Cardiac autonomic neuropathy in diabetes: comparison of measures of R-R interval variation

Improvement in diabetic neuropathy 4 years after successful pancreatic and renal transplantation

We have studied the fate of diabetic neuropathy and autonomic function in 13 patients with long standing Type 1 (insulin-dependent) diabetes mellitus following combined pancreas and kidney transplantation. Fifteen diabetic patients with a kidney graft only served as controls. After initial improvement of the neuropathy in both groups, probably caused by the elimination of uraemia, a continuous improvement during the 48 months study was seen in the euglycaemic pancreas graft recipients only. Autonomic (parasympathetic) function improved only slightly and to a similar extent in both groups.

Nocturnal airflow obstruction, histamine, and the autonomic central nervous system in children with allergic asthma

A study was carried out to investigate whether an imbalance in the autonomic nervous system or release of histamine, or both, is responsible for the nocturnal increase in airflow obstruction in asthmatic children. The study comprised 18 children with allergic asthma, nine with (group 1) and nine without (group 2) nocturnal airflow obstruction, and an age matched control group. All drugs were withheld for three days before and during the study. On day 4 each child was admitted to hospital and a series of measurements was made every four hours for 24 hours. These included measurements of the forced expiratory volume in one second (FEV1), heart rate and sinus arrhythmia gap from an electrocardiogram (an indirect measure of parasympathetic activity) and urine sampling for determination of catecholamine and N'-methylhistamine concentrations (measures of sympathetic activity and histamine release respectively). Urinary N'-methylhistamine excretion was significantly higher over the 24 hours in children in group 1 than in children in group 2, and overnight values were also significantly higher in children in group 1 than those in group 2. Mean (SEM) values (mumol/mol creatinine) were 154.6 (11.2) in group 1 and 110 (11.2) in group 2 for 2400-0400 hours samples and 139.2 (13.1) and 101.2 (10.6) 0400-0800 hours samples. There was no evidence of decreased sympathetic or increased parasympathetic activity in association with the nocturnal airflow obstruction; noradrenaline concentrations were increased in group 1. These observations indicate that nocturnal airflow obstruction is associated with increased release of histamine overnight.

Effect of lead on cardiac parasympathetic function

A cross-sectional survey was performed on 172 male, lead exposed workers to clarify the effects of lead on the cardiac autonomic nervous system expressed as the decrease of R-R interval variation on an electrocardiogram and to obviate the dose-effect relationship between blood-lead level (Pb-B) and the degree of the decrease. For 132 workers who were exposed to lead for more than one year and whose Pb-B levels were relatively stable (Pb-B variation less than 20 micrograms/dl during recent one year), a significant dose-related decrease of R-R interval variation during deep breathing was observed. Age-adjusted R-R interval variation during deep breathing in those whose Pb-B were 30 micrograms/dl or above was significantly decreased compared with those whose Pb-B levels were 20 micrograms/dl or below. This decrease was observed more clearly in younger workers. These results suggest that an effect on autonomic nervous system expressed as decrease of R-R interval variation during deep breathing might be one of the earliest effects of lead exposure.

Effect of coronary arterial occlusion on vagal control of heart rate

Diminished variation in heart rate as a sign of impaired vagal control is common in coronary arterial disease. To evaluate the effect of short-term myocardial ischaemia induced by coronary arterial occlusion during therapeutic percutaneous transluminal coronary angioplasty we measured the variation in heart rate during controlled deep breathing in 50 patients before and during arterial occlusion. Variation in heart rate diminished from 11.1 +/- 4.5 to 9.5 +/- 5.1 beats/min (P less than 0.01) during occlusion. No change occurred in heart rate, blood pressure or levels of noradrenaline and adrenaline. The attenuation of variation in the heart rate was not significantly associated with the site or duration of arterial occlusion nor concomitant chest pain. Thus, brief coronary arterial occlusion seems to be associated with impairment of the vagal control of heart rate in patients with coronary arterial disease.

Heart rate variability and cardiac autonomic function in men with chronic alcohol dependence

Cardiac autonomic function was studied in 23 alcohol dependent men by standard tests of autonomic function and measurement of 24 hour heart rate variability. In all there was peripheral or central nervous system damage or both. Standard tests of autonomic function showed vagal neuropathy in seven. The remainder had normal autonomic function tests. Twenty four hour heart rate variability was measured as the standard deviation of the successive differences between RR intervals from an ambulatory electrocardiogram recording. Twenty four hour heart rate variability was significantly lower in both alcohol dependent groups than in controls, but the results in the two alcohol dependent groups were not significantly different from each other. The results of standard tests of autonomic function did not distinguish between the alcohol dependent men with normal autonomic function and controls. The differences in heart rate variability between this group and the controls may have been the result of the ability of this method to detect small changes in autonomic integrity. Cardiomyopathy may also account for some of these differences and such abnormalities should be excluded before results are to be regarded as a reflection of vagal function. Twenty four hour measurement of heart rate variability may be a more useful index of cardiac vagal neuropathy than currently available tests of autonomic function.

Accuracy of assessment of cardiac vagal tone by heart rate variability in normal subjects

The correlations of 11 indexes of heart rate variability were examined with pharmacologically determined cardiac vagal tone in 15 normal subjects at supine rest. After sympathetic influences by intravenous propranolol were eliminated, RR interval variability was measured for 10 minutes under controlled respiration (0.25 Hz), and cardiac vagal tone was determined as the decrease in mean RR interval following complete vagal blockade with atropine. Time domain indexes (standard deviation, coefficient of variance and mean successive difference) correlated strongly with vagal tone (r = 0.87, 0.81 and 0.92, respectively; p less than 0.001 for all). The same was true for frequency domain indexes for the high-frequency (0.25 Hz) component calculated both by autoregressive spectrum analysis (square root of power and coefficient of component variance) and by fast Fourier transform (mean amplitude) (r = 0.91, 0.85 and 0.86, respectively; p less than 0.0001 for all). However, frequency domain indexes for the low-frequency spectral component (0.03 to 0.15 Hz) correlated less strongly (r = 0.69, 0.55 and 0.70, respectively), and the fraction of power [power/(total power greater than 0.03 Hz)] of both components showed no correlation. Principal component analysis showed that the first 6 indexes with strong correlations contained solely the first principal component closely related to vagal tone, whereas the remaining 5 indexes also contained the second component unrelated to vagal tone. These results indicate that most of the time and frequency domain analyses in use provides an accurate and common measure of cardiac vagal tone at rest.

