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[Spectrum analysis of vestibular nystagmus].

A procedure for the spectral analysis of nystagmograms obtained by rotary stimulation with the rate of 180 degrees/s for 20 s has been developed with the aim to reveal the most typical changes in the vestibular nystagmus with one or another form of the cochleovestibular pathology. A signal recorded in the analogous form was processed by computer EC-1022. Periodograms were calculated by the method of the fast Fourier transform and periodogram smoothing by averaging of realization sites. In case of Ménière's disease the third harmonic was not recorded on periodograms when right and left labyrinths were stimulated and in the case of neurites of acoustic nerves, the third or fifth harmonic was not observed. A supposition is advanced that the third harmonic reflects the state of the peripheral area of the vestibular analyzer, while the fifth harmonic--the central one.

Adolescent↗
PubMed1984

[Ultrasound and atheromatous disease : current contribution of Doppler spectrum analysis in carotid stenoses].

The carotid bifurcation plaque is a common pathology. Specific pathologic atheromatous findings have been studied in three hundred patients-carotid bifurcations. This study was carried with the Doppler technics and especially the spectral analysis of the Doppler. From that study it appeared that the most frequent disturbances could be classified according five grades, corresponding to the importance of the stenosis. The first grade corresponds to a stenosis responsible of an obstruction less than 40% of the vessel. The second one is a stenosis from 40% to 60% of the lumen. The third grade is the witness of a extended plaque and a stenosis between 60% to 75%. The fourth grade corresponds to a stenosis between 60% and 90%. The fifth grade is a stenosis superior to 90% of the surface of the artery, also called pre-occlusive grade. This ultrasonic method has been compared to the data provided by the angiography, the echotomography and the anatomopathology. The correlation is excellent in the three cases, and is of 95%. The authors emphasize that this method is the most accurate among the non invasive investigations and let hope that it might replace the traumatic ones in the future.

Arteriosclerosis↗
PubMed1983

Theoretical framework for spectrum analysis in ultrasonic tissue characterization.

An analytic model is described for application in ultrasonic tissue characterization. The model is applicable to clinical broadband pulse echo systems. It treats spectra derived from received echo signals and relates them to physical tissue properties. The model can be applied to deterministic tissue structures (e.g., retinal detachments, larger blood vessels, and surface layers of the kidney) and to stochastic tissue structures (e.g., various tumors). The beam patterns included in the model are those generated by focused transducers typically used in high-resolution clinical ultrasound. Appropriate calibration procedures are also treated; these are needed for interpretation of absolute spectral parameters. The results obtained with the analytic model have been used to design a digital processing system and the associated techniques which are now being applied during examinations of the eye and abdominal organs. The results have proven useful in interpreting data from various types of tissues. To illustrate the application of these results, representative clinical data, obtained from the digital system, are presented for two types of tissue architectures. The first case is a detached retina representing a deterministic structure characterized by well-defined thickness and reflection coefficients. The second case is asteroid hyalosis and represents a stochastic entity in which the positions of small scattering particles are best described in statistical terms, and characterization is accompanied by means of normalized power spectra.

Eye Diseases↗
PubMed2005

Marked fetal acidosis and specific changes in power spectrum analysis of fetal heart rate variability recorded during the last hour of labour.

OBJECTIVE: To assess whether intrapartum acidosis affects specific components of fetal heart rate variability. DESIGN: Prospective clinical study. SETTING: Twelve Nordic delivery units. SUBJECTS: Fetal heart rate variability was studied in 334 fetuses divided into two groups according to cord pH value: the acidotic group (cord arterial pH < 7.05 at birth, n= 15) and the control group (cord arterial pH > or =7.05 at birth, n= 319). METHODS: In spectral analysis of fetal heart rate variability, frequencies were integrated over the total frequency band (0.04-1.0 Hz), low-frequency band (0.04-0.15 Hz) and high-frequency band (0.15-1.0 Hz). We also calculated the low-to-high frequency ratio. MAIN OUTCOME MEASURES: The spectral bands of fetal heart rate variability were compared between the acidotic and control fetuses. RESULTS: We found that during the last hour of monitoring, baseline fetal heart rate gradually decreased, whereas total, low-frequency and high-frequency fetal heart rate variability initially increased but then, near the delivery, decreased in the acidotic fetuses when compared with the controls. Low-to-high frequency ratio was greater in the acidotic group during the whole study period (P= 0.002). Cord artery pH was inversely associated with total fetal heart rate variability (P < 0.001), low-frequency fetal heart rate variability (P < 0.001) and low-to-high frequency ratio (P= 0.004). CONCLUSIONS: Marked fetal acidosis was associated with frequency-specific changes in fetal heart rate variability as reflecting the compensation ability of autonomic nervous activation during the last hour of labour.

