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Results for “Dimensionality Reduction”

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At least 1,603 records · Page 89Linked to original sources
PubMed1996

Cardiovascular effects of anabolic steroids in weight-trained subjects.

The effects of large doses of anabolic steroids on 24-hour blood pressure, cardiac structure and function, and lipid profiles were studied in 10 body builders using anabolic steroids and 14 body builders who did not use steroids (control subjects). All subjects underwent noninvasive 24-hour blood pressure monitoring, echocardiography, Doppler analysis of transmitral flow, and analysis for lipoprotein and gonadotropin levels. Anabolic steroid users were studied at the end of a steroid cycle and after a period of withdrawal. Average 24-hour blood pressure was similar in the two groups, but anabolic steroid users exhibited a smaller pressure reduction during sleep than did nonusers. This finding was present both at the end of treatment and after the period of withdrawal. Echocardiographic dimensional and functional indexes did not differ substantially between anabolic steroid users and the nonusers, and were similar in anabolic steroid users during use and after withdrawal. Anabolic steroid users also had higher LDL and lower HDL cholesterol levels than nonusers; Lp(a) was higher in nonusers, although this difference did not attain the level of statistical significance. These differences were more striking at the end of the treatment period. The results of this study show that chronic anabolic steroid intake causes an abnormal 24-hour blood pressure pattern, characterized by a flattening of the diurnal curve, and minor changes of the dimensional echocardiographic parameters.

Adult↗
PubMed2002

Graphical models for multivariate time series from intensive care monitoring.

Nowadays physicians are confronted with high-dimensional data generated by clinical information systems. The proper extraction and interpretation of the information contained in such massive data sets, which are often observed with high sampling frequencies, can hardly be done by experience only. This yields new perspectives of data recording and also sets a new challenge for statistical methodology. Recently graphical models have been developed for analysing the partial correlations between the components of multivariate time series. We apply this technique to the haemodynamic system of critically ill patients monitored in intensive care. In this way we can appraise the practical value of the new procedure by re-identifying known associations within the haemodynamic system. From separate analyses for different pathophysiological states we can even conclude that distinct clinical states are characterized by distinct partial correlation structures. Hence, this technique seems useful for automatic statistical analysis of high-dimensional physiological time series and it can provide new insights into physiological mechanisms. Moreover, we can use it to achieve an adequate dimension reduction of the variables needed for online monitoring at the bedside.

Blood Pressure↗
PubMed1998

New N-glycans in horseradish peroxidase.

We describe here the structures of several new N-glycan oligosaccharides from horseradish peroxidase (HRP). Glycopeptides from HRP were digested with glycoamidase A (from sweet almond) to release the N-glycans. The oligosaccharides were reductively aminated with 2-aminopyridine, and separated by high-performance liquid chromatography on octadecylsilyl- and amide-silica columns for two-dimensional mapping (Tomiya et al., Anal. Biochem. 171, 73-90, 1988). The N-glycans were also analyzed by electrospray ionization mass spectrometry. Two different lots of HRP showed a considerable difference in their N-glycan composition.

Amidohydrolases↗
PubMed1996

Recognition of a surface loop of the lipoyl domain underlies substrate channelling in the pyruvate dehydrogenase multienzyme complex.

In the pyruvate dehydrogenase multienzyme complex of Bacillus stearothermophilus, the interaction between the pyruvate decarboxylase (E1p) component and the lipoyl domain of the dihydrolipoyl acetyltransferase (E2) component was investigated using a combination of site-directed mutagenesis and NMR spectroscopy. Residues 11 to 15 (EGIHE) of the lipoyl domain, part of a surface loop close in space to the beta-turn containing the lipoyl-lysine residue (position 42), were deleted or replaced. The mutant domains all retained their three-dimensional structures and ability to become lipoylated, but in the absence of the loop the lipoyl-lysine residue could no longer be reductively acetylated by E1p. A mutation (N40A) in the N- terminal part of the lipoyl-lysine hairpin showed that it is involved in recognition of the domain by E1p but other mutations in the loop (E15A) and close to the lipoyl-lysine hairpin (V44S, V45S and E46A) were without effect. The heteronuclear multiple quantum coherence NMR spectra of 15N-labelled lipoyl domain in the presence and absence of B. stearothermophilus E1p were recorded. Of the 85 amino acid residues in the lipoyl domain, 13 exhibited significant differences in chemical shift. These differences, most of which were associated with residues in the surface loop between positions 8 and 15 and in, or close to, the lipoyl-lysine hairpin, indicate that E1p makes contact with the lipoyl domain in these areas. The combined results of directed mutagenesis and NMR spectroscopy point to the surface loop as a major determinant of the interaction of lipoyl domain with E1p. The specificity of this essential interaction provides the molecular basis of substrate channelling in this, the first committed, step of the enzyme reaction mechanism.

