Frequency Domain Parameters Research Articles

Effects of yoga breathing practice on heart rate variability in healthy adolescents: a randomized controlled trial

BackgroundThis study was conducted among healthy adolescents to assess the effects of a yoga breathing practice (Bhramari pranayama, Bhr.P) towards cardiac autonomic function using heart rate variability (HRV) parameters. MethodsOf the 730 eligible subjects screened, 520 healthy adolescents who met the inclusion and exclusion criteria were randomly assigned to either yoga breathing group (n = 260) or control group (n = 260). The yoga breathing group practiced Bhr.P. five days a week for a duration of six months while the control group continued with their daily routine without any intervention. Outcome measures were time and frequency domain of HRV in both groups which were assessed before and after the intervention using Lead II ECG. Linear models were used in the analysis of short term HRV. ResultsAfter 6 months of yoga breathing, the time domain parameters of short term HRV showed significant (P < 0.05) improvement towards the parasympathetic domain. Frequency domain parameters also showed the same direction of changes. In contrast, control group subjects showed a trend towards a sympathetic domain. ConclusionThe present study showed a positive shift in cardiac autonomic modulation towards parasympathetic predominance after 6 months of yoga breathing practice among apparently healthy adolescents.

Delirium in patients with hip fracture is associated with increased heart rate variability.

Heart rate variability (HRV) is a method to assess the autonomic nervous system and reflects possibly central brain states. HRV has previously not been examined in patients with hip fracture and delirium. To explore HRV parameters in hip fracture patients with and without delirium. Patients admitted to Oslo University Hospital with hip fracture and sinus rhythm in electrocardiogram (ECG) were included. Delirium was diagnosed using the confusion assessment method. HRV was assessed preoperatively after a relaxing period of five minutes, by measuring an ECG signal over 5min. Parameters in time domain (the standard deviation of the QRS distances-SDNN) and frequency domain (total power (TP), low frequency (LF), high frequency (HF) and LF/HF ratio) were calculated. Seventy-five patients were included in the study, and 21 of them had subsyndromal delirium and were excluded from the analysis. Fifty-four patients with a mean age of 83.5years (SD 8.6, 78% females) were included. Twenty-six patients (48%) had preoperative delirium, 11 (20%) developed delirium postoperatively, whereas 17 (31%) never developed delirium. SDNN, TP and HF values were significantly higher in patients with delirium compared to patients without delirium, and LF and LF/HF were lower. Patients developing postoperative delirium had decreased LF and increased HF before symptom onset. Increased SDNN, TP and HF and decreased LF values might reflect an abnormal stress response in delirium. HRV measurements in patients with hip fractures provide additional information beyond heart rate and might be used to identify relevant pathophysiological factors in delirium.

Reduced heart rate variability predicts fatigue severity in individuals with chronic fatigue syndrome/myalgic encephalomyelitis

BackgroundHeart rate variability (HRV) is an objective, non-invasive tool to assessing autonomic dysfunction in chronic fatigue syndrome/myalgic encephalomyelitis (CFS/ME). People with CFS/ME tend to have lower HRV; however, in the literature there are only a few previous studies (most of them inconclusive) on their association with illness-related complaints. To address this issue, we assessed the value of different diurnal HRV parameters as potential biomarker in CFS/ME and also investigated the relationship between these HRV indices and self-reported symptoms in individuals with CFS/ME.MethodsIn this case–control study, 45 female patients who met the 1994 CDC/Fukuda definition for CFS/ME and 25 age- and gender-matched healthy controls underwent HRV recording-resting state tests. The intervals between consecutive heartbeats (RR) were continuously recorded over three 5-min periods. Time- and frequency-domain analyses were applied to estimate HRV variables. Demographic and clinical features, and self-reported symptom measures were also recorded.ResultsCFS/ME patients showed significantly higher scores in all symptom questionnaires (p < 0.001), decreased RR intervals (p < 0.01), and decreased HRV time- and frequency-domain parameters (p < 0.005), except for the LF/HF ratio than in the healthy controls. Overall, the correlation analysis reached significant associations between the questionnaires scores and HRV time- and frequency-domain measurements (p < 0.05). Furthermore, separate linear regression analyses showed significant relationships between self-reported fatigue symptoms and mean RR (p = 0.005), RMSSD (p = 0.0268) and HFnu indices (p = 0.0067) in CFS/ME patients, but not in healthy controls.ConclusionsOur findings suggest that ANS dysfunction presenting as increased sympathetic hyperactivity may contribute to fatigue severity in individuals with ME/CFS. Further studies comparing short- and long-term HRV recording and self-reported outcome measures with previous studies in larger CFS/ME cohorts are urgently warranted.

