Standard Deviation Of All RR Intervals Research Articles

Association between respiratory mechanics and autonomic function in morbid obesity

This study aimed to investigate the association between respiratory mechanics and autonomic modulation in morbidly obese patients. We evaluated 10 morbidly obese subjects (BMI = 52.9 ± 11.2 kg/m 2 ), aged 23---58 years. Assessment of respiratory mechanics was done by the forced oscillation technique (FOT), and cardiovascular autonomic function was recorded by heart rate variability analysis (HRV). The Pearson correlation coefficient was used to test the associations between respiratory mechanics and HRV variables. There were associations between the standard deviation of all RR intervals (SDNN) and airway resistance (Rm) (r = −0.82; p = 0.004), SDNN and respiratory system resistance (R0) (r = −0.79; p = 0.006), root mean square of successive differences between adjacent normal RR intervals (rMSSD) and respiratory system resistance (R5) (r = −0.643; p = 0.0451), rMSSD and R0 (r = −0.64; p = 0.047), and rMSSD and Rm (r = −0.658; p = 0.039). We concluded that the airway and respiratory system resistances are negatively associated with parasympathetic activity in patients with morbid obesity. © 2013 Sociedade Portuguesa de Pneumologia. Published by Elsevier Espana, S.L. All rights reserved.

MBTI성격유형에 따른 병원 임상실습 중인 응급구조학과 학생의 심박변이도 변화에 관한 연구

This study examined the relationship between the MBTI character types and heart rate variability. The subjects were 25 students in the department of emergency medical technology in C city, Chungnam, Korea. The heart rate variability was measured under two conditions: a stable state, and in the second week and fourth week in clinical practice. The period of the heart rate variability measurements was from Jun. 21, 2013 to Jul. 26, 2013.The changes in the HRV at the stable state and during clinical practice depending on the MBTI character types, and the HRV at the stable state and during clinical practice according to the distribution chart of four character types showed a significant difference in the nHF and standard deviation of all R-R intervals (SDNN). In the changes in the HRV at the stable state and during clinical practice depending on the preference distribution chart of each indicator, the T-F group and J-P group in the nLF, T-F group and J-P group in the nHF, S-N group in the standard deviation of all R-R intervals (SDNN) and the J-P group in the mHR showed a significant difference.

Comparative Study of Heart Rate Variability in Patients with Schizophrenia, Bipolar Disorder, Post-traumatic Stress Disorder, or Major Depressive Disorder

ObjectiveHeart rate variability (HRV) changes as a function of psychiatric illness. This study aimed to evaluate HRV among patients with various psychiatric disorders.MethodsThe present study recruited patients with schizophrenia (n=35), bipolar disorder (n=41), post-traumatic stress disorder (PTSD; n=34), or major depressive disorder (n=34) as well as healthy controls (n=27). The time-domain analysis (the standard deviation of all RR intervals [SDNN] and the square root of the mean squared differences of successive normal sinus intervals [RMSSD]), the frequency-domain analysis (very low frequency, low frequency [LF], high frequency [HF], and total power [TP]), and a non-linear complexity measure the approximate entropy were computed.ResultsSDNN and HF were significantly reduced in patients with schizophrenia compared with healthy controls. SDNN, RMSSD, TP, LF, and HF were significantly reduced in bipolar patients compared with healthy controls. HF was significantly reduced in PTSD patients compared with healthy controls.ConclusionOur findings indicate that HRV is not sufficiently powerful to discriminate among various psychiatric illnesses. However, our results suggest that HRV, particularly HF, could be used as a tool for discriminating between psychiatric patients and healthy controls.

Heart Rate Variability Is a Predictor of Mortality in Chronic Kidney Disease: A Report from the CRIC Study

