Pathological changes in the vagus nerve in diabetes and chronic alcoholism

Ultrasound assessment of the brachial plexus nerve root cross-sectional areas in asymptomatic patients with type 2 diabetes

Type 2 diabetes mellitus (T2D) is one of the most common metabolic diseases and is often associated with cervical radiculoplexus neuropathies. Magnetic resonance imaging is the modality of choice for evaluating the brachial plexus, however, the use of ultrasound for its evaluation has increased and has been shown to be an additional reliable method. We aimed to compare the cross-sectional areas of the C5, C6, and C7 nerve roots of the brachial plexus, at the interscalene groove, in asymptomatic patients with T2D to that of an asymptomatic control cohort without T2D. A total of 25 asymptomatic patients with T2D were recruited from outpatient clinics. A total of 18 asymptomatic subjects without T2D were also recruited from hospital staff volunteers to form the control cohort. High-resolution ultrasound imaging of the bilateral C5, C6, and C7 nerve roots of the brachial plexus was performed in the short axis, at the level of the interscalene grooves. The nerve root cross-sectional areas were recorded and compared. In the patients with T2D, HbA1c and fasting blood glucose (FBG) levels were obtained as well as the duration of T2D in years and correlated with cross-sectional areas. The cross-sectional areas of C6 and C7 were significantly smaller in the T2D cohort. Additionally, HbA1c, and FBG levels as well as the duration of T2D were negatively correlated with the C5, C6, and C7 cross-sectional areas. Our study demonstrated smaller brachial plexus nerve root cross-sectional areas in asymptomatic patients with T2D which negatively correlated with HbA1c, and FBG levels as well as the duration of T2D.

The vagus nerve cross-sectional area on ultrasound in patients with type 2 diabetes

Diabetic neuropathy, including autonomic neuropathy is a serious complication related to type 2 diabetes mellitus (T2D). The vagus nerve (VN) is the longest nerve in the autonomic nervous system, and since diabetic neuropathy manifests first in longer nerves, the VN is commonly affected in early diabetic autonomic neuropathy. The use of high-resolution ultrasound for peripheral and cranial nerve imaging has significantly increased over the past 2 decades. The aim of the study is to compare the cross-sectional area of the VN in patients with T2D to that of a control cohort without T2D. A total of 52 VN cross-sectional areas were recorded from patients with T2D. A total of 56 VN cross-sectional areas were also recorded from asymptomatic subjects without T2D. In each subject, high-resolution ultrasound imaging of the bilateral VNs was performed in the short-axis between the common carotid artery and the internal jugular vein. The VN cross-sectional areas were recorded and compared. In the patients with T2D, HbA1c and fasting blood glucose levels were obtained as well as the duration of T2D in years and correlated with the cross-sectional areas. The bilateral VN cross-sectional areas were similar in both cohorts. Additionally, no correlation was seen between the VN cross-sectional areas, demographics, or clinical data of T2D. Our study demonstrated normal VN cross-sectional areas in patients with T2D without any significant relation with the patients' demographic or clinical data.

Validated computational models predict vagus nerve stimulation thresholds in preclinical animals and humans

Objective.We demonstrated how automated simulations to characterize electrical nerve thresholds, a recently published open-source software for modeling stimulation of peripheral nerves, can be applied to simulate accurately nerve responses to electrical stimulation.Approach.We simulated vagus nerve stimulation (VNS) for humans, pigs, and rats. We informed our models using histology from sample-specific or representative nerves, device design features (i.e. cuff, waveform), published material and tissue conductivities, and realistic fiber models.Main results.Despite large differences in nerve size, cuff geometry, and stimulation waveform, the models predicted accurate activation thresholds across species and myelinated fiber types. However, our C fiber model thresholds overestimated thresholds across pulse widths, suggesting that improved models of unmyelinated nerve fibers are needed. Our models of human VNS yielded accurate thresholds to activate laryngeal motor fibers and captured the inter-individual variability for both acute and chronic implants. For B fibers, our small-diameter fiber model underestimated threshold and saturation for pulse widths >0.25 ms. Our models of pig VNS consistently captured the range ofin vivothresholds across all measured nerve and physiological responses (i.e. heart rate, Aδ/B fibers, Aγfibers, electromyography, and Aαfibers). In rats, our smallest diameter myelinated fibers accurately predicted fast fiber thresholds across short and intermediate pulse widths; slow unmyelinated fiber thresholds overestimated thresholds across shorter pulse widths, but there was overlap for pulse widths >0.3 ms.Significance.We elevated standards for models of peripheral nerve stimulation in populations of models across species, which enabled us to model accurately nerve responses, demonstrate that individual-specific differences in nerve morphology produce variability in neural and physiological responses, and predict mechanisms of VNS therapeutic and side effects.

The effect of the COVID-19 pandemic on substance use patterns and physiological dysregulation in pregnant and postpartum women

BACKGROUND

The SARS-CoV-2/COVID-19 pandemic has been associated with increased stress levels and higher alcohol use, including in pregnant and postpartum women. In the general population, alcohol use is associated with dysregulation in the autonomic nervous system (ANS), which is indexed by heart rate variability (HRV). The objectives of this study were to: (1) characterize changes in substance use during the SARS-CoV-2/COVID-19 pandemic via a baseline self-report survey followed by mobile ecological momentary assessment (mEMA) of substance use; and (2) examine the associations between momentary substance use and ambulatory HRV measures in pregnant and postpartum women.

METHODS

Pregnant and postpartum women were identified from the ENRICH-2 prospective cohort study. Participants were administered a baseline structured phone interview that included the Coronavirus Perinatal Experiences (COPE) survey and ascertained the prevalence of substance use. Over a 14-day period, momentary substance use was assessed three times daily, and HRV measurements were captured via wearable electronics. Associations between momentary substance use and HRV measures (root mean square of successive differences [RMSSD] and low frequency/high frequency [LF/HF] ratio) were examined using a mixed effects model that included within-subject (WS) and between-subject (BS) effects and adjusted for pregnancy status and participant age.

RESULTS

The sample included 49 pregnant and 22 postpartum women. From a combination of a baseline and 14-day mEMA surveys, 21.2% reported alcohol use, 16.9% reported marijuana use, and 8.5% reported nicotine use. WS effects for momentary alcohol use were associated with the RMSSD (β = -0.14; p = 0.005) and LF/HF ratio (β = 0.14; p = 0.01) when controlling for pregnancy status and maternal age. No significant associations were observed between HRV measures and instances of marijuana or nicotine use.

CONCLUSIONS

These findings highlight the negative effect of the SARS-CoV-2/COVID-19 pandemic on the psychological health of pregnant and postpartum women associated with substance use, and in turn, ANS dysregulation, which potentially puts some women at risk of developing a substance use disorder.

Autonomic Cardiovascular Control in Health and Disease

Autonomic neural control of the cardiovascular system is formed of complex and dynamic processes able to adjust rapidly to mitigate perturbations in hemodynamics and maintain homeostasis. Alterations in autonomic control feature in the development or progression of a multitude of diseases with wide-ranging physiological implications given the neural system's responsibility for controlling inotropy, chronotropy, lusitropy, and dromotropy. Imbalances in sympathetic and parasympathetic neural control are also implicated in the development of arrhythmia in several cardiovascular conditions sparking interest in autonomic modulation as a form of treatment. A number of measures of autonomic function have shown prognostic significance in health and in pathological states and have undergone varying degrees of refinement, yet adoption into clinical practice remains extremely limited. The focus of this contemporary narrative review is to summarize the anatomy, physiology, and pathophysiology of the cardiovascular autonomic nervous system and describe the merits and shortfalls of testing modalities available. © 2023 American Physiological Society. Compr Physiol 13:4493-4511, 2023.