Does the frequency domain parameters among pregnant women with gestational hypertension associated with levels of serum zinc, magnesium, and copper? A cross-sectional study

Back ground: In addition to the imbalance in the cardiac autonomic function, deficiency of micronutrients such as zinc (Zn), magnesium, and copper (Cu) was also found to be one of the cause of hypertensive disorders of pregnancy. Although there are number of studies done to know the autonomic balance and serum trace elements among preeclamptic women, none of the studies were done among the gestational hypertensives, hence, we have chosen this study on association between the level of micronutrients and frequency domain parameters of heart rate variability (HRV) among newly diagnosed gestational hypertensives. Aim and Objective: This study aims to estimate the serum levels of Zn, magnesium, and Cu and its association with frequency domain parameters of HRV among non-pregnant, normotensive pregnant, and gestational hypertensives. Materials and Methods: The study was done in Sri Venkateswara Medical College and Hospital. Blood pressure and heart rate were recorded after 15 min rest. HRV was analyzed using Kubios HRV analyzer by recording 5 min resting electrocardiogram in supine position with PHYSIOPAC-PP4, MEDICAID system, Chandigarh, among 35 normal pregnant, 35 gestational hypertensive, and 35 non-pregnant women of 20–35 years of age group. Serum Zn, magnesium, and Cu analysis were done in the same day using standardized autoanalyzer method. Results: With GraphPad Prism software, statistical analysis was done. Kolmogorov–Smirnov test was done to test the normality. Data following Gaussian distribution are tabulated as mean ± SD or it is expressed as median (interquartile range). Either one-way ANOVA, Turkey’s multiple comparison, or Kruskal–Wallis and Dunn’s multiple comparison test were done to compare the parameters among all the three groups. Spearman correlation was done to know the association of Zn, magnesium, and Cu with frequency domain parameters of HRV in all three groups. Conclusion: Frequency domain parameters of HRV show a significant higher sympathetic and lower parasympathetic activity among the study group (P < 0.0001). There is no significant variation in the level of micronutrients among the groups and all were within normal limit. There is no significant association between the frequency domain parameters and the level of micronutrients.

Autonomic functions in metabolic syndrome in Indian subpopulation using heart rate variability - A pilot study

Background: The global industrialization and sedentary lifestyle has led to rise in obesity, hypertension, and diabetes which is associated with increased prevalence of metabolic syndrome (MS) all over the world, with rising trend among the younger population. Individuals with MS are at a higher risk of impaired cardiovascular autonomic function. Aim and Objective: Our study aims to understand the relationship between the MS and autonomic functions in order to improvise the wellbeing of the people who are at either risk of developing or are suffering from MS and promote healthy lifestyle. Materials and Methods: Heart rate variability (HRV) was recorded in 10 participants with MS. The HRV analysis included estimation of time domain parameters and frequency domain parameters, total power and low frequency/high frequency (LF/HF). Results: The HRV parameters showed a decrease in value along with a high LF/HF ratio in the study participants. Conclusion: The study shows that MS significantly leads to dysfunction of autonomic nervous system.

Preliminary Comparison of Zero-Gravity Chair With Tilt Table in Relation to Heart Rate Variability Measurements.

