Low Spectral Power Research Articles

1166 POOR SLEEP IS ASSOCIATED WITH MORNING HIGH SYMPATHETIC ACTIVITY AND LOW PARASYMPATHETIC ACTIVITY IN RESTING NEUROTYPICAL AND AUTISTIC ADULTS

Individuals with autistic spectrum disorder (ASD) display higher sympathetic activity during wakefulness. In typically developing individuals (TD) higher sympathetic activity is observed in the morning compared to evening levels. The main objectives of this study were to compare autonomic nervous system (ANS) activity during wakefulness in the evening and in the morning in a group of adults with ASD and a group of TD adults, as well as to explore the association between ANS activity and self-reported sleep measures. The electrocardiogram of 33 adults (16 ASD; 17 TD) was recorded during wakefulness, before and after a night of sleep. The following heart rate variability (HRV) parameters were measured: low (LF) frequencies, high frequencies (HF) and total spectral power. Values were compared between groups using two-way ANOVAs (ASD vs TD) and one repeated measure (Evening vs Morning). Pearson correlations coefficients between self-reported sleep measure and morning HRV parameters were calculated. Compared to the TD group, the ASD group displayed significantly lower morning HF values (34.98 ± 20.55 vs. 53.35 ± 22.17) and higher LF/HF ratios (1.52 ± 2.22 vs. 3.02 ± 2.28) compared to the TD group. No group differences were observed in the evening. When all participants were pooled together, longer nocturnal awakenings and lower sleep efficiency were correlated with higher sympathetic activity (respectively r = 0.52; p<0.01 and r = -0.43; p=0.04) and lower parasympathetic activity (respectively r= -0.54; p<0.01 and r = 0.42; p = 0.04) in the morning. 1) A higher morning sympathovagal balance prevails in ASD compared to TD individuals; 2) This is associated with self-reported markers of poor sleep. Canadian Institutes of Health Research and “Fonds de la recherche du Québec en santé”.

Effect of Temperature on Heart Rate Variability in Neonatal ICU Patients With Hypoxic-Ischemic Encephalopathy

To determine whether measures of heart rate variability are related to changes in temperature during rewarming after therapeutic hypothermia for hypoxic-ischemic encephalopathy. Prospective observational study. Level 4 neonatal ICU in a free-standing academic children's hospital. Forty-four infants with moderate to severe hypoxic-ischemic encephalopathy treated with therapeutic hypothermia. Continuous electrocardiogram data from 2 hours prior to rewarming through 2 hours after completion of rewarming (up to 10 hr) were analyzed. Median beat-to-beat interval and measures of heart rate variability were quantified including beat-to-beat interval SD, low and high frequency relative spectral power, detrended fluctuation analysis short and long α exponents (αS and αL), and root mean square short and long time scales. The relationships between heart rate variability measures and esophageal/axillary temperatures were evaluated. Heart rate variability measures low frequency, αS, and root mean square short and long time scales were negatively associated, whereas αL was positively associated, with temperature (p < 0.01). These findings signify an overall decrease in heart rate variability as temperature increased toward normothermia. Measures of heart rate variability are temperature dependent in the range of therapeutic hypothermia to normothermia. Core body temperature needs to be considered when evaluating heart rate variability metrics as potential physiologic biomarkers of illness severity in hypoxic-ischemic encephalopathy infants undergoing therapeutic hypothermia.

Activity/rest rhythm of depressed adolescents undergoing therapy: case studies.

Disorders of circadian rhythms have been reported in studies of both depressed children and of depressed adolescents. The aim of this study was to evaluate whether there is a relationship between the 24-hour spectral power (24h SP) of the activity/rest rhythm and the clinical course of depression in adolescents. Six 14 to 17-year-old adolescents were recruited for the study. They were all suffering from major depressive disorder, according to the Diagnostic and Statistical Manual of Mental Disorders, 4th edition (DSM-IV) criteria, as identified by the Schedule for Affective Disorders and Schizophrenia for School Aged Children: Present and Lifetime Version (K-SADS-PL). Depressive symptoms were assessed using the Children's Depression Rating Scale - Revised (CDRS-R) and clinical evaluations. Locomotor activity was monitored over a period of 13 consecutive weeks. Activity was measured for 10-minute periods using wrist-worn activity monitors. All patients were prescribed sertraline from after the first week up until the end of the study. We found a relationship between high CDRS values and low 24-hour spectral power. The 24h SP of the activity/rest rhythm correlated significantly (negatively) with the clinical ratings of depression.

