Frequency Domain Parameters Research Articles

Spectrum Extreme Purification and Modulation of DBR Fiber Laser With Weak Distributed Feedback

Highly coherent lasers with spectral hyperpurity can further advance the fields of science and engineering. Especially, a light source with controllable frequency domain parameters can be adapted to a variety of emerging application scenarios. Herein, we report on an implementation of a novel ultra-high spectral purity distributed Bragg reflector (DBR) all-fiber laser based on weak distributed feedback, and its spectrum can be modulated in a certain extent by precisely controlling the intensity of the distributed feedback signal. Eventually, an ultra-high spectral purity laser with a spectral signal-to-noise ratio of 64 dB, a side mode suppression ratio (SMSR) of 83 dB, an output Lorentz linewidth of 115 Hz and a relative intensity noise of less than -122 dB/Hz is successfully obtained under normal conditions. Also, the frequency noise limit of the fiber laser with weak distributed feedback in the high frequency white noise flat region is 4.8 Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /Hz, corresponding to a fundamental linewidth of ∼15.1 Hz. In particular, the SMSR and Lorentz linewidth of the laser can be continuously adjusted from 53 dB to 83 dB and 115 Hz to 8.2 kHz, respectively. In addition, we also investigated the effect of different pumping configurations on the performance of the DBR fiber laser. The proposed controllable mechanism of laser spectrum also provides a new perspective for extreme regulation of other laser parameters.

Advancements in the Theory and Practice of Flight Vehicle System Identification

System identification methods have played an essential role in the research and industry projects at the Institute of Flight System Dynamics of the Technical University of Munich. Besides the application of the established system identification approaches to multiple aircraft, novel methods have been developed at the institute to deal with the challenges associated with fixed- and rotary-wing aircraft system identification in the time and frequency domains. This paper provides an overview of these new developments, as well as practical application examples from the past and ongoing projects at the institute. After a brief introduction to the work at the institute, the paper describes the new advancements in the fields of time domain system identification and optimal input design by introducing optimal control methods. It continues with an alternative problem formulation for applying frequency domain system identification and parameter estimation methods to a novel flight control design and tuning approach. Additional topics from the past and ongoing research at the institute such as novel methods and practical findings in rotorcraft system identification and flight path reconstruction for different applications will be discussed and referenced.

Vagal cardiac control in rats with LPS-induced lung injury

Heart rate variability (HRV) as an index of cardiac autonomic control in acute lung injury (ALI) has been evaluated in anaesthetized rats intratracheally instilled with bacterial lipopolysaccharide (LPS) and ventilated with breathing frequency of 60/min, 40% oxygen, inspiratory time 40%, tidal volume of 6 mL/kg. ECG was recorded before and 30, 60, 120, 180 and 240 min after LPS or saline (control) administration. HRV was quantified by time and frequency-domain analysis (mean RR interval, SDRR, RMSSD and spectral power in high frequency (HF) band. Lactate in plasma, and oxidative stress, IL-1β, IL-5, IL-12p70 and IL-13 and galectin-3 in heart tissue raised in LPS-injured rats. Overall HRV magnitude (SDRR) and marker of vagal heart rate control (RMSSD), as well as frequency domain parameter, spectral power HF was increased 120 and 180 min since ALI onset. In conclusion, LPS-induced ALI is accompanied by altered vagal cardiac control mediated by autonomic nervous system, likely based on the close relationship between immune response and vagally mediated autonomic nervous activity.

A Study to Correlate Stress Score with Heart Rate Variability among MBBS Students at a Tertiary Care Center, Jaipur

