Frequency-domain Measurements Research Articles

Comparative Study of Machine Learning Algorithms in Classifying HRV for the Driver’s Physiological Condition

Heart Rate Variability (HRV) may be used as a psychological marker to assess drivers’ states from physiological signals such as an electrocardiogram (ECG), electroencephalogram (EEG), and photoplethysmography (PPG). This paper reviews HRV acquisition methods from drivers and machine learning approaches for driver cardiac health based on HRV classification. The study examines four publicly available ECG datasets and analyzes their HRV features, including time domain, frequency domain, short-term measures, and a combination of time and frequency domains. Eight machine learning classifiers, namely K-Nearest Neighbor, Decision Tree, Naive Bayes, Linear Discriminant Analysis, Support Vector Machine, Random Forest, Gradient Boost, and Adaboost, were used to determine whether the driver's state is normal or abnormal. The results show that K-Nearest Neighbor and Decision Tree classifiers had the highest accuracy at 92.86%. The study concludes by assessing the performance of machine learning algorithms in classifying HRV for the driver's physiological condition using the Man-Whitney U test in terms of accuracy and F1 score. We have statistical evidence to support that the prediction quality is different when HRV analysis applies these three sets: (i) time domain measures or frequency domain measures; (ii) frequency domain measures or short-term measures; and (iii) combining time and frequency domains or only frequency domains. Doi: 10.28991/CEJ-2023-09-09-013 Full Text: PDF

SNR Improvement of Optical Frequency Domain Polarimetry Against Laser Frequency Sweep Nonlinearity

A high-precision measurement of distributed polarization crosstalk (DPC) is necessary for developing the device with an ultrahigh polarization extinction ratio of even more than 80 dB. Optical frequency domain polarimetry (OFDP) is a novel DPC measurement method with a potential ultra-wide dynamic range. The degradation of dynamic range caused by interference phase error is a common issue in optical frequency domain measurement techniques. In this work, we enhanced the dynamic range by solving the phase error problem induced by the laser frequency sweep nonlinearity to improve the measurement precision of weak polarization crosstalk. The aliasing issue caused by the fluctuation of the frequency sweep rate is the primary reason for the limited dynamic range. We proposed a modified dynamic range limit model of OFDP considering the aliasing issue. The experimental results agree with the inflection points predicted by the modified dynamic range limit model. Under the guidance of the model, we achieved a dynamic range of more than 115 dB with different optical path differences of the interferometer and various sweep rates of the laser. Compared to the DPC measurement method with a dynamic range of 100 dB, the measurement repeatability is improved from 7.0 dB to <1.0 dB for polarization crosstalk less than -95 dB.

Long-term stability of respiratory sinus arrhythmia among adults with and without a history of depression.

Respiratory sinus arrhythmia (RSA) is an index of parasympathetic nervous system activity reflecting respiratory influences on heart rate. This influence is typically measured as high frequency heart rate variability (HF-HRV) or root mean square of successive differences (RMSSD) of adjacent inter-beat intervals. Examining the long-term stability of its measurement is important as levels of resting RSA have been conceptualized as a marker of individual differences; in particular, of an individual's autonomic regulation and affect-related processes, including emotion regulation. At present, it is not known if resting RSA levels reflect stable differences over a long-term period (i.e., >1 year). Even less is known about how RSA stability differs as a function of depression history and whether it relates to depression risk trajectories. In the present study, we examined the 1.5-year test-retest reliability of resting RSA using the intraclass correlation coefficient (ICC) in 82 adults: n = 41 with a history of depression (ever-depressed); n = 41 controls with no depression history (never-depressed). HF-HRV was fairly stable in both groups (ever-depressed ICC = 0.55, never-depressed ICC = 0.54). RMSSD was also fairly stable in ever-depressed adults (ICC = 0.57) and never-depressed controls (ICC = 0.40). ICC values for both indices did not differ between groups per overlapping 95% confidence intervals. Therefore, RSA stability as assessed by both frequency (HF-HRV) and time domain (RMSSD) measures was not attenuated by a depression history. Implications and the need for future research are discussed.

Altered Heart Rate Variability During Rest in Schizophrenia: A State Marker.

