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PubMed2006

Echocardiographic estimation of pulmonary pressures.

Cardiac ultrasound plays a pivotal role in assessing pulmonary artery pressures. Estimation of right atrial pressure can be derived from the dimensions and respiratory variation of the inferior vena cava and Doppler modalities provide an accurate and comprehensive evaluation of right ventricular and pulmonary artery pressures. Peak pulmonary artery pressure can be calculated from continuous wave Doppler sampling of the tricuspid regurgitant jet, while pulsed wave Doppler sampling of the pulmonary regurgitant jet allows evaluation of mean and diastolic pulmonary artery pressures. In patients with tricuspid regurgitation that is either absent or not adequately detectable by Doppler method, Doppler right ventricular outflow tract investigation can be helpful. Recent data indicate that analysis of right ventricular function using myocardial Doppler echocardiography may also provide new insights for the non-invasive estimation of pulmonary artery pressures. In particular, right ventricular isovolumic relaxation time measured by myocardial Doppler echocardiography at the tricuspid annulus may provide an alternative method for estimating pulmonary artery pressure, especially in patients with tricuspid regurgitation not detectable or spectral Doppler not properly interpretable.

Atrial Function, Right↗

PubMed2002

Effects of lifetime ethanol consumption on postural control: a computerized dynamic posturography study.

The relationship between lifetime alcohol consumption and postural control was investigated in 35 subjects with no clinically-detectable neurologic abnormalities, using computerized dynamic posturography (CDP) procedures. The estimated total number of lifetime alcoholic drinks was positively correlated with anteroposterior sway spectral power within the 2-4 Hz and 4-6 Hz frequency bands, in three Sensory Organization Test (SOT) conditions: eyes closed with stable support surface (SOT 2), eyes open with sway-referenced support (SOT 4), and eyes closed with sway-referenced support (SOT 5). All correlations remained significant after controlling for subject age, and were increased after excluding nine drug-abusing subjects. In contrast to the strong findings for frequency-based measures, no correlation was observed using conventional amplitude-based sway measures. These results suggest that 1) alcohol consumption compromises postural control in an exposure-dependent manner, and 2) sway frequency analysis reveals pathological processes not manifested in conventional CDP measures of sway amplitude.

Adult↗

PubMed1993

1H NMR studies of gamma-irradiated polynucleotides and DNA in N2O-saturated aqueous solutions: release of undamaged and modified bases.

In the 400-MHz 1H NMR spectra of gamma-irradiated, N2O-saturated aqueous solutions of polyuridylic acid (polyU), polycytidylic acid (polyC), polyadenylic acid (polyA), and single-stranded DNA from calf thymus, well-resolved signals of the undamaged free bases were identified. Upon incubation of the solutions at 95 degrees C for 2 h after irradiation, the amount of release of undamaged bases increased and in the case of polyA and DNA additional signals in the region 7.7-8.3 ppm due to 4,6-diamino-5-(formylamino)-pyrimidine and 8-hydroxyadenine (8-OH-adenine) were identified. Probably because of their low solubility guanine and modified guanine bases were not detected, whereas the lack of signals of low molecular weight pyrimidine derivatives is explained by the stability of the corresponding glycosidic bonds toward hydrolysis under our conditions. From the spectral intensities G values for release of unaltered and modified nucleic bases were estimated for radiation doses corresponding to approximately 2.5% conversion for polyU and polyC, to approximately 6% conversion for polyA and to approximately 30-60% conversion for DNA. The NMR data were in agreement with G values reported for release of undamaged bases from irradiated polyU and for double-strand DNA obtained on the basis of chromatographic procedures in combination with UV absorption (D.J. Deeble, D. Schulz, and C. von Sonntag, Int. J. Radiat. Biol. 49, 915-926, 1986; J.F. Ward and I. Kuo, Radiat. Res. 66, 485-498, 1976). Broadening of the NMR peaks of the polymers at high radiation doses (> 10 kGy) was dependent on the magnetic field strength. Therefore, it is ascribed to chemical shift heterogeneity caused by a variety of irradiation products with strongly overlapping signals rather than to a decrease in internal mobility caused by crosslinking of the polymer chains.

