Common Waveform Research Articles

The ability of qualitative assessment of the common femoral doppler waveform to screen for significant aortoiliac disease

To study the ability of a qualitative assessment of the common femoral Doppler waveform to screen for significant aortoiliac disease. Prospective, semi-blind study. Vascular laboratory, University Hospital. A total of 118 aortoiliac segments were studied in 73 patients. Each aortoiliac segment was graded as normal or abnormal from visual interpretation of the common femoral Doppler waveform obtained by colour duplex ultrasound. Full ultrasound assessment of the aortoiliac vessels acted as the "gold standard". Abnormal aortoiliac segments were defined by the presence of at least one > or = 50% diameter reducing lesion, whereas vessels considered "normal" included those with disease between 0-49% diameter reduction. An increase in peak systolic velocity of two-fold or greater was used to define a > or = 50% diameter reducing stenosis. Agreement between common femoral waveform analysis and the duplex scans was measured by the Kappa statistic. The Kappa value for the agreement between common femoral waveform analysis and duplex scans was 0.74 (95% CI; 0.62-0.86). This represents substantial agreement. Doppler waveform analysis had a sensitivity of 95%, specificity of 80% and accuracy of 87% for the prediction of a significant aortoiliac stenosis seen by ultrasound. Visual interpretation of the common femoral Doppler waveform is a sensitive and accurate technique for the prediction of significant aortoiliac stenosis. It is of particular value when full ultrasound aortoiliac assessments are not feasible due to time constraints, obesity or the presence of bowel gas.

Locomotor Rhythms in the Fiddler Crab, Uca subcylindrica

The locomotor activities of individual specimens of Uca subcylindrica (Stimpson) collected from semi-arid, supratidal habitats in south Texas and northeastern Mexico were studied in the laboratory using periodogram analysis. When crabs were placed under constant darkness (DD) or constant illumination (LL), free-running circadian rhythms were observed in the activity recordings. The locomotor activity of strongly rhythmic crabs in LL has an average period length of 24.4 h. Crabs held in DD express motor rhythms with periods of approximately 24.0 h. In LL the most common wave form for activity is unimodal, while under DD it is bimodal. Recordings under natural illumination (NL) revealed that both period length and the time of maximum activity (phasing) varied through the year. During winter months, the crabs are primarily diurnal with peaks in activity occurring between 0900 and 2100 h and possess a circadian rhythm with a 23.9 h period. During summer, crabs were nocturnal with maximal activity between 1300 and 0600 and a circadian period closer to 24.0 h. In these experiments, the rhythmic locomotor activities of U. subcylindrica are best described as “circadian”. This is unusual for a genus known for its expression of circatidal and circalunidian rhythms.

Synaptic Interactions between Primate Precentral Cortex Neurons Revealed by Spike-Triggered Averaging of Intracellular Membrane PotentialsIn Vivo

To document synaptic interactions between neurons in the precentral cortex of macaque monkeys, we recorded in vivo the intracellular (IC) membrane potentials of cortical neurons simultaneously with extracellular (EC) action potentials of neighboring cells. The synaptic potentials correlated with EC spikes were obtained by spike-triggered averages (STA) of the IC membrane potentials for 373 cell pairs recorded in anesthetized and awake behaving monkeys. Sixty-three STAs (17%) showed excitatory postsynaptic potentials (EPSPs), beginning after the trigger spike. Pure EPSPs had onset latencies of 0.9 +/- 0.7 msec (mean +/- SD) and amplitudes of 226 +/- 130 microV. Sixteen STAs (4%) showed postspike inhibitory postsynaptic potentials (IPSPs), with onset latencies of 0.4 +/- 0.4 msec and amplitudes of -274 +/- 188 microV. The most common waveform, observed in 82% of the STAs with features, was a broad depolarization straddling the trigger spikes, reflecting synchronized synaptic input to both IC and EC neurons. These average synchronous excitation potentials (ASEPs) began 14.3 +/- 6.6 msec before the trigger spike and had amplitudes of 1064 +/- 867 microV. Twenty-three STAs (6%) showed an average synchronous inhibitory potential (ASIP): a hyperpolarization beginning before the trigger spike and reflecting IPSPs produced by a group of local inhibitory cells synchronized with the trigger cell. ASIPs had an onset latency of -5.5 +/- 2.7 msec and amplitude of -589 +/- 502 microV. Combinations of synchronous and postspike potentials were also observed. Successive recordings provided examples of convergent and divergent connections between EC and IC cells. Neuron pairs with depolarizing postsynaptic potentials (PSPs) in the STA yielded peaks in the cross-correlograms of the IC and EC action potentials; the peak area was proportional to the amplitude of the PSP. These data suggest that a significantly larger proportion of cortical neurons interact through synchronous activity than through simple serial interactions; moreover, synchronous excitation affected more widely separated cell pairs than EPSPs and IPSPs, which were seen most often among the closest cells.

