Parasympathetic Activity Research Articles

Heart rate variability and its association with symptoms of orthostatic hypotension in spinal cord injury

Context/objective To assess differences in autonomic function using heart rate variability (HRV) parameters between people with and without orthostatic hypotension (OH), and to determine symptoms of OH in people with spinal cord injury (SCI). Methods R-R interval and blood pressure (BP) data were recorded using Finometer PRO® in both the supine position and at a 60-degree tilt using a tilt table, each lasting for 6 minutes. R-R interval data were processed using the Kubios HRV analysis software to convert R-R interval into time and frequency domains for further analysis. Results Compared to the non-OH group, the SCI group with OH exhibited lower values for root mean square of the successive differences (RMSSD) and standard deviation of normal-to-normal interval (SDNN), along with an elevated heart rate during tilt-up. Participants with OH symptoms had a lower average heart rate in the supine and 60-degree positions compared to asymptomatic participants. Logistic regression analysis indicated that SDNN in the supine position correlated with the presence of OH, and that the mean heart rate in the 60-degree position was related to the presence of symptoms. Conclusions Differences in HRV parameters were observed in people with SCI and OH, suggesting a reduced parasympathetic activity in the supine position, likely as a response to maintain homeostasis in BP regulation. Despite the presence or absence of OH symptoms, there was no difference in HRV parameters. This finding suggests that autonomic function may not be the primary determinant of these symptoms, with other factors likely being more influential.

Effects of transcutaneous auricular vagus nerve stimulation at left cymba concha on experimental pain as assessed with the nociceptive withdrawal reflex, and correlation with parasympathetic activity.

The aim of this study was to clarify the effects of transcutaneous auricular vagus nerve stimulation (taVNS) to the left cymba concha on the pain perception using nociceptive withdrawal reflex (NWR), which is known to be associated with chronic pain, and to investigate whether there is a relationship between taVNS-induced suppression of the NWR and parasympathetic activation. We applied either 3.0mA, 100 Hz taVNS for 120 s on the left cymba concha (taVNS condition) or the left earlobe (Sham condition) for 20 healthy adults. NWR threshold was measured before (Baseline), immediately after (Post 0), 10min (Post 10) and 30 min after (Post 30) stimulation. The NWR threshold was obtained from biceps femoris muscle by applying electrical stimulation to the sural nerve. During taVNS, electrocardiogram was recorded, and changes in autonomic nervous activity measured by heart rate variability (HRV) were analyzed. We found that the NWR thresholds at Post 10 and Post 30 increased compared with baseline in the taVNS group (10min after: p = .008, 30 min after: p = .008). In addition, increased parasympathetic activity by taVNS correlated with a greater increase in NWR threshold at Post 10 and Post 30 (Post 10: p = .003; Post 30: p = .001). The present results of this single-blinded study demonstrate the pain-suppressing effect of taVNS on NWR threshold and suggest that the degree of parasympathetic activation during taVNS may predict the pain-suppressing effect of taVNS after its application.

Prognostic value of cardiac deceleration capacity in patients with atrial fibrillation after catheter ablation: A systematic review and meta-analysis.

Cather ablation (CA) is a well-recognized treatment alternative for atrial fibrillation (AF) patients despite more than 20% ablation-treated patients suffering from AF recurrence. The underlying mechanism of AF recurrence postablation is probably associated with high cardiac parasympathetic activity, which can be assessed with deceleration capacity (DC) of heart rate. Given that the relationship between DC and AF recurrence is still controversial, this systematic review and meta-analysis was performed to investigate the characteristics of DC in patients with and without AF recurrence, evaluating the prognostic value of DC in AF patients after CA. A literature search was systematically performed in the Embase, PubMed, Web of Science, China National Knowledge Infrastructure (CNKI), and Wanfang databases until October 01, 2023. The observational studies reporting either the pre- and postablation DC in both recurrence and non-recurrence groups or the ratios based on DC for predicting AF recurrence were mainly included. Weighted mean differences (WMD) or odds ratios (OR) based on DC would be calculated with a random-effect model, if heterogeneity estimated with the I2 index and Q statistic was significant (I2 > 50% or p < .05); otherwise, a fixed-effect model would be utilized. A total of eight observational studies involving 914 AF patients treated with radiofrequency or cryoballoon ablation were included in this study. Ablation-treated patients with AF recurrence had the higher DC postablation in relation to those without recurrence (WMD, 1.00; 95% confidence interval [CI], 0.33-1.67; p < .01), which was present up to 3 months of follow-up (WMD, 1.54; 95%CI, 1.11-1.96; p < .01), whereas there was no statistical significance in DC before ablation between recurrence and non-recurrence groups (WMD, 0.34; 95%CI, -0.12 to 0.79; p = .15). The high DC postablation was a risk factor for AF recurrence in ablation-treated patients (OR, 2.17; 95%CI, 1.44-3.25; p < .01). The high DC postablation was associated with the risk of AF recurrence, suggesting that DC may act as a prognostic indicator in AF patients treated with CA.