Introduction: Medical students have high levels of stress that could be due to stressors related to the academic workload, time pressure competency, professionalism, physical, mental, and emotional issues. This study aimed to find out subjective assessment of stress, stressors, and coping strategies and objective assessment of stress with heart rate variability (HRV) and correlate subjective and objective assessment of stress scores among 1st year MBBS students at RUHS College of Medical Sciences. Materials and Methods: Institutional ethical clearance (EC-P-21/RUHS) was obtained after that study was conducted among a total of 150 1st year MBBS students. The students were asked to fill out a validated general health questionnaire (GHQ-12), “medical student stress questionnaire 40,” and a brief COPE inventory to assess stress, stressors, and various coping strategies for subjective assessment and objective assessment done by time and frequency domain parameters of HRV. Results: The mean age was 20.85 ± 1.56. The severity of stress categorized as mild, moderate, high, and severe were 17%, 40%, 13%, and 10%, respectively. The most affected stressor was academic contributed to 80% followed by teaching–learning related, social, intra- and interpersonal, group activities, drive, and desire-related stressors 78%, 75%, 73%, 70%, and 68%, respectively. Overall, the students’ coping strategies were mostly avoidant followed by emotional and problem based. HRV is measured by time domain, i.e., PNN50, standard deviation of normal to normal RR intervals, root mean square of successive differences, and “frequency domain parameters,” i.e., low frequency (LF), high-frequency (HF), and LF/HF ratio. Conclusion: In the present study, a positive correlation was observed between HRV and stress score. More than 75% of RUHSCMS 1st year medical students were suffering from measurable academic stress. Time domain and frequency domain parameters were positively correlated with stress score.

Activities of the hypothalamo-pituitary-adrenal axis and autonomic nervous system following a strong earthquake.

This study aimed to investigate the effects of post-traumatic stress, caused by a strong earthquake, on the hypothalamo-pituitary-adrenal axis (HPA) and autonomous nervous system activity (ANS). Activities of the HPA (as salivary cortisol) and ANS (as heart-rate variability [HRV]) were measured following the 2020 Elazig (Türkiye) earthquake (6.8 Richter Scale, classified as strong). A total of 227 participants (103 men (45%) and 124 women (%55)) provided saliva samples twice, namely, 1week and 6weeks after the earthquake. Of these participants, HRV was measured in 51 participants by 5min continuous electrocardiogram (ECG) recording. Frequency- and time-domain parameters of the HRV were calculated to assess the activity of ANS and low/high frequency (LF/HF) ratio was used as surrogate for sympathovagal balance. Salivary cortisol levels decreased from week 1 towards week 6 (17.40±1.48 and 15.32±1.37ng/mL, respectively, p<0.05). There were no gender differences (17.99±2.63 and 16.90±1.60ng/mL, respectively for females and males, p>0.05) for salivary cortisol levels. There were no differences in time- and frequency domain parameters of the HRV including LF/HF ratio (2.95±0.38 ms2 and 3.60±0.70 ms2 , respectively for week 1 and 6, p>0.05). The data show that HPA axis activity, but not that of the ANS, remains higher 1week after the earthquake but decreases afterwards towards the sixth week, suggesting that the HPA axis might be responsible for the long-term effects of a traumatic event like a strong earthquake.

Effect of Preferential Relaxing Music on Exercise-Induced Changes in Autonomic Function of the Heart

Context: Music has been used for healing purposes since ancient times. Music therapy is a growing branch which can facilitate and promote a healthy mind and body. Autonomic nervous system (ANS) may serve as one path by which music exerts its therapeutic effects. Interaction between the ANS and cardiovascular system during exercise can be of prognostic importance in many cardiovascular diseases. The measurement of the effects of musical auditory stimulation, using non-invasive test of heart rate variability (HRV), on cardiac auditory response while under stressful condition, like exercise, would help understand the usability of musical interventions in prevention and treatment of cardiovascular diseases. Aim: To gauge the effects of preferential relaxing music on exercise-induced changes in frequency domain parameters (LF, low frequency; HF, high frequency; LF: HF ratio) of HRV. Setting and Design: Experimental study design. Methods and Materials: Sample size—52 healthy young adult volunteers (18–25 years). HRV was measured from the ECG obtained at rest, while listening to preferential relaxing music, after doing moderate exercise and after doing moderate exercise while listening to preferential relaxing music. Statistical Analysis Used: Comparison of frequency domain HRV variables was done using paired t-test. Results: Non-significant increase in HF component (P value = 0.3) and non-significant decrease in LF: HF ratio (P value = 0.06) after doing moderate exercise with music when compared with after doing moderate exercise without music was observed. Conclusion: Preferential relaxing music attenuated exercise-induced decrease in parasympathetic activity post-exercise.