Background/Aims: Low heart rate variability (HRV) is a risk factor for adverse outcomes in the general population. We aimed to determine the factors associated with HRV and evaluate the association between low HRV and clinical outcomes in patients with chronic kidney disease (CKD). Methods: A 10-second electrocardiogram was obtained at baseline in the Chronic Renal Insufficiency Cohort (CRIC) Study. HRV was measured by the standard deviation of all R-R intervals (SDNN) and the root mean square of successive differences between R-R intervals (RMSSD). Results: In 3,245 CRIC participants with available baseline SDNN and RMSSD, lower HRV was associated with older age, lack of exercise, heart failure, elevated phosphorus and hemoglobin A1c, and low estimated glomerular filtration rate. After a median follow-up of 4.2 years, in fully adjusted models, lower HRV was not associated with renal [SDNN: hazard rate, HR = 0.96 (95% confidence interval, CI 0.88-1.05); RMSSD: HR = 0.97 (95% CI 0.88-1.07)] or cardiovascular outcomes [SDNN: HR = 1.02 (95% CI 0.92-1.13); RMSSD: HR = 1.00 (95% CI 0.90-1.10)]. There was a nonlinear relationship between RMSSD and all-cause mortality with increased risk with both low and high RMSSD (p = 0.04). Conclusions: In a large cohort of patients with CKD, multiple risk factors for renal and cardiovascular diseases were associated with lower HRV. Lower HRV was not associated with increased risk for renal or cardiovascular outcomes, but both low and high RMSSD were associated with increased risk for all-cause mortality. In conclusion, HRV measured by RMSSD may be a novel and independent risk factor for mortality in CKD patients.

Monitoring changes in heart rate, as an indicator of the cardiovascular autonomic nervous function, among patients at the sub-acute phase post-brain damage during a physiotherapy session: A preliminary investigation

Objectives: To assess cardiovascular autonomic nervous system function of patients post-brain-injury in the sub-acute phase during a physiotherapy session (PTS).Participants: Fourteen patients post-ischaemic stroke and 11 post-severe traumatic brain injuries.Intervention: Continuous electrocardiogram recording at rest, during active cycling and during routine PTS.Main outcome measure: Heart rate (HR) and Heart rate variability (HRV) parameters included the standard deviation of all R-R intervals (SDNN), the square root of the mean squared differences of successive differences (RMSSD), the Low-frequency (LF) power, High-frequency (HF) power and the LF/HF ratio.Results: The median HR at rest was 76 bpm (interquartile range 61–81). Significant increments were noted during activities; median HR during cycling was 93 bpm, during the most intense activity 91 bpm (p-value < 0.001). A significant decline in HRV parameters’ median values during cycling and PTS was observed only among patients post-stroke.Conclusions: Among patients post-brain injury, HR increased significantly during PTS in different activities and varied positions; therefore, therapists should be aware and monitor HR frequently during training. In addition, HRV values were low at rest and did not respond to activity among patients post-TBI, compared with higher values at rest and some response among patients post-stroke. This may indicate that autonomic impairment post-brain insult is more likely a consequence of central nervous system damage and less likely a result of pre-event cardiovascular illness.

Associação entre a mecânica respiratória e função autonómica na obesidade mórbida

This study aimed to investigate the association between respiratory mechanics and autonomic modulation in morbidly obese patients. We evaluated 10 morbidly obese subjects (BMI=52.9±11.2kg/m2), aged 23-58 years. Assessment of respiratory mechanics was done by the forced oscillation technique (FOT), and cardiovascular autonomic function was recorded by heart rate variability analysis (HRV). The Pearson correlation coefficient was used to test the associations between respiratory mechanics and HRV variables. There were associations between the standard deviation of all RR intervals (SDNN) and airway resistance (Rm) (r=−0.82; p=0.004), SDNN and respiratory system resistance (R0) (r=−0.79; p=0.006), root mean square of successive differences between adjacent normal RR intervals (rMSSD) and respiratory system resistance (R5) (r=−0.643; p=0.0451), rMSSD and R0 (r=−0.64; p=0.047), and rMSSD and Rm (r=−0.658; p=0.039). We concluded that the airway and respiratory system resistances are negatively associated with parasympathetic activity in patients with morbid obesity.

Catheter-Based Renal Sympathetic Denervation Significantly Inhibits Atrial Fibrillation Induced by Electrical Stimulation of the Left Stellate Ganglion and Rapid Atrial Pacing

