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At least 19 recordsLinked to original sources
PubMed1978

The acceleration of methanesulfonylation of acetylcholinesterase with cationic accelerators as an electrostatic effect.

1. In order to check our hypothesis of the electrostatic nature of the acceleration of methanesulfonylation of acetylcholinesterase (acetylcholine hydrolase, EC 3.1.1.7) with cationic accelerators, equations were solved for methane-sulfonylation with two accelerators and the reaction was studied in the presence of some single accelerators, including the sodium cation, and in the presence of two acclerators simultaneously. 2. The second-order rate constants for methanesulfonylation of the complexes between the enzyme and accelerators decamethonium, tetraethylammonium and tetramethylammonium are 90, 88 and 17 1 - mol-1 - s-1, respectively, which corresponds to a maximal acceleration of 29, 28 and 5.5 times, respectively. The dissociation constants for the binding of these accelerators to the enzyme, obtained from our acceleration experiments, are 3.7 - 10(-6), 3.2 - 10(-4) and 1.4 - 10(-3) M, respectively. These values are in good agreement with the dissociation constants of these ligands as inhibitors of acetylcholinesterase. It is interesting to note that the sodium cation also accelerates the methane-sulfonylation up to around three times, the corresponding second-order rate constant and the dissociation constant being 10 1 - mol-1 - s-1 and 1.3 M, respectively. 3. All tested cations compete in the acceleration with each other; they seem to accelerate the reaction in the same way and from the same site, the catalytic anionic site. 4. These findings confirm the hypothesis of the electrostatic nature of acceleration.

Acetylcholinesterase↗
PubMed1975

Experimental brain damage from fluid pressures due to impact acceleration. 4. comparative studies with acceleration-concussion.

In order to elucidate the cause of brain damage in head injuries experiments are often designed to cause impacts to the intact skull of animals. To study the injurious significance of the contre-coup part of the impact acceleration pressure pattern we have previously applied direct loading through a parietal opening to the rabbit skull cavity. In order to evaluate the effects of the acceleration, similar impacts were delivered with greater magnitudes of such movements of the intact reinforced rabbit skull with the same equipment attached but without trephine opening. Varied and predictable acceleration, velocity and displacement of the head, and minimized skull deformation were possible with this model. Threshold levels of such impact acceleration were studied with regard to changes in respiratory and vasomotor activities ("concussive response"). Vascular permeability changes in the brain and spinal cord were studied with Ean's blue-albumin injection before the impact. Morphological observations were also made at the end of the experiments. No significant pathophysiological or morphological effects were elicited below peak acceleration of 2000 gn (duration 0.7 ms), peak velocity of 5 m/s or total dislocation of the head of 30 mm. At higher levels of impact a "concussive response" was elicited without fractures of the skull bone or significant brain lesions. Thus, in impact tests resulting in acceleration magnitudes far below those levels the signs of brain damage induced might mainly be related to the mechanical effects added--i.e. the fluid pressure loading.

Acceleration↗
PubMed1977

The relationship between accelerated pulmonary maturity and accelerated neurological maturity in certain chronically stressed pregnancies.

Two studies were done. In the first, 51 infants from high-risk pregnancies were evaluated for accelerated clinical neurological maturation. Eight infants had accelerated neurological maturation 3 or more weeks in excess of gestational age. In the second study, a sample of 25 infants with documented acceleration of pulmonary surfactant (lecithin/sphingomyelin ratio greater than or equal to 2 at gestational age less than or equal to 32 weeks) all infants showed accelerated neurological maturation (range 3 to 8 weeks) with the conditions studied associated with accelerated pulmonary maturation (for instance, retroplacental bleeding, prolonged rupture of membranes, placental infarction, severe toxemia, hypertensive disease, circumvallation, and amnionitis). Chronic retroplacental bleeding was associated with the most dramatic pulmonary and neurological accelerations.

Birth Weight↗
PubMed1978

On the mechanism of the acceleration of methanesulfonylation of acetylcholinesterase with cationic accelerators.

1. In order to elucidate some features of the mechanism of the acceleration of methanesulfonylation of acetylcholinesterase (acetylcholine hydrolase, EC 3.1.1.7) with cationic accelerators, the methanesulfonylation of this enzyme by high concentrations of methanesulfonylfluoride, in the absence and presence of accelerators decamethonium and tetraethylammonium, was studied. 2. The results showed that the accelerator accelerates the reaction by electrostatically improving the binding between acetylcholinesterase and methanesulfonylfluoride without effecting the rate of the decomposition of the enzyme-inhibitor complex into the methanesulfonylated enzyme and product.

