Wave Amplitude Changes Research Articles

Cardiac Magnetic Resonance Elastography

To develop cardiac magnetic resonance elastography (MRE) for noninvasively measuring left ventricular (LV) pressure-volume (P-V) work. The anterior chest wall of 8 healthy volunteers was vibrated by 24.3-Hz acoustic waves for stimulating oscillating shear deformation in myocardium and adjacent blood. The induced motion was recorded by an electrocardiogram-gated, vibration-synchronized and segmented gradient-recalled echo MRE sequence acquiring 360 phase-contrast wave images with a temporal resolution of 5.16 milliseconds in the short-axis view during controlled breathing. Relative changes in wave amplitudes served as a measure of LV pressure variation during the cardiac cycle. MRE pressure data were combined with LV volumes obtained from segmentation of 3D cine-steady-state free precession data sets. Shear wave amplitudes decreased from diastole to systole, which reflects the dynamics of myocardial shear modulus variations during the cardiac cycle. Assuming spherical shear stress, a linear relationship between myocardial stiffness and LV pressure was derived. The MRE-measured pressure was plotted as a function of LV volumes. Characteristic P-V cycles displayed an isovolumetric increase in pressure during early systole, whereas less pronounced volume conservation was observed in early diastole. Mean cardiac P-V work in all volunteers was 0.85 +/- 0.11 J. In vivo cardiac MRE is a noninvasive method for measuring pressure-related heart function determined by shear modulus variations in the LV wall. This is the first noninvasive mechanical test of cardiac work in the human heart and is potentially useful for assessing pathologies associated with increased myocardial stiffness such as diastolic dysfunction.

Radio remote sensing of the corona and the solar wind

AbstractModern radio telescopes are extremely sensitive to plasma on the line of sight from a radio source to the antenna. Plasmas in the corona and solar wind produce measurable changes in the radio wave amplitude and phase, and the phase difference between wave fields of opposite circular polarization. Such measurements can be made of radio waves from spacecraft transmitters and extragalactic radio sources, using radio telescopes and spacecraft tracking antennas. Data have been taken at frequencies from about 80 MHz to 8000 MHz. Lower frequencies probe plasma at greater heliocentric distances. Analysis of these data yields information on the plasma density, density fluctuations, and plasma flow speeds in the corona and solar wind, and on the magnetic field in the solar corona. This paper will concentrate on the information that can be obtained from measurements of Faraday rotation through the corona and inner solar wind. The magnitude of Faraday rotation is proportional to the line of sight integral of the plasma density and the line-of-sight component of the magnetic field. Faraday rotation provides an almost unique means of estimating the magnetic field in this part of space. This technique has contributed to measurement of the large scale coronal magnetic field, the properties of electromagnetic turbulence in the corona, possible detection of electrical currents in the corona, and probing of the internal structure of coronal mass ejections (CMEs). This paper concentrates on the search for small-scale coronal turbulence and remote sensing of the structure of CMEs. Future investigations with the Expanded Very Large Array (EVLA) or Murchison Widefield Array (MWA) could provide unique observational input on the astrophysics of CMEs.

Differential effects of osmotherapy on static and pulsatile intracranial pressure*

A bolus infusion of 7.2% saline in 6% hydroxyethyl starch 200/0.5 (HS) attenuates static intracranial pressure (mean ICP) in subarachnoid hemorrhage patients. This study addressed how HS affects intracranial pulsatility, which is more indicative of intracranial compliance than static ICP. Retrospective analysis of prospectively collected data. Intensive care unit in a university hospital. Sedated and mechanically ventilated patients suffering from spontaneous subarachnoid hemorrhage. Twenty patients received an infusion of HS, mean 1.5 mL/kg. Static ICP was characterized by mean ICP and intracranial pulsatility by mean ICP wave amplitude, both parameters determined simultaneously during consecutive 6-sec time windows. We compared average values of these parameters during 15-min periods just before the infusion and after maximum effect was reached. Mean ICP wave amplitude decreased 3.4 mm Hg from a baseline of 9.8 mm Hg, p < 0.0001. However, even though a target level of <15 mm Hg was reached for mean ICP in 65% of interventions, the target of <5 mm Hg for mean ICP wave amplitude was reached in only 30% of interventions. We found no correlation between changes in mean ICP wave amplitude and mean systemic arterial blood pressure wave amplitude, p = 0.27. The results confirm that osmotherapy attenuates both static ICP (mean ICP) and pulsatile ICP (mean ICP wave amplitude). Most importantly, however, during the majority of HS infusions, the target value of mean ICP wave amplitude was not reached even though the targets for mean ICP and mean cerebral perfusion pressure were reached. This suggests that the intracranial compliance state was still unfavorable even though mean ICP and mean cerebral perfusion pressure had reached normal ranges. The reduction in intracranial pulsatility could not be explained by attenuation in arterial pulsatility because there was no correlation between ICP and arterial blood pressure wave amplitudes.