Autonomic response to an experimental psychological stressor in healthy subjects: measurement of sympathetic, parasympathetic, and pituitary-adrenal parameters: test-retest reliability

A mental arithmetic test (the stressor; 15 min) significantly increased systolic and diastolic blood pressure, heart rate and plasma adrenaline by 11%, 12%, 28% and 152% respectively, with a prompt return to resting values after the test. Plasma noradrenaline and serum cortisol did not increase significantly during the 15 min of stress. Afterwards, however, the concentrations of both hormones increased, resulting in a total and significant increase averaging 19% and 23%, respectively. Plasma adrenocorticotrophic hormone (ACTH) did not rise significantly, but it was only measured before and at the end of the stressor. As a measure of parasympathetic nervous function, the beat-to-beat variation of heart rate, expressed as the mean successive square difference (MSSD), was employed. Four to 14 months later, the investigation was repeated, and resting values of all measures were found to be stable. The increments in systolic blood pressure and heart rate were significantly lower at retest. MSSD at stress, but not at rest, was significantly lower at retest. The mental arithmetic stress test as described here produces a sufficient autonomic response to make it viable for laboratory stress research. However, if repeated examinations are desired, the lower response at retest should be taken into consideration.

Unawareness of hypoglycaemia and inadequate hypoglycaemic counterregulation: no causal relation with diabetic autonomic neuropathy

OBJECTIVE

To examine the traditional view that unawareness of hypoglycaemia and inadequate hypoglycaemic counterregulation in insulin dependent diabetes mellitus are manifestations of autonomic neuropathy.

DESIGN

Perspective assessment of unawareness of hypoglycaemia and detailed assessment of autonomic neuropathy in patients with insulin dependent diabetes according to the adequacy of their hypoglycaemic counterregulation.

SETTING

One routine diabetic unit in a university teaching hospital.

PATIENTS

23 Patients aged 21-52 with insulin dependent diabetes mellitus (seven with symptoms suggesting autonomic neuropathy, nine with a serious clinical problem with hypoglycaemia, and seven without symptoms of autonomic neuropathy and without problems with hypoglycaemia) and 10 controls with a similar age distribution, without a personal or family history of diabetes.

MAIN OUTCOME MEASURES

Presence of autonomic neuropathy as assessed with a test of the longest sympathetic fibres (acetylcholine sweatspot test), a pupil test, and a battery of seven cardiovascular autonomic function tests; adequacy of hypoglycaemic glucose counterregulation during a 40 mU/kg/h insulin infusion test; history of unawareness of hypoglycaemia; and response of plasma pancreatic polypeptide during hypoglycaemia, which depends on an intact and responding autonomic innervation of the pancreas.

RESULTS

There was little evidence of autonomic neuropathy in either the 12 diabetic patients with a history of unawareness of hypoglycaemia or the seven patients with inadequate hypoglycaemic counterregulation. By contrast, in all seven patients with clear evidence of autonomic neuropathy there was no history of unawareness of hypoglycaemia and in six out of seven there was adequate hypoglycaemic counterregulation. Unawareness of hypoglycaemia and inadequate hypoglycaemic counterregulation were significantly associated (p less than 0.01). The response of plasma pancreatic polypeptide in the diabetic patients with adequate counterregulation but without autonomic neuropathy was not significantly different from that of the controls (change in plasma pancreatic polypeptide 226.8 v 414 pmol/l). The patients with autonomic neuropathy had a negligible plasma pancreatic polypeptide response (3.7 pmol/l), but this response was also blunted in the patients with inadequate hypoglycaemic counterregulation (72.4 pmol/l) compared with that of the controls (p less than 0.05).

CONCLUSIONS

Unawareness of hypoglycaemia and inadequate glucose counterregulation during hypoglycaemia are related to each other but are not due to autonomic neuropathy. The blunted plasma pancreatic polypeptide responses of the patients with inadequate hypoglycaemic counterregulation may reflect diminished autonomic activity consequent upon reduced responsiveness of a central glucoregulatory centre, rather than classical autonomic neuropathy.

In vivo evidence that human atrial natriuretic factor-(99-126) (hANF) stimulates parasympathetic activity in man

In a double-blind study 8 healthy male subjects received 100 micrograms human atrial natriuretic facotr-(99-126) (hANF) and NaCl0.9% in random order on different days. Following hANF injection a significant increase in cardiac beat-to-beat variation was observed (4.65% vs 5.95%). This shows that in vivo human atrial natriuretic factor stimulates cardiac parasympathetic activity in man.

Respiratory sinus arrhythmia is a limited measure of cardiac parasympathetic control in man

1. Respiratory modulation of cardiac parasympathetic activity and the relationship between respiratory sinus arrhythmia and parasympathetic control has been studied in twenty-nine conscious, healthy young adult subjects. 2. Changes in heart period in propranolol-treated subjects were taken as the measure of changes in cardiac parasympathetic activity; respiratory sinus arrhythmia was quantified as the difference between maximum and minimum heart periods in a given respiratory cycle; cardiac parasympathetic control was defined as the change in heart period after administration of a full dose of atropine. 3. During normal quiet breathing the inspiratory level of cardiac parasympathetic activity was not reduced to zero. The expiratory level was influenced by excitatory inputs whose activation was related to respiratory cycle length. 4. Slow breathing was associated with augmented sinus arrhythmia, but in different individuals the influence on minimum and maximum heart periods varied so that mean heart period was increased in some subjects but decreased in others. This occurred both in control conditions and after administration of a full dose of propranolol. 5. During normal breathing the correlation across subjects between respiratory sinus arrhythmia and parasympathetic control, although significant, was not close (r = 0.61). The relationship was not affected by beta-adrenergic blockade (r = 0.63). The strength of the correlation improved when multiple regression of respiratory sinus arrhythmia was performed on three variables: parasympathetic control, respiratory cycle length and tidal volume (R = 0.93). 6. It is concluded that in conscious human subjects the respiratory modulation of cardiac parasympathetic activity is different from that observed in the anaesthetized dog, and that variations in the amplitude of respiratory sinus arrhythmia do not necessarily reflect proportional changes in cardiac parasympathetic control.