Designing Unimodular Waveform with Low Range Sidelobes and Stopband for Cognitive Radar via Relaxed Alternating Projection

Cognitive radar could adapt the spectrum of waveforms in response to information regarding the changing environment, so as to avoid narrowband interference or electronic jamming. Besides stopband constraints, low range sidelobes and unimodular property are also desired. In this paper, we propose a Spectral Approximation Relaxed Alternating Projection (SARAP) method, to synthesize unimodular waveform with low range sidelobes and spectral power suppressed. This novel method, based on phase retrieval and relaxed alternating projection, could convert the correlation optimization into the spectrum approximation via the Fast Fourier Transform (FFT). Moreover, by virtue of the relaxation factor and accelerated factor, SARAP can exploit local area and more likely converge to the global solution. Numerical trials have demonstrated that SARAP could achieve excellent performance and computational efficiency which will facilitate the real-time design.

Effects of Cognitive Behavioral Stress Management on Negative Mood and Cardiac Autonomic Activity in ICD Recipients.

Behavioral intervention studies in patients with an implantable cardioverter-defibrillator (ICD) show promise in improving psychosocial outcomes but inconclusive effects on cardiovascular outcome. We assessed the effects of cognitive behavioral stress management (CBSM) on mood state and potentially arrhythmogenic cardiovascular responses to mental stress in ICD patients, in support of further larger scale arrhythmia trials. A total of 103 ICD recipients were randomly assigned to 10-week programs of CBSM or "Patient Education" (ED). Of these, 83 patients continued to either CBSM (n = 44) or ED (n = 39) intervention. Study end points were mood change, heart rate variability (HRV), double product elevation (DP = heart rate × systolic blood pressure) by math and anger-recall stress, and arrhythmia up to 6 months follow-up. Adjusting for multiple testing, CBSM was associated with moderate effect size reductions in tension/anxiety (P = 0.010), anger/hostility (P = 0.020), perceived stress (P = 0.037), and total mood disturbance (P = 0.025), greatest immediately following intervention (P < 0.05), and partially attributable to increased negative mood following ED (P < 0.01). No significant intervention effects on high frequency or low frequency spectral power of HRV, DP responses, or cardiac arrhythmias were demonstrated. CBSM intervention in ICD recipients resulted in reduced anxiety, anger, and perceived stress, not sustained at 6 months follow-up, and without conclusive effect on cardiac autonomic or hemodynamic responses to mental stress, or arrhythmia. Findings support conduct of larger behavioral intervention arrhythmia trial, with consideration of reinforcement training and targeting of subgroup responders to therapy.

Intra-session stability of short-term heart rate variability measurement: gender and total spectral power influence

Cipryan, L., & Litschmannova, M. (2014). Intra-session Stability of Short-term Heart Rate Variability Measurement: Gender and Total Spectral Power Influence. J. Hum. Sport Exerc., 9(1), pp.68-80. Heart rate variability (HRV) has been increasingly analysed under numerous research settings. HRV measurement reliability is, however, still an unresolved issue. The main purpose is to carry out an intra-session stability evaluation of HRV parameters from short-term recordings by means of orthoclinostatic stimulation in a study group which is stratified by gender or Total Power (PT) magnitude. The goal is to make as homogeneous a study group as possible and investigate whether the reproducibility level could be influenced by these factors. The study group consisted of 103 participants (age 22.3 ± 1.2). Standard HRV indexes were computed: PT (total spectral power), PHF (high frequency spectral power), PLF (low frequency spectral power) and LF/HF. Absolute reliability is assessed by the standard error of measurement and 95% limits of agreement; the relative reliability is assessed by the intraclass correlation coefficient. The markedly different standard error of measurement (SEM) between the Male and Female groups was not observed for any HRV parameters. The intraclass correlation coefficient (ICC) values ranged from 0.67 to 0.95 for males and from 0.69 to 0.97 for females. According to the SEM and ICC, there is no difference between the groups of High PT and Low PT. There are not any significant differences in absolute or relative reliability between the more homogeneous study groups and we have therefore