Acetylation↗
PubMed1994

Reductive methylation and pKa determination of the lysine side chains in calbindin D9k.

The Lys residues in the 75-residue Ca(2+)-binding protein calbindin D9k were reductively methylated with 13C-enriched formaldehyde. The possible structural effects resulting from the chemical modification were critically investigated by comparing two-dimensional NMR spectra and the exchange rates of some of the amide protons of the native and the modified protein. Our results show that the protein retains its structure even though 10 Lys out of a total of 75 amino acid residues were modified. In the Ca(2+)- and apo-forms of the protein, the 13C-methylated Lys residues can be detected with high sensitivity and resolution using two-dimensional (1H, 13C)-heteronuclear multiple quantum coherence (HMQC) NMR spectroscopy. The pKa values of the individual Lys residues in Ca(2+)-calbindin D9k and apo-calbindin D9k were obtained by combining pH titration experiments and (1H, 13C)-HMQC NMR spectroscopy. Each Lys residue in the Ca(2+)- and apo-forms of calbindin D9k has a unique pKa value. The Lys pKa values in the calcium protein range from 9.3 to 10.9, while those in the apo-protein vary between 9.7 and 10.7. Although apo-calbindin D9k has a very similar structure compared to Ca(2+)-calbindin D9k, the removal of two Ca2+ ions from the protein leads to an increase of the pKa values of the Lys residues.

Calbindins↗
PubMed1999

A chaos-based model for low complexity predictive coding scheme for compression and transmission of electroencephalogram data.

A method for low complexity, low bit rate transmission of EEG (electroencephalogram) data, based on chaotic principles, is presented. The EEG data is assumed to be generated by a non-linear dynamical system of E dimensions. The E dynamical variables are reconstructed from the one-dimensional time series by the process of time-delay embedding. A model of the form X[n + 1] = F(X[n], X[n - 1], ... , X[n - p]) is fitted for the data in the E-dimensional space and this model is used as predictor in the predictive coding scheme for transmission. This model is able to give a reduction of nearly 50% of the dynamic range of the error signal to be transmitted, with a reduced complexity, when compared to the conventionally used linear prediction method. This implies that a reduced bit rate of transmission with a reduced complexity can be obtained. The effects of variation of model parameters on the complexity and bit rate are discussed.

Adult↗
PubMed1993

Two-dimensional photographic posture recording and description: a validity study.

Posture recording and description is necessary to yield data by which postural load can be assessed. In this paper an inexpensive and simple method to gather these data is described, ie two-dimensional (2-D) posture recording and description by means of photography. A disadvantage of this method, perspective error, is discussed and guidelines are given to reduce it. The validity of the method was experimentally tested for a situation slightly conflicting with some guidelines, ie recording of the whole body, with a small distance between camera and subject. For this purpose posture recording with 2-D photography was compared with posture recording by means of a three-dimensional optoelectronic system (Vicon). In general, 2-D photographic posture recording and description is a valid method as long as some guidelines for reduction of perspective error are followed.

Journal Article↗
PubMed1985

Cell cycle variations in ADP-ribosylation of HeLa nuclear proteins.

