Search PubMed⌕ Search

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.

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

At least 829 records · Page 46Linked to original sources
PubMed1995

Kinetic images of neuronal activity of the human brain based on the spatio-temporal MNLS inverse: a theoretical study.

Prior work proved that it is possible to find a unique solution to the problem of defining the configuration of electric current underlying observed extracranial magnetic fields, if sufficient priori knowledge of the source configuration is available. This minimum-norm least-squares (MNLS) inverse solution for a magnetic source image (MSI) is extended here to include temporal as well as spatial parameters of the underlying current pattern. This capitalizes on the temporal resolution of magnetoencephalography (MEG), which is on the order of milliseconds. Other forms of functional brain imaging are far less sensitive to the rate of change of states of the brain. Influences on the quality of the resulting MSI by measurement noise and errors in determining the image surface are characterized. A new technique for reducing noise in the inverse problem is developed by taking into consideration the spatial and time-dependence of the noise detected by the sensors. This new approach to regularization reduces the contribution from noisy measurements to the inverse calculation, and therefore improves the stability of the inverse.

Brain Mapping↗
PubMed1980

[Inversion versus amputation of the appendix: an objective comparison of 440 randomized cases (author's transl)].

Normal or scarred appendixes may be removed by amputation or inversion. Inversion is appealing for its high degree of asepsis, but criticized for the possibility of organ retention with consecutive invagination. The risks and advantages of amputation appear to be exactly the opposite. For objective comparison, a prospective study was undertaken, using both procedures in 400 cases of solitary and 40 cases of complementary appendectomies at a random number key. Wound infection was observed in 0.5% following inversion, in 8% following amputation as a solitary procedure. Both methods were equally followed by wound infections which performed as complementary procedures. However, inversion was free of enterogenous infection in all cases. Technical precautions were taken to facilitate sloughing of inverted appendixes. No clinical symptoms indicating retention or correlated complications were observed.

Adolescent↗
PubMed1990

Inversion of extracellular current and axial voltage profile in Chara and Nitella.

Reducing the pH of the bathing solution from 8.2 to pH 6 can induce an inversion of the extracellular current pattern that develops at the surface of Chara corallina internodal cells. A similar result can be obtained on some cells by changing the medium to a pH value of 10. In noninverting Chara cells the currents were strongly reduced when the pH value of the medium was changed between 3 and 11. Simultaneous measurements of the Chara transmembrane potential in the acid and alkaline regions revealed that a light-induced electrical potential gradient of approximately 24 mV was present in the axial (or longitudinal) direction. Correlated to the external current pattern inversion was an inversion of this internal longitudinal voltage gradient. Reillumination of Nitella cells, after a period of darkness, often resulted in a complete inversion of the extracellular current pattern. These results are discussed in terms of spatial and temporal control of membrane transport processes, and in particular the control of current loops that pass through these cells.

Chlorophyta↗
PubMed1989

The complete sequence of the rice (Oryza sativa) chloroplast genome: intermolecular recombination between distinct tRNA genes accounts for a major plastid DNA inversion during the evolution of the cereals.

The entire chloroplast genome of the monocot rice (Oryza sativa) has been sequenced and comprises 134525 bp. Predicted genes have been identified along with open reading frames (ORFs) conserved between rice and the previously sequenced chloroplast genomes, a dicot, tobacco (Nicotiana tabacum), and a liverwort (Marchantia polymorpha). The same complement of 30 tRNA and 4 rRNA genes has been conserved between rice and tobacco. Most ORFs extensively conserved between N. tabacum and M. polymorpha are also conserved intact in rice. However, several such ORFs are entirely absent in rice, or present only in severely truncated form. Structural changes are also apparent in the genome relative to tobacco. The inverted repeats, characteristic of chloroplast genome structure, have expanded outward to include several genes present only once per genome in tobacco and liverwort and the large single copy region has undergone a series of inversions which predate the divergence of the cereals. A chimeric tRNA pseudogene overlaps an apparent endpoint of the largest inversion, and a model invoking illegitimate recombination between tRNA genes is proposed which accounts simultaneously for the origin of this pseudogene, the large inversion and the creation of repeated sequences near the inversion endpoints.