Acetylcholinesterase↗
PubMed1978

[Linear accelerators in oncoradiology. Comparison of the effciency of four clinically utilized electron linear accelerators with energies up to 20 MeV (author's transl)].

Further development of linear accelerators for medical purposes results in leaving off the principle of circular acceleration. The present investigation, comparing four clinically utilized electron linear accelerators with different constructional systems, reveals a large scale of clinical applicability, advantages and disadvantages partly compensating one another. None of the four machines examined offers a total of decisive advantages as compared to the other ones. Some essential data from the side of radiation exit are tested: depth dose data and photon contamination during operation with electrons, field sizes and homogeneity, penumbral width and penetration power for electron and X radiations. The appreciation of electron therapy by the radiologist may be a factor as well the handling of the machine, but in many cases the space available in an existing locality or the confidence in the ready service of a contracting firm, considerations concerning failure periods, estimate of repair and subsequent costs are influencing the decision for a certain type of equipment.

Electrons↗
PubMed1976

[Sugar consumption and prenatal acceleration. II. Studies on the etiology and pathophysiology of secular prenatal acceleration].

The pathophysiologic considerations support the causal relationship between the secular trend of sugar consumption in industrialized society and the development of prenatal acceleration, which is evident on the basis of epidemiological data. The excessive consumption of sugar and the other quickly absorbed "refined" carbohydrates enhances the hormonogenic effect of food which is also potentiated by the proteins. Together with the caloric overloading, provoked also by the excess in fat, characteristic for the affluent society, the excessive sugar consumption enhances in the pregnant women obesity and "protodiabetes" (PFEIFFER), in the predisposed child the tendency to hyperinsulinism with its consequences. In a prediabetic mother with normal glucose-tolerance the regularly repeated postprandial overfloating of the fetus with maternal glucose changes the feto-maternal hormonal regulation and enhances together with the overloading of substrate, i.e. energy and elements of biosyntheses, the accelerated fetal growth and especially the obesity of the large baby.

Birth Weight↗
PubMedDate not supplied

Comparison of moving-strip therapy using a Cobalt-60 teletherapy unit, a Varian 4-MV linear accelerator, and a Varian 10-MV linear accelerator.

Cobalt-60 gamma rays and 4- and 10-MV x rays are compared for moving-strip therapy in terms of the dose uniformity and the given dose needed to deliver a prescribed tumor dose. Dose distributions in phantoms of 14--32-cm thickness were calculated for each therapy unit. Individual given doses which would deliver the most uniform dose along the midline of the treatment volume were determined by computer and were verified experimentally by thermoluminescent dosimetry. Using computer optimization techniques, the midplane dose uniformity is improved significantly for the three therapy units considered.

Cobalt Radioisotopes↗
PubMed1975

Incidence and description of accelerated ventricular rhythm complicating acute myocardial infarction.

One hundred and nineteen episodes of accelerated ventricular rhythm (less than 125/min) were noted in 37 patinets with acute myocardial infarction during a 1 year period. The incidence was 12.7 per cent. Twenty-seven episodes of fast ventricular tachycardia (less than 125/min) were noted in 16 of these patients. Eighteen patients had anterior myocardial infarction and 19 inferior myocardial infarction. The mechanism of onset of accelerated ventricular rhythm was classified as escape in 65 episodes. Ventricular premature beats were noted close to episodes of accelerated ventricular rhythm in 31 patients and fast ventricular tachycardia in 14 patients. The morphology of accelerated ventricular rhythm was similar to the ventricular premature beats in 27 patients and similar to the fast ventricular tachycardia in 12. In 11 patinets the morphology of ventricular premature beats, accelerated ventricular rhythm and fast ventricular tachycardia were all the same. In six patients the coupling time of the ventricular premature beats and the onset of the accelerated ventricular rhythm were the same. In seven patients the morphology of the accelerated ventricular rhythm and fast ventricular tachycardia were the same, and the rate of the accelerated ventricular rhythm was exactly half that of the fast ventricular tachycardia. There were three deaths due to shock and heart failure. Three episodes of fast ventricular tachycardia progressed to ventricular fibrillation and were successfully cardioverted. It is concluded that accelerated ventricular rhythm and fast ventricular tachycardia were all the same. In six patients the coupling time of the ventricular premature beats and the onset of the accelerated ventricular rhythm were the same. In seven patients the morphology of the accelerated ventricular rhythm and fast ventricular tachycardia were the same, and the rate of the accelerated ventricular rhythm was exactly half that of the fast ventricular tachycardia. There were three deaths due to shock and heart failure. Three episodes of fast ventricular tachycardia progressed to ventricular fibrillation and were successfully cardioverted. It is concluded that accelerated ventricular rhythm is a relatively common complication of both anterior and inferior myocardial infarction. The high incidence of concomitant fast ventricular tachycardia, the frequency of ventricular premature beats with similar morphology and coupling time, and the instances of two arrhythmias having common rate multiples, suggest that at least in some instances accelerated ventricular rhythm may represent an ectopic focus with exit block.