Structure and Functions of the Vagus Nerve in Mammals

We review the structure and function of the vagus nerve, drawing on information obtained in humans and experimental animals. The vagus nerve is the largest and longest cranial nerve, supplying structures in the neck, thorax, and abdomen. It is also the only cranial nerve in which the vast majority of its innervation territory resides outside the head. While belonging to the parasympathetic division of the autonomic nervous system, the nerve is primarily sensory-it is dominated by sensory axons. We discuss the macroscopic and microscopic features of the nerve, including a detailed description of its extensive territory. Histochemical and genetic profiles of afferent and efferent axons are also detailed, as are the central nuclei involved in the processing of sensory information conveyed by the vagus nerve and the generation of motor (including parasympathetic) outflow via the vagus nerve. We provide a comprehensive review of the physiological roles of vagal sensory and motor neurons in control of the cardiovascular, respiratory, and gastrointestinal systems, and finish with a discussion on the interactions between the vagus nerve and the immune system. © 2022 American Physiological Society. Compr Physiol 12: 1-49, 2022.

Cannabidiol activation of vagal afferent neurons requires TRPA1

Vagal afferent neurons abundantly express excitatory transient receptor potential (TRP) channels, which strongly influence afferent signaling. Cannabinoids have been identified as direct agonists of TRP channels, including TRPA1 and TRPV1, suggesting that exogenous cannabinoids may influence vagal signaling via TRP channel activation. The diverse therapeutic effects of electrical vagus nerve stimulation also result from administration of the nonpsychotropic cannabinoid, cannabidiol (CBD); however, the direct effects of CBD on vagal afferent signaling remain unknown. We investigated actions of CBD on vagal afferent neurons, using calcium imaging and electrophysiology. CBD produced strong excitatory effects in neurons expressing TRPA1. CBD responses were prevented by removal of bath calcium, ruthenium red, and the TRPA1 antagonist A967079, but not the TRPV1 antagonist SB366791, suggesting an essential role for TRPA1. These pharmacological experiments were confirmed using genetic knockouts where TRPA1 KO mice lacked CBD responses, whereas TRPV1 knockout (KO) mice exhibited CBD-induced activation. We also characterized CBD-provoked inward currents at resting potentials in vagal afferents expressing TRPA1 that were absent in TRPA1 KO mice, but persisted in TRPV1 KO mice. CBD also inhibited voltage-activated sodium conductances in A-fiber, but not in C-fiber afferents. To simulate adaptation, resulting from chronic cannabis use, we administered cannabis extract vapor daily for 3 wk. Cannabis exposure reduced the magnitude of CBD responses, likely due to a loss of TRPA1 signaling. Together, these findings detail a novel excitatory action of CBD at vagal afferent neurons, which requires TRPA1 and may contribute to the vagal mimetic effects of CBD and adaptation following chronic cannabis use.NEW & NOTEWORTHY CBD usage has increased with its legalization. The clinical efficacy of CBD has been demonstrated for conditions including some forms of epilepsy, depression, and anxiety that are also treatable by vagus nerve stimulation. We found CBD exhibited direct excitatory effects on vagal afferent neurons that required TRPA1, were augmented by TRPV1, and attenuated following chronic cannabis vapor exposure. These effects may contribute to vagal mimetic effects of CBD and adaptation after chronic cannabis use.

New description of vagal nerve commanted intrapancreatic taste buds and blood glucose level: An experimental analysis

Introduction: There have been thousands of neurochemical mechanism about blood glucose level regulation, but intrapancreatic taste buds and their roles in blood glucose level has not been described. We aimed to investigate if there are taste buds cored neural networks in the pancreas, and there is any relationship between blood glucose levels.

Methods: This examination was done on 32 chosen rats with their glucose levels. Animals are divided into owned blood glucose levels. If mean glucose levels were equal to 105 ± 10 mg/dL accepted as euglycemic (G-I; n = 14), 142 ± 18 mg/dL values accepted as hyperglycemic (G-II; n = 9) and 89 ± 9 mg/dL accepted as hypoglycemic (G-III; n = 9). After the experiment, animals were sacrificed under general anesthesia. Their pancreatic tissues were examined histological methods and numbers of newly described taste bud networks analyzed by Stereological methods. Results compared with Mann-Whitney U test P  < 0.005 considered as significant.

Results: The mean normal blood glucose level (mg/dL) and taste bud network densities of per cm³ were: 105 ± 10 mg/dL; 156±21 in G-I; 142 ± 18 mg/dL and 95 ± 14 in G-II and 89 ± 9 mg/dL and 232 ± 34 in G-III. P values as follows: P < 0.001 of G-II/G-I; P < 0.005 of G-III/G-I and P < 0.0001 of G-III/G-II. We detected periarterial located taste buds like cell clusters and peripherally located ganglia connected with Langerhans cells via thin nerve fibers. There was an inverse relationship between the number of taste buds networks and blood glucose level.

Conclusion: Newly described intrapancreatic taste buds may have an important role in the regulation of blood glucose level.

Vagus Nerve Ultrasound in Chronic Inflammatory Demyelinating Polyradiculoneuropathy and Charcot-Marie-Tooth Disease Type 1A

BACKGROUND AND PURPOSE

Both clinical autonomic dysfunction and involvement of autonomic nerves have been reported in a range of peripheral nerve disorders. We employed nerve ultrasound to assess the size of the vagus nerve in a serial study of patients with chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) and Charcot-Marie-Tooth type 1B (CMT1B) as compared to healthy controls (HCs). We correlated these findings with involvement of the median and ulnar nerves.

METHODS

Forty-three patients with CIDP, 8 with CMT1A, and 105 HC were prospectively recruited. The cross-sectional areas (CSAs) of the vagus, median, and ulnar nerves were measured bilaterally. The alteration of CSA of those nerves was followed longitudinally in CIDP.

RESULTS

The median (range) CSA of the vagus nerve was 2 (1-28) mm² in CIDP, 3 (2-6) mm² in CMT1A, and 1 (1-2) mm² in HC. The vagus nerve CSA was positively correlated with the maximum CSA of median/ulnar nerve in CIDP and CMT1A. The alteration in vagus nerve CSA was positively correlated with the alteration in mean median/ulnar nerve CSA in CIDP during follow-up.

CONCLUSIONS

The vagus nerve was involved to a similar extent as the median and ulnar nerves in CIDP and CMT1A, although no symptoms or signs of vagus nerve involvement were found. Further study should be performed to explore the clinical relevance of vagus nerve enlargement in these disorders.