BackgroundSympathetic activity involves the pathogenesis of atrial fibrillation (AF). Renal sympathetic denervation (RSD) decreases sympathetic renal afferent nerve activity, leading to decreased central sympathetic drive. The aim of this study was to identify the effects of RSD on AF inducibility induced by hyper-sympathetic activity in a canine model.MethodsTo establish a hyper-sympathetic tone canine model of AF, sixteen dogs were subjected to stimulation of left stellate ganglion (LSG) and rapid atrial pacing (RAP) for 3 hours. Then animals in the RSD group (n = 8) underwent radiofrequency ablation of the renal sympathetic nerve. The control group (n = 8) underwent the same procedure except for ablation. AF inducibility, effective refractory period (ERP), ERP dispersion, heart rate variability and plasma norepinephrine levels were measured at baseline, after stimulation and after ablation.ResultsLSG stimulation combined RAP significantly induced higher AF induction rate, shorter ERP, larger ERP dispersion at all sites examined and higher plasma norepinephrine levels (P<0.05 in all values), compared to baseline. The increased AF induction rate, shortened ERP, increased ERP dispersion and elevated plasma norepinephrine levels can be almost reversed by RSD, compared to the control group (P<0.05). LSG stimulation combined RAP markedly shortened RR-interval and standard deviation of all RR-intervals (SDNN), Low-frequency (LF), high-frequency (HF) and LF/HF ratio (P<0.05). These changes can be reversed by RSD, compared to the control group (P<0.05).ConclusionsRSD significantly reduced AF inducibility and reversed the atrial electrophysiological changes induced by hyper-sympathetic activity.

Preliminary Findings of the Relationship of Lower Heart Rate Variability with Military Sexual Trauma and Presumed Posttraumatic Stress Disorder

Decreased heart rate variability (HRV) occurs with physical and psychological disorders and is a predictor of cardiac and all-cause mortality. This study was the first of which we are aware to examine and report the relationship between military sexual trauma (MST) and HRV measures. In a historical cohort study of female veterans with (n= 27) and without (n= 99) MST who received Holter and electrocardiogram evaluation at a Veteran Affairs medical center during 2007-2010, we examined the relationship between MST and the standard deviation of all R-R intervals (SDNN) and the square root of the mean of the sum of the squares of differences between adjacent R-R intervals (RMSSD). Female veterans with MST were younger, p= .002, frequently had a probable posttraumatic stress disorder diagnosis, 80% versus 15%, p= < .0001, and had lower SDNN, p= .0001, and RMSSD, p= .001, than those without MST. The SDNN and RMSSD of a 25-year-old female veteran with MST were comparable to that of female veterans aged 69 to 81 years without MST. Further research is needed to evaluate relationships between MST and HRV measures.

Cardiac Autonomic Response to Saturated Fatty Meal in Overweight and Obese Young Females

The present study aimed to assess the effect of saturated fatty meal on heart rate variability (HRV) in overweight and obese young females.42 (18–23 years old) female volunteer students were included into the study. On 7th day of menstrual cycle, participants had high fat milkshakes at 8 a.m., 3 hours preceding HRV assessment.HRV indices included; standard deviation of all R‐R intervals (SDRR), root mean squares of successive differences between R‐R intervals (rMSSD), very low frequency waves (VLF), low frequency waves (LF), high frequency waves (HF). LF/HF ratio was calculated.The rMSSD and HF waves were significantly decreased in overweight and obese groups when compared to control group (P&lt; 0.01, P&lt; 0.001) and (P&lt;0.001, P&lt; 0.001) respectively.The LF waves showed significant increase in overweight group (P&lt;0.001) and significant decrease in obese group (P&lt;0.05).The LF/HF ratio was significantly increased in the overweight group (P&lt;0.001), and insignificantly different in the obese group. No significant correlations were found between body mass index, waist hip ratio and HRV parameters.The present study revealed loss of protective vagal influence on heart rate in overweight and obese young females.Interestingly, the present study showed a blunted sympathetic response to saturated fatty meal in obese young females, while in the overweight group, sympathetic hyperactivity was observed.

Prognostic Role of Heart Rate Variability in Patients with ST-Segment Elevation Acute Myocardial Infarction Treated by Primary Angioplasty

