Higher Parasympathetic Activity Research Articles

Inattentive and hyperactive preschool-age boys have lower sympathetic and higher parasympathetic activity

The presented study aimed to clarify the relationship between the autonomic nervous system and disruptive behaviors among preschoolers. Possible gender differences in autonomic activity were also examined. A total of 88 preschool-age children were enrolled in this study. Autonomic activities were measured by power spectrum analysis of heart rate variability (HRV). The Swanson, Nolan and Pelham parents and teachers rating scale (SNAP-IV) was applied to evaluate each subject's severity of disruptive behavior. The relationship between the HRV results and the SNAP-IV was evaluated by correlation analysis, which disclosed that the scores for inattention, hyperactivity/impulsivity and oppositional defiant disorder showed a negative association with LF % and LF/HF. The above scales, except for the hyperactivity subscale, also showed a positive association with HF. On separating the two genders, only boys showed the above correlations. Preschool-age boys who show more inattentive and hyperactive features have lower sympathetic and higher parasympathetic activity.

Neonatal nociception elevated baseline blood pressure and attenuated cardiovascular responsiveness to noxious stress in adult rats

Neonatal nociception has significant long-term effects on sensory perception in adult animals. Although neonatal adverse experience affect future responsiveness to stressors is documented, little is known about the involvement of early nociceptive experiences in the susceptibility to subsequent nociceptive stress exposure during adulthood. The aim of this study is to explore the developmental change in cardiovascular regulating activity in adult rats that had been subjected to neonatal nociceptive insults. To address this question, we treated neonatal rats with an intraplantar injection of saline (control) or carrageenan at postnatal day 1. The carrageenan-treated rats exhibited generalized hypoalgesia at basal state, and localized hyperalgesia after re-nociceptive challenge induced by intraplantar injections of complete Freund's adjuvant (CFA) as adults. Then we recorded baseline cardiovascular variables and 24-h responsiveness to an injection of CFA in the free-moving adult rats with telemetric technique.The carrageenan-treated rats showed significantly higher basal blood pressures (110.3±3.16 vs. control 97.0±4.28mmHg). In control animals, baroreceptor reflex sensitivity (BRS) decreased, sympathetic vasomotor activity increased, and parasympathetic activity was inhibited after CFA injection. Blood pressure elevation was evident (107.0±2.75 vs. pre-injection 97.0±4.28mmHg). Comparatively, the carrageenan-treated rats showed a higher BRS (BrrLF 1.03±0.09 vs. control 0.70±0.06ms/mmHg) and higher parasympathetic activity [0.93±0.17 vs. control 0.32±0.02ln(ms2)] after CFA injection. The change in blood pressure is negligible (111.9±4.05 vs. pre-injection 110.3±3.16mmHg). Our research has shown that neonatal nociception alters future pain sensation, raises basal blood pressure level, and attenuates cardiovascular responsiveness to nociceptive stress in adult rats.

The Study of Spectral Analysis of Heart Rate Variability in Different Blood Pressure Types in Euvolemic Peritoneal Dialysis Patients

Background: Heart rate variability (HRV) is an useful noninvasive tool to assess autonomic nervous system (ANS) function and may provide an insight into the understanding of the role of ANS in the pathogenesis of blood pressure (BP) abnormality in euvolemic continuous ambulatory peritoneal dialysis (CAPD) patients. Methods: In this cross-sectional study, 62 CAPD patients with normal hydration values (assessed by a bioimpedance spectroscopy device) were enrolled from our peritoneal dialysis (PD) unit. Patients were divided into three groups according to their BP: normotension (NT), hypertension (HT), and hypotension (HyT). Spectral analysis of HRV was measured by examination of the average heart rate using standard electrocardiogram in 5 min. Results: The HyT group had the lowest serum urea nitrogen among the three groups (all p < 0.05), and a lower serum potassium and albumin as compared with the NT group (p < 0.05). The HyT group also had the highest total power (TP) and highest frequency power (HF) among the three groups (all p < 0.05), and a lower normalized low frequency power (LF), LF/HF ratio, and a higher normalized HF as compared with the HT group (all p < 0.05). Conclusion: Our study suggested that autonomic insufficiency was present in euvolemic PD patients, and hypotensives had a relatively higher parasympathetic activity and blunted sympathetic activity.