Evoked K-complexes and altered interaction between the central and autonomic nervous systems during sleep in alcohol use disorder

There is evidence for impairment in both central nervous system (CNS) and autonomic nervous system (ANS) function with prolonged alcohol use. While these impairments persist into abstinence, partial recovery of function has been demonstrated in both systems during sleep. To investigate potential ANS dysfunction associated with cortical CNS responses (impairment in CNS-ANS coupling), we assessed phasic heart rate (HR) fluctuation associated with tones that did and those that did not elicit a K-complex (KC) during stable N2 non-rapid eye movement (NREM) sleep in a group of 16 recently abstinent alcohol use disorder (AUD) patients (41.6 ± 8.5 years) and a group of 13 sex- and age-matched control participants (46.6 ± 9.3 years). Electroencephalogram (EEG) and electrocardiogram (ECG) data were recorded throughout the night. Alcohol consumption questionnaires were also administered to the AUD patients. AUD patients had elevated HR compared to controls at baseline prior to tone presentation. The HR fluctuation associated with KCs elicited by tone presentation was significantly smaller in amplitude, and tended to be delayed in time, in the AUD group compared with the control group, and the subsequent deceleration was also smaller in AUD patients. In both groups, the increase in HR was larger and occurred earlier when KCs were produced than when they were not, and there was no difference in the magnitude of the KC effect between groups. Phasic HR changes associated with KCs elicited by tones are impaired in AUD participants, reflecting ANS dysfunction possibly caused by an alteration of cardiac vagal trafficking. However, only the timing of the HR response was found to relate to estimated lifetime alcohol consumption in AUD. The clinical meaning and implications of these novel findings need to be determined.

In vivo quantification of excitation and kilohertz frequency block of the rat vagus nerve

OBJECTIVE

There is growing interest in treating diseases by electrical stimulation and block of peripheral autonomic nerves, but a paucity of studies on the excitation and block of small-diameter autonomic axons. We conducted in vivo quantification of the strength-duration properties, activity-dependent slowing (ADS), and responses to kilohertz frequency (KHF) signals for the rat vagus nerve (VN).

APPROACH

We conducted acute in vivo experiments in urethane-anaesthetized rats. We placed two cuff electrodes on the left cervical VN and one cuff electrode on the anterior subdiaphragmatic VN. The rostral cervical cuff was used to deliver pulses to quantify recruitment and ADS. The caudal cervical cuff was used to deliver KHF signals. The subdiaphragmatic cuff was used to record compound action potentials (CAPs).

MAIN RESULTS

We quantified the input-output recruitment and strength-duration curves. Fits to the data using standard strength-duration equations were qualitatively similar, but the resulting chronaxie and rheobase estimates varied substantially. We measured larger thresholds for the slowest fibres (0.5-1 m s^-1), especially at shorter pulse widths. Using a novel cross-correlation CAP-based analysis, we measured ADS of ~2.3% after 3 min of 2 Hz stimulation, which is comparable to the ADS reported for sympathetic efferents in somatic nerves, but much smaller than the ADS in cutaneous nociceptors. We found greater ADS with higher stimulation frequency and non-monotonic changes in CV in select cases. We found monotonically increasing block thresholds across frequencies from 10 to 80 kHz for both fast and slow fibres. Further, following 25 s of KHF signal, neural conduction could require tens of seconds to recover.

SIGNIFICANCE

The quantification of mammalian autonomic nerve responses to conventional and KHF signals provides essential information for the development of peripheral nerve stimulation therapies and for understanding their mechanisms of action.

Evaluating the functional and structural changes in the vagus nerve: Should the vagus nerve be tested in patients with atrial fibrillation?

One of the multiple factors believed to contribute to the initiation and maintenance of atrial fibrillation (AF) is altered activity of the autonomic nervous system. Debate continues about the role of the vagus nerve (CNX) in AF since its effect depends on the level of its activation as well as on simultaneous sympathetic activation. Surplus either vagal or sympathetic activity may rarely induce the development of AF; however, typically loss of balance between the both systems mediates the induction and maintenance of AF. Vagal stimulation has been proposed as a novel treatment approach for AF because the anti-arrhythmic effects of low-level vagus nerve stimulation have been shown both in patients and animal models. We hypothesize that in typical cases of AF without any clear trigger by either autonomic nervous system, significant changes in vagus somatosensory evoked potentials and a smaller cross-sectional area of CNX could be detected, representing functional and structural changes in CNX, respectively.

Autonomic Nervous System Dysfunction: JACC Focus Seminar

Autonomic nervous system control of the heart is a dynamic process in both health and disease. A multilevel neural network is responsible for control of chronotropy, lusitropy, dromotropy, and inotropy. Intrinsic autonomic dysfunction arises from diseases that directly affect the autonomic nerves, such as diabetes mellitus and the syndromes of primary autonomic failure. Extrinsic autonomic dysfunction reflects the changes in autonomic function that are secondarily induced by cardiac or other disease. An array of tests interrogate various aspects of cardiac autonomic control in either resting conditions or with physiological perturbations from resting conditions. The prognostic significance of these assessments have been well established. Clinical usefulness has not been established, and the precise mechanistic link to mortality is less well established. Further efforts are required to develop optimal approaches to delineate cardiac autonomic dysfunction and its adverse effects to develop tools that can be used to guide clinical decision-making.

Stimulation Pattern Efficiency in Percutaneous Auricular Vagus Nerve Stimulation: Experimental Versus Numerical Data

OBJECTIVE

Percutaneous electrical stimulation of the auricular vagus nerve (pVNS) is an electroceutical technology. The selection of stimulation patterns is empirical, which may lead to under-stimulation or over-stimulation. The objective is to assess the efficiency of different stimulation patterns with respect to individual perception and to compare it with numerical data based on in-silico ear models.

METHODS

Monophasic (MS), biphasic (BS) and triphasic stimulation (TS) patterns were tested in volunteers. Different clinically-relevant perception levels were assessed. In-silico models of the human ear were created with embedded fibers and vessels to assess different excitation levels.

RESULTS

TS indicates experimental superiority over BS which is superior to MS while reaching different perception levels. TS requires about 57% and 35% of BS and MS magnitude, respectively, to reach the comfortable perception. Experimental thresholds decrease from non-bursted to bursted stimulation. Numerical results indicate a slight superiority of BS and TS over MS while reaching different excitation levels, whereas the burst length has no influence. TS yields the highest number of asynchronous action impulses per stimulation symbol for the used tripolar electrode set-up.

CONCLUSION

The comparison of experimental and numerical data favors the novel TS pattern. The analysis separates excitatory pVNS effects in the auricular periphery, as accounted by in-silico data, from the combination of peripheral and central pVNS effects in the brain, as accounted by experimental data.

SIGNIFICANCE

The proposed approach moves from an empirical selection of stimulation patterns towards efficient and optimized pVNS settings.

Heart rate variability in alcohol use: A review

BACKGROUND

Prior studies have shown that resting heart rate variability (HRV) is reduced in those with alcohol use disorders (AUD). However, HRV following an acute stressful stimulus (reactive HRV), and the relationship between resting or reactive HRV and drinking, craving and relapse in AUD have received less attention.

METHODS

Studies using HRV in relationship to acute or chronic alcohol consumption were included in this review. Manuscripts that related to alcohol in the context of cardiovascular disease were excluded.

RESULTS

Thirty-three articles were included and findings are presented in healthy social drinkers, moderate/heavy drinkers without AUD and individuals with AUD. Results on resting and reactive HRV were presented separately. Acute alcohol reduced resting HRV in healthy subjects but healthy controls had higher resting HRV then AUD subjects and moderate/heavy drinkers (in some studies). Resting HRV improved in AUD subjects only after at least 4 months of abstinence. AUD subjects had higher reactive HRV scores when compared to controls. In AUD subjects increased reactivity was related to more craving, faster relapse and more negative mood. Reactive HRV showed slower improvement with abstinence in AUD subjects.

CONCLUSIONS

Chronic, heavy alcohol has a negative effect on the autonomic nervous system and may be a sensitive biomarker of craving and relapse.

On the parameters used in finite element modeling of compound peripheral nerves

OBJECTIVE

Computational modeling is an important tool for developing and optimizing implantable neural stimulation devices, but requires accurate electrical and geometrical parameter values to improve predictive value. We quantified the effects of perineurial (resistive sheath around each fascicle) and endoneurial (within each fascicle) parameter values for modeling peripheral nerve stimulation.