Autonomic nervous system (ANS) imbalance has been reported in a number of psychiatric disorders such as depression, schizophrenia, panic disorder, etc. Autonomic dysfunction in schizophrenia has been associated with the symptoms and manifestation of psychosis. Heart rate variability (HRV) as a tool has been widely used to assess ANS activity and the effect of disease on the sympathovagal balance. Therefore, in the present study, HRV derived from electrocardiogram (ECG) lead II at rest was investigated in order to understand the changes in frequency domain measures in patients with schizophrenia and their first-degree relatives compared to healthy controls. Twenty-five patients with schizophrenia, 24 first-degree relatives of patients, and 24 healthy controls (Diagnostic and Statistical Manual of Mental Disorders (DSM)-5; 18-45 years) were included in the study. HRV of the subjects was measured after five minutes of rest. ECG lead II was recorded for five minutes and HRV was analysed in the frequency domain: low frequency (LF), high frequency (HF), total power, and LF/HF ratio. HRV parameters and heart rate were statistically analysed for group comparisons using general linear model multivariate analysis. Patients had significantly higher minimum heart rate and lower HF (normalized units (nu)) compared to their first-degree relatives. A trend was observed in HF (nu) with the lowest in patients followed by healthy controls and first-degree relatives and LF/HF ratio was the highest in patients followed by healthy controls and first-degree relatives, although not statistically significant. No significant difference was found between first-degree relatives and healthy controls. The alteration of HRV in schizophrenia could be attributed to reduction in vagal tone and sympathetic dominance, which in turn could serve as state markers of schizophrenia.

Three-dimensional oxygen concentration monitoring in hydrogels using low-cost phosphorescence lifetime imaging for tissue engineering.

Oxygen concentration measurement in 3D hydrogels is vital in 3D cell culture and tissue engineering. However, standard 3D imaging systems capable of measuring oxygen concentration with adequate precision are based on advanced microscopy platforms, which are not accessible in many laboratories due to the system's complexity and the high price. In this work, we present a fast and low-cost phosphorescence lifetime imaging design for measuring the lifetime of oxygen-quenched phosphorescence emission with 0.25 µs temporal precision and sub-millimeter spatial resolution in 3D. By combining light-sheet illumination and the frequency-domain lifetime measurement using a commercial rolling-shutter CMOS camera in the structure of a conventional optical microscope, this design is highly customizable to accommodate application-specific research needs while also being low-cost as compared to advanced instruments. As a demonstration, we made a fluidic device with a gas-permeable film to create an artificial oxygen gradient in the hydrogel sample. Dye-embedded beads were distributed in the hydrogel to conduct continuous emission lifetime monitoring when nitrogen was pumped through the fluidic channel and changed oxygen distribution in the sample. The dynamics of the changes in lifetime co-related with their location in the gel of size 0.5 mm×1.5 mm×700 µm demonstrate the ability of this design to measure the oxygen concentration stably and precisely in 3D samples.

A calibration method of ground-airborne frequency domain electromagnetic receving system based on magnetic source excitation

In the ground-airborne frequency domain electromagnetic detection, the receving system converts the magnetic field signal into an electrical signal representing the magnetic field signal. In order to accurately obtain the relationship between the magnetic field signal and the electrical signal, it is necessary to avoid the influence of environment and other factors on the system accuracy through on-site calibration. This requires high calibration accuracy, simple operation, portable equipment and strong adaptability to the environment. However, the existing calibration methods put forward higher requirements for instruments and environment. For example, the calibration of uniform magnetic field generated by Helmholtz coil needs to shield external magnetic field interference. In this paper, an overall calibration method of measurement system based on magnetic source excitation is proposed to meet the requirements of electromagnetic field accurate measurement in ground-airborne frequency domain. Firstly, based on the electromagnetic measurement method in ground-airborne frequency domain, the overall calibration method and principle of the detection system are introduced. Then, based on the computable standard magnetic field generated by the magnetic source transmitting coil, determine the measured voltage obtained by the receiving system, get the calibration coefficient of the receiving system. At last,the source of standard uncertainty related to calibration is analyzed, and the uncertainty is evaluated. In addition, the method is verified by comparing the calibration results with those obtained by Braunbeck coil calibration.

The Cardiac Comeback-Beating Stronger: Exploring the Remarkable Resilience of the Heart in COVID-19 Recovery through Cardiac Autonomic Analysis.

