Frequency Domain Indices Research Articles

Cardiac autonomic changes elicited by energy-based healing modality: pilot study

Energy-based healing techniques have rarely been explored in current complementary therapies literature. This therapy is appropriate for cardiac nursing and can be implemented as part of nursing care. The authors investigated the acute effects of a standardised energy-based healing technique on cardiac autonomic regulation. Method: This study was conducted on 18 healthy students (15 female, three male), all non-smokers aged 18–35 years. Heart rate variability (HRV) was analysed 10 minutes before and 10 minutes after the energy-based healing technique was carried out. Geometric, time and frequency domain indices of HRV were examined. The subjects were blindfolded and sat at rest for 10 minutes, then received a standardised energy-based healing technique from an experienced male healer; they remained blindfolded and seated for a further 10 minutes. Results: Time and frequency domain indices of HRV were not significantly different before and after the energy-based healing technique. TINN (triangular interpolation histogram of RR intervals) (P=0.04) and RRTri (triangular index) (P=0.02) were increased after the therapy. A Poincaré plot indicated a slight increase in RR intervals dispersion after energy-based healing technique. Conclusion: A standardised energy-based healing technique marginally improved cardiac autonomic function in healthy subjects.

Effects of Low-Frequency Vibration on Physiological Recovery from Exhaustive Exercise

Objective: This study examined the effects of low-frequency vibration on physiological recovery from exhaustive exercise. Methods: Twelve college males were recruited in this randomized crossover-designed study, and were asked to perform one of three treatments following a graded cycling exercise test: nonvibration (0 Hz, 0 mm, CON), high-amplitude vibration (8 Hz, 8 mm, HVT), or low-amplitude vibration (8 Hz, 2 mm, LVT). After the 10-min treatment, participants were asked to rest in a supine position for a 1-h recovery. The oxygen uptake, heart rate (HR), and blood lactate concentration (La) were measured during the trials. Results: The oxygen uptake during HVT were significantly higher than those in the CON and LVT (p < 0.05, effect size = 1.52−1.63). The La immediately following HVT was significantly lower than that following CON (HVT vs. CON = 11.52 ± 1.85 vs. 12.95 ± 1.78 mmol•L-1, p < 0.05, effect size = 1.94). Additionally, the Las following HVT and LVT at the post 30-min were significantly lower than that following the CON (HVT vs. LVT vs. CON = 4.72 ± 0.97 vs. 4.58 ± 1.06 vs. 5.98 ± 1.49 mmol•L-1, p < 0.05). No significant differences were found on the HRs, or on the time and frequency domain indices of HR variability among treatments during the recovery period. Conclusion: These results indicated that vibration with low frequency (8 Hz) can facilitate the removal of metabolic by-products after exhaustive exercise, but it has little effect on the autonomic nervous modulation of HR recovery.

Modulation by NADPH oxidase of the chronic cardiovascular and autonomic interaction between cyclosporine and NSAIDs in female rats

Cyclosporine (CSA) and nonsteroidal antiinflammatory drugs (NSAIDs) are used together to manage arthritic disorders with an immune component. Previous reports showed contrasting effects for NSAIDs on CSA nephrotoxicity and acute elevations in blood pressure. Both effects were ameliorated or exaggerated after selective cyclooxygenase-2 (COX2) and nonselective COX inhibition, respectively. Here we investigated: (i) the interaction of CSA with NSAIDs possessing variable COX1/COX2 selectivities on hemodynamic, left ventricular (LV) and cardiac autonomic and histologic profiles, and (ii) role of NADPH-oxidase (NOX)/Rho-kinase (ROCK) pathway in the interaction. Female rats were pre-instrumented with femoral catheters and treated for 10 days with CSA (25mg/kg/day), diclofenac (nonselective NSAIDs, 1mg/kg/day), celecoxib (COX2 inhibitor, 10mg/kg/day), or their combinations. CSA-mediated hypertension was maintained upon co-administration of either NSAID whereas the concomitant reductions in time- and frequency-domain indices of heart rate variability (HRV) were accentuated in presence of diclofenac but not celecoxib. The isovolumic relaxation time (Τau), a measure of diastolic function, was reduced by all regimens whereas LV contractility (dP/dtmax) remained unaffected. The CSA/diclofenac regimen, but not individual treatments, increased cardiac NOX2 expression and caused more cardiac structural damage. The inhibition of NOX by diphenyleneiodonium reversed CSA/diclofenac-evoked increases in MAP, decreases in HRV and Tau, cardiac structural damage, and increased NOX2 expression. No such effects were observed after ROCK inhibition by fasudil, despite concomitant decreases in NOX2 expression. In conclusion, CSA/diclofenac-treated female rats exhibit exacerbated hemodynamic, autonomic, LV, and histopathologic disturbances via ROCK-independent NOX2 upregulation.