Compassion training influences heart-rate variability within severe depression

BackgroundHeart-rate variability (HRV) is a marker of parasympathetic nervous system activity, and is a robust predictor of improved mental and physical health. Current psychotherapeutic interventions are effective at reducing self-report depressive symptoms, but few have improved HRV within a sample of severe depressive symptomatology. MethodThis study explores the impact of a brief Compassion Focused Therapy exercise (CFT) on HRV response. ResultsResults indicate that a brief CFT exercise can successfully target depressive physiology via increasing HRV, at two distinct timepoints, pre- and post- a two-week self-directed training period, even when controlling for respiration. Specifically, we first show that CFT can significantly increase HRV. Second, we show that CFT exercise can increase a subset of participants’ HRV level above a clinical cut-off value of low resting-HRV. Third, we describe how participant engagement with the CFT audio during the two-week training was very low, with 50% of individuals not accessing the audio during this period. Finally, during the CFT practice at post-two-week training, HRV was shown to decrease across time, potentially indicating a greater participant engagement in the ‘threat’ component of the exercise. LimitationsAlmost 50% of the sample did not listen to the CFT exercise during the two-week training period, a feature that has implications for self-directed delivery of experimental and treatment interventions. ConclusionsCFT can significantly improve HRV for those with severely depressed symptoms at the state-level, and future work should continue to examine CFT's effectiveness for those with depression.

The Performance of Using the Parasympathetic Tone Activity (PTA) Index to Assess Intraoperative Nociception in Cats.

The monitoring of nociception/antinociception poses a significant challenge during anesthesia, making the incorporation of new tools like the Parasympathetic Tone Activity (PTA) monitor an added value in feline anesthesia. To compare the effectiveness and speed of PTA monitoring when compared to heart rate (HR) in detecting surgical stimuli (SS) during the intraoperative period in 49 female cats undergoing ovariectomy (OV). Instantaneous Parasympathetic Tone Activity (PTAi) values, HR, fR, and non-invasive SAP and MAP were continuously monitored and systematically assessed. The time required for HR (HR time) and PTAi (PTAi time) to reach their minimum peak values following each surgical stimulus was collected at five points for each anaesthetized cat. Each collected surgical stimulus was categorized into 3 groups for statistical analysis: no nociception detection, no hemodynamic reaction and a PTAi > 50 (Nhre); no hemodynamic reaction and a PTAi < 50 (Nhre < 50); and hemodynamic reaction and PTAi < 50 (Hre < 50). PTAi response demonstrated effectiveness in detecting nociception compared to HR. The SS were categorized as 36.1% in the Nhre group, 50% in the Nhre < 50 group, and only 13.9% in the Hre < 50 group. In the Hre < 50 group, PTAi time and HR time had similar speeds in detecting the SS (p = 0.821); however, PTA time was significantly slower in the Nhre < 50 group when compared to the Hre < 50 group (p = 0.001). PTA monitoring may be a useful tool to complement HR monitoring for detecting nociception. PTA monitoring demonstrated a superior diagnostic value compared to HR for detecting nociception in cats undergoing OV and a similar speed to HR in detecting SS when HR increases above 20%. Future studies are needed to understand in a clinical setting the meaning of sympathetic activation/nociception detected using the PTA monitor when the HR increase is not clinically relevant.