Experimental study of wave–wave nonlinear interactions using the wavelet-based bicoherence

The wavelet-based bicoherence, which is a new and powerful tool in the analysis of nonlinear phase coupling, is used to study the nonlinear wave–wave interactions of breaking and non-breaking gravity waves propagating over a sill. Two cases of mechanically generated random waves based on J onswap spectra are used for this purpose. Values of relative depth, k p h ( k p is the wave number of the spectral peak and h is the water depth) for this study range between 0.38 and 1.22. The variations of wavelet-based total bicoherence for the test cases indicate that the degree of quadratic phase coupling increases in the shoaling region consistent with a wave profile that is pitched shoreward, relative to a vertical axis as seen in the experiments, but decreases in the de-shoaling region. For the non-breaking case, the degree of quadratic phase coupling continues to increase until waves reach the top of the sill. Breaking waves, however, achieve their highest level of quadratic phase coupling immediately before incipient breaking and the degree of phase coupling decreases sharply following breaking. In addition the wavelet-based bicoherence spectra provide evidence of the harmonics' growth which is reflected in the energy spectra. The bicoherence spectra also show that quadratic phase coupling between modes within the peak frequency as well as between modes of the peak frequency and its higher harmonics are dominant in the shoaling region, even though there are relatively high levels of quadratic phase coupling occurring between other frequencies. Furthermore, using the temporal resolution property of the wavelet-based bicoherence, we find that the quadratic wave interactions occur more readily during segments of time with large change of wave amplitude, rather than those segments having large wave amplitudes, but small gradients in amplitude.

Characterization of stiffness degradation caused by fatigue damage in textile composites using circumferential plate acoustic waves

The aim of this paper is to show the possibility of fatigue damage characterization in GFRP-tube-like components by using circumferential plate waves. For that purpose, fatigue tests with different loading directions have been conducted and the stiffness degradation has been monitored. After a preset number of loading cycles, non-destructive ultrasonic tests using circumferential plate waves were performed. The correlation between damage induced amplitude changes of the plate waves and stiffness degradation in non-crimped fabric composites is discussed. The results indicate that the technique is applicable to fatigue damage assessment in complex-shaped components of composite materials and is relevant to a wide field of applications.

Potenciais evocados auditivos pré e pós-tratamento em indivíduos gagos: estudo piloto

P300 event-related potential has been used as an instrument to establish the diagnosis of several disorders as well as to assess therapeutic outcomes. to investigate the relationship between stuttering amelioration and cerebral activity. P300 event-related potentials were obtained in three adult males, all stutterers, aged 20 to 31 years, pre and post-treatment, verifying changes in wave amplitude and latency between waves. results indicate a significant positive correlation between the reduction in the percentage of stuttered syllables and the improvement in wave amplitude for the right ear. stutterers can exhibit different patterns of interhemispheric activity with a tonal P300 task after undergoing a fluency-enhancing program.