Common iliac artery flow velocity waveforms in fetuses with a single umbilical artery: a longitudinal study.

In fetuses with a single umbilical artery the entire blood flow to the placenta is transported through the common and internal iliac arteries from the side of the single artery, whereas the pelvic vessels from the side of the missing artery do not participate in the fetoplacental circulation. The aim of this study was to investigate the effect of gestational age on pelvic arterial blood flow in fetuses with single umbilical artery. In 15 fetuses with a single umbilical artery (SUA), common iliac artery flow velocity waveforms were studied longitudinally using high resolution colour Doppler ultrasonography at three gestational ages: 18 to 20 weeks, 28 to 30 weeks, and 35 to 37 weeks. The pulsatility index was measured in each common iliac artery and mixed model analysis of variance was used to examine the effect of gestational age and side. There was a highly significant difference in pulsatility index between common iliac arteries at all gestational ages, the values always being higher on the side that did not participate in the fetoplacental circulation (P < 0.001). For increasing gestation, the pulsatility index fell significantly in the SUA side but remained high in the non-SUA side (P < 0.001). This study shows that the asymmetry in the pelvic arterial blood flow in fetuses with SUA increases as pregnancy progresses, consistent with decreasing vascular resistance in the placenta and increasing resistance in the lower extremities.

Effective Defibrillation in Pigs Using Interleaved and Common Phase Sequential Biphasic Shocks

Previous studies have shown that low internal defibrillation thresholds (DFTs) can be attained by using two pairs of electrodes and combining biphasic shocks with sequential timing. The purpose of this two-part study was to test the defibrillation efficacy of two new shock sequences, an interleaved biphasic, and a common phase sequential biphasic, that utilized two pairs of electrodes and were developed from the concept of sequential biphasic shocks. In the first part, defibrillation catheters were placed in the right ventricle and the superior vena cava of six anesthetized pigs. A small patch electrode was placed on the LV apex through a subxiphoid incision and a cutaneous patch was placed on the left thorax. The mean DFT energies for the interleaved biphasic (5.2 +/- 0.4 J) and the common phase sequential biphasic waveforms (5.4 +/- 0.4 J) were substantially less (P < 0.0001) than those for either the sequential monophasic (10.6 +/- 1.0 J) or single biphasic waveforms (9.0 +/- 1.0 J). In the second study, which used nine anesthetized pigs, the importance of phase reversal was demonstrated by the finding that the DFT energy of a common phase sequential biphasic shock (6.2 +/- 0.4 J) was much less than a common phase sequential monophasic shock (17.9 +/- 1.3 J, P < 0.0001); furthermore, the average DFT for four common phase sequential biphasic configurations (5.7 +/- 0.2 J) was much less than for a configuration that was similar except that current flow was not reversed in one phase so that no biphasic effect was present (19.7 +/- 1.2 J). The efficacy of common phase sequential biphasics was comparable to that of sequential biphasics. The effectiveness of sequential biphasics, interleaved biphasics, and common phase sequential biphasics is possibly due to two mechanisms: (A) an increase in the potential gradient during a later phase in regions that were low during the first phase, and (B) the exposure of most of the myocardium to a biphasic shock that reduces the minimum extracellular potential gradient needed to defibrillate.

Clockless synchronisation of distributed concurrent processes

For synchronising operations in a distributed computer or control system where the units are closely coupled, the three-wire synchroniser, originally developed for the 1987 IEEE Futurebus Standard, has some advantages over the use of common clock waveforms. After pointing out these advantages and reviewing the operation of the synchroniser, the paper presents a recent development in which each unit of the system can carry out several sequences of operations concurrently, the sequences being largely independent of one another. Within any unit, the different sequences will generally operate on the same set of registers, and so precautions have to be taken to prevent operations in two or more of the sequences from accessing the same register at the same time. This is done by arranging for any sequence to be able, when necessary, to cause other sequences to pause, but otherwise each of them proceeds at its own maximum speed.

