Autonomic System Regulation Research Articles

Can HRV Biofeedback Training Improve the Mental Resilience of Icelandic Police Officers?

High heart rate variability (HRV) is increasingly recognized as an indicator of a healthy regulatory system, reflecting the dynamic balance between sympathetic (SNS) and parasympathetic (PSNS) nervous system activity. According to the neurovisceral integration model, this balance is managed by the central autonomic network (CAN), comprised of specific brain regions involved in emotional, attentional, and autonomic regulation. HRV thus reflects the performance of the cognitive, affective, and autonomic regulation system. Numerous studies support the relationship between HRV and the CAN, including research on HRV biofeedback training (HRVBF). Studies on the effectiveness of HRVBF for professions such as police officers have shown improvements in self-regulation, decision-making, and performance. However, few studies have specifically explored HRVBF's influence on HRV metrics in police officers, highlighting a need for further research. This study addresses this gap by randomly assigning 27 Icelandic police officers to intervention or wait-list control groups. The intervention group underwent a five-week HRVBF program, including group and individual training sessions. Results showed significant increases in HRV metrics for the intervention group, indicating improved autonomic function and stress resilience. Mental resilience increased significantly as measured by subjective measures of attentional control, mindful awareness, and reduced fatigue. These findings support the efficacy of HRVBF in enhancing HRV and mental resilience for police officers, suggesting its applicability and potential for integration into existing training programs.

Особливості психічного стану у кваліфікованих борців

Purpose: research of psychical state in qualified wrestlers in stage of special basic fitness. Material and methods. The study involved 31 skilled Greco-Roman wrestlers aged 14-16 years, pupils of the wrestling club in Kremenchuk. To assess the mental state of skilled wrestlers, the Luscher color test was used. According to the results of the study, the following indicators were obtained: performance, fatigue, anxiety, deviation from the autogenous norm, eccentricity, concentricity, vegetative coefficient, heteronomy and autonomy. Heart rate variability was studied as an indicator of mental stress. The cardiac monitor «Fazagraf» was used. Based on the results of the study, we obtained statistical processing indicators and spectral characteristics of cardiac intervals. Non-parametric statistics with the determination of the median, lower and upper quartiles were used to assess the differences between the studied parameters. Results: in wrestlers with high tension of the autonomic regulation system, a deterministic functional system aimed at ensuring the mental state is revealed. At the same time, an increase in the tension of autonomic regulation is accompanied by mental fatigue, anxiety, passivity and the presence of mental stress. Prevention of mental stress in skilled wrestlers may be associated with the activation of the athlete to external environmental stimuli, optimism and a mood for positive behavior. The relationship between the indicators of mental state and the parameters of mental functions in skilled wrestlers was revealed. The moderate tension of the heart rate regulation system in skilled wrestlers is accompanied by an increase in mental performance and a decrease in anxiety. In turn, the increase in the tension of autonomous regulation is reflected in the presence of internal psychological discomfort and independence in the formation of decision-making. However, there is an increase in anxiety and a decrease in mental performance. Conclusions. The relationship between indicators of mental state and parameters of psychical functions in qualified wrestlers was revealed. Moderate tension of the heart rhythm regulation system in qualified wrestlers is accompanied by an increase in mental capacity and a decrease in anxiety. The increase in the tension of autonomous regulation in qualified wrestlers is reflected in the presence of internal psychological discomfort and independence in decision-making. Keywords: mental state, qualified wrestlers, heart rate regulation, indicators, analysis.

Heart Rate Variability as a Translational Dynamic Biomarker of Altered Autonomic Function in Health and Psychiatric Disease.

