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PubMed1990

A spatial power spectrum analysis of the electroencephalogram.

The method of spatial power-spectrum analysis has been applied to measurements of the distribution of rms alpha-band potential on the scalp. Data was recorded using the 31-Electrode System and spatial power-spectrum estimates (PSEs) were obtained from Mercator projections of the potential interpolated using the triangular method. PSEs were calculated using the Lim and Malik algorithm for maximum-entropy power-spectrum estimation. In order to investigate the utility of spatial power-spectrum analysis, PSEs were obtained from subjects in two conditions; resting with eyes closed (EC) and resting with eyes open and fixed on a single point (EO). A stepwise discriminant analysis was performed with features from the PSEs and the resultant discriminant function was applied to data not considered in the formulation of the function. Over 92% of test data was correctly classified. The features used in the discriminant function identify spatial waves which are most useful in separating data. The results demonstrate that waves oriented along front-back and right-left lines are most important in separating data into EC and EO groups.

Brain↗
PubMed1995

[An analysis of heart rate variability. Spectrum analysis methods and complex signal demodulation].

The analysis of heart rate variability provides valuable information in the noninvasive study of neurovegetative activity and its modifications induced by drugs, physiological maneuvers or disease processes, and in the evaluation of prognosis and risk stratification in different cardiovascular diseases. A review is made of the different methods used to study heart rate variability, and an account is given of the information provided by spectral methods and the new procedures based on the complex demodulation of the time series composed of consecutive cardiac cycles. The limitations of the spectral methods are deal with, particularly in defining the time-dependent changes in variability and their relation to clinical events. Likewise, a description is given of the ability of complex demodulation to define the time course of the oscillations into which the analyzed time series is decomposed. Complex demodulation based on the fast Fourier transform and its inverse is able to establish the instantaneous amplitude and frequency of each of the oscillations contained in the time series, separated by specific filters in the previously selected frequency bands (high: 0.15-0.40 Hz, low: 0.04-0.15 Hz, or very low: < 0.04 Hz), and from which the original signal may be reconstructed. The evaluation of the different methodological approaches, and the analysis of the causal relations between the variability modifications and clinical events will further extend the clinical relevance of the study of heart rate variability.

Electrocardiography↗
PubMed1985

Doppler frequency spectrum analysis and digital subtraction angiography in carotid artery disease.

The aim of the study was to evaluate the diagnostic accuracy of frequency spectrum analysis complementary to direct Doppler sonography in comparison to conventional biplane arteriography and transvenous digital subtraction angiography in internal carotid artery stenosis. In a group consisting of 229 carotid arteries visualized by conventional biplane arteriography, Doppler frequency spectrum analysis had a specificity of 97% and concerning all stenoses and occlusions, a sensitivity of 89%. In a second group consisting of 198 carotid arteries imaged by transvenous digital subtraction angiography, Doppler sonographic examination had a specificity of 65% only, and concerning all categories of stenoses and occlusions a sensitivity of 85%. These differences concerning specificity are not interpreted as false positive diagnoses in Doppler spectrum analysis but are considered to be due to false negative findings of digital subtraction angiography in stenoses of less than 50% vessel diameter reduction.

Carotid Artery Diseases↗
PubMed2001

Bilirubin calculi crushing by laser irradiation at a molecular oscillating region wavelength based on infrared absorption spectrum analysis using a free-electron laser: an experimental study.

We investigated a new laser technique of crushing bilirubin calculi, our aim being to crush calculi in isolation using a minimally invasive procedure. Infrared absorption spectrum analysis of the bilirubin calculi was conducted, revealing maximum absorption spectrum at a wavelength of the C=O stretching vibration of ester binding that exists within the molecular structure of bilirubin calcium. As an experiment to crush calculi using the free-electron laser, we set the laser at the effective irradiation wavelength of ester binding, and conducted noncontact irradiation of the bilirubin calculi. The calculi began to slowly ablate until the irradiated site had been completely obliterated after 20s of irradiation. Moreover, absorption spectrum analysis of the irradiated site, from a comparison of absorption peak ratios, revealed that absorption peak intensities decreased over time at the absorption wavelength of ester binding. These findings suggest that irradiation of molecular oscillating region wavelengths peculiar to calculi based on infrared absorption spectrum analysis results in the gradual crushing of calculi in isolation by breaking down their molecular structure.

Bilirubin↗
PubMed1987

Power spectrum analysis in the study of ocular mechanisms.