Acute effects of different Tai Chi practice protocols on cardiac autonomic modulation

Tai Chi serves as an effective exercise modality for enhancing autonomic regulation. However, a majority of existing studies have employed the single routine (SR) protocol as the basis for health interventions. The extent to which the gong routine application (GRA) protocol achieves similar levels of exercise load stimulation as traditional single practice routines remains uncertain. Therefore, this study the distinct characteristics of autonomic load stimulation in these different protocols, thus providing a biological foundation to support the development of Tai Chi health promotion intervention programs. we recruited a cohort of forty-five university students to participate in the 15 min GRA protocol and SR protocol. We collected heart rate and heart rate variability indicators during periods of rest, GRA protocol, and SR protocol utilizing the Polar Scale. Additionally, we assessed the mental state of the participants using the BFS State of Mind Scale. In summary, the autonomic load is lower in the GRA protocol compared to the SR protocol, with lower sympathetic activity but higher parasympathetic activity in the former. Results are specific to college students, additional research is necessary to extend support for frail older adults. It is advised to incorporate GRA protocol alongside SR protocol in Tai Chi instruction. This approach is likely to enhance Tai Chi skills and yield greater health benefits.

‘Hidden’ anger as a risk factor for operational health: An exploratory approach among French military personnel

ABSTRACT Military personnel are repeatedly exposed to multiple stressors, and are sometimes characterized by high levels of anger. Evidence suggests that this anger can become dysfunctional, and impact the health status of populations chronically exposed to stress. In particular, rumination (understood as perseverative thoughts about a past event), provides a theoretical framework for investigating how anger may impact stress regulation abilities in military personnel declared fit for deployment. This exploratory study aimed therefore to examine the impact of the anger profile on psychological suffering in terms of burnout and post-traumatic stress disorder (PTSD), along with the reactivity of the autonomic nervous system, measured as cardiac variability. One hundred and seventeen French soldiers were tested before deployment to Operation BARKHANE. Anger rumination, burnout, and PTSD symptoms were assessed using questionnaires, and cardiac variability was measured as the questionnaires were completed. The results revealed two profiles related to anger trait and anger rumination. Burnout and PTSD scores were higher among military personnel with high levels of anger trait and rumination, and this group also had lower parasympathetic activity and flexibility after completing the questionnaires. These results suggest that there may be a link between an angry profile and psychological suffering, notably burnout and PTSD. Rumination could be involved in this link, as it is associated with poor adaptation to stress in a military context. Prospective researches including post-deployment will establish whether this ruminative response can account for the relationship between problematic anger, stress regulatory capacities and psychological health in military populations.

Is Takotsubo syndrome induced by patent ductus arteriosus occlusion?

Takotsubo syndrome (TTS), commonly referred to as "broken heart syndrome," is a distinctive form of acute and reversible heart failure that primarily affects young to middle-aged individuals, particularly women. While emotional or physical stressors often trigger TTS, rare cases have been linked to interventional procedures for congenital heart disease (CHD). Despite its recognition, the exact causes of TTS remain elusive. Research indicates that dysregulation in autonomic nerve function, involving sympathetic and parasympathetic activities, plays a pivotal role. Genetic factors, hormonal influences like estrogen, and inflammatory processes also contribute, unveiling potential gender-specific differences in its occurrence. Understanding these multifaceted aspects of TTS is crucial for refining clinical approaches and therapies. Continued research efforts will not only deepen our understanding of this syndrome but also pave the way for more targeted and effective diagnostic and treatment strategies. In this report, we conduct an in-depth analysis of a case involving a TTS patient, examining the illness progression and treatment procedures. The aim of this analysis is to enhance the understanding of TTS among primary care physicians. By delving into this case, we aspire to prevent misdiagnosis of typical TTS cases that patients may present, thereby ensuring a more accurate diagnosis and appropriate treatment.

The relationship between alpha power and heart rate variability commonly seen in various mental states.

The extensive exploration of the correlation between electroencephalogram (EEG) and heart rate variability (HRV) has yielded inconsistent outcomes, largely attributable to variations in the tasks employed in the studies. The direct relationship between EEG and HRV is further complicated by alpha power, which is susceptible to influences such as mental fatigue and sleepiness. This research endeavors to examine the brain-heart interplay typically observed during periods of music listening and rest. In an effort to mitigate the indirect effects of mental states on alpha power, subjective fatigue and sleepiness were measured during rest, while emotional valence and arousal were evaluated during music listening. Partial correlation analyses unveiled positive associations between occipital alpha2 power (10-12 Hz) and nHF, an indicator of parasympathetic activity, under both music and rest conditions. These findings underscore brain-heart interactions that persist even after the effects of other variables have been accounted for.