Investigation on Features Extraction of Defect Signals Using Support Vector Machine and Multi-feature Fusion

This article investigated the sensitivity of each acoustic feature to steel plate defects through the coin-tapping method in order to improve acoustic detection methods precision and intelligent detection efficiency. 87 acoustic characteristic parameters of detection signals were researched including time domain, frequency domain, and time-frequency domain. 10 kinds of percussion conditions were designed to meet the two classifications of acoustic signals. The degree of contribution of acoustic parameters to damage detection was arranged by sensibility analysis, which could be used as a basis for selecting acoustic parameters for similar structural damage detection. The characteristic vectors of various parameter combinations were determined as the inputs of the acoustic detection method by analysing the sensitivity and correlation of different parameters. The multi-parameter feature vector with low redundancy was obtained by correlation analysis, which could be used as a combination method of the input value of the damage recognition classifier. The results show that the zero-crossing rate, main frequency and time-frequency domain parameters have high damage sensitivity, and there are always low-correlation feature pairs between them. The research results provide solutions for the selection and combination of feature parameters for similar data classification problems.

Transcatheter aortic valve implantation improves endothelial and autonomic function

Abstract Funding Acknowledgements Type of funding sources: None. Background Degenerative aortic stenosis is the leading native valve pathology in developed countries. Its degeneration process is affected by aging, common cardiovascular risk factors and an atherosclerotic-like process preceded by endothelial and autonomic dysfunction. With the increasing integration of transcatheter aortic valve implantation (TAVI) in the treatment of aortic stenosis in the elderly, research is being intensively oriented into its beneficial effect on the cardiovascular system. Measurements of vascular function with flow mediated dilatation (FMD) and autonomic cardiac function using heart rate variability parameters represent a validated method for treatment evaluation at different time-points. Purpose The purpose of our study was to assess whether haemodynamic and structural changes after TAVI will have a positive impact on endothelial and autonomic cardiac function on early and late follow-up. Methods 50 patients with severe aortic stenosis destinated to TAVI were prospectively included. Data was collected at baseline (24 hours before the procedure), on early follow-up (48 hours after the procedure) and on late follow-up (6 months after the procedure). While different heart rate variability parameters were obtained using a high-resolution electrocardiogram, FMD was assessed using a standardized ultrasound-based process with induced forearm hyperaemia. Results 43 patients completed the study (mean age 81 (75-85); 60% women). FMD measurements significantly changed from baseline to early follow-up (2.8 ± 1.5 % to 4.7 ± 2.7 %, p &amp;lt; 0.001). Improvement was persistent on late follow up (4.8 ± 2.7 %, p = 0.936). Moreover, heart rate variability parameters remained unchanged on early follow-up and improved 6 months after. Late follow-up statistical significance was reached by HF, a frequency-domain parameter (5231 ± 1783 to 6507 ± 1789 ms2; p = 0.029) and two Poincare diagram parameters: RR ecc (682 to 906 ms2; p &amp;lt; 0.001) and SDRR (9.6 to 23.9 ms; p = 0.001). Significant predictors of FMD change were as following: baseline maximal aortic valve velocity (R = 0.415; p = 0.011), mean aortic gradient (R = 0.373; p = 0.018), indexed stroke volume (R = 0.503; p = 0.006) and NT-proBNP (R = 0.491; p = 0.001). Conclusions Both endothelial and autonomic function improved after TAVI. While FMD seems to change early due to acute haemodynamic changes attributed to aortic valve stenosis resolution, autonomic cardiac functions remain stable and ameliorate late after procedure, likely reflecting left ventricular reverse remodelling.

HEART RATE VARIABILITY PARAMETERS WERE NOT ASSOCIATED WITH 30-DAY ALL-CAUSE MORTALITY IN INTENSIVE CARE UNIT PATIENTS WITH OR WITHOUT ATRIAL FIBRILLATION: A RETROSPECTIVE STUDY OF THE MIMIC-IV DATABASE.