Early Exposure to a High-Fat Diet has more Drastic Consequences on Metabolism Compared with Exposure During Adulthood in Rats

The aim of this study was determine whether the introduction of a high-fat diet during the peripubertal phase induces significant changes in body weight control, glucose homeostasis and the parasympathetic tonus compared with the administration of this diet to adult rats. High-fat diet was offered to male Wistar rats at weaning or during adulthood. A group of rats received high-fat diet for 60 days, from weaning to 81-day-old (HF81) or from 60 to 120-day-old (HF120), whereas 2 other groups received a normal-fat diet (i. e., NF81 and NF120). We analyzed adiposity, glucose homeostasis, insulin sensitivity, and vagal nerve activity. High-fat diet increased the accumulation of adipose tissue in all of the rats, but the difference was greater in the rats that were fed the high-fat diet since weaning (p<0.001). The HF rats showed glucose intolerance with high levels of insulin secretion during the glucose tolerance test (p<0.01). Rats that were fed the high-fat diet presented severe insulin resistance, indicated by a low K itt (p<0.01). Interestingly, the HF81 rats exhibited greater insulin resistance compared with the HF120 rats (p<0.05). The recordings of vagus nerve activity showed that the HF rats had higher parasympathetic activity than the NF rats irrespective of age (p<0.01). Our results show that a high-fat diet offered to rats just after weaning or in adulthood both cause impairment of glycemic homeostasis and imbalance in parasympathetic activity. Importantly, the consumption of high-fat diet immediately after weaning has more drastic consequences compared with the consumption of the same diet during adulthood.

The moderating role of the emotional valence on the relationship between big five personality dimensions and parasympathetic activity

Method According to the Polyvagal theory (Porges, 1995, 2001), affective states that follow the perception of a safe environment are characterized by higher parasympathetic activation in contrast to more distressing states. Data from numerous studies partly support this notion. Studies that relate vagal activation to major personality traits are scarce and studies that would investigate interactions between major personality traits and emotional valence on the VT are completely missing. Extraversion is previously found to be positively associated with VT during baseline (Oveis et al., 2009) and negatively associated with VT during mental arithmetic task (Knyazev et al., 2002). Other Five factor model dimensions are not found to be related to neither resting VT nor to VT reactivity. Nevertheless, there are numerous data on the links between resting VT as well as VT reactivity and other personality traits that are subsumed under Big five dimensions. Many studies have shown that aggressiveness and hostility (as components of Agreeableness and Neuroticism) are related to greater vagal reactivity, while anxiety and depressiveness (as components of Neuroticism) are related to low resting VT and low vagal reactivity. This study replicates findings on the relations between positive and negative emotions and VT and extends them in the context of individual differences.

Heart rate variability during long truck driving work.

We recorded ambulatory electrocardiograms of 6 long distance truck drivers during their work period in order to observe the affect of autonomic nervous function and symptoms while doing their work. We also recorded their work patterns every minute. The RR50 value and the LFP/HFP ratio were calculated every two minutes based on R-R interval data. RR50 was significantly higher during taking naps than during other periods of work shifts, while, the LFP/HFP ratio showed significantly lower during taking naps than during other periods of work shifts. RR50 in the morning was significantly higher than that in the afternoon. On the contrary, the LFP/HFP ratio showed opposite tendency. Only on the times of driving, RR50 was significantly higher in the morning than that in the afternoon. On the other hand, the LFP/HFP ratio showed an opposite tendency. These results show that the parasympathetic nervous activities were more dominant than sympathetic nervous activities in the morning during the subjects were doing long distance truck driving including midnight work. Driving while in high parasympathetic nervous activity levels may add to cardiovascular stress and lead to drowsiness. And this may result in disrupted attention. It is necessary to decrease work time and improve working conditions of truck drivers working long-hour shifts.

