Autonomic neuropathy in asymptomatic subjects with non-insulin-dependent diabetes mellitus and microalbuminuria

Impaired heart rate variability, Valsalva and 30:15 ratio indexes are associated with reduced submaximal exercise capacity in subjects with diabetes mellitus

AIMS

To assess cardiac autonomic control and its association with submaximal exercise measured using the 6-minute walk test (6MWT) in subjects with type-2 diabetes mellitus (DM2).

METHODS

Cardiac autonomic control was assessed using Ewing's tests and heart rate variability (HRV) in DM2 volunteers (DG, n = 22) and sex-, age- and body mass index-matched non-diabetic controls (CG, n = 22) before, during and after 6MWT.

RESULTS

Before the 6MWT, DG presented lower HRV represented by reduced SDNN [median 28.9 ms² (IQR:18.6-35.4) vs. 45.1 (IQR:39.2-62.67), p < 0.001] and Total Power [median 785 ms² (IQR:256-1264) vs. 1757 ms² (IQR:1006-2912), p = 0.004]. Exercise capacity was reduced in DG [maximal predicted distance (%) = 88.4 ± 6.4 vs. 95.2 ± 11.0%, p = 0.018]. DG demonstrated lower global HRV during recovery and lower parasympathetic drive, represented by reduced RMSSD, during all phases of the 6MWT. Moreover, supine HR (r = -0.32), HR orthostatism (ρ = -0.40), SDNN pre-6MWT (ρ = 0.39), TP pre-6MWT (ρ = 0.38), Valsalva ratio (ρ = 0.39) and 30:15 ratio (ρ = 0.38) were all correlated with maximal walked distance.

CONCLUSIONS

DM2 subjects presented abnormal HRV during and after submaximal exercise. Furthermore, autonomic control impairment in orthostatism, represented by lower global HRV (SDNN, Total power) and lower Ewing's indexes (Valsalva and 30:15 ratios), was associated with lower exercise capacity.

Cardiovascular autonomic dysfunction predicts increasing albumin excretion in type 1 diabetes

OBJECTIVE

To determine the potential role of cardiovascular autonomic dysfunction in the development of renal complications in young people with type 1 diabetes (T1D).

METHODS

In this prospective study, 199 children and adolescents recruited to the Oxford Regional Prospective Study underwent assessment of autonomic function ~5 years after diagnosis, and were subsequently followed with longitudinal assessments of HbA_1c and urine albumin-creatinine ratio (ACR) over 8.6 ± 3.4 years. Autonomic function was assessed with 4 standardized tests of cardiovascular reflexes: heart rate (HR) response to (1) Valsalva Maneuver, (2) deep breathing, (3) standing, and (4) blood pressure (BP) response to standing. Linear mixed models were used to assess the association between autonomic parameters and future changes in ACR.

RESULTS

Independent of HbA_1c , each SD increase in HR response to Valsalva Maneuver predicted an ACR increase of 2.16% [95% CI: 0.08; 4.28] per year (P = .04), while each SD increase in diastolic BP response to standing predicted an ACR increase of 2.55% [95% CI: 0.37; 4.77] per year (P = .02). The effect of HR response to standing on ACR reached borderline significance (-2.07% [95% CI: -4.11; 0.01] per year per SD increase, P = .051).

CONCLUSIONS

In this cohort of young people with T1D, enhanced cardiovascular reflexes at baseline predicted future increases in ACR. These results support a potential role for autonomic dysfunction in the pathogenesis of diabetic nephropathy.

Urinary albumin, protein excretion and circadian blood pressure in patients with fibromyalgia

Recent evidence suggests that patients with fibromyalgia (FM) have increased oxidative stress, inflammation, endothelial dysfunction and autonomic dysfunction. These factors are also shown to be responsible for increased urinary albumin and protein excretion and deranged circadian blood pressure (BP). However, no study has examined the 24-h urinary albumin excretion (UAE), 24-h urinary protein excretion (UPE) and 24-h ambulatory BP measurements in FM patients. The sociodemographic, laboratory parameters, depressive symptoms, sleep problems and 24-h ambulatory BPs were measured for all patients. Diagnosis of FM was based on the criteria for the classification of FM by the American College of Rheumatology. After diagnosis of FM, these patients underwent to complete the Fibromyalgia Impact Questionnaire (FIQ). In total, 30 patients with FM and 61 patients without FM were included. Among FM patients, the average number of tender points was 13.1 ± 1.57 and the mean FIQ score was 57.9 ± 8.86. The number of tender points did not show any correlation with office and ambulatory BPs. There were also no correlations between the number of tender points, UPE and UAE. The stepwise linear regression did not show any relation between UPE and FM. However, 24-h UAE was independently correlated with office systolic BP (P 0.008) and the presence of FM (P 0.045). The logistic regression analysis revealed no association between FM and non-dipping status. We suggest that circadian blood pressure and UPE are not independently associated with FM. However, UAE was related with the presence of FM. Studies are needed to confirm our findings and to highlight pathophysiologic mechanisms.

