Diabetic autonomic neuropathy

Heart rate variability is reduced in acromegaly patients and improved by treatment with somatostatin analogues

BACKGROUND

Cardiovascular complications, including arrhythmias and cardiac sudden death, are the most common causes of enhanced mortality in acromegaly. However, few data are available on cardiac autonomic functions and sympathovagal balance in acromegalic patients.

OBJECTIVE

The aim of this study was to investigate both the time and frequency domain parameters of Heart Rate Variability (HRV), in order to characterize the cardiac autonomic functions in patients affected by acromegaly. This study correlated anthropometric, metabolic, echocardiographic parameters and blood pressure with those relating to HRV, to identify the main factors responsible for the HRV related alterations possibly present. We also aimed to analyze the effects of the treatment with somatostatin analogues (SSAs) on HRV.

MATERIALS AND METHODS

This study enrolled 47 acromegalic patients (23 males, age 49.1 ± 13.5 years) and 37 (13 males) age matched (52.3 ± 13.3 years) healthy subjects. All participants underwent 12-lead 24 h ECG Holter recordings and a HRV analysis of the ECG tracings was performed. The parameters obtained from the time domain analysis of HRV included pNN50, SDNN, SDNN index, SDANN and RMSSD. The power spectral analysis of HRV was obtained by summing powers of the LF (low frequency) and the HF (high frequency) band. Sympathovagal balance was estimated by calculating the LF/HF ratio during 24 h and 15 min of clinostatism. The HRV of 28 acromegalic patients was studied before and after SSAs treatment.

RESULTS

Acromegalic patients showed significantly lower SDNN and SDANN compared to controls. Diabetic and non-diabetic acromegalic patients showed decreased SDNN and SDANN, when compared to healthy subjects. Diabetic acromegalic patients had a lower LF/HF ratio during 24 h when compared to non-diabetic acromegalic patients. Similar results were obtained analyzing patients affected by acromegaly and impaired glucose tolerance. SDNN and SDANN were lowered by hypertension in the acromegalic population, when compared to controls, and hypertensive acromegalic patients also displayed a decreased LF/HF ratio during 24 h when compared to normotensive acromegalic subjects. Patients with ventricular arrhythmias in Lown classes 3-5 showed a decreased SDANN compared to patients in Lown class 0-2. The treatment with SSAs was able to ameliorate all the time domain parameters of HRV, without altering the 24 h LF/HF ratio.

CONCLUSION

Cardiac autonomic functions and sympathovagal balance are altered in patients affected by acromegaly and could be ameliorated by SSAs therapy. HRV analysis allows an estimation of the autonomic sympathovagal balance and may be a useful clinical tool for the cardiac risk stratification in acromegalic patients.

Association of VO2 and VCO2 rate variability with serum glucose, insulin, and glucose intolerance

Changes in the cellular metabolism assessed by the variability of oxygen consumption (VO(2) ) and carbon dioxide production (VCO(2) ) as well as the association of serum glucose and insulin to energy spectral density (ESD) of VO(2) and VCO(2) were evaluated. Ten nonglucose intolerant and 10 glucose intolerant subjects, aged 21-70 years, were included. Glucose and insulin concentrations and VO(2) and VCO(2) records were collected every 10 min during 3 h. ESD of VO(2) and VCO(2) was estimated and associated with glucose and insulin concentrations. Statistical significance in glucose levels, insulin, and ESD of VO(2) and VCO(2) among nonglucose intolerant subjects and glucose and insulin among glucose intolerance subjects at postload glucose (PLG) state compared with basal state was found. Moreover, glucose was significantly higher in glucose intolerance subjects than nonglucose intolerant subjects for basal and PLG states. These results show an increment in ESD of VO(2) and VCO(2) at PLG state among nonglucose intolerant subjects and suggest that their measurement may be a key indicator of the variability of cellular metabolic activity and contribute to confirm disturbances in glucose metabolism.