Temporal patterns of muscle activation for arm movements in three- dimensional space

Little is known about the patterns of muscle activation that subserve arm movement in three-dimensional space. In this study, activation patterns of seven arm muscles were related to the spatial direction of human arm movement. Twenty movement directions defined two orthogonal vertical planes in space. The arm movements were moderately paced; each movement lasted approximately 500 msec. New techniques of EMG analysis were developed to describe the temporal pattern of muscle activation. For each muscle, a principal component analysis revealed a common phasic and tonic waveform for all directions of movement, within one plane. A temporal shifting procedure based on best covariance values revealed activation delays associated with different movement directions. The results show a consistent pattern of temporal shifting of the common waveform for movements in different directions. Coupled with past results showing that activation amplitude is a function of the cosine angle of movement or force direction, the present results suggest a relatively simple control strategy for mechanically complex arm movements: neural circuits produce a common phasic and tonic activation waveform that is scaled in amplitude and delayed in time, depending on the desired movement direction.

Data compression of the ECG using neural network for digital Holter monitor

A data-compression algorithm for digital Holter recording using artificial neural networks (ANNs) is described. A three-layer ANN that has a hidden layer with a few units is used to extract features of the ECG (electrocardiogram) waveform as a function of the activation levels of the hidden layer units. The number of output and input units is the same. The backpropagation algorithm is used for learning. The network is tuned with supervised signals that are the same as the input signals. One network (network 1) is used for data compression and another (network 2) is used for learning with current signals. Once the network is tuned, the common waveform features are encoded by the interconnecting weights of the network. The activation levels of the hidden units then express the respective features of the waveforms for each consecutive heartbeat.

Evaluation of a computerised test for the assessment of peripheral vascular disease

This paper reports a study carried out in 200 patients to assess the effectiveness of a clinical vascular laboratory in the routine assessment of peripheral vascular disease (PVD) of the lower limb. Laboratory assessments involved a computer based hierarchical testing system incorporating pedal pressure indices, maximum walking distances and principal component analysis of the common femoral artery blood velocity waveform. The study fell into two parts. In the first, the laboratory assessments of 100 patients referred six years ago were compared retrospectively with their eventual clinical outcome. In this comparison, the laboratory provided a "diagnosis" which was 79% correct. In the second, a double blind prospective study was carried out in 100 patients to compare the vascular laboratory "diagnosis" with the diagnosis and prognosis of a skilled clinician, the outcome being compared one year after the initial assessment. In this study the laboratory proved to be correct in 78% of cases, the clinician in 70%. With a slightly modified computer protocol for the non vascular diagnosis, the computer would have been correct in 85% of cases. This test provides a quantitative and objective assessment of PVD which can assist in the patient's clinical diagnosis and management.

Precision limits of lifetime estimation algorithms as determined by Monte Carlo simulation: A comparison of theory and experiment

The estimation of exponential decay lifetimes is important in many areas of physics, but often difficult if the waveform produced by some particular process (say, fluorescence decay) is noisy. We have used a simulation technique which makes it possible to model accurately two common waveform analysis methods. Results from actual experiments can be compared with those produced by the simulation in order to investigate the nature of the measurement system’s precision limits and thereby effect a reduction of the measurement error. Specifically, an algorithm calculating decay lifetime from two data points exhibited a one-sigma error of 4% when the measurement signal-to-noise ratio was 40:1, compared with a 0.1% error of a least-squared error algorithm under similar conditions.

Equations for some transient overvoltage test waveforms

Simple equations are provided that satisfy the definitions of five of the most common transient overvoltage test waveforms: the ringwave specified in ANSI C62.41-1980, the fast transient specified in IEC 801, and the 8/20- mu s 1.2/50- mu s, and 10/1000- mu s waveforms. These equations are useful for performing computer simulations of the response of electronic circuits to transient overvoltages.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Relation of olfactory EEG to behavior: Time series analysis.

