmonline.com/text.asp?2004/50/3/233/12585
Cardiovascular autonomic neuropathy (CAN) is the most clinically important and well-studied form of diabetic autonomic neuropathy because of its association with a variety of adverse outcomes including cardiovascular deaths. The objective of this study was to assess the presence of CAN in 24 Type 2 diabetic patients diagnosed within six months, by performing a battery of cardiovascular autonomic function tests, which included blood pressure changes and power spectral analysis of heart rate variability on 700 head-up tilt. Patients were compared with a control group of 17 subjects similar in age, sex and BMI.
Mean age and sex ratio of diabetic cases was 45.5 ± 7.5 years and 1.4 respectively; and that of controls was 45.5 ± 8.1 years and 1.8 respectively. The mean duration of diagnosis for the diabetic patients was 3.8 ± 1.7 months. There were no significant differences in baseline characteristics between the two groups. At the time of diagnosis, the mean fasting and postprandial blood glucose levels in the diabetic patients was 185 ± 55 mg/dl and 337 ± 80 mg/dl respectively. The comparison of values between diabetics and control subjects, of various parameters obtained from the autonomic function tests are shown in [Table:1] and [Table:2].
The diastolic blood pressure (DBP) was significantly (p=0.004) reduced in diabetics, immediately and at 2 min after 70 º head-up tilt [Table:1] implying a delayed or inadequate response of the peripheral sympathetic vasomotor system in the diabetics compared to controls.
Power spectral analysis of heart rate variability [Table:2] showed a significant decrease in the mean R-R intervals in diabetics, both during supine rest and head-up tilt , reflecting a reduced vagal tone in the diabetics. The standard deviation (SD) of R-R intervals and the coefficient of variation (CV ) about the mean R-R interval (CV=SD/Mean X 100 ) which are measures of heart rate variability, were significantly low (p= 0.003 and 0.009 respectively ) in diabetic patients during head-up tilt but there was no significant difference in these parameters during supine rest between the two groups. Flapan et al (1990) reported that reduced heart rate variation occurs in cardiac failure. As the heart rate variability in the diabetic cases is significantly reduced only during the head-up tilt but not during supine rest, it shows that the head-up tilt in these patients produces a low cardiac output similar to that seen in cardiac failure, due to inadequate peripheral sympathetic vasoconstriction.
High-frequency (HF) power, which is a measure of HF peak, is used to asses the parasympathetic activity on heart rate variability, whereas Low-frequency (LF) power is mediated by both parasympathetic and sympathetic pathways., As shown in [Table:2], the HF power during head-up tilt was significantly low (p=0.040) in diabetics, which again reiterates cardiac parasympathetic dysfunction and there was no significant difference in the HF power during supine rest, indicating that the cardiac parasympathetic dysfunction maybe mild, and is unmasked on head-up tilt. The LF power during supine rest was significantly (p=0.044) low in diabetic patients which indicates a cardiac sympathetic overactivity, possibly due to parasympathetic withdrawal. These findings suggest that the cardiac sympathetic system is relatively spared and dysfunction is predominantly seen in the cardiac parasympathetic function.
A plausible explanation for this pattern of autonomic nervous dysfunction is the presence of long axons in cardiac parasympathetic and peripheral sympathetic systems, which are relatively more sensitive to the metabolic derangements as compared to the relatively short axons in the cardiac sympathetic system. Although it has not yet been shown that the treatment of hyperglycaemia in Type 2 diabetics will improve cardiac autonomic function, identification and treatment of CAN at the time of diagnosis of diabetes will improve the quality of life and should be a part of routine care for diabetic patients.
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