Objectives: The aim of our study was to assess the prognostic value of heart rate variability (HRV) in ST-segment elevation acute myocardial infarction (STEMI) patients treated by percutaneous transluminal coronary angioplasty (PTCA) and optimal medical therapy. Methods: We enrolled 182 consecutive patients with a first STEMI (59.1 ± 11 years; 82.4% men) treated by primary PTCA. HRV was assessed on 24-hour Holter ECG recordings before discharge and 1 and 6 months after discharge. The primary end point was the occurrence of major clinical events (MCE), defined as death or new acute myocardial infarction (AMI). Results: At a follow-up of 42 ± 23 months, MCE occurred in 14 patients (7.6%; 3 deaths and 11 re-AMIs). HRV parameters before discharge were significantly lower in patients with MCE, with standard deviation of all RR intervals (SDNN) and very low frequency and low frequency (LF) amplitude being the most predictive variables. HRV assessed at follow-up instead did not significantly predict MCE. At multivariate analysis, only SDNN (HR 0.97; p = 0.02) and LF (HR 0.90; p = 0.04) remained significantly associated with MCE. Lower tertile SDNN and LF values were associated with a multivariate HR of 3.91 (p = 0.015) and of 2.92 (p = 0.048), respectively. Similar results were observed considering re-AMI only as the end point. Conclusions: In STEMI patients treated by PTCA, HRV assessed before discharge was an independent predictor of MCE and re-AMI.

Nocturnal heart rate variability analysis as a screening tool for obstructive sleep apnea syndrome

BackgroundRecurrent intermittent hypoxia and subsequent increased sympathetic nervous system activity have been adopted as possible mechanisms underlying cardiac rhythm disturbances in obstructive sleep apnea syndrome (OSAS). MethodsWe analyzed nocturnal heart rate variability(HRV) in 80 patients (74 males, 6 females, mean age 47.01±10yrs) with polysomnographically verified OSAS to assess the changes in nocturnal HRV indices, and to investigate the correlation between these changes to the severity of OSAS. The 80 patients were subdivided into 2 subgroups based upon the severity of OSAS; the first subgroup consisted of 27 patients with mild-to-moderate OSAS, while the second subgroup consisted of 53 patients with severe OSAS. For control group, 25 healthy individuals were included in the study. ResultsIn time-domain analysis, the mean of the standard deviation of all RR intervals for all 5-min segments (SDNN index) was significantly different between patients with OSAS and control as well as among different stages of severity of OSAS (p=0.02, and p=0.046, respectively). The standard deviation of all RR intervals (SDNN) was significantly different between patients with OSAS and control (p=0.039). HRV triangular index was significantly different among different stages of severity of OSAS (p=0.023). Frequency-domain variables namely total power, very low frequency (VLF) power, and low frequency (LF) power were significantly increased in patients with OSAS in comparison to control (p=0.01, p=0.024, and p=0.018, respectively), as well as among OSAS subgroups (p=0.01, p=0.02, and p=0.04, respectively). Stepwise multiple logistic regression analysis revealed that AHI correlated positively with SDNN (r=0.247, p=0.036), SDNN index (r=0.306, p=0.009), total power (r=0.323, p=0.006), VLF power (r=0.248, p=0.037), LF power (r=0.384, p=0.001), and LF/HF ratio (r=0.342, p=0.004), but correlated negatively with RR interval (r=−0.247, p=0.036). ConclusionOSAS predisposes to clinically significant nocturnal impairment of the cardiac autonomic function as evidenced by nocturnal HRV analysis and this impairment was correlated to the severity of OSAS. Accordingly, HRV can serve as a simple, powerful screening tool for cases with suspected OSAS.

Heart rate variability in the subsyndromal depressive phase of bipolar disorder

To compare the heart rate variability of bipolar patients in the subsyndromal depressive phase with healthy controls and to evaluate the relationship between severity of subsyndromal depressive symptoms and heart rate variability. Thirty-three bipolar patients in the subsyndromal depressive phase and 59 healthy controls were enrolled. A patient was considered to be in a subsyndromal depressive phase when the Montgomery-Åsberg depression rating scale score was ≤10 and the Clinical Global Impression-Severity scale (CGI-S) was ≤3 for the previous 1 month. After approximately 10 min of supine rest, all participants underwent resting electrocardiograms for 5 min in the supine position using limb leads. Different parameters of heart rate variability were analyzed in the time and frequency domains. Bipolar patients had significantly lower standard deviation of all RR intervals (SDNN), proportion of adjacent NN intervals that differ by >50 ms (pNN50), log total power (log TP) and very low frequency power (VLF) compared to healthy controls. There were significant negative correlations between CGI-S score and some heart rate variability parameters, including heart rate variability index, SDNN, root mean square successive difference (RMSSD), pNN50, log TP, VLF, low frequency power (LF) and high frequency power (HF). Patients with bipolar disorder in the subsyndromal depressive state have reduced heart rate variability relative to healthy controls, and reduction of heart rate variability appears to be correlated with severity of symptoms in bipolar patients.

