SEARCH · Search PubMed

Results for “Inversion”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 847 records · Page 47Linked to original sources

PubMed1994

Inverse dynamic optimization including muscular dynamics, a new simulation method applied to goal directed movements.

This paper presents a new method for estimating muscular force and activation from experimental kinematic data. The method combines conventional inverse dynamics with optimization utilizing a dynamic muscle model. The method uses only very limited computational power, which makes it a useful tool especially for complex systems like the shoulder or the locomotor system. The net torques/forces are calculated by using conventional inverse dynamics. A solution of the load sharing problem is determined by minimization of the weighted sum of squared muscle forces. The load sharing problem is solved with a dynamic constraint reflecting physiological muscle properties. This constraint takes into account the nonlinear dynamics of the contractile element (CE) and the series elastic element (SE), active state dynamics and neural excitation dynamics. This physiological constraint is determined with an inverse muscle model. With this model, muscular states and neural inputs are also estimated. The method of inverse dynamics requires position, velocity and acceleration signals as input. A method to prepare such signals from noisy measured data is presented.

Acceleration↗

PubMed1989

Echocardiographic study of U wave inversion in the electrocardiograms of hypertensive patients.

The prevalence of U wave inversion was evaluated in 58 adult patients with hypertension, and a possible mechanism for it was examined using M-mode echocardiographic indices. U wave inversion was the most common electrocardiographic abnormality, occurring in 34% of patients; voltage criteria for left ventricular hypertrophy were present in only 14% of patients, and ventricular strain pattern was not detected in any patient. Nonetheless, on echocardiography left ventricular posterior wall thickness was increased in 58% of patients. However, neither U wave inversion nor conventional voltage criteria for left ventricular hypertrophy was strongly predictive for this finding. The authors conclude that U wave inversion is a frequent finding in patients with hypertension, often occurring alone. Although it does not appear to be closely linked to the presence of left ventricular hypertrophy, it may relate to other, perhaps subtle, abnormalities of diastolic ventricular relaxation.

Adult↗

PubMed1988

3-Ethoxy-beta-carboline: a high affinity benzodiazepine receptor ligand with partial inverse agonist properties.

3-Ethoxy-beta-carboline binds with high affinity to benzodiazepine receptors in the central nervous system (Ki approximately equal to 10.1, 15.3, and 25.3 nM in rat cerebellum, cerebral cortex, and hippocampus, respectively). This compound has pharmacological actions reminiscent of benzodiazepine receptor partial inverse agonists such as FG 7142 and 3-carboethoxy-beta-carboline. Thus, while not a convulsant, 3-ethoxy-beta-carboline potentiated the convulsant actions of pentylenetetrazole in mice. Furthermore, this compound reduced both the time spent and the total entries in the open arms of an elevated plus maze and also inhibited stress-induced ulcer formation, effects that are also observed with benzodiazepine receptor inverse agonists. These findings suggest that 3-ethoxy-beta-carboline is a partial inverse agonist at benzodiazepine receptors which may prove useful for in vivo studies since it has a higher affinity for benzodiazepine receptors and better solubility than the commonly used partial inverse agonist FG 7142. Furthermore, 3-ethoxy-beta-carboline appears to be less vulnerable to metabolic degradation than ester analogs with a similar pharmacological profile such as 3-carboethoxy-beta-carboline.

Animals↗

PubMed1991

A model study of instability of the inverse problem in electrocardiography.

The inverse problem in electrocardiography is studied analytically using a concentric spheres model with no symmetry assumptions on the potential distribution. The mathematical formulation is presented, and existence and uniqueness of the solution are briefly discussed. Solution to the inverse problem is inherently very unstable. The magnitude of this instability is demonstrated using the derived analytical inverse solution for the spherical model. Regularization methods used to date are based on a regularization parameter that does not relate to any measurable physiological parameters. This paper presents a regularization method that is based on a parameter in the form of an a priori bound on the L2 norm of the inverse solution. Such a bound can be obtained from the theoretical estimates based on the measured values of the body surface potentials together with experimental knowledge about the magnitudes of the epicardial potentials. Based on the presented regularization, an exact form of the regularized solution and estimates of its accuracy are derived.