Amino Acid Sequence↗
PubMed1999

Depth and intensity of equivalent current dipoles estimated through an inverse analysis of surface electromyograms using the image method.

The depth and intensity of equivalent current dipoles that can create the surface potentials of active motor units in human skeletal muscles are estimated through an inverse analysis of surface electromyographic (EMG) potentials in an attempt to measure detailed muscular activity non-invasively. The inverse analysis is conducted by repetition of forward analyses. In the study, the image method is used for forward analysis, because it is the simplest potential calculation method for electric currents in a semi-infinite volume conductor. Using this method, surface EMG potentials are calculated for current sources assumed to be located in a muscle. An inverse analysis is then carried out by searching for the depth and intensity of such current sources that would minimise the sum of squares difference between measured and calculated surface EMG potentials. The inverse analysis is applied to surface EMG potentials measured from the biceps brachii of three healthy subjects. As a result, the individual current sources are estimated to be 2.7 +/- 1.6 mm deep and 0.5 +/- 0.9 nAm in intensity, whereas the total current intensity for individual motor units is 2.4 +/- 2.9 nAm.

Adult↗
PubMed2003

Stereotactic intensity-modulated radiation therapy (IMRT) and inverse treatment planning for advanced pleural mesothelioma. Feasibility and initial results.

BACKGROUND AND PURPOSE: Complex-shaped malignant pleural mesotheliomas (MPMs) with challenging volumes are extremely difficult to treat by conventional radiotherapy due to tolerance doses of the surrounding normal tissue. In a feasibility study, we evaluated if inversely planned stereotactic intensity-modulated radiation therapy (IMRT) could be applied in the treatment of MPM. PATIENTS AND METHODS: Eight patients with unresectable lesions were treated after failure of chemotherapy. All patients were positioned using noninvasive patient fixation techniques which can be attached to the applied extracranial stereotactic system. Due to craniocaudal extension of the tumor, it was necessary to develop a special software attached to the inverse planning program KonRad, which can connect two inverse treatment plans and consider the applied dose of the first treatment plan in the area of the matchline of the second treatment plan. RESULTS: Except for one patient, in whom radiotherapy was canceled due to abdominal metastasis, treatment could be completed in all patients and was well tolerated. Median survival after diagnosis was 20 months and after IMRT 6.5 months. Therefore, both the 1-year actuarial overall survival from the start of radiotherapy and the 2-year actuarial overall survival since diagnosis were 28%. IMRT did not result in clinically significant acute side effects. By using the described inverse planning software, over or underdosage in the region of the field matchline could be prevented. Pure treatment time ranged between 10 and 21 min. CONCLUSION: This study showed that IMRT is feasible in advanced unresectable MPM. The presented possibilities of stereotactic IMRT in the treatment of MPM will justify the evaluation of IMRT in early-stage pleural mesothelioma combined with chemotherapy in a study protocol, in order to improve the outcome of these patients. Furthermore, dose escalation should be possible by using IMRT.

Aged↗
PubMed2002

Enhanced stability of wild-type and constitutively active alpha(2A)-adrenoceptors by ligands with agonist, silent and inverse agonist properties.

