Adaptation Of Autonomic Nervous System Research Articles

Autonomic nervous system activity in response to stress and cardiac coherence breathing exercise depending on body composition differences

ABSTRACT This study investigated the effects of stress and cardiac coherence breathing exercises on psychological and psychophysiological responses, and also determined whether these effects differed depending on body composition. The study participants included 33 individuals with a favourable body composition in the fit group and 25 individuals with a less favourable body composition in the unfit group. Before the experiment, the participants completed psychological questionnaires to determine psychological differences at baseline. We recorded an electrocardiogram to analyze heart rate variability (HRV) for five minutes under three conditions: rest, an arithmetic task to induce stress, and a breathing exercise. This was followed by measurements of stress, anxiety, relaxation, and confidence using the visual analogue scale. Baseline analyses revealed that the fit group had lower depression, state and trait anxiety, and stress levels than the unfit group. The HRV indices of the standard deviation of the N-N interval (SDNN) and the root mean square of successive difference (RMSSD) decreased during the arithmetic task with increased stress and heart rate. In contrast, the breathing exercise increased SDNN, RMSSD, total power, and low-frequency power, reduced anxiety and stress, and increased relaxation and confidence. The stress condition and breathing exercise affected the groups differently. The fit group demonstrated a more significant increase in sympathetic activity during stress situations, followed by a greater increase in parasympathetic activity and recovery from stress during the breathing exercise. These findings illustrate that individuals with a more favourable body composition may have greater autonomic nervous system adaptability.

Mild daily stress, in interaction with NR3C1 DNA methylation levels, is linked to alterations in the HPA axis and ANS response to acute stress in early adolescents

BackgroundDaily Hassles (DH) or daily stress - is a mild type of stressor with unique contributions to psychological distress. Yet, most prior studies that investigate the effects of stressful life experiences focus on childhood trauma or on early life stress and little is known about the effects of DH on epigenetic changes in stress system related genes and on the physiological response to social stressors. MethodsIn the present study, conducted among 101 early adolescents (mean age = 11.61; SD = 0.64), we investigated whether Autonomic Nervous System (ANS) (namely heart rate and heart rate variability) and Hypothalamic-Pituitary-Adrenal (HPA) axis functioning (measured as cortisol stress reactivity and recovery) are associated with DNA methylation (DNAm) in the glucocorticoid receptor gene (NR3C1), the level of DH and their interaction. To assess the stress system functioning the TSST protocol was used. ResultsOur findings show that higher NR3C1 DNAm in interaction with higher levels of daily hassles, is associated with blunted HPA axis reactivity to psychosocial stress. In addition, higher levels of DH are associated with extended HPA axis stress recovery. In addition, participants with higher NR3C1 DNAm had lower ANS adaptability to stress, specifically lower parasympathetic withdrawal; for heart rate variability this effect was strongest for participants with higher level of DH. ConclusionsThe observation that interaction effects between NR3C1 DNAm levels and daily stress on the functioning of the stress-systems, are already detectable in young adolescents, highlights the importance of early interventions, not only in the case of trauma, but also daily stress. This might help to prevent stress-induced mental and physical disorders later in life.

Heart rate variability modifications in response to different types of exercise training in athletes.

Spectral analysis of heart rate variability (HRV) is a long-standing technique to indirectly assess neural cardiac regulation. This article specifically addressed how spectral analysis of HRV could help to understand neural cardiovascular adaptations to long-term exercise training; and inform us on training status in athletes. We reviewed literature searching for articles investigating resting cardiovascular adaptations to long-term exercise training through spectral analysis of HRV in athletes, from amateur to world class categories, practicing different sport disciplines, and focusing, in particular, on a series of work performed over time in our laboratory, which may highlight how different types of exercise training differently affect neural cardiac regulation. Spectral analysis of HRV has been shown its capability of detecting different adaptational changes in cardiac autonomic nervous system (ANS) regulation attending physical training in athletes of different sport disciplines. Studies showed that spectral analysis of HRV provide results that are sport-dependent and differ at individual level. ANS adaptations to exercise training are presented and discussed. Reported studies indicate that spectral analysis of HRV is an effective tool to monitor and optimize the training process and to predict athletic achievements in competitions. Cardiac ANS adaptations are strongly dependant on the type of training being performed. The individual nature of cardiac ANS adaptations should be considered to properly interpret the observed findings.