Oscillatory electroencephalographic bursts were measured from 64 electrodes implanted on the olfactory bulbs of rabbits. Oscillatory bursts that occurred before and during presentation of odorant conditioned stimuli (CSs) were selected in brief segments. Comparisons between the 64 traces and their spectra showed that, despite amplitude differences between channels, every burst had a common waveform over the entire array. The spectra showed 2 to 5 distinct peaks in each burst. Each trace was fitted with the sum of 5 cosines to express the burst in ten 8 X 8 matrices of amplitude and phase values at its peak frequencies. Two types of burst were identified. Those with dominant frequencies greater than 55 Hz had one narrow dominant spectral peak and reproducible spatial patterns of its amplitude within subgroups of bursts relating to control and odorant CS conditions. Those with dominant frequencies less than 55 Hz were disorderly; their spectra were broad, and their spatial patterns of amplitude did not reproduce within subgroups. A behavioral assay showed that the high- and not the low-frequency bursts contained odor-specific information.

Maturation of cortical potentials evoked by tibial-nerve stimulation in newborns, infants and children aged four and eight years.

This study traced changes in cortical activity (SsCEP) evoked by electrical stimulation of leg nerves during the period of fast morphological and functional development of the nervous system from birth to eight years of age. The study revealed complex waveform changes in the SsCEP during this period. At birth low-amplitude potentials with well-defined, simple, three-phasic waveform (P1, N2P2N3, P3) were present in only eight of 26 newborns: no SsCEP could be detected in 13 cases. At one year the SsCEP had a higher amplitude and the simple three-phasic waveform was seen in the majority of cases (15 of 22). At four years an SsCEP with a notch in the middle negative wave was the most common waveform, observed in nine of 18 cases. At eight years adult-like SsCEPs prevailed in the records: they showed well-defined peaks P1 (corresponding to P40 of adults), N2, P2 and N3 (probably corresponding to N75 of adults). Such waveforms were observed in 16 of 24 children. In newborns P1 had a latency of 37 . 5 +/- 2 . 54ms: at one year the latency decreased to 32 +/- 3 . 81ms and increased again in older children, corresponding to increasing body-length.

Evoked potentials from passive elbow movements. I. quantitative spatial and temporal analysis

Evoked potentials following perturbations of the forearm were recorded monopolarly at 8 scalp sites. Successive 10 msec bins of individual EPs were compared across subjects to determine intervals of consistent potential change. From this analysis it was possible to objectively sort subjects into two subpopulations with different common wave forms. Spatial vectors (potential gradient between two adjacent leads) were computed as well as Laplacian derivatives, to identify electrodes closest to source activity. Subsequently, temporal derivatives of the vectors were computed to define the timing of statistically significant response phases. To more precisely localize the largest potential gradients, component vectors (or their derivatives) in the Laplacians were resolved algebraically on a scaled representation of the scalp. Convergence of these resultant vectors from adjacent areas, identified zones of significant potential change which corresponded to known somatosensory areas. The two subpopulations had initial responses of similar topography localized to the central sulcal region. Subsequently, for one group the area of activated cortex expanded to include posterior parietal and more frontal areas. Prestimulus negative potential shifts had different distributions for the two groups and are described in relation to the poststimulus differences.

Analysis of femoral artery Doppler signals by LaPlace transform damping method.

The LaPlace transform damping (LTD) method of common femoral artery Doppler waveform analysis is a new method for assessing aortoiliac stenosis. A microcomputer was used to analyze the waveform to determine the value of the damping parameter, which is related to inflow stenosis. The study included 60 limbs with arterial disease and 20 limbs in normal control subjects. With a damping value of 0.60 used as the cutoff point between nonocclusive lesions and iliac stenoses of greater than 50% diameter reduction, we found a sensitivity of 100% and a specificity of 93% (overall accuracy 95%). Unlike Doppler waveform analysis by the pulsatility index method, the accuracy of the LTD method is not affected by occlusion of the superficial femoral artery. The Doppler signal processor and the computer currently used for the LTD analysis are simple to operate and fully suitable for routine use in a clinical vascular laboratory. Our experience indicates that the LTD method of waveform analysis provides the best noninvasive method for detection of significant inflow disease.