The use of power-spectrum analysis in the study of ocular dynamics is becoming increasingly widespread. This paper summarizes the key points of signal acquisition and power-spectrum analysis, emphasizing aspects which we have found to be of relevance when the technique is applied to experiments in binocular accommodation. The considerations and conclusions are relevant to other areas of investigation into ocular dynamics and similar biological systems.

Accommodation, Ocular↗
PubMed2004

Ultrasonic tissue characterization using 2-D spectrum analysis and its application in ocular tumor diagnosis.

We are investigating the utility of a new ultrasonic tissue characterization technique, specifically two-dimensional (2-D) spectrum analysis of radio-frequency backscatter signals, which promises to provide quantitative measures of the physical properties of tissue microstructures. Previously successful 1-D spectrum analysis is expanded to 2-D to more fully characterize diagnostically significant features of biological tissue. Two new spectral functions, radially integrated spectral power (RISP) and angularly integrated spectral power (AISP), are defined to quantitatively characterize tissue properties. This new approach is applied to the diagnosis of in vivo ocular melanomas. Our initial results indicate that 2-D spectrum analysis can provide significant new information on tissue anisotropy that are not apparent in 1-D spectra. Acoustic scattering models are applied to relate the 2-D spectral parameters to the physical properties (e.g., size and shape) of biological tissues.

Algorithms↗
PubMedDate not supplied

Performance evaluation of implantable artificial organs by sound spectrum analysis.

In this paper, a sound spectrum analyzing method was proposed to pre detect malfunctions of implantable artificial organs, such as an electromechanical total artificial heart (TAH) or prosthetic valves, without any percutaneous invasion. For this purpose, a sound detecting device was developed using a high sensitivity condenser microphone with a frequency range of more than 13 kHz. Output signals of this device are sampled at 100 kHz maximally, and sampled data are stored in an IBM PC (SamBo, Korea). To remove environmental noises in the measured sound, an adaptive least-mean square algorithm was employed. Using the squared value of the sound signal, the best position where only sounds from mechanical components can be measured was found. The sound spectrum was obtained by the periodogram spectral estimating method. Experiments were performed with this system, and the results indicated that: 1) by using an adaptive noise cancelling algorithm, a more noise-free signal can be obtained; 2) the harmonics from the mechanical components of a pendulum type electromechanical TAH were approximately 1.3 KHz; 3) a spectral change was observed when we compared the power spectral densities of a normal and failed TAH; 4) the spectral shift to higher harmonics occurred with an increase in heart rate; and 5) the sound propagation properties of tissue were investigated with animal experiments. The method proposed was found to be applicable in the detection of implantable artificial organ mechanical failure by sound spectrum analysis without the need for percutaneous invasion.

Acoustics↗
PubMed1995

Resolving receptor heterogeneity using Fourier-derived affinity spectrum analysis and LIGAND: benzodiazepine receptors in the rat spinal cord.

In the present study, we combined a powerful and novel receptor binding data analysis technique. Fourier-derived affinity spectrum analysis (FASA), with the nonlinear regression analysis program LIGAND to resolve benzodiazepine receptor heterogeneity in rat spinal cord. With FASA, we identified three distinct [3H]Ro15-1788 binding populations: two high-affinity sites (0.4 and 5 nM) for the radioligand and a lower-affinity site (150 nM) that is insensitive to the imidazopyridine alpidem. With the affinities for the radioligand determined with FASA, the Ki values of 13 competing ligands were calculated with LIGAND. All of the ligands studied displayed the highest affinity for site 1 (the highest-affinity [3H]Ro15-1788 binding site), with the exception of AHR 11797. Site 2 had high affinity for Ro15-1788, lower affinity for flunitrazepam and beta-CCM and very low, but measurable, affinity for zolpidem. The alpidem-insensitive binding site, studied in isolation by performing competitive binding assays in the presence of 65 microM alpidem, showed relatively low affinity for all of the ligands studied, and its physiological relevance is not yet known.

Animals↗
PubMed2001

Spectrum analysis of respiratory sounds in exercising horses with experimentally induced laryngeal hemiplegia or dorsal displacement of the soft palate.