Increased Sympathetic and Decreased Parasympathetic Activity Rather Than Changes in Hypothalamic-Pituitary-Adrenal Axis Activity Is Associated with Metabolic Abnormalities

Stress is suggested to lead to metabolic dysregulations as clustered in the metabolic syndrome, but the underlying biological mechanisms are not yet well understood. We examined the relationship between two main str systems, the autonomic nervous system and the hypothalamic-pituitary-adrenal (HPA) axis, with the metabolic syndrome and its components. The design was baseline data (yr 2004-2007) of a prospective cohort: the Netherlands Study of Depression and Anxiety (NESDA). The study comprised general community, primary care, and specialized mental health care. This study included 1883 participants aged 18-65 yr. Autonomic nervous system measures included heart rate, respiratory sinus arrhythmia (RSA; high RSA reflecting high parasympathetic activity), and preejection period (PEP; high PEP reflecting low sympathetic activity). HPA axis measures included the cortisol awakening response, evening cortisol, and a 0.5 mg dexamethasone suppression test as measured in saliva. Metabolic syndrome was based on the updated Adult Treatment Panel III criteria and included high waist circumference, serum triglycerides, blood pressure, serum glucose, and low high-density lipoprotein cholesterol. RSA and PEP were both independently negatively associated with the presence of the metabolic syndrome, the number of metabolic dysregulations as well as all individual components except high-density lipoprotein cholesterol (all P < 0.02). Heart rate was positively related to the metabolic syndrome, the number of metabolic dysregulations, and all individual components (all P < 0.001). HPA axis measures were not related to metabolic syndrome or its components. Our findings suggest that increased sympathetic and decreased parasympathetic nervous system activity is associated with metabolic syndrome, whereas HPA axis activity is not.

Variabilidad de la frecuencia cardíaca como indicador de salud en el deporte: validación con un cuestionario de calidad de vida (SF-12)

Introduction and backgroundIn sports medicine, heart rate variability (HRV) analysis is used to assess adaptation to athletes’ training. Our goal was to validate HRV analysis as a health indicator by comparing HRV parameters with Short Form-12 Health Survey Questionnaire (SF-12) scores in a sample of healthy individuals. MethodsWe performed an experimental study in 32 healthy individuals (18 men and 14 women) with a mean age of 26.19 years. The SF-12 questionnaire was used to evaluate quality of life and a S810i Polar heart rate monitor was used to recode HRV through the R-R interval. HRV parameters were obtained with Polar Precision Performance software. ResultsThe root mean square of the differences between adjacent R-R intervals in milliseconds (RMSSD), the percentage of the adjacent R-R intervals differing by more than 50milliseconds in the entire recording (pNN50) and the high frequency (HF) parameters of HRV showed a significant and positive correlation with the perceived physical health scores obtained in the physical component summary scale, the role-physical dimension and the total scale of the SF-12 questionnaire. Participants with greater perceived health showed the highest HRV. Higher parasympathetic activation at rest was related to greater health-related quality of life. ConclusionsOur results confirm that HRV analysis is a good marker of health status and could be used to diagnose stress states (overtraining, burnout, fatigue, exhaustion, anxiety) quickly and easily (at rest and non-invasively), both in the general population and, in particular, in elite athletes.