Heart rate variability (HRV) measurements are performed using a tilt-table (TT) to diagnose dysfunctionality in the autonomic nervous system (ANS) and the cardiovascular system. To maintain homeostasis, the ANS adapts to body position changes through alterations in sympathetic and parasympathetic responses that can be quantified by extracting time-domain and frequency-domain parameters from the heart rate signal. When body position is changed from supine to erect, a healthy subject’s response also shows changes in ANS activity. However, TT can be unsafe or uncomfortable for elderly or overweight subjects. Furthermore, it may induce anxiety which alters the HRV measurements. This study proposes an alternative strategy to replace the TT with a zero-gravity chair (ZGC). The statistical analysis between HRV parameters from the TT and the ZGC shows that ZGC can be a feasible alternative to TT. Therefore, ZGC can be used as a more convenient, secure, stable and safer option to the traditional HRV analysis with TT.

Fault detection of rolling bearing based on principal component analysis and empirical mode decomposition

For the problem of inconsistent quantitative standards for running status analysis of rolling bearings, this paper uses principal component analysis (PCA) to extract a new index F, which is the joint parameters of time domain and frequency domain, and by establishing the value of F to analyze the running states of the rolling bearings. Firstly, the acceleration sensors are used to collect the vibration signal of the whole life cycle of the rolling bearings. Secondly, empirical mode decomposition (EMD) method is used to denoise the acquired vibration signal. Then, the main components of the denoised vibration signal are used to propose the characteristic parameters and synthesized into new parameter indicators. Finally, envelope analysis spectrum is used to analyze the fault classification under the new parameter index. The exepriment results show that the whole life cycle of the rolling bearings can be classified into five different operating periods by using the new parameter index, and each period represents a different bearing operating state.

Recognition of driver emergency braking behaviour based on support vector machine optimised by memetic algorithm

Surface electromyography (sEMG) is one of the main information sources of human motion detection and has been widely used. The lower limb sEMG signal is introduced into the recognition model of emergency braking behaviour, and the features from time domain, frequency domain and model parameters are extracted to construct a feature vector. The emergency driving behaviours are identified by using support vector machine (SVM), and a memetic algorithm (MA) based on particle swarm optimisation and hill climbing algorithm is proposed to optimise the parameters of SVM. The results show that the model has better classification performance than that without optimisation. The final recognition rate of emergency braking behaviour of same individual is up to 92.3%, and that of different individuals can reach 85.6%. Moreover, the system can detect emergency braking 220 ms earlier than operating brake pedal. At 100 km/h driving speed, the braking distance is reduced by 6.1 m.

Recognition of driver emergency braking behaviour based on support vector machine optimised by memetic algorithm

Surface electromyography (sEMG) is one of the main information sources of human motion detection and has been widely used. The lower limb sEMG signal is introduced into the recognition model of emergency braking behaviour, and the features from time domain, frequency domain and model parameters are extracted to construct a feature vector. The emergency driving behaviours are identified by using support vector machine (SVM), and a memetic algorithm (MA) based on particle swarm optimisation and hill climbing algorithm is proposed to optimise the parameters of SVM. The results show that the model has better classification performance than that without optimisation. The final recognition rate of emergency braking behaviour of same individual is up to 92.3%, and that of different individuals can reach 85.6%. Moreover, the system can detect emergency braking 220 ms earlier than operating brake pedal. At 100 km/h driving speed, the braking distance is reduced by 6.1 m.

Recognition of Subtle Gestures by 2-Channel sEMG Using Parameter Estimation Classifiers Based on Probability Density

The abundant movement information carried by the surface electromyography (sEMG) signal can comprehensively reflect the muscle movement patterns on the surface of the human body, and the characteristics of physiological signals involving movement information have promoted the vigorous development in the field of human-computer interaction in machine learning. This paper takes subtle gestures as the research objects, and proposes a subtle gestures recognition system that uses two-channel sEMG signal and utilizes Quadratic Discriminant Analysis (QDA) and Linear Discriminant Analysis (LDA) which are parameter estimation classifiers based on probability density. First, combining the raw sEMG signal and the envelope sEMG signal, the number of channels for sensors and corresponding position of the muscle groups are preferably selected. Then, we propose to use the Pearson correlation coefficient to optimize the four types of features extracted in the time domain, frequency domain, time-frequency domain and AR model parameters, which effectively ensures the uniqueness of each gesture and eliminates individual differences. Finally, this paper compares four classifiers of QDA, LDA, Support Vector Machine (SVM), and K-Nearest Neighbor (KNN), and explores the pattern recognition classifier suitable for subtle actions. The experiment collects 9 kinds of subtle gestures from 8 subjects. The results show that the system can use only two channels of sEMG signal to recognize 9 kinds of subtle gestures which include multi-finger clicking or pinching or holding objects, and the most suitable classifiers QDA and LDA have the average recognition rates of 95.79% and 95.01%, respectively.