Opposite Modulatory Effects of Selective and Non-Selective Cyclooxygenase Inhibition on Cardiovascular and Autonomic Consequences of Cyclosporine in Female Rats.

Non-steroidal anti-inflammatory drugs (NSAIDs) and the immunosuppressant drug cyclosporine (CSA) are concurrently administered in arthritis. Here, we investigated whether diclofenac (non-selective inhibitor of cyclooxygenase-1 and 2, COX-1/COX-2), celecoxib (selective COX-2 inhibitor) or SC560 (selective COX-1 inhibitor) interact variably with haemodynamic effects of CSA in conscious female rats. Changes caused by CSA (10 mg/kg i.v.) in blood pressure (BP), heart rate (HR), HR variability (HRV) and myocardial contractility were assessed in the absence and presence of individual NSAIDs (10 mg/kg each). Compared with vehicle values, CSA caused immediate and sustained (i) increases in BP and decreases in pulse pressure index (PPI) and HR, (ii) elevations in left ventricular (LV) contractility (dP/dtmax ) and isovolumic relaxation constant (Τau) and (iii) increases in the time- and frequency-domain indices of HRV and shifted the cardiac sympathovagal balance towards parasympathetic dominance. CSA hypertension was abolished in rats pre-treated with celecoxib and intensified in the presence of diclofenac or SC560. Alternatively, the CSA-evoked decreases in PPI, increases in HRV indices and cardiac parasympathetic dominance were blunted by celecoxib in contrast to no effect for diclofenac or SC560. Similarly, celecoxib, but not other NSAIDs, eliminated the elevated LV contractility (dP/dtmax ) and isovolumic relaxation constant (Τau, τ), which reflect cardiac systolic and diastolic function, respectively, that accompanied the CSA-induced pressure load. The data underscore the preferential capacity of selective COX-2 inhibition by celecoxib to mitigate CSA hypertension and consequent alterations in cardiac performance and autonomic balance. By contrast, CSA effects are preserved or even exacerbated after COX-1 inhibition.

Differences in photoplethysmography morphological features and feature time series between two opposite emotions: Happiness and sadness

It has been well established that change in emotion state is associated with the change in physiological signals. This paper aimed to investigate the differences of finger photoplethysmography (PPG) morphological features and feature time series between happiness and sadness emotion states. Fifty-three volunteers were enrolled. Finger PPG signals were recorded under two emotion states with a random measurement order (first happiness emotion measurement then sadness or reverse). Seven morphological features were extracted, including three temporal features (T, T1 and T2), three area features (A, A1 and A2) and one amplitude feature (Amp). Five variability indices from the 5-min feature time series were calculated, including two time-domain indices (SDNN and RMSSD) and three frequency-domain indices (LFn, HFn and LF/HF). Results showed that temporal features T2 and T were critical features for identifying the two emotion states since not only they themselves but also their three frequency-domain variability indices had significant differences between the two emotion states. For area features, only two frequency-domain variability indices of LFn and HFn for A1 feature time series reported significant differences. Amplitude feature Amp itself, as well as its variability indices, did not had significant differences between the two emotion states. These results indicated that temporal features were more sensitive to response to emotion change than area and amplitude features. Moreover, compared with time-domain variability indices, frequency-domain variability indices were more suitable for short-term 5-min time series analysis for exploring the inherent but slight change due to the emotion effect.

