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The frequency spectrum of the center of gravity in normal subjects while standing was recorded by using a platform-strain gauge system and a digital computer. Individual differences of the spectral patterns resulted in the classification of three types. Averaged divisional frequency of each type was calculated in the range below 1 Hz in which the main change between the values with eyes open and those with eyes closed appeared as the frequency shift.
Two new methods for estimating frequency-dependent attenuation are proposed which improve the compromise between the estimation variance of this parameter and the analyzed tissue volume: 1) parametric spectral estimation of the demodulated signal, based on fast Kalman filtering (ARC), 2) implementation of a new mean frequency estimator derived from all the available autocorrelation lags (ACn) of the demodulated signal. Both methods are applied to simulated echo signals. The results are compared to those of other already existing estimators. Both ARC and ACn methods provide equivalent results and a better estimation of attenuation (accuracy ranging from 1.3 to 8%) than the previous methods do (accuracy ranging from 4 to 66%), for analysis windows ranging from 1.5 to 20 microseconds.
1. The structure of a previously reported but uncharacterized major metabolite of deflazacort in man, designated V, has been characterized by nmr, MS and IR spectral techniques. 2. The major changes in V relative to deflazacort are deacetylation to form the 21-alcohol and A-ring modification to the 1,2-epoxy-3-hydroxy analogue. 3. Based on the spectral data and comparison with model compounds the structure, including relative stereochemistry, is (1 beta, 2 beta, 3 beta, 11 beta, 16 beta,)-1,2-epoxy-3,11,21-trihydroxy-2'-methyl-5H'-pregn-4-4-eno [17,16-d]oxazol-20-one.
The goal of this paper is to design experiments that confirm the evidence of cognitive responses in functional near infrared spectroscopy and to establish relevant spectral subbands. Hemodynamic responses of brain during single-event trials in an odd-ball experiment are measured by functional near infrared spectroscopy method. The frequency axis is partitioned into subbands by clustering the time-frequency power spectrum profiles of the brain responses. The predominant subbands are observed to confine the 0-30 mHz, 30-60 mHz, and 60-330 mHz ranges. We identify the group of subbands that shows strong evidence of protocol-induced periodicity as well as the bands where good correlation with an assumed hemodynamic response models is found.
We have studied the effects of prenatal protein malnutrition on development of the hippocampal and frontal cortical electroencephalographic (EEG) activity. Using power spectral analyses in rats of several age groups we found that protein malnutrition, instituted prenatally and continued postnatally, produces marked alterations in power spectral measures, i.e., alterations in peak theta frequency in the hippocampus during rapid eye movement (REM) sleep. Peak theta frequency was found to be significantly retarded in malnourished animals, especially during the preweaning period of development. Protein malnutrition, therefore, appears to affect mechanisms responsible for generating the tonic component of theta activity.
The 1/3-oct spectra of nine different vowels, sung by 14 professional male and female singers in nine different modes of singing, were analyzed to reveal spectral characteristics of individual singers and modes of singing. The main spectral differences between singers could be described in two dimensions characterizing, respectively, differences among male and among female singers. Spectral characteristics of these dimensions suggested that interindividual differences among males, like the average difference between males and females, arise mainly from differences in vocal tract dimensions, whereas interindividual differences among females may have a glottal basis. The spectral characteristics of the modes of singing could be represented for each vowel in two dimensions. Differences among the soft (pianissimo), light, neutral, free, straight, extra vibrato, and loud (fortissimo) modes were mainly due to the spectral effect of vocal effort, which constituted a very dominant first spectral dimension. This dimension essentially reflected the slope of the spectrum. The second dimension mainly described the spectral differences between the dark and pressed modes of singing. A possible explanation of the results in terms of glottal and supraglottal morphological variation is discussed.
