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

Relationships of autonomic dysfunction with disease severity and neuropathic pain features in fibromyalgia: is it really a sympathetically maintained neuropathic pain?

Background

The pathophysiology of fibromyalgia (FM) involves many mechanisms including central nervous system sensitization theory, autonomic nervous system (ANS) dysfunction, and recently small fiber neuropathy. While the small fiber neuropathy itself can cause ANS dysfunction and neuropathic pain (NP), it is still unknown whether ANS problems have an association with severity of disease and NP in patients with FM. The aim of this study was to evaluate ANS dysfunction in FM patients and to explore possible associations of ANS dysfunction with disease severity and NP.

Methods

Twenty-nine FM patients and 20 healthy controls were included in this cross-sectional study. Participants were tested using sympathetic skin responses (SSR) and R-R interval variation analyses for sympathetic and parasympathetic ANS dysfunction, respectively. Disease severity and somatic symptoms of patients with FM were evaluated using the ACR-2010 scales and Fibromyalgia Impact Questionnaire, and NP symptoms were evaluated using the Pain Detect Questionnaire and Douleur Neuropathique questionnaire.

Results

FM patients were found to have ANS dysfunction characterized by increased sympathetic response and decreased parasympathetic response. SSR amplitudes were found to be correlated with a more severe disease. Although non-significant, NP severity tended to be associated with a decrease in sympathetic and parasympathetic activities.

Conclusions

ANS dysfunction may play a role in the pathophysiology of FM. The trend of decreased ANS functions in FM patients exhibiting NP contradicts the notion that FM is a sympathetically maintained NP and may be explained with small fiber involvement.

Validation of cooling detection threshold as a marker of sensorimotor polyneuropathy in type 2 diabetes

AIM

We aimed to validate the performance cooling detection thresholds (CDT) to detect diabetic sensorimotor polyneuropathy (DSP) in type 2 diabetes.

METHODS

Two hundred and twenty participants with type 2 diabetes underwent clinical and electrophysiological examinations including 3 small fiber function tests: CDT, heart rate variability (HRV) and LDIFLARE. Clinical DSP was defined by consensus criteria whereas preclinical DSP was defined by presence of at least one electrophysiological abnormality. Area under the curve (AUC) and optimal thresholds were determined by receiver operating characteristic curves.

RESULTS

Participants were aged 63 ± 11 years with mean HbA1c of 7.5 ± 1.6%. The 139 (63%) clinical DSP cases had mean CDT values of 18.3 ± 8.9°C; the 52 (24%) preclinical DSP cases had 25.3 ± 3.5°C; and the 29 (13%) controls had 27.1 ± 3.8°C; (p-value<0.02 for all comparisons). For identification of clinical DSP cases, AUCCDT was 0.79 which exceeded AUCHRV (0.60, p=<0.0001) and AUCLDI FLARE (0.69, p=0.0003), optimal threshold <22.8°C (64% sensitivity, 83% specificity). Preclinical DSP AUCCDT was 0.80, also exceeding the other 2 measures (p<0.02 for both comparisons), optimal threshold ≤27.5°C (83% sensitivity, 72% specificity).

CONCLUSIONS

CDT had good diagnostic performance for identification of both clinical and preclinical neuropathy in type 2 diabetes. Its use as a non-invasive screening tool should be considered for research and clinical practice.

Evaluation of autonomic nervous system function in children with overactive bladder syndrome

PURPOSE

We aimed to evaluate the autonomic nervous system activity in children with overactive bladder (OAB) syndrome.

METHODS

Included in the study were 40 children with overactive bladder and 28 healthy controls. Autonomic tests were performed on all participants, including heart rate interval variation (RRIV), heart rate response to valsalva maneuver, and sympathetic skin response (SSR).

RESULTS

Mean valsalva rates in the overactive bladder and control groups were 1.53 ± 0.29 and 1.30 ± 0.18, respectively, a statistically significant difference (P < 0.001). Also significantly different were deep breathing RRIV values of the study and control groups: 56.65 ± 14.66 and 47.92 ± 10.15, respectively (P = 0.008). No statistical differences were found in SSR when OAB patients were compared with controls (P > 0.05).

CONCLUSIONS

This study demonstrated a parasympathetic hyperactivity in children with OAB, results suggesting a dysfunction in their autonomic nervous systems. Neurourol. Urodynam. 36:673-676, 2017. © 2016 Wiley Periodicals, Inc.

Measurement of cooling detection thresholds for identification of diabetic sensorimotor polyneuropathy in type 1 diabetes

Objective

Compared to recently-studied novel morphological measures, conventional small nerve fiber functional tests have not been systematically studied for identification of diabetic sensorimotor polyneuropathy (DSP). We aimed to determine and compare the diagnostic performance of cooling detection thresholds (CDT) in a cross-sectional type 1 diabetes cohort.