Gravity, the hydrostatic indifference concept and the cardiovascular system

Gravity, like any acceleration, causes a hydrostatic pressure gradient in fluid-filled bodily compartments. At a force of 1G, this pressure gradient amounts to 10 kPa/m. Postural changes alter the distribution of hydrostatic pressure patterns according to the body's alignment to the acceleration field. At a certain location--referred to as hydrostatically indifferent--within any given fluid compartment, pressure remains constant during a given change of position relative to the acceleration force acting upon the body. At this specific location, there is probably little change in vessel volume, wall tension, and the balance of Starling forces after a positional manoeuvre. In terms of cardiac function, this is important because arterial and venous hydrostatic indifference locations determine postural cardiac preload and afterload changes. Baroreceptors pick up pressure signals that depend on their respective distance to hydrostatic indifference locations with any change of body position. Vascular shape, filling volume, and compliance, as well as temperature, nervous and endocrine factors, drugs, and time all influence hydrostatic indifference locations. This paper reviews the physiology of pressure gradients in the cardiovascular system that are operational in a gravitational/acceleration field, offers a broadened hydrostatic indifference concept, and discusses implications that are relevant in physiological and clinical terms.

Sympathovagal imbalance in transsexual subjects

CONTEXT

Autonomic nervous system imbalance is related to cardiovascular risk. Heart rate variability (HRV) indexes are associated with age, race, and sex, but the role of sex hormones is still unknown.

OBJECTIVE

To evaluate sympathovagal balance (SB) in transsexuals.

PATIENTS

Eighteen transsexual subjects, 12 male-to-female (group 1) and 6 female- to-male (group 2), compared with 34 age-matched controls: 17 males (group 3) and 17 females (group 4). Autonomic testing of SB was performed by Power Spectral Analysis (PSA) of HRV in clinostatism (c) and orthostatism (o). PSA identifies power peaks: high frequency (HF) expresses vagal activity, while low frequency (LF) expresses sympathetic activity.

RESULTS

Group 1 showed lower LFc than groups 2, 3, and 4 (p<0.001, p=0.05, p<0.001, respectively), and lower LFo than groups 3 and 4 (p=0.01); HFc was lower than in groups 2, 3, and 4 (p=0.02, p=0.02, p<0.001, respectively), and HFo was lower than in groups 3 and 4 (p<0.001). LFo/HFo ratio was higher in group 1 than in group 4 (p<0.001). No differences emerged between groups 2 and 3. Group 2 showed lower HFo than group 4 (p=0.03), and a higher LFo/HFo ratio (p=0.01). Group 3 showed lower HFo and HFc than group 4 (p=0.02, p=0.05, respectively), and a higher LFo/HFo ratio (p=0.03).

CONCLUSION

In this study we found a sympathovagal imbalance due to a reduced sympathetic and parasympathetic influence on heart rate. Sex hormone therapy per se may play a role in this imbalance, and HRV measurement could be useful in detecting cardiovascular risk in transsexuals.

Autonomic neuropathy increases the risk of obstructive sleep apnea in obese diabetics

BACKGROUND

Nonobese diabetics with diabetic autonomic neuropathy (DAN) show an elevated prevalence of obstructive sleep apnea-hypopnea (OSAH).

OBJECTIVE

It was the aim of this study to assess if the presence of DAN could further increase the risk of developing OSAH in obese diabetics.

METHODS

Eighteen obese diabetic patients, 8 with DAN [age 57 +/- 5 years, body mass index (BMI) 35 +/- 4] and 10 without DAN (age 56 +/- 8 years, BMI 37 +/- 5), were recruited. Ten age-matched obese subjects were studied as controls (age 53 +/- 12 years, BMI 34 +/- 3). All subjects underwent a cardiorespiratory sleep study in the in-hospital sleep laboratory to obtain the apnea-hypopnea index (AHI) and oxygen desaturation indices.

