Cardiovascular autonomic function testing: an automated method for measuring heart rate variation

SUDOSCAN: A Simple, Rapid, and Objective Method with Potential for Screening for Diabetic Peripheral Neuropathy

Clinical methods of detecting diabetic peripheral neuropathy (DPN) are not objective and reproducible. We therefore evaluated if SUDOSCAN, a new method developed to provide a quick, non-invasive and quantitative assessment of sudomotor function can reliably screen for DPN. 70 subjects (45 with type 1 diabetes and 25 healthy volunteers [HV]) underwent detailed assessments including clinical, neurophysiological and 5 standard cardiovascular reflex tests (CARTs). Using the American Academy of Neurology criteria subjects were classified into DPN and No-DPN groups. Based on CARTs subjects were also divided into CAN, subclinical-CAN and no-CAN. Sudomotor function was assessed with measurement of hand and foot Electrochemical Skin Conductance (ESC) and calculation of the CAN risk score. Foot ESC (μS) was significantly lower in subjects with DPN [n = 24; 53.5(25.1)] compared to the No-DPN [77.0(7.9)] and HV [77.1(14.3)] groups (ANCOVA p<0.001). Sensitivity and specificity of foot ESC for classifying DPN were 87.5% and 76.2%, respectively. The area under the ROC curve (AUC) was 0.85. Subjects with CAN had significantly lower foot [55.0(28.2)] and hand [53.5(19.6)] ESC compared to No-CAN [foot ESC, 72.1(12.2); hand ESC 64.9(14.4)] and HV groups (ANCOVA p<0.001 and 0.001, respectively). ROC analysis of CAN risk score to correctly classify CAN revealed a sensitivity of 65.0% and specificity of 80.0%. AUC was 0.75. Both foot and hand ESC demonstrated strong correlation with individual parameters and composite scores of nerve conduction and CAN. SUDOSCAN, a non-invasive and quick test, could be used as an objective screening test for DPN in busy diabetic clinics, insuring adherence to current recommendation of annual assessments for all diabetic patients that remains unfulfilled.

Coexistence of impaired indices of autonomic neuropathy and diabetic nephropathy in a cohort of children with type 1 diabetes mellitus

One hundred and twenty-nine (87%) out of a county population of 150 eligible children with type 1 diabetes mellitus (DM) and 144 age- and sex-matched control children participated in a longitudinal, epidemiological study of the evolution of diabetic microvascular disease. The mean (SD) age of the children with DM was 12.4 (+/- 3.4) years with a mean DM duration of 4.5 (+/- 3.2) years and a mean HbA1c of 11.1 (+/- 2.2)%. Two sets of measurements were made over a period of 18 months. Pupillary adaptation in darkness (PD), as an index of sympathetic dysfunction, was assessed using a portable Polaroid pupillometer. Urinary albumin excretion, as an index of incipient nephropathy, was assessed in children with DM from a fraction of all voidings during two separate 48-h periods and was expressed as urinary albumin/creatinine ratio (A/C). Heart rate variation (HRV), as an index of cardiovascular autonomic dysfunction, was assessed using a heart rate monitor and computer. Blood pressure (BP) was measured using a random zero sphygmomanometer. Reduced PD was found in 14/129 (13.8%) children with DM and in 5.8% of the controls. The diabetic children with reduced PD had longer DM duration, higher HbA1c, raised diastolic BP and higher urinary A/C than those with normal PD. Fifty percent of these children also had increased A/C and impaired HRV, in addition to impaired PD. Another group of 25/129 (19.4%) children with DM presented intermittently raised mean urinary A/C, while five children presented persistently raised A/C in both 48-h urine collections. The characteristics which differentiated the microalbuminuric group from the normoalbuminuric one were older age, longer DM duration, poorer glycemic control, reduced PD, impaired HRV and raised diastolic BP. It seems that diabetic nephropathy (DN) and autonomic neuropathy (DAN) exist in concert in childhood DM. Diabetic children with impaired indices of DN and DAN are older, pubertal and have longer DM duration and higher HbA1c values than the rest of the diabetic population.

The prevalence of autonomic and peripheral neuropathy in insulin-treated diabetic subjects

