Complex Demodulation Research Articles

Does exposure to an artificial ULF magnetic field affect blood pressure, heart rate variability and mood?

The aim of this study was to determine whether an artificial magnetic field with an amplitude and frequency equivalent to those of geomagnetic pulsations during geomagnetic storms could affect physiology and psychology. Three healthy volunteers wore an ambulatory BP monitor and an ECG recorder around the clock for 12 consecutive weekends in Winnipeg, Manitoba, Canada. In a room shielded against ELF and VLF waves, they were exposed for 8 hours per week to either a 50 nT 0.0016 Hz or a sham magnetic field at one of six circadian stages. Real exposure randomly alternated with sham exposure. They provided saliva and recorded mood and reaction time every 4 hours while awake. Systolic (S) and diastolic (D) blood pressure (BP), and heart rate (HR) were recorded every 30 minutes. Spectral analysis of HR variability (HRV) was performed using the maximum entropy method and a complex demodulation method. For these variables, daily means were compared between real and sham exposure, using paired t-tests. Their circadian MESOR, amplitude, and acrophase were analyzed and summarized using single cosinor and population-mean cosinor. Circadian rhythms were demonstrated for HR, SBP, DBP for sham exposure, salivary flow rate, positive affect, vigor, and subjective alertness ( p<0.001, ∼0.02). One participant showed higher HR, lower LF, HF, and VLF powers, and a steeper power-law slope ( p<0.005, ∼0.0001) in an early night exposure to the real magnetic field, but not in other circadian stages. There was no significant difference between circadian responses to real and sham exposure in any variable at any circadian stage.

Heart rate variability during exercise performed below and above ventilatory threshold.

To examine whether differences in heart rate variability (HRV) can distinguish sub- from supra-ventilatory-threshold exercise and whether the exercise duration at supra-threshold intensity alters cardiorespiratory synchronization. Beat-to-beat RR interval, VO2, VCO2, VE, and blood lactate concentration of 11 healthy well-trained young subjects were collected during two exercise tests: 1) a moderate-intensity test: 15 min performed below the power at ventilatory threshold (pVT); and 2) a heavy-intensity test: above pVT until exhaustion. Fast Fourier transform, smoothed pseudo Wigner-Ville distribution, and complex demodulation were applied to RR time series. 1) Moderate exercise shows a prevalence of low-frequency (LF) spectral energy compared with the high-frequency (HF) one (LF = 80 +/- 10% vs HF = 20 +/- 10%, P < 0.001), whereas the reverse is observed during heavy exercise (LF = 11 +/- 8% vs HF = 89 +/- 8%, P < 0.001). 2) During heavy exercise, the HF amplitude and the tidal volume (Vt) remained constant, whereas the breathing frequency (BF) increased (BF: 0.70 +/- 0.18 vs 0.93 +/- 0.31, P < 0.01) and mean RR decreased (342 +/- 15 vs 317 +/- 16, P < 0.01). Despite the RR series and the breathing signal remaining synchronized, HR/BF ratio decreased and stabilized at 3 RR for one breathing cycle, whatever the initial ratio. 1) HRV allows us to differentiate sub- from supra-ventilatory-threshold exercise and 2) exercise duration at supra-threshold intensity does not alter the cardiorespiratory synchronization.

Time-series analysis and cyclostratigraphy: examining stratigraphic records of environmental cycles

Increasingly environmental scientists, palaeoceanographers and geologists are collecting quantitative records of environmental changes (time-series) from sediments, ice cores, cave calcite, corals and trees. This book explains how to analyse these records, using straightforward explanations and diagrams rather than formal mathematical derivations. All the main cyclostratigraphic methods are covered including spectral analysis, cross-spectral analysis, filtering, complex demodulation, wavelet and singular spectrum analysis. Practical problems of time-series analysis, including those of distortions of environmental signals during stratigraphic encoding, are considered in detail. Recent research into various types of tidal and climatic cycles is summarised. The book ends with an extensive reference section, and an appendix listing sources of computer algorithms. This book provides the ideal reference for all those using time-series analysis to study the nature and history of climatic and tidal cycles. It is suitable for senior undergraduate and graduate courses in environmental science, palaeoceanography and geology.