The autonomic nervous system (ANS) is responsible for the precise regulation of tissue functions and organs and, thus, is crucial for optimal stress reactivity, adaptive responses and health in basic and challenged states (survival). The fine-tuning of central ANS activity relies on the internal central autonomic regulation system of the central autonomic network (CAN), while the peripheral activity relies mainly on the two main and interdependent peripheral ANS tracts, the sympathetic nervous system (SNS) and the parasympathetic nervous system (PNS). In disease, autonomic imbalance is associated with decreased dynamic adaptability and increased morbidity and mortality. Acute or prolonged autonomic dysregulation, as observed in stress-related disorders, affects CAN core centers, thereby altering downstream peripheral ANS function. One of the best established and most widely used non-invasive methods for the quantitative assessment of ANS activity is the computerized analysis of heart rate variability (HRV). HRV, which is determined by different methods from those used to determine the fluctuation of instantaneous heart rate (HR), has been used in many studies as a powerful index of autonomic (re)activity and an indicator of cardiac risk and ageing. Psychiatric patients regularly show altered autonomic function with increased HR, reduced HRV and blunted diurnal/circadian changes compared to the healthy state. The aim of this article is to provide basic knowledge on ANS function and (re)activity assessment and, thus, to support a much broader use of HRV as a valid, transdiagnostic and fully translational dynamic biomarker of stress system sensitivity and vulnerability to stress-related disorders in neuroscience research and clinical psychiatric practice. In particular, we review the functional levels of central and peripheral ANS control, the main neurobiophysiologic theoretical models (e.g., polyvagal theory, neurovisceral integration model), the precise autonomic influence on cardiac function and the definition and main aspects of HRV and its different measures (i.e., time, frequency and nonlinear domains). We also provide recommendations for the proper use of electrocardiogram recordings for HRV assessment in clinical and research settings and highlight pathophysiological, clinical and research implications for a better functional understanding of the neural and molecular mechanisms underlying healthy and malfunctioning brain-heart interactions in individual stress reactivity and psychiatric disorders.

Maturation of the cardiac autonomic regulation system, as function of gestational age in a cohort of low risk preterm infants born between 28 and 32weeks of gestation.

The maturation of the sympathetic nervous system (SNS) occurs steadily throughout gestation while the myelinated vagus has accelerated maturation periods, between 25 and 32weeks of gestation and a further increase around 37-38weeks of gestation. The aim was to quantify the cardiac autonomic regulation maturation, as a function of gestational age (GA) in a cohort of low risk preterm infants born between 28 and 32weeks of gestation by assessing heart rate variability (HRV) at week 32, and at week 35 postmenstrual age (PMA). Forty preterm infants were recruited, 24h recordings of breathing rate and RR intervals were obtained at week 32 and week 35 PMA. A significant difference was noted between preterm infants born before 32weeks GA and preterm infants born at week 32; the latter present higher HRV values throughout the follow-up period. No significant change over time was noted for the parasympathetic HRV measures while a significant increase was found in the sympathetic system. Moreover, a significant interaction effect of time and system was found, the increase in values of the sympathetic system over time was significantly larger than the change noted in the vagal HRV measures. Given the beneficial influence of vagal tone on health and developmental outcomes in preterm infants, the findings of the current study highlight the need for further studies on the impact of specifics gestational age on vagal development and later assessing interventions associate with its continue development and maturation at these specific periods.

Microcirculatory and vegetative changes in children with different phenotypes of allergic rhinitis

Microcirculation mechanisms and vegetative-vascular mechanisms have an important pathogenetic significance in the development of allergic inflammation.The purpose of our study was to assess capillaroscopy and heart rate variability in children with allergic rhinitis (AR), depending on the presence of comorbid pathology. All children were divided into three groups: the main group – 29 children with AR in combination with herpes infection or the presence of pathogenic microflora in nasopharyngeal swabs in the amount of more than 106, the comparison group – 23 children with AR, the control group – 26 healthy children. All children with AR had pronounced changes in the microvasculature, which varied depending on the presence of concomitant pathology, along with reactive changes in autonomic regulatory systems towards an increase in the dominance of central regulation mechanisms and the predominance of parasympathetic tone. Children with AR and concomitant pathology did not have a pronounced parasympathetic effect, in contrast to children with AR and children without concomitant pathology, which should be taken into account when drawing up a plan for personalized treatment and rehabilitation.