APPROACH

We implemented 3D finite element models of compound peripheral nerves and cuff electrodes to quantify activation and block thresholds of model axons. We also implemented a 2D finite element model of a bundle of axons to estimate the bulk transverse endoneurial resistivity; we compared numerical estimates to an analytical solution.

MAIN RESULTS

Since the perineurium is highly resistive, potentials were approximately constant over the cross section of a fascicle, and the perineurium resistivity, longitudinal endoneurial resistivity, and fascicle diameter had important effects on thresholds. Activation thresholds increased up to ~130% for higher perineurium resistivity (~400 versus 2200 Ω m) and by ~35%-250% for lower longitudinal endoneurial resistivity (3.5 versus 0.75 Ω m), with larger increases for smaller diameter axons and for axons in larger fascicles. Further, thresholds increased by ~30%-180% for larger fascicle radii, yielding a larger increase with higher perineurium resistivity. Thresholds were largely insensitive to the transverse endoneurial resistivity, but estimates of the bulk resistivity increased with extracellular resistivity and axonal area fraction; the numerical and analytical estimates were in strong agreement except at high axonal area fractions, where structured axon placements that achieved tighter packing produced electric field inhomogeneities.

SIGNIFICANCE

We performed a systematic investigation of the effects of values and methods for modeling the perineurium and endoneurium on thresholds for neural stimulation and block. These results provide guidance for future modeling studies, including parameter selection, data interpretation, and comparison to experimental results.

Modeling the response of small myelinated axons in a compound nerve to kilohertz frequency signals

OBJECTIVE

There is growing interest in electrical neuromodulation of peripheral nerves, particularly autonomic nerves, to treat various diseases. Electrical signals in the kilohertz frequency (KHF) range can produce different responses, including conduction block. For example, EnteroMedics' vBloc® therapy for obesity delivers 5 kHz stimulation to block the abdominal vagus nerves, but the mechanisms of action are unclear.

APPROACH

We developed a two-part computational model, coupling a 3D finite element model of a cuff electrode around the human abdominal vagus nerve with biophysically-realistic electrical circuit equivalent (cable) model axons (1, 2, and 5.7 µm in diameter). We developed an automated algorithm to classify conduction responses as subthreshold (transmission), KHF-evoked activity (excitation), or block. We quantified neural responses across kilohertz frequencies (5-20 kHz), amplitudes (1-8 mA), and electrode designs.

MAIN RESULTS

We found heterogeneous conduction responses across the modeled nerve trunk, both for a given parameter set and across parameter sets, although most suprathreshold responses were excitation, rather than block. The firing patterns were irregular near transmission and block boundaries, but otherwise regular, and mean firing rates varied with electrode-fibre distance. Further, we identified excitation responses at amplitudes above block threshold, termed 're-excitation', arising from action potentials initiated at virtual cathodes. Excitation and block thresholds decreased with smaller electrode-fibre distances, larger fibre diameters, and lower kilohertz frequencies. A point source model predicted a larger fraction of blocked fibres and greater change of threshold with distance as compared to the realistic cuff and nerve model.

SIGNIFICANCE

Our findings of widespread asynchronous KHF-evoked activity suggest that conduction block in the abdominal vagus nerves is unlikely with current clinical parameters. Our results indicate that compound neural or downstream muscle force recordings may be unreliable as quantitative measures of neural activity for in vivo studies or as biomarkers in closed-loop clinical devices.

Neuromuscular ultrasound of cranial nerves

Ultrasound of cranial nerves is a novel subdomain of neuromuscular ultrasound (NMUS) which may provide additional value in the assessment of cranial nerves in different neuromuscular disorders. Whilst NMUS of peripheral nerves has been studied, NMUS of cranial nerves is considered in its initial stage of research, thus, there is a need to summarize the research results achieved to date. Detailed scanning protocols, which assist in mastery of the techniques, are briefly mentioned in the few reference textbooks available in the field. This review article focuses on ultrasound scanning techniques of the 4 accessible cranial nerves: optic, facial, vagus and spinal accessory nerves. The relevant literatures and potential future applications are discussed.

Poor autonomic nervous system functioning during sleep in recently detoxified alcohol-dependent men and women

BACKGROUND

Alcoholism is considered an important risk factor for cardiovascular (CV) disease. Autonomic nervous system (ANS) function is a major indicator of CV health. Sleep is a suitable model to investigate ANS activity free from wake-related confounders. We investigated nighttime ANS functioning, and the relation between ANS activity and severity of alcohol dependence in chronic alcoholism.

METHODS

Fourteen recently abstaining alcoholics (age: 42.0 ± 9.0 years, 7 women) and 16 age- and sex-matched controls (age: 45.2 ± 9.1 years, 8 women) underwent a night of standard clinical polysomnography, including electrocardiographic recording. Time- and frequency-domain spectral analysis of heart rate variability (HRV) was performed across hours of the night and during artifact-free epochs of stable sleep and wakefulness (presleep wakefulness, rapid-eye-movement [REM], and non-REM sleep).

RESULTS

Alcoholics had a poorer subjective and objective sleep quality compared to controls. Across the night, alcoholic men and women had elevated heart rate, reduced total HRV, that is, lower standard deviation of normal-to-normal interbeat intervals, and reduced high frequency (HF) activity (assessed by the HF power and by the square root of the mean squared of successive heart period differences). This ANS pattern was most apparent at the beginning of the night. None of the ANS measures was associated with lifetime alcohol consumption or duration of alcohol dependence.

CONCLUSIONS

Our results show that ANS functioning is disrupted during the night, even in undisturbed sleep periods, indicating poor CV functioning in recently detoxified alcohol-dependent men and women.

Effect of methamphetamine dependence on heart rate variability

Methamphetamine (METH) is an increasing popular and highly addictive stimulant associated with autonomic nervous system (ANS) dysfunction, cardiovascular pathology and neurotoxicity. Heart rate variability (HRV) has been used to assess autonomic function and predict mortality in cardiac disorders and drug intoxication, but has not been characterized in METH use. We recorded HRV in a sample of currently abstinent individuals with a history of METH dependence compared to age- and gender-matched drug-free comparison subjects. HRV was assessed using time domain, frequency domain, and non-linear entropic analyses in 17 previously METH-dependent and 21 drug-free comparison individuals during a 5 minute rest period. The METH-dependent group demonstrated significant reduction in HRV, reduced parasympathetic activity, and diminished heartbeat complexity relative to comparison participants. More recent METH use was associated with increased sympathetic tone. Chronic METH exposure may be associated with decreased HRV, impaired vagal function, and reduction in heart rate complexity as assessed by multiple methods of analysis. We discuss and review evidence that impaired HRV may be related to the cardiotoxic or neurotoxic effects of prolonged METH use.