Relationship between autonomic nervous system activity during sleep and fasting glucose in Japanese workers

Although autonomic nervous system activity is reportedly related to diurnal glucose tolerance impairment, the relationship with glucose tolerance during sleep is unclear. Since work styles have recently diversified, it is important to assess the effect of sleep on workers' health. Elucidation of the relationship between autonomic nervous system activity during sleep and glucose tolerance in workers may facilitate preventive measures against diabetes using non-pharmacological means (e.g., sleep hygiene education, relaxation techniques and stress management). We examined whether autonomic nervous system activity during sleep is related to fasting glucose or glycated hemoglobin (HbA1c) in individuals with either normal or impaired fasting glucose tolerance. The subjects were 77 apparently healthy Japanese workers with normal or impaired fasting glucose. We used high frequency (HF) and the ratio of low frequency to high frequency (LF/HF) obtained by pulse wave analysis to estimate autonomic nervous system activity. The data were analyzed using a generalized estimating equation adjusted for potential confounders (age, gender, engagement in shift work, sleep duration, and body mass index). Fasting glucose was significantly negatively related to HF, the parasympathetic component during sleep. Our results suggest that parasympathetic activity during sleep is associated with fasting glucose in apparently healthy Japanese workers.

β-Blocker Prophylaxis for Atrial Fibrillation After Coronary Artery Bypass Grafting in Patients With Sympathovagal Imbalance

BACKGROUND

Atrial fibrillation (AF) is the most common arrhythmia after coronary bypass grafting (CABG) resulting in a prolonged hospital stay and higher costs. The withdrawal of beta-blocker and a sympathovagal imbalance were identified as risk factors for AF.

METHODS

In our study we performed a measuring of standard deviation of all normal RR intervals (SDNN) among 142 consecutive patients with beta-blocker therapy before CABG in order to identify a collective who had an increased risk due to a withdrawal of beta-blocker medication. A sympathovagal imbalance was predefined as a SDNN below 30 ms. Patients were divided into four groups according to the results of SDNN and the continuous beta-blocker therapy: group I: SDNN < or = 30 ms or less and withdrawal of beta-blocker therapy (26 patients); group II: SDNN < or = 30 ms and continuously beta-blocker therapy (33 patients); group III: SDNN > 30 ms and withdrawal of beta-blocker therapy (40 patients); group IV: SDNN > 30 ms and continuous beta-blocker therapy (43 patients).

RESULTS

Atrial fibrillation occurred in 39 patients (27%) after surgery. Patients of group I showed a higher incidence of AF (14 of 26 patients, 54%) than patients of group II (7 of 33 patients, 21%; p < 0.009), patients of group III (8 of 40 patients, 20%; p < 0.004), or patients of group IV (10 of 43 patients, 23%; p < 0.01). We found a significantly higher incidence of diabetes mellitus (47 vs 14% of patients; p < 0.0001) in patients with a sympathovagal imbalance than patients with a SDNN above 30 ms.

CONCLUSIONS

The results of our study suggest a sympathovagal imbalance and withdrawal of a beta-blocker therapy increase the risk of postoperative AF. A continuous beta-blocker therapy reduces the risk especially in patients with a sympathovagal imbalance and should always be practiced.

Microalbuminuria, cardiovascular autonomic dysfunction, and insulin resistance in patients with type 2 diabetes mellitus

Urinary albumin excretion/microalbuminuria and cardiovascular autonomic dysfunction are associated with high mortality in type 2 diabetic patients. We tested the hypothesis that the presence of microalbuminuria would correlate with cardiovascular autonomic dysfunction and insulin resistance in type 2 diabetic patients. The study group consisted of 15 Japanese patients with type 2 diabetes and microalbuminuria (age: 56 +/- 10 years, mean +/- SD). The control group consisted of 19 age-matched patients with normalbuminuria (56 +/- 7 years). Cardiovascular autonomic function was assessed by baroreflex sensitivity (BRS), heart rate variability, plasma norepinephrine concentration, and cardiac 123I-metaiodobenzylguanidine (MIBG) scintigraphy. BRS was lower in the microalbuminuria group than in the normalbuminuria group (P < .05). Early and delayed 123I-MIBG myocardial uptake values were lower (P < .05 and P < .005, respectively) and the percent washout rate of 123I-MIBG was higher (P < .0005) in the microalbuminuria group than in the normalbuminuria group. Fasting plasma glucose (P < .05) and insulin concentrations (P < .05), and the homeostasis model assessment (HOMA) index (P < .01) were higher in the microalbuminuria group than in the normalbuminuria group. Multiple regression analysis showed that urinary albumin excretion was independently predicted by the myocardial uptake of 123I-MIBG at delayed phase, fasting plasma insulin concentration, and the HOMA index. Our results indicate that the presence of microalbuminuria in our Japanese patients with type 2 diabetes is characterized by depressed cardiovascular autonomic function and insulin resistance, and that the myocardial uptake of 123I-MIBG at delayed phase, fasting plasma insulin, and HOMA index are independent predictors of urinary albumin excretion.

