Cardiovascular autonomic neuropathy (expiration and inspiration ratio) in type 1 diabetes. Incidence and predictors

A new test for autonomic cardiovascular and neuroendocrine responses in diabetes mellitus: evidence for early vagal dysfunction

AIMS/HYPOTHESIS

Diabetic autonomic neuropathy affects many physiological systems, producing a variety of important clinical manifestations. It is associated with high morbidity and mortality, particularly during times of stress. This is thought to be due to an increased risk of cardiac arrhythmias, although the exact mechanisms involved have yet to be fully elucidated. The aim of the present study was to investigate the endocrine, cardiac autonomic and psychological responses of diabetic patients with and without autonomic neuropathy to a single breath of 35% CO(2).

METHODS

The 35% CO(2) challenge was performed in 20 male diabetic subjects, 11 of whom had autonomic neuropathy.

RESULTS

Baseline and stimulated cortisol, prolactin, systolic blood pressure and emotional arousal were similar in the two groups. However, subjects with autonomic neuropathy failed to demonstrate the expected CO(2)-induced bradycardia seen in the non-neuropathic patients (p<0.0001).

CONCLUSIONS/INTERPRETATION

The CO(2) challenge can be safely and easily administered to produce hypothalamic-pituitary-adrenal axis and cardiac autonomic activation, as well as emotional arousal. The test clearly distinguishes between subjects with and without cardiac autonomic neuropathy and could be an important adjunct to the methods currently available for the investigation and diagnosis of diabetic autonomic neuropathy.

Risk factors for cardiac autonomic neuropathy in type 1 diabetes mellitus

AIMS/HYPOTHESIS

Cardiac autonomic neuropathy (CAN) is associated with increased morbidity and mortality in type 1 diabetes. Apart from glycaemic control, risk factors for CAN have not been extensively studied.

METHODS

As part of the EURODIAB Prospective Complications Study, CAN--defined as either a loss of heart rate variability or postural hypotension on standing--was assessed at baseline and follow-up (7.3+/-0.6 years from baseline) in patients with type 1 diabetes.

RESULTS

Follow-up measurements were available for 956 participants without CAN at baseline (age at baseline 31.3+/-8.9 years, duration of diabetes 13.5+/-8.3 years). During follow-up, 163 (17%) subjects developed CAN, yielding an incidence of 23.4 per 1,000 person-years. Blood pressure, weight, the presence of cardiovascular disease, albuminuria, distal symmetrical polyneuropathy (DSP) and retinopathy at baseline were associated with the incidence of CAN after adjustment for sex, duration of diabetes and HbA(1)c. In a multivariate regression model, baseline factors associated with an increased risk of developing CAN were age [odds ratio (OR)=1.3 per decade, 95% CI 1.1-1.7], HbA(1)c (OR=1.2 per percentage point, 95% CI 1.1-1.4), systolic blood pressure (OR=1.1 per 10 mmHg, 95% CI 1.0-1.3), feeling faint on standing (OR=2.0, 95% CI 1.2-3.2), DSP (OR=1.9, 95% CI 1.2-3.0) and retinopathy (OR=1.7, 95% CI 1.1-2.6).

CONCLUSION/INTERPRETATION

This study confirms the importance of exposure to hyperglycaemia as a risk factor for CAN. A small set of variables, including HbA(1)c, hypertension, DSP and retinopathy, predict the risk of CAN. Clinical trials are needed to address the impact of intensive antihypertensive treatment on CAN in type 1 diabetes.

Marked abnormalities in heart rate variability are associated with progressive deterioration of renal function in type I diabetic patients with overt nephropathy

BACKGROUND

Cardiac autonomic neuropathy is a common complication of long-standing, type 1 diabetes and is associated with increased morbidity and mortality. Impaired heart rate variability is a sensitive and reproducible marker of cardiac autonomic neuropathy. We sought to examine the relationship between cardiac autonomic neuropathy as assessed by heart rate variability and overt nephropathy, with emphasis on the progression of renal dysfunction over 1 year.

METHOD

Baseline and 12 month clinical and biochemical characteristics, as well as autonomic function tests, were analyzed in 23, type 1 diabetic patients (mean age 37+/-10 years, 65% males), who were prospectively enrolled as a part of a multi-center investigation. In addition, ambulatory, 24-h, 3-channel electrocardiograms were recorded, and heart rate variability indices were assessed in the time and frequency domains over the same period.

RESULTS

All heart rate variability indices were markedly decreased in our study population. On univariate analysis, heart rate variability was associated with creatinine clearance, and to a lesser extent, mean 24-h blood pressures and cholesterol. On multivariate analysis, only heart rate variability was a significant and independent predictor of abnormalities in creatinine clearance. Severe reduction in heart rate variability at baseline was also significantly associated with the further deterioration in renal function at 1 year.

CONCLUSION

Heart rate variability is significantly reduced in long-standing, type 1 diabetics with proteinuria or overt nephropathy. Marked abnormalities in heart rate variability are significantly associated with and predictive of progressive renal deterioration at 1 year. These findings may have implications for aggressive medical intervention to improve prognosis and survival in this population.

Autonomic neuropathy is associated with increased cardiovascular risk factors: the EURODIAB IDDM Complications Study

AIMS

To assess the prevalence of and risk factors for autonomic neuropathy in the EURODIAB IDDM Complications Study.