Background and Objectives: Analyzing the cardiac autonomic function in COVID-19 patients can provide insights into the impact of the virus on the heart's regulatory mechanisms and its recovery. The autonomic nervous system plays a crucial role in regulating the heart's functions, such as heart rate, blood pressure, and cardiac output. This study aimed to investigate the impact of COVID-19 on heart rate variability (HRV) during a 6-min walk test (6MWT). Materials and Methods: The study included 74 participants, consisting of 37 individuals who had recovered from mild to moderate COVID-19 and 37 healthy controls. The study assessed heart rate variability (HRV) and blood pressure both before and after a 6-min walk test (6MWT). Results: The study found significant differences in a few time domains (SDNN and pNN50) and all frequency domain measures, whereas there were no significant differences in demographic characteristics or blood pressure between COVID-19-recovered individuals and healthy controls at rest. There were significant 6MWT effects on average HR, time-domain (SDNN and pNN50) measures of HRV, and all frequency domain measures of HRV. A significant group × 6MWT interaction was found for SDNN, pNN50, total power, Ln total power, LF, HF, Ln LF, Ln HF, and LF nu. Conclusions: Cardiac Autonomic analysis through HRV is essential to ensure the continued health and well-being of COVID-19 survivors and to minimize the potential long-term impacts of the disease on their cardiovascular system. This suggests that HRV analysis during the recovery phase following exercise could serve as a valuable tool for evaluating the physiological effects of COVID-19 and monitoring the recovery process.

Investigating the Effect of Data Length on the Performance of Frequency-Domain fNIRS Functional Connectivity Measures.

Resting-state functional connectivity is a promising tool for understanding and characterizing brain network architecture. However, obtaining uninterrupted long recording of resting-state data is challenging in many clinically relevant populations. Moreover, the interpretation of connectivity results may heavily depend on the data length and functional connectivity measure used. We compared the performance of three frequency-domain connectivity measures: magnitude-squared, wavelet and multitaper coherence; and the effect of data length ranging from 3 to 9 minutes. Performance was characterized by distinguishing two groups of channel pairs with known different connectivity strengths. While all methods considered improved the ability to distinguish the two groups with increasing data lengths, wavelet coherence performed best for the shortest time window of 3 minutes. Knowledge of which measure is more reliably used when shorter fNIRS recordings are available could make the utility of functional connectivity biomarkers more feasible in clinical populations of interest.

Circadian patterns of heart rate variability in fetal sheep after hypoxia-ischaemia: A biomarker of evolving brain injury.

Hypoxia-ischaemia (HI) before birth is a key risk factor for stillbirth and severe neurodevelopmental disability in survivors, including cerebral palsy, although there are no reliable biomarkers to detect at risk fetuses that may have suffered a transient period of severe HI. We investigated time and frequency domain measures of fetal heart rate variability (FHRV) for 3weeks after HI in preterm fetal sheep at 0.7 gestation (equivalent to preterm humans) until 0.8 gestation (equivalent to term humans). We have previously shown that this is associated with delayed development of severe white and grey matter injury, including cystic white matter injury (WMI) resembling that observed in human preterm infants. HI was associated with suppression of time and frequency domain measures of FHRV and reduced their circadian rhythmicity during the first 3 days of recovery. By contrast, circadian rhythms of multiple measures of FHRV were exaggerated over the final 2weeks of recovery, mediated by a greater reduction in FHRV during the morning nadir, but no change in the evening peak. These data suggest that the time of day at which FHRV measurements are taken affects their diagnostic utility. We further propose that circadian changes in FHRV may be a low-cost, easily applied biomarker of antenatal HI and evolving brain injury. KEY POINTS: Hypoxia-ischaemia (HI) before birth is a key risk factor for stillbirth and probably for disability in survivors, although there are no reliable biomarkers for antenatal brain injury. In preterm fetal sheep, acute HI that is known to lead to delayed development of severe white and grey matter injury over 3weeks, was associated with early suppression of multiple time and frequency domain measures of fetal heart rate variability (FHRV) and loss of their circadian rhythms during the first 3 days after HI. Over the final 2weeks of recovery after HI, exaggerated circadian rhythms of frequency domain FHRV measures were observed. The morning nadirs were lower with no change in the evening peak of FHRV. Circadian changes in FHRV may be a low-cost, easily applied biomarker of antenatal HI and evolving brain injury.