Research Design and Methods

136 subjects with type 1 diabetes and 52 healthy volunteers underwent clinical and electrophysiological examination for DSP classification concomitantly with the Toronto Clinical Neuropathy Score (TCNS) and three small fiber function tests: CDT, heart rate variability (HRV), and laser doppler imaging of axon-mediated neurogenic flare responses to cutaneous heating (LDI_FLARE). Area under the curve (AUC) and optimal thresholds were determined by receiver operating characteristic (ROC) curves in the type 1 diabetes cohort.

Results

Type 1 diabetes subjects were 42±17 years of age with mean HbA1c 7.9±1.7%. Fifty-nine (45%) met the case definition for DSP. CDT values were lowest in cases with DSP (18.3±8.4°C) compared to controls without DSP (28.4±3.5°C) and to healthy volunteers (29.6±1.8°C; p-value for both comparisons<0.0001). AUC_CDT was 0.863 which was similar to AUC_TCNS (0.858, p = 0.24) and AUC_HRV (0.788, p = 0.05), but exceeded AUC_LDIFLARE (0.750, p = 0.001). The threshold of <25.1°C was equivalent to the lower bound of the healthy volunteer 95% distribution [25.1, 30.8°C] and performed with 83% sensitivity and 82% specificity.

Conclusions

Akin to novel small fiber morphological measures, CDT is a functional test that identifies DSP with very good diagnostic performance. These findings support further research that revisits the role of CDT in early DSP detection.

The clinical & neurophysiological study of leprosy

OBJECTIVES

The aim of this study was to evaluate neurological and neurophysiological features of leprosy.

METHODS

Seventy seven hospitalized leprosy patients (52 male, 25 female) were examined neurological and neurophysiologically between 2010 and 2012. Standard procedures were performed for evaluating sensory and motor conduction studies to all patients. Motor studies were carried out on median, ulnar, tibial and common peroneal nerves. Sensory studies were carried out on median, ulnar and sural nerves. Sympathetic skin response (SSR) recordings on both hands and feet, and the heart rate (R-R) interval variation (RRIV) recordings on precordial region were done in order to evaluate the autonomic dysfunction.

RESULTS

The mean age was 59.11±14.95 years ranging between 17 and 80 years. The mean duration of disease was 35.58±18.30 years. Clinically, the patients had severe deformity and disability. In neurophysiological examinations, sensory, motor conduction studies of the lower extremities were found to be more severely affected than upper, and sensory impairment predominated over motor. Abnormal SSRs were recorded in 63 (81.8%) cases of leprosy. Abnormal RRIVs were recorded in 41 (53.2%) cases and abnormal RRIVs with hyperventilation were recorded in 55 (71.4%) cases of leprosy. Significant differences were found between SSR and sensory conduction parameters of median, ulnar nerves as well as motor conduction parameters of median, ulnar and peroneal nerves (p<0.05).

CONCLUSION

Peripheral nervous system dysfunction is accompanied by autonomic nervous system dysfunction in leprosy patients. Sympathetic involvement may predominate over parasympathetic involvement.

Structure-function relationship between corneal nerves and conventional small-fiber tests in type 1 diabetes

OBJECTIVE

In vivo corneal confocal microscopy (IVCCM) has been proposed as a noninvasive technique to assess small nerve fiber structural morphology. We investigated the structure-function relationship of small fibers in diabetic sensorimotor polyneuropathy (DSP).

RESEARCH DESIGN AND METHODS

Ninety-six type 1 diabetic subjects with a spectrum of clinical DSP and 64 healthy volunteers underwent IVCCM examinations to determine corneal nerve structure, including corneal nerve fiber length (CNFL), fiber density (CNFD), branch density (CNBD), and fiber tortuosity (CNFT). Small nerve fiber function was assessed by cooling detection thresholds (CDTs), axon reflex-mediated neurogenic vasodilatation in response to cutaneous heating by laser Doppler imaging flare technique (LDIFLARE), and heart rate variability (HRV). Linear associations between structural and functional measures in type 1 diabetic subjects were determined using Spearman correlation coefficients and linear regression analysis.

RESULTS

Of the type 1 diabetic subjects, with a mean age of 38.2 ± 15.5 years and a mean HbA1c of 7.9 ± 1.4%, 33 (34%) had DSP according to the consensus definition. Modest correlations were observed between CNFL, CNFD, and CNBD and all functional small-fiber tests (rs = 0.25 to 0.41; P ≤ 0.01 for all comparisons). For example, quantitatively every 1 mm/mm(2) lower CNFL was associated with a 0.61°C lower CDT, a 0.07 cm(2) lower LDIFLARE area, and a 1.78% lower HRV. No significant associations were observed for CNFT and the functional small-fiber measures.