The role of stress reactivity and pre-injury psychosocial vulnerability to psychological and physical health immediately after traumatic injury

BackgroundTraumatic injuries can have long-term negative impacts on health, especially psychological health. A biopsychosocial approach is recommended to identify those likely to experience psychosocial stress, however large individual differences exist in stress reactivity and post-injury health that remain unexplored. Therefore, we investigated autonomic nervous system (ANS) stress responses and pre-existing psychosocial vulnerability as contributors to health in individuals who sustained a traffic-related injury. Methods120 adults with traffic-related injury and 112 non-injury controls underwent an integrative ANS (cardiac and skin conductance) assessment and a health-related assessment at 3–6 weeks post-injury. Propensity score matching based on six pre-injury psychosocial vulnerability factors (age, sex, education, prior mental/physical health, socioeconomic status) guided the definition of high vulnerability (HV) and low vulnerability (LV) injury subgroups, with the LV subgroup having similar propensity scores to non-injury controls. A three-group comparative analysis of ANS responsivity (baseline, reactivity, recovery/rebound) and post-injury health was performed. ResultsThe HV subgroup exhibited the most negative immediate post-injury mental health profile and less adaptive ANS response patterns, indicating greater stress vulnerability/reactivity. Significant differences were found for psychological health (elevated psychological distress and catastrophizing), but not physical health (injury factors, pain, fatigue, physical wellbeing). HV participants showed sympathetic predominance at resting baseline (lower parasympathetic activity and/or elevated heart rate) compared to the LV and control groups, as well as smaller parasympathetic decrease during a cognitive task compared to controls. Despite preserved capacity for restoring initial homeostasis in both injury subgroups during recovery, there was some indication of blunted post-task sympathetic deactivation (larger sympathetic decrease) and reduced overall ANS adaptability (reduction in total power of heart rate variability spectrum), suggesting relative reduced capacity to face stressors compared to controls. ConclusionsFindings suggest that baseline resting ANS regulation, particularly parasympathetic activity, and pre-injury psychosocial factors are key contributors to individual psycho-biological responses following traumatic injury, and are therefore potential stress vulnerability markers. Post-stress recovery patterns may represent a novel physiological signature for a “biological intrinsic” vulnerability early after the injury. These findings provide direction for improved early identification and management of injured individuals, including innovative preventive interventions that target ANS regulation.

Autonomic nervous system responses to strength training in top-level weight lifters.

In athletes, spectral analysis of HR variability (HRV) has been shown capable to detect the adaptational changes in sympatho‐vagal control attending physical training. So far, studies investigated autonomic nervous system (ANS) changes occurring with endurance training, whereas adaptations to markedly different exercise modes, for example, strength training, have never been investigated. We assessed the changes in cardiac ANS parameters during long‐term training in weight lifters of the Italian team preparing for the European Championship, where athletes competed for obtaining the pass for Olympic Games. We investigated nine athletes. Subject trained 3 sessions/day, 6 days a week. The intensity of strength exercises varied from 70% to 95% 1 RM. Training load (TL) was calculated as: volume (min) × intensity (%1RM).All ANS parameters were significantly and highly correlated on an individual basis to the dose of exercise with a second‐order regression model (r 2 ranged from 0.96 to 0.99; P < 0.001). The low‐frequency (LF) component of HRV and LF/HF ratio showed an initial increase with the progression of TL and then a decrease, resembling a bell‐shaped curve with a minimum at the highest TL. The high‐frequency (HF) component of HRV and R‐R interval showed a reciprocal pattern, with an initial decrease with progression of TL followed by an increase, resembling an U‐shaped curve with a maximum at the highest TL. These adaptations were at the opposite to those previously reported in endurance athletes. These results suggest that in Olympic weight lifters, ANS adaptations to training are dose‐related on individual basis and that ANS adaptations are mainly sport‐specific.