Acidosis↗
PubMed2006

Performance characteristics of the limulus amebocyte lysate assay and gas chromatography-mass spectrum analysis of lipopolysaccharides relative to nitric oxide production by peritoneal exudates of cells.

Limulus amebocyte lysate (LAL) assay and gas chromatography-mass spectrum (GC-MS) analysis are usually used for the quantification of lipopolysaccharides (LPS) from the environment. The LAL assay measures endotoxin units to represent the LPS biological function but GC-MS analysis measures decanoic (C(10:0)) and dodecanoic (C(12:0)) 3-hydorxy fatty acids (3-OH FA) concentration to represent the LPS chemical composition. A study was carried out using these methods to evaluate their degree of correlation. Using the culture supernatants of 30 independent strains of Pseudomonas aeruginosa, the bacterial supernatants gave of 0.53+/-0.45 and 2.49+/-1.75mg/l of C(10:0) and C(12:0) 3-OH FA, respectively, compared to 17.96+/-13.28mg/l of LPS with the LAL assay (1ng/ml of LPS congruent with0.78EU/ml). The 3-OH FA concentration relative to the endotoxin unit dose in the supernatants exhibited a positive correlation (r(2)=0.5182, C(10:0); r(2)=0.4359, C(12:0)). When supernatants having a high level of endotoxin were used to treat peritoneal exudates cells, nitric oxide (NO) was generated in a dose-dependent manner (r(2)=0.6174). To determine if either C(10:0) or C(12:0) 3-OH FA can act as an indictor of LPS quantity was correlated with this immunostimulatory effect, the correlation of these 3-OH FA concentrations against the produced NO levels was evaluated. This also exhibited a positive correlation; however, the two indicators of 3-OH FA gave different dose-responsible performances (r(2)=0.3211, C(10:0); r(2)=0.4527, C(12:0)).

Animals↗
PubMed1994

Spectrum analysis of diaphragmatic global electromyograms in cattle, with special regard to appropriate strategy for detection of fatigue.

Although the respiratory tract of healthy and diseased cattle has been intensively studied during the past few years, only a few attempts to detect dysfunctions of bovine inspiratory muscles have been reported. Such technique would be useful in assessing the possibility of inspiratory muscle fatigue in the context of ventilatory failure. Fatigue in skeletal muscle is associated with characteristic changes in the electromyographic power spectrum. Power spectral analysis was therefore applied to cattle diaphragmatic electromyograms (EMGdi) to precisely determine the exact influence of motion and ECG artifacts, describe its basic frequency content, and extract a spectral index capable of providing an accurate warning of fatigue. The EMGdi was recorded via intramuscularly placed fishhook electrodes in 5 healthy young bulls during resting and stimulated respiration. The EMGdi and EGC signals were analyzed by use of power spectral density analysis after band-pass filtering (20 to 1,800 Hz). The EMGdi spectrum was concentrated in the band width 20 to 530 Hz. Electrode motion artifacts were absent, and it was always possible to find an electrode pair giving ECG-free EMGdi. Of the 12 power and frequency values used to quantitate the spectrum, the most stable was the centroid frequency. It was reproducible within and between calves and was only minimally altered by changing inspiratory load.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2006

Broadband radio-frequency spectrum analysis in spectral-hole-burning media.

We demonstrate a 20 GHz spectrum analyzer with 1 MHz resolution and >40 dB dynamic range using spectral-hole-burning (SHB) crystals, which are cryogenically cooled crystal hosts lightly doped with rare-earth ions. We modulate a rf signal onto an optical carrier using an electro-optic intensity modulator to produce a signal beam modulated with upper and lower rf sidebands. Illuminating SHB crystals with modulated beams excites only those ions resonant with corresponding modulation frequencies, leaving holes in the crystal's absorption profile that mimic the modulation power spectrum and persist for up to 10 ms. We determine the spectral hole locations by probing the crystal with a chirped laser and detecting the transmitted intensity. The transmitted intensity is a blurred-out copy of the power spectrum of the original illumination as mapped into a time-varying signal. Scaling the time series associated with the transmitted intensity by the instantaneous chirp rate yields the modulated beam's rf power spectrum. The homogeneous linewidth of the rare-earth ions, which can be <100 kHz at cryogenic temperatures, limits the fundamental spectral resolution, while the medium's inhomogeneous linewidth, which can be >20 GHz, determines the spectral bandwidth.