Absence of cardiovascular autonomic dysfunction and vagal pancreatic impairment in idiopathic achalasia of the oesophagus

Extra-oesophageal autonomic dysfunction in idiopathic achalasia is not well documented, due to contradictory results reported. We aimed to study the cardiovascular and pancreatic autonomic function in patients with idiopathic achalasia. Thirty patients with idiopathic achalasia (16M/14F; 34.5 +/- 10.8 years) and 30 healthy volunteers (13M/17F; 34.8 +/- 10.7 years) were prospectively studied. Age >60 years and conditions affecting results of autonomic evaluation were excluded. Both groups underwent the sham feeding test and plasmatic levels of pancreatic polypeptide (PP) were determined by radioimmunoassay (basal, at 5, 10, 20 and 30 min). Cardiovascular parasympathetic (deep breathing, standing, Valsalva) and sympathetic function (postural decrease of systolic blood pressure, Handgrip test) were assessed. Statistical comparison of basal and increase levels of PP and parasympathetic/sympathetic cardiovascular parameters was performed between groups. Basal levels of PP were similar in controls and patients and maximum increase of PP during sham feeding test. A similar rate of abnormal cardiovascular tests was found between groups (P > 0.05). E/I ratio was the mostly impaired parameter (patients: 36.7% vs controls: 20%, P = 0.15, chi-squared test). Autonomic cardiovascular tests and pancreatic response to vagal stimulus are not impaired in patients with primary achalasia of the oesophagus.

Impairment of transneuronal traffic in Streptozotocin-induced diabetes, a WGA-HRP neurohistochemical study in the rat

Retrograde transport of Wheat germ agglutinin conjugated to Horseradish peroxidase (WGA-HRP) was used in labeling vagal neurons projecting to the stomach from the dorsal motor nucleus of the vagus nerve (DMNV) in Streptozotocin (STZ)-induced diabetic rats. Diabetes was induced in the experimental rats by intraperitoneal injection of buffered STZ. Control rats were injected with an equivalent volume of the citrate buffer not containing STZ. The experimental rats, which became diabetic about 24 h after intraperitoneal injection of STZ, were kept alive for a period of 24 weeks to attain a chronic state of diabetes. Control euglycaemic rats were also kept alive for 24 weeks. At the end of 24 weeks, the two groups of rats were prepared for stomach surgery. Following anaesthesia laparotomy was performed and the stomach exteriorized. The anterior and posterior walls of the stomach were injected with 0.1 ml of 5% WGA-HRP in 0.5 M sodium chloride. Experimental and control rats were sacrificed 48-72 h after tracer injection by transcardial perfusion with normal saline, fixative and buffered sucrose. Transverse serial frozen sections of the brainstem were processed for WGA-HRP neurohistochemistry and analyzed under light and dark-field microscopy. The analyses of the sections taken from the chronic diabetic rats revealed fewer WGA-HRP labeled neurons in the DMNV than sections taken from the control euglycaemic rats. The depletion of labeled neurons in the diabetic rats compared with the euglycaemic rats is indicative of an interference with the mechanism of retrograde neuronal transport of WGA-HRP by chronic diabetic state.

Erectile dysfunction as a sentinel symptom of cardiovascular autonomic neuropathy in heavy drinkers

Because autonomic neuropathy (AN) is not routinely assessed in chronic alcoholism, its features and relationship with other disease parameters remain undefined. The very existence of true alcohol-related autonomic dysfunction, in the absence of alcoholic hepatopathy, is even controversial. We aimed this study at evaluating the frequency and pattern of AN in a population of heavy drinkers without liver dysfunction. We also investigated the putative risk factors for AN as well as its relationship to peripheral neuropathy (PN). Autonomic function was evaluated in 70 detoxified alcoholics and 70 well-matched controls by heart-rate response to deep breathing, heart-rate response to standing from lying position, and blood pressure response to standing up. PN was assessed by electroneurography (ENG). Detailed information about sensorimotor and autonomic symptoms, nutritional status, and parameters reflecting alcohol intake were recorded. No patients showed signs of caloric/protein malnutrition. PN was found in 74% and AN (abnormal test results in two of three tests performed) in 26%; abnormalities in at least one autonomic test were found in 62%. All patients with PN were symptomatic, mainly due to sensory disturbances. In line with this, ENG abnormalities were more evident at sural nerves. AN was symptomatic in 10 of 18 patients, and its sole clinical expression was impotence: indeed, the pattern of autonomic involvement was mainly parasympathetic. AN did not correlate with PN, nor with any parameter reflecting the amount of alcohol intake; only performances on heart-rate response to standing from lying position were related to the duration of abuse. The lack of correlation between PN and AN may suggest a different pathophysiology for these two complications. Unlike PN, AN is often asymptomatic. Among symptomatic patients (55%), erectile dysfunction seems to be the sole symptom, in line with the higher degree of parasympathetic damage.

α-Lipoic acid treatment prevents the diabetes-induced attenuation of the afferent limb of the baroreceptor reflex in rats

Autonomic neuropathies, common complications of prolonged diabetes, may result from diabetes-induced increased oxidative stress. Recently, we found that the afferent component of the baroreceptor reflex is attenuated in streptozotocin-induced diabetic rats. This study sought to determine the influence of the anti-oxidant, alpha-lipoic acid on the diabetes-induced deficits of the afferent limb of the baroreceptor reflex and on plasma malondialdehyde (a measure of lipid peroxidation). The number of c-Fos-ir neurons in the nucleus tractus solitarius in response to phenylephrine-induced baroreceptor activation was used as an index of the integrity of the afferent limb of the baroreceptor reflex. Groups of streptozotocin-induced diabetic and non-diabetic control rats, maintained from 8 to 16 weeks, were treated with alpha-lipoic acid (100 mg kg(-1) IP, 5x/week), or vehicle for the last 4 weeks prior to the experimental procedure. Vehicle-treated diabetic rats had elevated plasma malondialdehyde levels when compared to non-diabetic rats. alpha-Lipoic acid-treated diabetic rats had plasma malondialdehyde levels similar to those seen in non-diabetic rats and less than those of vehicle-treated diabetic rats at both the 8- and 16-week time points.alpha-Lipoic acid treatment did not affect the baseline (absence of baroreceptor activation) presence of c-Fos-ir in the nucleus tractus solitarius. In response to phenylephrine and regardless of treatment, the diabetic and control rats displayed increases in blood pressure and reflex bradycardia. As previously reported, phenylephrine-induced baroreceptor activation resulted in significantly fewer c-Fos-ir neurons in the nucleus tractus solitarius (commissural and caudal subpostremal regions) of diabetic rats when compared to non-diabetic rats at both 8- and 16-week time points. Four weeks of alpha-lipoic acid treatment reversed the diabetes-induced decrement in the numbers of c-Fos-ir neurons in the nucleus tractus solitarius in response to baroreceptor activation. alpha-Lipoic acid-treated diabetic rats showed the same phenylephrine-induced c-Fos response in the nucleus tractus solitarius as those of alpha-lipoic-acid- and vehicle-treated control rats at both 8- and 16-week time points. These data suggest that diabetes-induced oxidative stress plays a role in diabetes-induced baroreceptor dysfunction and that the alpha-lipoic acid may have a beneficial effect in treatment of diabetic autonomic neuropathy.

Effects of glucagon-like peptide-1 and feeding on gastric volumes in diabetes mellitus with cardio-vagal dysfunction

Glucagon-like peptide-1 (GLP-1) increases gastric volume in humans possibly through the vagus nerve. Gastric volume response to feeding is preserved after vagal denervation in animals. We evaluated gastric volume responses to GLP-1 and placebo in seven diabetic patients with vagal neuropathy in a crossover study. We also compared gastric volume response to feeding in diabetes with that in healthy controls. We measured gastric volume using SPECT imaging. Data are median (interquartile range). In diabetic patients, GLP-1 did not increase gastric volume during fasting [5 mL (-3; 30)] relative to placebo [4 mL (-14; 50) P = 0.5], or postprandially [Delta postprandial minus fasting volume 469 mL (383; 563) with GLP-1 and 452 mL (400; 493) with placebo P = 0.3]. Change in gastric volume over fasting in diabetic patients on placebo was comparable to that of healthy controls [452 mL (400; 493)], P = 0.5. In contrast to effects in health, GLP-1 did not increase gastric volume in diabetics with vagal neuropathy, suggesting GLP-1's effects on stomach volume are vagally mediated. Normal gastric volume response to feeding in diabetics with vagal neuropathy suggests that other mechanisms compensate for vagal denervation.