On the Standardization of Approximate Entropy: Multidimensional Approximate Entropy Index Evaluated on Short‐Term HRV Time Series

Background. Nonlinear heart rate variability (HRV) indices have extended the description of autonomic nervous system (ANS) regulation of the heart. One of those indices is approximate entropy, ApEn, which has become a commonly used measure of the irregularity of a time series. To calculate ApEn, a priori definition of parameters like the threshold on similarity and the embedding dimension is required, which has been shown to be critical for interpretation of the results. Thus, searching for a parameter‐free ApEn‐based index could be advantageous for standardizing the use and interpretation of this widely applied entropy measurement. Methods. A novel entropy index called multidimensional approximate entropy, MApEnmax, is proposed based on summing the contribution of maximum approximate entropies over a wide range of embedding dimensions while selecting the similarity threshold leading to maximum ApEn value in each dimension. Synthetic RR interval time series with varying levels of stochasticity, generated by both MIX(P) processes and white/pink noise, were used to validate the properties of the proposed index. Aging and congestive heart failure (CHF) were characterized from RR interval time series of available databases. Results. In synthetic time series, MApEnmax values were proportional to the level of randomness; i.e., MApEnmax increased for higher values of P in generated MIX(P) processes and was larger for white than for pink noise. This result was a consequence of all maximum approximate entropy values being increased for higher levels of randomness in all considered embedding dimensions. This is in contrast to the results obtained for approximate entropies computed with a fixed similarity threshold, which presented inconsistent results for different embedding dimensions. Evaluation of the proposed index on available databases revealed that aging was associated with a notable reduction in MApEnmax values. On the other hand, MApEnmax evaluated during the night period was considerably larger in CHF patients than in healthy subjects. Conclusion. A novel parameter‐free multidimensional approximate entropy index, MApEnmax, is proposed and tested over synthetic data to confirm its capacity to represent a range of randomness levels in HRV time series. MApEnmax values are reduced in elderly patients, which may correspond to the reported loss of ANS adaptability in this population segment. Increased MApEnmax values measured in CHF patients versus healthy subjects during the night period point to greater irregularity of heart rate dynamics caused by the disease.

Increased Telomere Length and Improvements in Dysautonomia, Quality of Life, and Neck and Back Pain Following Correction of Sagittal Cervical Alignment Using Chiropractic BioPhysics® Technique: a Case Study

Objective: To present a prospective case study on the increase of telomere length, improvement in nocturnal polyuria, neck and mid-back pain, autonomic nervous system adaptability, and health-related quality of life following correction of the sagittal cervico-thoracic spinal alignment and posture using chiropractic biophysics® (CBP®) technique. Clinical features: A 35-year-old white female elementary school teacher presented with chronic neck and midback pain for 5 years following a motor vehicle collision as well as nocturnal polyuria. Examination and radiography revealed forward head posture and loss of cervical lordosis consistent with vertebral subluxation. Patient telomere length was derived from nucleated white blood cells obtained from a blood test. Quality of life measures were determined by the Short-Form 36 health survey and heart rate variability was measured. Intervention and outcome: The patient received CBP® spinal care including Mirror Image® corrective spinal exercises, adjustments, and traction. Full spine and drop table adjustments were administered. After 36 visits, she reported improvement in her nocturnal polyuria, neck and mid-back pain, and quality of life. Cervical x-rays showed correction of cervical lordosis and forward head posture. A blood test showed significant improvement in patient telomere length and heart rate variability improved from a health risk to within normal limits. Conclusion: Our case suggests that correction of cervical lordosis and forward head postures by CBP® Mirror Image® methods improved the sagittal spinal alignment and posture and was temporally associated with lengthened telomeres, improved nocturnal polyuria, neck and mid-back pain, quality of life, and autonomic nervous system adaptability.

Impact of Stimulant Medication Use on Heart Rate and Systolic Blood Pressure During Submaximal Exercise Treadmill Testing in Adolescents.