OBJECTIVE: To record respiratory sounds in exercising horses and determine whether spectrum analysis could be use to identify sounds specific for laryngeal hemiplegia (LH) and dorsal displacement of the soft palate (DDSP). ANIMALS: 5 Standardbred horses. PROCEDURE: Respiratory sounds were recorded and pharyngeal pressure and stride frequency were measured while horses exercised at speeds corresponding to maximum heart rate, before and after induction of LH and DDSP. RESULTS: When airway function was normal, expiratory sounds predominated and lasted throughout exhalation. After induction of LH, expiratory sounds were unaffected; however, all horses produced inspiratory sounds characterized by 3 frequency bands centered at approximately 0.3, 1.6, and 3.8 kHz. After induction of DDSP, inspiratory sounds were unaffected, but a broad-frequency expiratory sound, characterized by rapid periodicity (rattling) was heard throughout expiration. This sound was not consistently detected in all horses. CONCLUSIONS AND CLINICAL RELEVANCE: The technique used to record respiratory sounds was well tolerated by the horses, easy, and inexpensive. Spectrum analysis of respiratory sounds from exercising horses after experimental induction of LH or DDSP revealed unique sound patterns. If other conditions causing airway obstruction are also associated with unique sound patterns, spectrum analysis of respiratory sounds may prove to be useful in the diagnosis of airway abnormalities in horses.

Animals↗
PubMed1985

Toward quantification of athetotic movements by frequency spectrum analysis.

The frequency spectrum of the elbow movements of one normal subject and six handicapped subjects were obtained in order to investigate the possibility of using this technique in quantifying athetosis. The frequency spectrum technique appears to be useful but data from more subjects must be obtained and specific details regarding scaling need to be investigated.

Adolescent↗
PubMed1982

Real-time Doppler spectrum analysis: predictive value in defining operable carotid artery disease.

A prospective study compared the sensitivity, specificity, and predictive value of indirect periorbital Doppler screening and direct carotid Doppler interrogation using real-time sound spectrum analysis to detect operable extracranial carotid occlusive disease. The results of noninvasive studies were compared with independently assessed contrast arteriograms of carotid arteries of patients studied for symptomatic cerebrovascular disease. Periorbital Doppler ultrasound was insensitive to carotid stenosis of less than 75% and did not distinguish operable stenosis from inoperable occlusion of the internal carotid artery. Carotid Doppler spectrum analysis was sensitive to 98% of hemodynamically significant disease and correctly discriminated 77% of carotid occlusions, 96% of stenoses larger than 50%, and 70% of stenoses of less than 50%. The predictive value for direct carotid interrogation in identifying carotid occlusion or operable stenosis was 94% and 86%, respectively. Real-time spectrum analysis of direct carotid Doppler signals substantially improves the diagnostic accuracy of noninvasive identification of operable carotid artery disease.

Arterial Occlusive Diseases↗
PubMedDate not supplied

Direct and indirect evaluation of lesions obstructing the carotid bifurcation. A comparison of Doppler spectrum analysis with angiography.

The diagnostic accuracy of real-time continuous wave (c.w.) Doppler spectrum analysis and of indirect periorbital Doppler examination for detecting carotid bifurcation disease was evaluated. The results of non-invasive studies were compared with contrast arteriograms of patients studied for symptomatic cerebrovascular disease (91%) or for asymptomatic bruits (9%). Periorbital examination was insensitive to less than 75% carotid stenoses and sensitivity to severe stenoses or occlusions was respectively 56% and 85% (mean 73%). Mean sensitivity of real-time C.W. Doppler spectrum was 93% and sensitivity to stenoses of less than 45% diameter reduction was equal to 76%, while specificity in identifying normal carotid arteries was 89% for an accuracy of the method of 91%. Positive and negative predicting values were respectively 89% and 93%. Direct Doppler interrogation of the carotid arteries with real-time C.W. Doppler spectrum analysis was able to distinguish operable stenoses from inoperable occlusions in 87% of the cases.

Angiography↗
PubMed1997

Power spectrum analysis of circadian oscillations of heart rate variability in patients with left ventricular dysfunction.

OBJECTIVES: The physiological significance of diurnal fluctuations in heart rate variability (HRV) has not been established to a full extent. The aim of our investigation was to assess a new method of power spectrum analysis of circadian oscillations in HRV in patients with left ventricular systolic and diastolic dysfunction. METHODS: Holter ECG monitoring and echocardiography were performed in 101 patients with coronary artery disease and arterial hypertension: 55 patients with systolic left ventricular dysfunction (LVD) and 46 patients with diastolic LVD, and also in 32 subjects of the control group. The original method of HRV assessment was based on spectrum analysis of time series of consecutive 5-minute measures of standard deviations of mean RR intervals. RESULTS: The study revealed oscillations of HRV with a periodicity of 12 hours and 80-120 minutes. Their amplitude was highest in the control group and lowest in patients with systolic LVD. CONCLUSIONS: Power spectrum analysis of circadian oscillations of heart rate variability reveals information about the character of LVD. Regular oscillations of time domain indices of HRV were observed in the patients with LVD and in the control group; their amplitude is highest in the control group and lowest in systolic LVD.