Objective: Our study aims to evaluate the association between heart rate variability (HRV) and short- and long-term prognosis in patients admitted to intensive care unit (ICU). Methods and Results: Adult patients continuously monitored for over 24 h in ICUs from the the American Medical Information Mart for Intensive Care (MIMIC)-IV Waveform Database were recruited in our study. Twenty HRV-related variables (8 time domain, 6 frequency domain, and 6 nonlinear variables) were calculated based on RR intervals. The association between HRV and all-cause mortality was assessed. Ninety-three patients met the inclusion criteria and were classified into atrial fibrillation (AF) and sinus rhythm (SR) groups, which were further divided into 30-day survivor group and nonsurvivor\groups based on their survival status. The 30-day all-cause mortality rates in AF and SR groups were 36.3% and 14.6%, respectively. All the time domain, frequency domain, and nonlinear HRV parameters did not differ significantly between survivors and nonsurvivors with or without AF (all P > 0.05). Presence of renal failure, malignancy, and elevated blood urea nitrogen level were associated with increased 30-day all-cause mortality in SR patients, while presence of sepsis, infection, higher platelet count, and magnesium level were associated with increased 30-day all-cause mortality in AF patients. Conclusions: Heart rate variability variables were not associated with increased 30-day all-cause mortality in ICU patients with or without AF.

COVID-19-induced Stress in Health-care Workers: Effect of 8-week Common Yoga Protocol on Autonomic Function and Inflammatory and Oxidative Stress Markers.

COVID-19 pandemic posed a huge stress on health-care givers affecting their physical and mental health. Wellness strategies like yoga can improve flexibility, resilience, and outlook. The present study explored the effect of 8-week standard common yoga protocol (CYP) intervention on autonomic functions, emotional stress, oxidative stress, and inflammation markers in the nurse group of health-care givers. It is a randomized controlled trial where 50 nurses underwent CYP and 50 participated as controls. Anthropometric parameters, cardiovascular parameters, autonomic function including time and frequency domain parameters, biochemical parameters, and psychological stress using the questionnaire were assessed before and after 8-week CYP. Total 88 nurses completed the study with 42 and 46 participants, respectively, in the CYP and control groups. CYP intervention resulted in a significant reduction in cardiovascular parameters systolic blood pressure, diastolic blood pressure, mean arterial pressure, pulse pressure, and rate pressure product (P < 0.001, P < 0.001, P < 0.001, P < 0.001, and P = 0.002, respectively), perceived stress score and Depression, Anxiety, and Stress Scale psychological variables of depression, anxiety, and stress, and serum lipid parameters compared to the control group. CYP significantly increased total power, low frequency, high frequency, root mean square of successive differences between adjacent NN intervals, change in successive normal sinus (NN) intervals exceeds 50 ms, and pNN50% (P < 0.001, P = 0.006, P = 0.006, P = 0.039, P < 0.001, and P = 0.013, respectively) suggesting improved resting autonomic modulation and parasympathodominance due to higher vagal efferent activity. There were significant reductions in serum cortisol, tumor necrosis factor-alpha, interleukin (IL)-1, and IL-6 in both the groups. Serum telomerase significantly reduced (P = 0.024) and total antioxidant capacity (P = 0.036) increased in the CYP group post intervention. CYP intervention was beneficial in improving psychophysiological, autonomic, and biochemical profile of the nurse group of health-care workers.