Vascular Reactivity: Evaluation of an acute suprasystolic occlusion with impedance plethysmography

In the clinical set, the evaluation of endothelium- dependent vasodilator response of large vessels is carried out using ultrasound equipment for vascular flow determinations and during administration of vasoactive drugs. This work proposes to use a substantially cheaper technique and a sustained cuff arterial occlusion in order to cause vasodilation. Impedance plethysmography is used to detect the arterial pulse wave over radial artery while the forearm is occluded by above the recording site. From these plethysmographic waves, three indexes and their changes -between control and maximal response post-occlusion- were calculated. 33 complete records obtained from healthy low-risk volunteers were analyzed. Between control and post-occlusion maximal response, "average percentual change of pulse wave amplitude" were (35±13)%, "stiffness index" did not show significant differences (6,38±0,98 vs 6,38±0,94 and "reflection index" was significant lower (58±15 vs 35±16)%. These results indicate that: 1- cuff occlusion maneuver was effective to cause endothelium-dependent vasodilation, 2-changes of pulse wave amplitude and reflection index could be used as markers of athero-arteriosclerotic damage in the vascular bed, even in sub-clinical conditions.

A Psychophysiological Study of Auditory Illusions of Approach and Withdrawal in the Context of the Perceptual Environment

Auditory perception of the depth of space is based mainly on spectral and amplitude changes of sound waves originating from the sound source and reaching the listener. The perceptive illusion of movement of an auditory image caused by changes in amplitude and/or frequency of the signal tone emanating from an immobile loudspeaker was studied. Analysis of data obtained from the participants revealed the diapason of combinations of amplitude and frequency changes for which the movement direction was perceived similarly by all participants, despite significantly different movement assessment criteria. Additional auditory and visual information of the conditions of radial movement (near or far fields) determined listeners' interpretation of changes in the signal parameters. The data obtained about the perception of approach and withdrawal models are evidence of the fact that the principal cues of the perception of the distance of immobile sound sources manifests similarly to that of an auditory image moving along a radial axis.

Optimization of Hydrophone Centering in Circular Ultrasonic Transducer during Field Characterization Using Edge Waves: A Feasibility Study

In this article, we present a feasibility study using transducer edge waves to center a hydrophone during field characterization. A mathematical analysis is presented to study amplitude changes in edge waves; this analysis is based on the impulse response method and considers the transducer as a piston embedded in a rigid planar baffle. The experimental setup used to measure the edge waves is also presented. It has been observed, mathematically and experimentally, that edge wave amplitude reaches its maximum when the hydrophone is centered and that these amplitude changes are very sensitive to position, approximately 70% of its maximal amplitude; however, amplitude changes in front planar waves are less evident (10%). Agreement between experimental and calculated results demonstrates that changes in edge wave amplitude can be used to center the hydrophone in an objective way.

Impedance Progress

Changes in global arterial function and blood pressure pulsatility play an important role in the exponential increase in the incidence of various common afflictions of aging. However, our current approach to hemodynamics, evaluating the peak (systolic blood pressure) and trough (diastolic blood pressure) of the blood pressure waveform in the arm, provides a limited view of pulsatile hemodynamics. As a first refinement, blood pressure can be separated into steady-flow and pulsatile components, mean arterial pressure (MAP) and pulse pressure (PP), respectively. Numerous recent studies have shown that many serious clinical events may be more closely linked to PP, which is related to large artery stiffness, rather than MAP, which is determined by small artery function and cardiac output. However, systolic blood pressure or PP in the arm probably does not tell the full story. Conventional brachial systolic blood pressure represents a variable composite of PP (large arteries) and MAP (small arteries), depends on ventricular ejection characteristics and arterial properties, and, because of transmission delays and wave reflection, may not be fully representative of central aortic pressure, which may be more relevant to cardiac and cerebral function. These additional sources of variability may have important implications for the pathogenesis of cardiovascular disease and response to treatment. The study by Segers et al1 in the current issue of Hypertension represents an important step forward in our quest to quantify the effects of regional arterial function on the pathogenesis of cardiovascular disease in the community. The authors are reporting pulsatile hemodynamics from the first round of evaluations in a planned longitudinal, observational study of >2000 initially healthy men and women between 35 and 55 years of age recruited from 2 adjacent communities in the suburbs of Brussels, Belgium. The Asklepios investigators assessed pulsatile hemodynamics using a noninvasive approach first developed by Kelly …