Dry carbon/salt adhesive electrodes for recording electrodermal activity

In this work, dry carbon/salt adhesive (CSA) electrodes are found to be suitable for collecting electrodermal activity (EDA) signals. Silver/silver chloride (Ag/AgCl) electrodes have been considered as a reliable media to obtain EDA signals. However, mainly the cost and the need for a hydrogel layer make it difficult to disseminate the practice of using EDA signals in practical applications. A mixture of carbon salt and adhesive has shown to be suitable for collecting bioelectric signals (FLEXcon’s Patent #8,673,184). With the objective of testing how these electrodes compare for collecting EDA signals, AC and DC source devices were employed. Sixteen subjects underwent electric shocks and tonic emotional and cognitive stress. No significant differences were found in amplitude, onset-to-peak time and onset time between CSA and Ag/AgCl electrodes. Frequency-domain index, EDASympn, was not found to be different between the two electrode types. The time-varying spectral index was different between Ag/AgCl and EDA electrodes for DC devices, not for the AC devices. Ag/AgCl electrodes often polarized impeding the collection of EDA signals, suggesting that CSA electrodes provide better fidelity EDA measures. We conclude that CSA electrodes are a suitable surrogate of Ag/AgCl electrodes for collecting EDA signals.

Analysis of beat-to-beat blood pressure variability response to the cold pressor test in the offspring of hypertensive and normotensive parents.

Abnormal autonomic nervous regulation has an important role in the development of hypertension. As to whether blood pressure (BP) or BP variability represents the proper characteristics for predisposition to hypertension in Chinese young adults remains controversial. We studied the properties of the indices extracted from beat-to-beat BP during a 13 min cold pressor test (CPT). In this study, 69 Chinese young adults including 34 offspring of hypertensive parents (OHPs; 25.6±2.5 years) and 35 offspring of normotensive parents (ONPs; 25.3±2.3 years) were analyzed. We assessed the differences between the two groups regarding mean beat-to-beat BP and variability indices. Beat-to-beat BP variability indices included time-domain indices and frequency-domain indices. Our results showed that the differences in beat-to-beat systolic BP and mean BP levels between the OHPs and the ONPs were statistically significant (P<0.05). Furthermore, more BP variability indices in the frequency domain were significantly different between the two groups. We concluded that BP variability was superior to BP as an index to evaluate the cardiovascular and sympathetic reactivity to the CPT. Moreover, compared with time-domain BP variability, we found more differences in frequency-domain BP variability between the two groups, thus indicating that frequency-domain BP variability may be a potential index of predisposition to hypertension.

Lack of heart rate variability during sleep-related apnea in patients with temporal lobe epilepsy (TLE)-an indirect marker of SUDEP?

Apneas occurring during sleep may precipitate autonomic instability in epilepsy patients making them susceptible to sudden death (SUDEP). Literature on heart rate variability (HRV) during apnea among patients with temporal lobe epilepsy (TLE) is sparse. The aim of this study was to characterize the HRV during the peri-apneic period in patients with TLE and compare with HRV of matched healthy individuals during the overnight polysomnographic (PSG) recording. Further, the role of carbamazepine (CBZ) in modulating peri-apneic HRV in the above cohort was also assessed. Twenty patients diagnosed to have TLE (drug naive (n=10) or on CBZ monotherapy (n=10)) were compared with ten healthy controls. In both patients and controls, the time domain, frequency domain, and non-linear HRV indices were analyzed for 2min before and after apnea/hypopnea termination and compared using paired t test (p≤0.05). Additionally, the changes in HRV parameters in the peri-apnea/hypopnea period were compared between the three groups using one-way ANOVA followed by post hoc comparison (p≤0.05). The three study groups were age (p=0.21) and gender (p=0.27) matched. In controls (M/F=5:5; mean age 24.3±5.0years), there were significant changes in standard deviation of RR interval (SDNN), low frequency (LF) component and long-term HRV (SD2) parameters in the peri-apnea/hypopneic period. Conversely, in drug-naive TLE (M/F=6:4; mean age: 22.8±4.1years), all the HRV parameters, including non-linear measures were comparable in the pre- and post-apneic period. On the other hand, patients on CBZ (M/F=6:4; mean age 20.5±4.8years) showed significant changes in low-frequency nu (LFnu) and high-frequency nu (HFnu) components in the peri-apnea/hypopneic period. Comparison of the changes in HRV parameters in the peri-apnea/hypopnea period in patients with TLE and controls showed significantly lower changes in drug-naive TLE patients in SDNN, LF, and SD2 as compared to controls. This study showed that there was a lack of apnea-mediated HRV changes in patients with drug-naive TLE. This might suggest a possible alteration in reflex baroreceptor activation in patients with TLE, predisposing them to SUDEP, and this may be worsened with CBZ.