Adenine↗

PubMed2005

A nonparametric method for analysis of fluorescence emission in combined time and wavelength dimensions.

We report a method for accurate recovery of tissue intrinsic fluorescence emission characteristics, including fluorescence lifetimes and spectral profiles, from complex two-dimensional (spectro-temporal) emission waveforms. Most algorithms for analysis of fluorescence data address separately the characteristics of either spectral emission or fluorescence relaxation time. We developed a novel nonparametric analytical method that allows for identification and estimation of the intrinsic Fluorescent Impulse Response Kernel (FIRK) simultaneously in time and wavelength dimensions. Modeling of FIRK was based on the characteristics of spectro-temporal fluorescence waveforms. Due to the decaying behavior of the fluorescence, a linear combination of discrete Laguerre functions was used to model the fluorescence response in time. To address the large variability of spectral profiles of distinct fluorophores, a discrete Fourier series expansion was used to model the variation of fluorescence intensity across wavelength. The proposed method was validated on synthetic fluorescence data and data measured from fluorescence lifetime standards and tissue endogenous fluorescent biomolecules. We determined that this method provides a direct recovery of the two-dimensional FIRK and accurate estimation (residual error < 6%) of a broad range of fluorescence lifetimes including the sub-nanosecond range. The FIRK retrieved using this method can further facilitate modeling and recognition of pathological and physiological conditions in tissues.

Algorithms↗

PubMed1993

A feedback control system for real-time formant estimation. II--Analysis of a hysteresis effect and F2 estimation.

This paper presents the second part of the analysis of a feedback control system for real-time formant estimation. The system behavior is analyzed for an input signal composed of two sinusoids. If the frequency difference between the two input spectral lines is sufficiently great and the amplitude ratio is within certain limits, a hysteresis effect occurs. Then the system shows a tendency to select one of the two input spectral lines. The existence of the second line has only little influence on the accuracy of the detection of the selected line. From the analysis, conclusions of the system behavior regarding formant estimation can be drawn. A design example for second formant detection is simulated and compared with the results obtained by simulation of a zero-crossing system for F2 estimation and LPC analysis.

Computer Simulation↗

PubMed1997

An extended difference of coherence test for comparing and combining several independent coherence estimates: theory and application to the study of motor units and physiological tremor.

Recently there has been an increase in the use of spectral methods for the analysis of experimental data. These analytical methods allow the study of interactions between simultaneously recorded signals and are particularly suited to the study of systems displaying rhythmic behaviour. A useful parameter in this context is the coherence function which provides a bounded measure of linear association between two signals. In this report we introduce two new techniques for dealing with an arbitrary number of independent coherence estimates. The first technique provides a test to compare the coherence estimates for statistically significant differences. The second allows the original coherence estimates to be combined, or 'pooled' into a single representative estimate. These two measures, taken together, provide a powerful tool for characterising and summarising the correlations within data sets. Applications of the techniques are illustrated by analysing the interactions between single motor unit discharges and finger tremor, and between pairs of motor unit discharges in human subjects.

Humans↗

PubMedDate not supplied

Quantitative magnetic resonance spectroscopy by optimized numerical curve fitting.

A technique is reported for generating the quantitative area under selected peaks within a 31P NMR spectrum. A numerical iterative method generates the fitted curve so as to minimize the RMS deviation between the fit and the experimental data. The curve is constructed from elemental grains of spectral density ('spexels'), each of which represents an elemental Lorentzian distribution, where the centre frequency and line width of the spexel may be varied within predetermined limits. This provides a fit that in principle is not restricted to a Lorentzian model. The method allows peak areas to be estimated, including the case of overlapping peaks. The method has been tested using simulated spectra containing six overlapping spectral lines each of known amplitude (ranging from 367 to 661 mV) and area; together with additional Gaussian noise with a standard deviation ranging from 30 to 646 mV. The results of fitting both unfiltered and filtered spectra were compared. The variation of quality of fit with spectral noise and filtering has been evaluated. In all cases, the method fitted the peak amplitudes to within 1% of the simulated value. The optimization processes provide an excellent non-linear spectrum filtering algorithm. Provided the noise in the spectra did not exceed ca 400 mV, prefiltered data could be adequately fitted.