IDENTIFICATION OF THE NATURAL FREQUENCY OF THE OFFSHORE TRUSS STRUCTURE FROM MULTIPLE SIMULATED MEASURED DATA

This article presents identification methods of the natural frequency of structures from single or multiple measurements in the frequency domain and its application to identify the natural frequencies of the offshore truss structure. The simulated measurements of structural vibrations in the time domain are determined by analyzing the finite element model of the offshore truss structure subjected to random dynamic loads using SAP2000 software. The frequency domain measurements are obtained by the fast Fourier transform of time domain measurements using MATLAB software. The identification method from the multiple combined frequency response function measurements can estimate more natural frequencies than using a single measurement. A study of the considered frequency range was also performed showing the accuracy of the identification methods compared with the finite element model. By subdividing the considered frequency range, it is possible to improve the accuracy of the obtained natural frequencies.

Motor Skills, Heart Rate Variability, and Arterial Stiffness in Children with Autism Spectrum Disorder.

The prevalence of autism spectrum disorder (ASD) among children has been recently increasing. The severity of symptoms greatly varies between individuals with ASD, ranging from relatively mild to extremely severe. It is important to have a clearer understanding of the possible adverse consequences resulting from this disorder, such as delayed motor development, autonomic dysregulation, and arterial stiffness. Thus, the objective of this study was to investigate differences in motor skills, heart rate variability (HRV), and arterial stiffness between children with ASD and typically developing children. In this study, the school-aged children with mild symptoms of ASD (n = 17, 11.1 ± 1.0 years old) and typically developing peers (n = 15, 11.0 ± 0.5 years old) were recruited. Motor skills, HRV, and arterial stiffness were measured in these two groups. Motor skills were evaluated by the Bruininks-Oseretsky Test of Motor Proficiency-Second Edition. Moreover, HRV was measured through a short-term recording using the Polar heart rate monitor, and arterial stiffness was assessed by non-invasive computerized oscillometry. Compared with the typically developing group, children with ASD displayed significant deficits in some areas of motor skills, including manual coordination, strength and agility, and total motor composite. Moreover, children with ASD exhibited significantly reduced HRV, including time- and frequency-domain measures. However, the results did not demonstrate any statistically significant differences in arterial stiffness between the groups. Our findings demonstrated the presence of motor skill deficits and autonomic dysregulation in children with ASD.

Heart Rate Variability in Normotensive and Hypertensive Adults After a Year of Receiving Oxford/AstraZeneca COVID-19 Vaccine: A Cross-Sectional Observational Study.

Background and aim Heart rate variability (HRV) helps in assessing the autonomic nervous system's function, which has been implicated in cardiovascular disease risk. HRV has been found to be deranged in hypertension. In addition, studies have shown that COVID-19 infection and vaccination can affect HRV. However, the long-term effect of HRV on hypertension has not been explored after COVID-19 vaccination. The objective of this study was to observe the HRV in hypertensive adults after one year of receiving the Oxford/AstraZeneca COVID-19 vaccine and to compare it with normotensive adults. Methods The study included 105 normotensives (blood pressure below 120/80 mmHg) and 75 hypertensive participants who had received the Oxford/AstraZeneca COVID-19 vaccine one year prior. HRV was measured using the PowerLab system (ADInstruments) with the participants in a sitting posture. The HRV parameters assessed included the time domain, frequency domain, and nonlinear measures. Data were presented in descriptive and inferential statistical terms, and the parameters of two groups of individuals were compared by either an unpaired t-test or the Mann-Whitney U test. Results A total of 105 normotensive participants with a mean age of 42.51 ± 9.28 years and 75 hypertensive participants with a mean age of 44.24 ± 10.19 years comprised the sample (p=0.24). Normotensive individuals had a higher standard deviation of RR intervals, a higher coefficient of variation of RR intervals, a higher standard deviation of heart rate, and a higher percentage of successive differences in RR intervals in the time domain. They also had higher values of very low-frequency power, low-frequency (LF) power, and high-frequency (HF) power in the frequency domain. The LF/HF ratio was not significantly different between the two groups. In nonlinear analysis, SD2, a measure of long-term heart rate variability, was higher in normotensive individuals. Conclusion The Oxford/AstraZeneca COVID-19 vaccine did not have a significant effect on HRV parameters in normotensive and hypertensive adults one year after vaccination. However, changes in HRV parameters were observed between supine and standing positions, suggesting the importance of postural changes in HRV assessment.