Localized evaluation of actuator tracking for real-time hybrid simulation using frequency-domain indices

Accurate actuator tracking plays an important role in real-time hybrid simulation (RTHS) to ensure accurate and reliable experimental results. Frequency-domain evaluation index (FEI) interprets actuator tracking into amplitude and phase errors thus providing a promising tool for quantitative assessment of real-time hybrid simulation results. Previous applications of FEI successfully evaluated actuator tracking over the entire duration of the tests. In this study, FEI with moving window technique is explored to provide post-experiment localized actuator tracking assessment. Both moving window with and without overlap are investigated through computational simulations. The challenge is discussed for Fourier Transform to satisfy both time domain and frequency resolution for selected length of moving window. The required data window length for accuracy is shown to depend on the natural frequency and structural nonlinearity as well as the ground motion input for both moving windows with and without overlap. Moving window without overlap shows better computational efficiency and has potential for future online evaluation. Moving window with overlap however requires much more computational efforts and is more suitable for post-experiment evaluation. Existing RTHS data from Network Earthquake Engineering Simulation (NEES) is utilized to further demonstrate the effectiveness of the proposed approaches. It is demonstrated that with proper window size, FEI with moving window techniques enable accurate localized evaluation of actuator tracking for real-time hybrid simulation.

A Hybrid Domain Degradation Feature Extraction Method for Motor Bearing Based on Distance Evaluation Technique

The vibration signal of the motor bearing has strong nonstationary and nonlinear characteristics, and it is arduous to accurately recognize the degradation state of the motor bearing with traditional single time or frequency domain indexes. A hybrid domain feature extraction method based on distance evaluation technique (DET) is proposed to solve this problem. Firstly, the vibration signal of the motor bearing is decomposed by ensemble empirical mode decomposition (EEMD). The proper intrinsic mode function (IMF) component that is the most sensitive to the degradation of the motor bearing is selected according to the sensitive IMF selection algorithm based on the similarity evaluation. Then the distance evaluation factor of each characteristic parameter is calculated by the DET method. The differential method is used to extract sensitive characteristic parameters which compose the characteristic matrix. And then the extracted degradation characteristic matrix is used as the input of support vector machine (SVM) to identify the degradation state. Finally, It is demonstrated that the proposed hybrid domain feature extraction method has higher recognition accuracy and shorter recognition time by comparative analysis. The positive performance of the method is verified.

Gender differences in cardiovascular autonomic milieu and its association with academic performance in young adults

Background: Initiated by biological plausibility and supported by the pilot study, we observed possibility of associations between cardiovascular autonomic milieu and academic performances. As there are established cognitive ability differences among gender in literature, we designed a study to observe the differences in the basal autonomic activity as well as the manner of association between autonomic activity and academic performance between genders. Considerable lacunae in literature on this aspect also warranted for scientific introspection on this lacuna. Aims and Objective: The aim of this study is to observe the association between resting short-term heart rate variability (HRV) indices and University marks of anatomy, biochemistry, and physiology in young male and female medical students. Materials and Methods: Cross-sectional observational study with 102 healthy young participants in which 34 boys and 68 girls between 18 and 22 years were included by convenient sampling after assessing the inclusion and exclusion criteria. HRV is computed under standard conditions as per the task force recommendations in time and frequency domains. The academic performance is assessed by University examination marks at the end of the 1st year. The comparison of HRV parameters, academic performance, and their associations was analyzed separately by gender. Type 1 error allowance fixed at 5% but considering the high dispersion of HRV data, P values between 0.1 and 0.05 were also discussed. Results: Mean RR intervals showed a negative correlation with academic performance in males. Time domain and geometric indices of HRV showed a negative correlation in boys but not in girls. In case of frequency domain indices, all indices of sympathetic activity showed a positive correlation with academic performance in boys and not in girls. Furthermore, sympathetic indices are more in males compared to females. All indices of parasympathetic reactivity were negatively correlated with academic performance in males. Conclusion: High-sympathetic activity is correlated with better cognitive ability in males but the same association is not seen in females.