Relationship between heart rate variability and the severity of psychotic symptoms in schizophrenia.

Kim J-H, Ann J-H, Lee J. Relationship between heart rate variability and the severity of psychotic symptoms in schizophrenia.Objective: The relationship between autonomic neurocardiac function and schizophrenia remains elusive. This study investigated the relationship between the heart rate variability (HRV) parameters and the severity of psychotic symptoms in schizophrenic patients.Methods: Twenty-one patients receiving risperidone monotherapy and 21 matched normal control subjects were evaluated for HRV analysis. The severity of schizophrenic symptoms was assessed using the Positive and Negative Syndrome Scale (PANSS) and a five-factor model of the PANSS was used.Results: The value of the ratio of low-to-high frequency spectral power was significantly higher in the patient group. The patient group also showed a significantly lower value of approximate entropy. After controlling the dosage of risperidone, the PANSS total score had significant negative correlations with the standard deviation of all RR intervals (SDNN) and the square root of the mean squared differences of successive normal sinus intervals (RMSSD). With respect to the PANSS factors, the score of the PANSS cognitive/disorganisation factor had significant negative correlations with SDNN and RMSSD.Conclusion: These results provide some evidence that the severity of psychotic symptoms, especially cognitive/disorganisation symptom dimensions, may be associated with reduced HRV, suggesting a potential involvement of neuroautonomic dysfunction in the pathophysiology of specific symptoms of schizophrenia.

Comparison of heart rate variability and treadmill exercise score in patients with stable coronary artery disease

Depressed heart rate variability (HRV) is associated with increased mortality and morbidity with various forms of heart disease, and the Duke treadmill score (DTS) provides diagnostic and prognostic information for the evaluation of patients with coronary artery disease (CAD). Our study was aimed at assessing any possible correlation between HRV and DTS in stable CAD. We evaluated the correlation between the HRV assessed by using 24 hour ambulatory ECG monitoring, and treadmill exercise score in 37 patients with angiographically proven and clinically stable CAD. In univariate analysis, DTS showed a significant negative correlation with age (r=−0.89, p 50 ms (PNN50) (r=0.69, P<0.05), and mean of the standard deviation of all R-R intervals in all the 5-minute intervals (HRVM) (r=0.63, P<0.05). There is no significant correlation between DTS and standard deviation of all R-R intervals (SDNN), standard deviation of the averages of R-R intervals in all 5-minute segments of the entire recordings (SDANN) and standard deviation of the SDNN in all the 5-minute intervals (HRVSD). In multiple regression analysis, age was the only independent significant predictor of DTS (p<0.01). DTS decreased with advancing age. SDNN, SDANN, RMSSD, HRVM and HRVSD were not apparent predictors for detecting of DTS. Age was an independent predictor of DTS. Although DTS was correlated with RMSSD, PNN50 and HRVM in patients with stable CAD, time domain parameters of HRV were not appearent predictor for DTS.

Obesity is associated with impaired cardiac autonomic modulation in children

To examine the cross-sectional association between measurements of obesity and subclinical impairment of cardiac autonomic modulation (CAM) in a population-based sample of children. Data from 616 grade K-5 children randomly selected from Central Pennsylvania were utilized. Obesity was defined using the International Obesity Task Force (IOTF) age- and sex-specific cut-off criteria and classified as normal weight, overweight, and obese. CAM was measured by heart rate variability (HRV) analysis of beat-to-beat RR intervals, including time domain measures i.e., the standard deviation of all RR intervals (SDNN), the square root of the mean of the sum of squares of differences between adjacent RR intervals (RMSSD), and mean heart rate (HR); and frequency domain measures i.e., high frequency power (HF), low frequency power (LF), and LF/HF ratio. The prevalence of obesity and overweight in children was 12.3%, and 16.5%, respectively. Age, race, sex, and sleep disorder breathing (SDB) adjusted means (standard error, SE) of SDNN were 98 (1.24), 90.2 (2.58), and 81.9 (3.03) milliseconds (ms) in normal weight, overweight, and obese groups, respectively; and that for (log) HF were 6.83 (0.04), 6.56 (0.08), and 6.35 (0.09) ms(2), respectively. Comparing the magnitude of effects from body mass index (BMI), weight, and height percentiles, and waist circumference on HRV indices revealed that body weight was the strongest correlate of HRV indices. Childhood obesity is significantly associated with lower HRV, indicative of sympathetic overflow unopposed by parasympathetic modulation. These findings support the need to target childhood-obesity before traditional "high risk age" for cardiac events.