Journal Article↗
PubMed1991

[Spectrum analysis of the variability of heart rate in athletes].

OBJECTIVES: Characterize power spectrum pattern of the heart rate variability and assessment of the relative contributions of sympathetic and parasympathetic cardiac nervous system control in athletes. STUDY DESIGN: Prospective study of athletes and sedentary healthy control group sex and age matched. SUBJECT AND METHODS: 8 athletes, 3 female and 5 male, swimming (4), canoeing (2) and cycling (2), aged 17.4 +/- 3.6 years, and 8 sedentary healthy controls. ECG signals were recorded after a period of 15 minutes in supine rest with controlled breathing at 15 cycles/min. Signal acquisition was done at 300 samples/sec. From 512 consecutive heart beats, we calculated the average, the standard deviation, the maximum and the minimum values and the rate between the longest and the shortest R-R interval (E/I). We also calculated, after computing the fast Fourier transform, the total spectrum power, the low frequency component (LF, from 0.01 to 0.15 Hz) and the high frequency component (HF, greater than 0.15 Hz) and its ratio (LF/HF). RESULTS: The average R-R interval was 921 +/- 154.2 msecs and 673.2 +/- 98 msecs, the standard deviation was 72.5 and 29.4 msecs and the ratio E/I 1.63 +/- 0.14 and 1.28 +/- 0.08, respectively for athletes and control group. Differences between groups were significant (p less than 0.01) for all parameters, with higher variability in the athletes. Both spectral bands (LF and HF) and higher power in athletes (LF = 0.54 +/- 0.23 and HF = 0.76 +/- 0.14) than in the control group (LF = 0.14 +/- 0.10 and HF = 0.18 +/- 0.15) (p less than 0.001). There were no significant differences for LF/HF ratio, or normalized LF (LF%) or normalized HF (HF%) between groups. CONCLUSIONS: The present results indicates higher power of both spectral bands (LF and HF) and higher amplitude of the respective peaks in athletes when compared with healthy sedentary, with a clear predominance of the HF band in the total spectral power density, which suggest that the higher heart rate variability observed in athletes reveals the predominance of parasympathetic activity, without reduction of the sympathetic tone.

Adolescent↗
PubMed2005

Spectral hole burning for wideband, high-resolution radio-frequency spectrum analysis.

We present experimental results for what is to our knowledge the first spectral-hole-burning based rf spectrum analyzer to cover 10 GHz of rf analysis bandwidth. The rf signal of interest is modulated onto an optical carrier, and the resultant optical sidebands are burned into the inhomogeneously broadened absorption band of a Tm3+:YAG crystal. At the same time a second, frequency-swept laser reads out the absorption profile, which is a double-sideband replica of the rf spectrum, and thus the rf spectrum can be deduced after spectral calibration of the nonlinear readout chirp. This initial demonstration shows spectral analysis covering 10 GHz of bandwidth with >5500 spectral channels and provides 43 dB of dynamic range.

Journal Article↗
PubMed2005

[Spectrum analysis of crop and weeds at seedling].

The infestation information on field weeds is the basis of variable spraying herbicides. It was found that the method using the spectral characteristics of plant is superior in real-time respect. The Fourier transform infrared spectrum technique was applied to measure the reflectance of wheat and weeds in the range from 700 to 1100 nm. The discrimination analysis was done using the SPSS software. Firstly, the source spectrum data were compressed and normalized. Secondly, the characteristic wavelengths were selected by using stepwise method. Thirdly, the discrimination model was set up to use the selected wavelengths as the variables for detecting wheat and weeds. It was shown by the result of discrimination analysis that the correct classification rate of wheat and weeds detection with the selected wavelength points achieved 97%. In addition, the selected wavelength points were marked in the "red edge" of reflectance within some range, and the rate of correct classification increased with the increase in the numbers of the selected wavelength points. According to the selected wavelength points, the proper filters were chosen to perform the multi-spectral images captured and processed with the machine vision system.

Capsella↗
PubMed2004

Awareness and the EEG power spectrum: analysis of frequencies.