The effect of a novel lifestyle intervention on autonomic and haemodynamic function in individuals with hypertrophic cardiomyopathy

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – EU funding. Main funding source(s): This project has received funding from the European Union’s Horizon 2020 Research and Innovation Programme under Grant Agreement no. 777204. Background Autonomic nervous system may play an important role in the pathophysiology of hypertrophic cardiomyopathy (HCM). Lifestyle interventions have been shown to improve signs and symptoms in individuals with heart failure. Purpose To evaluate the effect of a novel lifestyle intervention incorporating physical activity and dietary nitrate supplementation on cardiac autonomic and haemodynamic function in individuals with HCM. Methods Twenty-eight individuals with HCM were recruited into a single-centre pilot study (N=7 females, age 54±15 years) and randomised into the intervention (N=20) or control (N=8) group. Participants completed short-term (5-minute) non-invasive heart rate variability (HRV) measurements under resting (supine) conditions using the TaskForce (CNSystems, Graz, Austria). Frequency-domain HRV measures including spectral analysis of RR interval (i.e. absolute and normalised low frequency power (LF), high frequency power (HF) and LF/HF ratio) were recorded. Non-invasive haemodynamic variables including cardiac output (CO), and stroke volume (SV)were simultaneously recorded using bioimpedance technology integrated within the TaskForce. Intervention participants consumed 6 mmol of nitrate daily (concentrated beetroot juice) and increased and maintained their daily physical activity by ≥2000 steps/day above baseline for 16 weeks. Participants in the control group continued with their usual lifestyle and monitored daily step counts. Physical activity was evaluated objectively using pedometers (Omron Health, Japan). All participants were monitored weekly via telephone calls and average daily activity levels were recorded using diaries. However, participants in the control group were asked not to change their physical activity and dietary habits. Results Participants in the intervention group significantly increased their average physical activity by 3029 steps post intervention (i.e, 6234±2389 vs 9263± 3341 steps/day, p&amp;lt;0.01) compared to control (7559±3257 vs 7604± 2901 steps/day, p=0.96). There was a significant increase in post-intervention HF power (7.54±2.14 vs. 8.78±1.60 ms2, p&amp;lt;0.01) and LF power (6.89±2.33 vs. 8.17±1.55, p&amp;lt;0.01) respectively, but not in the control group (i.e., HF (7.05±3.39 vs. 7.64±2.56 ms2, p=0.33) and LF power (6.78±3.31 vs. 7.06±2.43 ms2 p=0.63)). There was a non-significant change in SV index in the intervention (33±9.83 vs. 29±8.56 ml/beat/m2, p=0.06) and control groups (34±6.27 vs. 33±8.1 ml/beat/m2, p=0.79). Similarly, there was no significant change in cardiac index in the intervention or control groups (intervention: 2.35±0.44 vs. 2.38±0.52 L/min/m2, p=0.77; control: 2.27±0.40 vs. 2.67±0.78, p=0.06). Conclusions Lifestyle intervention incorporating physical activity and dietary nitrate supplementation led to a significant increase in daily physical activity and improved parasympathetic activity in hypertrophic cardiomyopathy.

On the performance stability of MCF-based SDM system affected by inter-core crosstalk fluctuation.

The inter-core crosstalk (IC-XT) of multi-core fiber (MCF) limits the capacity of space division multiplexing system (SDM) fundamentally. We develop a closed-form expression of the magnitude of IC-XT for various types of signals, which can well explain the mechanism of different fluctuation behaviors of the real-time short-term average crosstalk (STAXT) and bit error ratio (BER) for the optical signals with and without strong optical carrier. The experimental verifications with the real-time measurement of the BER and outage probability in a 7 × 10-Gb/s SDM system agree well with the proposed theory and confirm that the unmodulated optical carrier plays a substantial role in fluctuation of BER. The range of fluctuation can be reduced by 3 orders of magnitude for the optical signal without optical carrier. We also investigate the effect of IC-XT in a long-haul transmission system based on a recirculating 7-core fiber loop and develop a frequency-domain IC-XT measurement technique. Longer transmission distance is shown to have a narrower BER fluctuation range, since IC-XT is no longer the only dominant factor on transmission performance.