The prevalence of autonomic and peripheral neuropathy was examined in 506 diabetic subjects treated with insulin, mean age 43 years, diabetes duration 15 (range 1-54) years. Autonomic neuropathy was present if two or more (of four) cardiovascular autonomic function tests were abnormal using age-related ranges derived from 310 normal control subjects. Peripheral neuropathy was defined as a vibration threshold > 95th centile for age combined with absent/impaired ankle reflexes. Eighty-four (16.6%) of diabetic subjects had abnormal autonomic function and 119 (23.5%) peripheral neuropathy, concordant in 44/506 (8.7%). Of the diabetic subjects with autonomic neuropathy 40/84 (47.6%) did not have peripheral neuropathy and only 44/119 (37.0%) with peripheral neuropathy had abnormal autonomic function (p < 0.001). The prevalence of both neuropathies increased in relation to diabetes duration (both p < 0.001). Autonomic neuropathy was more common in subjects diagnosed < 20 years of age (18.2%) vs age > 40 years (11.1%) (p < 0.05). In contrast peripheral neuropathy was more common with older age at diagnosis (< 20 years 13.5% vs 36.8% > 40 years, p < 0.001). The age-related prevalence of autonomic neuropathy peaked at age 40-49 years while peripheral neuropathy increased progressively with age (p < 0.001). The prevalence of peripheral exceeded autonomic neuropathy 20 years after diagnosis (40.2% vs 30.7%, p < 0.001).

Pupil size in diabetes

Sympathetic function was studied in 101 diabetic children and 102 age and sex matched control children, as part of a longitudinal study of the evolution of microvascular disease in the population of diabetic children and adolescents in Avon County. The median (range) age of the diabetic population was 13.5 (6.0-17.2) years, the duration of diabetes was 4.0 (0.4-13.9) years, and glycated haemoglobin (HbA1) was 10.9 (7.0-18.1)%. Pupillary adaptation in darkness, as an index of sympathetic neuropathy, was measured using a Polaroid portable pupillometer. Diabetic children had a significantly smaller median pupillary diameter, measured as the pupil/iris ratio and expressed as a percentage, than control children (median (range) 62.9 (50.3-72.1) v 65.9 (52.2-73.8)). Pupillary diameter was significantly related to diabetes duration (r = -0.22), HbA1 (r = -0.34), systolic blood pressure (r = -0.25), diastolic blood pressure (r = -0.49), and mean albumin/creatinine ratio on random urine samples (r = -0.26). Pupillary diameter was not related to age (r = -0.1). Eight (7.9%) diabetic and four (3.9%) control children were identified as having abnormal pupillary dilation in darkness. In comparison with the rest of the diabetic population, these diabetic children had longer diabetes duration and poorer glycaemic control. Polaroid pupillometry has demonstrated subclinical autonomic neuropathy in a population of diabetic children and adolescents. These abnormalities were related to poor metabolic control, long diabetes duration, and also to other indices of microvascular disease.

Cardiovascular autonomic reflex tests: normal responses and age-related reference values

One hundred and forty-three healthy unmedicated subjects from a random sample, aged 20-80 years, were examined and cardiovascular autonomic function tests (Valsalva manoeuvre, deep and quiet breathing tests and active orthostatic test) were performed in order to study normal responses to these tests and to determine age-related reference values. Most of the cardiovascular indices reflecting autonomically mediated heart rate responses decline with advancing age and this leads inevitably to the need for age-related reference values. The indices are in general independent of sex but most indices are dependent on resting heart rate. The inter-individual variation is very marked so that the normal ranges are wide, and because the indices diminish with age, the lower reference values are less suitable for use in aged subjects. The reference values make it possible to use the indices for diagnostic purposes in young and middle-aged subjects (up to 65 years), whereas in older subjects the indices can be used in order to exclude autonomic disturbances. Reproducibility of heart rate indices is satisfactory or good whereas reproducibility of blood pressure indices is poor.

Hormonal response to blood volume expansion in diabetic subjects with and without autonomic neuropathy

The hormonal and renal response to volume expansion, produced by water immersion for 4 h, was studied in 14 insulin-dependent diabetic subjects (seven without complications, seven with autonomic neuropathy) and in 14 age-and-sex-matched normal control subjects. The diabetic subjects showed an impaired natriuretic response to volume expansion (total amount of sodium excreted 21 mmol compared to 39 mmol in normals, P less than 0.01) but the response did not differ in those with and without autonomic neuropathy. There was no significant difference in the suppression of plasma renin or aldosterone during immersion in either group. Plasma catecholamines suppressed on immersion in all groups. Basal values were lowest in the group with autonomic involvement. Atrial natriuretic peptide levels showed a twofold rise (from 4.8 to 9.6 pmol/l, P less than 0.01) on immersion. There was no significant difference in the levels of this hormone between diabetic patients and normal subjects or between those diabetics with and those without autonomic neuropathy. The present study confirms that diabetic subjects retain sodium avidly during volume expansion. This enhancement cannot be ascribed to any measurable difference in the levels of circulating hormones known to be involved in natriuresis and is not influenced by the presence of autonomic neuropathy.