The prevalence of autonomic neuropathy in the primary glaucomas

The results of systemic autonomic nerve function studies in patients with closed-angle glaucoma and ocular hypertension are reviewed. Autonomic neuropathy has been demonstrated in 58% of patients with closed-angle glaucoma and 42% of ocular hypertensive subjects, with significantly increased prevalence in ocular hypertensives with narrow iridocorneal angles. The implications are discussed, with particular reference to the pathogenesis of raised intraocular pressure.

Influence of cardiovascular diseases upon the results of the cardiovascular reflex tests in diabetic and nondiabetic subjects

Cardiovascular reflex tests are used to assess cardiac autonomic neuropathy in diabetes mellitus. Cardiovascular diseases (CVD) are known to alter baroreflex mechanisms. Diabetic patients are at a high risk for cardiovascular complications. In order to prove whether cardiovascular diseases reduce the diagnostic value of the cardiovascular reflex tests in diabetic autonomic neuropathy unselected groups of 274 nondiabetic and 103 diabetic patients were studied: E/I, 30/15, and Valsalva ratios, sustained handgrip test and blood pressure response to standing. Both groups were subdivided into young (less than or equal to 45 years) and older (greater than 45 years) patients and into subjects with and without CVD. In young nondiabetic patients with CVD, E/I and Valsalva ratios were significantly lower than in those without CVD. In young diabetic patients with CVD, only E/I ratios were significantly reduced compared to those without CVD. The tests reflecting sympathetic nerve function did not differ between patients with and without CVD, neither in the nondiabetic nor in the diabetic subjects. In the older nondiabetic and diabetic patients, cardiovascular reflexes were generally impaired, but did not show any difference between subjects with and without CVD. In young diabetic patients suffering from CVD, the diagnostic value of cardiovascular reflex tests is reduced as far as cardiac autonomic neuropathy is concerned. In older patients, the tests are not suitable for the diagnosis of diabetic autonomic neuropathy. More specific methods are required.

Automatic analysis of heart rate variation: I. Method and reference values in healthy controls

Many patients referred to an electrophysiological laboratory may have autonomic dysfunction. Some parasympathetic tests are based on the assessment of heart rate variation induced by breathing, Valsalva maneuver, and standing. We have developed fast and practical computer-based methods to analyze heart rate variation using standard EMG equipment and a personal computer. For quantitative description we have evaluated different algorithms, both earlier described and new ones. Findings in patients with diabetes have been compared with those obtained from healthy subjects in order to determine the diagnostic utility of the various algorithms. The optimal algorithm has been chosen by this and other criteria, and a reference database from healthy subjects has been developed.

Fibrinolytic capacity following stimulation with desmopressin acetate in patients with diabetes mellitus

Tissue plasminogen activator (t-PA), tissue plasminogen activator inhibitor, (PAI), and von Willebrand factor (vWF) were measured in 30 diabetics and 17 control subjects. These studies were performed to clarify the role of obesity in causing abnormalities of the fibrinolytic system in diabetics. The t-PA antigen response measured after the infusion of desmopressin acetate (DDAVP) was similar in all groups. Peak responses to DDAVP for controls, type I diabetics, and type II diabetics were 21.2 +/- 9.5 ng/mL, 27.5 +/- 9.0 ng/mL, and 28.8 +/- 11.0 ng/mL (NS), respectively. These responses did not correlate with the body mass index (BMI) or any other of the indices examined. A significant decrease of t-PA activity as contrasted with t-PA antigen following DDAVP occurred in type II diabetics only. The decrease of t-PA activity strongly correlated with greater basal levels of plasminogen activator inhibitor in these same subjects. The plasma level of plasminogen activator inhibitor correlated with BMI but with no other index examined. In contrast to t-PA activity and PAI, vWF responses to DDAVP inversely correlated to basal vWF concentration in all groups. Basal concentrations of vWF were increased in both type I and II diabetics and showed no relationship to degree of obesity. In summary, these results suggest that type II diabetic subjects have decreased t-PA activity, which is best explained by increased levels of PAI. The increased PAI appears related to obesity and not diabetes per se.

Impaired parasympathetic control of heart rate after myocardial infarction

We measured the variation in heart rate during deep breathing, a sensitive non-invasive measure of cardiac parasympathetic activity, in 95 patients 3 weeks after myocardial infarction and in 40 asymptomatic healthy controls. The variation in rate was significantly lower (11.6 +/- 6.1 vs 17.6 +/- 7.3 beats/min, P less than 0.001) in patients with myocardial infarction than in controls. Forty-nine patients (52%) and 5 controls (13%) were considered to have diminished (less than or equal to 10 beats/min) variation of rate. The diminution in this variation was not related to the type or location of myocardial infarction, to maximum release of CK-MB or to cardiovascular medication. Our results suggest that impairment of vagal control of heart rate is common after myocardial infarction. The impairment cannot be predicted by any specific feature of the disease.

Diphtheritic neuropathy, an analysis based on muscle and nerve biopsy and repeated neurophysiological and autonomic function tests

A patient with diphtheritic neuropathy was investigated with repeated tests of parasympathetic and sympathetic vasomotor and sudomotor functions for one year after the onset of symptoms. Somatic nerve function was tested with nerve conduction studies and an index based on ten variables was used to follow the course of the neuropathy. Sural nerve and anterior tibial muscle biopsies were performed. A severe but shortlasting impairment of the parasympathetic vagal reflex arc was found. The recovery of this function paralleled the clinical course. Sympathetic functions were normal. The neurophysiological variables of somatic nerve function showed signs of a mainly demyelinating mixed sensory/motor neuropathy. The recovery of these variables was slow. The nerve and muscle biopsies demonstrated mild changes consistent with a mixed, demyelinating, non-inflammatory neuropathy.