Electronic cigarettes exposures modulate Heart Rate and Heart Rate Variability

Background: Despite a lack of empirical data, an unprecedented rise in electronic cigarettes (ECs) has been widely perceived as safe. Multiple studies support a causal link between tobacco cigarette (TC) use and cardiovascular (CV) diseases; however, there is a lack of data with EC use. We have previously shown that chronic and acute EC use decreases heart rate variability (HRV) in humans, likely via increased sympathetic nervous system activation. Objective: We aimed to evaluate HRV effects induced by brief EC exposures utilizing an in-vivo model for freely moving C57BL/6 mice. Methods and Results: Telemetry devices were implanted in the abdomen of six 10-week-old C57BL/6 male mice to monitor electrocardiographic activity continuously. Mice underwent an exposure protocol designed to reflect human vaping topography with two EC exposures, each lasting 15-minutes (4-sec puff/ 26-sec Air) followed by 45-min post-exposure periods. Air (primary control) and PBS (secondary control) were also included, each with their own post-exposure events. During EC exposures, we observed bradycardic effects in heart rate (HR) with the standard deviation of NN intervals (SDNN), root mean square of successive differences (RMSSD), and the proportion of adjacent normalized RR intervals that differed by more than 6 ms (pNN 6 ) significantly (p&lt; 0.05) altered as compared to Air exposures. After EC exposures, SDNN, RMSSD and pNN 6 parameters significantly decreased compared to Air. No significant differences between Air and PBS were observed in these parameters. Frequency domain parameters also indicated significant changes in HRV; the low frequency (LF) and high frequency (HF) bands showed marked increases during and after the EC exposures, while the log (LF/HF) ratio remained relatively unchanged, suggesting a possible coactivation of both parasympathetic and sympathetic branches of the autonomic nervous system. Conclusion: Short-term EC exposures lower heart rate and altered HRV in mice in an acute manner, suggesting that ECs may not be safe as previously assumed. This work was funded by the Tobacco-Related Disease Research Program (TRDRP) which included the High Impact Pilot Research Award [28IP-0036], the Cornelius Hopper Diversity Award Supplement and the Student Research Award Supplement, the UCLA Center for Occupational and Environmental Health (COEH) Student Project Award, and in part by the National Institute of Environmental Health Sciences (NIEHS) via the Student-to-Scientist Bridge program at California State University, Northridge [5R25ES025507]. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Parasympathetic activity and total fibrotic kidney in autosomal-dominant polycystic kidney disease patients: a pilot study

PurposeRenin–angiotensin system hyperactivation in autosomal-dominant polycystic kidney disease (ADPKD) patients leads to early hypertension. Cystic enlargement probably causes parenchymal hypoxia, renin secretion, and endothelial dysfunction. Sympathetic and parasympathetic balance is altered in this condition, especially during the night, also affecting blood pressure circadian rhythm. Aim of this study was to evaluate sympathetic/parasympathetic balance using heart rate variability (HRV) parameters and find a correlation between HRV and renal damage progression, as total kidney volume enlargement, in ADPKD patients.MethodsSixteen adult ADPKD patients were enrolled in the study. Eleven patients (68.8%) were male, and the median age was 42 years (IQR 36–47.5). HRV parameters were calculated using 24 h-ECG Holter. A kidney magnetic resonance imaging (MRI) scan 3 Tesla was performed to evaluate total kidney volume (TKV) and total fibrotic volume (TFV).ResultsA statistically significant positive linear correlation was observed between length of kidneys and frequency domain parameters as low frequency (LF) (r = 0.595, p < 0.05) and LFday (r = 0.587, p < 0.05). Moreover, a statistically significant positive linear correlation exists between high frequency (HF) and TFV (r = 0.804, p < 0.01) or height-adjusted (ha) TFV (r = 0.801, p < 0.01). Finally, we found a statistically significant positive linear correlation between HFnight and TKV (r = 0.608, p < 0.05), ha-TKV (r = 0.685, p < 0.01), TFV (r = 0.594, p < 0.05), and ha-TFV (r = 0.615, p < 0.05).ConclusionWe suppose that the increase in TKV and TFV could lead to a parasympathetic tone hyperactivation, probably in response to hypoxic stress and vasoconstriction due to cystic enlargement.

Association of heartbeat complexity with survival in advanced non-small cell lung cancer patients.