Heart rate variability is reduced in normal pregnancy irrespective of trimester: A cross-sectional study from Gujarat, India.

Background:Pregnancy is associated with profound cardiovascular adaptation with altered cardiac autonomic balance. It can be studied by heart rate variability (HRV) which indicates beat to beat RR interval variation on ECG.Objective:We studied 5 min HRV in normal pregnant females divided by trimesters, compared to matched control.Methodology:We recruited 89 normal pregnant females and 30 age matched controls. Five minutes resting HRV was measured by Variowin HR, software-based instrument, by standard protocols to yield time-domain, frequency domain, and Poincare plot parameters. They were further compared between groups for difference.Results:Case groups (three based on trimesters) and control group were comparable. There was reduced HRV in case than control group, with statistical significance for all, more for frequency domain than time-domain or Poincare plot parameters. There was no pattern of HRV trend across three trimesters, but mostly second trimester was associated with major decline. Primipara revealed significantly reduced HRV than multipara, but anemia or working status was not significantly associated with HRV in case group.Conclusion:There is global HRV reduction in normal pregnancy across all trimesters, associated with primiparity. This indicates pregnancy as a significant risk with reference to altered cardiac balance and use of HRV as a good tool to assess the same.

Assessment of cardiac sympathovagal activity with change in body weight in young adult males

Background: Today in the modern era, sedentary lifestyle is continuously escalating the problem of increasing weight in the young population. It is an alarming issue because increase in weight causes many health hazards mainly autonomic imbalance and altered cardiovascular functions. These cardiovascular changes can be assessed by calculating heart rate variability (HRV), which is an economical tool and non-invasive method. Aims and Objectives: The present study was carried out to assess the effect of increase weight on HRV and to find out the association between body mass index (BMI) and HRV parameters. Materials and Methods: Sixty male subjects, age ranges from 17 to 35 years, were included. The subjects were categorized into three groups as normal, obese, and overweight based on their BMI. The electrocardiogram was recorded and frequency domain parameters of HRV were obtained from it. Parameters were compared between all the three groups using ANOVA test and post hoc test. Results: Frequency domain variable high-frequency (HF) (nu) which mainly depicts parasympathetic influences was significantly lower in overweight and obese group as compared to normal weight group, whereas low frequency (LF) (nu) and LF/HF ratio marker of sympathovagal imbalance were significantly higher in overweight and obese group. Conclusion: The sympathovagal balance is sloped toward sympathetic predominance which is a predisposed risk for the cardiovascular disorders and cardiac morbidity. Hence, a timely intervention in lifestyle and obesity regime can prove to be a useful tool for improving the quality and longevity of life.

Parameters Identification and Application of Equivalent Circuit at Low Frequency of Oil-Paper Insulation in Transformer

The low frequency section of frequency domain spectroscopy (FDS) of oil-paper insu- lation system can effectively reflect the ageing state and moisture of the oil-immersed paper. Meanwhile, steady-state insulation resistance is the one of indexes for the condition of transformer. In actual measurement, these two both are time-consuming and poor accessibility, thereby restraining their field applications. Aim at this problem, this paper analyses the polarization process of the oil-paper insulation in transformer, and adopts a low frequency equivalent circuit model for the oil-paper insulation to characterize the polarization process at low frequency. The simulated annealing particle swarm optimization (SAPSO) algorithm is proposed to identify the parameters in equivalent circuit, which are affected by change of insulation state. Compared with the experimental results, the errors of the steady-state insulation resistance and the tan $\delta $ below 10−3 Hz, which are calculated by the identified parameters, are less than 2.5%. This method can avoid the influence from external environment and reduce the measurement time. The time and frequency domain parameters calculated can provide reference for the ageing assessment of oil-immersed paper.