Changes in ADP-ribosylation of nuclear proteins during the HeLa cell cycle were determined. Portions of synchronized cultures were withdrawn at intervals and cells were permeabilized by resuspension in hypotonic buffer containing detergents. Nuclear proteins were radioactively labeled by incubating samples with [32P]NAD. Modified species were resolved using one-dimensional and two-dimensional polyacrylamide gel electrophoresis. Measurements of the incorporation of [32P]NAD by permeabilized cells showed that ADP-ribosylation is a significant modification throughout the cell cycle. A twofold increase was detected during S phase. Autoradiograms of one-dimensional sodium dodecyl sulfate-polyacrylamide gels revealed that many nuclear nonhistones are modified, though the major acceptors of 32P were the histones and a 116,000-Da species (poly(ADP-ribose) polymerase). The same modified proteins were present through the cell cycle, but densitometry of autoradiograms demonstrated a general increase in the level of incorporation in S phase. Autoradiograms of two-dimensional gels of nuclear proteins labeled with [32P]NAD were consistent with these results. Although nonhistones of isolated metaphase chromosomes show a substantial reduction in ADP-ribosylation, histone modification is essentially unchanged in metaphase.

Adenosine Diphosphate Ribose↗
PubMed1995

Hemodynamics of an artery with mild stenosis.

In this study the hemodynamics in the early stages of the atherosclerotic process--when a neointimal hyperplasia or an intimal fibrocellular hypertrophy takes place--is theoretically investigated. A local, slight increase in the wall thickness of a canine femoral artery is simulated using an original two-dimensional mathematical model of arterial hemodynamics and the effects induced on the velocity field by the simulated mild stenosis--only 2% of area reduction--are analysed. The model incorporates: fluid non-linear inertial forces, viscoelastic wall motion, anatomical taper, unsteady flow, pressure propagation and reflections on both the proximal and distal vessel ends. Two different physiological pulsatile flows are considered: a basal flow condition and a light vasodilation state inducing in the vessel segment a limited increase in mean flow (50%). The distribution along the vessel during the cardiac cycle of both the velocity profile and wall shear stress, are shown. The shape of velocity distributions is strongly perturbed by the stenosis and disturbances are clearly evident whatever instant of the cardiac cycle is considered. After vasodilatation, during the phase of systolic deceleration, a vortex circulation appears in the post-stenotic region. The vortex persists for the whole diastolic phase, causing a very strong stress at the arterial wall: wall shear stress in the distal part of the simulated mild stenosis is at least five times the basal value. The reported results provide a coherent explanation of the critical role that hemodynamic factors may play in the early stages of atherogenic process.

Algorithms↗
PubMed1985

The operative stabilization and grafting of thoracic and lumbar spinal fractures.

In this paper several concepts of surgical treatment of thoracic and lumbar fractures are reviewed. Most classifications of these fractures are primarily radiologic, but pathomechanical aspects are very important as these guide the insight into and the rationale of the different modes of treatment. The segment of movement can be considered biomechanically as a three-dimensional system, built up from two rings, linked together at five functional points of support. Our principal mode of surgical therapy after closed reduction by halo-femoral traction is anterolateral decompression, stabilization and grafting to induce fusion. In suitable cases, a dorsal or posterolateral approach and instrumentation can be combined with ventral methods. By using the primary anterolateral approach, one can reduce malalignment at the site where it is needed. Decompression can be carried out where it is truly necessary. One can give support within the segment of movement at the logical place from a biomechanical point of view: the weight bearing part, i.e., the anterior ring. By excision of the injured bony and ligamentous tissue, motion in the damaged segment of movement is eliminated, the original height is restored by grafting, and at the same time the load-bearing capacity of the fractured area is repaired. By applying Zielke instrumentation one can compress the grafts in accordance with modern views on fracture treatment. This "philosophy" is illustrated with case histories and a decision making flow chart.

Adolescent↗
PubMed1994

Radiology in survivors of traumatic atlanto-occipital dislocation.