OBJECTIVES: Characterize power spectrum pattern of heart rate variability (HRV) and assessment of relative cardiac nervous system in patients with acute myocardial interaction of sympathetic and parasympathetic infarction. We also compared the spectral power with some known prognostic risk variables. STUDY DESIGN: Study of patients with acute myocardial infarction (AMI) and sedentary healthy subjects sex matched. SUBJECT AND METHODS: 19 postinfarction patients aged 55.7 +/- 10.5 years and 19 healthy subjects controls aged 53.9 +/- 11.0. ECG signals were recorded after 15 minutes of supine rest with controlled breathing at 15 cycles/min. Signal acquisition was done at 300 samples/sec. From 512 consecutive sinus beats, we calculated the average, standard deviation, maximum and minimum values and rate between the longest and shortest R-R interval (E/I). We also calculated, after computing the fast Fourier transform, the total spectrum power, low frequency component (LF, from 0.01 to 0.15 Hz), high frequency component (HF, from 0.15 to 0.50 Hz) and its ratio (LF/HF). Thereafter, we correlated these results with radionuclide ejection fraction, duration of treadmill test, Holter ventricular premature complex and localization of infarction. RESULTS: The average R-R interval was 757.9 +/- 116.3 and 850.9 +/- 133.9 msec (p less than 0.05), the R-R corrected standard deviation was 15.3 +/- 6.0 and 38.2 +/- 8.5 msec (p less than 0.001) and ratio E/I was 1.13 +/- 0.06 and 1.32 +/- 0.09 (p less than 0.001) in AMI and control group, respectively. In AMI group, low frequency spectral band was very decreased (LF = 0.03 +/- 0.02 sec2) and high frequency was virtually absent (HF = 0.01 +/- 0.01 sec2) compared with control group (LF = 0.13 +/- 0.06 and HF = 0.14 +/- 0.15 sec2), p less than 0.001; ratio LF/HF was increased in AMI group. There were no significant differences between groups for normalized LF (LF%) and HF (HF%). CONCLUSIONS: These results showed that spectral pattern in AMI patients had very low LF and HF power density. Decreased HRV in that group was mainly due to diminished parasympathetic influence in cardiac regulation; nevertheless ratio LF/HF was increased which represents an imbalance of sympatho-vagal activity with predominance of sympathetic tone. We found poor correlation between frequency domain indices and other risk variable; best correlation was between total spectral power and radionuclide ejection fraction (r = 0.642, p less than 0.01), which could express independent prognostic value in AMI patients risk stratification.
A new computerized method for the assessment of electrical activity of muscles is described. The method is based on statistical processing of the spectral parameters of circumscribing EMG. The method is intended for examination of normal and pathological tremor. The authors describe the results of the use of the method for examination of physiological tremor which may serve as standard criteria for the identification of pathological deviations.
In the past it was reported in several studies that both depressive and schizophrenic patients exhibit reduced P300 amplitudes compared to healthy controls. In order to elucidate the underlying mechanisms of spectral P300 generation, we analysed P300 responses in depression and schizophrenia by a frequency based approach. Herefore, the amplification (poststimulus/prestimulus) of spectral power in different frequency bands was evaluated for non-target and target epochs. Generally, we found that P300 responses are accompanied by a pronounced frequency amplification in the delta and theta range. For the depressive patients we detected only under target condition a statistically significant reduction of alpha and gamma amplification compared to controls. In contrast to this, we observed a highly significant reduction of delta amplification in schizophrenic patients, under both target and non-target conditions.