Short-Term Heart Rate Variability and Blood Biomarkers of Gastric Cancer Prognosis

Inflammation, nutrition, and coagulation play significant roles in cancer prognosis. Autonomic function is also actively involved in tumorigenesis. Previous studies have shown that an elevated C-reactive protein (CRP) level, a serum marker for inflammation, is associated with low heart rate variability (HRV), a common clinical tool for the assessment of autonomic function. It is yet to be investigated whether HRV links to these prognostic factors in cancer patients. Sixty-one patients who were first diagnosed with gastric cancer (GC) were enrolled in this study. Fasting blood samples were collected in the morning seven days before surgery. Blood CRP, prealbumin (PA), and fibrinogen (FIB) were used to assess the inflammation level, nutritional status, and coagulation function respectively. Five-minute resting electrocardiogram (ECG) signals were collected one day before surgical treatment. Short-term HRV time-series were extracted from ECG recordings and were analyzed using commonly-used time- and frequency-domain parameters including standard deviation of normal-to-normal intervals (SDNN), root mean square of successive heartbeat interval differences (RMSSD), very-low-frequency power (VLF), low-frequency power (LF), high-frequency power (HF), total power (TP), LF power in normalized units (LF n.u.), HF power in normalized units (HF n.u.), and ratio of LF to HF (LF/HF). After adjusted for sex, age, body mass index, alcohol consumption, history of diabetes, left ventricular ejection fraction, and hemoglobin levels, our results demonstrated negative associations of HRV with levels of CRP and FIB, while positive associations between HRV and PA level, with effect sizes of as high as 35%-52% standard deviations (SD) changes in CRP, FIB, or PA per 1-SD change in HRV parameters. Therefore, decreased HRV in patients with GC predicts increased burdens of inflammation and coagulation and perturbed nutrition, suggesting that short-term HRV measurement can potentially be a noninvasive biomarker for GC prognosis.

Electroencephalogram-Based Pain Classification Using Artificial Neural Networks

This study investigates the variations in electroencephalogram (EEG) signals due to pain stimuli and proposes an optimal network configuration of the multilayer perceptron neural network (MLPNN) for pain state detection. EEG signals were recorded from 39 volunteers under the normal resting state and by applying external pain stimuli. Time, frequency, and wavelet domain parameters were computed and analysed. Decrease in Hjorth mobility, relative alpha power, minima of approximation coefficients (a5), mean and median frequency; increase in Hjorth complexity, root mean square value, relative delta power along with standard deviation, and maxima of approximation coefficients (a5) were observed at all the electrode positions. Several combinations of backpropagation algorithms and error functions were investigated to find the optimal configuration of MLPNN. We had classified pain state with an accuracy of 87.53%, 90.25%, 93.34%, and 90.62% in FP1, FP2, P3, and P4 electrode positions, respectively.

Association between chocolate consumption frequency and heart rate variability indices

BackgroundPrevious studies have shown favorable effects of chocolate products on the cardiovascular system and reported an inverse relationship between chocolate consumption and adverse cardiac events; however, relationships between chocolate eating habits and heart rate variability have not yet been studied. The purpose of the present research was to determine the relationship, if any, between chocolate consumption frequency and heart rate variability. MethodsA cross-sectional study was carried out in a group of 98 young females (19–21 years old). The study included the evaluation of chocolate eating habits by a questionnaire and heart rate variability parameters by Finometer and Powerlab as primary outcomes along with measuring anthropometry, blood pressure and fasting blood sugar levels as predictors to account for potential confounding. ResultsThree chocolate eating patterns were distinguished: “No regular chocolate consumption (n:42), 2–4 servings/week (n:20), 5 or more servings/week (n:36)”. An ANOVA test revealed insignificant differences (p > 0.05) in heart rate variability parameters (time domain: Heart rate, RRms, SDNN, RMSSD; frequency domain: LF, HF, LF/HF) and pressures (systolic, diastolic, pulse, mean arterial) among three groups of individuals having different chocolate eating habits. Relative frequency of chocolate intake did not correlate with any of the cardiovascular, time-domain or frequency-domain parameters of heart rate variability in study participants. ConclusionBased on our results, we conclude that relative frequency of chocolate eating may not affect autonomic regulation of the heart in young females. Also, it may have no correlation with any of the cardiovascular, time-domain or frequency-domain parameters of heart rate variability.