Intraocular pressure responses to systemic autonomic stimulation

The intraocular pressure (IOP) responses to two standard tests of autonomic nerve function were studied in 15 healthy subjects, mean age 33 years (range: 20-64). Both tests are based on cardiovascular reflexes: (1) The rise in diastolic blood pressure provoked by sustained isometric muscle contraction, a response mediated by the sympathetic nervous system and (2) The heart-rate responses to the Valsalva manoeuvre, a response mediated by the parasympathetic nervous system. During sustained isometric exercise, the mean IOP decreased significantly from baseline values of 12.60 mmHg (SEM 0.55) to 11.26 mmHg (SEM 0.32, p less than 0.05) while mean diastolic blood pressure increased by 20.80 mmHg (range: +12 to +53 mmHg). However there was no direct correlation between them (r = -0.05). Post exercise the mean IOP remained significantly lower than baseline values for five minutes (p less than 0.01). During the Valsalva manoeuvre, there was a significant increase in IOP of 7.20 mmHg from a baseline of 12.80 mmHg (SEM 0.45) to 20.00 mmHg (SEM 0.78, p less than 0.001); during the recovery period, mean IOP was significantly lower than baseline values at 12.13 mmHg (SEM 0.39, p less than 0.05). The mean Valsalva ratio was normal at 1.68 (range: 1.2-2.6). The possible mechanisms involved in these responses are discussed.

Effect of passive tilt on sympathetic and parasympathetic components of heart rate variability in normal subjects

Decreased heart rate (HR) variability has been shown to be an independent predictor of poor outcome after acute myocardial infarction. Presumably, both reduced parasympathetic activity and increased sympathetic activity contribute to this observed HR variability response. To elucidate the physiologic contributions of the sympathetic and parasympathetic nervous systems to HR variability, the effect of passive head-up tilt (+70 degrees) was investigated on 4 indexes of HR variability in 17 healthy subjects. The standard deviation of the mean of 512 consecutive RR intervals, a traditional marker of HR variability and a purported index of cardiac parasympathetic neural tone, was compared with the mean difference of 512 consecutive RR intervals, with the maximal expiratory RR interval to minimal inspiratory RR interval ratio (respiratory RR ratio) and with the low- and high-frequency components of the power spectrum of 512 consecutive RR intervals. Passive tilt produced a nonsignificant decrease in the standard deviation of RR intervals. There was, however, a highly significant decrease in the mean difference of consecutive RR intervals and the high-frequency component of the RR-interval spectrum. Both the respiratory RR ratio and the low-frequency component of the RR-interval spectrum increased with tilt. It was concluded that the mean difference of consecutive RR intervals and the high-frequency component of the RR-interval spectrum are potentially superior indexes of "pure" parasympathetic neural tone and may be preferable for future use in cardiovascular studies of autonomic dysfunction.

Vasopressin secretion during insulin-induced hypoglycaemia: exaggerated responses in people with type 1 diabetes

Insulin hypoglycaemia causes a rise in plasma vasopressin concentrations in man and the rat, and vasopressin stimulates glucagon secretion and increases hepatic glucose output in man. Vasopressin has also been suggested to have an important synergistic role with corticotrophin releasing factor in the release of adrenocorticotrophin hormone, and a counter-regulatory role for the hormone has been proposed. As diminished anterior pituitary hormone responses to hypoglycaemia have been reported in diabetes mellitus, we studied the plasma vasopressin responses to insulin-induced hypoglycaemia in 10 patients with established Type 1 diabetes and 10 matched control subjects. Blood glucose fell from 4.5 +/- 0.3 to 1.6 +/- 0.1 mmol l-1 (p less than 0.001) in the diabetic group and from 4.6 +/- 0.2 to 1.5 +/- 0.2 mmol l-1 (p less than 0.001) in control subjects, with delayed blood glucose recovery in the diabetic patients. Plasma vasopressin rose in the diabetic patients from 0.9 +/- 0.2 to 6.9 +/- 2.8 pmol l-1 (p less than 0.001), a significantly greater rise (p less than 0.05) than in the control subjects, 0.8 +/- 0.1 to 2.4 +/- 1.0 pmol l-1 (p less than 0.001). Plasma osmolalities remained unchanged and haemodynamic changes were similar in both groups. There is an exaggerated rise in plasma vasopressin concentrations in diabetic patients in response to insulin-induced hypoglycaemia. The putative mechanisms and potential significance of the exaggerated rise are discussed.

Cardiovascular autonomic function in multiple sclerosis

The autonomic nervous function of the cardiovascular system was investigated by non-invasive methods in 30 multiple sclerosis patients between 20 and 50 years of age. The results were compared to those of 30 healthy controls in the same age group. Minor abnormalities of parasympathetic and sympathetic function occurred. Heart rate variation at deep breathing was reduced and more than half of the patients had abnormal responses during an orthostatic procedure, mainly as an increased rise in heart rate. Decreased rise in blood pressure at sustained handgrip was also demonstrated. The abnormalities correlated poorly with other clinical signs and symptoms in the patients.

Microcomputer collection and analysis of RR-interval data in the BB-rat

An analog to digital converter and microcomputer system for the collection of real-time RR-interval data in the BB-rat is described. Calculation of the statistic R is discussed and a commented program listing in Microsoft basic, for performing this transformation, is included as an appendix.

Retinal circulation responses to systemic autonomic nerve stimulation

The retinal vessel calibre responses to controlled stimulation of the autonomic nervous system were studied in 10 healthy subjects, using sustained isometric muscle contraction as stimulus. Each subject was studied twice using different mydriatic agents, (1) g.tropicamide 1% a parasympatholytic agent and (2) g. phenylephrine 10% a sympathetic agonist. In the tropicamide study, there was a mean arteriolar constriction of 8.1% (SEM 1.67, p less than 0.001) and venule constriction of 3.7% (SEM 0.85, p less than 0.001) with a mean rise in diastolic blood pressure of 27.4 mmHg (SEM 2.95, range: 13-45 mmHg). When g. phenylephrine 10% was used, there was a mean arteriolar constriction of 8.6% (SEM 1.68, p less than 0.001) and venule constriction of 4.8% (SEM 1.22, p less than 0.001) with a mean rise in diastolic blood pressure of 29.2 mmHg (SEM 2.56, range: 17-44 mmHg). There was no significant difference in retinal vessel calibre in the recovery phase compared to baseline phase (p greater than 0.05) or between the two mydriatic agents on vessel responses (p greater than 0.05). There was no correlation between the rise in diastolic blood pressure and the degree of retinal vessel constriction, during handgrip contraction in either study. This study has demonstrated a significant association between retinal vessel calibre and systemic autonomic nerve stimulation. The possible mechanisms for the retinal vessel constriction observed in this study are discussed.