Electrocardiography↗

PubMed1994

Inverse electrocardiographic transformations: dependence on the number of epicardial regions and body surface data points.

The inverse problem of electrocardiography, the computation of epicardial potentials from body surface potentials, is influenced by the desired resolution on the epicardium, the number of recording points on the body surface, and the method of limiting the inversion process. To examine the role of these variables in the computation of the inverse transform, Tikhonov's zero-order regularization and singular value decomposition (SVD) have been used to invert the forward transfer matrix. The inverses have been compared in a data-independent manner using the resolution and the noise amplification as endpoints. Sets of 32, 50, 192, and 384 leads were chosen as sets of body surface data, and 26, 50, 74, and 98 regions were chosen to represent the epicardium. The resolution and noise were both improved by using a greater number of electrodes on the body surface. When 60% of the singular values are retained, the results show a trade-off between noise and resolution, with typical maximal epicardial noise levels of less than 0.5% of maximum epicardial potentials for 26 epicardial regions, 2.5% for 50 epicardial regions, 7.5% for 74 epicardial regions, and 50% for 98 epicardial regions. As the number of epicardial regions is increased, the regularization technique effectively fixes the noise amplification but markedly decreases the resolution, whereas SVD results in an increase in noise and a moderate decrease in resolution. Overall the regularization technique performs slightly better than SVD in the noise-resolution relationship. There is a region at the posterior of the heart that was poorly resolved regardless of the number of regions chosen. The variance of the resolution was such as to suggest the use of variable-size epicardial regions based on the resolution.

Adult↗

PubMed1980

High frequencies of inversions and translocations of chromosomes 7 and 14 in ataxia telangiectasia.

The R-banding of more than 1100 lymphocytes and fibroblasts from 11 patients with ataxia telangiectasia (AT) showed rearrangements of chromosomes 7 and/or 14 in about 7% of the cells. Among these rearrangements, pericentric inversion of chromosome 7 was the most frequent, and the paracentric inversion of chromosome 14 not very rare. These inversions are believed to be fairly specific of AT, and their absence in the previously reported literature may be due to technical problems. Inversions were also observed in the lymphocytes of presumed heterozygote carriers with a lower frequency, and may be of some help for the detection of healthy heterozygote carriers of the AT gene.

Ataxia Telangiectasia↗

PubMed1993

Benzodiazepine inverse agonists augment long-term potentiation in CA1 and CA3 of guinea pig hippocampal slices.

The effects of benzodiazepine inverse agonists on the long-term potentiation of synaptic transmission in hippocampal slices of the guinea pig were examined using an extracellular recording technique. Benzodiazepine inverse agonists, beta-carboline-3-carboxylate (beta-CCE), 2-phenylpyrazolo [4,3-c]quinolin-3(5H)-one (CGS-8216) and 2-[5-methylthien-3-yl]-2,5-dihydro-3H-pyrazolo [4,3-c]quinolin-3-one (S-135), augmented the magnitude of long-term potentiation induced by tetanic stimulation of input fibers in both the CA1 and the CA3 regions. beta-Carboline-3-carboxylate was more effective in augmenting long-term potentiation in CA1 than in CA3. Augmentation of long-term potentiation produced by beta-CCE was antagonized by concomitant application of flumazenil, a benzodiazepine receptor antagonist. Therefore, the enhancing action of benzodiazepine inverse agonists on long-term potentiation, which is suggested to be a specific action, mediated by the GABA/benzodiazepine receptor complex, might help to explain the mechanism of the memory-enhancing effects of benzodiazepine inverse agonists, observed in some in vivo behavioral paradigms.

Animals↗

PubMed1982

Face recognition by monkeys: absence of an inversion effect.

The effect of inversion of faces upon learning visual discriminations by macaque monkeys was studied with simultaneous discriminations, concurrent discriminations, and transfer tests. In no case was performance with upright stimuli superior to that with inverted stimuli; that is, there was no obvious inversion effect. Studies of human face recognition indicate that the inversion effect is mediated by an orientation-dependent face recognition mechanism that matures within the right hemisphere during childhood. Absence of an inversion effect would indicate that monkeys may not have such a mechanism. It was hypothesized that the macaque's relatively precocious development, smaller cortex, and lack of hemispheric specialization may preclude the maturation of such a mechanism.