Optimizing a two-layer method for hybrid diffuse correlation spectroscopy and frequency-domain diffuse optical spectroscopy cerebral measurements in adults.

The sensitivity to extracerebral tissues is a well-known confounder of diffuse optics. Two-layer (2L) head models can separate cerebral signals from extracerebral artifacts, but they also carry the risk of crosstalk between fitting parameters. We aim to implement a constrained 2L head model for hybrid diffuse correlation spectroscopy (DCS) and frequency-domain diffuse optical spectroscopy (FD-DOS) data and to characterize errors in cerebral blood flow and tissue absorption with the proposed model. The algorithm uses the analytical solution of a 2L cylinder and an a priori extracerebral layer thickness to fit multidistance FD-DOS (0.8 to 4cm) and DCS (0.8 and 2.5cm) data, assuming homogeneous tissue reduced scattering. We characterized the algorithm's accuracy for simulated data with noise generated using a 2L slab and realistic adult head geometries and for in vitro phantom data. Our algorithm recovered the cerebral flow index with 6.3 [2.8, 13.2]% and 34 [30, 42]% (median absolute percent error [interquartile range]) for slab and head geometries, respectively. Corresponding errors in the cerebral absorption coefficient were 5.0 [3.0, 7.9]% and 4.6 [2.4, 7.2]% for the slab and head geometries and 8 [5, 12]% for our phantom experiment. Our results were minimally sensitive to second-layer scattering changes and were robust to cross-talk between fitting parameters. In adults, the constrained 2L algorithm promises to improve FD-DOS/DCS accuracy compared with the conventional semi-infinite approach.

Evidence of Sympathetic Overactivity in Subjects with REM Behavior Disorder at Risk for Parkinson’s Disease (P6-13.002)

<h3>Objective:</h3> To evaluate sympathetic nervous system (SNS) activity in subjects with REM sleep behavior disorder (RBD) at risk of Parkinson’s disease, using imaging and autonomic functions markers. <h3>Background:</h3> While the nature of RBD is not completely understood, there is evidence that enhancement of noradrenergic activity may play a causative role, as suggested by evidence of persistent tonic discharge of locus coeruleus (LC) and RBD-triggering action of selective norepinephrine reuptake inhibitors. <h3>Design/Methods:</h3> Subjects &gt;50 years old with RBD with at least one pre-motor PD symptom (hyposmia, constipation, depression) were tested with a battery of autonomic evaluations including SCOPA-AUT questionnaire, cardiac MIBG scintigraphy, Heart Rate Variability (HRV) and neuromelanin sensitive MRI (NSMRI) of LC and substantia nigra (SN). Analyzed variables included: 1) for MIBG, late heart/mediastinum (H/M) ratio and washout ratio (WR); 2) for HRV, time and frequency domain measures; 3) for NSMRI, contrast-to-noise ratio (CNR) between LC and pons and between substantia nigra (SN) and cerebral peduncles. Results were compared with available normative ranges. <h3>Results:</h3> 14 subjects (11M, age 66.2±8.2) were enrolled. Average total SCOPA-AUT score was increased (12.1±6.7 vs 8.8±5.4), with gastrointestinal (2.4±2.1 vs 1.4±1.6), urinary (5.4±2.7 vs 3.9±2.4) and cardiovascular (0.86±1.10 vs 0.3±0.6) scores above normal ranges. MIBG late H/M ratio was reduced (1.45±0.31) with increased WR (33.0±14.8). HRV results showed enhanced sympathetic and low parasympathetic activity both in time (SDNN 106.8±73.2ms; RMSSD 21.9±10.9ms; PNN50% 6.7±8.4%) and frequency domain (LF/HF 3.4±1.8). NMSMRI showed high LC CNR (right 3.26±1.9 vs 2.08±0.5; left 2.95±0.9 vs 2.79±0.5). SN CNR was high (Medial 6.24±1.9 vs 4.57±0.8; Central 6.26±1.6 vs 3.43±0.6; Lateral 3.44±2.1 vs 3.05±0.5) and MDS-UPDRS motor scores were low (2.9±3.3). <h3>Conclusions:</h3> RBD subjects at risk for PD show abnormal autonomic scores, which appears to be driven by SNS overactivity, as suggested by increased MIBG WR, elevated LF/HF HRV ratios and increased LC and SN NSMRI signal. <b>Disclosure:</b> Dr. Tagliati has received personal compensation in the range of $10,000-$49,999 for serving as a Consultant for Abbott. Dr. Tagliati has received personal compensation in the range of $10,000-$49,999 for serving as a Consultant for Boston Scientific. Dr. Tagliati has received personal compensation in the range of $500-$4,999 for serving as a Consultant for Supernus. Dr. Tagliati has received personal compensation in the range of $500-$4,999 for serving as a Consultant for NeuroDerm. Dr. Tagliati has received publishing royalties from a publication relating to health care. Dr. Gregorio has nothing to disclose. Dr. Maghzi has nothing to disclose. Gloria Obialisi has nothing to disclose. Dr. Hogg has nothing to disclose. Dr. Malatt has nothing to disclose. Dr. Tan has received personal compensation in the range of $5,000-$9,999 for serving on a Speakers Bureau for Allergan. Dr. Artal has received personal compensation in the range of $5,000-$9,999 for serving on a Speakers Bureau for Jazz Pharmaceuticals. Dr. Artal has received personal compensation in the range of $10,000-$49,999 for serving as an Expert Witness for Private Parties. The institution of Dr. Artal has received research support from Jazz Pharma. The institution of Dr. Artal has received research support from Axsome. The institution of Dr. Artal has received research support from Suven. Dr. Shehata has received personal compensation in the range of $500-$4,999 for serving as a Consultant for Abbott. Brian Renner has nothing to disclose. The institution of Dr. Sati has received research support from National Multiple Sclerosis Society. The institution of Dr. Sati has received research support from National Institutes of Health. Dr. Sati has received publishing royalties from a publication relating to health care.