Aldose reductase inhibition in diabetic neuropathy: clinical and neurophysiological studies of one year's treatment with sorbinil

In a double-blind placebo-controlled trial the effect of Sorbinil (250 mg daily) on diabetic neuropathy was examined. After a 2-month run-in placebo period (with three major assessments) 21 patients were randomized to Sorbinil and 10 to placebo, and all were studied for a further 12 months with neurophysiological measurements at 3-month intervals of nerve conduction velocity in multiple nerves, autonomic function tests, vibration thresholds as well as clinical examination and an extensive self-assessment of symptoms. Two subjects on Sorbinil treatment developed a hypersensitivity reaction and were withdrawn. Metabolic control and severity of neuropathy was not significantly different between groups. There were no changes in symptoms as judged by self-assessment scores. No patient entered the trial with neuropathic ulcers but ulceration developed in 4 patients during Sorbinil treatment and in 1 of the placebo group. No beneficial effect of Sorbinil was demonstrated on either the clinical manifestation or on the neurophysiological measurements made in these neuropathic diabetic patients over 12 months of treatment.

Autonomic neuropathy: its diagnosis and prognosis

Autonomic neuropathy is now well established as a relatively common and significant complication of diabetes mellitus. Its importance has been clarified in recent years during which the extent of autonomic control over all areas of body function has been defined. Using simple cardiovascular reflex tests, autonomic abnormalities can be demonstrated without any corresponding symptoms. The often stated concept of 'patchy' involvement in diabetic autonomic neuropathy should now be rejected as too should the view that autonomic neuropathy is either 'present' or 'absent' based on a single test result. When generalized and predominantly metabolic disturbances, as in diabetes, give rise to impaired nerve function, autonomic as well as somatic components of the nerve are affected. Where damage is severe this leads to the characteristic florid picture of symptomatic autonomic neuropathy with its particularly poor prognosis. For the physician in a busy clinic, much of the theoretical and experimental basis for autonomic neuropathy may not appear of direct relevance. However, he has now to be aware of the clinical implications of autonomic damage in the diabetic. This may have particular relevance in the care of the diabetic foot (see Chapter 10), the recognition of many of the vague symptoms associated with autonomic damage, the treatment of disabling features such as postural dizziness and nocturnal diarrhoea, and an awareness of the poor prognosis associated with symptomatic autonomic neuropathy. He will also need to be alert to the dangers of general anaesthesia in such patients, and the possibility of sudden unexpected deaths. Diabetic autonomic neuropathy causes widespread abnormalities, some of which are clinically apparent, some of which can be detected by sensitive tests, and others which have yet to be discovered. Inclusion of the neuropeptides and other hormones within the compass of autonomic control has opened up a whole new area of investigative interest, with many complex interrelationships which still need to be unravelled. This should lead to better understanding of the pathophysiological processes that cause damage to diabetic nerves. With so much research effort directed towards better glycaemic control and aldose reductase inhibitors (see Chapter 8), it may eventually be possible to reverse or prevent this potentially disabling and lethal complication of diabetes.

Heart rate variability in healthy subjects: effect of age and the derivation of normal ranges for tests of autonomic function

The diagnosis of autonomic neuropathy frequently depends on results of tests which elicit reflex changes in heart rate. Few well-documented normal ranges are available for these tests. The present study was designed to investigate the effect of age upon heart rate variability at rest and in response to a single deep breath, the Valsalva manoeuvre, and standing. A computerised method of measurement of R-R interval variation was used to study heart rate responses in 310 healthy subjects aged 18-85 years. Heart rate variation during each procedure showed a skewed distribution and a statistically significant negative correlation with age. Normal ranges (90% and 95% confidence limits) for subjects aged 20-75 years were calculated for heart rate difference (max-min) and ratio (max/min) and standard deviation (SD). Heart rate responses were less than the 95th centile in at least one of the four procedures in 39 (12.6%) out of the 310 subjects, and were below this limit in two or more tests in five (1.6%) subjects. In view of the decline in heart rate variation with increasing age, normal ranges for tests of autonomic function must be related to the age of the subject.

Oesophageal function in diabetes mellitus and its association with autonomic neuropathy

We have evaluated oesophageal function in 34 diabetics and in 16 non-diabetic controls by a timed bolus transit method derived from dynamic oesophageal scintiscans (water transit time: WTT) and barium swallow. The diabetics were screened for autonomic neuropathy using standard cardiovascular responses and 10 patients were classified as abnormal. WTT was significantly prolonged in autonomic neuropaths compared with other diabetics (p less than 0.01) and controls (p less than 0.001). Abnormal peristalsis on barium swallow was seen more frequently in autonomic neuropaths (9/10) than in other diabetics (11/24, p less than 0.002). WTTs from all diabetic patients correlated with abnormal heart rate responses at rest (Rs = - 0.49, p less than 0.005), on deep inspiration (Rs = -0.48, p less than 0.005), and on standing (Rs = -0.39, p less than 0.025) but not with the Valsalva manoeuvre. A weaker correlation was found between the postural fall in blood pressure (Rs = 0.3, p less than 0.05). Diabetics with autonomic neuropathy frequently have asymptomatic oesophageal dysfunction which may result from a vagal neuropathy in view of its association with abnormalities of vagally mediated cardiovascular responses.