BACKGROUND: Power spectral analysis is a well-established method for the analysis of EEG signals. Spectral parameters can be used to quantify pharmacological effects of anaesthetics on the brain and the level of sedation. This method, in numerous variations, has been applied to depth of anaesthesia monitoring and has been incorporated into several commercially available EEG monitors. Because of the importance of EEG spectral analysis, we evaluated the performance of each frequency in the power spectrum regarding detection of awareness. METHODS: Ninety artefact-free EEG segments of length 8 s were obtained from a database that contains perioperatively recorded EEG data. For the present analysis, EEG data were selected from 39 patients with propofol-remifentanil or sevoflurane-remifentanil anaesthesia with a period of awareness. Half of the EEG segments were recorded during periods of awareness as defined by an adequate response to the command 'squeeze my hand'. The other half were from unresponsive patients. The power spectral density was calculated for each segment. The performance of each frequency bin of the power spectrum as a detector of awareness was assessed with a remapped prediction probability rPK, i.e. the prediction probability PK mapped to a range of 0.5-1. RESULTS: The remapped prediction probability was high (rPK>0.8) for low frequencies (<15 Hz) and for high frequencies (>26 Hz), with a minimum (rPK<0.55) at 21 Hz. Indentations in the 'performance spectrum' occur at the power-line frequency (50 Hz) and its harmonics and at 78 Hz, probably caused by the continuous impedance measurement of another device used in parallel. With the exception of the indentations, the remapped prediction probability of the high frequencies (>35 Hz) was >0.95. CONCLUSIONS: The best performance for the detection of awareness was achieved by EEG power spectral frequencies from >35 Hz up to 127 Hz. This frequency band may be dominated by muscle activity. The frequency band between 15 and 26 Hz may be of limited value, as reflected by lower rPK values.

Anesthetics, Combined↗
PubMed1997

[Perioperative plasma amino acid spectrum analysis in portal hypertensive cirrhotic patients undergoing portacaval H-graft shunt].

Perioperative plasma amino acid spectrum (PAAS) was analysed in 10 portal hypertensive patients (PH) receiving portacaval H-graft shunt (D = 8 mm) and 10 gastroenteropathic patients (GE) without hepatic disease. In both groups, arterial, peripheral and hepatic venous blood was drawn for analysis immediately pre- and post-operation on the table, postoperative day 1 and 3, respectively. It was found that amino acid concentration decreased in both groups but in PH group it was changed significantly. The preoperative branched chain amino acid (BCAA)/aromatic amino acid (AAA) ratio was less than 2 in the PH group and larger than 3 in the GE group after operation. The ratio did not change significantly in both groups after operation. In the PH group, the pre- and post-operative BCAA and AAA level in hepatic vein was higher than in other sites. The immediately BCAA and AAA levels were lower than preoperative levels. Among the changes the postoperative decrease of VAL and LEU was significant. Both BCAA and AAA reached preoperative level at postoperative day3. The results reveal that small diameter portacaval shunt has no significant influence on PAAS. The temporary decrease of amino acid levels postoperatively may be related to the stress of operation and liver impairement.

Adult↗
PubMed1979

Isolating low frequency activity EEG spectrum analysis.

A method for isolating and removing very slow activity from EEG records prior to spectrum computation is presented. This is accomplished by an autoregressive filter whose frequency transfer characteristic can be easily controlled. Examples of spectra computed for various filter parameter values are shown.

Computers↗
PubMed1992

Mathematical modeling and spectrum analysis of the physiological patello-femoral pulse train produced by slow knee movement.

Analysis of vibration signals emitted by the knee joint has the potential for the development of a noninvasive procedure for the diagnosis and monitoring of knee pathology. In order to obtain as much information as possible from the power density spectrum of the knee vibration signal, it is necessary to identify the physiological factors (or physiologically relevant parameters) that shape the spectrum. This paper presents a mathematical model for knee vibration signals, in particular the physiological patello-femoral pulse (PFP) train produced by slow knee movement. It demonstrates through the mathematical model that the repetition rate of the physiological PFP train introduces repeated peaks in the power spectrum, and that it affects the spectrum mainly at low frequencies. The theoretical results also show that the spectral peaks at multiples of the PFP repetition rate become more evident when the variance of the interpulse interval (IPI) is small, and that these spectral peaks shift toward higher frequencies with increasing PFP repetition rates. To evaluate the mathematical model, a simulation algorithm was developed, which generates PFP signals with adjustable repetition rate and IPI variance. Signals generated by simulation were seen to possess representative spectral characteristics typically observed in physiological PFP signals. This simulation procedure allows an interactive examination of several factors which affect the PFP train spectrum. Finally, in vivo measurements of physiological PFP signals of normal volunteers are presented. Results of simulations and analysis of signals recorded from human subjects support the mathematical model's prediction that the IPI statistics play a very significant role in determining the low-end power spectrum of the physiological PFP signal.(ABSTRACT TRUNCATED AT 250 WORDS)

Algorithms↗
PubMed1992

Spectrum analysis of sympathetic nerve activity and blood pressure in conscious rats.