Wave Gradiometry in Two Dimensions

The spatial displacement gradient of a seismic wave is related to dis- placement and velocity through two spatial coefficients for any one dimension. One coefficient gives the relative change of wave geometrical spreading with distance and the other gives the horizontal slowness and its change with distance. The essential feature of spatial gradient analysis is a time-domain relation between three seismo- grams that yields information on the amplitude and phase behavior of a seismic wave. Filter theory is used to find these coefficients for data from 2D areal arrays of seismometers, termed gradiometers. A finite-difference star is used to compute the displacement gradient for irregularly shaped gradiometers, and a relation for the frequency-dependent error in the displacement gradient is obtained and applied to ensure accurate estimates. This kind of array analysis is useful for gradiometers at any distance from a source and yields a variety of time-domain and frequency-domain views of wave-amplitude changes and horizontal phase velocity estimates across the gradiometer. For example, time-dependent horizontal slowness and wave-azimuth plots are natural results of the analysis. These time-domain maps may be used in conjunction with time-distance and horizontal slowness-distance models to locate seismic sources or may be used directly to study earth structure. These methods are demonstrated by using data from a small-aperture (40 m) seismic gradiometer.

SPR response of stimuli-sensitive microgel on sensor chip

Behavior of stimuli-sensitive microgels on SPR (surface plasmon resonance) sensor chip was studied using poly( N-isopropylacrylamide- co-acrylic acid) microgels. The microgels were prepared by aqueous free-radical precipitation copolymerization. They were monodisperse spheres with a diameter less than 200 nm. The dispersions of microgels in different buffer solutions were run over the SPR chip which was covered with a self-assembled monolayer (SAM) having amine functional groups at the top surface. The number of microgels bound to the chip was inversely proportional to the hydrodynamic size of microgel. SPR response of microgels bound to the chip was found to be controlled by two factors: the microgel-inducing change in evanescent wave amplitude and the number of microgels. The former is a function of depth-depending evanescent field strength, refractive index, and volume of swollen microgel. The simulated SPR response based on this function was consistent with experimental response.

Monitoring of scoliosis surgery with epidurally recorded motor evoked potentials (D wave) revealed false results

Objective To elucidate the mechanism behind D wave amplitude changes after surgical correction of scoliosis. Methods We collected D wave and muscle MEP data from 93 patients (78 female, 15 male, age range 4–19 years, mean age 15.9 years), who underwent surgical correction of scoliosis. D waves were recorded via a catheter electrode inserted epidurally through the flavectomy. Muscle MEPs from lower limb muscles were also recorded. Muscle MEPs/D wave were elicited by short trains/single transcranial electrical stimuli. SEPs were elicited through bilateral percutaneous stimulation of the tibial nerves at the ankle and an averaged response from 100 to 200 single sweeps were recorded over the scalp at Cz’/Fz. In addition, we analyzed intraoperatively obtained X-ray images of the spine in 9 patients and preoperative spinal MRI in two of those nine. Results After surgical correction of scoliosis in 25 of 93 (27%) patients, the D wave amplitude changed by more than 20% of its baseline value. A decremental change occurred in 21 (84%) and an incremental change in 4 (16%) patients. D wave decrements of more than 50% were observed in 5 patients without significant SEP changes in any of these cases. In 9 patients, intraoperatively obtained X-rays of the spine (before and after correction of spine curvature) showed no catheter displacement. Muscle MEPs did not change and postoperative sensory-motor status was normal. In 2 patients, preoperative MRI revealed displacement of the spinal cord towards the concave side of the scoliotic curvature. Conclusions During scoliosis surgery, D wave amplitude changes should be interpreted cautiously until the definitive cause(s) of these changes are found. One possible mechanism to explain D wave changes during scoliosis correction could involve rotation of the spinal cord within the spinal canal, and the relative position of the epidural recording catheter (ERC). Rotation of the spinal cord after correction of scoliosis could introduce a new relationship between the ERC and the corticospinal tracts (CTs). Due to high incidence of false D wave amplitude changes we suggest that this methodology should not be used to assess the functional integrity of the CTs during scoliosis surgery. Significance This study provides new insight into the methodology of D wave monitoring as well as strong evidence of a high incidence of false positive results using D wave monitoring during surgical correction of scoliosis.