RESULTS

Diabetics with DAN (Ob-DAN+) had a higher AHI than diabetics without DAN (Ob-DAN-) and controls, amounting to 39.5 +/- 13 versus 15.8 +/- 12 (p < 0.01) and 19.3 +/- 21 (p < 0.05), respectively. A moderate-to-severe OSAH (AHI > or = 15) occurred in all Ob-DAN+ and only in 4 Ob-DAN- and 4 control patients. Moreover, the indices reflecting the impairment of oxygen saturation (SaO(2)) during sleep such as the mean lowest SaO(2) and sleep time with a SaO(2) <90% were more severely affected in Ob-DAN+ patients compared with the other groups and were associated with longer obstructive respiratory events.

CONCLUSIONS

Apneas-hypopneas are more frequent and last longer in Ob-DAN+ than in other obese subjects, with or without diabetes.

Parasympathetic versus sympathetic control of the cardiovascular system in young patients with type 1 diabetes mellitus

Autonomic neuropathy and cardiovascular dysregulation are common complications of the diabetes mellitus (DM). The aim of the study was to test the hypothesis that cardiovascular regulation is abnormal in young patients with type 1 DM. Patients with type 1 DM (17, 10 females, 7 males) aged 12.9-31.5 years (mean+/-SEM: 22.4+/-1.0 years) were investigated. The mean duration of DM was 12.4+/-1.2 years. The control group consisted of 17 healthy probands matched for sex and age. The length of R-R intervals was measured using telemetric system (VariaCardio TF4; Sima Media) where ECG signal (sampling frequency 1000 Hz) from thoracic belt was transferred into PC for further analysis. Systolic blood pressure (SBP) was monitored beat-to-beat using volume-clamp method by Finapres 2300 (Ohmeda). Spectral power in HF band of HRV (HRV-HF) was taken as an index of parasympathetic control and spectral power in LF band of systolic BPV (BPV-LF) as an index of sympathetic control. In young patients with type 1 DM significant reduction of spectral power in HF band of the heart rate variability was found, whereas no significant difference between DM group and control group was observed in spectral power in LF band of blood pressure variability. In conclusion, we found impaired parasympathetic control of heart rate in young patients with type 1 DM. No differences in blood vessels sympathetic control were detected using spectral analysis of BPV. We suggest that abnormalities in cardiac parasympathetic regulation precede impairment of blood vessels sympathetic control in young diabetics.

Sympathovagal imbalance in acromegalic patients

CONTEXT

Sympathovagal imbalance is a common finding in diabetes and is considered to be a cardiovascular risk factor. No data are available on sympathovagal balance (SB) in acromegalic patients.

OBJECTIVE

The objective of this study was to evaluate SB in acromegalic patients.

PATIENTS

Twenty nondiabetic, nonhypopituitary, acromegalic patients (13 women and seven men; mean age +/- sem, 51.30 +/- 3.09 yr) were compared with age-matched subjects (21 normal subjects, 20 patients with type 1 diabetes mellitus, and 15 patients with type 2 diabetes mellitus).

INTERVENTIONS

Autonomic tests, used to evaluate SB, were performed by power spectral analysis of heart rate variability in clinostatism (c) and orthostatism (o), using a frequency domain method. Power spectral analysis identifies peaks of power: high frequency (HF), which expresses vagal activity, and low frequency (LF), which expresses sympathetic activity.

RESULTS

Acromegalic patients displayed significantly lower LFc/HFc (P = 0.002) and LFo/HFo (P < 0.001) ratios than normal subjects. HFo was significantly higher in acromegalic patients than in normal subjects (P < 0.001) and patients with type 1 diabetes mellitus (P = 0.004), but no different from that in type 2 diabetes mellitus patients (P = 0.069). In untreated acromegalic patients, the alterations found in the whole group were confirmed; no statistically significant differences were found between untreated acromegalic patients and those treated with somatostatin analogs. Similarly, the same alterations found in the whole group were evident in the controlled acromegalic patients, and no significant differences were found between controlled and uncontrolled patients.