CONCLUSIONS

Small nerve fiber structural morphology assessed by IVCCM correlated well with functional measures of small nerve fiber injury. In particular, CNFL, CNFD, and CNBD demonstrated clear structure-function relationships.

Heart rate variability and sensorimotor polyneuropathy in type 1 diabetes

OBJECTIVE

Reduced heart rate variability (HRV) is classically viewed as an early phenomenon in diabetic sensorimotor polyneuropathy (DSP). We aimed to determine the characteristics of HRV across the spectrum of clinical DSP in type 1 diabetes.

RESEARCH DESIGN AND METHODS

Eighty-nine diabetic subjects and 60 healthy volunteers underwent assessment of RR interval variation (RR(var)) during deep breathing and clinical and electrophysiological examination. We examined the distribution of age-standardized RR(var) across the spectrum of clinical DSP, identified variables associated with RR(var) in multivariate regression, and compared RR(var) with validated measures of neuropathy.

RESULTS

Age-standardized RR(var) had a significant, step-wise, inverse relationship with ordinal categories of increasing DSP severity (β = -5.4, P < 0.0001) among subjects with diabetes. Case subjects with DSP had substantially lower age-standardized RR(var) compared with diabetic control subjects without DSP (β = -5.2, P < 0.01), although there was substantial overlap of RR(var) between diabetic case subjects and control subjects and the healthy volunteer cohort. In multivariate analysis, advanced age was independently associated with lower RR(var) in both healthy volunteers and diabetic subjects, whereas higher glycated hemoglobin A(1c) and systolic blood pressure were independently associated with lower RR(var) in diabetic subjects. RR(var) had a significant association with validated measures of large and small fiber neuropathy.

CONCLUSIONS

HRV may be a biomarker for clinical DSP and is associated cross-sectionally with both early and late measures of neuropathy. The low HRV observed in some control subjects without DSP and in most case subjects with severe DSP may signify that HRV has different prognostic implications in these groups, requiring further longitudinal study.

Analysis of heart rate variability with electromyography in heart transplant recipients

OBJECTIVE

To investigate vagal parasympathetic functions by electromyographic R-R interval variation analyses in heart transplant recipients.

DESIGN

Cross-sectional and longitudinal study.

SETTING

Department of physical medicine and rehabilitation, university hospital.

PARTICIPANTS

Early (n=8; <3 mo) and late (n=17; >1 y) heart transplant recipients and healthy volunteers (n=20) were included.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

The R-R interval variations at rest and in response to deep breathing, Valsalva, and tilt/standup maneuvers were analyzed in all patient and control groups. Further, 8 early heart transplant recipients were followed up at the sixth and twelfth months after transplantation.

RESULTS

Compared with controls, both early and late transplant recipients had significantly lower R-R interval variation ratios (P<.05). There were no statistically significant differences between the early and late groups (P>.05). R-R interval variation ratios showed no significant changes from baseline (P>.025) in the early heart transplant recipients.

CONCLUSIONS

The findings of the study suggest that parasympathetic activities are suppressed in the early stage after heart transplantation and do not significantly recover with time. The electromyographic analysis of R-R interval variation is a simple test that may offer an attractive alternative for routine evaluation of autonomic dysfunction in heart transplant recipients.

COMPARATIVE NEUROPHYSIOLOGICAL STUDY FOR THE DIAGNOSIS OF MILD POLYNEUROPATHY IN PATIENTS WITH DIABETES MELLITUS AND GLUCOSE INTOLERANCE

This article evaluates diagnostic sensitivity of minimal F-wave latency, sural/radial amplitude ratio (SRAR), dorsal sural/radial amplitude ratio (DSRAR), sympathetic skin response (SSR), and R-R interval variability (RRIV) for detecting early polyneuropathy in patients with glucose intolerance and diabetic patients. F-wave latencies were more prolonged in diabetic patients with normal and abnormal nerve conduction studies than control subjects (p < .001). SRAR was lower, SSR latency was more prolonged, and RRIV was lower in diabetic patients with abnormal nerve conduction studies than healty controls (p < .001). SSR latency was more prolonged and RRIV was lower in diabetic patients with normal nerve conduction studies than healty controls (p < .01, p < .05, respectively). DSRAR was lower in diabetic patients with normal and abnormal nerve conduction studies than control subjects (p < .001). DSRAR was also lower in patients with glucose intolerance than control subjects (p < .01). DSRAR was the most sensitive and specific test in either of diabetic patients with normal nerve conduction studies (sensitivity 66%, specificity 90%) and diabetic patients with abnormal nerve conduction studies (sensitivity 100%, specificity 90%). DSRAR is the most reliable method for detection of early nerve pathology. Patients with glucose intolerance might have subclinical neuropathy that can be demonstrated with DSRAR analysis.