The hypothesis that prolonged treatment of a constitutively active receptor with inverse agonists may lead to increased receptor density was tested for the alpha(2)-adrenoceptor (AR) inverse agonist (+)-RX 811059 at both the wild-type (WT) and Thr(373)Lys alpha(2A) ARs in CHO-K1 cells by monitoring [(3)H]RX 821002 and [(35)S]GTPgammaS binding responses. One-hundred micromolar KCl instead of NaCl in the [(35)S]GTPgammaS membrane binding assay favoured the detection of a high-magnitude constitutive alpha(2A) AR activity. Under this condition, (+)-RX 811059 was an inverse agonist [ E(max) (% vs. basal): Thr(373)Lys alpha(2A) AR (-52+/-2) > WT alpha(2A) AR (-31+/-6)] while atipamezole was a silent neutral antagonist for both WT and Thr(373)Lys alpha(2A) ARs. The B(max) value of [(3)H]RX 821002 binding sites to membranes of transfected CHO-K1 cells was <90% for the Thr(373)Lys alpha(2A) AR compared with the WT alpha(2A) AR (9.1+/-1.4 pmol/mg protein); K(d) values were similar (1.16+/-0.19 nM and 1.51+/-0.15 nM, respectively). Forty-eight-hours' pre-treatment of cells with either 0.1 microM (+)-RX 811059, 1 microM atipamezole or 1 microM of the efficacious agonist d-medetomidine increased the amount of [(3)H]RX 821002 binding sites of both WT (52%-59%) and mutant (306%-447%) Thr(373)Lys alpha(2A) ARs. The same alpha(2) AR ligands also prevented the loss of [(3)H]RX 821002 binding sites as induced by incubation of transfected CHO-K1 cellular membranes at 37 degrees C for 4 h (WT alpha(2A) AR) and 2 h (Thr(373)Lys alpha(2A) AR); 0.1 microM (+)-RX 811059 and 1 microM atipamezole caused an increase compared with the control amount of [(3)H]RX 821002 binding sites to the Thr(373)Lys alpha(2A) AR by 73% and 50%, respectively. In conclusion, no relationship was found between inverse agonism and alpha(2A) AR up-regulation. It is suggested that this is due to structural stabilisation of the alpha(2A) AR, irrespective of the nature of the ligand.

Adrenergic alpha-Antagonists↗
PubMed2005

The reproducibility of left ventricular volume and mass measurements: a comparison between dual-inversion-recovery black-blood sequence and SSFP.

The aim of this study was to compare a dual-inversion-recovery black-blood (BB) magnetic resonance imaging (MRI) sequence with steady-state free precession (SSFP) for the assessment of left ventricular parameters. The improved endocardial border definition seen with SSFP was not observed at the epicardial border. Improvements in segmentation at the left ventricular epicardial border have been observed with this black-blood sequence. Left ventricular (LV) mass and LV end-diastolic volume (EDV) measurements as well as inter-observer and intra-observer variability were compared between images acquired with a dual inversion BB and SSFP sequence. The mean+/-1 standard deviation (SD) for LV EDV was 178.3+/-52.7 ml measured with SSFP and 158.8+/-62.2 ml with BB. This difference was not statistically significant (p=0.22). For SSFP, the mean value of LV mass was 124.0+/-27.0 g and 147.5+/-37.4 g for BB, a statistically significant difference (p<0.0001). The dual-inversion-recovery BB imaging showed improved reproducibility for LV mass measurements compared with SSFP and improved spatial resolution. For studies requiring LV mass measurements, the dual-inversion-recovery BB sequence offers improved spatial resolution and improved reproducibility to SSFP.

Adult↗
PubMed2006

Muscle activation following sudden ankle inversion during standing and walking.

Dynamic response characteristics of ankle musculature following sudden ankle inversion have traditionally been tested in a static, standing position. However, this model does not take into consideration muscle activity and loading characteristics associated with active gait. This study compared muscle reaction times and amplitudes from sudden ankle inversion during standing (standing group) and walking (walking group) using one of two similar devices for each of these conditions. Surface EMG was collected from the peroneus longus (PL), brevis (PB), and tibialis anterior (TA) of the dominant leg from 25 subjects (age 20 +/- 1 years, height 174.0 +/- 10.2 cm, mass 74.3 +/- 12.9 kg) for each condition (walking and standing). Time to total inversion ROM (28 degrees ) was greater in the walking group (114.9 +/- 15.0 ms) than the standing group (65.6 +/- 17.8 ms, P < 0.05), whereas reaction time was less in the peroneals in the walking group (PL 56.9 +/- 8.4 ms, PB 60.1 +/- 10.6 ms, TA 65.0 +/- 14.9 ms) compared to the standing group (PL 74.3 +/- 8.5 ms, PB 73.5 +/- 8.2 ms, TA 73.3 +/- 8.3, P < 0.05). Additionally, Peak normalized EMG (% MVIC) for the walking condition (PL 367 +/- 254, PB 405 +/- 359, TA 84 +/- 39) exceeded that of the standing condition (PL 310 +/- 239, PB 328 +/- 215, TA 76 +/- 39, P < 0.05), and average normalized EMG (% MVIC) was greater in the peroneals for the walking condition (PL 233 +/- 171, PB 280 +/- 255) than the standing condition (PL 164 +/- 131, PB 193 +/- 137, P < 0.05). The differences noted between the conditions provide evidence that a dynamic response to ankle injury mechanisms is much different in a walking model compared to a traditional standing model. A walking model may be a more functional approach for evaluating dynamic response characteristics of ankle musculature due to sudden ankle inversion.

