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AIMS: To investigate dysregulation of the autonomic nervous system as a potential mechanism for early insulin resistance in the development of Type 2 diabetes. METHODS: Thirteen healthy individuals with first-degree relatives with Type 2 diabetes (R) were compared with 14 control subjects without family history of diabetes (C), matched for age, body mass index and sex. An oral glucose tolerance test and a hyperinsulinaemic euglycaemic clamp were performed. Analysis of heart rate variability during rest, controlled breathing, an orthostatic manoeuvre and a standardized physical stress (cold pressor test (CPT)), were used to evaluate the activity of the autonomic nervous system. RESULTS: Fasting blood glucose, HbA1c and serum insulin were similar in the R and C groups. The M-value, reflecting insulin sensitivity, did not differ significantly between the groups. Total spectral power and high-frequency power were lower in R during controlled breathing (P = 0.05 and P = 0.07, respectively), otherwise there were no significant differences between R and C in heart rate variability. However, low-frequency (LF)/high-frequency (HF) spectral power ratio during CPT, reflecting sympathetic/parasympathetic balance, was negatively associated with insulin sensitivity (r = -0.53, P = 0.006). When all subjects were divided into two groups by the mean M-value, the low M-value group displayed an overall higher LF/HF ratio (P = 0.04). HF power was lower in the low M-value group during controlled breathing and CPT (P = 0.01 and P = 0.03, respectively). CONCLUSION: An altered balance of the parasympathetic and sympathetic nervous activity, mainly explained by an attenuated parasympathetic activity, might contribute to the development of insulin resistance and Type 2 diabetes.

Aims To investigate dysregulation of the autonomic nervous system as a potential mechanism for early insulin resistance in the development of Type 2 diabetes. Methods Thirteen healthy individuals with first-degree relatives with Type 2 diabetes (R) were compared with 14 control subjects without family history of diabetes (C), matched for age, body mass index and sex. An oral glucose tolerance test and a hyperinsulinaemic euglycaemic clamp were performed. Analysis of heart rate variability during rest, controlled breathing, an orthostatic manoeuvre and a standardized physical stress (cold pressor test (CPT)), were used to evaluate the activity of the autonomic nervous system. Results Fasting blood glucose, HbA1c and serum insulin were similar in the R and C groups. The M-value, reflecting insulin sensitivity, did not differ significantly between the groups. Total spectral power and high-frequency power were lower in R during controlled breathing (P = 0.05 and P = 0.07, respectively), otherwise there were no significant differences between R and C in heart rate variability. However, low-frequency (LF)/high-frequency (HF) spectral power ratio during CPT, reflecting sympathetic/parasympathetic balance, was negatively associated with insulin sensitivity (r = −0.53, P = 0.006). When all subjects were divided into two groups by the mean M-value, the low M-value group displayed an overall higher LF/HF ratio (P = 0.04). HF power was lower in the low M-value group during controlled breathing and CPT (P = 0.01 and P = 0.03, respectively). Conclusion An altered balance of the parasympathetic and sympathetic nervous activity, mainly explained by an attenuated parasympathetic activity, might contribute to the development of insulin resistance and Type 2 diabetes.

PURPOSE: To investigate relationships between heart rate variability (HRV) and peripheral and central performance measures, 17 cross-country (X-C) skiers and seven canoeists were studied before and after a training period of 7 months. METHODS: For the skiers and canoeists respectively, leg and arm peak torque (Tq), time to peak torque (TiTq), and total work (Wrk) were measured in an isokinetic dynamometer. Maximal oxygen uptakes (VO(2max)) were obtained from treadmill tests. Power spectral analysis of HRV was performed on electrocardiographic recordings in the resting supine position and after a tilt to yield power in the low-frequency (0.04--0.15 Hz) and high-frequency (0.15--0.45 Hz) components of HRV. RESULTS: The change in normalized LF-variability in standing (Delta LFnT) correlated (P < 0.01) with the changes in TiTq (r = 0.63), max lactate (r = -0.63), and VO(2max) (r = -0.53). The change in absolute LFT was inversely correlated with the change in Tq. Subjects who improved VO(2max) were characterized by consistently higher high-frequency and total HRV than subjects with deteriorated aerobic capacity (P < 0.05). CONCLUSION: The results suggest that improved measures of both peripheral and central (aerobic) work capacities were associated with a reduction of low-frequency HRV in the tilted position. High-frequency and total HRV did not change in proportion with changes in muscle performance or aerobic capacity, but the ability to further improve VO(2max) with training in these already fit subjects seemed to depend on their average levels of these HRV measures, interpreted to reflect parasympathetic activity.