Sympathetic skin response and RR interval variation in patients with cardiac syndrome X

Sympathetic skin response (SSR) and R-R interval variation (RRIV) are noninvasive electrophysiological tests used in the assessment of sympathetic and parasympathetic nervous system function, respectively. Cardiac syndrome X (CSX) is usually diagnosed in the presence of typical angina pectoris, a positive response to exercise testing, and normal-appearing coronary angiograms without spasm induced by hyperventilation or ergonovine. Alterations of autonomic nervous system control of cardiac function have been described in CSX. The aim of the study was to investigate autonomic nervous system function in patients with CSX. Nine patients with CSX (2 men, 7 women) and healthy controls (11 men, 19 women) were included in the study. SSRs were recorded from palm of hands by stimulation of the median nerve. RRIV recordings were taken from precordium during both rest position (R%) and deep inspiration of 6 times per minute (D%). In addition D% - R% and D%/R% values were calculated. SSR amplitude of CSX was lower than in controls (3.64 +/-4.78 vs 6.36 +/-3.4 mV, p = 0.017). There was no difference between groups for SSR latency values (CSX: 1,366 +/-99; controls: 1,383 +/-85 msec). Also, R% (CSX: 13.04 +/-6.3; controls: 12.92 +/-3.91) and D% (CSX: 16.63 +/-8.88; controls: 21.43 +/-7.3) values were similar in the 2 groups. However, D% - R% (CSX: 3.59 +/-10.11; controls: 8.51 +/-7.01) and D%/R% (CSX: 1.45 +/-0.93; controls: 1.78 +/-0.69) values were slightly lower in patients with CSX but were not statistically significant. A linear correlation was found between SSR amplitude and D%/R% (r = 0.336, p = 0.036). The authors conclude that, among patients with CSX, there are alterations of autonomic nervous control of skin as well as of other organs (ie, heart). SSR and RRIV testing can be done easily in the neurophysiology laboratory to assess the sympathetic and parasympathetic system, respectively.

R-R Interval Variation and Sympathetic Skin Response in Fibromyalgia

BACKGROUND

This study proposed to assess the autonomic nervous system (ANS) functions in fibromyalgia (FM) by using two electrophysiological tests, sympathetic skin response (SSR) and the heart rate variability named R-R interval variation (RRIV).

METHODS

Sympathetic skin response and RRIV were studied in 29 female patients with FM and 22 healthy age-matched female controls. R-R interval variation at rest (R%), during deep breathing (D%), the difference between D% and R% (D-R) and the ratio of D-R% (D/R) were determined. Pain threshold was measured using a mechanical algometer.

RESULTS

R-R interval variation at rest (R%) and D/R did not show significant difference between patients and controls, whereas D% and D-R were significantly lower in patients compared to controls. SSR latencies of patients' hands and feet had no significant difference compared to controls' hand and feet SSR latencies. SSR latencies of patients' hands correlated significantly with control point score, total myalgic score, Hamilton Anxiety Rating Scale (HARS) and Hamilton Depression Rating Scale. Sympathetic skin response latencies of patients' feet correlated only with HARS.

CONCLUSIONS

Analysis of heart rate variability may be useful and complementary to clinical examination in patients with symptoms of dysfunction in cardiovascular reflex pathways.

Relationship between the frequency of autonomic dysfunction and the severity of chronic obstructive pulmonary disease

OBJECTIVE

The relationship between the frequency of autonomic dysfunction (AD) and the severity of chronic obstructive pulmonary disease (COPD) has not been exactly known, despite its importance in the pathogenesis of COPD. Therefore, we aimed to evaluate the relationship between the clinical stage severity of the disease and the frequency of AD in COPD patients.

METHODS

The frequency and type of AD were determined according to the clinical severity of 35 stable COPD patients. The results were compared between the mild and moderate-severe COPD groups. Sympathetic system (SS) was evaluated with sympathetic skin response (SSR), QT and QTc intervals (ms) analyses. Parasympathetic system was evaluated with the heart rate interval variations (RRIV).

RESULTS

For the total group, an AD was detected in 20 patients (57%), a parasympathetic dysfunction (PD) in 14 (40%), a mixed-type dysfunction in five (14%) and a sympathetic dysfunction (SD) in only one patient (3%). For the 12 mildly affected patients, there were cases of isolated SD in only one patient (8.5%), isolated PD in five (42%) and AD in six patients (50%). For the 23 moderate-severe COPD patients, mixed AD was detected in five patients (22%), isolated PD in nine (39%) and AD in 14 patients (61%). There were no significant differences between the two patient groups, neither for isolated parasympathetic and sympathetic, mixed form nor for total AD (P>0.05).

CONCLUSIONS

The results suggested that PD was dominant in patients with COPD. However, the frequencies of autonomic parasympathetic and sympathetic dysfunction did not increase significantly with the severity of COPD. The severity of hypoxemia and/or airflow limitation may not be the only unique or definite reason for AD in COPD, as there was not an exact correlation between the presence of AD and the severity of airflow limitation and hypoxemia.