Computer Simulation↗

PubMed2004

A novel ultrasound instrument for investigation of arterial mechanics.

The study of arterial mechanics concerns functional characteristics depending on wall elasticity and flow profile. Wall elasticity can be investigated through the estimation of parameters like the arterial distensibility, which is of high clinical interest because of its known correlation not only with the advanced atherosclerotic disease, but also with aging and major risk factors for cardiovascular disease. The flow velocity profile is also clinically relevant, because it modulates endothelial function and can be responsible for the development and distribution of atherosclerotic plaques. A clinically relevant variable extracted from the blood velocity profile is the wall shear rate (WSR), which represents the spatial velocity gradient near the vessel wall. This paper describes an integrated ultrasound system, capable of detecting both the velocity profile and the wall movements in human arteries. It basically consists of a PC add-on board including a single high-speed digital signal processor. This is dedicated to the analysis of echo-signals backscattered from 128 range cells located along the axis of the interrogating ultrasound (US) beam. Echoes generated from the walls (characterized by high amplitudes and low Doppler frequencies) and from red blood cells (characterized by low amplitudes and relatively high Doppler frequencies) are independently processed in real-time. Wall velocity is detected through the autocorrelation algorithm, while blood velocity is investigated through a complete spectral analysis of all signals backscattered by erythrocytes and WSR is extracted from the estimated velocity profile. Preliminary applications of the new system, including the simultaneous analysis of blood flow and arterial wall movement in healthy volunteers and in a diseased patient, are discussed, and first results are presented.

Adult↗

PubMed1997

Color flow mapping.

Color flow mapping systems have become widely used in the short time since their development. These systems overlay a pseudo-color velocity map upon the gray-scale two-dimensional image. Between 4 and 16 pulses are directed to each line-of-sight, and this requirement reduces the frame rate in comparison with the gray-scale image. Other limitations of color flow mapping include its ability to estimate only the velocity toward or away from the transducer and an increase in the variance in comparison with spectral Doppler. Potential artifacts include aliased velocities and the detection of flow in hypoechoic or hyperechoic nonvascular structures. Clinical applications include cardiology, studies of the abdominal and peripheral vasculature, evaluation of organ perfusion and the differentiation of tumors. Most current systems use narrowband estimators that examine a fixed sample volume and detect a change in phase between two pulses. Wideband estimators that can track red blood cells in two or three dimensions are under evaluation. Narrowband estimators, including the autocorrelator, the short Fourier transform and second order autoregressive filters, are compared with wideband estimators including cross-correlation, sum-absolute-difference and the wideband maximum likelihood estimator. Because the intensity of blood echoes is far smaller than echoes from surrounding tissue, high pass filters have been developed that can reject the larger signal from tissue using the return from a small number of pulses. Other areas of research include strategies for flow estimation with contrast agents, three-dimensional color flow mapping and power Doppler flow mapping.

Echocardiography, Doppler, Color↗

PubMed1979

Empirical examination of the threshold model of neuron firing.

An elementary model of neuronal activity involves temporal and spatial summation of postsynaptic currents that are elicited by presynaptic spikes and that, in turn, elicit postsynaptic potentials at a trigger zone; when the potential at the trigger zone exceeds a "threshold" level, a postsynaptic spike is generated. This paper describes three methods of estimating the "summation function", that is, the function of time that converts the synaptic current into potential at the trigger zone: namely, maximum likelihood, cross-correlation analysis and cross-spectral analysis. All three methods, when applied to input-output data collected on various neurons of Aplysia californica, give comparable results. As estimated, the summation function involved in the explored cells has an early positive-going swing that is large and brief. In the cell L5, but not in R2, there was also a late negative-going swing of longer duration.

Animals↗

PubMed2001

Performance of time-frequency representation techniques to measure blood flow turbulence with pulsed-wave Doppler ultrasound.