A New Testing Method for the Dielectric Response of Oil-Immersed Transformer

Oil-immersed transformer is one of the most important electrical equipment in power distribution and transmission systems. Dielectric response method is a well-recognized method to diagnose the insulation defect of oil-immersed transformers. However, the applicability of this method is restricted due to the long testing time. Under some special field conditions, the method is not even applicable. In this article, a novel testing method is proposed based on the following ideas: first, the low-frequency dielectric parameters are extracted by using mixing frequency excitation; then, parameters of the extended Debye equivalent circuit are determined based on cuckoo search optimization algorithm; finally, the specific parameters are used to the established simulation model and obtain the recovery voltage curve. Compared with the traditional method, the testing time of the proposed method has been greatly reduced. Besides, dielectric parameters in both frequency domain and time domain can be obtained simultaneously. The applicability of the proposed method is verified by the dielectric response measurements on a laboratory transformer and a real power transformer in a substation.

Identification of unbalance in a rotor-bearing system using Kalman filter–based input estimation technique

Unbalance is a common machinery fault, which occurs because of uneven distribution of mass of a rotating component about its axis. Vibration-based monitoring techniques have been widely accepted for machinery fault diagnosis. This article presents experimental verification of a recently developed Kalman filter–based method for the identification of unbalance in rotor systems. The method is tested on an experimental test rig for different unbalance configurations and shaft speeds. The proposed technique is a model-based method, which requires a mathematical model of the rotor system along with response measurements. A rigid rotor model is used, and measured accelerations at bearing pedestals are used for unbalance parameter estimation. Bearing stiffnesses are estimated using a frequency domain parameter estimation technique with measured unbalance responses. Sensitivity analysis is also performed by altering the values of these estimated stiffnesses.

Study on the relationship of National Institutes of Health Stroke Scale score with heart rate variability and cardiac complication in elderly patients with acute cerebral infarction