Previous studies have shown that the predictive value of traditional linear (time domain and frequency domain) heart rate variability (HRV) for the survival of patients with advanced non-small cell lung cancer (NSCLC) is controversial. Nonlinear methods, based on the concept of complexity, have been used to evaluate HRV, providing a new means to reveal the physiological and pathological changes in HRV. This study aimed to assess the association between heartbeat complexity and overall survival in patients with advanced NSCLC. This study included 78 patients with advanced NSCLC (mean age: 62.0 ± 9.3 years). A 5-min resting electrocardiogram of advanced NSCLC patients was collected to analyze the following HRV parameters: time domain indicators, i.e., standard deviation of the normal-normal intervals (SDNN) and root mean square of successive interval differences (RMSSD); frequency domain indicators, i.e., total power (TP), low frequency power (LF), high frequency power (HF), and the ratio of LF to HF (LF/HF); nonlinear HRV indicators characterizing heartbeat complexity, i.e., approximate entropy (ApEn), sample entropy (SampEn), and recurrence quantification analysis (RQA) indexes: mean diagonal line length (Lmean), maximal diagonal line length (Lmax), recurrence rate (REC), determinism (DET), and shannon entropy (ShanEn). Univariate analysis revealed that the linear frequency domain parameter HF and nonlinear RQA parameters Lmax, REC, and DET were significantly correlated with the survival of advanced NSCLC patients (all p < 0.05). After adjusting for confounders in the multivariate analysis, HF, REC, and DET were found to be independent prognostic factors for the survival of patients with advanced NSCLC (all p < 0.05). There was an independent association between heartbeat complexity and survival in advanced NSCLC patients. The nonlinear analysis method based on RQA may provide valuable additional information for the prognostic stratification of patients with advanced NSCLC and may supplement the traditional time domain and frequency domain analysis methods.

Heart rate variability modification as a predictive factor of sudden unexpected death in epilepsy: How far are we? A systematic review and meta-analysis.

Sudden unexpected death in epilepsy (SUDEP) is a sudden, unexpected death in people with epilepsy, with or without evidence of an epileptic seizure. The pathophysiological mechanism underlying SUDEP appears to be partly associated with an autonomic nervous system (ANS) dysfunction. Heart rate variability (HRV) analysis is a reliable, non-invasive method for detecting fluctuations in the ANS. In this systematic review we analyzed the data available in the literature on changes in HRV parameters in patients with SUDEP. We carried out a systematic search of the literature to identify the quantitative variations of HRV in epileptic patients with SUDEP. The following databases were used: Pubmed, Google Scholar, EMBASE, and CrossRef. A pooled analysis was carried out, and the results obtained were compared using mean difference (MD). The review was registered on the PROSPERO platform (CRD42021291586). Seven articles were included, with a total of 72 SUDEP cases associated with altered HRV parameters. Generally, a reduction of SDNN (standard deviation of the RR intervals) and RMSSD (root mean square differences of successive RR intervals) was reported in most SUDEP patients. According to MD, the SUDEP patients showed no differences in time and frequency domain parameters compared to controls. However, a trend toward increased low frequency and high frequency ratio (LF/HF) was observed in the SUDEP patients. HRV analysis is a valuable method for assessing cardiovascular risk and cardioautonomic impairment. Although a possible association between HRV variation and SUDEP has been reported, further studies are needed to assess the potential role of HRV modifications as a SUDEP biomarker.

AUTONOMIC DYSFUNCTION IN EXTREME OBESITY

Abstract: Heart rate variability (HRV) provides valuable information in various clinical settings. Limited information exists on changes in cardiac autonomic modulation in extremely obese patients (BMI&gt;40). The aim of this study was to investigate the influence of extreme (morbid) obesity and concomitant diseases on cardiovascular autonomic function. Participants of this study are 40 women and 40 men in mean age 47,9 years old diagnosed with morbid obesity (mean BMI 47,49) and hospitalized to further bariatric treatment. In 42 patients diagnosed with hypertension (treated with beta blockers and ACE inhibitors along with well controlled blood pressure), type 2 diabetes (treatment with the oral drugs) also occurred. Furthermore, 46 patients were diagnosed with depression. None of the participants used antidepressants or sedative agents. Total of 80 healthy (40 women and 40 men) in mean age 42,7 years old and with mean BMI 24,6 were formed in group of controls. All of patients had 24-hour ECG monitoring with Holter method in order to evaluate the autonomic activity with time and frequency domain analysis (heart rate variability - HRV). Results: Obese group showed a significant reduction of parasympathetic activity and a significant increase in sympathetic activity. No significant differences in cardiac autonomic modulation were noted between the Hypertensive-Diabetic patients and those, only with morbid obesity. However, in studied group, obese patients with depression had lower time and frequency domain parameters (p&lt;0.05) except SDNN, SDANN and LF/HF ratio in contrast to obese non-depressive individuals. Additional load of diabetes and hypertension in depressed patients did not affect the cardiac autonomic modulation differences. Further prospective study can be undertaken within the same subjects to evaluate the effect of weight loss on the cardiac autonomic activity. Conclusions: 1. Extreme obesity altered cardiac autonomic activity independently of hypertension and diabetes. 2. Depression associated with morbid obesity intensified HRV reduction.