Inappropriately decreased heart rate (HR) during peak exercise and delayed heart rate recovery (HRR) has been observed in adult users of stimulant medications who underwent exercise testing, suggesting autonomic adaptation to chronic stimulant exposure. In the general population, this pattern of hemodynamic changes is associated with increased mortality risk. Whether the same pattern of hemodynamic changes might be observed in adolescent stimulant medication users undergoing exercise testing is unknown. Among adolescents (aged 12 to 20 years) that underwent submaximal exercise treadmill testing from 1999 to 2004 in the National Health and Nutrition Examination Survey, propensity score matching of stimulant medication users (n = 89) to matched nonusers (n = 267) was conducted. Testing consisted of a 3-minute warm-up period, two 3-minute exercise stages, and three 1-minute recovery periods, with the goal of reaching 75% of the predicted HR maximum. A linear mixed model analysis was used to evaluate the effect of stimulant exposure on each of the exercise outcomes. Stimulant medication users compared to matched nonusers had a lower peak HR in Stage 2 (154.9 vs. 158.3 beats/minute [bpm], p = 0.055) and lower HR at 1-minute recovery (142.2 vs. 146.4 bpm, p = 0.030). However, submaximal HRR at 1 minute did not differ between stimulant users and matched nonusers (13.0 vs. 12.1 bpm, p = 0.38). Duration of stimulant use was not related to these outcomes. Adolescent stimulant medication users compared to matched nonusers demonstrated a trend toward decreased HR during submaximal exercise, which is potential evidence of chronic adaptation with stimulant exposure. There was no evidence for delayed HRR in this study, and thus, no evidence for decreased parasympathetic activity during initial exercise recovery. Exercise testing outcomes may have utility in future research as a method to assess stimulant-associated autonomic nervous system adaptations.

Abstract 18497: Hospital-based Exercise Training Program Post Coronary Artery Bypass Graft Surgery: Impact of Once and Twice Daily Exercise Program on Cardiac Autonomic Modulation

Introduction: Coronary artery bypass surgery (CABG) patients with postoperative decreased cardiac autonomic modulation (CAM) have a higher mortality rate and although cardiovascular rehabilitation and exercises have substantial benefits in CAM, there is a paucity of information about its effects considering a possible "dose-dependent” autonomic adaptation in a hospital-based exercise program. The aim was to evaluate the impact of once daily versus twice daily dosing regimens of hospital-based exercise training on CAM in post CABG patients. Hypothesis: We hypothesized that there is a dose-dependent exercise adaptation on CAM and greater benefit to twice daily exercise group. Methods: Thirty-seven patients post-CABG were divided into: GEX1 (n = 12) and GEX2 (n = 11), composed of patients who underwent exercises one and two daily sessions, respectively; and of a control group (CG, n = 14) who received usual care (respiratory therapy). GEX patients initiated the exercises on post-operative day 1 (PO1), following a whole progressive program until discharge. CAM was assessed by indices of heart rate variability (HRV) analyzed from heart rate and R-R intervals signals recording at rest during 10 minutes on PO1 (baseline) and discharge time. Results: At the time of discharge after the hospital rehabilitation conclusion, GEX2 presented higher values of rMSSD index, representative of parasympathetic modulation, and also higher values of RRtri, TINN and STDRR indices, representative of overall variability of RRi compared to GC, respectively (rMSSD: 7.5±1.9 vs 5.2±1.8 ms; RRtri: 3.2±1.4 vs 2.0±0.7ms; TINN: 46.0±30.5 vs 25.7±11.0 ms and STDRR: 10.0±6.3 vs 5.4±3.3 ms), while GEX1 presented only higher values of rMSSD compared to CG (rMSSD: 7.8±2.5 vs 5.2±1.8 ms). However, no differences were observed between groups on HRV baseline and at discharge time between groups GEX1 and GEX2. Conclusion: Our results suggested that twice daily hospital-based exercise program stimulated more favorably the cardiac autonomic nervous system adaptations in patients post-CABG. Although a daily exercise session promotes beneficial adaptations, two sessions should be encouraged to additional benefits in the cardiac autonomic modulation FAPESP 2015/2015 / 16730-3.

