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PubMed2005

Assessment of wavelet analysis of gait in children with typical development and cerebral palsy.

The objective of this study was to examine the use of the continuous wavelet transform (CWT) on surface electromyographic (sEMG) signals acquired from the lower extremity muscles during gait in children with typical development (TD) and cerebral palsy (CP). This was done to explore the possibility of developing a quantitative assessment scale of motor function based on time-frequency information. An initial study was conducted on retrospective gait data from three children, matched in gender and in anthropometric variables but with differing levels of walking ability. EMG data were extracted from five lower extremity muscles to assess the degrees of differentiation. The data were processed using the CWT to derive an average scalogram, from which the instantaneous mean frequency (IMNF) was calculated. Principal component analysis was used to assess the differences between the curves. Preliminary results indicated that for select lower extremity muscles, there was a significant deviation in the IMNF curves in the child with CP as compared to the child with TD. Furthermore, as motor impairment increased, total percent explained variance to the TD curves decreased. This suggests that it might be possible to derive a physiologically based quantitative index for assessing motor function and for assessing clinical treatments in CP using the wavelet analysis.

Algorithms↗
PubMed2006

A new general-purpose fully automatic baseline-correction procedure for 1D and 2D NMR data.

A new procedure for automatic baseline correction of NMR data sets is presented. It is based on an improved automatic recognition of signal-free regions that uses a Continuous Wavelet transform derivative calculation, followed by a baseline modelling procedure based on the Whittaker smoother algorithm. The method has been proven to automatically flatten 1D and 2D NMR spectra with large baseline distortions arising from different sources, is tolerant to low signal-to-noise ratio spectra, and to signals of varying widths in a single spectrum. Even though this procedure has so far only been applied to NMR spectra, we believe it to also be applicable to other spectroscopies having relatively narrow peaks (e.g., mass spectrometry), and potentially to those with broad peaks (e.g., near infrared or ultraviolet).

Algorithms↗
PubMed2004

A new method for the extraction and classification of single motor unit action potentials from surface EMG signals.

It has been shown that multi-channel surface EMG allows assessment of anatomical and physiological single motor unit (MU) properties. To get this information, the action potentials of single MUs should be extracted from the interference EMG signals. This study describes an automatic system for the detection and classification of MU action potentials from multi-channel surface EMG signals. The methods for the identification and extraction of action potentials from the raw signals and for their clustering into the MUs to which they belong are described. The segmentation phase is based on the matched Continuous Wavelet Transform (CWT) while the classification is performed by a multi-channel neural network that is a modified version of the multi-channel Adaptive Resonance Theory networks. The neural network can adapt to slow changes in the shape of the MU action potentials. The method does not require any interaction of the operator. The technique proposed was validated on simulated signals, at different levels of force, generated by a structure based surface EMG model. The MUs identified from the simulated signals covered almost the entire recruitment curve. Thus, the proposed algorithm was able to identify a MU sample representative of the muscle. Results on experimental signals recorded from different muscles and conditions are reported, showing the possibility of investigating anatomical and physiological properties of the detected MUs in a variety of practical cases. The main limitation of the approach is that complete firing patterns can be obtained only in specific cases due to MU action potential superpositions.

Action Potentials↗
PubMed2006

Detecting time-dependent coherence between non-stationary electrophysiological signals--a combined statistical and time-frequency approach.

Various time-frequency methods have been used to study time-varying properties of non-stationary neurophysiological signals. In the present study, a time-frequency coherence estimate using continuous wavelet transform (CWT) together with its confidence intervals are proposed to evaluate the correlation between two non-stationary processes. The approach is based on averaging over repeat trials. A systematic comparison between approaches using CWT and short-time Fourier transform (STFT) is carried out. Simulated data are generated to test the performance of these methods when estimating time-frequency based coherence. In contrast to some recent studies, we find that CWT based coherence estimates do not supersede STFT based estimates. We suggest that a combination of STFT and CWT would be most suitable for analysing non-stationary neural data. Tests are presented to investigate the time and frequency discrimination capabilities of the two approaches. The methods are applied to two experimental data sets: electroencephalogram (EEG) and surface electromyogram (EMG) during wrist movements in a healthy subject, and local field potential (LFP) and surface EMG recordings during resting tremor in a Parkinsonian patient. Supporting software is available at and .

Algorithms↗
PubMed2005

Practical issues in the evaluation of methods for the prediction of shock outcome success in out-of-hospital cardiac arrest patients.