A laboratory experiment to monitor the contact state of a fault by transmission waves

We performed a series of laboratory experiments in which elastic waves were transmitted across a simulated fault. Two types of experiments were carried out: (1) Normal Stress Holding Test (NSHT): normal stress was kept constant for about 3 h without shear stress and transmission waves were observed. (2) Shear Stress Increasing Test (SSIT): shear stress was gradually increased until a stick-slip event occurred. Transmission waves were continuously observed throughout the process of stress accumulation. We focused on the change in transmission waves during the application of shear stress and especially during precursory slips. It was found in NSHT that the amplitude of transmission waves linearly increased with the logarithm of stationary contact time. The increase amounted to a few percent after about 3 h. Creep at asperity contacts is responsible for this phenomenon. From a theoretical consideration, it was concluded that the real contact area increased with the logarithm of stationary contact time. We observed in SSIT a significant increase in wave amplitude with shear stress application. This phenomenon cannot be attributed to the time effect observed in NSHT. Instead, it can be explained by the mechanism of “junction growth” proposed by Tabor. Junction growth yields an increase in real contact area. It is required for junction growth to occur that the material in contact is already plastic under a purely normal loading condition. A computer simulation confirmed that this requirement was satisfied in our experiments. We also found that the rate at which the amplitude increased was slightly reduced prior to a stick-slip event. The onset time of the reduction well coincides with the onset of precursory slip. The cause of the reduction is attributed to the reset of stationary contact time due to displacement. This interpretation is supported by the result of NSHT. Taking the time of stationary contact in SSIT into account, we may expect the change in wave amplitude to be, at most, only a few percent. The observed slight reduction in increasing rate is, in this sense, reasonable. The static stiffness of the fault also decreases with precursory slip. It was also found that low frequency waves are a better indicator of precursory slip than high frequency waves. This might suggest that low frequency waves with longer wavelength are a better indicator of average behavior of faults. The problem, however, merits a further investigation. The shifts in phase were also found to be a good indicator of the change in contact state of the fault. The changes in both amplitude and phase of transmission waves are unifyingly understood through the theory of transmission coefficient presented by Pyrak-Nolte et al. Rough surfaces have a tendency to give larger stick-slips than smooth surfaces. The amount of precursory slip is larger for rough surfaces than for smooth surfaces. Although it was confirmed by a computer simulation that rough surfaces have larger contact diameters than smooth surfaces, the rigorous relationship between the surface roughness (contact diameter) and the amount of precursory slips was not established.

Stiffness‐weighted magnetic resonance imaging

An imaging method is introduced in which the signal in MR images is affected by the stiffness distribution in the object being imaged. Intravoxel phase dispersion (IVPD) that occurs during MR elastography (MRE) acquisitions decreases the signal in soft regions more than in stiff regions due to changes in shear wave amplitude and wavelength. The IVPD effect is enhanced by lowpass filtering the MR k-space data with a circular Gaussian lowpass filter. A processing method is introduced to take the time series of MRE magnitude images with IVPD and produce a final stiffness-weighted image (SWI) by calculating the minimum signal at each pixel from a small number of temporal samples. The SWI technique is demonstrated in phantom studies as well as in the case of a preserved postmortem breast tissue specimen with a stiff lesion created by focused ultrasound ablation to mimic a breast cancer. When free of significant sources of depth-dependent wave attenuation, interference, and boundary effects, SWI is a simple, fast, qualitative technique that does not require the use of phase unwrapping or inversion algorithms for localizing stiff regions in an object.