The state of vegetative regulatory systems of pupils with different academic performance

The transition to primary school requires pupils to adapt to new conditions of the educational environment, accompanied by the use of physiological reserves of the body. School stress can hinder the academic success of children and adolescents, creative solutions to complex and new problems, which, in turn, can lead to underestimation of abilities and underestimation of pupils self-esteem. Chronic exposure to academic stress can lead to school burnout and the formation of psychosomatic disorders. The aim of the study was to compare the functional state of autonomic regulatory systems among pupils with different levels of academic achievement. 60 children (10-13 years old) took part in the longitudinal study. The functional state of the autonomic regulatory systems was determined by analyzing 5-minute recordings of the electrocardiogram in a state of quiet wakefulness with eyes closed in a sitting position. Pupils were divided into 3 groups depending on the level of their academic performance, which was determined by the average score of 8 basic subjects. Statistical data processing was performed using the Mann-Whitney, Kraskell-Wallis, Dunnett, Fisher’s φ-test. Significant differences in heart rate variability (HRV) parameters depending on the level of academic achievement were found only in the 5th and 6th years of study, which reflected the different physiological cost of adaptation to primary school. The vegetative profile of pupils with academic performance lower than the average in the 5th year of study indicated overstrain of regulatory systems and fatigue. Among pupils with academic performance higher than the average in the 6th year of study 2.4 times more often than pupils with average academic performance, the optimal state of autonomic regulatory systems was observed (respectively, 46.2% and 19.1%, p≤0,05), and in the 7th year of study – 2.5 times compared to pupils with academic performance below average (respectively, 46.2% and 18.2%, p≤0.05), which may indicate a higher physiological price for adaptation to primary school pupils with academic performance below average. Fatigue and overexertion of the mechanisms of autonomic regulation are characteristic of pupils with academic performance below average, while pupils with academic performance above average had a high level of stress adaptive-compensatory mechanisms in the 6th year of study. The category of pupils with a level of academic performance below average should be assigned to the risk group in terms of the development of autonomic dysfunction and psychosomatic diseases.

Prenosological screening of autonomic regulatory systems tension in secondary school students

Adolescence is characterized by increased reactivity to stress factors, among the sources of which the educational environment plays a significant role. The content of education and educational process organization, as well as interpersonal relationships, is the predominant stress factors of the educational environment. In the context of education reform, new pedagogical projects are being introduced, in particular, on the basis of meritocratic education, providing for the intensification of the educational process. It may affect the state of the autonomic regulatory systems of students. The purpose of the research is to study the activity level of autonomic regulatory systems among students of secondary school, who are studying in meritocratic and traditional gymnasium education systems. The study involved 60 students: 42 studied in meritocratic system (19 in SG-1, 23 in SG-2), and 18 in traditional system (SG-3). Heart rate variability (HRV) was used as a physiological marker of stress. ECG was recorded during 5 minutes in a darkened room in a rest state with closed eyes in a sitting position at the 5th, 6th and 7th grades. Intergroup comparisons of HRV parameters were carried out according to the Mann-Whitney, Kruskell-Wallis, Dunnett criteria, and the φ-criterion of the angular Fisher transformation. Differences were considered significant at р≤0.05. In the 6th grade, there was a tendency (0.05<р≤0.07) to lower values of Mean, SDNN, TR, ΔX, RMSSD, pNN50 among students in meritocratic system compared to the traditional one. However, this trend reached the level of statistical significance in the students of SG-1 compared to the control (SG-3). In meritocratic education different student groups differed in the level of school stress in 6th and 7th grades. Students in SG-1, compared to SG-2, characterized by lower values % HF, HFn, pNN50 against the background of higher values of % LF, LFn, LF/HF, IC, CC1, CC0. Thus, a higher level of school-based stress in conditions of meritocratic education is determined not so much by the intensification of the educational process as by social factors of the educational environment and/or individual typological traits of students.