Traumatic atlanto-occipital dislocation is fatal, but survivals are reported. Six cases of survival after atlanto-occipital dislocation are presented. Lateral cervical spine radiographs demonstrated retropharyngeal swelling in all patients, and Powers' ratio was abnormal in five of six patients. Reformatted computed tomography (CT) images or three-dimensional CT were useful in confirming the diagnosis. Initial treatment consisted of immobilization with halo or collar, and, in one patient, Crutchfield tongs. Reduction of the dislocation was associated with decreasing Powers' ratio in five long-term survivors. Residual neurologic deficits, however, were seen in these patients. Atlanto-occipital dislocation should be suspected in trauma patients with findings of brain stem injury--especially agonal respirations, irregular heart rate, lower cranial nerve abnormality, and asymmetrical motor deficits.

Accidents, Traffic↗
PubMed1991

Improved MR imaging in extremely inhomogeneous radio-frequency fields.

An improvement to the method for imaging with extremely inhomogeneous radio-frequency fields is presented which uses a pseudo-noise-modulated selective (PNMS) excitation prepulse to randomize the signal from outside the selected slice. This prepulse reduces the problems that arise from imperfect subtraction involved with the one-dimensional ISIS-type slice selection procedures. The results demonstrate two to three times improvement in the signal-to-noise ratio and reduction in the image artifacts when this prepulse is used.

Computer Simulation↗
PubMed2006

Myocardial adaptation to short-term high-intensity exercise in highly trained athletes.

We aimed to clarify the myocardial adaptation to short-term high-intensity exercise among trained athletes. We screened 17 participants in the 2004 World Indoor Rowing Championships before and after a 2000-m sprint. Echocardiography included standard measurements and tissue Doppler-derived strain (epsilon), strain rate, and 2-dimensionally derived speckle-tracking imaging for left ventricular (LV) torsion. LV volumes and ejection fraction were unchanged after exercise. There was a reduction in early and an increase in late diastolic filling velocities and a decrease in the flow propagation velocity. Annular systolic velocities, slope of the systolic acceleration, septal and lateral epsilon, and speckle tracking-derived torsion were increased. The increased LV torsion was a result of increased basal and apical rotation. Right ventricular apical epsilon decreased. In conclusion, maximal intensity short-duration exercise was associated with attenuation of LV diastolic function, augmentation of LV systolic function, and a reduction in apical right ventricular contractility.

Adaptation, Physiological↗
PubMed2006

Plasma homovanillic acid correlates inversely with history of learning problems in healthy volunteer and personality disordered subjects.

Central dopaminergic activity is critical to the functioning of both motor and cognitive systems. Based on the therapeutic action of dopaminergic agents in treating attention deficit hyperactivity disorder (ADHD), ADHD symptoms may be related to a reduction in central dopaminergic activity. We tested the hypothesis that dopaminergic activity, as reflected by plasma homovanillic acid (pHVA), may be related to dimensional aspects of ADHD in adults. Subjects were 30 healthy volunteer and 39 personality disordered subjects, in whom morning basal pHVA concentration and a dimensional measure of childhood ADHD symptoms (Wender Utah Rating Scale: WURS) were obtained. A significant inverse correlation was found between WURS Total score and pHVA concentration in the total sample. Among WURS factor scores, a significant inverse relationship was noted between pHVA and history of "childhood learning problems". Consistent with the dopaminergic dysfunction hypothesis of ADHD and of cognitive function, pHVA concentrations were correlated with childhood history of ADHD symptoms in general and with history of "learning problems" in non-ADHD psychiatric patients and controls. Replication is needed in treated and untreated ADHD samples to confirm these initial results.

Adult↗
PubMed2005

A simple electron-beam lithography system.

A large number of applications of electron-beam lithography (EBL) systems in nanotechnology have been demonstrated in recent years. In this paper we present a simple and general-purpose EBL system constructed by insertion of an electrostatic deflector plate system at the electron-beam exit of the column of a scanning electron microscope (SEM). The system can easily be mounted on most standard SEM systems. The tested setup allows an area of up to about 50 x 50 microm to be scanned, if the upper limit for acceptable reduction of the SEM resolution is set to 10 nm. We demonstrate how the EBL system can be used to write three-dimensional nanostructures by electron-beam deposition.