Adult↗
PubMed1992

Value of acceleration flow signals proximal to the leaking orifice in assessing the severity of prosthetic mitral valve regurgitation.

To test the value of acceleration flow signals proximal to the leaking orifice in assessing the severity of prosthetic mitral valve regurgitation, 39 consecutive patients undergoing left ventriculography were examined by Doppler color flow imaging. Acceleration flow signals proximal to the regurgitant orifice were detected in 27 of the 31 patients who had prosthetic mitral regurgitation by left ventriculography (sensitivity 87%). All four patients without acceleration flow signals had mild prosthetic mitral regurgitation by angiography. No acceleration flow signals were detected in any patient without prosthetic regurgitation by left ventriculography (specificity 100%). Individual values of the maximal area of acceleration flow signals obtained from three orthogonal planes in seven patients with mild prosthetic mitral regurgitation by angiography ranged from 0 to 17 mm2 (mean 4 +/- 6). In 8 patients with moderate prosthetic mitral regurgitation by angiography, the maximal area of acceleration flow signals ranged from 21 to 58 mm2 (mean 33 +/- 15), whereas the maximal area of acceleration flow signals in 16 patients with severe prosthetic regurgitation ranged from 20 to 173 mm2 (mean 102 +/- 41). The maximal area of the acceleration flow signals from three planes correlated well with the angiographic grade of prosthetic mitral regurgitation. There was a significant difference in the maximal area of acceleration flow signals between mild and moderate (p less than 0.001), moderate and severe (p less than 0.001) and mild and severe (p less than 0.001) prosthetic mitral regurgitation. Thus, measurement of acceleration flow signals by Doppler color flow imaging is useful in assessing the severity of prosthetic mitral regurgitation.

Bioprosthesis↗
PubMed2026

Comparison of the clinical efficacy, safety and EEG functional connectivity changes between 18-Hz rTMS and iTBS of accelerated dTMS treatment for major depressive disorder: a randomized controlled trial.

Although the antidepressant efficacy of 18-Hz deep transcranial magnetic stimulation (dTMS) has been validated, its prolonged treatment duration has considerable limitations for treatment capacity and patient adherence. Therefore, novel short-course protocols such as accelerated dTMS and intermittent theta burst stimulation (iTBS) present promising alternative options. Here we addressed the question of whether iTBS of accelerated dTMS achieves comparable therapeutic and electrophysiological effects to accelerated dTMS with the conventional 18-Hz rTMS protocol in patients with major depressive disorder (MDD). In a randomized controlled trial (n&#x2009;=&#x2009;73), participants received either 18-Hz rTMS of accelerated dTMS (rTMS-dTMS group), iTBS of accelerated dTMS (iTBS-dTMS group), or pharmacotherapy alone (drug group). Both dTMS protocols were administered twice daily for 10 days targeting the left lateral prefrontal cortex including the dorsolateral region. Results showed that Hamilton Depression Rating Scale (HAMD) score of the iTBS-dTMS group decreased significantly from 22.5&#x2009;&#xb1;&#x2009;3.7 before treatment to 8.2&#x2009;&#xb1;&#x2009;4.1 after treatment (t&#x2009;=&#x2009;15.900, p&#x2009;<&#x2009;0.001). HAMD score of the rTMS-dTMS group decreased significantly from 21.3&#x2009;&#xb1;&#x2009;2.9 before treatment to 8.0&#x2009;&#xb1;&#x2009;3.8 after treatment (t&#x2009;=&#x2009;17.232, p&#x2009;<&#x2009;0.001). The drug group also exhibited significantly improved patients' mood symptoms, and the HAMD score decreased from 24.7&#x2009;&#xb1;&#x2009;6.8 to 14.0&#x2009;&#xb1;&#x2009;5.0 (t&#x2009;=&#x2009;6.363, p&#x2009;<&#x2009;0.001). The treatment response rate was 85.7% in the iTBS-dTMS group and 76.9% in the rTMS-dTMS group, which was much higher than that of the drug group (42.1%). The remission rate was 50.0% in the iTBS-dTMS group and 42.3% in the rTMS-dTMS group, which was significantly higher than 10.5% of the drug group. We demonstrate here that both accelerated dTMS protocols significantly reduced HAMD scores, improved the response rates, and remission rates, outperforming pharmacotherapy alone. Resting-state EEG analysis further revealed unique frequency-specific functional connectivity (FC) modulation effects: the rTMS-dTMS group primarily exhibited weakened alpha-band functional connectivity within the fronto-occipital, fronto-temporal and fronto-central networks after treatment, whereas the iTBS-dTMS group predominantly demonstrated reduced theta-band functional connectivity within the fronto-parietal, fronto-occipital and fronto-temporal pathways after treatment. These findings indicate that iTBS of accelerated dTMS demonstrates comparable efficacy and tolerability to 18-Hz rTMS of accelerated dTMS, whilst inducing treatment-specific network-level neurophysiological alterations. In the rTMS-dTMS group, relative changes in FC between the frontal and temporal/precentral regions showed significant negative correlation with HAMD score reduction rates, while relative changes in FC between the frontal lobe and parietal lobe showed a significant positive correlation with the rate of HAMD score reduction for the iTBS-dTMS group. This study revealed novel mechanisms by which accelerated dTMS protocols modulate brain networks, providing evidence for the clinical application of accelerated iTBS-dTMS as an efficient, evidence-based treatment for MDD.