Temperature-insensitive fiber Bragg grating accelerometer

A cantilever beam and fiber Bragg grating is used to measure acceleration. The cantilever induces strain on the grating, resulting in a Bragg wavelength modification that is subsequently detected. The output signal is insensitive to temperature variations and for a temperature change from -20/spl deg/C to 40/spl deg/C, the output signal fluctuated less than 5% without any temperature compensation schemes. Because the accelerometer does not utilize expensive and complex demodulation techniques, it is potentially cost effective. For the experimental system, a linear output range of 8 g could be detected.

Temperature insensitive measurements of static displacements using a fiber Bragg grating

We report a chirped fiber Bragg grating transducer for the measurement of acceleration, in which a cantilever beam and fiber Bragg grating are used. The cantilever induces strain on the grating resulting in a Bragg grating wavelength modification that is subsequently detected. The output signal is insensitive to temperature variations and for a temperature change from -20 degrees C to 40 degrees C, the output signal fluctuated less than 5 % without any temperature compensation schemes. Because the accelerometer does not utilize the complex demodulation techniques it is potentially inexpensive. For the experimental system a linear output range of 8 g could be detected.

Extracting Envelopes of Rossby Wave Packets

Abstract Packets of Rossby waves play an important role in the transfer of kinetic energy in the extratropics. The ability to locate, track, and detect changes in the envelope of these wave packets is vital to detecting baroclinic downstream development, tracking the impact of the analysis errors in numerical weather forecasts, and analyzing the forecast effects of targeted weather observations. In this note, it is argued that a well-known technique of digital signal processing, which is based on the Hilbert transform, should be used for extracting the envelope of atmospheric wave packets. This technique is robust, simple, and computationally inexpensive. The superiority of the proposed algorithm over the complex demodulation technique (the only technique previously used for this purpose in atmospheric studies) is demonstrated by examples. The skill of the proposed algorithm is also demonstrated by tracking wave packets in operational weather analyses from the National Centers for Environmental Prediction...

CO 2 laser polarimeter for electron density profile measurement on the Large Helical Device

We developed a three-channel tangential CO2 laser polarimeter to measure electron densities on the Large Helical Device. Our system aims to obtain not only the line averaged electron density but also the electron density profile. The achieved resolution of the Faraday rotation angle was 0.01° with a response time of 3 ms by digital complex demodulation combined with digital filtering. The phase fluctuations whose amplitude is typically 0.05° with a time constant of several seconds were observed. It was found that they were caused by beam axis fluctuations from bench top experiments. In the case of pellet injected plasmas it was demonstrated that the polarimeter could measure the time evolution of the Faraday rotation with high reliability and resolution. The calibrated rotation angle of all chords were well consistent with interferometer data. Assuming the functional dependence of the density profile, we estimated the density profile after pellet injections from three-channel polarimeter data iteratively. As a result, obtained profiles agreed with those measured with the 13-channel far infrared interferometer.

Automatic profile reconstruction for millimeter-wave frequency-modulated continuous-wave reflectometry on NSTX

UCLA operates a set of millimeter-wave/microwave reflectometers on the National Spherical Torus Experiment (NSTX) for routine measurements of electron density profiles and fluctuations. The system has a combined frequency coverage of 12 to 50 GHz (in the bands 12–18, 20–32, and 33–50 GHz) or a corresponding ordinary-mode cutoff range of 1.8×1012 to 3.1×1013 cm−3 to cover both the plasma core and edge. Profile measurements via frequency-modulated continuous-wave operation are typically made in O-mode reflectometry, with sweep times down to 50 μs over the full band. Automated profile analysis of the reflectometry data is available with limited between-shot analysis and full batch analysis capabilities. The reconstruction algorithm uses complex demodulation with the short-time Fourier transform for signal processing. The unknown portion of the edge profile below the lowest cutoff density is modeled by fitting a family of polynomial density profiles to the experimental data. Uncertainties due to edge profile modeling and comparisons to Thomson scattering measurements are discussed. The reconstructed profiles have documented fast events such as L–H transitions and edge-localized modes in NSTX.

Progressive increases in complexity of T-wave oscillations herald ischemia-induced ventricular fibrillation.