There is a need for robust, effective predictors of the outcome from shock for out-of-hospital cardiac arrest patients. Such technology would enable the emergency responder to provide a therapy tailored to the patient's needs. Here we report our most recent findings while dwelling intentionally on the rationale behind the decisions taken during system development. Specifically, we illustrate the need for sensible data selection, fully cross-validated results and the care necessary when evaluating system performance. We analyze 878 pre-shock ECG traces, all of at least 10 s duration from 110 patients with cardiac arrest of cardiac aetiology. The continuous wavelet transform was applied to preshock segments of ECG trace. Time-frequency markers are extracted from the transform and a linear threshold derived from a training set to provide high sensitivity prediction of successful defibrillation. These systems are then evaluated on a withheld test set. All experiments are cross-validated. When compared to popular Fourier-based techniques our wavelet transform method, COP (Cardioversion Outcome Predictor), provides a 10-20% improvement in performance with values of 66 +/- 4 specificity at 95 +/- 4 sensitivity, 61 +/- 4 specificity at 97 +/- 2 sensitivity and 56 +/- 1 specificity at 98 +/- 2 sensitivity achieved for datasets limited to 3, 6, and 9 shocks per patient, respectively. Thus, the assessment of the wavelet marker was associated with a high specificity value at or above 95% sensitivity in comparison to previously reported methods. Therefore, COP could provide an optimal index for the identification of patients for whom shocking would be futile, and for whom an alternative therapy could be considered.

Animals↗
PubMed1989

Structure of the fully hydrated gel phase of dipalmitoylphosphatidylcholine.

X-ray diffraction intensities for lamellar repeats, h = 1 to 7, and wide-angle x-ray scattering were measured for the gel phase of fully hydrated dipalmitoylphosphatidylcholine. A hybrid model, which represents the electron density along the lamellar repeat direction as a continuous function composed of constant strips and superimposed Gaussians, is defined. The data were used to determine the best parameters in hybrid models and also in the older strip models. The most successful results were obtained when the density of the methylene region was constrained to the value obtained from the wide-angle scattering. Further analysis utilized the lipid volume obtained from absolute specific volume measurements. Together with the fundamental relations derived in the previous paper, the electron density modeling yielded the headgroup volume (340 +/- 10 A3) and the methylene volume (25.3 +/- 0.2A3). The results were in agreement whether the hybrid model or the strip model was used and whether our data or the data of Torbet and Wilkins were used. Additional structural results, such as the area (45.9 +/- 2.0 A2) and the number of waters of hydration per lipid (10.6 +/- 2.0), required one additional piece of information, which we took to be the tilt angle theta, which is 30 +/- 3 degrees from other experiments in the literature. Absolute electron density profiles, which clearly indicate two features in the headgroup region, are presented. The analysis yielded an accurate value of F(0), which contributes to the continuous scattering transform F(X), which is also given.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1990

High-resolution electron density profiles reveal influence of fatty acids on bilayer structure.

Small-angle x-ray diffraction studies were performed on gel phase-oriented bilayers of dipalmitoylphosphatidylcholine (DPPC) and DPPC containing 40 mol% of either palmitic acid (PA) or palmitic acid brominated at the 2-position (BPA). Oriented samples were prepared using a method developed by us, which is as simple as powder sample preparations while offering all the advantages of oriented samples made by traditional methods. Phases were determined using swelling experiments with structure factors plotted in reciprocal space, creating a relatively smooth curve as the amount of water between the bilayers was changed. Continuous Fourier transforms were also calculated to further test the consistency of the phase assignments. The diffraction data were used to calculate absolute electron density profiles for different bilayers to a resolution of 5-6 A. Analysis indicates the following: (a) The electron density profiles for the three preparations are virtually identical in the hydrocarbon chain region. (b) There is a decrease in the electron density of the glycerol backbone-headgroup region and d-space in DPPC-PA compared to DPPC. (c) The bromine of fatty-acid brominated at the 2-position is in the vicinity of the glycerol backbone. (d) The bilayer thickness of DPPC containing either brominated or unbrominated fatty acid remains relatively constant with increased levels of hydration, unlike DPPC bilayers.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1991

Location of two antioxidants in oriented model membranes. Small-angle x-ray diffraction study.