Animals↗

PubMed1988

Ro 15-4513: partial inverse agonism at the BZR and interaction with ethanol.

The imidazobenzodiazepinone derivative Ro 15-4513 has the activity profile of a partial inverse (low efficacy) agonist at the benzodiazepine receptor (BZR). It reverses central nervous depressant effects of diazepam, and, in part, of phenobarbitone and ethanol in mice, rats and cats in behavioural, electrophysiological, and neurochemical paradigms. The interaction of Ro 15-4513 with barbiturates and ethanol is due to its inverse agonistic (negative allosteric modulatory) property at the BZR, as it was reversed by the selective BZR blocker flumazenil (Ro 15-1788). In the present experiment situations, other BZR partial inverse agonists in subconvulsant or overt convulsant doses were less effective against ethanol effects than Ro 15-4513. Possible mechanisms for this differential activity of BZR inverse agonists are discussed.

Animals↗

PubMed1990

Effects of two benzodiazepine inverse agonists, RO 15-4513 and FG 7142, on recovery from pentobarbital and halothane anesthesia in the rat.

A new class of drugs, the benzodiazepine inverse agonists, have recently been shown to antagonize some of the behavioral and sedative effects of benzodiazepines, barbiturates, and alcohol. Preliminary studies suggested that at least one of these drugs, RO 15-4513, may also be able to reverse the general anesthetic properties of volatile halogenated agents. Another inverse agonist, FG 7142, exhibits a similar ability to antagonize alcohol or benzodiazepines. However, FG 7142 is less potent than RO 15-4513 and has less affinity for the benzodiazepine receptor (BZR). The present studies were therefore undertaken to compare the analeptic effects and relative potencies of RO 15-4513 and FG 7142 on the anesthetic properties of pentobarbital compared with the general anesthetic agent halothane as measured by the time for recovery of the righting reflex in the rat. Three basic experimental paradigms were employed. Drug (FG or RO) or carrier was administered 5 minutes prior to the induction of pentobarbital anesthesia. Drug or carrier was administered to anesthetized animals 60 minutes after pentobarbital injection. Lastly, drug or carrier was administered 5 minutes prior to 15 minutes of halothane anesthesia. In addition, the selective benzodiazepine antagonist, flumazenil (RO 15-1788), was used to determine if the effects of the benzodiazepine inverse agonists on recovery from barbiturate or halothane anesthesia were due to activity at the BZR. The results revealed that RO was both more potent and more effective than FG at speeding recovery from barbiturate anesthesia in the rat. RO's effects appeared to be primarily due to BZR inverse agonist activity since it could be reversed by the BZR antagonist, flumazenil.(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthesia Recovery Period↗

PubMed1992

Discriminative stimulus properties of RU 33965, a benzodiazepine receptor weak partial inverse agonist.

Rats were trained to discriminate the low-efficacy benzodiazepine receptor inverse agonist RU 33965 from vehicle in a two-lever discrimination task on a fixed ratio (FR) 20 schedule. Consistent discrimination was obtained at 0.5 mg/kg PO RU 33965. Both leptazol and stronger inverse agonists (FG7142, S-135, RU 34000) substituted for the cue. The weak inverse agonists/antagonists RU 33094, RU 34030, Ro 15-1788, and ZK 93426 also substituted for the cue with the latter two compounds being particularly potent. The agonist and partial agonists diazepam, RU 33203, and RU 39419 did not substitute for the RU 33965 cue but RU 39419 antagonised it. The full agonists diazepam and loprazolam only consistently antagonised the cue when given IP 5 min pretest. These data suggest that the RU 33965 cue results from its weak inverse agonist activity at benzodiazepine receptors, but kinetic factors must be considered when interpreting drug effects in discrimination studies.

Animals↗

PubMed1989

Mold inversion and abrasion resistance of a type IV stone.