T-wave alternans (TWA), an ABAB oscillation, has been postulated as the initial pattern in a stepwise progression to higher-order oscillations, culminating in sudden arrhythmic death. The present study is the first to provide experimental evidence to support this intriguing concept. Epicardial and endocardial ECGs from 12 dogs were monitored during 8-minute left anterior descending coronary artery occlusion with right atrial pacing at 150 bpm. TWA magnitude was measured by modified moving average beat analysis, and the complexity of T-wave oscillations was assessed by complex demodulation. In 6 animals with subsequent ventricular fibrillation (VF), TWA achieved a threshold of 5.00+/-1.30 mV in epicardial ischemic-zone electrograms, which then exhibited a stepwise increase in T-wave oscillation complexity to quadrupling (ABCDABCD, 3 cases) or tripling (ABCABC, 2 cases) and to more complex forms (5 cases) preceding VF (6 cases). In dogs without VF, peak TWA levels did not increase from baseline, measuring a maximum of 0.35+/-0.10 mV (P=NS), or only 7% the value of those with VF, and T-wave multupling was not observed (0 of 6 versus 5 of 6, P<0.005). Discordant TWA episodes, with T waves alternating out of phase, were associated with increased T-wave complexity and fibrillation in 4 of 6 dogs with VF but in none of the 6 dogs without VF (P<0.025). TWA appears to be the first step in an orderly progression of T-wave complexity, episodes of discordant TWA, and VF. This demonstrated increase in T-wave complexity points to a fundamental mechanistic link underlying the ability of TWA to predict lethal arrhythmias.

Blood Pressure and Heart Rate Variability in Taxi Drivers on Long Duty Schedules

Blood Pressure and Heart Rate Variability in Taxi Drivers on Long Duty Schedules: Fumio KObayashi, et al. Department of Health and Psychosocial Medicine, Aichi Medical University School of MedicineObjectiveTo clarify the mechanisms of excessive risk of cardiovascular disease among taxi drivers, the effects of taxi driving with long work hours on taxi drivers' blood pressure and heart rate variability were examined.MethodsWe measured the physical activity level, ambulatory blood pressure, and Holter ECG in 34 healthy middleaged male taxi drivers over one work day and the two following non‐work days. The subjects worked for a 24‐h period starting at 07:00, then rested from work for 48 h. Ambulatory blood pressure was recorded automatically at 30‐min intervals over the 72‐h period. Holter ECG records were also kept for the 72 h, and temporal changes in the R‐R interval were analyzed by the complex demodulation method (COM). The amplitude of the high frequency (HF) components (central frequency 0.30 Hz), and the ratio of lowfrequency components (central frequency 0.09 Hz) to high‐frequency components (LlH) was calculated.ResultsBlood pressure during the work day was significantly higher than that during the non‐work days, with a stronger effect in the hypertensive subjects. There were no significant overall differences in heart rate variability between the work day and the non‐work days, but the temporal patterns of HF and UH on the work day revealed a potent effect of reversed‐phased circadian rhythm for work at night.ConclusionsLong duty taxi driving raises blood pressure and may increase cardiovascular risk as a result. The conflict between the circadian rhythms of autonomic nervous activity and work activity at night may also result in increased risk.

HF radar observations of Pc5 ULF pulsations driven by the solar wind

We present HF radar observations of Pc5 field line resonances in the post‐midnight Antarctic ionosphere on April 28/29 1997. Simultaneous oscillations were seen in the solar wind parameters observed by WIND. The spectra of both sets of data show peaks near 1.3 mHz, 1.9 mHz, 2.7 mHz and 3.3 mHz. The data were bandpass filtered and a complex demodulation technique applied to calculate the instantaneous energy flux in the solar wind in each band and hence the power incident on the front of the magnetosphere 70 minutes later. The magnitude of the instantaneous power deposited in the ionosphere at each frequency through Joule heating followed this closely and was an order of magnitude smaller. We conclude that, at least on this occasion, the field line resonances could have been directly driven by the solar wind oscillations.

Augmentation of respiratory sinus arrhythmia in response to progressive hypercapnia in conscious dogs.

Respiratory sinus arrhythmia (RSA) may serve to enhance pulmonary gas exchange efficiency by matching pulmonary blood flow with lung volume within each respiratory cycle. We examined the hypothesis that RSA is augmented as an active physiological response to hypercapnia. We measured electrocardiograms and arterial blood pressure during progressive hypercapnia in conscious dogs that were prepared with a permanent tracheostomy and an implanted blood pressure telemetry unit. The intensity of RSA was assessed continuously as the amplitude of respiratory fluctuation of heart rate using complex demodulation. In a total of 39 runs of hypercapnia in 3 dogs, RSA increased by 38 and 43% of the control level when minute ventilation reached 10 and 15 l/min, respectively (P < 0.0001 for both), and heart rate and mean arterial pressure showed no significant change. The increases in RSA were significant even after adjustment for the effects of increased tidal volume, respiratory rate, and respiratory fluctuation of arterial blood pressure (P < 0.001). These observations indicate that increased RSA during hypercapnia is not the consequence of altered autonomic balance or respiratory patterns and support the hypothesis that RSA is augmented as an active physiological response to hypercapnia.