RR-variation: the autonomic test of choice in diabetes

RR-variation is a sensitive, reproducible, and noninvasive autonomic test. It is simple to perform and easy for both the operator and the subject. Furthermore, RR-variation correlates to known physiologic function. It therefore fulfills many of the characteristics of a practical diagnostic test. Many of the confounding factors are known, and with proper standardization the test may not only have diagnostic capabilities but also predictive value. RR-variation should be included in clinical research trials of diabetic neuropathy and should be considered in routine clinical management of the diabetic patient.

Impaired vagal heart rate control in coronary artery disease

Heart rate variation in deep breathing, a sensitive non-invasive measure of cardiac parasympathetic activity, was measured in 63 patients with coronary artery disease, in 22 patients with atypical chest pain, and in 20 healthy symptom free volunteers. There was significantly less heart rate variation in deep breathing in the patients with coronary artery disease than in the healthy subjects. Twenty patients (32%) with coronary artery disease had lower than normal variation in heart rate. The patients with chest pain showed an intermediate heart rate response to deep breathing. Sinus arrhythmia in the patients with coronary artery disease was not related to the functional class, medication, number or location of narrowed vessels, or to the left ventricular ejection fraction, and end diastolic pressure. These results suggest that impairment of the parasympathetic nervous function is common in coronary artery disease.

Effects of combined pancreatic and renal transplantation on diabetic neuropathy: a two-year follow-up study

To investigate whether diabetic neuropathy can be reversed after pancreatic transplantation 13 diabetic patients were examined by means of conventional electroneurography and tests on autonomic function before and 6, 12, and 24 months after combined renal and pancreatic transplantation. 15 diabetic patients receiving a kidney graft only and 15 non-diabetic kidney graft recipients served as controls. Before transplantation neuropathy was most advanced in the two diabetic groups. Both diabetic groups showed a similar slight but significant improvement of nerve conduction after transplantation. In the non-diabetic group nerve conduction became essentially normal. No group showed improvement in autonomic dysfunction. The improvement in nerve conduction after combined kidney and pancreas transplantation was most probably due to the elimination of uraemia. Furthermore, 2 years of normoglycaemia did not reverse the diabetic neuropathy to an important extent at this late stage of the disease.

Abnormal autonomic function in diabetic and nondiabetic patients after first acute myocardial infarction

We performed autonomic function testing in 68 patients, 34 with diabetes mellitus (group A) and 34 without (group B), at 72 h after a first acute myocardial infarction (MI) to determine the prevalence of autonomic dysfunction in these patients. Heart rate (HR) variation during 6 breaths/min obtained from mean of longest RR interval during expiration(E)/mean of shortest RR interval during inspiration (I) (E:I ratio), immediate HR response to standing = RR at 30th beat/RR at 15th beat (30:15 ratio) and postural fall of blood pressure were evaluated. In group A, 25 (78 percent) of 32 patients had an abnormal expiration-inspiration ratio compared with 28 (85 percent) of 33 in group B. Twenty-six (76 percent) patients in group A and 16 (47 percent) in group B had an abnormal 30:15 ratio. Abnormal postural fall of blood pressure was seen in 16 (47 percent) patients in group A compared with ten (29 percent) in group B. During follow-up, four women in group A with an initial autonomic dysfunction died, and in group B, three patients with a normal autonomic function died. Thus, autonomic dysfunction does not seem to contribute to the high mortality among diabetics after an acute MI.

Cardiovascular reflexes in monozygotic twins discordant for exposure to organic solvents

Eighteen pairs of monozygotic twins discordant for long-term occupational exposure to organic solvents were examined for disturbances of cardiovascular reflexes. All of the subjects were asymptomatic, and considered themselves healthy. No significant differences were observed between the exposed and the nonexposed twins. The finding suggests that occupational solvent exposure at these particular levels is unlikely to cause disturbances of the autonomic nervous function.

Analysis of sinus cycle variation: a new method for evaluation of suspected sinus node dysfunction

Momentary sinus cycle variations in 30 patients with unequivocal sinus node disease (SND) were compared with those found in 18 healthy control subjects to assess their potential diagnostic value. The range of variation of sinus cycle length (SCL; standardized by dividing by mean SCL) and the maximal change in SCL between any two consecutive cycles (max delta SCL) were measured in short (about 1 minute) continuous ECG recordings from invasive electrophysiologic investigations. Age-stratified reference values from 1 minute surface ECG recordings obtained at rest during quiet breathing in about 70 healthy persons were applied. For diagnosing SND, an increased standardized variation range had a sensitivity of 63%, a specificity of 94%, and a predictive value of a positive test of 95%. The corresponding figures for an increased max delta SCL were 77%, 78%, and 85%, respectively. A combination of increased range of variation and increased max delta SCL was observed in 63% of the patients but not in any healthy subject, which gives a specificity and a predictive value of a positive test of 100% for this combination.

Autonomic neuropathy in proliferative diabetic retinopathy

Autonomic nerve function was assessed in 28 diabetic patients with proliferative retinopathy and 61 age- and sex-matched control subjects, using a series of tests based upon cardiovascular reflex responses to standardised stimuli. Autonomic neuropathy was present in 75 per cent of diabetics with proliferative retinopathy, compared with 5.2 per cent of the control group. The implications of a significant association between cardiovascular autonomic neuropathy and proliferative diabetic retinopathy are discussed.