The current processing performed by commercial instruments to obtain the time-frequency representation (TFR) of pulsed-wave Doppler signals may not be adequate to characterize turbulent flow motions. The assessment of the intensity of turbulence is of high clinical importance and measuring high-frequency (small-scale) flow motions, using Doppler ultrasound (US), is a difficult problem that has been studied very little. The objective was to optimize the performance of the spectrogram (SPEC), autoregressive modeling (AR), Choi-Williams distribution (CWD), Choi-Williams reduced interference distribution (CW-RID), Bessel distribution (BD), and matching pursuit method (MP) for mean velocity waveform estimation and turbulence detection. The intensity of turbulence was measured from the fluctuations of the Doppler mean velocity obtained from a simulation model under pulsatile flow. The Kolmogorov spectrum, which is used to determine the frequency of the fluctuations and, thus, the scale of the turbulent motions, was also computed for each method. The best set of parameters for each TFR method was determined by minimizing the error of the absolute frequency fluctuations and Kolmogorov spectral bandwidth measured from the simulated and computed Doppler spectra. The results showed that different parameters must be used for each method to minimize the velocity variance of the estimator, to optimize the detection of the turbulent frequency fluctuations, and to estimate the Kolmogorov spectrum. To minimize the variance and to measure the absolute turbulent frequency fluctuations, four methods provided similar results: SPEC (10-ms sine-cosine windows), AR (10-ms rectangular windows, model order = 8), CWD (w(N) and w(M) = 10-ms rectangular windows, sigma = 0.01), and BD (w(N) = 10-ms rectangular windows, alpha = 16). The velocity variance in the absence of turbulence was on the order of 0.04 m/s (coefficient of variation ranging from 8.0% to 14.5%, depending on the method). With these spectral techniques, the peak of the turbulence intensity was adequately estimated (velocity bias < 0.01 m/s). To track the frequency of turbulence, the best method was BD (w(N) = 2-ms rectangular windows, alpha = 2). The bias in the estimate of the -10 dB bandwidth of the Kolmogorov spectrum was 354 +/- 51 Hz in the absence of turbulence (the true bandwidth should be 0 Hz), and -193 +/- 371 Hz with turbulence (the simulated -10-dB bandwidth was estimated at 1256 Hz instead of 1449 Hz). In conclusion, several TFR methods can be used to measure the magnitude of the turbulent fluctuations. To track eddies ranging from large vortex to small turbulent fluctuations (wide Kolmogorov spectrum), the Bessel distribution with appropriate set of parameters is recommended.

Blood Flow Velocity↗

PubMed2000

Spontaneous fluctuations in cerebral blood flow: insights from extended-duration recordings in humans.

To determine the dependence of cerebral blood flow (CBF) on arterial pressure over prolonged time periods, we measured beat-to-beat changes in mean CBF velocity in the middle cerebral artery (transcranial Doppler) and mean arterial pressure (Finapres) continuously for 2 h in six healthy subjects (5 men and 1 woman, 18-40 yr old) during supine rest. Fluctuations in velocity and pressure were quantified by the range [(peak - trough)/mean] and coefficients of variation (SD/mean) in the time domain and by spectral analysis in the frequency domain. Mean velocity and pressure over the 2-h recordings were 60 +/- 7 cm/s and 83 +/- 8 mmHg, associated with ranges of 77 +/- 8 and 89 +/- 10% and coefficients of variation of 9.3 +/- 2.2 and 7.9 +/- 2.3%, respectively. Spectral power of the velocity and pressure was predominantly distributed in the frequency range of 0.00014-0.1 Hz and increased inversely with frequency, indicating characteristics of an inverse power law (1/f(alpha)). However, linear regression on a log-log scale revealed that the slope of spectral power of pressure and velocity was steeper in the high-frequency (0.02-0.5 Hz) than in the low-frequency range (0.002-0.02 Hz), suggesting different regulatory mechanisms in these two frequency ranges. Furthermore, the spectral slope of pressure was significantly steeper than that of velocity in the low-frequency range, consistent with the low transfer function gain and low coherence estimated at these frequencies. We conclude that 1) long-term fluctuations in CBF velocity are prominent and similar to those observed in arterial pressure, 2) spectral power of CBF velocity reveals characteristics of 1/f(alpha), and 3) cerebral attenuation of oscillations in CBF velocity in response to changes in pressure may be more effective at low than that at high frequencies, emphasizing the frequency dependence of cerebral autoregulation.