Neuropathology and pathogenesis of diabetic autonomic neuropathy

Autonomic neuropathy is a significant complication of diabetes resulting in increased patient morbidity and mortality. A number of studies, which have shown correspondence between neuropathologic findings in experimental animals and human subjects, have demonstrated that axonal and dendritic pathology in sympathetic ganglia in the absence of significant neuron loss represents a neuropathologic hallmark of diabetic autonomic neuropathy. A recurring theme in sympathetic ganglia, as well as in the pot-ganglionic autonomic innervation of various end organs, is the involvement of distal portions of axons and nerve terminals by degenerative or dystrophic changes. In both animals and humans, there is a surprising selectivity of the diabetic process for subpopulations of autonomic ganglia, nerve terminals within sympathetic ganglia and end organs, from end organ to end organ, and between vascular and other targets within individual end organs. Although the involvement or autonomic axons in somatic nerves may reflect an ischemic pathogenesis, the selectivity of the diabetic process confounds simple global explanations of diabetic autonomic neuropathy as the result of diminished blood flow with resultant tissue hypoxia. A single unifying pathogenetic hypothesis has not yet emerged from clinical and experimental animal studies, and it is likely that diabetic autonomic neuropathy will be shown to have multiple causative mechanisms, which will interact to result in the variety of presentations of autonomic injury in diabetes. Some of these mechanisms will be shared with aging changes in the autonomic nervous system. The role of various neurotrophic substances and the polyol pathway in the pathogenesis and treatment of diabetic neuropathy likely represents a two-edged sword with both salutary and exacerbating effects. The basic neurobiologic process underlying the diabetes-induced development of neuroaxonal dystrophy, synaptic dysplasia, defective axonal regeneration, and alterations in neurotrophic substance may be mechanistically related.

Streptozotocin-induced diabetes reduces retrograde axonal transport in the afferent and efferent vagus nerve

Diabetes-induced alterations in nerve function include reductions in the retrograde axonal transport of neurotrophins. A decreased axonal accumulation of endogenous nerve growth factor (NGF) and neurotrophin-3 (NT-3) in the vagus nerve of streptozotocin (STZ)-induced diabetic rats was previously shown. In the current study, no changes in the NGF and NT-3 protein or mRNA levels in the stomach or atrium, two vagally innervated organs, were noted after 16 or 24 weeks of diabetes. Moreover, the amounts of neurotrophin receptor (p75, TrkA, TrkC) mRNAs in the vagus nerve and vagal afferent nodose ganglion were not reduced in diabetic rats. These data suggest that neither diminished access to target-derived neurotrophins nor the loss of relevant neurotrophin receptors accounts for the diabetes-induced alteration in the retrograde axonal transport of neurotrophins. To assess whether diabetes causes a defect in axonal transport that may not be specific to neurotrophin transport, we studied the ability of a neuronal tracer (FluoroGold, FG) to be retrogradely transported by vagal neurons of control and diabetic rats. After vagal target tissue (stomach) injections of FG, the numbers of FG-labeled afferent and efferent vagal neurons were counted in the nodose ganglion and in the dorsal motor nucleus of the vagus, respectively. After 24 weeks of diabetes, FG was retrogradely transported to more than 50% fewer afferent and efferent vagal neurons in the STZ-diabetic compared to control rats. The diabetes-induced deficit in retrograde axonal transport of FG is likely to reflect alterations in basic axonal transport mechanisms in both the afferent and efferent vagus nerve that contribute to the previously observed reductions in neurotrophin transport.

Attenuation of the afferent limb of the baroreceptor reflex in streptozotocin-induced diabetic rats

Diabetic autonomic neuropathy is a common complication following prolonged diabetes. Alterations of cardiovascular reflexes contribute to the increased cardiovascular morbidity and mortality seen in diabetic patients. This study sought to better characterize these complications by investigating the afferent limb of the baroreceptor reflex in an experimental rat model of diabetes. Streptozotocin (STZ)-induced diabetic and euglycemic control rats were studied at 8- and 16-week time points after initiation of the experiment. Activation of the afferent limb of the baroreceptor reflex was assessed by measuring the numbers of c-Fos-immunoreactive (ir) neurons in the CNS site of termination of the baroreceptor afferent neurons, the nucleus of the solitary tract (NTS). Initial experiments established that baseline cardiovascular parameters and NTS expression of c-Fos-ir neurons were not different between diabetic and control rats at either time point. Phenylephrine (PE)-induced activation of baroreceptors resulted in a significant elevation in the numbers of c-Fos-ir neurons in the NTS of control rats. Although diabetic rats showed similar pressor responses to PE, the activation of c-Fos-ir neurons in the NTS of diabetic rats was significantly attenuated. At both 8 and 16 weeks, STZ-induced diabetic rats had significantly fewer c-Fos-ir neurons in the commissural NTS and in the caudal subpostrernal NTS when compared to the non-diabetic control animals receiving PE. These data suggest that STZ-induced diabetes, for a period of 8 and 16 weeks, results in reduced activity in the afferent baroreceptor input to the NTS, and are consistent with diabetes-induced damage to baroreceptor afferent nerves.

Autonomic dysfunction in Chagas disease: lack of participation of the vagus nerve

To evaluate the possible role of the vagus nerve in the development of the dysautonomia in Chagas disease, we examined 18 nerves from chagasic patients and 8 from non-chagasic patients, autopsied at the Department of Pathology, Ribeirão Preto School of Medicine, Brazil. Histological analysis showed mild inflammatory infiltrate composed predominantly of T lymphocytes, in epi-, peri- and endoneurium. No parasites were observed. Semithin sections showed swollen unmyelinated fibres, occasional thinly myelinated fibres, degenerated and atrophic axons, related to myelinated fibres. These findings were confirmed by electron microscopy, and in teased fibres. The changes were observed both in chagasic and in non-chagasic patients. Statistical analysis of the morphometric findings (myelinated fibre density, axonal and fibre diameters) failed to show significant differences between the 2 groups. The frequency of myelinated fibres of various diameters was also similar in the 2 groups. The morphological and morphometrical findings in chagasic patients are mild, non-specific, and could be related to the age of the patients, or with artefacts, since they have also been observed in non-chagasic patients. Retrograde changes due to the ganglionic lesions in the innervated organs cannot be completely ruled out. Our results do not allow us to implicate the vagus nerve in the dysautonomia in Chagas disease.

Impaired stimulation of intestinal glucose absorption by portal insulin via hepatoenteral nerves in chronically ethanol-intoxicated rats

In the isolated, jointly perfused small intestine and liver of rats insulin, infused into the portal vein, induced an increase in intestinal glucose absorption via hepatoenteral cholinergic nerves. The possible loss of function of these nerves due to ethanol-induced neuropathy was investigated with 6 weeks ethanol-fed rats. Portal insulin or arterial carbachol failed to increase intestinal glucose absorption but cAMP still did so. The intact stimulatory effect of cAMP indicated an undisturbed capacity of the enterocytes. The loss of action of portal insulin and of arterial carbachol can be explained by the impairment of the hepatoenteral nerves in line with an ethanol-induced neuropathy.