Incipient breaking of unsteady waves on sheared currents

Incipient breaking of unsteady waves on sheared currents is experimentally investigated. A new wave-generation technique, based on the iterative frequency-focusing concept with the consideration of effects of Doppler shift and current shear, is developed. The surface displacement, the wavelength, and the phase speed of waves at the breaking onset on shear currents are measured. It is found that the steepness of unsteady, incipient breaking waves is altered by the sign and magnitude of current shear (or vorticity). A current with a positive shear, as would be the case in a wind-driven current, reduces the steepness of an unsteady incipient breaking wave. A negatively sheared current, such as the jet-like ebb current at a tide inlet, leads to steeper incipient breaking waves. The magnitude of reduction/increase in wave steepness is proportional to the strength of a current shear. In particular, a negative shear can alter the wave steepness more significantly in comparison to a positive shear of the same magnitude. Interestingly, the trend of crest-trough asymmetry with respect to the change of a current shear is in contrast to the limiting wave steepness. A positively sheared current can dramatically increase crest-trough asymmetry for unsteady waves. Dimensionless amplitudes of unsteady waves at incipient breaking are well correlated with surface current drifts. Positive/negative surface drifts lead to the reduced/increased dimensionless wave amplitudes. However, the change in dimensionless wave amplitude of unsteady waves is much smaller than that of steady waves.

Obstructive sleep apnea syndrome: effect of respiratory events and arousal on pulse wave amplitude measured by photoplethysmography in NREM sleep

The objective of the study is to evaluate changes in finger pulse wave amplitude (PWA), as measured by photoplethysmography, and heart rate (HR), related to obstructive respiratory events and associated arousals during sleep. We analyzed 1,431 respiratory events in NREM sleep from 12 patients according to (1) the type of event (apnea, hypopnea, upper airway resistance episode) and (2) the duration of the associated EEG arousal (>10, 3-10, <3 s). Obstructive respiratory events provoked a relative bradycardia and vasodilation followed by HR increase and vasoconstriction. Relative PWA changes were significantly greater than HR changes. These responses differed significantly according to EEG-arousal grades (time x arousal interaction, p<0.0001), with longer arousals producing greater responses, but not to the type of respiratory event (time x event interaction, p = ns). Obstructive respiratory events provoke HR and PWA changes, the magnitude seemingly related to the intensity of central nervous activation, with PWA changes greater than HR. PWA obtained from a simple pulse oxymeter might be a valuable method to evaluate sleep fragmentation in sleep breathing disorders.

Brainstem auditory-evoked responses in full-term newborn infants with temporary low Apgar score

ConclusionsNo abnormalities, with the exception of maturational changes, in BAER were found during the neonatal period. The results suggest that a temporary low Apgar score is not accompanied by any significant auditory impairment.ObjectiveTo examine brainstem auditory function in newborn infants with a temporary low Apgar score but no clinical signs of hypoxic–ischaemic encephalopathy (HIE).Material and methodsThe subjects were 36 full-term infants with Apgar scores of ≤7 at 1 and/or 5 min and ≥8 at 10 min but without HIE. The brainstem auditory-evoked response (BAER) was serially recorded at click rates of 21, 51 and 91/s on Days 1, 3, 5, 7 and 30 after birth.ResultsOn Day 1 and Days 3–5, the latencies of waves I, III and V tended to increase slightly at all click rates but did not differ significantly from normal control values. Thereafter, all latencies tended to decrease, reaching control values on Day 30. The I–V interval was similar to the control values at all click rates during the first 5 days, tended to decrease from Day 7 and did not differ from the control values on Day 30. There were no significant changes in BAER wave amplitudes at any of the click rates on any day.

P Wave Amplitude Changes in Patients with Normal and Abnormal Exercise Tests

P Wave Amplitude Changes in Patients with Normal and Abnormal Exercise Tests

The triangular wave test for electrocardiographic devices: A historical perspective

Baseline wander makes interpretation ECG recordings difficult, especially the assessment of ST deviation. Eliminating baseline wander without distorting the ST segment is a problem. The traditional high pass filter with a 0.5 Hz low frequency cutoff effectively suppresses baseline but introduces considerable distortion in the level of the ST segment. This distortion results from phase nonlinearities that occur when frequency content and wave amplitude change abruptly, as occurs where the end of the QRS complex meets the ST segment. Since the 1980s nonlinear, digital filters have been designed that can increase the low frequency cutoff without the introduction of phase distortion. The triangular wave test, first described in the 1990 AHA Recommendations, is an objective method for measuring the ability to suppress baseline wander without affecting the ST segment. This methodology was adopted in 3 American National Standards (Diagnostic ECG in1991; Ambulatory ECGs in 1998; and Cardiac Monitors in 2002)