Assessing attention and cognitive function in completely locked-in state with event-related brain potentials and epidural electrocorticography

Objective. Patients in the completely locked-in state (CLIS), due to, for example, amyotrophic lateral sclerosis (ALS), no longer possess voluntary muscle control. Assessing attention and cognitive function in these patients during the course of the disease is a challenging but essential task for both nursing staff and physicians. Approach. An electrophysiological cognition test battery, including auditory and semantic stimuli, was applied in a late-stage ALS patient at four different time points during a six-month epidural electrocorticography (ECoG) recording period. Event-related cortical potentials (ERP), together with changes in the ECoG signal spectrum, were recorded via 128 channels that partially covered the left frontal, temporal and parietal cortex. Main results. Auditory but not semantic stimuli induced significant and reproducible ERP projecting to specific temporal and parietal cortical areas. N1/P2 responses could be detected throughout the whole study period. The highest P3 ERP was measured immediately after the patient's last communication through voluntary muscle control, which was paralleled by low theta and high gamma spectral power. Three months after the patient's last communication, i.e., in the CLIS, P3 responses could no longer be detected. At the same time, increased activity in low-frequency bands and a sharp drop of gamma spectral power were recorded. Significance. Cortical electrophysiological measures indicate at least partially intact attention and cognitive function during sparse volitional motor control for communication. Although the P3 ERP and frequency-specific changes in the ECoG spectrum may serve as indicators for CLIS, a close-meshed monitoring will be required to define the exact time point of the transition.

Involvement of the sympatho-vagal balance in the formation of respiration-dependent oscillations in the human cardiovascular system

The effect of deep breathing controlled in both rate and amplitude on the heart rate variability (HRV) and respiration-dependent blood flow oscillations was studied in the forearm and finger-pad skin of healthy 18- to 25-year-old volunteers. In order to reveal the effects of the divisions of the autonomic nervous system on the amplitudes of respiratory sinus arrhythmia (RSA) and skin blood flow oscillations, we studied the indices of the cardiovascular system in two groups of subjects with respectively lower and higher values of the sympatho-vagal balance. This index was calculated as a ratio of low frequency and high frequency HRV spectral power (LF/HF) under the conditions of spontaneous breathing. It was found that, in subjects with a predominant parasympathetic tone, the amplitudes of RSA and the rate of blood flow in the finger-pad skin were higher compared to subjects with a predominant sympathetic tone during respiration with the frequency lower than 4 cycle/min. In the forearm skin, where sympathetic innervation is weaker compared to the finger-pad skin, there were no significant differences in respiration-dependent oscillations of the rate of blood flow in two groups of subjects.

Comparison of ivabradine and metoprolol tartrate impact on the heart rate variability in patients with angina pectoris

Abstract Background: Heart rate variability (HRV) is an effective way to estimate heart rate (HR) autonomic regulation. In some cardiovascular diseases increased sympathetic activity (low frequency spectral power of

Autonomic Reflexes May Contribute to the Symptomatology of Mal de Debarquement Syndrome

Mal de debarquement syndrome (MdDS) is the phantom perception of self‐motion triggered by a passive motion event such as sea or air travel. To test the hypothesis that autonomic reflexes are altered in MdDS, head‐down rotation (HDR) was used to test vestibular reflexes and 60° head‐up tilt (HUT) was used to test combined baroreceptor and vestibular reflexes in 9 female MdDS patients and 9 age‐ and sex‐matched controls. Heart rate (HR, ECG), arterial blood pressure (ABP, finger photoplethysmography), and cardiac output (CO), stroke volume and systemic vascular resistance (SVR) were calculated (Modelflow) in 6 min bins for steady‐state and dynamic (FFT) analysis during baseline, perturbation (HDR or HUT), and recovery. HDR decreased stroke volume and CO in both groups, but SVR increased in MdDS. No changes in the ABP power spectrum were observed during HDR. HUT increased mean ABP, HR, and SVR while decreasing pulse pressure, stroke volume, and CO in both groups. Increases in mean ABP and SVR in MdDS were augmented compared to controls. HUT increased the ABP low frequency spectral power and R‐to‐R interval low frequency/high frequency ratios in both groups. These pilot data identified exaggerated vascular resistances to a postural change in MdDS possibly due to increased sympathetic reflex gain. Thus, altered autonomic reflexes appear to be a part of MdDS symptomatology.Funding: MdDS Balance Disorder Foundation