CONCLUSION

Our study evidenced that sympathovagal imbalance in acromegalic patients, due to vagal hypertone, is difficult to reverse and is not influenced by medical therapy. This could be a new cardiovascular risk factor.

Heart rate variability in young patients with diabetes mellitus and healthy subjects explored by Poincaré and sequence plots

Autonomic neuropathy is a common complication of the diabetes mellitus (DM). The significance of its early diagnosis is very high because the mortality of the patients with this complication is elevated. Considering the effort to apply new mathematical methods to cardiac dysregulation diagnosis, the major aim of the study was to ascertain which of the new heart rate variability (HRV) parameters are different in young patients with DM type 1 compared with control group. The next aim was to assess the HRV changes during prolonged (40 min) supine rest. The heart rate was continuously recorded during supine rest in 17 young patients with DM type 1 (10 women, 7 men) aged 22.4 +/- 1.0 years (mean +/- SEM). The control group consisted of 17 healthy matched probands. The HRV (time/frequency domains, Poincare and sequence plots, sample entropy) was analysed in two intervals - T1 starting at fifth minute and T2 starting at 30th minute of supine rest. The major results of our study are: the reduced Poincare plot pattern measures in the young DM group; the lower percentage of points in the third quadrant of sequence plot (this parameter was not correlated with the mean heart rate) and significant changes in HRV during supine rest in DM group (in contrast to control subjects). In conclusion, HRV parameters based on nonlinear dynamics were able to distinguish cardiac dysregulation in young patients with DM from the control group. The percentage of points in the third quadrant of sequence plot provides information that is not dependent on mean heart rate. Poincare and sequence plots, together with the rate of HRV changes during supine rest, can provide clinically relevant information usable in diagnosis of the cardiac dysregulation.

Cardiac autonomic activity and Type II diabetes mellitus

CAN (cardiac autonomic neuropathy) is a common complication of diabetes. Meta-analyses of published data demonstrate that reduced cardiovascular autonomic function, as measured by heart rate variability, is strongly associated with an increased risk of silent myocardial ischaemia and mortality. A major problem in ischaemia-induced impairment of vascular performance in the diabetic heart is unrecognized cardiac sympathetic dysfunction. Determining the presence of CAN is based on a battery of autonomic function tests and techniques such as SPECT (single-photon emission computed tomography) and PET (positron emission tomography). Nevertheless, spectral analysis of heart rate variability seems to remain the primary technique in evaluating CAN, due to its low cost, easy use and good intra-individual reproducibility.

Neuronal Ca2+ disregulation in diabetes mellitus

The Ca(2+) hypothesis of brain ageing and dementia may account for part of the available data on the pathogenesis of dementia and certain neurodegenerative disorders. The hypothesis proposes that disturbances in the homeostasis of neuronal cytosolic free Ca(2+) are part of a final common pathway, ultimately leading to neuronal dysfunction and cell death. The hypothesis also proposes that a small change in cytosolic free Ca(2+) sustained over a long period of time will result in similar damage as a large change over a short period. Diabetes mellitus is associated with neurological complications in the peripheral and central nervous system, as reflected in peripheral neuropathy, modest cognitive impairments and an increased risk of dementia. In animal models of diabetes, learning impairments are associated with alterations in Ca(2+) -dependent forms of hippocampal synaptic plasticity. Disturbances in the homeostasis of cytosolic free Ca(2+) may present a final common pathway in the multifactorial pathogenesis of neurological complications of diabetes, which involves vascular changes, oxidative stress, and non-enzymatic protein glycation. In line with the Ca(2+) hypothesis of neurodegenerative disorders, a prolonged, small increase in basal cytosolic Ca(2+) levels indeed exists in sensory neurones of diabetic animals. In addition, Ca(2+) dynamics are affected. Ca(2+) channel blockers, such as nimodipine, have been shown to improve experimental peripheral neuropathy, through a vascular mechanism, possibly in combination with direct neuronal effects. Preliminary studies indicate that nimodipine may also improve Ca(2+)-dependent forms of synaptic plasticity in the hippocampus of diabetic rats.