The Role of Negative Emotions in the Aetiology of Non-Impact Sports Injuries: Interactions of the Stress Response and Motor Control Systems

The Role of Negative Emotions in the Aetiology of Non-Impact Sports Injuries: Interactions of the Stress Response and Motor Control Systems

Intrinsic cardiovascular autonomic regulatory system of astronauts exposed long-term to microgravity in space: observational study

The fractal scaling of the long-term heart rate variability (HRV) reflects the ‘intrinsic’ autonomic regulatory system. Herein, we examine how microgravity on the ISS affected the power-law scaling β (beta) of astronauts during a long-duration (about 6 months) spaceflight. Ambulatory electrocardiographic (ECG) monitoring was performed on seven healthy astronauts (5 men, 52.0±4.2 years of age) five times: before launch, 24±5 (F01) and 73±5 (F02) days after launch, 15±5 days before return (F03), and after return to Earth. The power-law scaling β was calculated as the slope of the regression line of the power density of the MEM spectrum versus frequency plotted on a log10–log10 scale in the range of 0.0001–0.01 Hz (corresponding to periods of 2.8 h to 1.6 min). β was less negative in space (−0.949±0.061) than on Earth (−1.163±0.075; P<0.025). The difference was more pronounced during the awake than during the rest/sleep span. The circadian amplitude and acrophase (phase of maximum) of β did not differ in space as compared with Earth. An effect of microgravity was detected within 1 month (F01) in space and continued throughout the spaceflight. The intrinsic autonomic regulatory system that protects life under serious environmental conditions on Earth is altered in the microgravity environment, with no change over the 6-month spaceflight. It is thus important to find a way to improve conditions in space and/or in terms of human physiology, not to compromise the intrinsic autonomic regulatory system now that plans are being made to inhabit another planet in the near future.

Muscle Strength, Function and Heart Autonomic Regulation System Recovery at the Sub-Acute Stage Post Stroke

Background: To compare the rate of recovery of motor and functional ability and heart rate variability (HRV) parameters during the inpatient rehabilitation period. Summary: Twenty-three patients post first stroke at the sub-acute phase underwent motor and functional ability and HRV assessments 20 and 50 days after the event. A significant improvement was noted in motor and functional ability performance during the follow-up period, while no such change was noted in the HRV parameters. Key Messages: Patients post first-ever stroke exhibited a significant motor and functional improvement during the sub-acute phase post stroke, while no change was noted in their HRV parameters, which may imply that no significant changes in the sympatho-vagal balance took place during this period.

Daily Dysfunction of Autonomic Regulation Based on Ambulatory Blood Pressure Monitoring in Patients with Neurally Mediated Reflex Syncope

The onset of neurally mediated reflex syncope (NMRS) is associated with dysfunction of the autonomic regulatory system. Yet relatively little is known about the daily conditions of the autonomic regulation system in patients with NMRS. This study elucidated characteristics of daily autonomic function using ambulatory blood pressure monitoring (ABPM) and evaluated the utility of ABPM for NMRS diagnosis. Patients with syncope underwent the head-up tilt test (HUT) (80°, 30 minutes). If no syncope occurred, the HUT was repeated with drug loading. ABPM was performed on a different day. The enrolled subjects were 152 consecutive patients with syncope and 12 controls. Sixty-four patients with other diseases related to autonomic dysfunction were excluded. HUT with/without drug loading was positive in 40 patients (Group P) and negative in 48 patients (Group N). The average systolic blood pressure (SBP) in daytime was lower in Groups P and N than in the control group (Group C) (P < 0.05). The average diastolic blood pressure in daytime was also lower in Group P than in Group C (P < 0.05). The average standard deviation-SBP at nighttime was higher in Groups P and N than in Group C (P < 0.05). In heart rate variability analysis, Group P had higher high frequency normalized unit in daytime than Groups C and N (P < 0.05, P < 0.1). Low frequency/high frequency was lower in Group P than in Group N in both daytime and nighttime (P < 0.1, P < 0.05). This study suggests that patients with NMRS present with daily vagal hyperactivity and sympathetic dysfunction. ABPM may support the diagnosis of NMRS.