Intra-day and inter-day reliability of heart rate variability measurement

At present, analysis of heart rate variability (HRV) is becoming widely used as a clinical or research tool. Supported reliability studies for HRV measurement are, however, still limited. The main purpose was to perform an assessment of the absolute and relative reliability of HRV parameters from short-term recordings by means of orthoclinostatic stimulation and to investigate, whether there is a difference in repeating the retest immediately or after several days. The study group consisted of 99 participants (mean age 22 ± 1.24 years). Standard HRV indexes were computed: PT (total spectral power), PHF (high frequency spectral power), PLF (low frequency spectral power) and LF/HF. Absolute reliability was assessed by the standard error of measurement and 95% limits of agreement; relative reliability was assessed by the intraclass correlation coefficient. There was also an estimate of the sample size needed to detect the mean difference ≥ 30% of the between-subject standard deviation. In conclusion, a large random variation (within individuals) of HRV parameters was revealed, regardless of whether the retest was repeated immediately or with an interruption. For most HRV parameters (particularly in the immediately repeated test-retest), however, random variation represents a limited portion of the between-subject variability.

Stage level, volume and time‐frequency information content of Lake Tana using stochastic and wavelet analysis methods

AbstractLake Tana is the largest fresh water body situated in the north‐western highlands of Ethiopia. In addition to its ecological services, it serves for local transport, electric power generation, fishing, recreational purposes, and source of dry season irrigation water supply. Evidence shows that the lake has dried at least once at about 15,000–17,000 before present owing to a combination of high evaporation and low precipitation events. Past attempts to understand and simulate historical fluctuation of Lake Tana based on simplistic water balance approach of inflow, outflow, and storage have failed to capture well‐known events of drawdown and rise of the lake that have happened in the last 44 years. This study tested different stochastic methods of lake level and volume simulation for supporting Lake Tana operational planning decision support. Three stochastic methods (perturbations approach, Monte Carlo methods, and wavelet analysis) were employed for lake level and volume simulation, and the results were compared with the stage level measurements. Forty‐four years of daily, monthly, and mean annual lake level data have shown a Gaussian variation with goodness of fit at 0.01 significant levels of the Kolmogorov–Smirnov test. The stochastic simulations predicted the lake stage level of the 1972, 1984, and 2002/2003 historical droughts 99% of the time. The information content (frequency) of fluctuation of Lake Tana for various periods was resolved using Wigner's Time‐Frequency Decomposition method. The wavelet analysis agreed with the perturbations and Monte Carlo simulations resolving the time (1970s, 1980s, and 2000s) in which low frequency and high spectral power fluctuation has occurred. The Monte Carlo method has shown its superiority for risk analysis over perturbation and deterministic method whereas wavelet analysis reconstructed historical record of lake stage level at daily and monthly time scales. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Hemorheology and heart rate variability in patients with diabetes mellitus type 2

Our study aimed to investigate the relationship between hemorheological parameters and heart rate variability (HRV) in patients with diabetes mellitus type 2. Hemorheological variables, including hematocrit (Ht), fibrinogen (Fib), whole blood (WBV) and plasma viscosity (PV) at shear rates of 0.0237 s(-1) to 128.5 s(-1) were examined in 20 patients with diabetes mellitus type 2 and in 10 control subjects. They all underwent non-invasive short-term monitoring of heart rate at rest and after passive head-up tilt. Measurement of the R-R intervals and calculation of the time domain parameters and the power spectral data were performed by our softwear, using fast Fourier transformation. Significant increase of Fib and WBV in the patients in comparison to controls was found within the range of shear rates 0.0237 s(-1) to 128.5 s(-1). In the diabetic patients parallel decrease of the total power (TP), the low frequency spectral power (LF) and of the mean RR and mild increase of the low frequency-high frequency ratio (LF/HF) at rest were established. This tendency was kept after the passive tilt. In patients with diabetes mellitus type 2 the increased blood viscosity was associated with reduced HRV.