Adult↗
PubMed2004

Consistency of Listing's law and reciprocal innervation with pseudo-inverse control of eye position in 3-D.

Pseudo-inverse kinematics, under which small movements are produced by the least possible sum square changes in motor command, has been proposed as a unifying principle for the elimination of redundancy in general biological motor control systems (Pellionsz 1984) and in particular in the oculomotor system (Daunicht 1988, 1991). We have noted elsewhere (Dean et al, 1999) that this principle is incomplete without first specifying a parameterisation of motor command space and we proposed that the relevant motor-command parameter is summed motor unit firing rate. Under this assumption we were able to show that pseudo-inverse control of the horizontal extraocular muscles is consistent with available motor pool firing rate data. In this paper we extend this result to three dimensions and six extraocular muscles, showing that pseudo-inverse control is consistent with published firing rate date for a realistic model of oculomotor kinematics. We suggest that pseudo-inverse control may represent a common currency for modular control of many degree of freedom systems while its implementation may be a consequences of the minimisation of a more ecologically relevant parameter such as post-saccadic retinal slip.

Biomechanical Phenomena↗
PubMed2000

The inverse dynamics problem of neuromuscular control.

The myoskeletal inverse dynamics problem and the myocybernetic control inverse problem were investigated with respect to their ill-posedness. The first problem consists of finding from observed experimental motion and reaction force data the resultant muscle moments that generated the observed motion, while the second aims at finding the corresponding neural controls. It is shown that both problems belong to the class of incorrectly posed (ill-posed) problems that, by definition, do not possess unique solutions. To illustrate this point, results of a forward dynamics simulation of a comprehensive neuromusculoskeletal model of the human body are presented. These results demonstrate that fairly chaotic neural control perturbations have very little influence on the resulting motion trajectory, at least in the present example. While a regularization procedure may be applied to solve successfully the myoskeletal inverse dynamics problem, the myocybernetic control inverse problem is unsolvable. The latter fact has the important implication that, based on the somatosensory inputs it receives, the pars intermedia in the cerebellum is not able to control individual motor unit stimulation rates and recruitment patterns but only whole muscles by means of a single compound signal. The latter signal is identified as the "common drive." Presumably at the spinal level, special neural circuits are used to decompose the common drive signal into motor unit recruitment patterns and stimulation rates that are specific for a given mode of contraction and probably obey certain optimality principles.

Computer Simulation↗
PubMed2006

Mechanisms of inverse agonism at histamine H(2) receptors - potential benefits and concerns.

It is well established that histamine exerts its effects by activating histamine receptors that belongs to the family of seven transmembrane G-protein coupled receptors (GPCRs). Many ligands with important therapeutic actions that had been assumed to be antagonists at histamine H2 receptor have been shown to be inverse agonists. The mechanism whereby these drugs achieve their effects seems to be not unique. Theoretical models predict at least three ways in which inverse agonists can exert their action that are supported by experimental observations. These different mechanisms have crucial consequences on basic pharmacology and clinical treatments. The pharmacological models, the feasible mechanisms of action of H2 inverse agonists, findings about molecular basis of tiotidine inverse agonism in particular, and their impact on clinical protocols will be discussed.

Animals↗
PubMed1986

The metabolic chiral inversion of 2-phenylpropionic acid in rat, mouse and rabbit.