Eighteen years of fair glycemic control preserves cardiac autonomic function in type 1 diabetes

OBJECTIVE

To study the association between 18 years of mean HbA(1c) and cardiac autonomic function in type 1 diabetic patients having used intensive insulin treatment.

RESEARCH DESIGN AND METHODS

A total of 39 patients with type 1 diabetes were followed during 18 years, and HbA(1c) was measured yearly. At 18 years follow-up heart rate variability (HRV) measurements were used to assess cardiac autonomic function. Standard cardiac autonomic tests during normal breathing, deep breathing, the Valsalva maneuver, and the tilt test were performed. Maximal heart rate increase during exercise electrocardiogram and minimal heart rate during sleep were also used to describe cardiac autonomic function.

RESULTS

We present the results for patients with mean HbA(1c) <8.4% (two lowest HbA(1c) tertiles) compared with those with HbA(1c) > or = 8.4% (highest HbA(1c) tertile). All of the cardiac autonomic tests were significantly different in the high- and the low-HbA(1c) groups, and the most favorable scores for all tests were seen in the low-HbA(1c) group. In the low-HbA(1c) group, the HRV was 40% during deep breathing, and in the high-HbA(1c) group, the HRV was 19.9% (P = 0.005). Minimal heart rate at night was significantly lower in the low-HbA(1c) groups than in the high-HbA(1c) group (P = 0.039). With maximal exercise, the increase in heart rate was significantly higher in the low-HbA(1c) group compared with the high-HbA(1c) group (P = 0.001).

CONCLUSIONS

Mean HbA(1c) during 18 years was associated with cardiac autonomic function. Cardiac autonomic function was preserved with HbA(1c) <8.4%, whereas cardiac autonomic dysfunction was impaired in the group with HbA(1c) > or = 8.4%.

R-R interval variation and the sympathetic skin response in the assessment of the autonomic nervous system in leprosy patients

OBJECTIVES

The aim of this study was to evaluate possible autonomic nervous system (ANS) dysfunction in leprosy patients with the sympathetic skin response (SSR) and the heart rate (R-R) interval variation (RRIV) measurements which are easy and reliable methods for evaluation of autonomic functions.

MATERIAL AND METHODS

We studied 37 lepromatous leprosy patients (mean age: 38 +/- 17 years, range 23-62 years, 20 females and 17 males) and 35 age-matched healthy subjects (mean age: 34.19 +/- 12.74 years, range 24-48 years, 20 females and 15 males). Non-invasive bedside tests (orthostatic test, Valsalva ratio), R-R interval variation (RRIV) during at rest and deep breathing, the SSR latency and amplitude from both palms, and nerve conduction parameters were studied in all the subjects.

RESULTS

The mean values of RRIV in leprosy patients during at rest [mean RRIV in patients, 17.42 +/- 8.64% vs controls, 22.71 +/- 3.77% (P < 0.05)] and during deep breathing [mean RRIV in patients, 21.64 +/- 9.08% vs controls, 30.70 +/- 5.99% (P < 0.005)] was significantly lower compared with the controls. The mean latency of SSR in leprosy patients [mean SSR latency in patients, 1.72 +/- 1.13 ms vs controls, 1.30 +/- 0.41 ms (P < 0.05)] was significantly prolonged compared with the controls. The mean amplitude of SSR in leprosy patients [mean SSR amplitude in patients, 0.54 +/- 0.57 microV vs controls, 1.02 +/- 0.56 microV (P > 0.05)] was smaller compared with the controls, but this difference was not significant. The mean Valsalva ratio in leprosy patients [mean in patients, 1.11 +/- 0.13 vs controls, 1.16 +/- 0.07 (P > 0.05)] was smaller compared with the controls, but not statistically significant. The mean difference of systolic and diastolic blood pressure between supine rest and during standing in leprosy patients were higher compared with the controls [mean systolic pressure in patients, 7 +/- 6 mmHg vs controls, 6 +/- 8 mmHg (P > 0.05) and mean diastolic pressure in patients, 3 +/- 3 mmHg vs controls, 3 +/- 2 mmHg (P > 0.05)], but they did not reach statistical significance. Furthermore, lower RRIV and the prolonged SSR latencies in leprosy patients were closely correlated to some parameters of sensorimotor nerve conduction and each other [median nerve distal latency and RRIV, r = -0.67 (P < 0.05), ulnar nerve distal latency and RRIV, r = -0.59 (P < 0.05), RRIV and SSR latency, r = -0.33 (P < 0.02)]. These data indicate that leprosy patients have the functional abnormalities of ANS.

CONCLUSION

We conclude that combined use of these two tests, both of which can be easily and rapidly performed in the electromyogram (EMG) laboratory using standard equipment, allows separate testing of parasympathetic and sympathetic function, and are very sensitive methods in assessing of ANS function in peripheral neuropathy in leprosy patients.