Autonomic regulation in patients with diabetic neuropathy

Cardiac and vascular damage resulting from autonomic neuropathy is a complication of diabetes that often goes undiagnosed. The aims of this study were 1) to quantify damage to cardiac and vascular function in patients diagnosed with peripheral neuropathy, and 2) to develop noninvasive measures to diagnose autonomic neuropathy.METHODSContinuous blood pressure, ECG, blood flow and respiration were monitored in 7 able‐bodied subjects (AB), 9 diabetics without (D0), and 7 diabetics with (D1), neuropathy during supine rest and 70° head up tilt (HUT). Mean values, spectral power and partial coherence analyses were used to discriminate groups.RESULTSIn response to HUT, diabetics increased heart rate to higher levels, but were unable to maintain BP as well as did AB. Low frequency spectral power of SBP and high frequency power of RRI were higher in AB than diabetics during rest and HUT. AB had the highest, and D1 the lowest, slope of baroreflex sequences during rest and HUT.CONCLUSIONSOur results support the concept that diabetes diminishes both sympathetic and parasympathetic influence on cardiac and vascular function and suggest that noninvasive indices may help discriminate patients with autonomic neuropathy. Supported by NIH RO1 NS39774, Kentucky NASA EPSCOR WKU 52611, and UK GCRC USPHS grant #M01RR02602. We acknowledge contributions of A Hartman, RN, L Krompak, L Mohney, D Silcox and R Schneider.

Spread spectrum techniques in wireless communication

This article discusses about spread-spectrum technique, the goal is to deliberately spread the transmitted electromagnetic energy in the frequency domain and receive the user data signal using the same pseudo random code used in the transmitter. Critical advantages of DSSS systems are related to their ability to provide secure communication and be robust against continuous time narrow band jamming with low spectral density power.

Highly efficient temporally stable narrow linewidth cryogenically cooled Yb-fiber laser

Cryogenic cooling is an effective way of increasing the efficiency in many solid-state lasers. In fiber lasers however, while the efficiency is increased, a reduced reabsorption in combination with reduced homogeneous broadening tends to broaden the linewidth, yielding a low spectral power density of the laser emission. In this work we lock a cryogenically-cooled Yb-doped fiber laser with a volume Bragg grating to overcome this problem and achieve a temporally stable narrow linewidth highly efficient laser. We extract 11.4-W of output power in spectral window of less than 0.4-nm with 14.5-W of launched pump light.

Modulation of heart rate variability by dietary carbohydrate in healthy adolescent African‐Americans

Low heart rate variability (HRV) after eating may be a risk factor for obesity among African‐Americans because of its association with a limitation of postprandial sympathetic regulation of adipokinesis and fat utilization.PurposeThe present study was designed to test the hypothesis that a subpopulation of adolescents may be differentiated by changes in HRV after ingesting beverages of high carbohydrate or high fat content.MethodsHRV was computed as the standard deviation of the normal‐normal (SDNN) and as the very low, low and high frequency spectral powers measured on electrocardiogram (ECG) RR intervals during paced breathing. Respiratory exchange ratio (RQ) and metabolic energy expenditure were measured.ResultsThe results showed that RQ consistently increased after ingestion of the high carbohydrate and did not change consistently after ingestion of the high fat beverages. The peak increment in RQ was associated with an increase in the very low frequency and a decrement in the high frequency in the absence of consistent changes in the low frequency ECG spectral power.ConclusionThese findings suggest that ingestion of high‐carbohydrate may produce sympathetic modulation of metabolism and thermogenesis in healthy adolescent African‐Americans. Furthermore, carbohydrate induced production of carbon dioxide may function as a metabolic signal for autonomic nervous system activity and HRV. The results of this study suggest that the increment in very low frequency ECG spectral power associated with ingestion of carbohydrate may be a physiological marker for postprandial sympathetic mediated adipokinesis, a limitation of which could be a marker of increased risk for obesity.