극초단파치료기를 사용하는 물리치료실의 환경이 물리치료사의 인체자율신경계에 미치는 영향

PURPOSE: The purpose of this study is to investigate the effect of the physical therapy treatment room environment using microwave diathermy on the autonomic nervous system of human body. METHODS: Participants were 24 healthy adults. Standard deviation of all normal R-R intervals(SDNN), root mean square of successive differences(RMSSD), low frequency(LF), high frequency(HF), LF/HF ratio were compared in microwave irradiation and non-irradiation group. Data were analyzed in Wilcoxon's signed-ranks test and Mann-Whitney U test. RESULTS: Standard deviation of all normal R-R intervals (SDNN), root mean square of successive differences (RMSSD), low frequency(LF), high frequency(HF), LF/HF ratio were not significantly different in microwave irradiation group. Standard deviation of all normal R-R intervals(SDNN), root mean square of successive differences (RMSSD), low frequency(LF), high frequency(HF), LF/HF ratio were not significantly different in microwave non-irradiation group. Standard deviation of all normal R-R intervals(SDNN), root mean square of successive differences (RMSSD), low frequency(LF), high frequency(HF), LF/HF ratio were not significantly different between two groups. CONCLUSION: There was no significant change in the sympathetic nervous system and parasympathetic nervous system regardless of the presence of microwave irradiation. There was no significant change in the autonomic nervous system adaptability regardless of the presence of microwave irradiation.According to this study, microwave diathermy does not have significant effect on the autonomic nervous system.Future study is necessary to investigate the long term effect of the physical therapy treatment room environment using microwave diathermy on the autonomic nervous system of the human body.

Validation of rate of perceived exertion-based exercise training in patients with heart failure: Insights from autonomic nervous system adaptations

BackgroundExercise prescription in cardiac patients is based on heart rate (HR) response to exercise. How to prescribe long-term exercise training outside medically-supervised settings also considering changes in individual physical capacity over time is unknown. In this study we hypothesized that in patients with chronic heart failure (CHF) the session-rate of perceived exertion (RPE), a subjective-based training methodology, provides autonomic and functional capacity changes superimposable to those observed with HR-based Training Impulses (TRIMPi) method. MethodsTwenty patients with stable CHF were randomized to either aerobic continuous training (ACT) or aerobic interval training (AIT) for 12weeks. For each TRIMPi-guided exercise session, the session-RPE was recorded. By this method, internal training load (TL) is quantified by multiplying the RPE of the whole training session, using the Borg CR10-scale, by its duration. Heart rate variability (HRV), and baroreflex sensitivity (BRS) were assessed at baseline and at 3weeks intervals. ResultsSignificant correlations were found between TRIMPi and individual session-RPE, for both ACT and AIT (r=0.63 to 0.81), (P<0.05). The same occurred when ACT and AIT groups were pooled together (r=0.72; P<0.01). R–R interval, HRV and BRS were significantly and very highly correlated with weekly RPE-session (r2 ranged from 0.77 to 0.97; P<0.001). A significant relationship between session-RPE and performance at the 6MWT was also found. ConclusionsSession-RPE is an easy-to-use, inexpensive and valid method for exercise prescription and health maintenance, consistent with objective physiological indices of training, that could be used for long-term physical activity in patients with CHF.

Decreased heart rate variability during emotion regulation in subjects at risk for psychopathology

Dysfunctions in the regulation of emotional responses are related to poor psychological well-being and increased impact of cardiovascular disease. It has been suggested that the relationship between negative affect and higher morbidity could be mediated by a dysregulation of the autonomic nervous system (ANS), for example, of heart rate variability (HRV). Neuroticism is a personality trait associated with a maladaptive emotion regulation and also with alterations in ANS function. However, it is unknown whether subjects with high neuroticism present with specific biases in emotion regulation associated with reduced HRV. In total, 33 healthy subjects (n=13, highly neurotic) performed an emotion regulation task, during which they were instructed to either passively view negative pictures or attempt to down-regulate the affect elicited by the images. During the task an electrocardiogram was recorded and HRV was measured by calculation of the high frequency spectrum (HF-HRV). A significant interaction between task condition and personality group was observed on HF-HRV measures (F 1,31=6.569, p=0.016). This was driven by subjects with low neuroticism presenting higher HF-HRV during down-regulation compared to passive exposure to negative stimuli, while subjects with high neuroticism reported an opposite tendency. Our results show reduced HF-HRV during cognitive reappraisal of negative stimuli in high neuroticism and indicate a specific link between loss of flexibility in the parasympathetic cardiovascular tone and emotion regulation, consistent with previous work. Such findings support the importance of exploring the combination of ANS adaptability and emotional dysregulation in neuroticism as different facets of a common psychosomatic vulnerability factor.