Autonomic dysfunction and ambulatory blood pressure in renal transplant recipients

BACKGROUND

Abnormal circadian blood pressure (BP) rhythm (nondipping) and autonomic dysfunction are both common in end-stage renal disease (ESRD). It is not known whether these abnormalities are related or if they are associated with greater left ventricular hypertrophy.

METHODS

Nineteen renal transplantation (RT) recipients, aged 22-67 years, who were transplanted at least 12 months (1-29 years) previously, were studied with 24-hr ambulatory blood pressure monitoring (ABPM). Autonomic function was tested by automated analysis of heart rate variations and echocardiography was used to estimate left ventricular mass index (LVMI).

RESULTS

Thirteen patients (68%) were nondippers. Although seven (37%) patients had significant parasympathetic dysfunction, this was not related to dipper status. Neither abnormality showed a tendency to diminish with time after RT. Systolic hypertension, diagnosed by ABPM, occurred in 5% of patients during the awake period and in 52% during sleep, whereas diastolic hypertension occurred in 47% when awake and in 63% when asleep. Awake systolic BP was the strongest predictor of LVMI (r=0.7, P<0.001), and was considerably better than systolic BPs recorded at the clinic (r=0.48, P<0.05).

CONCLUSIONS

Nondipping is common after RT but is not related to the degree of autonomic dysfunction. These findings suggest that autonomic dysfunction is not a major contributor to nondipping in ESRD. In RT patients, ABPM is a more sensitive measure of hypertension and a stronger predictor of LVMI than clinic BP.

Respiratory sinus arrhythmia during anaesthesia: assessment of respiration related beat-to-beat heart rate variability analysis methods

Beat-to-beat heart rate variability analysis is a powerful tool for the diagnosis of neuropathy. Respiration-related heart rate variability (respiratory sinus arrhythmia, RSA) reflects the function of parasympathetic nervous system during spontaneous ventilation while awake. RSA is also claimed to monitor the depth of anaesthesia. Power spectrum analysis or various averaging techniques of the heart rate variability are usually applied. The current literature, however, does not usually interpret the ground rules and limitations of the method used, and this may sometimes lead to erroneous conclusions on the data. The aim of our study was to compare and analyse critically the performance of different methods of evaluating RSA during anaesthesia and positive pressure ventilation. Power spectrum analysis, the root mean square of the successive RR-interval difference (RMSSD), and two respiration related methods, RSA index and average phase RSA, were included in the comparison. To test these methods, 11 patients were anaesthetised with isoflurane and their lungs were ventilated mechanically with a frequency of 6 cycles min-1. Each patient received a bolus dose of atropine (20 micrograms kg-1) during the trial. Electrocardiogram, electroencephalogram and tracheal pressure signal from respirator were recorded and analyses were performed off-line. We demonstrated that general indices, such as RMSSD, may be strongly affected by heart rate level and other non-respiration related variations in heart rate. We also showed that the effect of unwanted fluctuations on RSA can be reduced with respiration dependent beat-to-beat methods. Furthermore we confirmed that in addition to the amplitude, also the pattern of respiratory sinus arrhythmia is of interest: the pattern is reversed in phase compared to spontaneous breathing while awake, as we have shown earlier. To analyse RSA during anaesthesia, we recommend the use of an average phase RSA method based on beat-to-beat variability that shows both the amplitude and pattern of RSA. Finally, no measure of RSA should be used without a presentation of the actual beat-to-beat heart rate curve.

AAEM minimonograph #48: autonomic nervous system testing

The autonomic nervous system maintains internal homeostasis by regulating cardiovascular, thermoregulatory, gastrointestinal, genitourinary, exocrine, and pupillary function. Testing and quantifying autonomic nervous system function is an important but difficult area of clinical neurophysiology. Tests of parasympathetic cardiovagal regulation include heart rate analysis during standing (the 30:15 ratio), heart rate variation with deep breathing, and the Valsalva ratio. Tests of sympathetic adrenergic vascular regulation include blood pressure analysis while standing, the Valsalva maneuver, sustained handgrip, mental stress, and cold water immersion. Tests of sympathetic cholinergic sudomotor function include the sympathetic skin response, quantitative sudomotor axon reflex test, sweat box testing, and quantification of sweat imprints. Pupil function is tested pharmacologically and with pupiilographic techniques. Tests of gastrointestinal and genitourinary function do not satisfactorily isolate autonomic regulation from their other functions. The available tests have various sensitivities and ease of administration. They are typically administered in a battery of multiple tests, which improves sensitivity and reliability, and allows probing of various autonomic functions.