The metabolic chiral inversion of the 2-arylpropionic acids has been investigated in laboratory animals, using the simplest congener, 2-phenylpropionic acid, as a model compound. The chiral inversion was found to occur after administration of the racemate to the rat and rabbit, but not in the mouse. The formation of the ester glucuronide was enantioselective for the S-(-)-isomer in the rat and mouse, but showed no stereoselectivity in the rabbit. [corrected] In the rat, the extent of inversion from R-(-) to S-(+) was greater at a dose of 30 mg/kg than at 150 or 300 mg/kg. The enantiomeric composition of the acid in urine was the same when the racemate was given orally or by i.p. injection. When the R-(-)isomer was given to rats, some 30% of the excreted acid was in the S-(+)-form, but when the S-(+)-isomer was given, the inversion was much less evident. In this case, the S/R ratio of the excreted phenylproprionic acid was ca 9:1. Following the administration of the racemate to rats, the plasma elimination half-life of the R-(-)-form was shorter (3.0 vs 4.8 hr for the S-(-)-isomer); this was due to its considerably greater plasma clearance (65.9 vs 43.6 micrograms/ml hr), since the volumes of distribution of the enantiomers were the same. The S/R ratio of 2-phenylpropionic acid in plasma rose progressively with time, from 1:1 in the dose solution to 2.1:1 at 8 hr.

Administration, Oral↗
PubMed1988

The metabolic chiral inversion and dispositional enantioselectivity of the 2-arylpropionic acids and their biological consequences.

The 2-arylpropionic acids are currently an important group of non-steroidal anti-inflammatory agents. They contain a chiral centre, and in vitro studies on inhibition of prostaglandin synthesis show that their activity resides almost exclusively in the S(+)-isomers. However, this stereoselectivity of action is not manifest in vivo, due to the thus-far-unique unidirectional metabolic inversion of the chiral centre from the inactive R(-)-isomers to the S(+)-antipodes. Available evidence strongly suggests that this reaction proceeds via the formation of the acyl CoA thioesters of the 2-arylpropionates, but the participation of enzyme(s) in the inversion process remains uncertain. Although the chiral inversion is seemingly a general feature of the fate of 2-arylpropionates, there do occur important combinations of acid and species where the reaction is not extant. The stereochemistry of the chiral centre of these acids also influences other aspects of their disposition, including the oxidative metabolism of the aryl/arylakyl moiety, glucuronidation of the -COOH group and plasma protein binding, and the importance of certain of these becomes more evident when renal function is impaired. The biological consequences of the metabolic chiral inversion and enantioselective disposition of the 2-arylpropionates have been summarized in terms of their implications for the development and use of safer and more effective drugs of this class.

Animals↗
PubMed1990

Comparison of graphical procedures for estimating the intrinsic molar fluorescence of protein-bound drugs for drug-binding studies. A reevaluation of existing plots and introduction of two inverse hyperbolic plots.

A theoretical evaluation of existing and new graphical procedures for estimating the intrinsic molar fluorescence (psi B) of a protein-bound drug has been undertaken. The results do not concord with a recent proposition that psi B should be obtained by direct reading from a graph of emitted fluorescence intensity (I) against the logarithm of the binding protein concentration ([P]) rather than by extrapolation of a double reciprocal plot. The calculated errors in estimates of psi B obtained by direct reading or by extrapolation of standard plots and of three new inverse hyperbolic plots showed that, independently of binding affinity: 1. Direct reading from the logarithmic plot gave the least accurate estimates. 2. The single reciprocal plot gave more accurate estimates than the double reciprocal plot providing the (constant) drug concentration was similar to or greater than its dissociation constant in the binding system. At lower drug concentrations the double reciprocal plot gave more accurate estimates. 3. Extrapolation of an inverse hyperbolic sine plot (sinh-1 (1/I) against 1/[P]) did not give more accurate estimates than the standard reciprocal plots. 4. If the drug concentration was close to its dissociation constant the most accurate estimates were obtained with an inverse hyperbolic cosine plot of cosh-1 (I + 1) against 1/[P]. For a low affinity binding system in which non-specific binding is significant an inverse hyperbolic sine plot of 1/sinh-1I against 1/[P] gave the most accurate estimates at low drug concentrations. An experimental and theoretical procedure for optimizing the estimation of psi B is proposed on this basis.