Circadian Rhythm↗
PubMedDate not supplied

Chloral hydrate anesthesia: EEG power spectrum analysis and effects on VEPs in the rat.

This paper describes the use of EEG power spectrum analysis as a tool in identifying and controlling the state of an animal, a major source of variability in evoked potential (EP) data. Also described is a procedure of anesthetic administration combined with on-line EEG power spectrum analysis that permits an animal to be maintained in a stable, moderately anesthetized state during which VEP's are qualitatively comparable to those seen in the unanesthetized animal. Anesthesia level in acute preparations was varied by IV injections of chloral hydrate, and the EEG and light-flash VEP's were recorded from visual cortex. Under deep anesthesia, EEG activity was concentrated in the 0.1 Hz to 3 Hz band with very little contribution from frequencies higher than 10 Hz. After this period of deep anesthesia, EEG frequency distribution became bimodal with peaks in the 0.1-3 Hz and 5-7 Hz ranges, and a minor frequency band between 10 and 30 Hz. This moderate anesthetic state persisted for about 30 min. Two distinct forms of VEP's were highly correlated with these EEG frequency distributions. VEP's associated with the moderate anesthetic state were comparable to those reported from awake, chronic preparations. In VEP's associated with deep anesthesia, negative components were greatly attenuated or entirely absent; amplitudes of the positive components were increased as were the latencies of all components.

Animals↗
PubMed1987

Effect of epoch length on power spectrum analysis of the EEG.

To study the effect of epoch length on the variability of power spectrum analysis of the EEG, 22 64-s segments of EEG were analyzed using epoch lengths of 2, 4, 8, 16, and 32 s. Nine of these segments exemplified EEG changes during transient anesthetic states or surgical conditions. Epoch-to-epoch variability was computed within frequency bins for all segments, and ANOVA with hierarchal classification was used to determine the length of the EEG segment necessary to identify a statistically significant change in those EEG segments recorded during changing conditions. In 16 segments, the epoch-to-epoch variability with power spectra were computed using 2-s epochs was significantly less than the variability when power spectra were computed using longer epoch lengths. In five segments, no significant difference existed between the variance at 2-s epochs and longer (4-s) epochs. In one case, an EEG containing a burst-suppression pattern, the variability was significantly increased when 2-s epochs were used. Analysis using 2-s epochs also identified changes more rapidly than analysis using any longer epoch length in eight of nine segments, and the differences were clinically significant as well (over 30 s faster when 2-s epochs were used instead of 16-s epochs). These findings suggest the preferability of short epoch lengths when power spectrum analysis is used for intraoperative EEG monitoring.

Analysis of Variance↗
PubMed2002

Power spectrum analysis of compound muscle action potential in carpal tunnel syndrome patients.

The objective of using wave-form analysis to assess compound muscle action potential (CMAP) in entrapment neuropathy had not been fully developed. We applied the power spectrum analysis to patients with carpal tunnel syndrome (CTS) for this purpose. 24 patients with CTS were divided into three stages according to Mackinnon s classification, and 50 normal volunteers were examined. CMAP was obtained from the abductor pollicis brevis with supramaximal stimulation to median nerve. Mean and peak frequencies were measured by power spectrum analysis. The distal latencies of CMAP and the sensory nerve conduction velocities showed some prolongation in CTS patients. Integral values of CMAP were also decreased in CTS patients. Mean and peak frequencies of power spectrum of CMAP in volunteers were 134 Hz and 98 Hz, respectively. These values shifted into lower frequencies in CTS patients, namely 102 Hz and 61 Hz. Regardless of clinical stage, distal latency of CTS patients correlated with mean frequency.

Action Potentials↗
PubMed1995

Velocity matched spectrum analysis: a new method for suppressing velocity ambiguity in pulsed-wave Doppler.

A new approach to spectrum analysis, which is capable of suppressing velocity ambiguity in pulsed-wave ultrasonic Doppler, is presented. By simultaneous processing of several data samples from a range in depth, the movement of the scatterers along the ultrasonic beam can be tracked from pulse to pulse for each velocity component in the spectrum. In this way the correlation length of the signal component arising from a specific velocity increases when that velocity matches the expected velocity. The resulting velocity/time spectral display shows a more clearly defined spectral envelope of the maximum velocity than with conventional methods based on the discrete Fourier transform of the Doppler signal. This makes it possible to delineate velocity waveforms with peak velocity up to several times the Nyquist limit. Experimental data from human subclavian and aortic arteries are presented, where the new method is compared to conventional spectrum analysis.

Blood Flow Velocity↗