Equipment Design↗
PubMed1997

Identification of human liver carboxylesterase as one of the proteins involved in Plasmodium falciparum malaria sporozoite invasion in primary cultures of human hepatocytes.

BACKGROUND/AIMS: In a previous study, we have demonstrated that primary human hepatocytes in culture are susceptible for Plasmodium falciparum sporozoite invasion and for development of parasites into exo-erythrocytic forms. In a separate study we demonstrated the involvement of two human liver plasma membrane proteins (55 kD and 20 kD) in the invasion of P. falciparum sporozoites in vitro. In this study, we have unravelled the nature of the 55 kD protein. METHODS: For the identification of this protein, a 53-58 kD membrane protein fraction from human liver was isolated, radioactively labelled, incubated with sporozoites and cross-linked. After reduction of the cross-linker, the released proteins were mixed with unlabelled 53-58 kD protein fraction and separated on two-dimensional SDS-PAGE. Autoradiography showed a single spot corresponding to a protein of 55 kD and pI of 5.7-5.8. RESULTS: Amino acid sequencing revealed the 55 kD protein as carboxylesterase. The biological activity of purified human liver carboxylesterase and of an antiserum against carboxylesterase on sporozoite invasion in vitro was evaluated. Human carboxylesterase as well as a rabbit antiserum against carboxylesterase inhibited the invasion of P. falciparum sporozoites into primary human hepatocytes in culture. A number of carboxylesterase cDNA clones were isolated from a human liver cDNA library. Sequence analysis revealed two different iso-types. Immunoaffinity purified recombinant human carboxylesterase was shown also to inhibit the invasion of sporozoites into primary human hepatocytes. Immunocytochemical analysis of the localisation of carboxylesterase in primary cultures of human hepatocytes using specific antibodies, showed its presence inside the hepatocytes and on the membrane. CONCLUSIONS: Carboxylesterase plays a role in the invasion process of P. falciparum sporozoites into human hepatocytes in vitro. The implications of these findings are further discussed.

Amino Acid Sequence↗
PubMed2002

Quantitative analysis of gait in Parkinson's disease: a pilot study on the effects of bilateral sub-thalamic stimulation.

Four patients with Parkinson's disease who had a Subthalamic Nucleus (STN) stimulator implanted and four age-matched controls underwent gait analysis using a three-dimensional system. STN stimulation substantially improved most of the key variables in the patients, without producing inefficient compensatory movements of the trunk. A reduction of ankle power production during push off was the most persistent abnormality seen when the patients were stimulated. We also found a reduction of trunk lateral bending and torsion when the patients were not stimulated when compared with controls.

Biomechanical Phenomena↗
PubMed1987

Structure and proteolysis of the growth hormone receptor on rat hepatocytes.

125I-Labeled human growth hormone is isolated in high molecular weight (Mr) (300,000, 220,000, and 130,000) and low molecular weight complexes on rat hepatocytes after affinity labeling. The time-dependent formation of low molecular weight complexes occurred at the expense of the higher molecular weight species and was inhibited by low temperature or inhibitors of serine proteinases. Exposure to reducing conditions induced loss of Mr 300,000 and 220,000 species and augmented the amount of Mr 130,000 complexes. The molecular weight of growth hormone (22,000) suggests that binding had occurred with species of Mr 280,000, 200,000, and 100,000. Two-dimensional gel electrophoresis demonstrated that the 100,000-dalton receptor subunit is contained in both the 280,000- and 200,000-dalton species. Reduction of interchain disulfide bonds in the growth hormone receptor did not alter its elution from gel filtration columns, but intact, high molecular weight receptor constituents were separated from lower molecular weight degradation products. Digestion of affinity-labeled growth hormone-receptor complexes with neuraminidase increased the mobility of receptor constituents on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. These observations show that the growth hormone receptor is degraded by hepatic serine proteinases to low molecular weight degradation products which can be separated from intact receptor by gel filtration. Intact hormone-receptor complexes are aggregates of 100,000-dalton sialoglycoprotein subunits held together by interchain disulfide bonds and by noncovalent forces.

Animals↗