The HISS story overview: a novel hepatic neurohumoral regulation of peripheral insulin sensitivity in health and diabetes

Data are reviewed that are consistent with the following working hypothesis that proposes a novel mechanism regulating insulin sensitivity, which when nonfunctional, leads to severe insulin resistance. Postprandial elevation in insulin levels activates a hepatic parasympathetic reflex release of a putative hepatic insulin-sensitizing substance (HISS), which activates glucose uptake at skeletal muscle. Insulin causes HISS release in fed but not fasted animals. The reflex is mediated by acetylcholine and involves release of nitric oxide in the liver. Interruption of the release of HISS is achieved by surgical denervation of the anterior hepatic nerve plexus, muscarinic receptor blockade, or nitric oxide synthase antagonism and leads to immediate severe insulin resistance. The nitric oxide donor, SIN-1, reverses L-NAME-induced insulin resistance. Denervation-induced insulin resistance is reversed by intraportal but not intravenous administration of acetylcholine or SIN-1. Liver disease is often associated with insulin resistance; the bile duct ligation model of liver disease results in parasympathetic neuropathy and insulin resistance that is reversed by intraportal acetylcholine. Possible relevance of this HISS-dependent control of insulin action to insulin resistance in diabetes, liver disease, and obesity is discussed.Key words: insulin resistance, parasympathetic nerves, liver, obesity, nitric oxide.

Heart rate variability and cardiovascular tests in young patients with diabetes mellitus type 1

The aim of this study was to obtain information about parameters of heart rate variability (HRV) in three frequency bands (high frequency - HF, low frequency - LF and very low frequency - VLF), the sensitivity of cardiovascular tests, and subjective feelings depending on autonomic nervous system balance in a group of young patients with diabetes mellitus type 1 (IDDM). Sixty-four subjects were examined: 32 patients with diabetes with a mean age of 16.1 +/- 0.7 years and a mean duration of IDDM of 6.3 +/- 0.8 years, and 32 healthy controls matched for age, sex and BMI. Shorter R-R intervals and abnormal values reflecting HRV were found in the diabetic group. In particular, parameters of total power, and HF and LF bands were reduced. The ratio VLF/HF power revealed predominance of sympathetic tone in the diabetic subjects. Although relative power VLF was increased in the supine position, the reactive rise of the VLF band activity in orthostasis was lower in the IDDM group. Using cardiovascular tests (deep breathing, Valsalva, orthostasis), significant differences in reactions were found only in the deep breathing test. Evaluation of sympathetic:parasympathetic:indifferent subjective feelings by questionnaire did not reveal any differences between the diabetic and healthy groups.

Power spectra of arterial pressure and heart rate in streptozotocin-induced diabetes in rats

BACKGROUND

Chronic diabetes is associated with alterations in autonomic modulation of the cardiovascular system. Although the rat has been used extensively in studies of experimental diabetes, there have been no reports on the changes in autonomic modulation of the cardiovascular function in chronic diabetic rats.

OBJECTIVE

To examine chronic diabetic rats to determine the autonomic modulation of arterial pressure and heart rate variabilities in the time and frequency domain.

MATERIALS AND METHODS

Diabetes was induced in rats by a single injection of streptozotocin, and 30 min of pulsatile arterial pressure was recorded in conscious rats, 5, 10-20 days and 12-18 weeks after the streptozotocin injection. Control rats were injected with vehicle. Beat-by-beat systolic arterial pressure and heart rate were obtained from pulsatile pressure. The spectral density powers of systolic arterial pressure and heart rate were calculated using fast Fourier transformation, and integrated in low-(0.015-0.25 Hz), mid- (0.25-0.75 Hz) and high- (0.75-3.0 Hz) frequency bands. The standard deviations of systolic arterial pressure and heart rate were also calculated.