A combined heart rate variability biofeedback and progressive aerobic exercise intervention for remediating persistent post-concussive symptoms. (P7-1.006)

<h3>Objective:</h3> Evaluate the combined benefit of heart-rate variability biofeedback (HRVB) and progressive aerobic exercise (PAE) for remediating persistent post-concussive symptoms (PPCS). <h3>Background:</h3> Cardio-autonomic dysfunction is a key patho-physiological process underlying PPCS. Therefore, any interventions targeting cardioautonomic dysfunction should help ameliorate PPCS. Preliminary research suggests PAE and HRVB can improve cardio-autonomic dysfunction and clinical symptoms. However, none have evaluated whether there is a combined benefit. <h3>Design/Methods:</h3> Participants were randomized into a six-week intervention consisting of either HRVB, PAE or HRVB+PAE. Concussion symptoms, HRV, cognition, and mood states were assessed pre- and post-intervention. The HRVB group practiced resonant-frequency breathing for 20 minutes, four nights a week. The PAE group completed a three-day-a-week aerobic exercise protocol that gradually increased in intensity and duration. The HRVB+PAE group completed HRVB training four nights a week and PAE three days a week. <h3>Results:</h3> Each intervention resulted in significant improvement in concussion symptoms, HRV, cognition, and mood states (ps≤.05). PAE resulted in greater reductions in sleep disturbance, depressive symptoms, and total mood disturbance than HRVB (ps≤.05). HRVB+PAE resulted in the largest improvements in cognition, depressive symptoms, and mood disturbance (ps≤.05), but had no additional benefit beyond HRVB or PAE for concussion symptoms, or PAE for sleep disturbance. Each intervention improved cardio-autonomic function as indexed by changes in both time and frequency domain measures of HRV (ps≤.05). Surprisingly, HRVB did not result in greater changes on any HRV metric than PAE (ps≥.19). However, HRVB+PAE resulted in greater changes in the time domain (RMSDD) and frequency domain (HF, coherence ratio) metrics beyond HRVB or PAE. <h3>Conclusions:</h3> Both HRVB and PAE can help ameliorate cardio-autonomic dysfunction but HRVB+PAE resulted in additive benefits in cardio-autonomic function, cognition, and psycho-affective health beyond HRVB or PAE alone. These interventions are low-cost, easy to implement, and may be a feasible non-pharmacological treatment for PPCS. <b>Disclosure:</b> Dr. Moore has nothing to disclose. Mr. Gunn has nothing to disclose. Mr. Kay has nothing to disclose.