Hypotension, Heart Rate Variability, and Altered Autonomic Function

We thank Dr. Latson for and appreciate his interesting comment on our study. As he stated, we demonstrated that the ratio of low frequency (LF) to high frequency (HF) of heart rate variability (HRV) predicts postspinal hypotension with high sensitivity and specifity.1,2These findings were confirmed in the control group of another study.3In addition, we demonstrated significant differences of normalized HF spectral power before subarachnoid block. These results may indicate that baseline HF is of predictive value as well, confirming the conclusions of Latson et al. 4We agree with the author that the type of HRV analysis may crucially influence the results. Latson et al. investigated absolute values, whereas we analyzed the different frequency bands of the power spectrum as normalized units.Currently, HRV-derived data are processed and presented in different ways. First, absolute HRV values are frequently analyzed and, as the author stated, may have advantages in the analysis of autonomic reflex integrity. Nevertheless, total power of HRV and its different parts decrease with increasing age, underlying cardiovascular disease, and impaired autonomic regulation.5–7Thus, an absolute HF of, for example, 1,000 ms2/Hz may be considered as below normal in young and healthy patients, normal in older healthy patients, and even above normal range in patients with coronary artery disease. Therefore, absolute values do not reflect the specific impact of the parasympathetic or the sympathetic activity of the autonomic regulation. Second, HRV data are normalized to total power. If the total power is high (e.g. , 10,000 ms2/Hz), an HF of 1,000 ms2/Hz is only 10%, reflecting a low parasympathetic activity in the individual. If the total power is only 2,000 ms2/Hz, the same absolute HF value would reflect a considerably higher parasympathetic activity. The aim of our studies was to identify a general predictor of postspinal hypotension; therefore, we investigated the different frequencies in normalized units and cannot comment on absolute HF values in our patients. Absolute values were analyzed as well, but demonstrated only a trend toward higher HF in normotensive patients compared with hypotensive patients. Therefore, we cannot recommend the analysis of absolute values for prediction of postspinal hypotension based on our data.The guidelines of the Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology do not favor any one of the mathematical techniques, and each may have advantages and disadvantages.8However, the ratio of LF to HF was demonstrated to be the most valuable parameter of HRV in terms of prediction of postspinal hypotension.1–3This parameter reflects the balance of the autonomic nervous system and is independent of relative or absolute values because the ratio of absolute and normalized values is mathematically identical. Risk stratification based on the analysis of this autonomic balance was demonstrated to successfully guide prophylactic therapy.3We conclude that in a homogenous group of patients, analysis of absolute values of HRV parameters is probably the best method to determine reflex integrity or “gain.” If the trial’s patient population demonstrates a large variation with respect to age, sex, and underlying diseases, relative values may be more appropriate. LF to HF ratio may be particularly useful for HRV analysis because it is independent of this difference.*University-Hospital Schleswig-Holstein, Campus Kiel, Kiel, Germany. hanss@anaesthesie.uni-kiel.de

The influence of xenon on regulation of the autonomic nervous system in patients at high risk of perioperative cardiac complications

As xenon anaesthesia (XE) does not produce haemodynamic depression its use may be of benefit in patients at high risk of intraoperative haemodynamic instability and perioperative cardiac complications. XE (n=22) was compared with total i.v. anaesthesia (TIVA, n=22) for differences in autonomic regulation, peri- and postoperative performance. Patients undergoing abdominal aortic surgery were studied at five events: T1: baseline awake; T2: anaesthesia induction; T3: before aortic cross-clamping; T4: after aortic cross-clamping; T5: after aortic declamping. T3-T5: end-tidal xenon concentration 60 (5)%. Intraoperative analysis: heart rate, heart rate variability, blood pressure and cardiac output. Postoperative analysis: 24 h Holter ECG, intensive care unit and hospital stay, and patient's outcome after 6 months. XE in contrast to TIVA increased parasympathetic and decreased sympathetic activity. Median low to high frequency decreased significantly in the XE group after start of XE (P<0.05) and remained significantly lower during all events after start of XE as compared with TIVA (P=0.0001). After start of XE heart rate of these patients was significantly lower as compared with TIVA (P=0.04). Cardiac output increased significantly in TIVA after aortic declamping (P<0.05). Outcome parameters did not differ significantly between groups. XE patients demonstrated lower sympathetic and higher parasympathetic activity as compared with TIVA patients. This was reflected by significant differences in haemodynamics but did not correlate with a better postoperative outcome. Thus, it remains controversial whether XE provides benefits in high risk patients.