Analysis of femoral artery Doppler signals by LaPlace transform damping method

The LaPlace transform damping (LTD) method of common femoral artery Doppler waveform analysis is a new method for assessing aortoiliac stenosis. A microcomputer was used to analyze the waveform to determine the value of the damping parameter, which is related to inflow stenosis. The study included 60 limbs with arterial disease and 20 limbs in normal control subjects. With a damping value of 0.60 used as the cutoff point between nonocclusive lesions and iliac stenoses of greater than 50% diameter reduction, we found a sensitivity of 100% and a specificity of 93% (overall accuracy 95%). Unlike Doppler waveform analysis by the pulsatility index method, the accuracy of the LTD method is not affected by occlusion of the superficial femoral artery. The Doppler signal processor and the computer currently used for the LTD analysis are simple to operate and fully suitable for routine use in a clinical vascular laboratory. Our experience indicates that the LTD method of waveform analysis provides the best noninvasive method for detection of significant inflow disease.

The use of common carotid waveform analysis in the diagnosis of carotid occlusive disease.

Duplex scanning with spectral analysis of the pulsed Doppler signal are currently used to detect and classify disease at the carotid bifurcation. Although the sensitivity of the test exceeds 90%, the method has a lower specificity which ranges between 8 and 50%. The poor specificity is due to the difficulty in distinguishing flow disturbances normally present at the carotid bifurcation from those produced by minimal amount of disease. In order to improve the ability of the method to predict normalcy, new features measured from the low common carotid waveform are evaluated on 150 sides. The difference of frequency from the systolic peak (a) to the point of first zero slope after peak systole (b) was used to define the ratio (a-b)/a. A ratio greater than 0.5 was associated with 76% of the normal sides and only 7% of the diseased sides. A ratio below 0.5 was associated with 83% of the diseased sides. This ratio, when used alone, can improve the specificity of the method to 76%.

Diagnosis of brain death by common carotid artery velocity waveform analysis.

In addition to neurologic criteria, some test of cessation of brain blood flow is recommended before diagnosing "brain death." Cerebral arteriography, radionuclide scintigraphy, and contrast computed axial tomography, though reliable, possess significant practical limitations. Analysis of the dimensions and contours of common carotid Doppler velocity tracings of brain-dead patients has identified qualitative and quantitative differences not only from normal subjects, but also from patients with complete atheromatous carotid occlusion and from those unconscious after brain injury. Though accurate separation was initially made using computer-assisted classification function analysis, a simplified algorithmic approach using only three velocity waveform variables has been developed without loss of accuracy. The speed, simplicity, portability, and inexpensiveness of this approach commend its use.

Cerebrovascular assessment using a Doppler carotid scanner and real-time frequency analysis.

The results of two methods for noninvasively diagnosing carotid disease are described. In the first study, a color-coded continuous-wave Doppler scanner was used. As evaluated by arteriography in 56 sides, the sensitivity and specificity of the Doppler scanner for diagnosing carotid lesions with greater than 50% stenosis was 71% and 82%, respectively. We found that many of our initial problems could be overcome by the concomitant use of a real-time frequency analyzer. Specifically, when the Doppler waveforms were displayed, we found that: 1) signals that had been attenuated by calcification or plaques, or had reduced velocity as a result of a proximal stenosis, could still be detected; 2) when the velocity of flow was increased to compensate for a contralateral carotid stenosis, the waveforms could still be of diagnostic value; 3) distinguishing between the internal and external carotid arteries was easier than relying on the audio signal alone; 4) when the scan showed internal carotid occlusion, morphological evaluation of the external and common carotid waveforms was helpful in verifying the scan result; and 5) artifactual noise on the Doppler waveform could be recognized. In the second study, frequency analysis recordings were evaluated semiquantitatively by measuring peak frequency and the fractional width of the Doppler frequency spectrum at peak systole Our preliminary results show that this approach is of diagnostic value in that it has the potential to detect minor stenoses.

Laser‐generated ultrasonic waveforms in metals

A Q‐switched, Nd:YAG laser has been used to generate elastic waves within aluminum and mild steel disks. A single 24‐ns pulse from the laser irradiated one face of each disk, and acoustic displacements were detected at the other face following propagation through the substrate. A capacitance transducer was used as the detector, providing undistorted displacement waveforms over a wide bandwidth. The displacement waveform depended markedly on the irradiation conditions. At low laser power densities, such that generation occurred primarily by thermoelastic expansion, a common waveform was produced whose amplitude varied linearly with optical energy. At higher power densities in the presence of material ablation, the longitudinal amplitude increased substantially whereas that of the shear decreased. Wave propagation theory in a plate has been applied to the problem, and theoretical waveforms in good agreement with experiment have been produced; this leads to conclusions concerning the nature of the acoustic source formed by laser irradiation.