The significance of autonomic neuropathy in the elevation of inactive renin in diabetes mellitus

Plasma renin activity (PRA) and inactive renin(IR, activated by trypsin) were measured in the plasma of 15 type II diabetics with autonomic neuropathy (group 3), 15 type II diabetics without (group 2), and 14 nondiabetic control subjects (group 1) in the recumbent position. There were no significant differences between the 3 groups with respect to age, ideal body weight, supine resting mean blood pressure, serum creatinine, daily urinary excretion of sodium, or renin substrate at the time of study. Autonomic neuropathy (AN) was assessed by measurement of the ratio of the longest to the shortest R-R interval during deep breathing (E/I-ratio) and by postural hypotension. PRA was significantly lower in group 3 than in group 1 (p less than 0.05). The IR level was significantly higher in group 3 than in groups 2 and 1 (p less than 0.005 for both comparisons). The ratio of active renin to total renin (TR) (PRA/(IR + PRA)) was significantly lower in group 3 than in groups 2 and 1 (p less than 0.001 for both comparisons). The IR level and PRA/(IR + PRA) were significantly correlated with E/I-ratio (r = -0.498, p less than 0.01 and r = 0.588, p less than 0.001, respectively) and with the severity of postural hypotension (r = 0.383, p less than 0.05 and r = 0.401, p less than 0.05, respectively), but not with the daily urinary excretion of protein or 24 h-creatinine clearance (24 h-Ccr) in the whole diabetics. From these results, we conclude that autonomic neuropathy might be a more important factor than nephropathy in the lower PRA and higher IR level in type II diabetics with AN.

Effects of haemodialysis on heart rate variability in chronic renal failure

The influence of haemodialysis (HD) on the heart rate variability (HRV) was investigated in nine non-diabetic patients on maintenance haemodialysis. The R-R intervals were measured in recordings during spontaneous quiet breathing and during controlled deep breathing before and after a single HD session. The HRV was expressed as the standard deviation of the mean R-R interval in 3 min ECG recordings. Heart rate variability is the irregularity in the heart rate mainly caused by autonomic control mechanisms. The long-term HRV during quiet breathing was statistically significantly (p less than 0.05) higher after the HD than before. The HRV in the intermediate frequency range of 0.075-0.125 Hz was also significantly increased by the HD. This suggests that some metabolic agents interfering with the heart rate regulation are removed by the haemodialysis, and as a result a better function of the autonomic cardiac control is achieved in uraemic patients.

Non-insulin-dependent diabetes in older patients. Complications and risk factors

Non-insulin-dependent diabetes mellitus is predominantly a disease of aging, with more than 70 percent of non-insulin-dependent (type II) diabetic patients older than 55 years of age. The prevalence of macrovascular, microvascular, and neurologic complications in outpatients with type II diabetes between the ages of 55 and 74 was compared with that in a similarly aged nondiabetic group of patients. The association between duration of diabetes, hypertension, age, and other putative risk factors that are prevalent in this elderly diabetic population and the occurrence of complications was explored. This cross-sectional survey confirmed a significant increase in retinopathy, neuropathy, impotence, and macrovascular complications in patients with type II diabetes. Within the diabetic population, duration of disease was associated with the occurrence of retinopathy and neuropathy, but not associated with such macrovascular complications as coronary artery disease. Gender, type of therapy, and previously identified risk factors for vascular disease such as hypertension had little impact on the prevalence of complications in this population. The notion that type II diabetes in the elderly represents "mild" diabetes with regard to complications must be discarded. Further identification of risk factors within this diabetic population may suggest therapeutic approaches that will prevent or ameliorate the development of complications.

Reduced intraindividual variability of repeated cardiovascular reflex tests: an additional marker of autonomic neuropathy in insulin-dependent (type I) diabetes mellitus?

The particular questions asked in our study were: 1. does the individual reproducibility of the cardiovascular reflex tests differ between healthy controls and patients suffering from type I diabetes mellitus and 2. if there is a difference, do the different cardiovascular reflexes vary in this regard? Nine healthy controls (4 women, 5 men, age 31 +/- 2.1 years) and 11 type I diabetics (4 women, 7 men, age 30.9 +/- 5.6 years, duration of diabetes 3.23 years) underwent the following tests 6 times in a 12-h period (07:00 to 19:00): variation of heart rate during deep breathing (E/I ratio), variation of heart rate during lying and standing (tachycardia/bradycardia or 30/15 ratio), Valsalva maneuver (Valsalva ratio), response of diastolic blood pressure to sustained hand grip, and response of systolic blood pressure to posture. The test results did not indicate a diurnal fluctuation nor were they systematically influenced by antecedent insulin injections or meals, either in diabetic patients or in healthy controls. The 11 diabetics had significantly lower intraindividual variations of E/I and Valsalva ratios than the controls (p less than 0.05, p less than 0.001, respectively). In the diabetics with parasympathetic failure the intraindividual variabilities of all cardiovascular reflex responses were lower than those of the patients with an intact autonomic nervous system as well as those of the control subjects. On the contrary, in the diabetic patients without autonomic neuropathy, only the intraindividual variability of the Valsalva maneuver was significantly attenuated (p less than 0.025), compared with the healthy volunteers. To conclude, the more pathological the single test result, the greater is its reproducibility and its clinical significance.

Cardiovascular reflex tests. Assessment of age-adjusted normal range

To assess the relationship between aging and autonomic control of heart rate and blood pressure, cardiovascular reflex tests were performed in 70 healthy volunteers in the age range 25-71 years. R-R interval variation, heart rate change with deep breathing, 30/15 ratio and blood pressure response to standing appeared significantly declining with age. For each test we calculated the P0.99 and P0.01 confidence limits for individual observations. On the other hand, Valsalva ratio and the blood pressure response to sustained handgrip appeared to be unrelated to age. These results suggest that there is an age-dependent degradation of the mechanisms involved in the cardiovascular reflexes. The assessment of age-adjusted normal values improves the criteria for delineating abnormal from normal results in individual testing of autonomic function.