Small-angle x-ray diffraction has been applied in locating either butylated hydroxytoluene (BHT) or delta-tocopherol and their brominated analogues at a concentration of 40 mol% in oriented bilayers of dipalmitoylphosphatidylcholine (DPPC) or DPPC + 15 mol% cholesterol at 20 degrees C. Phases were determined using swelling experiments with structure factors plotted in reciprocal space, creating a relatively smooth curve as the amount of water between the bilayers was changed. Continuous Fourier transforms were also calculated using sampling theory (Shannon, C. E. 1949. Proc. Inst. Radio Engrs. NY. 37:10-21) to further test the consistency of the phase assignments. Fourier synthesis of structure factors resulted in absolute electron density profiles for different bilayers to a resolution of 5-6 A. In addition, difference Patterson maps were constructed to confirm the positions of the bromine atoms in the unit cell. Analysis of the data indicates the following: (a) The BHT molecules are dispersed throughout the alkyl-chain region in DPPC samples with and without cholesterol. (b) The chromanol ring of delta-tocopherol is in the vicinity of the glycerol backbone-headgroup region in samples of DPPC or DPPC + 15 mol% cholesterol. (c) Difference Patterson maps confirm the localization of bromine atoms in the various delta-tocopherol samples and lack of bromine localization in the various BHT samples.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1998

Structure and interactions of fully hydrated dioleoylphosphatidylcholine bilayers.

This study focuses on dioleoylphosphatidylcholine (DOPC) bilayers near full hydration. Volumetric data and high-resolution synchrotron x-ray data are used in a method that compares DOPC with well determined gel phase dipalmitoylphosphatidylcholine (DPPC). The key structural quantity obtained is fully hydrated area/lipid A0 = 72.2 +/- 1.1 A2 at 30 degrees C, from which other quantities such as thickness of the bilayer are obtained. Data for samples over osmotic pressures from 0 to 56 atmospheres give an estimate for the area compressibility of KA = 188 dyn/cm. Obtaining the continuous scattering transform and electron density profiles requires correction for liquid crystal fluctuations. Quantitation of these fluctuations opens an experimental window on the fluctuation pressure, the primary repulsive interaction near full hydration. The fluctuation pressure decays exponentially with water spacing, in agreement with analytical results for soft confinement. However, the ratio of decay length lambda(fl) = 5.8 A to hydration pressure decay length lambda = 2.2 A is significantly larger than the value of 2 predicted by analytical theory and close to the ratio obtained in recent simulations. We also obtain the traditional osmotic pressure versus water spacing data. Our analysis of these data shows that estimates of the Hamaker parameter H and the bending modulus Kc are strongly coupled.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1999

Characteristics of female obstetrician-gynecologists in the United States.

OBJECTIVE: To describe characteristics of United States female obstetrician-gynecologists, a large and growing group, and to contrast them with other female physicians. METHODS: We contrasted data from 313 obstetrician-gynecologists to data from 4132 other female physician respondents to the Women Physicians' Health Study, a national questionnaire-based study. RESULTS: Obstetrician-gynecologists assumed fewer domestic responsibilities, reported higher personal and household incomes, and were more likely to be in a group practice than other female physicians. Female obstetrician-gynecologists' personal health behaviors and other personal characteristics, career satisfaction, and desire to remain in their specialty were similar to those of other female physicians. Obstetrician-gynecologists did more counseling and screening than primary care physicians (family and general practitioners and internists) with respect to breast cancer and hormone replacement therapy (HRT). Obstetrician-gynecologists performed equivalently to primary care physicians with respect to human immunodeficiency virus (HIV), colorectal cancer, blood pressure, weight, exercise, and smoking, performed like other specialists with respect to cholesterol, skin cancer, and flu vaccine, and between these two groups with respect to nutrition and alcohol. Obstetrician-gynecologists' perceived relevance of, training in, and confidence regarding counseling were higher for HRT and breast cancer compared with other physicians. CONCLUSION: Obstetrician-gynecologists have many similarities with other female physicians, including level of career satisfaction, but earned more and assumed fewer domestic responsibilities. Although obstetrician-gynecologists counseled more than other specialists, with the increasing role of obstetrician-gynecologists as primary care doctors, it is noteworthy that female obstetrician-gynecologists frequently provide gynecologic-specific preventive care, but are less likely to address other non-obstetric-gynecologic areas of prevention. This finding could be transformed by continued changes in the education of residents and practicing physicians.

Female↗
PubMed1997

Effect of cage size on ultradian locomotor rhythms of laboratory mice.