Correlation of heart rate with heart rate variability in sedentary young Indian women

Background: Autonomic nervous system (ANS) provides physiological balance in our body by regulating many bodily functions through its sympathetic and parasympathetic branches. Heart rate variability (HRV) is noninvasive method to assess ANS control at sinoatrial node of heart. HRV is derived from variations in heart rate (HR) over time through RR intervals. Aim: This study aims to investigate the correlation between HR and time and frequency domain indices of HRV. Materials and Methods: The study included 32 sedentary young women (20–24 years) from Jamia Millia Islamia, India. Twenty minutes electrocardiograph (ECG) recording was done for HRV analysis and 6 seconds ECG was recorded for HR measurement. Time domain indices of HRV such as SDNN, RMSSD, PNN50, and frequency domain indices of HRV such as total power, low-frequency (LF) power, high-frequency (HF) power, and LF/HF ratio were obtained. Results: There was significant inverse correlation between HR and RMSSD (P = 0.03, r = −0.37) and PNN50 (P = 0.003, r = −0.49) and total power (P = 0.02, r = −0.39). SDNN (P = 0.82, r = −0.03), HF power (P = 0.55, r = −0.10) showed nonsignificant inverse correlation trends with HR. LF power (P = 0.62, r = 0.09) and LF/HF ratio (P = 0.81, r = 0.04) demonstrated nonsignificant linear correlation trend with HR. Conclusion: The findings of this study demonstrated that there is an inverse correlation between HRV and HR of sedentary young women. Lower HR is associated with higher HRV and vice versa. Therefore, HR should be taken into consideration when recording HRV. HR may act as a method to quickly assess the function of ANS.

Heart Rate Variability Among Children With Acquired Brain Injury.

ObjectiveTo find evidence of autonomic imbalance and present the heart rate variability (HRV) parameters that reflect the severity of paroxysmal sympathetic hyperactivity (PSH) in children with acquired brain injury (ABI).MethodsThirteen children with ABI were enrolled and age- and sex-matched children with cerebral palsy were selected as the control group (n=13). The following HRV parameters were calculated: time-domain indices including the mean heart rate, standard deviation of all average R-R intervals (SDNN), root mean square of the successive differences (RMSSD), physical stress index (PSI), approximate entropy (ApEn); successive R-R interval difference (SRD), and frequency domain indices including total power (TP), high frequency (HF), low frequency (LF), normalized HF, normalized LF, and LF/HF ratio.ResultsThere were significant differences between the ABI and control groups in the mean heart rate, RMSSD, PSI and all indices of the frequency domain analysis. The mean heart rate, PSI, normalized LF, and LF/HF ratio increased in the ABI group. The presence of PSH symptoms in the ABI group demonstrated a statistically significant decline of the SDNN, TP, ln TP.ConclusionThe differences in the HRV parameters and presence of PSH symptoms are noted among ABI children compared to an age- and sex-matched control group with cerebral palsy. Within the ABI group, the presence of PSH symptoms influenced the parameters of HRV such as SDNN, TP and ln TP.

Differential heart rate variability and physiological responses associated with accumulated short- and long-term stress in rodents

In this study, we tested the hypothesis that chronic stress has cumulative effects over time on heart rate variability (HRV) and physiological responses in a rodent model of chronic mild stress. Rats were exposed to either short-term (2weeks) or long-term (4weeks) stress, followed by a 1-week recovery period. Controls were normally housed rats that did not undergo the stress procedure. For electrocardiogram recordings, transmitters were implanted in all rats 10days before the onset of the experiment to allow recovery from surgery. To investigate physiological responses, body weight, temperature, sucrose preference, and serum corticosterone levels were measured weekly. Rats exposed to both short- and long-term stress showed significant reductions in body weight, which did not normalize after the recovery period. A significant difference was observed between short- and long-term stress groups in serum corticosterone levels, with long-term stress significantly increasing serum corticosterone levels, which remained elevated after the recovery period (P<0.05). HRV analysis indicated that long-term stress significantly decreased time-domain indexes, whereas significantly increased frequency-domain indexes were observed in the low-frequency range (0.1–1Hz). These results may represent dysfunction in parasympathetic/vagal modulation with hyperactivation of the sympathetic nervous system after long-term exposures to stress. In addition, prolonged Q-to-T wave (QT) intervals were observed in rats exposed to long-term stress, which did not return to baseline levels after the recovery period. These findings are consistent with the view that chronic stress is associated with cardiac autonomic disorders and emphasize the importance of monitoring stress in our daily life since the effects of even mild stress may be cumulative.