Functional and histopathological evidence of cardiac parasympathetic dysautonomia in equine grass sickness

The parasympathetic terminal cardiac ganglia were examined in three normal horses and in five horses with grass sickness. Histopathological changes, consistent with those observed in other ganglia of horses with grass sickness, were identified in the terminal cardiac ganglia of the affected horses. A functional analysis of cardiac autonomic control by time domain analysis (TDA) of heart rate variability was applied to eight horses with grass sickness, and double-paired to 16 normal horses on the basis of their age, sex and breed, and the time of day at which the electrocardiographs were obtained. There were statistically significant differences between the normal and the affected horses in terms of the triangular index (P=0.01), a geometric method of TDA, the sNN100 index (P=0.009), a statistical method of TDA, and the R to R interval (P<0.0005). These results indicate that there is a pathological and functional parasympathetic decentralisation to the heart in equine grass sickness.

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.

Alcoholism, peripheral neuropathy (PNP) and cardiovascular autonomic neuropathy (CAN)

In contrast to diabetic autonomic neuropathy, cardiovascular autonomic neuropathy (CAN) in long-term alcoholics has been studied rarely. Using both standardized bedside tests and computer-assisted analysis of heart rate variability (HRV), we prospectively compared autonomic neurocardial function between 35 strictly selected, detoxified alcoholics (DSM-III-R), and 80 well matched healthy controls. Evidence for a potential CAN was found in 25.7% of all the alcoholics studied and in 41% of those with clinically manifest PNP (n=22). Overall, our results demonstrated a significant association between the presence of a CAN and peripheral neuropathy (PNP) amongst chronic alcoholics (chi-square test P<0.05); there was no evidence of a CAN in any of the alcoholics without a clinically manifest PNP. The CAN was characterized by a dissociated appearance of parasympathetic and sympathetic disorders. Our findings provide reason to suspect that the total lifetime dose of alcohol and the duration of alcohol dependence are the most important factors contributing to the pathogenesis of both PNP and sympathetic dysfunction. As is the case with diabetics, computer-assisted measurements of HRV including spectral analysis appear to be far superior to conventional bedside tests for detecting evidence of cardiovagal dysfunction in long-term alcoholics.

Impairment of metabolic hepatic nerve action by chronic but not acute ethanol intoxication studied in isolated perfused rat liver

BACKGROUND/AIMS

Liver carbohydrate metabolism and blood flow are regulated by hepatic nerves and hormones such as glucagon, insulin or catecholamines. Acute and chronic application of alcohol are known to depress the function of central and peripheral nerves. The extent of inhibition of the autonomic nervous system is not well characterized; thus, the possible impairment of hepatic nerve function by acute and chronic application of ethanol was investigated.

METHODS

Rat livers were perfused simultaneously via both the portal vein and hepatic artery. Hepatic nerves were stimulated electrically for 2 min (20 Hz, 20 V, 2 ms). As a control, noradrenaline (1 microM) was infused into the portal vein for 2 minutes.

RESULTS

During acute application of ethanol in portal concentrations of 50, 150 and 300 mM, which elevated basal glucose release, stimulation of hepatic nerves as well as portal noradrenaline infusion caused the same increase in glucose output and decrease in portal and arterial flow as in controls. Following chronic application of ethanol by feeding rats the Lieber-DeCarli liquid diet containing 5% (v/v) ethanol for 4 and 6 weeks, only nerve stimulation caused a significantly reduced enhancement of glucose output (50%, p < 0.025), whereas portal noradrenaline was as effective as in controls. Noradrenaline overflow was significantly reduced following nerve stimulation.

CONCLUSION

The decrease in nerve stimulation-dependent glucose output and noradrenaline overflow in chronically ethanol fed rats indicates an impaired function of hepatic nerves.

Assessment of autonomic neurotoxicity in occupational and environmental health as determined by ECG R-R interval variability: a review

Measurement of heart rate variability (coefficient of variation of ECG R-R intervals, CVRR) provides a useful approach for the objective assessment of the autonomic nervous function. It is noninvasive and clinically practical, although it tends to be distorted by confounding factors such as age, alcohol, and tobacco. Specifically, two component coefficients of variation of the respiratory sinus arrhythmia (RSA) and Mayer wave-related sinus arrhythmia (MWSA) in the CVRR (i.e., C-CVRSA and C-CVMWSA), computed from component spectral powers by autoregressive spectral and component analyses, are expected to reflect parasympathetic and sympathetic functions, respectively. This article is intended to present an overview of research, utilizing the CVRR method including the C-CVRSA and C-CVMWSA, in occupational and environmental health. The available literature, addressing the impact of some chemicals and work-related factors on human autonomic nervous system, indicates that parasympathetic activity appears to be more vulnerable to these factors than does sympathetic activity. Since decreased cardiac vagal tone is associated with an increased risk of sudden cardiac death or coronary artery disease, attention should be directed to further discovery of hazardous factors in the environment and work place, which are likely to affect the autonomic nervous system.

Autonomic neuropathy, II: Specific peripheral neuropathies

Autonomic dysfunction is a common complication of peripheral neuropathies. It is often of little clinical importance, but some conditions may cause profound disturbance of autonomic function. These conditions include acute dysautonomia, diabetes, primary and familial amyloidosis, Guillain-Barré syndrome, porphyria, and some inherited neuropathies. A wide range of neuropathies are associated with lesser degrees of autonomic dysfunction. These include hereditary neuropathies, and neuropathies associated with metabolic disturbances, alcohol abuse, malignancy, medications, infections, and connective tissue disorders.

Autonomic neuropathy, I. Clinical features, investigation, pathophysiology, and treatment

Autonomic dysfunction is a common complication of peripheral neuropathies. It is often of little clinical importance, but some conditions may cause profound disturbance of autonomic function, including postural hypotension, impotence and impairment of heart rate and bladder and bowel control. Autonomic function can be evaluated by a number of investigations, some of which can be performed in a neurophysiology laboratory. Diseases that primarily affect small nerve fibres or cause acute demyelination of small myelinated fibres are most likely to cause autonomic dysfunction. Management includes treating the underlying cause and symptomatic therapy.

Vagal nerve complex in normal development and sudden infant death syndrome

BACKGROUND

Although the pathogenesis of sudden infant death syndrome (SIDS) is not understood, one of the major hypotheses is that a subtle defect in respiratory circuitry is an important underlying factor. The vagus nerve is a critical component of respiratory control, but its neuroanatomic complexity has limited its investigation in human disease.

METHODS

Correlating developmental studies on different parts of the vagus nerve allows a more comprehensive assessment of its maturation process. Comparison of the normal developing vagus nerve with nerves examined in SIDS patients suggests alterations in the nucleus tractus solitarius and dorsal vagal nucleus as well as in the peripheral vagus nerve.

RESULTS AND CONCLUSIONS

The persistence of dendritic spines and lack of appropriate axonal growth implies delays in vagal maturation. Since nodose ganglia can be examined in vitro from autopsy material, perturbation to this system can be explored to evaluate further the mechanism involved in terminal vagal maturation. Although the reason for the delayed vagal maturation in SIDS is not apparent, the presence of astrogliosis in the region of the vagal nuclei is consistent with an exposure to hypoxic-ischemic events some time before death.