Dose-response relationship of autonomic nervous system responses to individualized training impulse in marathon runners

In athletes, exercise training induces autonomic nervous system (ANS) adaptations that could be used to monitor training status. However, the relationship between training and ANS in athletes has been investigated without regard for individual training loads. We tested the hypothesis that in long-distance athletes, changes in ANS parameters are dose-response related to individual volume/intensity training load and could predict athletic performance. A spectral analysis of heart rate (HR), systolic arterial pressure variability, and baroreflex sensitivity by the sequences technique was investigated in eight recreational athletes during a 6-mo training period culminating with a marathon. Individualized training load responses were monitored by a modified training impulse (TRIMP(i)) method, which was determined in each athlete using the individual HR and lactate profiling determined during a treadmill test. Monthly TRIMP(i) steadily increased during the training period. All the ANS parameters were significantly and very highly correlated to the dose of exercise with a second-order regression model (r(2) ranged from 0.90 to 0.99; P < 0.001). Variance, high-frequency oscillations of HR variability (HRV), and baroreflex sensitivity resembled a bell-shaped curve with a minimum at the highest TRIMP(i), whereas low-frequency oscillations of HR and systolic arterial pressure variability and the low frequency (LF)-to-high frequency ratio resembled an U-shaped curve with a maximum at the highest TRIMP(i). The LF component of HRV assessed at the last recording session was significantly and inversely correlated to the time needed to complete the nearing marathon. These results suggest that in recreational athletes, ANS adaptations to exercise training are dose related on an individual basis, showing a progressive shift toward a sympathetic predominance, and that LF oscillations in HRV at peak training load could predict athletic achievement in this athlete population.

Biological Mechanisms for the Cardioprotective Effects of Aerobic Exercise

Epidemiologic studies have consistently identified a strong inverse association between coronary heart disease (CHD) and regular, predominantly moderate-intensity physical activity and cardiorespiratory fitness. Supporting evidence of causative relationships has been provided by aerobic exercise training studies in both animals and humans. This research demonstrated multiple plausible cardioprotective biological mechanisms. These include direct antiatherosclerotic effects by improving artery endothelial function and reducing inflammation and indirectly via modification of other risk factor components of the metabolic syndrome, by reducing risk of a coronary thrombotic occlusion (antithrombotic effects), by decreasing myocardial oxygen demands and increasing its vascular supply (anti-ischemic effects), and by improving cardiomyocyte electrical stability and autonomic nervous system adaptations (antiarrhythmic effects). Although much additional research is needed to better define and establish optimal dose-response relationships, clearly these pleotropic effects strongly suggest that aerobic exercise can attenuate the risk of CHD at all stages of the underlying atherothrombotic process.

The sympathetic skin response habituation in sedentary subjects and sportsmen

The aim of the present study was to investigate the habituation rates of the sympathetic skin response (SSR) in sedentary subjects and trained sportsmen. A total of 52 voluntary male students (30 sedentary subjects and 22 trained sportsmen) participated in the experiment. SSR was recorded with the contralateral electrical stimulation of the ulnar nerve (of the upper extremities). In order to initiate the SSRs, 16 square-wave consecutive electrical shock stimuli were presented to each subject over the left ulnar nerve. In 52 subjects, 16 stimuli were applied at random time intervals (20-50 s). In sedentary subjects, the mean amplitude of the SSRs decreased from 4.83 +/- 0.36 mV at the first stimulus, to 0.80 +/- 0.12 mV at the 16th stimulus. In trained sportsmen, the mean amplitude of the SSRs decreased from 3.95 +/- 0.51 mV at the first stimulus, to 0.80 +/- 0.17 mV at the 16th stimulus. In the sedentary subjects, at the S1-S9 stimuli, the mean amplitudes of SSRs were higher than those of trained sportsmen. Depending upon these findings we can say that the trained sportsmen showed a more rapid habituation than sedentary subjects. In these processes, changes of amplitude and latency values reflect changes in amount of neuronal activation. Amplitude reflects the amount of neuronal activation, which is concerned with number of neuronal populations. Neuroplasticity, known as the habituation of the brain, is the adaptation of autonomic nervous system, which can be reflected by SSRs.