Trabecular bone structure and bone density contribute to the strength of bone and are potentially important in the study of osteoporosis. Fourier transforms of the textural patterns in radiographs of trabecular bone have previously been used for the measurement of trabecular bone structure in subjects, however, the relationship between these measures and biomechanical properties of bone have not previously been established. In this study radiographs were acquired of 28 cubic specimens of spinal trabecular bone along each of the three anatomic axes: cranio-caudal or superior-inferior (SI), medial-lateral (ML), and anterior-posterior (AP). The radiographs were digitized, background corrected, and uniformly aligned. The Fast Fourier transform (FFT) was performed on a region comprised solely of trabecular bone for each image. The zero (DC), first (FMO), and second moments (SMO) of the Fourier power spectrum and the fractal dimension (FD) as determined from the Fourier power spectrum were correlated with stereology measures, with bone mineral density (BMD) as well as with measured biomechanical properties [Young's elastic modulus (YM) and ultimate strength] of the cubes. The results show that the power spectra-based measures, when compared with structural parameters determined using 3D stereology, show good correlations with bone volume fraction, trabecular spacing, thickness, and number. These power spectral measures showed fair to good correlations with BMD and the biomechanical properties. Moreover, the correlations between the power spectral measures of trabecular structure and the BMD, YM, and stereology measures of structure depend on the orientation of the radiographic image. Specifically, these were significant differences in the measured biomechanical properties and the power spectral measures of the trabecular structure between the SI and ML and the SI and AP directions. In addition, depending on the spatial frequency range for analysis, the fractal dimension showed opposite trends with changes in BMD and biomechanical properties. Multivariate regression models showed the correlation coefficients increasing with the inclusion of some of the power spectral measures, suggesting that FFT-based texture analysis may play a potential role in studies of osteoporosis.
The purpose of this study is to give an experimental basis for the diagnosis of diseased eyes by using the electrical stimulation method. This paper describes the spectral differences in AC-EER (Electrically Evoked Response with Alternating Current stimulus) obtained by electrical stimulation of diseased and normal eyes.
Recent evidence suggests that nociceptive modulatory cells in the nucleus raphe magnus (RM) and adjacent nucleus reticularis magnocellularis (NRMC) may participate in the modulation of autonomic processing. Therefore, spectral analyses were used to determine component frequencies common to both arterial blood pressure and the activity of RM/NRMC neurons in rats lightly anesthetized with isoflurane. These analyses detected powerful, extremely low frequency (period length: 6.4-18.5 min) oscillations in arterial blood pressure and in the activity of two classes of RM/NRMC neurons, ON and OFF cells. All ON cells discharged during periods of low blood pressure, whereas all OFF cells discharged during periods of high blood pressure. In contrast, the discharge of NEUTRAL and REGULAR cells did not have a consistent relationship to blood pressure. The role of these cells in nociceptive modulation is also unclear. The results presented indicate that ON and OFF cells may participate in the modulation of both autonomic and nociceptive processing.
According to mathematic statistics, data for laser microemission spectroscopic analysis were selected, which were collected with the use of CCD (charge-coupled device) in arg on atmosphere at reduced pressure. By selection, the effects of some factors, such as the difference of bore ablated on the sample surface by the laser, the distribution nonuniformity of element in the sample, and the fluctuation of output energy of the laser, etc. were reduced. The method that improves analytic precision of laser microemission spectroscopic analysis was studied. And quantitative analysis of Cu, Zn and Mg in aluminum alloy standard samples was performed, using the Cu (I) line at 324.7 nm, the Zn (I) line at 334.5 nm, and the Mg (I) line at 383.8 nm. The results show that the RSDs of relative intensity of the spectral lines of Cu, Zn, Mg are 1.80%, 4.35% and 6.29% respectively, and the RSDs of quantitative analysis of them are 10.1%, 6.98% and 8.17% respectively. The relative errors of the average of analysis of them are -3.76%, 3.62% and -1.62% respectively.
BACKGROUND: The signal-averaged ECG has been used to detect late potentials, and it is considered a noninvasive marker for areas of slow conduction requisite for reentrant arrhythmia. Late potentials are not usually found in patients with idiopathic ventricular tachycardia (VT); nevertheless, fragmented electrograms are often recorded in those patients during endocardial mapping. The purpose of this study was to investigate the spectral content of the signal-averaged ECGs with use of fast Fourier transform analysis (FFT) in patients with idiopathic VT of left ventricular origin. METHODS AND RESULTS: Signal-averaged ECGs were recorded in 12 patients with idiopathic VT originating from the left ventricle (group 1) and 25 age-matched normal volunteers (group 2). Frequency analysis with FFT was performed with a Blackman-Harris window in a segment length of 120 msec from 40 msec before the end of the QRS complex, and the frequency spectrum was displayed in a three-dimensional graph. Area ratio 1 (area of 20-50 Hz/area of 10-50 Hz) and area ratio 2 (area of 40-100 Hz/area of 0-40 Hz) were calculated in all subjects. Late potentials defined by the time domain were negative in all subjects. The area ratios of group 1 were significantly higher than those of group 2. High-frequency components in the three-dimensional graph were confined within the QRS complex. CONCLUSIONS: These results suggest that frequency analysis of signal-averaged ECGs with FFT is an available method for detecting the high-frequency component within the QRS complex in some patients with idiopathic VT of left ventricular origin.