Association of brain-autonomic activities and task accuracy under cognitive load: a pilot study using electroencephalogram, autonomic activity measurements, and arousal level estimated by machine learning.

The total amount of mental activity applied to working memory at a given point in time is called cognitive load, which is an important factor in various activities in daily life. We have proposed new feature quantities that reflect the time-series changes in the power of typical frequency bands in electroencephalogram (EEG) for use in examining the relationship between brain activity and behavior under cognitive load. We also measured heart rate variability (HRV) and spontaneous skin conductance responses (SCR) to examine functional associations among brain activity, autonomic activity, and behavior under cognitive load. Additionally, we applied our machine learning model previously developed using EEG to the estimation of arousal level to interpret the brain-autonomic-behavior functional association under cognitive load. Experimental data from 12 healthy undergraduate students showed that participants with higher levels of infra-slow fluctuations of alpha power have more cognitive resources and thus can process information under cognitive load more efficiently. In addition, HRV reflecting parasympathetic activity correlated with task accuracy. The arousal level estimated using our machine learning model showed its robust relationship with EEG. Despite the limitation of the sample size, the results of this pilot study suggest that the information processing efficiency of the brain under cognitive load is reflected by time-series fluctuations in EEG, which are associated with an individual's task performance. These findings can contribute to the evaluation of the internal state of humans associated with cognitive load and the prediction of human behaviors in various situations under cognitive load.

Effect of Prenatal Yoga versus Moderate-Intensity Walking on Cardiorespiratory Adaptation to Acute Psychological Stress: Insights from Non-Invasive Beat-to-Beat Monitoring.

We recently reported enhanced parasympathetic activation at rest throughout pregnancy associated with regular yoga practice. The present study presents a secondary analysis of data collected within a prospective cohort study of 33 pregnant women practicing yoga once weekly throughout pregnancy and 36 controls not involved in formal pregnancy exercise programs. The objective was to assess the impact of prenatal yoga on the autonomic nervous system stress response. Healthy pregnant women with singleton pregnancies were recruited in the first trimester. There was no significant difference in the maternal body mass index (BMI) between the yoga group and the controls (24.06 ± 3.55 vs. 23.74 ± 3.43 kg/m2, p = 0.693). Women practicing yoga were older (28.6 ± 3.9 vs. 31.3 ± 3.5 years, p = 0.005) and more often nulliparous (26 (79%) vs. 18 (50%), p = 0.001). We studied heart rate variability (HRV) parameters in the time domain (SDNN, standard deviation of regular R-R intervals, and RMSSD, square root of mean squared differences of successive R-R intervals) and frequency domain (ln(LF/HF), natural logarithm of low-frequency to high-frequency power), as well as synchronization indices of heart rate, blood pressure and respiration during and immediately following acute psychological stress of a standardized mental challenge test. Measurements were performed once per trimester before and after yoga or a 30 min moderate-intensity walk. Statistical comparison was performed using three-way analyses of variance (p < 0.05 significant). Time domain HRV parameters during and following mental challenge in the yoga group were significantly higher compared to the controls regardless of the trimester (F = 7.22, p = 0.009 for SDNN and F = 9.57, p = 0.003 for RMSSD, respectively). We observed no significant differences in the yoga group vs. the controls in terms of ln(LF/HF) and synchronization indices. Regular prenatal yoga practice was associated with a significantly reduced sympathetic response to mental challenge and quicker recovery after acute psychological stress. These effects persisted throughout pregnancy with regular practice.

Sympathetic and parasympathetic central autonomic networks

Abstract The central-autonomic network (CAN) comprises brain regions that are functionally linked to the activity of peripheral autonomic nerves. While parasympathetic CAN (i.e., the CAN projecting onto parasympathetic branches) has recently been investigated and is known to be involved in neurological and neuropsychiatric disorders, sympathetic CAN (i.e., the CAN projecting onto sympathetic nerves) has not been fully characterized. Using functional magnetic resonance imaging (fMRI) data from the Human Connectome Project in conjunction with heartbeat dynamics and its orthonormal autoregressive descriptors as a proxy for sympathetic activity estimation, namely, the sympathetic activity index (SAI), we uncover brain regions belonging to the sympathetic CAN at rest. We uncover a widespread CAN comprising both cortical (in all lobes) and subcortical areas, including the cerebellum and brainstem, which is functionally linked to sympathetic activity and overlaps with brain regions driving parasympathetic activity. These findings may constitute fundamental knowledge linking brain and bodily dynamics, including the link between neurological and psychiatric disorders and autonomic dysfunctions.