Cardiovascular mechanisms are maintained by intermittent artificial gravity exposure during bed rest deconditioning

Successful countermeasures to adverse cardiovascular effects of spaceflight have not yet been developed. In this study cardiovascular parameters were measured at rest and in response to 30 minutes of 80° head up tilt (HUT) in two groups of men before, during and after 21 days of 6° head down bed rest (BR). 8 men received a daily, one hour dose (2.5 Gz at the foot decreasing to 1.0 Gz at the heart) of artificial gravity (AG), while 7 underwent no countermeasure. After 21 days of BR, AG‐treated subjects demonstrated greater orthostatic tolerance than control subjects (p = .012). Cardiovascular variables responsible for maintaining tolerance in AG treated subjects included an enhanced ability to increase heart rate (HR) and low frequency spectral power of blood pressure as well as to maintain stroke volume (SV) during tilt. Additionally, AG treated subjects demonstrated a more rapid return to pre‐BR responses to HUT than did control subjects by minimizing tilt‐induced increases of HR (p = .04) and decreases of SV (p = .05). Variables recorded during BR days are being analyzed to develop a model to predict orthostatic tolerance upon returning to gravity. Our data support the hypothesis that AG treatment lessens cardiovascular deconditioning in bed rested men by improving both cardiac and peripheral function and should be pursued as a space flight countermeasure. Supported by The NASA AG‐Bed Rest Project and KY NASA EPSCoR WKU52611.

Orthogonal frequency coded filters for use in ultra-wideband communication systems

The use of ultra-short pulses, producing very wide bandwidths and low spectral power density, are the widely accepted approach for ultra-wideband (UWB) communication systems. This approach is simple and can be implemented with current digital signal processing technologies. However, surface acoustic wave (SAW) devices have the capability of producing complex signals with wide bandwidths and relatively high frequency operation. This approach, using SAW based correlators, eliminates many of the costly components that are needed in the IF block in the transmitter and receiver, and reduces many of the signal processing requirements. This work presents the development of SAW correlators using orthogonal frequency coding (OFC) for use in UWB spread spectrum communication systems. OFC and pseudonoise (PN) coding provide a means for UWB spreading of data. The use of OFC spectrally spreads a PN sequence beyond that of code division multiple access (CDMA) because of the increased bandwidth providing an improvement in processing gain. The transceiver approach is still very similar to that of a CDMA but provides greater code diversity. Experimental results of a SAW filter designed with OFC transducers are presented. The SAW correlation filter was designed using seven contiguous chip frequencies within the transducer. SAW correlators with a 29% fractional bandwidth were fabricated on lithium niobate (LiNbO3) having a center frequency of 250 MHz. A coupling-of-modes (COM) model is used to predict the SAW filter response experimentally and is compared to the measured data. Good correlation between the predicted COM responses and the measured device data is obtained. Discussion of the design, analysis, and measurements are presented. The experimental matched filter results are shown for the OFC device and are compared to the ideal correlation. The results demonstrate the OFC SAW device concept for UWB communication transceivers.

Cerebral blood flow oscillations elicited by inspiratory resistance delays the reporting of orthostatic symptoms with central hypovolemia

We tested the hypothesis that breathing through an inspiratory threshold device (ITD) during progressive central hypovolemia would increase cerebral perfusion and attenuate the reporting of symptoms. Methods: Eight human subjects were exposed to lower body negative pressure (LBNP) until the presence of presyncopal symptoms while breathing through either an active ITD (−7 cmH2O impedance) or a sham ITD (0 cmH2O). Cerebral blood flow velocity (CBFV) was measured continuously via transcranial Doppler and analyzed in both time and frequency domains. Subjects were asked to report any presyncopal symptoms (e.g., dizziness, nausea) at the conclusion of each LBNP exposure. Results: Breathing on the active ITD increased LBNP tolerance time from 2005 ± 104 s to 2254 ± 137 s (p = 0.006). We compared CBFV responses at the time of presyncopal symptoms during the sham ITD trial with those at the same absolute time during the active ITD trial (when there were no symptoms). While there was no difference in mean CBFV at these time points (sham, 49 ± 3 cm/s vs. active, 45 ± 4 cm/s; p = 0.428), total oscillations (sum of high and low frequency spectral power) of cerebral blood flow were higher (p = 0.03) with the active ITD (45.7 ± 10.2 cm/s2) than the sham ITD (22.1 ± 5.4 cm/s2). Conclusion: Greater oscillations around the same absolute level of CBFV are induced by inspiratory resistance and may account for the delay in symptoms with central hypovolemia.