Assessment of heart rate variability and reaction time in traffic policemen

Introduction: Air Pollution can have a deleterious effect on cardiovascular function and cognition. Heart rate variability (HRV), which is a non-invasive and objective measure of cardiac autonomic function, is a cardiovascular risk predictor. Reaction time is a simple method of assessing the perceptual-cognitive processing capability of the central nervous system. Hence, the aim of the study was to assess the heart rate variability and reaction time in traffic police officers of Puducherry. Methods: Fifty-five age and BMI matched traffic police and healthy controls were recruited. Basal cardiovascular parameters; basal heart rate, systolic and diastolic blood pressure (BHR, SBP, DBP) were assessed. Short term HRV analysis was done. Time and frequency domain indices were computed. Simple and Choice Auditory and Visual reaction time (SART, CART, SVRT, CVRT) were measured. Results: BHR and DBP were significantly increased in traffic police. Time domain indices (Mean RR, SDNN, RMSSD, pNN50) were significantly reduced in traffic police. In frequency domain, Total Power was significantly reduced. LF-HF ratio was increased, though not significant. SVRT was significantly delayed in traffic police. CVRT, SART and CART were delayed in traffic police though not significant. Conclusion: Traffic police have decreased HRV with increased sympathetic and decreased vagal tone, and delayed reaction time.

Effect of an aerobic exercise intervention on cardiac autonomic regulation: A worksite RCT among cleaners

ObjectiveThe aim of this randomized controlled trial (RCT) was to determine whether aerobic exercise during work hours affects cardiac autonomic regulation in cleaners characterized by high levels of occupational physical activity and poor cardiorespiratory fitness. MethodEligible cleaners (n=116) were randomized to an aerobic exercise group (n=59) or a reference group (n=57) with lectures. The intervention group received two 30-min sessions per week of supervised aerobic exercise over 4months. Diurnal measurements of heart rate variability (HRV) and physical activity (accelerometry) were obtained at baseline and at 4-month follow-up. Time and frequency domain indices of HRV were derived during work, leisure time and sleep to evaluate cardiac autonomic regulation. Linear mixed models were used to determine the effect of the intervention on HRV indices, with adjustment for age, gender and daily use of antihypertensive and/or heart medication. ResultsCompared with the reference group, the exercise group increased all HRV indices apart from a reduction in LF/HF ratio from baseline to follow-up both during work (p<0.05) and leisure (p<0.05). In contrast, during sleep, the HRV indices tended to decrease in the exercise group compared with the reference group from baseline to follow-up, being significant for the HF spectral component (p=0.03). ConclusionAmong cleaners, a worksite aerobic exercise intervention improved cardiac autonomic regulation during work and leisure, but not during sleep. The health effect of this contrasting change in autonomic regulation needs further investigation.

Correlation between health-related quality of life in the physical domain and heart rate variability in asymptomatic adults.

BackgroundReduced health-related quality of life in the physical domain (HRQOLphysical) has been reported to increase risks for cardiovascular disease (CVD); however, the mechanism underlying this phenomenon is still unclear. The autonomic nervous system (ANS) that connects the body and mind is a biologically plausible candidate to investigate this mechanism. The aim of our study is to examine whether the HRQOLphysical independently contributes to heart rate variability (HRV), which reflects ANS activity.MethodsWe recruited 329 physically and mentally healthy adults. All participants completed Beck Anxiety Inventory, Beck Depression Inventory and World Health Organization Questionnaire on Quality of Life: Short Form-Taiwanese version (WHOQOL-BREF). They were divided into groups of individuals having high or low scores of HRQOLphysical as discriminated by the quartile value of WHOQOL-BREF. We obtained the time and frequency-domain indices of HRV, namely variance (total HRV), the low-frequency power (LF; 0.05–0.15 Hz), which may reflect baroreflex function, the high-frequency power (HF; 0.15–0.40 Hz), which reflects cardiac parasympathetic activity, and the LF/HF ratio.ResultsThere was an independent contribution of HRQOLphysical to explaining the variance in HRV after excluding potential confounding factors (gender, age, physical activity, alcohol use, depression and anxiety). Compared with the participants with high levels of HRQOLphysical, those with low levels of HRQOLphysical displayed significant reductions in variance and LF.ConclusionsThis study highlights the independent role of low HRQOLphysical in contributing to the reduced HRV in healthy adults and points to a potential underlying mechanism for HRQOLphysical to confer increased risks for CVD.