Association of Heart Rate Variability with Obstructive Sleep Apnea in Adults.

Background and Objectives: Heart rate variability (HRV) analysis is a noninvasive method used to examine autonomic system function, and the clinical applications of HRV analysis have been well documented. The aim of this study is to investigate the association between HRV and the apnea-hypopnea index (AHI) in patients referred for polysomnography (PSG) for obstructive sleep apnea (OSA) diagnosis. Materials and Methods: Patients underwent whole-night PSG. Data on nocturnal HRV and AHI were analyzed. We determined the correlation of time- and frequency-domain parameters of HRV with the AHI. Results: A total of 62 participants (50 men and 12 women) were enrolled. The mean age, body mass index (BMI), neck circumference, and AHI score of the patients were 44.4 ± 11.5 years, 28.7 ± 5.2, 40.2 ± 4.8 cm, and 32.1 ± 27.0, respectively. The log root mean square of successive differences between normal heartbeats (RMSSD) were negatively correlated with BMI (p = 0.034) and neck circumference (p = 0.003). The log absolute power of the low-frequency band over high-frequency band (LF/HF) ratio was positively correlated with the AHI (p = 0.006). A higher log LF/HF power ratio (β = 5.01, p = 0.029) and BMI (β = 2.20, p < 0.001) were associated with a higher AHI value in multiple linear regression analysis. Conclusions: A higher log LF/HF power ratio and BMI were positively and significantly associated with the AHI during whole-night PSG in adult patients.

Challenges and future trends in wearable closed-loop neuromodulation to efficiently treat methamphetamine addiction.

Achieving abstinence from drugs is a long journey and can be particularly challenging in the case of methamphetamine, which has a higher relapse rate than other drugs. Therefore, real-time monitoring of patients' physiological conditions before and when cravings arise to reduce the chance of relapse might help to improve clinical outcomes. Conventional treatments, such as behavior therapy and peer support, often cannot provide timely intervention, reducing the efficiency of these therapies. To more effectively treat methamphetamine addiction in real-time, we propose an intelligent closed-loop transcranial magnetic stimulation (TMS) neuromodulation system based on multimodal electroencephalogram-functional near-infrared spectroscopy (EEG-fNIRS) measurements. This review summarizes the essential modules required for a wearable system to treat addiction efficiently. First, the advantages of neuroimaging over conventional techniques such as analysis of sweat, saliva, or urine for addiction detection are discussed. The knowledge to implement wearable, compact, and user-friendly closed-loop systems with EEG and fNIRS are reviewed. The features of EEG and fNIRS signals in patients with methamphetamine use disorder are summarized. EEG biomarkers are categorized into frequency and time domain and topography-related parameters, whereas for fNIRS, hemoglobin concentration variation and functional connectivity of cortices are described. Following this, the applications of two commonly used neuromodulation technologies, transcranial direct current stimulation and TMS, in patients with methamphetamine use disorder are introduced. The challenges of implementing intelligent closed-loop TMS modulation based on multimodal EEG-fNIRS are summarized, followed by a discussion of potential research directions and the promising future of this approach, including potential applications to other substance use disorders.

Alterations in heart rate variability and pro-inflammatory cytokine TNF-alpha in individuals with panic disorder

Based on the autonomic flexibility–neurovisceral integration model, panic disorder (PD) has been associated with a generalized proinflammatory state and lower cardiac vagal tone. The heart rate variability (HRV) provides an index of cardiac autonomic function and reflects the parasympathetic innervation to the heart regulated by the vagus nerve. The aim of this study was to explore the heart rate variability, pro-inflammatory cytokines and their associations in individuals with PD. Short-term HRV with time and frequency domain indices as well as pro-inflammatory cytokines Interleukin-6 (IL-6) and Tumor Necrosis Factor alpha (TNF-alpha) were assessed in seventy individuals with PD (mean age: 35.64 ± 14.21 years) and thirty-three healthy controls (mean age: 38.33 ± 14.14 years). Individuals with PD showed significantly lower HRV in the time and frequency domain parameters during a short-term resting condition. A lower TNF-alpha concentration could be observed in individuals with PD in comparison to healthy controls, but no differences in IL-6. Furthermore, the HRV parameter absolute power in the low-frequency band 0.04–0.15 Hz (LF) predicted TNF-alpha concentrations. In conclusion, a lower cardiac vagal tone, decreased adaptive autonomic nervous system (ANS), and higher pro-inflammatory cytokine state could be observed in individuals with PD compared to healthy controls.