The effect of cage size on spontaneous locomotor rhythms of laboratory mice was studied under simulated light-dark (12:12) cycles. On-line image analysis of bodily displacement yielded a locomotor signal over a period of 3 days. Continuous wavelet transform was applied to the signal, and ensemble averaging of eight mice revealed in the time-frequency plot bouts of increased motor activities. Notably, there were two bouts in the dark corresponding to ultradians of periods below 5 h: a first bout at the dark onset (at 0.6-1.0 cycle/h), and a second bout during the second half of the dark period (at 0.4-0.7 cycle/h). These increases of activity were more intense and distinct when the animals were kept inside the larger cage. Furthermore, the first bout disappeared when the animals were kept in the small cage for 3 days.

Activity Cycles↗
PubMed2000

Adsorptive immobilization of erythrocyte membrane.

Immobilization of human erythrocyte membrane was carried out by adsorption on Fractosil, a porous form of silica. Acetylcholinesterase (AChE) was chosen as a representative membrane enzyme in this study. Dependency of adsorption on membrane concentration was determined. Positive cooperative interactions that occurred in the process of immobilization increased stability. Presence of hydrophobic ligands on derivatized Fractosil was found to enhance stability of immobilized preparations making them more effective for use in continuous catalytic transformations. It is suggested that adsorptive immobilization of membrane structures such as the human erythrocyte membrane fragments on Fractosil and other inexpensive supports may provide a convenient procedure for utilization of their catalytic potential. Such preparations may be used in diagnostic kits or for construction of biosensors.

Acetylcholinesterase↗
PubMed2003

An estimation of the influence of force decrease on the mean power spectral frequency shift of the EMG during repetitive maximum dynamic knee extensions.

Frequency analysis of myoelectric (ME) signals, using the mean power spectral frequency (MNF), has been widely used to characterize peripheral muscle fatigue during isometric contractions assuming constant force. However, during repetitive isokinetic contractions performed with maximum effort, output (force or torque) will decrease markedly during the initial 40-60 contractions, followed by a phase with little or no change. MNF shows a similar pattern. In situations where there exist a significant relationship between MNF and output, part of the decrease in MNF may per se be related to the decrease in force during dynamic contractions. This study estimated force effects on the MNF shifts during repetitive dynamic knee extensions. Twenty healthy volunteers participated in the study and both surface ME signals (from the right vastus lateralis, vastus medialis, and rectus femoris muscles) and the biomechanical signals (force, position, and velocity) of an isokinetic dynamometer were measured. Two tests were performed: (i) 100 repetitive maximum isokinetic contractions of the right knee extensors, and (ii) five gradually increasing static knee extensions before and after (i). The corresponding ME signal time-frequency representations were calculated using the continuous wavelet transform. Compensation of the MNF variables of the repetitive contractions was performed with respect to the individual MNF-force relation based on an average of five gradually increasing contractions. Whether or not compensation was necessary was based on the shape of the MNF-force relationship. A significant compensation of the MNF was found for the repetitive isokinetic contractions. In conclusion, when investigating maximum dynamic contractions, decreases in MNF can be due to mechanisms similar to those found during sustained static contractions (force-independent component of fatigue) and in some subjects due to a direct effect of the change in force (force-dependent component of fatigue). In order to compare MNF shifts during sustained static and repetitive dynamic contractions it is necessary to estimate the force-dependent component of fatigue of dynamic contractions. Our results are preliminary and have to be confirmed in larger experiments using single dynamic contractions when determining the MNF-force relationship of the unfatigued situation.

Adolescent↗
PubMed2003

A multivariate, spatiotemporal analysis of electromagnetic time-frequency data of recognition memory.