Effects of Heliox Breathing on R-R Interval Variability at Rest and During Exercise in COPD

1454 Patients with non-hypoxemic chronic obstructive pulmonary disease (COPD) have, in addition to high airway resistance and low exercise tolerance, high parasympathetic nervous system activity. Airway resistance, however, is reduced with high inspired fractions of helium (Heliox: 20% oxygen, 80% helium) through less turbulent airflow. PURPOSE: To test whether autonomic system function might be altered with Heliox breathing in COPD during exercise. This might occur through a mechanism linked to reduced dynamic hyperinflation and – possibly – smaller intrathoracic pressure. METHODS: Autonomic nervous system function was assessed at rest and during 20 Watt constant work rate exercise in eight non-hypoxemic COPD patients (72 ± 10 yrs; FEV1% predicted: 36.6 ± 9.1). This was achieved by analysis of R-R interval variability, derived from the ECG signal, using an autoregressive method. Subjects inspired air or Heliox from a balloon. The low-to-high frequency ratio (LF/HF) and the high-to-total frequency ratio (HF/TOT) were calculated as indices of sympathetic and parasympathetic autonomic tone, respectively (HF: 0.15 – 0.50 Hz; LF: 0.04 – 0.15 Hz). RESULTS: Heliox breathing slightly increased heart rate at rest, compared with air (73.6 ± 10.7 vs 68.9 ± 9.1 min−1, P < 0.05). During exercise both heart rate (93.8 ± 13.9 vs. 89.9 ± 11.6 min−1, P< 0.05) and breathing frequency (24.9 ± 3.6 vs. 23.4 ± 3.2 min−1) were higher on Heliox. While at rest there was no significant difference in autonomic tone indices between air and Heliox breathing, during exercise the HF/TOT ratio (parasympathetic index) was significantly lower with Heliox than with air (0.09 ± 0.08 vs. 0.17 ± 0.08, respectively, P < 0.05). Autonomic tone balance did not change from rest to exercise with air breathing; in contrast, the HF/TOT ratio was significantly reduced (0.09 ± 0.08 vs. 0.24 ± 0.11, P < 0.05) and the LF/HF ratio (sympathetic index) was significantly increased (1.56 ± 0.81 vs. 0.70 ± 0.28, P < 0.05) with Heliox breathing. CONCLUSIONS: During exercise Heliox breathing reduces PNS activity and shifts the autonomic tone balance towards sympathetic dominance in nonhypoxemic COPD patients. This may be conducive to improved airway function.

Effects of Heliox Breathing on R-R Interval Variability at Rest and During Exercise in COPD

1454 Patients with non-hypoxemic chronic obstructive pulmonary disease (COPD) have, in addition to high airway resistance and low exercise tolerance, high parasympathetic nervous system activity. Airway resistance, however, is reduced with high inspired fractions of helium (Heliox: 20% oxygen, 80% helium) through less turbulent airflow. PURPOSE: To test whether autonomic system function might be altered with Heliox breathing in COPD during exercise. This might occur through a mechanism linked to reduced dynamic hyperinflation and – possibly – smaller intrathoracic pressure. METHODS: Autonomic nervous system function was assessed at rest and during 20 Watt constant work rate exercise in eight non-hypoxemic COPD patients (72 ± 10 yrs; FEV1% predicted: 36.6 ± 9.1). This was achieved by analysis of R-R interval variability, derived from the ECG signal, using an autoregressive method. Subjects inspired air or Heliox from a balloon. The low-to-high frequency ratio (LF/HF) and the high-to-total frequency ratio (HF/TOT) were calculated as indices of sympathetic and parasympathetic autonomic tone, respectively (HF: 0.15 – 0.50 Hz; LF: 0.04 – 0.15 Hz). RESULTS: Heliox breathing slightly increased heart rate at rest, compared with air (73.6 ± 10.7 vs 68.9 ± 9.1 min−1, P < 0.05). During exercise both heart rate (93.8 ± 13.9 vs. 89.9 ± 11.6 min−1, P< 0.05) and breathing frequency (24.9 ± 3.6 vs. 23.4 ± 3.2 min−1) were higher on Heliox. While at rest there was no significant difference in autonomic tone indices between air and Heliox breathing, during exercise the HF/TOT ratio (parasympathetic index) was significantly lower with Heliox than with air (0.09 ± 0.08 vs. 0.17 ± 0.08, respectively, P < 0.05). Autonomic tone balance did not change from rest to exercise with air breathing; in contrast, the HF/TOT ratio was significantly reduced (0.09 ± 0.08 vs. 0.24 ± 0.11, P < 0.05) and the LF/HF ratio (sympathetic index) was significantly increased (1.56 ± 0.81 vs. 0.70 ± 0.28, P < 0.05) with Heliox breathing. CONCLUSIONS: During exercise Heliox breathing reduces PNS activity and shifts the autonomic tone balance towards sympathetic dominance in nonhypoxemic COPD patients. This may be conducive to improved airway function.