INTRODUCTION: Heart rate variability (HRV) is a predictor of outcome in acute myocardial infarction and head trauma. Its efficacy in predicting outcome in stroke has not been well documented. MATERIALS AND METHODS: Twenty-five patients (mean age 39 years) with acute stroke treated in a stroke intensive care unit were studied. Continuous echocardiogram recorded for a 1-hour period was digitized and stored for off-line analysis. Time and frequency domain HRV measures were derived for the filtered and rectified ECG data for each patient. Clinical and HRV profiles were compared among patients who died or survived. RESULTS: At admission, 16 patients were comatose (Glasgow Coma score<9 at admission), 16 had focal weakness, and all had abnormal brain computed tomography. Of the 25 patients,11 died, 10 had a poor outcome, and 4 had good outcome. Two variables low-frequency (LF) spectral power and very low-frequency (VLF) spectral power correlated with mortality. After adjustment for mechanical ventilation and vasopressor administration, LF, VLF, and Triangular index of RR interval (TINN) correlated with mortality. On multiple regression analysis weighed for mechanical ventilation and vasopressor administration, the eye-opening score on Glasgow Coma Scale and LF spectral power were factors that were independently predictive of mortality. CONCLUSION: HRV measurements are independent predictors of outcome in acute severe stroke.
This paper presents a new version of an EMG-based, hands-free, cursor control system, and compares its performance to that of a previous version. Both systems use classification algorithms that rely on the periodogram estimation of the power spectral density (PSD) of electromyogram (EMG) signals from muscles in the face. The older system requires three electrodes for EMG input, and utilizes an algorithm that calculates partial power accumulations over the frequency ranges of 0Hz - 145Hz and 145Hz - 600Hz in the PSDs of the EMG signals. The new system requires four electrodes for EMG input, and utilizes an algorithm that calculates mean power frequency (MPF) values to assist in distinguishing the cranial muscle that contracted. An experiment was devised to gauge the point-and-click capabilities of both systems. The experimental results were evaluated using Fitts' Law analysis. The results show that the new algorithm provides improved point-and-click performance over the old algorithm.
The fetal electrocardiogram (ECG) was recorded from the maternal abdomen together with sonographic detection of fetal states in four pregnant patients at 26 and 36 weeks of gestation. Computerised algorithms obtained a good recognition of maternal ECG and fetal ECG. The corresponding power spectral density (PSD) was estimated during epochs of quiet or breathing movements for 256 consecutive heart beats. At 36 weeks of gestation the PSD analysis showed heart rate variability components similar to an adult heart. A low frequency component was observed together with a high frequency component in the range of fetal breathing movements. This high frequency component (0.6 - 0.9 Hz) disappeared from the PSD analysis during epochs of apnea. To our knowledge this is the first demonstration of such a mechanism in the human fetus in utero. At 26 weeks no respiratory component was observed in the PSD analysis. The maturation of control mechanisms could be responsible for this difference.
This paper reported the structure of a main unknown compound which was isolated and purified by column chromatography from a new mould release agent used in plastics. Elemental analysis, infrared spectra and 1H nuclear magnetic resonance spectrum were used to study the structure characters. The structure was then confirmed by assigning infrared absorbing peaks and nuclear magnetic spectral bands of this compound and its hydrochloric acid-treated compound. It showed to be a surfactant, N,N-dihydroxyethyl dodecylamine. The result provides useful information for developing new mould release agents.