CORRELATION BETWEEN FASTING PLASMA GLUCOSE AND AUTONOMIC DYSFUNCTION IN HEALTHY SUBJECTS WITH NORMOGLYCEMIA: AN EARLY IMPAIRMENT IN CARDIOVASCULAR ADAPTATION: PP.17.144

Objective: Autonomic neuropathy associated with the higher risk of cardiovascular mortality. It is known, that the autonomic dysfunction appears in the early phases of the disturbances of the carbohydrate metabolism already. The aim of this study was to determine the correlations between autonomic dysfunction and the fasting plasma glucose in healthy subjects with a normal carbohydrate metabolism according to the WHO criteria, normal body weight and blood pressure. Design and Method: 14 healthy subjects were included. Autonomic function was investigated by means of the five standard cardiovascular reflex tests, heart rate variability (HRV) and the spontaneous baroreflex sensitivity (BRS). The blood pressure was measured continuously with the Finapres 2300. The ECG signal was detected continuously by means of a Siemens Sirecust 730 ECG. The signals were fed through an analog-digital converter into a computer and analysed off-line. The oscillation amplitude of R-R intervals were analysed as well as the time and frequency domain indexes of HRV. The spontaneous BRS was calculated in the supine position and after standing up and based on the analysis of the spontaneous fluctuations of blood pressure and interbeat intervals. Statistical analysis was performed by SPSS program. Results: There were statistical significant negative relationships between the fasting plasma glucose and the heart rate response to deep breathing (r = -0.58, p < 0.05), the heart rate response to standing up (r = -0.56, p < 0.05), standard deviation of all RR intervals (r = -0.59, p < 0.05), root mean square of successive RR differences (r = -0.57, p < 0.05), power of low frequency component of HRV (r = -0.56, p < 0.05), power of high frequency component of HRV (r = -0.57, p < 0.05) and the BRS after standing up (r = -0.56, p < 0.05). There were no statistical differences between the fasting plasma glucose and the another cardiovascular reflex tests. Conclusions: Our results suggest the existence of a close relationship between the increase of the normal range for fasting plasma glucose in healthy subjects and the autonomic dysfunction which may forecast the early cardiovascular adaptation damage.

The autonomic nervous system dysregulation in response to orthostatic stress in children with neurocardiogenic syncope

Neurocardiogenic syncope is a common disorder, which is considered as a benign condition. However, sudden loss of conscience and muscle tone causes anxiety among the family members due to its similarity to sudden death. Autonomic nervous system dysregulation is thought to be responsible in the aetiology. Heart rate variability is used for assessment of autonomic nervous system.We evaluated 24 children between 6 and 18 years (mean plus or minus standard deviation is equal to 12.5 plus or minus 3.28, with neurocardiogenic syncope and 10 healthy controls, mean plus or minus standard deviation is equal to 12.48 plus or minus 3.27) by using 24 hour Holter monitorisation and head-up tilt test. Heart rate variability analysis was performed using the Holter recordings obtained both during head-up tilt test and throughout the day.Our results revealed that, there is no significant difference between the study and the control groups in terms of the mean heart rate and all indices of the heart rate variability (p > 0.05). However, during the first 5 minutes of the head-up tilt test, standard deviation of all RR intervals and root mean square of successive differences were significantly lower in the syncope group compared with the control group, 42.17 plus or minus 12.56 versus 60.10 plus or minus 33.10 and 21.26 plus or minus 8.87 versus 36.80 plus or minus 31.03; p-values 0.02 and 0.03, respectively.In conclusion; autonomic functions in children with neurocardiogenic syncope are similar to healthy children. However, sympathetic hyperactivation occurs during the early phase of orthostatic stress in children with neurocardiogenic syncope comparing to healthy controls. Parasympathetic innervation is not sufficient in compensation of this sympathetic hyperactivation. Management strategy in neurocardiogenic syncope should be based on these pathophysiologic mechanisms.