Reproducibility of cardiovascular autonomic tests in diabetics with and without autonomic dysfunction and in normal controls

The present study evaluates the reproducibility of five cardiovascular reflex tests, deep breathing (DB), Valsalva maneuver (VM), sustained hand-grip (SHG), postural hypotension (PH) and lying to standing (LS) in normal subjects and in insulin dependent (type I) diabetic patients. The study was carried out in 10 normal subjects, in 10 diabetics with autonomic neuropathy and in 10 diabetics without autonomic neuropathy. The five cardiovascular reflex tests were performed five times on five consecutive days by the same investigator and in identical basal conditions. The intraindividual variability of DB, LS and VM was significantly reduced in diabetics with autonomic neuropathy compared with normal controls, but there was no difference between diabetics without neuropathy and normal controls. The intraindividual variability of PH was significantly increased in diabetics with autonomic neuropathy compared with diabetics without autonomic neuropathy and with normal controls. There was no difference among the three groups in the reproducibility of SHG. In normal subjects the intraindividual variability only exceptionally produced a shift from normal to abnormal values or vice versa; in diabetics with autonomic neuropathy this shift was more frequent.

Baroreflex control of plasma norepinephrine and heart period in healthy subjects and diabetic patients

Resting diabetic patients may have excessively rapid heart rates, reduced heart rate variability, and subnormal plasma catecholamine levels. Although all of these abnormalities may relate in some way to baroreceptor reflex function, there have been surprisingly few attempts to evaluate systematically baroreflex mechanisms in diabetic patients. Accordingly, we studied autonomic responses over a range of pharmacologically induced arterial pressure changes in 10 unselected young adult insulin-dependent diabetic patients who had no symptoms of autonomic neuropathy, and 12 age-matched nondiabetic subjects. Sympathetic responses were estimated from antecubital vein plasma norepinephrine levels, and parasympathetic responses were estimated from electrocardiographic R-R intervals and their variability (standard deviation). Both were correlated with other noninvasive indexes of peripheral and central nervous system function. Multiple derangements of baroreflex function were found in the diabetic patients studied. Sympathetic abnormalities included subnormal baseline norepinephrine levels, virtual absence of changes of norepinephrine levels during changes of arterial pressure, and supranormal pressor responses to phenylephrine infusions. Parasympathetic abnormalities included subnormal baseline standard deviations of R-R intervals, and R-R interval prolongations during elevations of arterial pressure which were unmistakably present, but subnormal. Our data suggest that in diabetic patients, subnormal baseline plasma norepinephrine levels may signify profound, possibly structural defects of sympathetic pathways. Subnormal resting levels of respiratory sinus arrhythmia may have different implications, however, since vagal, unlike sympathetic reflex abnormalities, can be reversed partly by arterial pressure elevations.

Bedside diagnosis of cardiac autonomic damage by computerized analysis of heart rate-respiration relationship

In this study we propose a method for the analysis of the relationship between heart rate changes and respiration as a possible diagnostic tool for cardiac autonomic damage. The method consists in recording R-R intervals and respiratory amplitude by a suitably equipped personal computer, and by evaluating the cross-correlation peak between the two signals. This mathematical function appeared to be more sensitive to the degree of concordance between the two signals, rather than their absolute amplitude. The cross-correlation appeared to be lower in diabetics with autonomic dysfunction, markedly decreased after injection of atropine (only in normals), slightly increased after propranolol. Hyperpnea increased the cross-correlation peak between 3-18 breaths/min in normals, but only at lower frequencies, if at all, in diabetic subjects with various degrees of autonomic dysfunction. The cross-correlation showed the best reproducibility among R-R change tests. These preliminary results suggest that this method may provide new information on autonomic integrity and a substantial advantage in terms of reproducibility.

Effects of sorbinil therapy in diabetic patients with painful peripheral neuropathy and autonomic neuropathy

Clinical investigations with the aldose reductase inhibitor sorbinil in patients with peripheral neuropathy due to diabetes are described. After an improvement in motor and sensory nerve conduction velocities was demonstrated in asymptomatic diabetic patients taking sorbinil (compared with velocities during a placebo period), 11 patients with painful diabetic neuropathy were treated with sorbinil for three weeks without alterations in diabetic management or control. Therapy was placebo-controlled in a single-blind fashion in eight patients. Pain (assessed by or on a zero to 20 rating scale), which had been constant for many months before entry into the study and unresponsive to numerous medications, improved from a mean score of 16 to 8 and returned when the drug was discontinued. Objective improvement in sensation and strength were observed in some cases. Improvements in nerve conduction velocity and cardiac autonomic function were also documented. Cardiac autonomic neuropathy was studied in 36 patients in a double-blind, placebo-controlled, randomized, noncrossover trial. Patients received one 250-mg sorbinil tablet or one placebo tablet daily for six weeks, after a one-week baseline period. Glycemic control did not change during the study period, as indicated by unaltered glycohemoglobin levels. Response was assessed by expiration-inspiration ratios, obtained on electrocardiography during six cycles per minute respiration, and by resting minimal heart rate, both measures of vagal function. In the sorbinil-treated group, expiration-inspiration ratios improved from 1.074 +/- 0.012 to 1.096 +/- 0.020 (p less than 0.03). There was a slight decrease in the ratios in the placebo-treated group, from 1.112 +/- 0.023 to 1.105 +/- 0.023 (not significant). The difference between the Week 0 to Week 6 changes in each group was significant (p less than 0.01). Resting minimal heart rate decreased in the sorbinil-treated group from 76.4 +/- 2.3 to 66.8 +/- 2.8 +/- 2.4 beats per minute (p less than 0.001), with a mean change of 10 +/- 2. In the placebo-treated group, heart rate was unchanged (77.9 +/- 3.9 to 77.5 +/- 3.3 beats per minute). The two-sample t test of the within-group differences was also significant (p less than 0.001). The changes in both expiration-inspiration ratios and resting minimal heart rate are consistent with a sorbinil-related improvement in cardiac parasympathetic nerve function. Several isolated cases of apparent sorbinil-related improvements in autonomic symptoms have been observed.(ABSTRACT TRUNCATED AT 400 WORDS)

Autonomic neuropathy in acute intermittent porphyria

Autonomic function was assessed in subjects with acute intermittent porphyria and age- and sex-matched controls using five different bedside tests of cardiovascular reflexes. During the acute attack both parasympathetic and sympathetic tests were impaired, but subsequently improved during remission. Early parasympathetic dysfunction was also detected during remission and in latent asymptomatic acute intermittent porphyria.