Cardiovascular vagosympathetic activity in rats with ventromedial hypothalamic obesity.

Rats with ventromedial hypothalamic lesion (VMH) are massively obese with endogenous hyperinsulinemia, insulin resistance, low sympathetic activity, and high parasympathetic activity, which are likely to induce hypertension. The goal was to follow in this model the long-term hemodynamic changes and to investigate the role of autonomic nervous system and insulin resistance in these changes. Heart rate and blood pressure were monitored for 12 weeks after operation using a telemetric system in VMH and sham rats. Plasma catecholamines and heart beta-adrenoceptors were measured. Glucose tolerance was studied after an intravenous glucose injection and insulin sensitivity during a euglycemic hyperinsulinemic clamp test. A marked bradycardia and only a mild increase in blood pressure occurred in VMH rats compared with sham animals. Response to autonomic-acting drugs showed an increase in heart vagal tone and responsiveness to a beta-agonist drug. Plasma catecholamine levels were markedly increased, and the density and affinity of heart beta-adrenoceptors were similar in VMH, sham, and control rats. Muscle glucose use was reduced by 1 week after operation in VMH animals. These results show the following in this model of massively obese rats with sympathetic impairment: 1). adrenal medulla secretion is increased, probably as a result of hyperinsulinemia and increased vagal activity; 2). cardiac responsiveness to beta-agonist stimulation is increased; and 3). despite these changes and suspected resistance to the vasodilative effect of insulin, blood pressure does not increase. We conclude that high vagal activity may be protective against hypertension associated with obesity.

Diminished Circadian Variation in Heart Rate Variability before Surgery in Patients Developing Postoperative Atrial Fibrillation

Objective - To evaluate the role of the autonomic nervous system for the development of atrial fibrillation (AF) after coronary artery bypass surgery. Design - Eighty patients without a previous history of AF were included. The sympathetic and parasympathetic activity were evaluated by the analysis of heart rate variability (HRV) in the frequency domain from 24-h Holter recordings and by measuring neuropeptides (neuropeptide Y, chromogranin A, chromogranin B, and pancreatic polypeptide (PP)) and catecholamines, obtained pre- and postoperatively. Results - Preoperatively, patients (36.3%) developing AF postoperatively showed a statistically significant less circadian variation in the HRV variables, the high-frequency (HF) component ( p = 0.013) and the low-frequency (LF)/HF ratio ( p = 0.007), than patients remaining in sinus rhythm. The HF component and PP, both reflecting parasympathetic activity, and all other variables in the frequency domain, decreased significantly after surgery in both patient groups ( p < 0.0001). Although catecholamines increased significantly postoperatively in both patient groups, neither catecholamines nor neuropeptides expressing sympathetic activity, differed between the two groups. PP was, however, significantly higher in patients with postoperative AF than in those with sinus rhythm post-operatively on day 1. Conclusion - The diminished circadian variation in HRV before surgery and the indirect signs of a higher parasympathetic activity in patients developing postoperative AF compared with patients remaining in sinus rhythm, may indicate a propensity for AF.

Endoscopic transthoracic sympathicotomy affects the autonomic modulation of heart rate in patients with palmar hyperhidrosis.