This study tests whether the power spectrum of blood pressure (BP) provides information toward the sympathovagal balance of BP control by comparing the BP (femoral arterial catheter) spectrum with the spectrum of the efferent sympathetic nerve activity (SNA, bipolar electrode around splanchnic nerve). A remarkable resemblance between both spectra was found. A high-frequency component (HF) linked to respiration and a slower fluctuation type between 0.15 and 0.6 Hz (LF) were identified. There was a large and significant coherence only in the HF range of the BP and SNA power spectrum (P < 0.01). The phase lag of SNA and BP was roughly 200 ms. The recordings were repeated during pharmacological blockade in nine Wistar-Kyoto rats (WKY) and nine spontaneously hypertensive rats (SHR). alpha 1-Adrenoceptor blockade (prazosin) reduced the proportional LF power of BP in both rat strains (WKY P < 0.01, SHR P < 0.05) in favor of HF (WKY P < 0.01, SHR P < 0.01). Parasympathetic blockade (methylscopolamine) had no effect on proportions of power. Similarly, there were no significant differences in the proportional HF and LF power spectra of WKY and SHR. These data provide direct evidence for a relationship between the BP and SNA power spectra; however, only the acute changes in the sympathetic tone changed the LF-HF relationship.

Animals↗
PubMed2003

Spatial spectrum analysis of wave-front correction with a segmented mirror.

An expression is derived for the spatial power spectrum of wave-front errors after correction with a segmented mirror. This includes estimates of the spectral contributions of segment piston and tilt corrections and spatial aliasing by a regular array of segments. The approach allows rapid computation of wave-front error spectra in systems with highly segmented mirrors.

Journal Article↗
PubMed2005

Spectrum analysis of motion parallax in a 3D cluttered scene and application to egomotion.

Previous methods for estimating observer motion in a rigid 3D scene assume that image velocities can be measured at isolated points. When the observer is moving through a cluttered 3D scene such as a forest, however, pointwise measurements of image velocity are more challenging to obtain because multiple depths, and hence multiple velocities, are present in most local image regions. We introduce a method for estimating egomotion that avoids pointwise image velocity estimation as a first step. In its place, the direction of motion parallax in local image regions is estimated, using a spectrum-based method, and these directions are then combined to directly estimate 3D observer motion. There are two advantages to this approach. First, the method can be applied to a wide range of 3D cluttered scenes, including those for which pointwise image velocities cannot be measured because only normal velocity information is available. Second, the egomotion estimates can be used as a posterior constraint on estimating pointwise image velocities, since known egomotion parameters constrain the candidate image velocities at each point to a one-dimensional rather than a two-dimensional space.

Algorithms↗
PubMed2004

Applying spectrum analysis and cepstrum analysis to examine the cavitation threshold in water and in salt solution.

The paper presents the way of determining the cavitation threshold by means of classical spectral analysis and proposes the usage of cepstrum analysis in examining the cavitation phenomenon. Cepstrum analysis enables a more lucid interpretation of signals generated in the cavitation process than the universally used Fourier analysis. This refers above all to evaluating the relationship between particular frequencies as well as frequency groups. The research conducted allowed us to observe the changes of spectrum near the cavitation threshold in water, in water partly degassed and in salt solution in the free field and in the standing wave field. Differences of spectrum structure for particular cases were noted, especially for the third harmonic and the first subharmonic. The measurements done in the standing wave field showed differences in spectrum, depending on whether the measurements were done in the loop or in the node of the wave. In particular, what was not observed was the occurrence of subharmonics with a frequency two times lower than the basic frequency which were typical of the free field. Other characteristic spectrum elements that could unmistakably point to reaching the cavitation threshold were not noticed either. The cepstrum analysis proved the existence of irregularities, hardly visible in the classical Fourier spectrum. This refers especially the range below the signal's basic frequency.

Journal Article↗