Objective To investigate the relationship of National Institute of Health Stroke Scale(NIHSS)with heart rate variability(HRV)and cardiac complication in elderly patients with acute cerebral infarction, and to clarify the effect of early drug intervention on the regulation of autonomic nerve function in patients with high NIHSS score. Methods One hundred twenty-six inpatients with first-onset acute cerebral infarction(ACI)(the cerebral infarction group)and 40 healthy subjects with no history of stroke(the control group)were retrospectively enrolled.All subjects underwent examinations of NIHSS and 24 h dynamic electrocardiogram.According to NIHSS score, patients in the cerebral infarction group were divided into 3 subgroups: NIHSS score 0-4 group(n=32), NIHSS score 5-15 group(n=66)and NIHSS score ≥ 15 group(n=28). The difference in HRV parameters were compared between ACI patients and the controls.Ninety-four ACI patients with NIHSS score ≥5 were randomly divided into 2 groups: (1)the traditional treatment group(n=44), taking routine drugs for cerebral infarction; (2)the special treatment group(n=42), taking metoprolol sustained release tablet and Shensonyangxin capsule as add-on to the routine drugs for cerebral infarction.The 24 h dynamic electrocardiogram examination were conducted 30 days after treatment.The differences in HRV parameters and cardiac complications were compared between the two treatment groups. Results In patients with acute cerebral infarction, the time-domain parameters of normal-to-normal intervals(NNI), standard deviation of normal-to-normal intervals(SDNN), square root of the mean squared successive differences between normal-to-normaI RR intervals(RMSSD), percentage of adjacent normal-to-normal intervals that differed more than 50 ms(PNN50), frequency domain parameters low-frequency(LF)power and high-frequency(HF)power were significantly reduced as compared with those in the control group(P<0.05). While, pulse rate and frequency domain parameters of sympathetic vagus balance index(LF/HF)were significantly increased(P<0.05). The time-domain parameters(NNI, SDNN, RMSSD and PNN50)and frequency domain parameters(LF, HF)were significantly reduced in the NIHSS score 5-15 group and NIHSS score ≥15 group as compared with the control group and the NIHSS score 0-4 group(P<0.05). The time-domain parameters(RMSSD and PNN50)and frequency domain parameters(LF and HF)were reduced(P<0.05), and the frequency domain parameters(LF/HF)were increased(P<0.05)in NIHSS score ≥15 group compared with in NIHSS score 5-15 group(P<0.05). Compared with pre-treatment, the special treatment group after treatment showed that the time domain parameters(NNI, SDNN, RMSSD and PNN50)and frequency domain parameters(LF and HF)were significantly increased(P<0.05), the frequency domain parameters(LF/HF)were significantly reduced(P<0.05)and the incidence of cardiac complication(total incidence of atrial arrhythmias and ventricular arrhythmias and cardiac complication)were significantly reduced(P<0.05). As compared with the traditional treatment group after treatment, the special treatment group after treatment showed that the time domain parameters(NNI, SDNN, RMSSD and PNN50)and frequency domain parameters(LF and HF)were significantly increased(P<0.05), frequency domain parameters(LF/HF)were significantly reduced(P<0.05)and the total incidence of cardiac complication were significantly reduced(18.4% or 7 cases vs.40.0% or 16 cases, P<0.05). Conclusions The HRV is decreased in patients with acute cerebral infarction.The reduction degree of HRV is more significant along with the higher NIHSS scores, which suggests that patients with high NIHSS scores are prone to an impairment of autonomic nerve function.For patients with high NIHSS scores after stroke, early drug intervention for regulating autonomic nerve function can effectively prevent the occurrence of cardiac emergencies and improve the prognosis of stroke. Key words: Cerebral infarction; Heart rate; Autonomic agents

The influence of temperature on the dielectric permittivity and complex electrical resistivity of porous media saturated with DNAPLs: A laboratory study

While some recent studies have discussed various effects of temperature on the electric and electromagnetic properties of multiphase porous media, the effect of temperature changes in multiphase porous media polluted by dense non-aqueous phase liquids (DNAPLs) has rarely been documented. We attempted to characterize how relative permittivity and electrical resistivity vary with temperature in multiphase porous media. The measurements were carried out using two different column sizes. Glass beads with a 1 mm diameter were used to simulate porous media. Spectral induced polarization (SIP) and time domain reflectometry (TDR) were used to measure complex electrical resistivity and relative permittivity, respectively. We investigated the geophysical characteristics of two DNAPLs, coal tar (CT) and chlorinated solvent (CS), from 20 to 50 °C; ultra-pure water was used as the reference fluid. Experimental data on the relative permittivity and complex resistivity of pure water obey empirical models, validating our experimental setup and protocol. Results demonstrated that the real parts of relative permittivity and electrical resistivity are functions of temperature in the medium with the presence or absence of a solid phase. While we did not study the imaginary part of relative permittivity, our observations in the DNAPL samples indicated that temperature increases decreased the imaginary parts of the complex electrical resistivity of DNAPLs tested, whether in the presence or absence of the solid phase. Temperature dependency of relative permittivity and complex resistivity were also studied in multiphase porous media, after drainage (80% DNAPL and 20% water) and after imbibition (8% DNAPL and 92% water). The effect of temperature increases on complex resistivity has a secondary effect on frequency domain and Cole-Cole parameters. It was found that the relationship between temperature and resistivity is linear; therefore, resistivity temperature coefficients were obtained for water and both DNAPLs with the presence and absence of solid phase.