Animals↗
PubMed1984

Sleep and purposive behavior: inverse deviations from randomness of neuronal firing patterns in the feline thalamus. A new form of homeostasis?

In behaving cats trained to press a bar for small aliquots of milk reward, single neuronal firing patterns were monitored from the nucleus reticularis (NR) thalami during bar bressing (BP), subsequent quiet wakefulness with EEG spindles (S- QW ), grooming behavior (GR) and slow-wave sleep (SWS). The temporal patterns in the neuronal spike trains were analyzed using a non-parametric method based on relative relations between sequential spike intervals. The deviations of pattern occurrences from the random model were quantified. During BP, specific patterns occurred much more often while others occurred much less often than predicted by the random model. Patterns that were dominant during BP, were selectively suppressed or virtually eliminated during S- QW , GR and SWS, despite the increased firing rate; and, vice versa, patterns that were suppressed below chance level during BP, became dominant during S- QW , GR and SWS. The magnitudes of these inversions of the statistical distribution of patterns were not random but graded and positively correlated, thus indicating that they were homeostatically controlled. Since the inversions were already evident shortly after the satiated ceased bar pressing, they may be related to the 'need' for sleep. On the basis of the known mechanisms of pattern generation and changes in receptors for putative transmitters, it was postulated that the inversions of pattern distribution are related to the recuperative function of SWS, i.e. resensitization of receptors that had been desensitized during the animal's stereotypic BP performance. The NR and other neuronal ensembles seem to constitute an oscillatory system with two modes of reciprocal connectivities : one is supporting wakefulness and emission of specific firing patterns, and the other is incompatible with wakefulness and instead is associated with inversion of statistical distribution of firing patterns and recuperative function of SWS.

Animals↗
PubMed1978

A new approach to spike detection using a combination of inverse and matched filter techniques.

For the detection of spikes and other types of transient signal, a combination of inverse and matched filter techniques can be used. The inverse filter improves the signal to noise (spike to EEG) ratio; the matched filter makes it possible to classify different types of spikes. When compared, the combined inverse matched filter techniques gave a higher detection rate than the inverse filter technique alone, for the same error probability. Both simulated and patient data were used for testing the methods.

Electroencephalography↗
PubMed1987

Chronic treatment with lorazepam and FG 7142 may change the effects of benzodiazepine receptor agonists, antagonists and inverse agonists by different mechanisms.

Treatment of mice with lorazepam 10 mg/kg p.o. or FG 7142 40 mg/kg i.p. once a day for 14 days changed the effects of benzodiazepine (BZ) receptor ligands injected acutely on the threshold of pentylenetetrazol (PTZ)-induced seizures. The effects of the two pretreatments differed qualitatively as well as quantitatively. Lorazepam elicited a shift in the effects of all BZ receptor ligands tested, whereby the agonists lorazepam and ZK 93423 now acted like partial agonists given acutely, the partial agonist ZK 91296 acted like an antagonist and the antagonists Ro 15-1788 and ZK 93426 like partial inverse agonists. The proconvulsant effects of the partial inverse agonist FG 7142 and the full inverse agonist DMCM on the PTZ-induced seizures did not change. However, FG 7142 became a full inverse agonist i.e. became convulsant, and DMCM may have increased in potency as a convulsant. After FG 7142 pretreatment lorazepam and ZK 93423 behaved like partial agonists given acutely whereas there was no change in effect for ZK 91296, Ro 15-1788 and ZK 93426. FG 7142 became convulsant (i.e. kindling occurred) and the potency of DMCM as a convulsant was non-significantly increased, while their proconvulsant effects with respect to PTZ-induced seizures were not altered. The fact that the effects of the two very different pretreatments on the BZ receptor ligand continuum were in the same direction may be explainable by assuming two different mechanisms, both of which may involve the GABA receptors.

Animals↗