Evaluating the indicators ofaheart rate variability analysis indogs using Poincaré plots.

Heart rate variability analyses using Poincaré plots can beuseful for evaluating the autonomic nervous system function. However, the interpretation ofthe quantitative indicators ofPoincaré plots remains controversial. Thus, few studies have verified the effectiveness ofthe quantitative indicators inveterinary medicine. This study aimed toverify the reliability ofPoincaré plot indicators using pharmacological models indogs. Four healthy beagles were used inthis study. Each dog was treated with propranolol, atropine, and propranolol-atropine toblock the sympathetic, parasympathetic, and sympathetic-parasympathetic functions, respectively. The quantitative indicators ofthe Poincaré plots were calculated based ondata from 300electrocardiogram beats collected before and after the administration ofeach drug and statistically analysed. The quantitative indicators ofthe Poincaré plots, such asthe standard deviation perpendicular tothe major axis (SD1), standard deviation along the major axis (SD2), and SD1×SD2, significantly decreased after the drug administration inboth the parasympathetic and sympathetic-parasympathetic blockade models. However, nosignificant differences were observed inSD1/SD2 between the groups. The Poincaré plots reflected the changes inthe autonomic nervous system ofdogs. Indogs, SD1, SD2, and SD1×SD2 can detect astate inwhich parasympathetic nerve activity issuppressed.

Correlation of fetal heart rate dynamics to inflammatory markers and brain-derived neurotrophic factor during pregnancy.

This study aims to show the relation between biomarkers in maternal and cord-blood samples and fetal heart rate variability (fHRV) metrics through a non-invasive fetal magnetocardiography (fMCG) technique. Twenty-three women were enrolled for collection of maternal serum and fMCG tracings immediately prior to their scheduled cesarean delivery. The umbilical cord blood was collected for measurement of biomarker levels. The fMCG metrics were then correlated to the biomarker levels from the maternal serum and cord blood. Brain-derived neurotrophic factor (BDNF) had a moderate correlation with fetal parasympathetic activity (0.416) and fetal sympathovagal ratios (-0.309;-0.356). Interleukin (IL)-6 also had moderate-sized correlations but with an inverse relationship as compared to BDNF. These correlations were primarily in cord-blood samples and not in the maternal blood. In this small sample-sized exploratory study, we observed a moderate correlation between fHRV and cord-blood BDNF and IL-6 immediately preceding scheduled cesarean delivery at term. These findings need to be validated in a larger population.

Circadian regulation of sinoatrial nodal cell pacemaking function: Dissecting the roles of autonomic control, body temperature, and local circadian rhythmicity.

Strong circadian (~24h) rhythms in heart rate (HR) are critical for flexible regulation of cardiac pacemaking function throughout the day. While this circadian flexibility in HR is sustained in diverse conditions, it declines with age, accompanied by reduced maximal HR performance. The intricate regulation of circadian HR involves the orchestration of the autonomic nervous system (ANS), circadian rhythms of body temperature (CRBT), and local circadian rhythmicity (LCR), which has not been fully understood. Here, we developed a mathematical model describing ANS, CRBT, and LCR in sinoatrial nodal cells (SANC) that accurately captures distinct circadian patterns in adult and aged mice. Our model underscores how the alliance among ANS, CRBT, and LCR achieves circadian flexibility to cover a wide range of firing rates in SANC, performance to achieve maximal firing rates, while preserving robustness to generate rhythmic firing patterns irrespective of external conditions. Specifically, while ANS dominates in promoting SANC flexibility and performance, CRBT and LCR act as primary and secondary boosters, respectively, to further enhance SANC flexibility and performance. Disruption of this alliance with age results in impaired SANC flexibility and performance, but not robustness. This unexpected outcome is primarily attributed to the age-related reduction in parasympathetic activities, which maintains SANC robustness while compromising flexibility. Our work sheds light on the critical alliance of ANS, CRBT, and LCR in regulating time-of-day cardiac pacemaking function and dysfunction, offering insights into novel therapeutic targets for the prevention and treatment of cardiac arrhythmias.