Standardized tests of heart rate variability: normal ranges obtained from 309 healthy humans, and effects of age, gender, and heart rate

The authors undertook this study to determine the effects of age, gender, and heart rate (HR) on the results of cardiac autonomic function tests for measuring heart rate variability (HRV) in a large sample of healthy subjects (n = 309). Conventional tests (deep breathing, maximum/minimum 30:15 ratio), and a standardized 5-minute resting study, including spectral analysis of HR, were used. The main findings included (1) the indices of all tests, except for the ratio of the low- (LF) to high-frequency (HF) spectral power (LF/HF ratio) and HR itself, are inversely related to age in both sexes; (2) the 5-minute spectral bands (except for the LF/HF ratio), the variation coefficient, expiratory-inspiratory ratio during deep breathing, and the maximum/minimum 30:15 ratio are independent of HR; (3) women up to the age of 55 years have a higher resting HR compared with men; (4) young and middle-aged women show a significantly lower LF power and LF/HF ratio compared with age-matched men, whereas no significant gender differences are observed in the absolute HF power. The authors computed age- and gender-dependent normal values for each of the HRV indices studied here and discuss the clinical consequences arising from gender differences in HRV.

Autonomic neuropathy in nondiabetic offspring of type 2 diabetic subjects is associated with urinary albumin excretion rate and 24-h ambulatory blood pressure: the Fredericia Study

The aim of this study was to examine the impact of parental type 2 diabetes on the autonomic nervous system and to determine whether autonomic neuropathy is present and associated with changes in 24-h ambulatory blood pressure (AMBP) and urinary albumin excretion rate (UAER) in nondiabetic subjects with parental type 2 diabetes. We examined 223 nondiabetic offspring of type 2 diabetic subjects and a control group of 258 offspring of nondiabetic subjects. The autonomic nervous system was assessed by three cardiovascular reflex tests, 24-h AMBP was measured with an oscillometric recorder (90207; Spacelabs, Redmond, WA), and UAER was determined through three overnight urine samples. The subjects with parental type 2 diabetes had significantly lower heart rate variation in all three bedside tests (P < 0.01) than subjects without parental diabetes. The prevalence of autonomic neuropathy in the nondiabetic offspring with parental type 2 diabetes (6.7%) was significantly (P < 0.01) higher compared with the control group (1.6%). Autonomic neuropathy was associated with a higher fasting insulin level (P < 0.05), higher UAER (P < 0.001), higher 24-h mean AMBP (P < 0.01), and reduced diurnal blood pressure variation (P < 0.001) after adjustment for age, sex, and BMI. In conclusion, parental type 2 diabetes was found to be associated with alterations in the autonomic nervous system in nondiabetic subjects. The presence of autonomic neuropathy in subjects with parental type 2 diabetes was associated with higher UAER, fasting insulin level, and 24-h AMBP and a reduced diurnal blood pressure variation. This study indicates that parental type 2 diabetes has an impact on the cardiac autonomic function in nondiabetic subjects.

Association of hyperglycemia with reduced heart rate variability (The Framingham Heart Study)

This study was designed to examine the association of heart rate variability (HRV) with blood glucose levels in a large community-based population. Previous reports have shown HRV to be reduced in diabetics, suggesting the presence of abnormalities in neural regulatory mechanisms. There is scant information about HRV across the spectrum of blood glucose levels in a population-based cohort. One thousand nine hundred nineteen men and women from the Framingham Offspring Study, who underwent ambulatory electrocardiographic recordings at a routine examination, were eligible. HRV variables included the SD of normal RR intervals (SDNN), high-frequency (HF, 0.15 to 0.40 Hz) and low-frequency (LF, 0.04 to 0.15 Hz) power, and LF/HF ratio. Fasting plasma glucose levels were used to classify subjects as normal (<110 mg/dl; n = 1, 779), as having impaired fasting glucose levels (110 to 125 mg/dl; n = 56), and as having diabetes mellitus (DM >/=126 mg/dl or receiving therapy; n = 84). SDNN, LF and HF power, and LF/HF ratio were inversely related to plasma glucose levels (p <0.0001). SDNN and LF and HF powers were reduced in DM subjects (4.28 +/- 0.03, 6.03 +/- 0. 08, and 4.95 +/- 0.09) and in subjects with impaired fasting glucose levels (4.37 +/- 0.04, 6.26 +/- 0.10, and 5.06 +/- 0.11) compared with those with normal fasting glucose (4.51 +/- 0.01, 6.77 +/- 0.02, and 5.55 +/- 0.02, all p <0.005), respectively. After adjusting for covariates (age, sex, heart rate, body mass index, antihypertensive and cardiac medications, systolic and diastolic blood pressures, smoking, and alcohol and coffee consumption), LF power and LF/HF ratio were lower in DM subjects than in those with normal fasting glucose (p <0.005). HRV is inversely associated with plasma glucose levels and is reduced in diabetics as well as in subjects with impaired fasting glucose levels. Additional research is needed to determine if low HRV contributes to the increased cardiovascular morbidity and mortality described in subjects with hyperglycemia.