Second harmonic injection locking of coupled spin torque vortex oscillators with an individual phase access

The synchronisation of magnetic tunnel junctions in the high frequency domain has attracted significant interest in the context of novel computation paradigms, specifically neuromorphic spintronics and probabilistic computing. In this work, a design for the coupling and synchronization of spin torque vortex oscillators (STVOs) is implemented. The geometry comprises the fabrication of adjacent pairs of STVO nanopillars (MgO-based magnetic tunnel junctions), with an edge-to-edge distance down to 100 nm, together with individual top contacts that allow an independent electrical access to each device. In this geometry, the magneto-dipolar coupling promotes the synchronization of the two oscillators, at the same time as the access to the frequency and phase of each individual oscillator is possible. Both frequency and time domain measurements confirm a successful synchronization, with the coupling being controlled by the relative DC bias in each oscillator. As a proof-of-concept towards an oscillator-based Ising machine, it is also shown that the second harmonic injection locking of an STVO can be controlled by tuning the magneto-dipolar coupling to its correspondent STVO pair. These results represent a step forward for the implementation of magneto-dipolar coupled magnetic tunnel junctions, specifically in the field of unconventional computing hardware.

Smartwatch-derived heart rate variability: a head-to-head comparison with the gold standard in cardiovascular disease.

We aimed to investigate the concordance between heart rate variability (HRV) derived from the photoplethysmographic (PPG) signal of a commercially available smartwatch compared with the gold-standard high-resolution electrocardiogram (ECG)-derived HRV in patients with cardiovascular disease. We prospectively enrolled 104 survivors of acute ST-elevation myocardial infarction, 129 patients after an ischaemic stroke, and 30 controls. All subjects underwent simultaneous recording of a smartwatch (Garmin vivoactive 4; Garmin Ltd, Olathe, KS, USA)-derived PPG signal and a high-resolution (1000 Hz) ECG for 30 min under standardized conditions. HRV measures in time and frequency domain, non-linear measures, as well as deceleration capacity (DC) were calculated according to previously published technologies from both signals. Lin's concordance correlation coefficient (ρc) between smartwatch-derived and ECG-based HRV markers was used as a measure of diagnostic accuracy. A very high concordance within the whole study cohort was observed for the mean heart rate (ρc = 0.9998), standard deviation of the averages of normal-to-normal (NN) intervals in all 5min segments (SDANN; ρc = 0.9617), and very low frequency power (VLF power; ρc = 0.9613). In contrast, detrended fluctuation analysis (DF-α1; ρc = 0.5919) and the square mean root of the sum of squares of adjacent NN-interval differences (rMSSD; ρc = 0.6617) showed only moderate concordance. Smartwatch-derived HRV provides a practical alternative with excellent accuracy compared with ECG-based HRV for global markers and those characterizing lower frequency components. However, caution is warranted with HRV markers that predominantly assess short-term variability.

Effects of Acute Hypoxia on Heart Rate Variability in Patients with Pulmonary Vascular Disease.

Pulmonary vascular diseases (PVDs), defined as arterial or chronic thromboembolic pulmonary hypertension, are associated with autonomic cardiovascular dysregulation. Resting heart rate variability (HRV) is commonly used to assess autonomic function. Hypoxia is associated with sympathetic overactivation and patients with PVD might be particularly vulnerable to hypoxia-induced autonomic dysregulation. In a randomised crossover trial, 17 stable patients with PVD (resting PaO2 ≥ 7.3 kPa) were exposed to ambient air (FiO2 = 21%) and normobaric hypoxia (FiO2 = 15%) in random order. Indices of resting HRV were derived from two nonoverlapping 5-10-min three-lead electrocardiography segments. We found a significant increase in all time- and frequency-domain HRV measures in response to normobaric hypoxia. There was a significant increase in root mean squared sum difference of RR intervals (RMSSD; 33.49 (27.14) vs. 20.76 (25.19) ms; p < 0.01) and RR50 count divided by the total number of all RR intervals (pRR50; 2.75 (7.81) vs. 2.24 (3.39) ms; p = 0.03) values in normobaric hypoxia compared to ambient air. Both high-frequency (HF; 431.40 (661.56) vs. 183.70 (251.25) ms2; p < 0.01) and low-frequency (LF; 558.60 (746.10) vs. 203.90 (425.63) ms2; p = 0.02) values were significantly higher in normobaric hypoxia compared to normoxia. These results suggest a parasympathetic dominance during acute exposure to normobaric hypoxia in PVD.