Method of assessing the state of a rolling bearing based on the relative compensation distance of multiple-domain features and locally linear embedding

To effectively assess different fault locations and different degrees of performance degradation of a rolling bearing with a unified assessment index, a novel state assessment method based on the relative compensation distance of multiple-domain features and locally linear embedding is proposed. First, for a single-sample signal, time-domain and frequency-domain indexes can be calculated for the original vibration signal and each sensitive intrinsic mode function obtained by improved ensemble empirical mode decomposition, and the singular values of the sensitive intrinsic mode function matrix can be extracted by singular value decomposition to construct a high-dimensional hybrid-domain feature vector. Second, a feature matrix can be constructed by arranging each feature vector of multiple samples, the dimensions of each row vector of the feature matrix can be reduced by the locally linear embedding algorithm, and the compensation distance of each fault state of the rolling bearing can be calculated using the support vector machine. Finally, the relative distance between different fault locations and different degrees of performance degradation and the normal-state optimal classification surface can be compensated, and on the basis of the proposed relative compensation distance, the assessment model can be constructed and an assessment curve drawn. Experimental results show that the proposed method can effectively assess different fault locations and different degrees of performance degradation of the rolling bearing under certain conditions.

SIMPLEX: Symbol-Level Information Multiplex

Internet of Things (IoT) heavily relies on wireless communication to interconnect various sensors and hubs. This paper proposes a symbol-level information multiplexing mechanism (SIMPLEX) that exploits link margin in wireless networks to minimize channel underutilization. Multiplexing is achieved by carrying extra information through a type of specially designed symbols inserted. The key enabler of the inserting and detecting such specially symbols is a per-bit channel assessment scheme that hierarchically estimates the error probability of a received symbol. On the GNU SDR testbed experiments, SIMPLEX shows an accuracy of 97% in recognizing the special symbols in demultiplexing. By varying the frequency domain indices of such specially symbols and their positions on I–Q constellation map, SIMPLEX provides a series of multiplexing rates that carry different amount of extra information. We also design an adaptive multiplexing rate selection scheme to dynamically achieve optimal exploitation of link margin upon instant channel conditions, which can find the optimal multiplexing rates over 90% of the time on the testbed. Multiplexing throughput gain has been theoretically derived and empirically validated of high accuracy with only a negligible deviation to experiment results. A throughput gain can be obtained as much as up to 55%.

Relationships between heart-rate variability and pulse-rate variability obtained from video-PPG signal using ZCA

In this paper, classical time– and frequency-domain variability indexes obtained by pulse rate variability (PRV) series extracted from video-photoplethysmography signals (vPPG) were compared with heart rate variability (HRV) parameters extracted from ECG signals. The study focuses on the analysis of the changes observed during a rest-to-stand manoeuvre (a mild sympathetic stimulus) performed on 60 young, normal subjects (age: years). The objective is to evaluate if video-derived PRV indexes may replace HRV in the assessment of autonomic responses to external stimulation.Video recordings were performed with a GigE Sony XCG-C30C camera and analyzed offline to extract the vPPG signal. A new method based on zero-phase component analysis (ZCA) was employed in combination with a fully-automatic method for detection and tracking of region of interest (ROI) located on the forehead, the cheek and the nose.Results show an overall agreement between time and frequency domain indexes computed on HRV and PRV series. However, some differences exist between resting and standing conditions. During rest, all the indexes computed on HRV and PRV series were not statistically significantly different (p > 0.05), and showed high correlation (Pearson’s r > 0.90). The agreement decreases during standing, especially for the high-frequency, respiration-related parameters such as RMSSD (r = 0.75), pNN50 (r = 0.68) and HF power (r = 0.76). Finally, the power in the LF band (n.u.) was observed to increase significantly during standing by both HRV ( versus (n.u.); rest versus standing) and PRV ( versus (n.u.); rest versus standing) analysis, but such an increase was lower in PRV parameters than that observed by HRV indexes.These results provide evidence that some differences exist between variability indexes extracted from HRV and video-derived PRV, mainly in the HF band during standing. However, despite these differences video-derived PRV indexes were able to evince the autonomic responses expected by the sympathetic stimulation induced by the rest-to-stand manoeuvre.