Selective autonomic screening in Guillain-Barré syndrome

Autonomic dysfunction is a common and important complication in Guillain-Barre syndrome (GBS) and may be the cause of significant morbidity or death. Objectives : To show the possible autonomic involvement in patients with GBS. The sympathetic skin response (SSR) and the parameters of heart rate variability gathered from a 24-h electrocardiogram recording were studied in 14 patients with GBS [13 with acute inflammatory demyelinating polyneuropathy (AIDP) and one with acute motor axonal neuropathy (AMAN)]. In two of the patients, SSR couldn't be elicited. In the rest of the patients, amplitude of SSR was found to be decreased when compared with the control subjects. In the time domain analysis of the 24-h electrocardiogram, SDNN (the standard deviation of all R-R intervals), SDANN (the standard deviation of the averages of R-R intervals during all 5-min periods that constitute the 24-h day), SDNN index (mean of the standard deviations of all R-R intervals for all 5-min segments of the 24-h recording); in the frequency domain analysis HF(high frequency), LF(low frequency), VLF (very low frequency) and total power were found decreased in patients when compared with the control subjects. When the mean values with standard deviations of controls were compared with the patients' values one by one, the pregnant patient with AMAN had increased heart rate variability parameters. The remaining 13 patients had decreased values. These findings reflect an involvement of both the parasympathetic and sympathetic systems in GBS. Our results suggest that SSR and heart rate variability parameters may be used for early detection of any autonomic dysfunction in patients with GBS.

Heart rate variability during sleep and sleep apnoea in a population based study of 387 women

Increased sympathetic activity during sleep has been suggested as a link between obstructive sleep apnoea syndrome and cardiovascular disease. Heart rate variability (HRV) is a measure of autonomic effect on the heart. Different parameters have been associated with sympathetic and parasympathetic activity. We have studied HRV in different sleep stages and related the HRV-pattern to sleep apnoea in a population-based sample of 387 women. We investigated the HRV-parameters standard deviation of all R-R intervals (SDNN), root of the averaged square of successive differences (RMSSD), low frequency component (LF), high frequency component (HF), ratio of low frequency component to high frequency component LF/HF and VSAI [variation in sympathetic activity between rapid eye movement (REM) and slow wave sleep, defined as LF(REM)-LF(SWS)]. The HRV-parameters were compared with the results of a full-night polysomnography. Hourly incidence of obstructive episodes was used for classifying the subjects into four apnoea-hypopnoea index (AHI)-groups (<5, > or =5 and <15, 15-30 and >30 events). Individual sleep stages were analysed by pooling all recordings. Women with high AHI had higher heart rate and LF/HF ratio. In subjects with AHI >30, LF/HF ratio however dropped to same level as with AHI <5. Subjects with high AHI had low VSAI. Levels of SDNN, LF and LF/HF ratio during REM and light sleep were similar to wakefulness. In slow wave sleep the parameters decreased. In conclusion, moderately increased prevalence of obstructive apnoeas was associated with signs of higher sympathetic activity. High AHI was however associated with a HRV-pattern suggestive of depressed sympathetic drive and lowered ability to increase it during REM.

Association between reduced pulmonary diffusing capacity and cardiac autonomic dysfunction in Type 1 diabetes

In Type 1 diabetes mellitus (DM), it has been suggested that autonomic nervous system dysfunction (NAD) impairs lung diffusion capacity. Heart rate variability (HRV), a measure of cardiac autonomic function, is a sensitive method of detecting NAD. To our knowledge, no previous study has assessed whether cardiac sympatho-vagal balance is associated with lung diffusion capacity in diabetes. Twenty Type 1 DM patients without pulmonary abnormalities and systemic NAD underwent measurement of lung diffusion capacity for carbon monoxide (DLCO) by single-breath method and assessment of cardiac autonomic function by HRV analysis on 24-h electrocardiographic Holter recordings. Standard respiratory function tests and peripheral autonomic tests were normal in all patients. DLCO was lower than normal reference values in six patients (30%). DLCO correlated significantly with most HRV variables, independent of the clinical and laboratory variables. The strongest correlation was found with standard deviation of all RR intervals (SDNN; r = 0.62, P = 0.003) in the time domain and low frequency (LF) power (r = 0.73, P < 0.001) in the frequency domain. In Type 1 diabetes, a significant association exists between cardiac NAD and reduced DLCO in the absence of clinical respiratory and autonomic abnormalities. Thus, NAD may be involved in the early reduction of DLCO in these patients, possibly through abnormalities in the regulation of pulmonary blood flow at the microvascular level.