Physiologic instability in panic disorder and generalized anxiety disorder

Background: Because panic attacks can be accompanied by surges in physiologic activation, we tested the hypothesis that panic disorder is characterized by fluctuations of physiologic variables in the absence of external triggers. Methods: Sixteen patients with panic disorder, 15 with generalized anxiety disorder, and 19 normal control subjects were asked to sit quietly for 30 min. Electrodermal, cardiovascular, and respiratory measures were analyzed using complex demodulation to quantify variability in physiologic indices. Results: Both patient groups reported equally more anxiety and cardiac symptoms than control subjects, but certain other somatic symptoms, including breathlessness, were elevated only in panic disorder patients. Mean end-tidal pCO 2 and respiratory rates were lower, and tidal volume and the number of sighs were higher in panic disorder patients than control subjects. Neither cardiovascular (heart rate, arterial pressure, cardiac output), nor electrodermal instability including sighs distinguished the groups; however, tidal volume instability was greater in panic disorder than generalized anxiety disorder patients or control subjects. Several other respiratory measures (pCO 2, respiratory rate, minute volume, duty cycle) showed greater instability in both patient groups than in control subjects. Conclusions: Respiration is particularly unstable in panic disorder, underlining the importance of respiratory physiology in understanding this disorder. Whether our findings represent state or trait characteristics is discussed.

An improved method for hardware-based complex demodulation

Carrier-based measurements usually obtain signals which are as well modulated in amplitude as in phase. Such complex modulated information needs to be separated with special methods extensively described in the literature. One problem is common for all methods: the costly processing of signals makes the use of microprocessors necessary. But this again raises the price of a measurement device so that a cheaper, completely hardware-based demodulation principle is desired. A basic method with hard restrictions concerning the modulation depth was introduced at the XVth IMEKO World Congress in Osaka and additional improvements for a more reliable device are shown in this paper.

Differential effects of hypoxia and hypercapnia on respiratory sinus arrhythmia in conscious dogs.

To test the hypothesis that hypoxia and hypercapnia have different effects on the genesis of respiratory sinus arrhythmia (RSA), the magnitude of RSA to these stimuli was compared in 3 unanesthetized dogs. Respiration was continuously monitored through a permanent tracheostomy, and the electrocardiogram and blood pressure were also monitored. The magnitude of RSA was assessed as an instantaneous amplitude of the R-R interval oscillation in the high-frequency band of 0.15-0.80Hz by means of complex demodulation. In a total of 47 runs with hypoxia, heart rate, mean arterial pressure, respiratory rate and tidal volume increased, but RSA magnitude decreased even after adjusting for the effects of respiratory rate and tidal volume. In a total of 39 runs with hypercapnia, heart rate and mean arterial pressure did not change, despite the increased respiratory rate and tidal volume. In contrast to hypoxia, RSA magnitude increased even after adjusting for the effects of respiratory rate and tidal volume. The different effects of the two respiratory stimuli on RSA magnitude were noted at any level of ventilation and support the original hypothesis.

Technique for the quantification of transient quadratic phase couplings between heart rate components.

A technique for the time-variant analysis of quadratic phase coupling (QPC) in heart rate data is introduced and tested in 6 human neonates during quiet sleep. The set up of the approach is based up on the assumption that QPCs in the heart rate variability (HRV) are related to amplitude modulation effects. The application of the biamplitude deals with the detection of the coupling pattern and the bicoherence is used for the statistical quantification of coupling. By means of the results of bispectral analysis the time-variant processing has been adapted. The frequency-selective complex demodulation of the HRV leads to the envelope of the respiratory sinus arrhythmia (RSA), this has been used as one input for a time-variant coherence analysis. The other input is the low-pass filtered 10-second-rhythm of the HRV. A time-continuous quantification of the QPC, caused by amplitude modulation (10-second-rhythm modulates the RSA), is possible using this approach. According to our observed results in neonatal HRV both a phase co-ordination between the 10-second-rhythm and RSA as well as a non-linear coupling (amplitude modulation) between these HRV components can be seen.