Use of Atrial Fibrillation Electrograms and T1/T2 Magnetic Resonance Imaging to Define the Progressive Nature of Molecular and Structural Remodeling: A New Paradigm Underlying the Emergence of Persistent Atrial Fibrillation.

The temporal progression states of the molecular and structural substrate in atrial fibrillation (AF) are not well understood. We hypothesized that these can be detected by AF electrograms and magnetic resonance imaging parametric mapping. AF was induced in 43 dogs (25-35 kg, ≥1 year) by rapid atrial pacing (RAP) (3-33 weeks, 600 beats/min), and 4 controls were used. We performed high-resolution epicardial mapping (UnEmap, 6 atrial regions, both atria, 130 electrodes, distance 2.5 mm) and analyzed electrogram cycle length, dominant frequency, organization index, and peak-to-peak bipolar voltage. Implantable telemetry recordings were used to quantify parasympathetic nerve activity over RAP time. Magnetic resonance imaging native T1, postcontrast T1, T2 mapping, and extracellular volume fraction were assessed (1.5T, Siemens) at baseline and AF. In explanted atrial tissue, DNA oxidative damage (8-hydroxy-2'-deoxyguanosine staining) and percentage of fibrofatty tissue were quantified. Cycle length and organization index decreased (R=0.5, P<0.05; and R=0.5, P<0.05; respectively), and dominant frequency increased (R=0.3, P n.s.) until 80 days of RAP but not thereafter. In contrast, voltage continued to decrease throughout the duration of RAP (R=0.6, P<0.05). Parasympathetic nerve activity increased following RAP and plateaued at 80 days. Magnetic resonance imaging native T1 and T2 times increased with RAP days (R=0.5, P<0.05; R=0.6, P<0.05) in the posterior left atrium throughout RAP. Increased RAP days correlated with increasing 8-hydroxy-2'-deoxyguanosine levels and with fibrosis percentage (R=0.5, P<0.05 for both). A combination of AF electrogram characteristics and T1/T2 magnetic resonance imaging can detect early-stage AF remodeling (autonomic remodeling, oxidative stress) and advanced AF remodeling due to oxidative stress and fibrosis.

Surge of Sympathetic Activity during Hyperventilation at the End of Apnea for Patients with Obstructive Sleep Apnea.

Background and Objectives: The mechanisms connecting obstructive sleep apnea (OSA) and cardiovascular disease are multifactorial, involving intermittent hypoxia, hypercapnia, and sympathetic activation. The aim of this study was to explore the oscillations of sympathetic activity during the sleep apnea episodes throughout the entire night in patients with OSA. Materials and Methods: The participants received whole-night polysomnography (PSG), and electrocardiogram (EKG) data from the PSG were collected for heart rate variability (HRV) analysis. HRV measurements were conducted in the time and frequency domains. The root mean square of successive differences between normal heartbeats (RMSSD), which reflects parasympathetic activity, and the ratio of the absolute power of the low-frequency band (0.04-0.15 Hz) to the absolute power of the high-frequency band (0.015-0.4 Hz) (LF/HF ratio), which indicates sympathetic activity, were computed. Results: A total of 43 participants (35 men and 8 women) were included in the analysis. The mean age of the participants was 44.1 ± 11.3 years old, and the mean BMI was 28.6 ± 5.4 kg/m2. The sleep apnea episodes throughout the entire night in patients with OSA were selected randomly and occurred most frequently during the non-REM stages (39, 90.7%). The selected sleep apnea episodes typically exhibited multiple apneas, often interrupted by snoring respiration and followed by hyperventilation at the end of the episode (HE). Our findings indicate that the centers of the 5 min HRV window for the lowest and highest LF/HF ratios, at 111.8 ± 88.2 and 117.4 ± 88.6 min after sleep onset, respectively, showed a statistically significant difference (p < 0.001). Similarly, the ratios of the lowest and highest LF/HF, at 0.82 ± 0.56 and 3.53 ± 2.94, respectively, exhibited a statistically significant difference (p < 0.001). Conclusions: In the current study, the selected sleep apnea episodes throughout the entire night in patients with OSA occurred primarily during the non-REM stages. Additionally, we observed that sympathetic activity reached its peak in the window that includes hyperventilation at the end stage of apnea, potentially posing a cardiovascular risk. However, additional studies are needed to validate these results.