Electrophysiological tests of autonomic function in patients with idiopathic autonomic failure syndromes

Three electrophysiological tests of autonomic function were performed in patients with autonomic nervous system dysfunction to define test sensitivities and specificities. The skin sympathetic response, Valsalva ratio, and heart rate variation with deep breathing were studied in 10 patients with multiple system atrophy (MSA) and in 7 patients with pure (also called progressive or primary) autonomic failure (PAF); control subjects were 17 normal individuals of similar age. Thirteen patients had abnormal skin sympathetic responses, and 16 had abnormal Valsalva ratios. Fourteen patients had an abnormal variation of the heart rate with deep breathing. Taking the three tests together, binary logistic regression for distinguishing between patients and normal subjects correctly classified 91% of the 33 individuals for whom there were complete data with sensitivity of 88% and specificity of 94%. However, only 69% of the patients could be correctly classified by a logistic regression for discriminating between MSA and PAF. Electromyography (EMG) studies showed that 7 of 8 patients with MSA but only 2 of 7 patients with PAF (both multiparous women) had denervation of the rectal sphincter muscle. The EMG study is, therefore, valuable in men, but has a high false positive rate in women, probably because of pudendal nerve injury from parturition.

Reduced heart rate variability after right-sided stroke

BACKGROUND AND PURPOSE

Recently, asymmetries have been demonstrated in skin sudomotor and vasomotor function after unilateral cerebral lesions. The present study was performed to determine whether other bedside tests reflecting sympathetic and parasympathetic cardiovascular functions would reveal differences with respect to the side of cerebrovascular lesions.

METHODS

Heart rate variability during deep breathing as well as blood pressure and heart rate changes during tilt and isometric handgrip was measured in a group of patients with a monofocal stroke and compared with similar data from age-matched patients with transient ischemic attack and healthy control subjects.

RESULTS

Compared with left-sided stroke and with the control subjects, stroke location on the right side was associated with a reduced respiratory heart rate variability (P > .01), a reflex mainly under parasympathetic control. In contrast, reflexes mainly reflecting peripheral sympathetic function were equal for right- and left-sided lesions.

CONCLUSIONS

Since an imbalance in cardiac autonomic innervation may be crucial for the generation of cardiac arrhythmias and since reduced heart rate variability has been associated with increased mortality, the findings suggest that the risk of sudden death may be correlated with lateralization and location of the brain infarct after stroke.

Autonomic profile of subjects prone to fainting

Syncope is the most common form of fainting that may occur at least once during a life-time in up to one-third of the general population. In 50% of patients the cause remains unknown. In an attempt to identify subtle disturbances of the autonomic nervous system, we examined 70 subjects, aged from 14 to 39 years, who suffered from recurrent neurally mediated syncope. We performed a battery of non-invasive tests assessing cardiovagal, sympathetic cholinergic and sympathetic adrenergic function. We compared the results with a group of 30 healthy, non-fainting subjects matched for age and sex. Basal records were similar in both groups. Patients had preserved cardiovagal function. The multivariate cluster analysis allowed us to find a homogeneous group of cases (46%) that simultaneously presented: greater fall in systolic and diastolic blood pressure after standing, increased 15:30 ratio, exaggerated absolute heart rate rise in response to standing and subclinical reduced sudomotor function in the foot. The results suggest the existence of a subclinical autonomic profile, with subtle sympathetic postganglionic impairment, evident in lower limbs. These findings may contribute to proving the existence of different types of neurally mediated syncope, all different in their onset and mechanism but with a common final manifestation: syncopal loss of consciousness.

Age-related diminution of the cardiovascular autonomic responses: diagnostic problems in the elderly

To study the usefulness of standard cardiovascular autonomic reflex tests in the elderly, 224 healthy controls and 49 aged diabetic patients were examined. Based on the data obtained from healthy controls, age-related reference values for several autonomic indices were calculated and their usefulness was tested with aged diabetic patients. It was found (1) that in elderly subjects (aged > or = 50 years) the indices based on heart rate differences are more suitable for the assessment the autonomic parasympathetic control than indices based on R/R interval ratios, (2) that the tests (and indices) of choice in the elderly subjects are the Valsalva manoeuvre (Valsalva difference and tachycardia difference) and the active orthostatic test (Max-Rest difference, immediate and later change in systolic blood pressure), (3) that the usefulness of the deep breathing test is limited in the elderly, (4) that such commonly used indices as the Valsalva ratio and the Max/Min ratio in orthostatic test are not useful in the elderly, and (5) that the isometric handgrip test is of little use in the assessment of the autonomic function in the elderly. In conclusion, standard cardiovascular autonomic reflex tests can be used in the assessment of autonomic function to some extent also in the elderly subjects. However, one must bear in mind the limitations in their applicability in that age group.