Evaluation of autonomic nervous system functions by using tilt table test and heart rate variability in epileptic children

Objective: The value of head-up tilt test (HUTT) for differential diagnosis of epilepsy and the autonomic nervous system functions in&#x0D; epileptic children using heart rate variability (HRV) are studied.&#x0D; Patients and Methods: The study group consisted of 16 children with idiopatic/criptogenic epilepsy and 12 controls. Heart rate, PR&#x0D; interval, corrected QT (QTc) interval, QT and QTc dispersion were calculated using 12-lead electrocardiogram (ECG), HRV analysis&#x0D; was performed using the Holter recordings obtained both during HUTT and throughout the day. Time domain parameters, standard&#x0D; deviation of all RR intervals (SDNN), the standard deviation of mean NN intervals in five-minutes recording (SDANN), mean standard&#x0D; deviation of NN intervals in five-minutes recordings (SDNNi), root mean square of successive differences (RMSSD), count divided&#x0D; by the total number of all NN intervals (pNN50) and frequency domain parameters low frequency (LF), high frequency (HF), lowfrequency/&#x0D; high-frequency ratio (LF/HF) were calculated in both and compared between the two groups.&#x0D; Results: Head-up tilt test was positive in 4 epileptic children (25%), none of controls were positive. The heart rate of the patients were&#x0D; higher than the controls (p=0.015). LF/HF ratio in 24-hour Holter recordings, were significantly lower (1.13±0.6, 1.83±0.7 respectively,&#x0D; p=0.002); the SDANN during HUTT (28.7±20.2, 18.2 ± 19.9 respectively, p=0.024) were significantly higher in the patients than the&#x0D; controls.&#x0D; Conclusion: Head-up tilt test positivity is frequent in epileptic children, and cannot be used in differential diagnosis. HRV calculated&#x0D; both from 24 hour Holter recordings and Holter recordings under orthostatic stress were impaired in favour of parasympathetic&#x0D; system in epileptic children.

Effect of a slow-paced breathing with heart rate variability biofeedback intervention on pro-inflammatory cytokines in individuals with panic disorder - A randomized controlled trial

A generalized proinflammatory state has been observed in individuals with panic disorder (PD). There is evidence that slow-paced breathing (SPB) with heart rate variability-biofeedback (HRV-BF) strengthens the nervus vagus with its anti-inflammatory pathway. Therefore, with this randomized controlled trial we aimed to investigate the effect of a four-week SPB with HRV-BF intervention on pro-inflammatory cytokines in people with PD. Fifty-five individuals with PD (mean age: 37.22 ± 15.13 years) were randomly allocated either to SPB-HRV-BF (intervention group) or to HRV-Sham-BF (active control group). SPB-HRV-BF was performed over four weeks while cytokine concentration and HRV during a short-term resting condition were measured before and after intervention. SPB-HRV-BF decreased concentration of Tumor Necrosis Factor alpha (TNF-alpha) (F(1, 53) = 4.396, p ≤ .05, η2 = 0.077) in individuals with PD. In addition, SPB-HRV-BF demonstrated an increase in the HRV-time and frequency domain parameters SDNN, Total Power and LF during short-term resting condition. There was no intervention effect in HRV-Sham-BF group. In conclusion, SBP-HRV-BF as a non-pharmacological treatment may reduce pro-inflammatory cytokine TNF-alpha via the cholinergic anti-inflammatory pathway in individuals with PD. Based on the generalized proinflammatory state in PD, decreasing TNF-alpha is highly beneficial to reduce risk of cardiovascular diseases and metabolic syndrome.