Adolescent↗

PubMed2002

Trial-to-trial variability of cortical evoked responses: implications for the analysis of functional connectivity.

OBJECTIVES: The time series of single trial cortical evoked potentials typically have a random appearance, and their trial-to-trial variability is commonly explained by a model in which random ongoing background noise activity is linearly combined with a stereotyped evoked response. In this paper, we demonstrate that more realistic models, incorporating amplitude and latency variability of the evoked response itself, can explain statistical properties of cortical potentials that have often been attributed to stimulus-related changes in functional connectivity or other intrinsic neural parameters. METHODS: Implications of trial-to-trial evoked potential variability for variance, power spectrum, and interdependence measures like cross-correlation and spectral coherence, are first derived analytically. These implications are then illustrated using model simulations and verified experimentally by the analysis of intracortical local field potentials recorded from monkeys performing a visual pattern discrimination task. To further investigate the effects of trial-to-trial variability on the aforementioned statistical measures, a Bayesian inference technique is used to separate single-trial evoked responses from the ongoing background activity. RESULTS: We show that, when the average event-related potential (AERP) is subtracted from single-trial local field potential time series, a stimulus phase-locked component remains in the residual time series, in stark contrast to the assumption of the common model that no such phase-locked component should exist. Two main consequences of this observation are demonstrated for statistical measures that are computed on the residual time series. First, even though the AERP has been subtracted, the power spectral density, computed as a function of time with a short sliding window, can nonetheless show signs of modulation by the AERP waveform. Second, if the residual time series of two channels co-vary, then their cross-correlation and spectral coherence time functions can also be modulated according to the shape of the AERP waveform. Bayesian estimation of single-trial evoked responses provides further proof that these time-dependent statistical changes are due to remnants of the evoked phase-locked component in the residual time series. CONCLUSIONS: Because trial-to-trial variability of the evoked response is commonly ignored as a contributing factor in evoked potential studies, stimulus-related modulations of power spectral density, cross-correlation, and spectral coherence measures is often attributed to dynamic changes of the connectivity within and among neural populations. This work demonstrates that trial-to-trial variability of the evoked response must be considered as a possible explanation of such modulation.

Animals↗

PubMed1992

[The spectral characteristics of the effect of central M-cholinolytics on rat behavior under open-field conditions].

Having estimated the rat behaviour in the open-field test, M-cholinolytics were divided into different groups. Haloperidol normalised the disturbance in the behaviour induced by one group M-cholinolytics and had no effect with the other group. The former group seems to have an explicit dopaminergic activity. The groups seem to correspond to different mechanisms of the behavioural activity.

Animals↗

PubMed2005

Auditory event related potentials and source current density estimation in phonologic/auditory dyslexics.

OBJECTIVE: To determine the generality of auditory processing impairment in phonologic dyslexics by studying their auditory Event-Related Potentials (ERPs) and the spatio-temporal distribution of their brain activity to auditory linguistic and non-linguistic stimuli with temporal and spectral discriminating cues. METHODS: Fourteen adult phonologic dyslexics and 14 normal reading students, all with high academic achievements, were compared. ERP waveform analysis and current density source estimation (Low resolution Electromagnetic Tomographic Analysis-LORETA) were conducted on 21-channel records from subjects who passively listened or actively discriminated 4 types of auditory stimuli: linguistic and non-linguistic stimuli that differed in spectral or temporal characteristics. RESULTS: Significant differences were found for all ERP latencies (N1, P2, N2, P3) in response to all stimuli, with dyslexics presenting longer latencies compared to normal readers. Current density distributions and their time courses also differed significantly, regardless of stimulus type or attention allocation. Among normal readers, early activity (around N1) was characterized by a rapid change of maximum activity from right to left temporal lobe. Later activity (around P3) was characterized by a stable temporal activity with bilaterally synchronous peak activity. Among the dyslexics, the early N1 activity was stable with left hemisphere prominence, with no alternation between the hemispheres, while the later P3 activity peaked earlier in the right hemisphere than in the left. CONCLUSIONS: Dyslexics were different from controls in processing all auditory stimuli: verbal and non-verbal stimuli with temporal as well as with spectral discriminating cues. The differences mainly consisted of latency and time courses of current density distributions, beginning as early as N1 and extending to the late P3. SIGNIFICANCE: Differences in processing auditory stimuli by phonologic dyslexics are not restricted to linguistic (phonological) stimuli, supporting a general auditory processing impairment in phonologic dyslexia.