Palmar hyperhidrosis has been associated with an increased activity of the sympathetic nervous system. The objective of this study was to assess the immediate and long-term effects of endoscopic transthoracic sympathicotomy on the autonomic modulation of the heart rate in patients with palmar hyperhidrosis. Power spectrum analysis of heart rate variability in the lying position and after passive tilt to the upright position was performed in thirteen patients the day before and after sympathicotomy. A follow-up recording was performed in ten patients approximately six months later. Recordings from 26 healthy subjects were used as a reference group. The patients had a tendency to higher power of the low-frequency (LF: 0.04-0.15 Hz) and high-frequency (HF; above 0.15 Hz) components than controls in the upright position. After sympathicotomy LF power was reduced, but HF power was unchanged. At follow-up LF power remained at a lower level, but now HF power was reduced. Patients with palmar hyperhidrosis have a sympathetic overactivity but also a compensatory high parasympathetic activity. Sympathicotomy results in an initial sympathovagal imbalance with a parasympathetic predominance, which is restored on a long-term basis.

Dependence of autonomic and behavioral reactions to pain-related emotional stress on individual typological characteristics of the autonomic nervous system

It was found that autonomic and behavioral reactions to pain-related emotional stress in the miners of deep coal mines depend on the individual typological characteristics of their autonomic nervous system. The normotonics with an initially high sympathetic and parasympathetic activity were characterized by low resistance to stress-inducing factors, while high resistance to emotional stress was typical of the subjects with the parasympathetic type of autonomic nervous system. The greatest shifts in autonomic indices were observed in the stress-anticipation period rather than on direct exposure to pain stimulus.

Association Between Parasympathetic Activity and Late Potentials at Low Noise Level

Background: Late potentials (LP) in the signal‐averaged ECG represent activation of myocardial areas with slow conduction and predicts re‐entrant malignant ventricular arrhythmias in coronary artery disease. Low heart rate variability, which reflects low vagal and concomitantly elevated sympathetic activation also predicts ventricular arrhythmia. This autonomic profile is associated with the presence of LP (detected at noise level 0.4 μ;V) early after myocardial infarction. In contrast, sympathetic stimulation and diminution of vagal tone influence LP parameters (detected at noise level 0.2 μ;V) in the opposite direction in healthy subjects. The aim of this study was to estimate the possible association between measures of cardiac autonomic function and LP (detected at 0.4 and 0.2 μ;V) in patients with chronic coronary artery disease.Methods: ECGs of 174 consecutive patients with angiographically documented coronary artery disease and without myocardial infarction during the last 3 months were signal‐averaged to noise level 0.2 and 0.4 μ;V. LP were considered to be present if any two of the following criteria were present: signal‐averaged QRS duration &gt; 120 ms, root‐mean‐square voltage of the terminal 40 ms of the averaged QRS complex &lt; 25 μ;V, and late potential duration &gt; 40 ms. Heart rate variability was measured at rest in 5‐minute ECG recordings as: the standard deviation (SD) of all RR intervals, SD corrected for RR (SD/mean RR), and the power of high frequency (HF) component (0.15–0.40 Hz).Results: One hundred seven (61%) of the patients had LP at noise level 0.2 μ;V. LPs were more frequently observed in patients with slow heart rate, high heart rate variability, and high levels of vagal activity (mean RR &gt;; 1000 ms, SD &gt;; 60 ms, and HF &gt;; 100 ms2) than in patients with higher heart rate, low heart rate variability and attenuated vagal activity: 73% vs 54% (P = 0.02), 71% vs 53% (P = 0.02), 72% vs 51% (P = 0.005) for mean RR, SD, and HF power, respectively. Adjustment for possible confounding from mean RR level, gender, previous acute myocardial infarction, treatment with betablocker, and left ventricular ejection fraction did not significantly alter these associations. At noise level 0.4 μ;V 26% (45/174) had LP and the diagnosis of LP was not significantly associated with heart rate variability.Conclusions: At low noise level (0.2 μ;V) higher parasympathetic activity is associated with the diagnosis of LP. The predictive power of presence of LP diagnosed at low noise level for development of sudden cardiac death may be reduced by this association. In order to increase the predictive accuracy of LP we recommend either the use of noise level 0.4 μ;V, or identification of high arrhythmia‐risk patients by a combination of the presence LP and impaired heart rate variability. However, a prognostic study is needed to further clarify this.