RESULTS

Basal systolic arterial pressure and heart rate were reduced in diabetic animals studied 10-20 days and 12-18 weeks after the streptozotocin injection. The standard deviations of systolic arterial pressure and heart rate were also reduced in the chronically diabetic animals. Diabetes reduced low- and mid-frequency variability but not the high-frequency variability of systolic arterial pressure. The low-frequency variability, but not the mid-frequency variability, of the heart rate was also reduced, while the high-frequency variability of the heart rate was reduced in the more chronically diabetic rats.

CONCLUSION

Our findings that the mid-frequency band variability of arterial pressure was reduced in diabetic patients suggest that sympathetic modulation of the cardiovascular system is impaired, corroborating other studies in such patients using this and other approaches.

Diabetic neuropathy: pathophysiology and prevention of foot ulcers

Diabetic neuropathy, which affects 60% to 70% of those with diabetes mellitus, is one of the most troubling complications for persons with diabetes, often leading to foot ulcers and potentially to lower limb amputations, both of which are preventable. The physiologic, structural, and functional changes associated with diabetic neuropathy and foot ulcers are discussed. Advanced practice nurses are in a unique position to implement strategies for the prevention of serious and debilitating complications from diabetic neuropathy, including foot assessment, education, and specialist referrals. Research evidence is given to support the use of the Semmes-Weinstein monofilaments to evaluate decreased plantar sensation, a common precursor to ulceration. Ongoing patient and family education can emphasize the importance of preventive self-care measures. Referrals for specialist care and therapeutic footwear can be made by advanced practice nurses. If begun early, these interventions can prevent foot ulcers from diabetic neuropathy, thereby improving the quality of life and reducing healthcare costs for this chronic disease.

The natural history of recently diagnosed autonomic neuropathy over a period of 2 years

BACKGROUND

Patients with diabetic autonomic neuropathy (DAN) have an increased cardiovascular mortality rate compared with normals or diabetic patients without DAN. Indices of standard cardiovascular autonomic function tests and heart rate variability (HRV) are reliable markers of the presence and severity of DAN.

OBJECTIVE

The present prospective study investigated the natural history of values of HRV indices and cardiovascular reflex tests in patients with recently diagnosed asymptomatic DAN, over a period of 2 years, at 3 month intervals.

PATIENTS AND METHODS

A total of 30 consecutive patients (nine men and 21 women), of median age 51 (range 25-65) years, eight with type 1 and 22 with Type 2 diabetes mellitus, were included in the study, at the time that the presence of DAN was confirmed, as this was established if at least two of cardiovascular autonomic function tests became abnormal. The expiration/inspiration (E/I) ratio. S.D. and mean circular resultant of R-R intervals, the Valsalva index, the 30:15 ratio, and the blood pressure response to standing as well as normalised spectral power indices of HRV were used.

RESULTS

All measured indices, except the Valsalva index, deteriorated in all 30 patients during the 2 year follow-up. Most of HRV indices values deteriorated significantly in comparison to baseline at month 12, while the values of cardiovascular reflex tests displayed significant deterioration, in comparison to baseline, between months 15 and 21. Fourteen patients developed symptoms of DAN during the 2 year period. Patients with better glycemic control exhibited deterioration of DAN markers at the same time period with those with poor glycemic control.

CONCLUSIONS

Our data suggest that the progression of DAN is significant during the 2 years subsequent to its discovery. This was defined by the deterioration of the mean values of HRV indices and standard cardiovascular autonomic function tests, and by the development of autonomic symptoms in some patients. HRV indices are the earlier markers of DAN deterioration.