The objective of this study was to determine whether placing the impression and diestone so the impression is on the top during setting affects the resulting die's abrasion resistance. Impressions of a brass bar with a milled 90 degrees edge were obtained by use of a polysulfide impression material in a rigid brass tray. A Type IV diestone was vacuum-mixed and vibrated into the impression. Eight procedures were compared: (1) no inversion; (2) inversion at initial set; (3,4) inversion one or two min before initial set; and (5,6,7,8) inversion 1.5, 3, 5, or 12 min after initial set. Each specimen was abraded 24 hours after mixing. Specimens inverted at 1.5 and 3 min after initial set were significantly more abrasion-resistant than were all other treatments.

Calcium Sulfate↗

PubMed1994

The potential and limitations of the inverse radiotherapy technique.

The objective of the work presented in this paper is to explore the scope of the applicability of the inverse radiotherapy technique for designing optimized intensity distributions to achieve a desired dose distribution. A specified desired uniform dose to the target volume is inverted, subject to constraints on the surrounding normal tissue dose, to produce optimum intensity distributions in a set of beams arranged around the target volume. We employed the inverse technique and software developed by Bortfeld and evaluated results both qualitatively and quantitatively using dose distribution displays, dose-volume histograms and biological indices including tumor control probability and normal tissue complication probabilities. So far we have applied this methodology to prostate and lung treatment plans. For prostate the inverse technique produces satisfactory approximations of the desired dose distributions. However, for lung its performance is considerably inferior. Our investigations point to a number of factors for this difference, the primary ones being differences in the tolerance doses of neighboring normal tissues, magnitudes of volume effect, tissue architectures, and the achievability of the specified desired dose distributions. We conclude that, for certain clinical situations, it is not sufficient to specify the objectives of optimization purely in terms of the desired pattern of the dose. The objectives must also include dose-volume effects and biological indices. Furthermore, the mathematics of optimization must be able to incorporate these factors into the process. We find that the inverse technique is not suitable for situations where dose-volume considerations and biological indices are important and that other methods of optimization of intensity distributions should be explored.

Adenocarcinoma↗

PubMed1990

Ultrastructure of E1 + 2 + 9 + 12 inversion breakpoints in Drosophila subobscura.

The ultrastructure of the Drosophila subobscura chromosome regions around the breakpoints of the complex E1 + 2 + 9 + 12 gene arrangement was analyzed. This overlapping inversion is formed by the association of the E1, E2, E9, and E12 simple inversions. Ultrastructure of sections involving 58D/59A, 61C/D, 62D/63A, 64B/C, 67A/B, and 68B/C breakpoints on Est chromosomes were compared with the ultrastructure of sections involving chromosomes were compared with the ultrastructure of sections involving 58D/68B, 62D/64C, 59A/63A, 64B/68C, 67B/61C, and 67A/61B breakpoints on E1 + 2 + 9 + 12 chromosomes. No detectable changes of structural organization on banding patterns induced by the E1 + 2 + 9 + 12 inversion were found. Ultrastructural analysis of the two E12 breakpoints has, however, facilitated the analysis of the left boundary of E12 inversion. Accordingly, we propose 61B/C as a new breakpoint instead of 61C/D.

Animals↗

PubMed1995

An iterative filtered backprojection inverse treatment planning algorithm for tomotherapy.

PURPOSE: An inverse treatment planning algorithm for tomotherapy is described. METHODS AND MATERIALS: The algorithm iteratively computes a set of nonnegative beam intensity profiles that minimizes the least-square residual dose defined in the target and selected normal tissue regions of interest. At each iteration the residual dose distribution is transformed into a set of residual beam profiles using an inversion method derived from filtered backprojection image reconstruction theory. These "residual" profiles are used to correct the current beam profile estimates resulting in new profile estimates. Adaptive filtering is incorporated into the inversion model so that the gross structure of the dose distribution is optimized during initial iterations of the algorithm, and the fine structure corresponding to edges is obtained at later iterations. A three dimensional, kernel based, convolutions/superposition dose model is used to compute dose during each iteration. RESULTS: Two clinically relevant treatment planning examples are presented illustrating the use of the algorithm for planning conformal radiotherapy of the breast and the prostate. Solutions are generally achieved in 10-20 iterations requiring about 20 h of CPU time using a midrange workstation. The majority of the calculation time is spent on the three-dimensional dose calculation. CONCLUSIONS: The inverse treatment planning algorithm is a useful research tool for exploring the potential of tomotherapy for conformal radiotherapy. Further work is needed to (a) achieve clinically acceptable computation times; (b) verify the algorithm using multileaf collimator technology; and (c) extend the method to biological objectives.