Influence of infarct-related artery patency on the indexes of parasympathetic activity and prevalence of late potentials in survivors of acute myocardial infarction

Objectives. The purpose of this study was to determine whether infarct-related coronary artery patency influence myocardial electrical stability as measured by the prevalence of late potentials or heart rate variability.Background. Several studies have suggested that loss of vagal activity is associated with an increased incidence of arrhythmic death after myocardial infarction.Methods. A short-duration, high resolution electrocardiogram (ECG) was performed before hospital discharge in 175 patients with a first myocardial infarction. Seventy-three patients received thrombolytic therapy. All patients underwent coronary angiography. Coronary occlusion was defined as minimal or no anterograde flow. Eighty-eight patients (50.3%) had an occluded infarct-related artery. Sixty-two healthy subjects served as control subjects to determine the normal range of heart rate variability.Results. Comparison between the control group and patients without patency of the infarct-related artery in the time domain and spectral analyses revealed in the latter patients a reduced heart rate variability (p < 0.0001) and a lower power spectrum density in both the 0.05- to 0.15-Hz band (p < 0.0001) and the 0.15- to 0.35-Hz band (p < 0.0001). The heart rate variability in patient with late potentials was lower than in those with a normal signal-averaged ECG. Those patients with spontaneous or thrombolysis-induced reperfusion have less occurrence of late potentials and higher parasympathetic activity than do patients with a closed artery.Conclusions. This study suggests that the patency of the infarct-related artery determines both the absence of late potentials and the preservation of vagal tone and may explain the reduction in mortality induced by thrombolytic therapy in myocardial infarction.

Power spectrum analysis and heart rate variability in Stage 4 and REM sleep: evidence for state-specific changes in autonomic dominance.

The present study investigated autonomic activity during NREM and REM sleep stages and wakefulness by spectral analysis of heart rate variability. The results demonstrated that NREM sleep in humans was characterized by a widely different autonomic activation pattern than REM sleep: high parasympathetic activity was found in NREM, while REM was characterized by attenuated vagal tone, and augmented sympathetic activity. The overall pattern during wakefulness showed an intermediate position between NREM and REM patterns; parasympathetic activity was lower than in NREM and higher than in REM, with an opposite trend for sympathetic activity.

Acute effects of fat and carbohydrate on metabolic rate in normal, cold-acclimated and lean and obese (fa/fa) Zucker rats

The rise in metabolic rate after intragastric feeding with fat and carbohydrate was enhanced in cold-acclimated (5°C) rats and diminished in warm-acclimated (30°C) rats compared to controls (24°C), but the response was largest in cold-acclimated animals intubated with fat. These acute effects of nutrients were almost completely abolished by β-adrenergic blockade with propranolol in all groups, while the parasympathetic antagonist atropine sulphate enhanced the responses in control rats, but had little effect in cold-acclimated animals. Feeding carbohydrate produced similar increases in interscapular brown adipose tissue (BAT) temperature in control and cold-acclimated rats, but fat caused a much greater rise in the latter group. The thermic effects of both nutrients were lower in genetically obese Zucker rats than in their lean littermates. Atropine slightly increased the thermic responses to fat and carbohydrate in the lean Zucker rats and caused marked potentiation in obese rats intubated with fat, but did not alter the effect of carbohydrate in the obese animals These data suggest that the size of the acute rise in metabolic rate after fat and carbohydrate is dependent on the thermogenic capacity of the animal. The response to fat was particularly large in cold-acclimated rats, where BAT activity is high, possibly due to a direct action of fat on the tissue. Genetically obese Zucker rats show defective thermogenesis which may be due to a combination of low sympathetic activity, high parasympathetic activity and insensitivity to substrate availability.