Electrocardiographic activity depends on the relative position between intimate persons

Interpersonal space (IPS) refers to the area surrounding the body in which we engage in social interactions while maintaining our comfort. Numerous previous studies have reported the psychological and physiological changes associated with the proximity of two people engaged in face-to-face interaction. Currently, there is limited knowledge about how the relative position between two socially intimate individuals affects their psychological and physiological states. This research measured the subjective discomfort and electrocardiographic responses of participants when standing static at various relative positions. The highest discomfort, lowest heart rate, and highest heart rate variability (HRV; parasympathetic activity index) were observed when the friend stood in the face-to-face position. Interestingly, heart rate also decreased when the friend stood on the right side, although HRV did not change. We interpreted the results as suggesting that the presence of a familiar person elicits the electrocardiographic responses associated with an increase in parasympathetic activity.

Impact of different cooling solutions on autonomic modulation in horses in a novice endurance ride

Cooling down is essential for horse recovery before veterinary inspection during an endurance ride. As salt potentially decreases water temperature, we tested whether adding salt to the water used to cool horses could aid their recovery. Twelve healthy Arabian horses participating in a novice endurance ride were divided evenly into two groups. Heart rate variability (HRV) variables, including time and frequency domains, non-linear results, and autonomic nervous system indices, were determined before recovery and at 1-min intervals for 9 min during recovery using either cold or cold-saline water. An interaction between water type and time was observed in the modulation of the SD of beat-to-beat (RR) intervals, square root of the mean squared differences between successive RR intervals (RMSSD), HRV triangular index, very low-frequency band (VLF), low-frequency band/high-frequency band ratio, and SD of the Poincaré plot perpendicular to the line of identity (SD1) non-linear results. A decrease in heart rate and the sympathetic nervous system index corresponding to an increase in RR intervals and the parasympathetic nervous system (PNS) index was observed over time. A rise in the triangular interpolation of the normal-to-normal intervals, number of successive RR interval pairs that differ more than 50 ms, low-frequency band, and total power, coinciding with decreased stress index, was detected at 9 min of recovery. A difference between RMSSD and SD1 was observed between groups, in which they were higher in horses cooling with cold-saline water when compared to cold water at 5 min after cooling began. An increase in VLF was seen at 9 min only in horses cooled with cold-saline water. In conclusion, different water types distinctly impacted HRV in horses. The predominant PNS activity in horses recovering with cold-saline water reflects its positive impact on cooling during an endurance ride.

Plank exercise improves respiratory capacity through positive changes in body composition, abdominis function, and autonomic nerves' activities

AbstractThis research aimed to explore the impact of plank exercise training (PET) on respiratory function, body composition, abdominis performance, and autonomic nervous system (ANS). Sixty‐one young adults participated and were divided into a control group (CG, n = 31) and an exercise group (EG, n = 30), wherein PET was administered 3 days per week for 12 weeks. After the experiment, the body composition of the CG deteriorated, whereas that of the EG improved (p &lt; 0.001). The EG exhibited a reduction of ∼34% in the mean maximum displacement and a rise of ∼20% in the mean contraction time of the abdominis. The sit‐up in the EG demonstrated a significant increase of ∼55%. In the EG, there was a substantial increase in peak expiratory force by ∼24% and forced expiratory volume in 1 s by ∼14%, accompanied by a reduction in resting respiratory rate by ∼ −9%. When compared to the CG, these alterations were significant between the two groups (p = 0.001). In the EG, there was a significant decrease in resting heart rate by ∼2%, accompanied by a decrease in sympathetic nervous activity by ∼ −5% and by an increase in parasympathetic nervous activity by ∼5%. When compared to the CG, these alterations were significant between the two groups (p = 0.001). The findings of this study revealed that implementing PET in young adults, while controlling for dietary intake and physical activity, resulted in noteworthy changes in respiratory capacity. These changes were coupled with improvements in body composition, abdominal functions, and the ANS.