Konzo: a distinct disease entity with selective upper motor neuron damage

Two Tanzanian patients with konzo were severely disabled by a non-progressive spastic paraparesis, since the sudden onset during an epidemic six years earlier. At the time of onset they had a high dietary intake of cyanide from exclusive consumption of insufficiently processed bitter cassava roots. MRI of brain and spinal cord were normal but motor evoked potentials on magnetic brain stimulation were absent, even in the only slightly affected upper limbs. Other neurophysiological investigations were largely normal but the more affected patient had central visual field defects. Konzo is a distinct disease entity with selective type upper motor neuron damage.

Determining heart-rate variability: comparing methodologies using computer simulations

Heart rate variation due to respiration is a window onto autonomic nervous system function and many measures exist that quantify this variability. Computer-based simulations of 1-minute deep-breathing tests, along with common artifacts, were used to compare the most frequently used measures. We found distinct differences in the performance of the measures. Some measures (e.g., SDRR and MSSD) are strongly influenced by the underlying mean heart rate while others (e.g., Max-Min and SDHR) are not. All of the measures tested, except R, were influenced by both shifting mean heart rate and single-beat anomalies. R, on the other hand, is strongly influenced by test duration and breathing asynchronies. Sensitivity to phenomena unrelated to ANS function can reduce the diagnostic discrimination of these measures. We suggest simple improvements to the measures and discuss how some measures may be theoretically superior to others.

Cardiovascular reflexes in Parkinson's disease: effect of domperidone and apomorphine

Cardiovascular reflexes were evaluated in 18 patients with idiopathic Parkinson's disease who had a Hoehn & Yahr score of III-IV. The effect of apomorphine and domperidone on blood pressure, heart rate, R-R interval variation, and the Valsalva ratio were studied. Autonomic dysfunction was not found in the patients and there were no differences between subgroups of patients on different treatments. Apomorphine altered cardiovascular reflexes to a greater degree in patients who received the drug for the first time than in chronically treated patients. The changes were antagonized by domperidone, a peripheral dopamine receptor antagonist. Apomorphine treated patients who were receiving long-term domperidone had similar abnormalities of cardiovascular reflexes to those who had been able to withdraw it.

Orthostatic reactions in the 85-year olds

Testing of the orthostatic reaction is recommended in the examination of elderly fallers. This test usually includes blood pressure and instantaneous heart rate measurement but is difficult to perform in very elderly people according to the guidelines suggested for younger subjects. One reason for this is that old people often stand up slowly. The use of a tilt table, which enables a rapid change in posture from recumbent to erect position, is tempting as it could provide a method for a better standardized test. To study the usefulness of the tilt table as well as the degree of orthostatic reaction in the very elderly, we examined a sample of 85-year olds who did not suffer from falls. All were tested both with the tilt table and with active rising. The drop in blood pressure was equal in the two test types, but the increase in heart rate was significantly larger in active rising. Many test subjects were afraid of the tilt table, and two developed cardiac arrhythmia, i.e., atrial fibrillation, during the test. In our opinion, active rising is the method of choice in old persons. While the test subjects were in unusually good health for their age and thus could provide a suitable reference group for this test, the systolic blood pressure dropped considerably in several during the test. Criteria and indexes developed for younger subjects are not useful, and different evaluation criteria should be developed for the very elderly.

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.

Central conduction and autonomic nervous function in HMSN I

CNS conduction and autonomic nervous function were investigated in 15 patients with HMSN I. Central motor conduction time (CMCT) was estimated with magnetic brain stimulation and electrical nerve root stimulation. Somatosensory evoked potential (SEP) and visual evoked potential (VEP) were used for assessment of central sensory and visual conduction. Autonomic effector organ functions were assessed with the R-R variation test for parasympathetic function, and the sympathetic skin response test (SSR) for skin sympathetic sudomotor activity. Five of the patients had prolonged CMCT. Central sensory conduction was normal in 3, and slightly prolonged in 1 of the patients, but could not be estimated in 11 due to lack of response from the cervical recording. VEP was abnormal in 2 patients. R-R variations during normal breathing were low in 8 of 15 patients, and low also during deep breathing in 1 of 15. The SSR test was pathological in 5 of 15 patients. Thus, impaired central conduction and/or autonomic dysfunction was not an uncommon finding in patients with HMSN I.

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

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

Automatic analysis of heart rate variation: II. Findings in patients attending an EMG laboratory

An automatic method was used to measure the heart rate variation with breathing in patients with different neuromuscular conditions attending a laboratory of electromyography (EMG). The objective was to determine the frequency of abnormalities in various conditions and the relationship between R-R variation and different nerve conduction parameters. The percentages of reduced R-R variation were 73% in diabetics, 35% in Guillain-Barré syndrome, 22% in amyotrophic lateral sclerosis, and 50% in amyloidosis. R-R variation in diabetics was significantly correlated to most parameters of nerve conduction. In Guillain-Barré syndrome it correlated significantly with the ulnar and median M-response amplitudes. Most patients with myopathies showed normal R-R variation.