Autonomic neurotoxicity of alcohol assessed by heart rate variability

Measurement of heart rate variability (CVR-R) provides a promising approach for evaluation of the autonomic nervous function. Specifically, high- and low-frequency component coefficients of variation of the CVR-R (C-CVHF and C-CVLF), computed from component spectral powers by autoregressive spectral and component analyses, are inferred to reflect parasympathetic and sympathetic activities, respectively. To assess the acute and chronic effects of alcohol on parasympathetic and sympathetic activities, ECGs in the supine posture were obtained in 11 male healthy volunteers, and in 23 male patients with severe alcoholic dependency together with the same number of age-matched healthy men. Significant changes in the CVR-R and heart rate were found 1 h after ethanol intake in the volunteers; also, the 1-h alteration in heart rate after intake was inversely correlated with that in the C-CVHF. The CVR-R, C-CVHF and C-CVLF were significantly depressed in the alcoholics compared to the matched controls. In the alcoholics, the age-adjusted correlation coefficients between not only the CVR-R but also C-CVHF and heart rate were negatively significant. These data suggest that acute and habitual intake of alcohol affects cardiac autonomic functions including sympathetic and parasympathetic activities; and, increase of heart rate in relation to alcohol, at least in alcoholics, seems to occur through reducing the parasympathetic activity.

Delayed maturation of the vagus nerve in sudden infant death syndrome

Abnormalities of the respiratory control system have been implicated in the cause of death in sudden infant death syndrome (SIDS). The vagus nerve is a major component of the neural regulation of respiration. Ultrastructural quantitative morphometry of myelinated and unmyelinated fibers was performed on cervical vagus nerves taken from 30 SIDS victims and 29 age-matched controls between 1 and 9 months of age. In SIDS infants, more small and fewer large myelinated vagal fibers were found than in controls, suggesting that the vagus nerve in SIDS is relatively immature. Delayed vagal nerve maturation, together with delays in central nervous system myelination and dendritic development, indicates a neural developmental delay in SIDS, the cause of which is undetermined.

Prolonged QT interval in alcoholic autonomic nervous dysfunction

QT prolongation on electrocardiography is related to sudden cardiac death and is frequently found in alcoholics. We studied QT prolongation in relation to the function of cardiac autonomic nerves assessed by the coefficient of variation of the R-R interval (CVRR) in three age-matched groups of men: 32 alcoholics with autonomic nervous dysfunction (AN), 32 alcoholics without AN, and 32 healthy controls. The QTc interval and CVRR were measured at rest on the 30th day of abstinence, when electrolyte imbalance had disappeared. Subjects with arrhythmia, conduction abnormality, cardiomegaly, ischemic heart disease or diabetes mellitus were excluded. A CVRR of less than 80% of standard predicted value was judged to represent AN. In alcoholics, QTc correlated negatively with the ratio of CVRR to its standard value (r = -0.49, p < 0.0001). The incidence of QTc prolongation was higher in alcoholics with AN (46.9%) than in alcoholics without AN (21.9%, p < 0.05). QTc prolongation was not observed in healthy controls. The QTc interval was significantly (p < 0.01) longer in alcoholics with AN (444 +/- 20 msec) than in alcoholics without AN (426 +/- 17) and in healthy controls (398 +/- 18). These results suggest that alcoholism causes dysfunction of the autonomic nerves as well as worsening QT prolongation, and this may predispose such patients to sudden cardiac death.

Invited review: autonomic dysfunction in peripheral nerve disease

The autonomic nervous system is affected in most peripheral neuropathies, but only in a small number of conditions, such as diabetes, amyloidosis, Guillain-Barré syndrome, porphyria, and familiar dysautonomia, is autonomic dysfunction of clinical importance. The pathological changes in the peripheral autonomic nervous system are similar to those in the peripheral somatic nerves. Autonomic disturbances are most likely to occur when there is acute demyelination or damage to small myelinated and unmyelinated fibers. Autonomic investigations should include tests of both sympathetic and parasympathetic function. Treatment consists of management of the underlying cause of peripheral neuropathy, physical and pharmacological measures.

Impaired autonomic nervous system in alcoholics assessed by heart rate variation

The suppression of heart rate variation reflects cardiac autonomic nervous dysfunction and is known to be associated with a poor prognosis or sudden death in diabetic patients. We investigated consecutive changes in the heart rate variation in 51 alcoholics using the coefficient of variation of R-R interval (CVRR). To correct for age effects, a ratio of CVRR to the standard predicted value (CVP) was calculated. On the whole, CVRR/CVP was suppressed on admission and on the 7th day of abstinence and increased on the 30th day. However, alcoholics could be divided into two groups by their CVRR/CVP on the 30th day: one group with transient autonomic dysfunction whose CVRR/CVP was more than 0.8 (n = 32), and the other group with persistent autonomic dysfunction whose CVRR/CVP was less than 0.8 (n = 19). Withdrawal hypertension occurred more frequently (63% vs. 19%) and mean systolic pressure (159 +/- 24 mmHg vs. 138 +/- 17 mmHg) was higher in the latter group than in the former, suggesting that persistent autonomic damage might, at least in part, contribute to withdrawal hypertension. To investigate further the relationship between the persistent autonomic damage and other complications, the CVRR/CVP on the 30th day of abstinence was analyzed in an additional 85 alcoholics (total n = 136). Persistent suppression of the CVRR/CVP was more frequently found in alcoholics with leg paresthesia (64%, n = 22), the Wernicke-Korsakoff syndrome (73%, n = 11), or diabetes mellitus (69%, n = 68), than in alcoholics without these complications (31%, n = 35).(ABSTRACT TRUNCATED AT 250 WORDS)

Abnormal cough reflex in canine acrylamide neuropathy

Coughing in response to irritation of the airways is a fundamental protective reflex that is dependent on rapidly adapting bronchopulmonary receptors and their vagal afferent fibers; reflex airway constriction, which is effected by vagomotor efferent fibers, usually accompanies coughing. Although dysfunction of vagally mediated cardiovascular and gastrointestinal reflexes is a well-documented complication of autonomic neuropathy, to date there have been no studies of the effect of peripheral autonomic failure on the cough reflex. In the study reported here, we examined the effect of acrylamide-induced neuropathy, a distal axonopathy, on the ventilatory and tracheomotor components of the cough reflex in conscious dogs. There was a reduction in the cough reflex in response to mechanical irritation of the large airways in the preclinical phase of the neuropathy, and the cough reflex was virtually abolished when the dogs had moderate neuropathy. Following withdrawal of the neurotoxin, there was a substantial recovery of the cough reflex in surviving animals. It is possible that the cough reflex may be reduced in patients with vagal neuropathy and that this might compromise protection of the airway.

A morphometric study of the carotid sinus nerve in patients with diabetes mellitus and chronic alcoholism

Morphometric studies were performed on the myelinated fibres of the carotid sinus nerve obtained at autopsy from 13 control subjects, 7 patients with diabetes mellitus and 11 with chronic alcoholism. The myelinated fibre-diameter distribution in control nerves was bimodal with peaks at 3-4 micron and at 8-10 micron. The mean myelinated fibre density was 14.8 X 10(3)/mm2 (SD 2.3 X 10(3)/mm2) in control nerves and was significantly reduced in the nerves of diabetics (mean, 11.7 X 10(3)/mm2; SD, 2.2 X 10(3)/mm2), and chronic alcoholics (mean, 12.7 X 10(3)/mm2; SD, 2.1 X 10(3)/mm2), although in 8 of 11 nerves from alcoholics, the density was within the control range. These findings demonstrate that autonomic afferent fibres are damaged in diabetes and chronic alcoholism, and provide a pathological basis for the disturbances of heart rate and blood pressure control in these conditions.