Algorithms↗

PubMed1990

Interactions between benzodiazepine antagonists, inverse agonists, and acute behavioral effects of ethanol in mice.

The behavioral manifestations of acute ethanol intoxication resemble those of benzodiazepines, barbiturates and general anesthetics. This has led to speculation that these drugs share common mechanisms or sites of actions within the brain. The discovery of a specific benzodiazepine receptor site, and the subsequent development of selective receptor antagonist and inverse agonist drugs, provides a framework to test the involvement of the benzodiazepine receptor complex in mediating ethanol's behavioral effects. The partial inverse agonist Ro15-4513, an analog of the benzodiazepine receptor antagonist Ro15-1788 (flumazenil), has been reported to block or reduce some of ethanol's acute effects in rodents by a benzodiazepine receptor-mediated action. There has been some controversy over whether the "antialcohol" effect of Ro15-4513 is a unique property of this compound or is shared by other benzodiazepine antagonists with inverse agonist activity. We have studied the effects of Ro15-4513 and other benzodiazepine receptor antagonists on acute ethanol intoxication in mice and have obtained evidence that 1) Ro15-4513 differentially affects acute effects of ethanol, 2) an "antialcohol" property is not a general feature of all benzodiazepine antagonists and inverse agonists, and 3) "antialcohol" activity may not be unique to Ro15-4513.

Animals↗

PubMed1993

Global T wave inversion: long-term follow-up.

OBJECTIVES: This study evaluated 11-year follow-up data from patients with global T wave inversion. BACKGROUND: In an 8-year prospective investigation, global T wave inversion was characterized by a long QT interval, unexplained marked female preponderance and, despite dramatic electrocardiographic (ECG) changes, an in-hospital prognosis not statistically different from that of the entire hospital population in which the condition it occurred. METHODS: To assess long-term prognosis, these and an additional 18 patients (total 118 patients; 92 women and 26 men) with global T wave inversion were followed up prospectively for up to 11 years (mean 33.9 +/- 37.3 months). The additional patients did not significantly affect the in-hospital death rate (7.6%; previously reported death rate 8%) and the total series continued not to differ from the entire in-hospital population in which it occurred (7.02%; p = NS). RESULTS: Long-term survival was shortened by digoxin, faster heart rates, atrial fibrillation and, especially, a malignant condition. Eighteen (78.3%) of 23 patients with a malignant condition died during the follow-up period (p < or = 0.0005), with a mean survival time of only 12 months. Kaplan-Meier curves also revealed the poor prognosis for those patients taking digoxin; 21 (63.9%) of 36 patients died (p = 0.008). Eleven of the 12 patients with atrial fibrillation were taking digoxin; 58.3% of these died, demonstrating a worse prognosis than that of patients with sinus rhythm, 35% of whom died (p = 0.005). CONCLUSIONS: Global T wave inversion continues to have an unexplained (78% vs. 22%) female preponderance. Although the long-term prognosis depends on underlying or associated diseases, the striking diffuse ECG changes do not in themselves imply a poor prognosis.

Aged↗

PubMed1996

Selective inversion investigations of slow molecular motion in solid state deuteron NMR spectroscopy.

Deuteron selective inversion experiments are reported for polycrystalline dimethyl sulfone-d6 as a function of temperature from 288 to 333 K. Double side-band modulation was used to achieve efficient off-resonance orientation-selective inversion. Fitting the selective inversion-recovery curves to two-site jump equations yields the motional rate. Temperature dependent jump rates, obtained from both selective inversion and deuteron quadrupole echo lineshapes, give an activation energy Ea = 86.5 +/- 1.4 kJ mol-1 and a frequency factor In(A) = 39.2 +/- 0.5. These values differ significantly from those of earlier 13C lineshape studies. At 298 K, variable power excitation was used to determine the underlying orientation dependent homogeneous linewidth, which is predominantly dipolar. The temperature dependence of the homogeneous linewidth is a sensitive indicator of large angle jump motion in the range 10(3)-10(4) s-1.

Anisotropy↗