Renal Tissue Blood Flow Regulation System in Acute Blood Pressure Modulation is Maintained in Elderly Wistar‐Kyoto Rats

Back ground: Systemic arterial pressure is maintained by sympathetic vasomotor tone regulated by autonomic nerve system. Therefore, attenuation of systemic arterial pressure causes reduction of peripheral tissue blood flow. On the other hand, renal tissue has specific blood flow regulatory system to maintain constant renal blood flow involving autonomic regulatory system. However, the effect of aging in maintenance of renal tissue blood flow regulatory system was not fully established. In this study, we used elderly Wistar-Kyoto (WKY) rats as an aged normotensive animal model, examined relation between systemic arterial pressure modulation and renal tissue blood flow regulation. Method: Aged WKY rats (56w-80w) and control group (16-24w) were anesthetized with chloralose, the arterial pressure, pulse rate and renal tissue blood flow were measured simultaneously. Results: Arterial pressure modulation by intravenous injection of phenylephrine, sodium nitroprusside and the activation of sympathetic vasomotor neurons in rostral ventrolateral medulla were not effected to renal tissue blood flow neither aged group nor control, although baro-reflex was attenuated in aged group. Conclusion These results suggest that renal tissue blood flow regulatory system was maintained in aged normotensive animals, though baro-receptor dependent systemic arterial pressure regulatory system was attenuated. Therefore, although in aged animals, renal tissue autonomic blood flow regulatory system still play important role.

Heart rate autonomic regulation system at rest and during paced breathing among patients with CRPS as compared to age-matched healthy controls.

The objective of this study is to assess the autonomic nerve heart rate regulation system at rest and its immediate response to paced breathing among patients with complex regional pain syndrome (CRPS) as compared with age-matched healthy controls. Quasiexperimental. Outpatient clinic. Ten patients with CRPS and 10 age- and sex-matched controls. Participants underwent Holter ECG (NorthEast Monitoring, Inc., Maynard, MA, USA) recording during rest and biofeedback-paced breathing session. Heart rate variability (HRV), time, and frequency measures were assessed. HRV and time domain values were significantly lower at rest among patients with CRPS as compared with controls. A significant association was noted between pain rank and HRV frequency measures at rest and during paced breathing; although both groups reduced breathing rate significantly during paced breathing, HRV time domain parameters increased only among the control group. The increased heart rate and decreased HRV at rest in patients with CRPS suggest a general autonomic imbalance. The inability of the patients to increase HRV time domain values during paced breathing may suggest that these patients have sustained stress response with minimal changeability in response to slow-paced breathing stimuli.

FEATURES OF IMMUNE REACTIONS IN STRESS CONDITIONS ASSOCIATED ASSOCIATED WITH EXAMS

Abstract. It has been widely accepted that routine psychophysiological stressors may influence immune functioning via their close interactions between nervous, autonomic, endocrine and immune regulatory systems. The aim of this study was to evaluate immune reactions to acute psychophysiological stress in 203 medical students before and after academic exams. The results showed significant decrease of absolute and relative contents CD3+ T cells, natural killer (NK) cell subpopulations and T-NK cells (CD3-CD16+CD56+ and CD3+CD16+CD56+), as well as declined NK cell activity were revealed immediately after exams, as compared to initial values for these indices. Moreover, a significant decrease in CD19+ B cells, CD4+ T-helpers and CD8+ T-cytotoxic lymphocyte counts was found after exams, in comparison with parameters assessed under stress-free conditions, but no differences were observed, when compared with pre-examination values. Serum concentrations of IgA, IgM, IgG were within normal physiological limits. Changes in immunological parameters during acute examination-associated stress depend on characteristics of autonomous and hormonal reactions in humans, and, under particular extreme conditions, such psycho-emotional stress may cause general disturbances of immune reactions. We conclude that acute psycho-physiological stress during the exams causes significant changes in some lymphocyte subpopulations, in particular, natural killers.