Humans↗
PubMedDate not supplied

[Determining factors of acceleration in sustained monomorphic ventricular tachycardias in response to bursts of stimuli].

To analyse the determinants of acceleration of sustained monomorphic ventricular tachycardias in response to bursts of rapid ventricular pacing, we studied 46 consecutive patients with 90 distinct ventricular tachycardias during which one or more burst of rapid pacing were delivered. Tachycardia acceleration was observed in 11 tachycardias in 8 patients. The highest incidence of acceleration was observed in patients with left ventricular dysfunction of non coronary origin. There was a non significant trend towards lower values of left ventricular ejection fraction in patients with acceleration. There were no significant differences between ventricular tachycardias with of without acceleration in respect to: clinical presentation, QRS morphology, tachycardia cycle length and treatment with antiarrhythmic drugs. The shortest cycle of bursts of rapid pacing, was lower in tachycardias with acceleration than in those without it (229 +/- 57 ms vs 283 +/- 67 ms; p = 0.006) and tachycardias with acceleration showed a lower relation between burst cycle length and tachycardia cycle length (69 +/- 9% vs 84 +/- 8%; p < 0.001). The negative predictive value of acceleration was 75% for bursts of rapid pacing with a cycle length > or = 250 ms, and 96% for values of the relation between the burst cycle length and the tachycardia cycle length > or = 70%. This parameter show a very high discriminating value with of without antiarrhythmic drugs effect. Acceleration of sustained monomorphic ventricular tachycardias in response to bursts of rapid pacing depends on, the pacing rate and the relation between pacing rate and tachycardia rate.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMedDate not supplied

Effects of acceleration on the accuracy of MR phase velocity measurements.

Acceleration in blood flow can affect the accuracy of phase velocity measurements. Convective acceleration is due to changes in flow geometry and is independent of the time-varying acceleration caused by flow pulsatility. To analyze the effects of convective acceleration on flow velocity measurements, phase velocity measurements were obtained in steady laminar flow in the convergent segment of a 90%, hourglass-shaped stenosis phantom at a Reynolds number of 1,500. Measurements at the stenosis indicated that convective acceleration caused the measured values of average cross-sectional velocity to deviate as much as 37% from the theoretical values. The magnitude of the error could be accounted for by including the convective acceleration term in the phase shift equation. Convective acceleration effects should not be ignored in flow velocity measurements through stenoses, even when time-dependent acceleration due to flow pulsatility can be neglected.

Acceleration↗
PubMed1979

Head acceleration and psychomotor performance.

Concussion resulting from head acceleration could explain the poor survival rates in some types of accidents. Experiments have been conducted on a decelerator using a tracking task to determine whether high head acceleration could affect psychomotor performance. Human subjects were exposed to impact acceleration of O (sham), 5, 10 and 12 -Gx facing forwards. Measurements were made of the linear and angular accelerations experienced at the head and a step tracking task was used to examine psychomotor performance. Electroencephalographs were also recorded. Both the linear and angular accelerations at the head were increased at the higher levels of impact acceleration. At -5Gx there were no significant differences in psychomotor performance when compared with controls, but at -10Gx, and especially -12Gx, significant differences were found. The EEG activity did not vary significantly and no concussive effects were observed in any subject. These results suggest that impairment of psychomotor performance severe enough to jeopardise survival could be produced by high accelerations of the head, though neither linear nor angular acceleration appear to have special significance.

Acceleration↗