The Time Evolution of Frequency Components of Heart Rate Variability Using Wavelets

The ruling action of the autonomic nervous system (ANS) controls is not static. Due to this dynamic action, the physiological parameters do not remain in the same stationary status but are modified by the evolving condition of the cardiovascular regulatory systems. Applications of conventional spectral approaches, such as Fourier transform (FT) or autoregressive (AR) model, to HRV analysis, thus, always remain problematic since they are applied based on the assumption of stationarity. Also capturing hidden dynamics in both healthy and chronically ill subjects could yield important insights into understanding physiological mechanisms. Heart rate variability analysis is complicated by the fact that these signals are typically both highly irregular and nonstationary i.e., their statistical character changes slowly or intermittently as a result of variations in background influences. FT and AR methods have served a critical role in the understanding of basal autonomic cardiac control. However, these algorithms have limitations in the study of heart rate for nonlinear variations and transient alterations. Here, the wavelet transform based heart rate variability analysis with emphasis on the time evolution of the different frequency components of HRV signal and sympathovagal balance has been shown to monitor ANS adaptations induced by physiological interventions like head up-tilt, forced breathing in the experimental protocol. The procedure was applied to quantify the time evolution of HRV parameters under steady state and to identify subperiods of steady-state during a sequence of physical activities. Results showed the capability of proposed techniques to provide additional practical diagnostic and prognostic insight by mapping autonomic abnormalities.

Autonomic nervous system adaptations to short-term exercise training

Autonomic nervous system adaptations to short-term exercise training

Autonomic Nervous System Adaptations to Short-term Exercise Training

Signs of sympathetic hyperactivity and low parasympathetic activity have been found during the acute and recovery phases of myocardial infarction and have been associated with an increased risk of cardiac mortality. Beneficial effects of physical training have been recently reported in post-myocardial infarction patients. We tested the hypothesis that physical training would be effective in improving the autonomic balance by studying 22 patients with a first and recent myocardial infarction who were randomly assigned to enter or not enter a 4-week in-hospital physical training program. Spectral indices of heart rate variability were analyzed at rest and during 70 degrees head-up tilt before and after the index training, not training period. As expected, physical training induced a significant increase in exercise duration (13.7 +/- 0.8 vs 17.1 +/- 0.1 min, p less than 0.001) and in the anaerobic threshold (9.5 +/- 0.7 vs 12.0 +/- 1.0 min, p less than 0.02) in trained patients, while no changes were observed in the untrained group. At entry, in both groups, spectral profile of heart rate variability was characterized by a predominant LF component and a smaller HF component with no further modification after head-up tilt. After 4 weeks, in resting conditions, no significant changes in spectral components were observed in both trained and untrained patients. After physical training, head-up tilt produced significant modifications in spectral profile with an increase in the LF component (84 +/- 3 vs 69 +/- 5 nu, p less than 0.01) and a decrease in the HF component (7 +/- 1 vs 19 +/- 4 nu, p less than 0.05) in trained patients, while no changes were observed in the untrained patients. Our data suggest that in postmyocardial infarction patients, 4 weeks of physical training may induce an improvement in the autonomic balance with a restoration toward normal in the reflex activity of the system.

The effects of exercise on plasma insulin.

The decrease of plasma insulin levels after physical training is explained mainly by a decreased insulin secretion, but also to a significant degree by an increased peripheral insulin metabolic clearance rate in several peripheral tissues and increased insulin uptake in the liver. The peripheral tissues demonstrate an increased insulin sensitivity, but this seems to be due to factors after the insulin receptor level. An increased turnover of insulin at the receptor level might be postulated. The explanation for the decrease of insulin secretion has been studied extensively. A decreased cortisol secretion might be a primary factor in physical training, followed by lower insulin levels. Autonomic nervous system adaptations could also be involved in the form of an increased alpha-adrenergic activity. Another alternative is that the effect is mediated via an influence of physical training on a gut "incretin" factor, facilitating insulin secretion, Finally, it might be considered that the increased insulin sensitivity of muscle following physical training is regulating insulin secretion via feedback mechanisms to the beta cell. Recent demonstrations of inhibited glucose uptake in the liver after exercise facilitates an explanation along these lines.