Heart rate and heart rate variability parameters at rest, during activity and passive standing among children with cerebral palsy GMFCS IV–V

Aims: To describe and compare heart rate (HR) and heart rate variability (HRV) at rest, during active movements and passive standing among children with cerebral palsy (CP), with Gross Motor Function Classification System (GMFCS) levels IV and V, and to describe the association between daily physical activity and HRV. Methods: Thirty children with CP were included aged 6–12 years. HR and HRV parameters were recorded during rest, during Gross Motor Functional Measure (GMFM) assessment, during two minutes of repeated performance of the highest activity achieved in the GMFM, and during passive standing. Parents were asked to inform about any habitual physical activities their child participates outside school in the previous 4 months. Results: Children with GMFCS IV increased their HR and reduced HRV values during the GMFM assessment, the repeated task and during passive standing, while no such effect was noted among children with GMFCS V. Children participated in a limited range of activities with a median frequency of three times a week (range 1–6 times), with insignificant differences between GMFCS levels. No significant differences were noted in HR or HRV parameters based on activity level. Conclusions: Only children with GMFCS IV responded to passive and active manipulation of the cardiac autonomic system. This may imply that the HR autonomic regulation system has an opportunity to be influenced by training in this group of children.

Brain nitric oxide production by a proline-rich decapeptide from Bothrops jararaca venom improves baroreflex sensitivity of spontaneously hypertensive rats

Baroreflex sensitivity is disturbed in many people with cardiovascular diseases such as hypertension. Brain deficiency of nitric oxide (NO), which is synthesized by NO synthase (NOS) in the citrulline-NO cycle (with argininosuccinate synthase (ASS) activity being the rate-limiting step), contributes to impaired baroreflex. We recently showed that a decapeptide isolated from Bothrops jararaca snake venom, denoted Bj-PRO-10c, exerts powerful and sustained antihypertensive activity. Bj-PRO-10c promoted vasodilatation dependent on the positive modulation of ASS activity and NO production in the endothelium, and also acted on the central nervous system, inducing the release of GABA and glutamate, two important neurotransmitters in the regulation of autonomic systems. We evaluated baroreflex function using the regression line obtained by the best-fit points of measured heart rate (HR) and mean arterial pressure (MAP) data from spontaneously hypertensive rats (SHRs) treated with Bj-PRO-10c. We also investigated molecular mechanisms involved in this effect, both in vitro and in vivo. Bj-PRO-10c mediated an increase in baroreflex sensitivity and a decrease in MAP and HR. The effects exerted by the peptide include an increase in the gene expression of endothelial NOS and ASS. Bj-PRO-10c-induced NO production depended on intracellular calcium fluxes and the activation of a G(i/o)-protein-coupled metabotropic receptor. Bj-PRO-10c induced NO production and the gene expression of ASS and endothelial NOS in the brains of SHRs, thereby improving baroreflex sensitivity. Bj-PRO-10c may reveal novel approaches for treating diseases with impaired baroreflex function.

Dynamic Causal Modelling and physiological confounds: A functional MRI study of vagus nerve stimulation