Electromagnetic indices of "fast" (above 12 Hz) oscillating brain activity are much more likely to be considerably attenuated by time-averaging across multiple trials than "slow" (below 12 Hz) oscillating brain activity. To the extent that both types of oscillations represent the activity of temporally and topographically separable neural populations, time averaging can cause a loss of brain activity information that is important both conceptually and for multimodal integration with hemodynamic techniques. To address this issue for recognition memory, simultaneous electroencephalography (EEG) and whole-head magnetoencephalography (MEG) recordings of explicit word recognition from 11 healthy subjects were analyzed in two different ways. First, the time course of neural oscillations ranging from theta (4.5 Hz) to gamma (42 Hz) frequencies were identified using single-trial continuous wavelet transforms. Second, traditional analyses of amplitude variations of time-averaged EEG and MEG signals, event-related potentials (ERPs), and fields (ERFs) were performed and submitted to distributed source analyses. To identify data patterns that covaried with the difference between correctly recognized studied (old) words and correctly rejected nonstudied (new) words, a multivariate statistical tool, partial least squares (PLS), was applied to both types of analyses. The results show that ERPs and ERFs are mainly displaying those neural indices of recognition memory that oscillate in the theta (4.5-7.5 Hz), alpha (8-11.5), and to some extent in the beta1 (12-19.5 Hz) frequency range. The sources of the ERPs/ERFs were in good agreement with the topography of theta/alpha/beta 1 oscillations in being confined to the anterior temporal lobe at 400 ms and being distributed across temporal, parietal, and occipital areas between 500 and 700 ms. Gamma oscillations covaried either positively or negatively with theta/alpha/beta1 oscillations. A positive covariance, for instance, was detected over left anterior temporal sensors as early as 200-350 ms and is compatible with studies in rodents showing that gamma and theta oscillations emerge together out of the interaction of the hippocampus and the entorhinal and perirhinal cortices. Fast beta oscillations (20-29.5 Hz), on the other hand, did not strongly covary with slow oscillations and were likely to arise from neural populations not adequately represented in ERPs/ERFs. In summary, by providing a more comprehensive description of electromagnetic signals, time-frequency data are of potential benefit for integrating electrophysiological and hemodynamic indices of brain activity and also for integrating human and animal electrophysiology.

Adolescent↗
PubMed1998

Adsorptive immobilization of submitochondrial particles on Fractosil.

(1) Submitochondrial particles prepared from beef liver mitochondria were immobilized on Fractosil, a porous form of silica, in order to stabilize their enzymatic activity. (2) The catalytic activity of succinate-cytochrome c reductase, an enzyme complex of the inner mitochondrial membrane, was followed in this study. Adsorption resulted in significant stabilization with a lowering of K(m) (app.) for succinate, in spite of mass transfer and diffusion limitations expected to occur in such a complex and heterogeneous system. An increase in catalytic potential was also observed upon immobilization. These observations, taken together, suggest that substantial degree of conversation of substrates to their respective products may be achieved by such immobilized preparations. (3) Positive cooperative interactions for binding of submitochondrial particles to the matrix was observed, apparently with two sets of sites, the second set indicating a much greater hill coefficient. (4) The present report indicates that adsorption with the use of a porous inorganic support such as Fractosil may provide a simple and efficient method of immobilization. Such preparations containing membrane enzymes in their native microenvironments would be useful for continuous catalytic transformations and also for construction of biosensors.

Adsorption↗
PubMed2003

Recent advances in the discovery of organometallic catalysts using high-throughput screening assays.

Combinatorial techniques were developed initially to accelerate the identification of molecules with biological activity. The successes of these techniques inspired the design of high-throughput methods to assist in the discovery of new catalysts. Over the past year, many groups in academia and industry have utilized high-throughput screening assays to reduce the time required to identify catalysts for asymmetric processes, cross-coupling reactions and other metal-catalyzed transformations. The continued success of combinatorial techniques in organometallic chemistry should propagate the development of new and improved methods to facilitate catalyst discovery.

Catalysis↗
PubMed2001

Evidence for distinct beta resonance frequencies in human EEG related to specific sensorimotor cortical areas.

OBJECTIVE: We studied event-related synchronization (ERS) of beta rhythms related to voluntary movement vs. stimulation of upper and lower limbs. The aim of this study was to investigate whether the frequency of the beta response is related to specific regions within the sensorimotor strip. METHODS: Self-paced movement and electrical stimulation of the dominant hand and foot/leg was investigated in 10 right-handed volunteers. The electroencephalogram was recorded from closely spaced electrodes over central areas and processed time-locked to movement-offset or stimulation. In order to identify the dominant frequency of the induced beta oscillations, time-frequency maps were calculated using the continuous wavelet transformation. For the specific beta frequency bands, the band power time courses were analyzed by quantifying the event-related (de-)synchronization (ERD/ERS). RESULTS: Both limb movement and somatosensory stimulation induced bursts of beta oscillations appearing within 1 s after movement/stimulation with a clear focus close to the corresponding sensorimotor representation area. The peak frequency was significantly lower over the hand area (below approximately 20 Hz) than at mid-central sites overlying the foot representation area (above approximately 20 Hz). But no difference was found between movement and stimulation of the respective limb. CONCLUSIONS: Analyzing the frequency of induced beta activity revealed concomitant oscillations at slightly different frequencies over neighboring cortical areas. These oscillations might be indicative for a resonance-like behavior of connected sub-networks in sensorimotor areas.

Adult↗