METHODS

The study involved the examination of randomly selected Type I (insulin-dependent) diabetic patients from 31 centres in 16 European countries. Neuropathic symptoms and two tests of autonomic function (changes in heart rate and blood pressure from lying to standing) were assessed and data from 3007 patients were available for the present analysis. Autonomic neuropathy was defined as an abnormality of at least one of the tests.

RESULTS

The prevalence of autonomic neuropathy was 36% with no sex differences. The frequency of one and two abnormal reflex tests was 30% and 6%, respectively. The R-R ratio was abnormal in 24% of patients while 18% had orthostatic hypotension defined as a fall in systolic blood pressure > 20 mmHg on standing. Significant correlations were observed between autonomic neuropathy and age (P < 0.01), duration of diabetes (P < 0.0001), HbA1c (P < 0.0001), diastolic blood pressure (P < 0.05), lower HDL-cholesterol (P < 0.01), the presence of retinopathy (P < 0.0001) and albuminuria (P < 0.0001). New associations have been identified from the study: the strong relationship of autonomic neuropathy to cigarette smoking (P < 0.01), total cholesterol/HDL-cholesterol ratio (P < 0.05) and fasting triglyceride (P < 0.0001). As a key finding, autonomic neuropathy was related to the presence of cardiovascular disease (P < 0.0001). All analyses were adjusted for age, duration of diabetes and HbA1c. However, data have been only partly confirmed by logistic regression analyses. Frequency of dizziness on standing up was 18%, while only 4% of patients had nocturnal diarrhoea and 5% had problems with bladder control.

CONCLUSION

Cardiovascular reflex tests, even in the form of the two tests applied, rather than a questionnaire, seem to be appropriate for the diagnosis of autonomic neuropathy. The study has identified previously known and new potential risk factors for the development of autonomic neuropathy, which may be important for the development of risk reduction strategies. Our results may support the role of vascular factors in the pathogenesis of autonomic neuropathy.

Relationship between autonomic function, 24-h blood pressure, and albuminuria in normotensive, normoalbuminuric patients with Type 1 diabetes

We performed a battery of cardiovascular reflex tests, 24-h ambulatory blood pressure (AMBP) and 24-h urinary albumin excretion (UAE) in 116 normoalbuminuric and normotensive patients with Type 1 diabetes. Tests of heart rate variation (HRV) included the coefficient of variation (CV) and the low-frequency (LF), mid-frequency (MF), and high-frequency (HF) bands of spectral analysis at rest, HRV during deep breathing (CV, mean circular resultant--MCR), Valsalva ratio, and maximum/minimum 30:15 ratio. Autonomic neuropathy, characterized as an abnormality of more than two tests, was found in 33 patients. Patients with neuropathy compared to those without neuropathy showed significantly higher mean day and night diastolic blood pressure (dBP), mean systolic night blood pressure (sBP), and mean day and night heart rate (HR). Mean night dBP was inversely related to MF, HF, and HRV during deep breathing; mean day dBP and mean night sBP to HF; mean night HR to CV at rest, MF, HF, HRV during deep breathing, 30:15 ratio; mean day HR to HF, HRV during deep breathing, Valsalva, and 30:15 ratio. Mean 24-h UAE was not significantly different in neuropathic than in nonneuropathic patients. UAE was inversely related to CV at rest and HF. In the stepwise multiple regression analysis, reduced MF, HF, HRV during deep breathing, and high levels of UAE and HbA1c were associated with high night dBP. Autonomic neuropathy is already present in normotensive Type 1 diabetic patients at the normoalbuminuric stage and related to BP and albuminuria.

Type 1 diabetes mellitus, xerostomia, and salivary flow rates

OBJECTIVE

The Oral Health Science Institute at the University of Pittsburgh has completed a cross-sectional epidemiologic study of 406 subjects with type 1 diabetes and 268 control subjects without diabetes that assessed the associations between oral health and diabetes. This report describes the prevalence of dry-mouth symptoms (xerostomia), the prevalence of hyposalivation in this population, and the possible interrelationships between salivary dysfunction and diabetic complications.

STUDY DESIGN

The subjects with diabetes were participants in the Pittsburgh Epidemiology of Diabetes Complications study who were enrolled in an oral health substudy. Control subjects were spouses or best friends of participants or persons recruited from the community through advertisements in local newspapers. Assessments of salivary function included self-reported xerostomia measures and quantification of resting and stimulated whole saliva flow rates.

RESULTS

Subjects with diabetes reported symptoms of dry mouth more frequently than did control subjects. Salivary flow rates were also impaired in the subjects with diabetes. Regression models of potential predictor variables were created for the 3 self-reported xerostomia measures and 4 salivary flow rate variables. Of the medical diabetic complications studied (ie, retinopathy, peripheral and autonomic neuropathy, nephropathy, and peripheral vascular disease), only neuropathy was found to be associated with xerostomia and decreased salivary flow measures. A report of dry-mouth symptoms was associated with current use of cigarettes, dysgeusia (report of a bad taste), and more frequent snacking behavior. Xerogenic medications and elevated fasting blood glucose concentrations were significantly associated with decreased salivary flow. Resting salivary flow rates less than 0.01 mL/min were associated with a slightly higher prevalence of dental caries. Subjects who reported higher levels of alcohol consumption were less likely to have lower rates of stimulated salivary flow.

CONCLUSIONS

Subjects with type 1 diabetes who had developed neuropathy more often reported symptoms of dry mouth as well as symptoms of decreased salivary flow rates. Because of the importance of saliva in the maintenance and the preservation of oral health, management of oral diseases in diabetic patients should include a comprehensive evaluation of salivary function.