Relationship between the R-R interval variation and metabolic states of diabetes

To investigate whether the metabolic state of diabetes affects the R-R interval variation, 82 diabetics were studied at intervals of about 1 month and of about 1 year. There was no significant relationship between the rate of change for FBG and that for R-R interval variation at both these intervals. However, in the cases that showed a change of HbA1 by more than 10% in a month, the rate of change for the R-R interval variation was 20 +/- 30% in the group with improved HbA1 and -9 +/- 17% in the group with aggravated HbA1, demonstrating a significant difference (P less than 0.05) between the 2 groups. There was a significant difference (P less than 0.02) in the rate of change for the R-R interval variation between the group with improved HbA1 by more than 5% and the group with aggravated HbA1 by more than 5%, when measured at intervals of 1 year. No special relationship was observed between the difference in R-R interval variation and each of the following: (1) the mean FBG for 1 year preceding the day of initial measurement of the R-R interval variation; (2) the mean FBG for the succeeding year; and (3) the difference in these 2. It was suggested that the R-R interval variation was likely to be affected by the metabolic state during the preceding 1-2 months.

A new index of autonomic neuropathy in diabetes mellitus: heat stimulated thermographic patterns

Autonomic neuropathy, especially sympathicopathy, a life-threatening complication of diabetes mellitus, has been difficult to evaluate, and remains undetermined. We studied the thermographic patterns of 62 patients (50-69 years old), revealing the vasodilated activities of one leg by immersing the other leg in a warm water bath, for the detection of sympathetic neuropathy, using Thermoviewer MDJTG-MD. The normal pattern shows an increase in skin temperature, while the flat pattern shows no rise or even a paradoxical decrease. The latter had a significantly longer duration of diabetes and poor blood sugar control. The thermographic pattern is closely related to microangiopathy, R-R interval variation and motor nerve conduction velocity. However, R-R interval variation is often abnormal in patients with normal thermographic patterns, showing vasosympathetic abnormalities appearing far later in the development of diabetic neuropathy. The flat pattern develops slowly after at least several years of poor blood sugar control. Change in the pattern is also gradual and slow. The reproducibility of the pattern is excellent and requires relatively simple and noninvasive techniques. Thermography is one of the most reliable, reproducible and noninvasive indexes for finding and following diabetic sympathetic abnormalities.

Autonomic dysfunction in experimental allergic neuritis

Beat-to-beat variation (R-R variation) in the electrocardiogram was studied in experimental allergic neuritis in the Sprague-Dawley rat. Reduced R-R variations were found in 2 of 10 animals, probably as a sign of autonomic dysfunction. The vagal nerves from these two animals, studied in vitro, showed disturbed conduction. In one animal prolonged conduction latencies to supramaximal electrical stimuli were found. Vagal nerves from controls and from animals without clinical symptoms showed normal conduction. Histologically, the vagal nerves from affected animals showed a slight inflammatory cell infiltration and signs of demyelination but there was no evidence of involvement of the brainstem vasomotor nuclei. Thus, we suggest that the autonomic dysfunction in experimental allergic neuritis, measured as reduced R-R variations, is caused by a peripheral vagal neuropathy.

Reflex heart rate control in asthma. Evidence of parasympathetic overactivity

The bronchial hyperreactivity characteristic of asthma may be related to enhanced parasympathetic nervous activity. We postulated that an abnormality in the autonomic control of airway caliber might be reflected by a parallel change in the reflex control of heart rate. We examined the heart-rate variations induced by deep breathing (respiratory sinus arrhythmia), the Valsalva maneuver, and standing up from the recumbent position in asthmatic subjects and nonasthmatic control subjects. The asthmatic patients had evidence of enhanced parasympathetic neural drive to the sinoatrial node, as manifested by a significantly greater magnitude of respiratory sinus arrhythmia, than the controls (p less than 0.0005). We were unable to induce a similar change in normal subjects by resistance breathing. A statistical analysis suggested the presence of a relationship between the magnitude of respiratory sinus arrhythmia and the degree of bronchial hyperreactivity in a group of asthmatic patients. Our results support the hypothesis that enhanced parasympathetic activity is an important factor in the pathogenesis of bronchial asthma.

Autonomic dysfunction in non-diabetic terminal uraemia

R-R variations in the ECG were studied as a sign of autonomic dysfunction in 44 non-diabetic patients with terminal uraemia treated with intermittent haemodialysis. A severe impairment of this parasympathetic vagal reflex was found though there were only mild signs of diffuse polyneuropathy. No acute effect was associated with haemodialysis. There was no correlation between either the R-R variations and the polyneuropathy-index or the total dialysis time. Patients with chronic glomerulonephritis, pyelonephritis and polycystic kidney disease were equally affected.

Blood pressure and heart rate responses during 24-hour ambulatory monitoring and exercise in men with diabetes mellitus

The heart rate (HR) variation of 25 normotensive and asymptomatic men, mean age 58 +/- 7 years, with diabetes mellitus (group I) was studied during deep respiration. Thirteen subjects (52%) had a variation of 10 beats/min or less, consistent with an autonomic neuropathy (AN) (group IA); 12 had variation in HR of more than 10 beats/min and were considered to have no neuropathy (group IB). The 24-hour ambulatory HR and systolic blood pressure (BP) values of group I were compared with those of 13 healthy men, mean age 48 +/- 8 years (group II). The mean of 5 maximal HR measurements during the 24-hour period was higher for group IA (106 +/- 11 beats/min) than for group IB (100 +/- 13 beats/min) or for group II (92 +/- 9 beats/min) (p less than 0.01). The mean of 5 maximal BP measurements was greater for group I (149 +/- 28 mm Hg) than for group II (128 +/- 13 mm Hg) (p less than 0.01), but no difference was observed between groups IA and IB. Maximal treadmill exercise was performed with 22 of the patients (11 with and 11 without AN), and no difference in HR was observed between the 2 groups during all stages of exercise or at maximal exertion. The increase in systolic BP and duration of exercise in these 2 groups were also similar. Seventeen of 25 diabetic men had peripheral neuropathy (PN). Of 13 patients with AN, 10 had PN; of 12 without AN, 7 had PN and 5 did not.(ABSTRACT TRUNCATED AT 250 WORDS)