To investigate the effects on cardiac autonomic control after a competitive cross-country skiing season, 9 females and 8 males, 16-19 years old, performed tilt-table heart rate variability (HRV) recordings and incremental treadmill tests before (August), and after (April the following year) the most intensive period of training and competition. Spectral analysis of HRV showed increased total variability at rest and reduced low frequency variability in the tilted position (LFtilt) at the second test (P<0.05). The female subgroup showed consistently higher high frequency (HF) and total heart rate variability than males. Total run time (RunT) increased from 18.5+/-1.9 min to 19.4+/-1.7 min (mean+/-SD) in the entire group (P<0.05), while VO2max only showed a non-significant increase (0.05 <0.10). Submaximal heart rates (HRsubm) were reduced by an average of 4 beats (P<0.01) but maximal HR was unchanged. Performance data suggest a positive training effect. Following training, the increased total HRV the reduced LFtilt (both at rest), and the lower submaximal heart rates indicate an altered control of heart rate both at rest and during exercise. The consistently higher HF and total variability in the females indicate an increased parasympathetic activity in females compared with males.

BACKGROUND: Palmar hyperhidrosis has been associated with an increased activity of the sympathetic nervous system. The objective of this study was to assess the immediate and long-term effects of endoscopic transthoracic sympathicotomy on the autonomic modulation of the heart rate in patients with palmar hyperhidrosis. METHODS: Power spectrum analysis of heart rate variability in the lying position and after passive tilt to the upright position was performed in thirteen patients the day before and after sympathicotomy. A follow-up recording was performed in ten patients approximately six months later. Recordings from 26 healthy subjects were used as a reference group. FINDINGS: The patients had a tendency to higher power of the low-frequency (LF: 0.04-0.15 Hz) and high-frequency (HF; above 0.15 Hz) components than controls in the upright position. After sympathicotomy LF power was reduced, but HF power was unchanged. At follow-up LF power remained at a lower level, but now HF power was reduced. INTERPRETATION: Patients with palmar hyperhidrosis have a sympathetic overactivity but also a compensatory high parasympathetic activity. Sympathicotomy results in an initial sympathovagal imbalance with a parasympathetic predominance, which is restored on a long-term basis.

BACKGROUND: Autonomic dysfunction, both adrenergic and cholinergic, has been associated with the irritable bowel syndrome (IBS). The accuracy of the methods in use, however, has been limited by the need for active co-operation by the patients, with consequent difficulties in standardization. The aim of this study was to investigate the function of the autonomic nervous system in patients with IBS by using spectral analysis of the heart rate variability, an accurate method depending very little on patient cooperation. METHODS: Eighteen patients with IBS were compared with 36 sex- and age-matched controls. Spectral analysis of heart rate variability was performed to quantify sympathetic and parasympathetic nerve activity. RESULTS: The patients with IBS had significantly higher sympathetic activity than controls (P = 0.005). There was no significant (P = 0.308) increase in parasympathetic activity. There were no significant differences in heart rate or blood pressure between the patients and controls. CONCLUSION: Spectral analysis of heart rate variability has been used to assess the function of the autonomic nervous system in patients with IBS. IBS patients have significantly increased symphathetic activity, whereas parasympathetic activity does not differ from that of controls.

BACKGROUND: Circulatory instability with severe hypotension frequently complicates liver transplantation in patients with familial amyloidotic polyneuropathy. Autonomic dysfunction is found early in the course of the disease by analysis of beat-to-beat heart rate variability (HRV). The aim of the present study was to investigate the impact of autonomic neuropathy on intraoperative circulatory instability during liver transplantation for familial amyloidotic polyneuropathy. METHODS: Twenty-two patients were evaluated at the Department of Medicine, Umea University Hospital, by spectral analysis of HRV and later received liver transplants at Huddinge University Hospital. The low-and high-frequency bands obtained by spectral analysis of HRV in the supine and upright positions, respectively, were used as representative of sympathetic and parasympathetic activity. Circulatory instability during transplantation was defined as a fall in systolic arterial blood pressure below 70 mmHg for more than 5 min during the preanhepatic phase. RESULTS: Both arrhythmia preventing spectral analysis of HRV and a sympathetic variability peak below 2.5 mHz2 were significantly more common among patients with intraoperative circulatory instability (P=0.03 and 0. 004, respectively). A diminished increase in pulse rate when tilting the patients from the supine to the upright position was also more pronounced among patients with circulatory instability (P<0.05). CONCLUSIONS: The majority of patients who will develop circulatory instability with a pronounced fall in arterial blood pressure can be identified by Poincare plots of R-R intervals and spectral analysis of HRV. A low sympathetic peak or arrhythmia precluding spectral analysis of HRV is significantly related to operative circulatory instability.