Dynamic Causal Modelling (DCM) has been proposed to estimate neuronal connectivity from functional magnetic resonance imaging (fMRI) using a biophysical model that links synaptic activity to hemodynamic processes. However, it is well known that fMRI is sensitive not only to neuronal activity, but also to many other psychophysiological responses which may be task-related, such as changes in cardio-respiratory activity. They are not explicitly taken into account in the generative models of DCM and their effects on estimated neuronal connectivity are not known. The main goal of this study was to report the face validity of DCM in the presence of strong physiological confounds that presumably cannot be corrected for, using an fMRI experiment of vagus nerve stimulation (VNS) performed in rats. First, a simple simulation was used to evaluate the principled ability of DCM to recover directed connectivity in the presence of a confounding factor. Second, we tested the experimental validity using measures of the BOLD correlates of left 5Hz VNS. Because VNS mostly activates the central autonomic regulation system, fMRI signals were likely to represent both direct and indirect vascular responses to such activation. In addition to the inference of standard statistical parametric maps, DCM was thus used to estimate directed neural connectivity in a small brain network including the nucleus tractus solitarius (NTS) known to receive vagal afferents. Though blood pressure changes may constitute a major physiological confound in this dataset, model comparison of DCMs still allowed the identification of the NTS as the input station of the VNS pathway to the brain. Our study indicates that current developments of DCM are robust to psychophysiological responses to some extent, but does not exclude the need to develop specific models of brain – body interactions within the DCM framework to better estimate neuronal connectivity from fMRI time series.

Regulation of autonomic nerve activities by central pituitary adenylate cyclase-activating polypeptide

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a peptidergic neurotransmitter that is expressed in high levels in nervous systems. Here, we investigated the roles of PACAP in autonomic system regulation by evaluating the changes caused in the autonomic nerve activities after injecting PACAP into the central nervous system (CNS) and examining stress-induced blood glucose changes in PACAP-deficient (PACAP−/−) mice. Renal sympathetic nerve activity (RSNA), blood pressure, and heart rate were elevated after injecting PACAP into the third cerebral ventricle (3CV). Similarly, other sympathetic nerve activities, including adrenal sympathetic nerve activity (ASNA), celiac sympathetic nerve activity (CSNA), and brown adipose tissue sympathetic nerve activity (BAT-SNA), were accelerated by PACAP injection. In contrast, injecting PACAP into 3CV significantly suppressed parasympathetic nerve activities, including gastric vagal nerve activity (GVNA) and celiac vagal nerve activity (CVNA). In addition, blood glucose elevations induced by stress, such as immobilization or ether exposure, were disrupted in PACAP−/− mice, although basal glucose levels in mutants were comparable to that in wild-type mice. These results suggest that CNS PACAP regulates autonomic function by maintaining a sympathetic–parasympathetic balance and contributes to peripheral homeostatic maintenance, especially under conditions of stress.

On direct sequential analysis of heart rate variability signals

Heart rate variability analysis represents one of the most promising and the most commonly used quantitative measures of the cardiovascular autonomic regulatory system. The analysis includes traditional statistical analytical tools and a number of new methods based on nonlinear system theory, recently developed to give better insight into complex HR. This paper introduces a direct sequential analysis.

Autonomic cardiovascular changes during and after 14 days of head-down bed rest

A 14-day, 6° head-down bed rest (HDBR) study was conducted with 12 healthy young men to determine whether there are transient responses of the cardiovascular autonomic regulatory system including cardiovascular, autonomic nervous, and cardiac baroreceptor reflex functions in the acute phases of HDBR and post-HDBR. Compared with the supine position before bed rest, the high-frequency band power (HF RRI) of RR intervals (RRIs) decreased significantly at 3, 6, and 24 h of HDBR. This tendency went on until 24 h post-HDBR. Three kinds of cardiac baroreceptor reflex sensitivity (BRS) were estimated from closed-loop approaches to simultaneously recorded spontaneous RRI and systolic arterial pressure (SAP) fluctuations. BRS sequence is based on the simultaneous changes between RRI and SAP. α LF and α HF are based on a cross-spectrum analysis for low- and high-frequency bands of RRI and SAP. Although BRS sequence decreased significantly at acute phases of both HDBR and post-HDBR, neither α LF nor α HF decreased significantly at any of the acute phases of HDBR and post-HDBR. Our results suggest that HF RRI and BRS sequence can be used effectively to reveal reductions in cardiac vagal nervous modulation on the sinus node and cardiac BRS within 24 h of both HDBR and post-HDBR.