Acoustic Stimulation↗

PubMed2004

Spectral analysis of burst periods in EEG from healthy and post-asphyctic full-term neonates.

OBJECTIVE: To investigate whether the periodic EEG patterns seen in healthy and sick full term neonates (trace alternant and burst suppression, respectively) have different frequency characteristics. METHODS: Burst episodes were selected from the EEGs of 9 healthy and 9 post-asphyctic full-term neonates and subjected to power spectrum analysis. Powers in two bands were estimated; 0-4 and 4-30 Hz, designated low- and high-frequency activity, respectively (LFA, HFA). The spectral edge frequency (SEF) was also assessed. RESULTS: In bursts, the LFA power was lower in periods of burst suppression as compared to those of trace alternant. The parameter that best discriminated between the groups was the relative amount of low- and high-frequency activity. The SEF parameter had a low sensitivity to the group differences. In healthy neonates, the LFA power was higher over the posterior right as compared to the posterior left region. CONCLUSIONS: Spectral power of low frequencies differs significantly between the burst episodes of healthy and sick neonates. SIGNIFICANCE: These results can be used when monitoring cerebral function in neonates.

Asphyxia Neonatorum↗

PubMed1999

Fractal and spectral dimension analysis of liver fibrosis in needle biopsy specimens.

OBJECTIVE: To evaluate the usefulness of a reliable and reproducible mathematical scoring system based on fractal geometry for quantifying the irregular pattern in fibrosis commonly seen in liver biopsy specimens from chronic liver diseases. STUDY DESIGN: The study used 26 standard liver biopsy specimens obtained from patients with chronic hepatitis C virus-related liver disease. The degree of fibrosis in each specimen was estimated using a quantitative scoring system based on the computer-assisted evaluation of both the fractal and spectral dimensions of deposited collagen. The fractal dimension was then compared with the percent area of collagen measured using an image analysis system. RESULTS: The fractional dimension of its irregular shape defines fibrosis as a natural fractal structure. The complex distribution of its collagenous components (unmeasurable by means of the usual morphometric parameters) can be optimally quantified using a single numerical score that seems to be a better alternative to the semiquantitative methods adopted so far. The proposed method is reproducible, rapid and inexpensive; furthermore, supported by specific software, its mathematical approach excludes subjectivity and eliminates the external factors capable of influencing staging and classification. CONCLUSION: This study demonstrated that it is possible to quantify the irregularity of the structures of the liver in an objective manner and that the box-counting fractal dimension does not depend on the amount of collagen deposited on the slide. Furthermore, as has been found in other fields of investigation, study of the fractal properties of the liver is likely to reveal more about its structure and the pathogenesis of liver diseases.

Biopsy, Needle↗

PubMed1986

Differences in the spectral interactions between NADPH-cytochrome P-450 reductase and a series of cytochrome P-450 enzymes.

The interaction between NADPH-cytochrome P-450 reductase and a series of cytochrome P-450 isozymes was investigated using UV-visible spectrophotometry. In the absence of substrate the interactions between the reductase and RLM3, RLM5, and RLM5a were tight, exhibiting sub-micromolar dissociation constants and resulted in type I spectra of varying magnitude from which the following increases in the proportion of high spin hemoprotein were calculated; RLM3 (7%), RLM5 (36%), RLM5a (6%), LM2 (29%), RLM2 (0%). Preincubation of LM2 with its type I substrate benzphetamine increased the affinity of the cytochrome for the reductase. Using initial estimates of the P-450 spin states in the absence of reductase in conjunction with the spectral binding data and equations relating these parameters to the microequilibria for the association of reductase with high or low spin P-450, RLM3, RLM5, RLM5a and LM2 were shown to bind significantly more tightly to high spin P-450. The relevance of this data to the understanding of spin state influence on P-450 reduction is discussed.

Animals↗