Faraday rotation densitometry for Large Helical Device

A CO2 laser polarimeter to measure the Faraday rotation in the large helical device (LHD) was developed and installed on a LHD. A CO2 laser whose wavelength is 10.6 μm was selected to avoid effects of the refraction. The Faraday rotation angle along toroidally tangential chords is of the order of one degree. The polarimeter utilizes the frequency-shift heterodyne technique with the use of acousto-optic modulators for high resolution. This polarimeter can be operated with a maximum of three channels. The accuracy of the Faraday rotation angle with a time resolution of 16 ms is about 0.01 deg by digital complex demodulation. We succeeded in performing preliminary measurements of the Faraday rotation angle from LHD plasmas and the values were 10%–30% larger than those estimated with the electron density profiles from interferometry.

Fiberoptic heterodyne magnetic field sensor for long-pulsed fusion devices

A heterodyne polarimeter which measures the Faraday effect has been under development as a magnetic field sensor for long-pulsed fusion devices. The wavelength of laser beam was chosen to be 850 nm since the radiation-induced loss in optical fibers is significant below 800 nm while the Faraday rotation angle decreases with increasing wavelength. By the use of a distributed Bragg reflector laser diode and a Faraday isolator, excellent stability of phase measurement was attained. The phase resolution was raised to up to 0.02° by the digital complex demodulation and digital bandpass filtering of beat signals. Although the Verdet constant of heavily Tb3+-doped paramagnetic glass is larger than that of ZnSe by about a factor of 1.4, ZnSe is superior to the former in terms of negligible temperature dependence. With a 40-mm-long ZnSe sensing rod, resolutions of the magnetic field strength of about 5 and 2 G were found to be possible with time responses of 1 and 10 ms, respectively.

Impact of acute hypoxia on heart rate and blood pressure variability in conscious dogs.

To examine whether the impacts of hypoxia on autonomic regulations involve the phasic modulations as well as tonic controls of cardiovascular variables, heart rate, blood pressure, and their variability during isocapnic progressive hypoxia were analyzed in trained conscious dogs prepared with a permanent tracheostomy and an implanted blood pressure telemetry unit. Data were obtained at baseline and when minute ventilation (VI) first reached 10 (VI10), 15 (VI15), and 20 (VI20) l/min during hypoxia. Time-dependent changes in the amplitudes of the high-frequency component of the R-R interval (RRIHF) and the low-frequency component of mean arterial pressure (MAPLF) were analyzed by complex demodulation. In a total of 47 progressive hypoxic runs in three dogs, RRIHF decreased at VI15 and VI20 and MAPLF increased at VI10 and VI15 but not at VI20, whereas heart rate and arterial pressure increased progressively with advancing hypoxia. We conclude that the autonomic responses to isocapnic progressive hypoxia involve tonic controls and phasic modulations of cardiovascular variables; the latter may be characterized by a progressive reduction in respiratory vagal modulation of heart rate and a transient augmentation in low-frequency sympathetic modulation of blood pressure.

Early onset and tropical forcing of 100,000-year Pleistocene glacial cycles.

Between 1.5 and 0.6 Myr ago, the period of the Earth's glacial cycles changed from 41 kyr, the period of the Earth's obliquity cycles, to 100 kyr, the period of the Earth's orbital eccentricity, which has a much smaller effect on global insolation. The timing of this transition and its causes pose one of the most perplexing problems in palaeoclimate research. Here we use complex demodulation to examine the phase evolution of precession and semiprecession cycles--the latter of which are phase-coupled to both precession and eccentricity--in the tropical and extratropical Atlantic Ocean. We find that about 1.5 Myr ago, tropical semiprecession cycles (with periods of about 11.5 kyr) started to propagate to higher latitudes, coincident with a growing amplitude envelope of the 100-kyr cycles. Evidence from numerical models suggests that cycles of about 10 kyr in length may be required to explain the high amplitude of the 100-kyr cycles. Combining our results with consideration of a modern analogue, we conclude that increased heat flow across the equator or from the tropics to higher latitudes around 1.5 Myr ago strengthened the semiprecession cycle in the Northern Hemisphere, and triggered the transition to sustained 100-kyr glacial cycles.