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PubMed2004

Kinetics of trace metal competition in the freshwater environment: some fundamental characteristics.

Freshwaters are recognized as dynamic systems that may be far-removed from equilibrium. A kinetic approach using the competing ligand exchange method with Chelex 100 as the competing ligand and inductively coupled plasmamass spectrometry to measure the dissociation kinetics was used to investigate the chemical speciation of Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), and Pb(II) in model solutions of a well-characterized fulvic acid (Laurentian fulvic acid) and a freshwater sample collected from the Grand River (Ontario, Canada). The kinetic distribution of the metal species were quantitatively characterized by their first-order dissociation rate constants. This kinetic speciation approach has the advantage of providing an objective method for estimating the dissociation rate constants without any a priori assumptions about the number of kinetically distinguishable components or the shape of the distribution. Three factors were found to influence the kinetics of trace metal competition in the freshwater environment: (i) metal-to-ligand ratio, (ii) ionic potential (z2/r), and (iii) ligand field stabilization energy. The results illustrate the importance of considering the valence-shell electron configuration in predicting the kinetics of trace metal competition in the freshwater environment. The markedly slow dissociation kinetics of Ni(II) and Cu(II) species suggest that the usual equilibrium assumption for freshwaters may not be valid. This study has demonstrated the ability of the kinetic model to correctly predict the relative rates of trace metal reactions, indicating that the kinetic model provides a chemically significant description of the kinetic processes in natural waters.

Kinetics↗

PubMed1999

Simplified reference region model for the kinetic analysis of [99mTc]TRODAT-1 binding to dopamine transporters in nonhuman primates using single-photon emission tomography.

Accurate quantification of neuroreceptors requires full kinetic modeling of the dynamic single-photon emission tomography (SPET) or positron emission tomography (PET) images, with highly invasive arterial blood sampling. This study investigated the application of a reference region kinetic model to the dynamics of [99mTc]TRODAT-1 in nonhuman primates, obviating the need for blood sampling. A series of dynamic SPET scans were performed on two baboons following the injection of approximately 700 MBq of [99mTc]TRODAT-1. Rapid arterial blood samples were taken automatically during scanning. Reconstructed SPET images were coregistered with magnetic resonance imaging (MRI) scans of the baboons, and regions of interest (ROIs) placed on the striatum, cerebellum and cerebral hemispheres. The ROI data were combined with metabolite-corrected blood data, and fitted to a three-compartment kinetic model using nonlinear least squares techniques. The same data were also used in a simplified reference region model, in which the input function was derived from the nondisplaceable tissue compartment. In addition, semiquantitative blinded analysis was performed by three raters to determine the point of transient equilibrium in the specific binding curves. All methods generated values for the ratio of the kinetic rate constants k3/k4, which gives an estimate of the binding potential, BP. These were compared with the full kinetic model. The mean values of k3/k4 for the three different analysis techniques for each baboon were: 1.17 +/- 0.21 and 1.12 +/- 0.13 (full kinetic model), 0.93 +/- 0.13 and 0.90 +/- 0.07 (reference region model), and 0.97 +/- 0.18 and 0.92 +/- 0.08 (equilibrium method). The reference region method gave significantly lower results than the full kinetic model (P = 0.01), but it also produced a much smaller spread and better quality fits to the kinetic data. The reference region model results for k3/k4 correlated very strongly with the full kinetic analysis (r2 = 0.992, P < 0.001), and with the equilibrium model (r2 = 0.88, P = 0.002). The subjectivity inherent in the equilibrium method produces inferior results compared with both kinetic analyses. It is suggested that the self-consistency of the reference region model, which requires no arterial blood sampling, provides a more precise and reliable estimate of the binding of [99mTc]TRODAT-1 to dopamine transporters than full kinetic modeling. The reference region method is also better suited to a routine clinical environment, and would be able to distinguish smaller differences in dopaminergic function between patient groups.

Animals↗

PubMed1997

Fluid dynamics of the CarboMedics kinetic bileaflet prosthetic heart valve.

OBJECTIVE: To compare hydrodynamic characteristics of a new bileaflet heart valve, the CarboMedics kinetic cardiac valve prosthesis, with those of a St. Jude Medical (SJM) heart valve. METHODS: Hydrodynamic characteristics were determined in the mitral and aortic positions of a Vivitro Systems pulse duplicator for size 23 Kinetic aortic values, size 23 SJM aortic valves, size 29 Kinetic mitral valves and size 29 SJM mitral valves. Test conditions were 72 beats per min with cardiac outputs of 2, 5 and 7 l/min. Values of forward flow pressure drop (delta P), regurgitant and energy loss were determined for each valve. The test results for the two valve designs were compared by valve size. RESULTS: The test results show that both the size 23 and size 29 Kinetic valves have 8-14% lower delta P values and 5-10% greater effective orifice area (EOA) values. The size 29 Kinetic mitral valve has a 1-2 ml lower regurgitant volume, while the size 23 Kinetic aortic valve has a 0.5 ml greater regurgitant volume than the corresponding SJM values. These factors combine to provide a 5-10% lower energy loss for size 23 Kinetic aortic valves and a 15-25% lower energy loss for size 29 Kinetic mitral valves over the cardiac cycle than for corresponding sizes of SJM valves. CONCLUSIONS: The Kinetic valve's fluid dynamics are superior to equivalent sizes of SJM valves. This is especially impressive considering that the tissue annulus diameters for Kinetic valves are approximately 0.5 mm less than equivalent size SJM valves. The primary reasons for the superior hydrodynamic performance of Kinetic valves are (1) the larger orifices which result in lower forward flow delta P values and (2) the opening angles, which have been customized for each valve size to minimize energy loss.

Aortic Valve↗

PubMed2004

Effect of kinetic therapy on pulmonary complications.

BACKGROUND: Optimal turning of critically ill patients is not well established. Kinetic therapy (systematic mechanical rotation of patients with 40 degree turns) may improve pulmonary function more than the improvement in function achieved via the standard of care (turning patients every 2 hours). OBJECTIVE: To determine (1) if patients receiving mechanical ventilation who tolerate kinetic therapy have better pulmonary function than do patients treated with standard turning and (2) the cost-effectiveness of kinetic therapy. METHODS: A prospective, randomized, multicenter study including 234 medical, surgical, and trauma patients (137 control patients, 97 patients receiving kinetic therapy). RESULTS: Kinetic therapy significantly decreased the occurrence of ventilator-associated pneumonia and lobar atelectasis. The risk of pneumonia developing was lower (P = .002) in patients receiving kinetic therapy than in the control patients. The risk of lobar atelectasis developing was decreased (P = .02) for the patients receiving kinetic therapy. Lengths of stay in the intensive care unit and in the hospital did not differ between the groups. Charges for intensive care were less in the kinetic therapy group (81,700 dollars) than in the control group (84,958 dollars), but not significantly less. Twenty-one patients did not tolerate kinetic therapy and were not included in the analysis. CONCLUSION: Kinetic therapy helps prevent ventilator-associated pneumonia and lobar atelectasis in critically ill patients. Costs to rent the bed may be offset by the potential cost reduction associated with kinetic therapy.

Cost-Benefit Analysis↗

PubMed1993

The fall and rise of prostate-specific antigen. Kinetics of serum prostate-specific antigen levels after radiation therapy for prostate cancer.

BACKGROUND: The serum kinetics of prostate-specific antigen (PSA) after radiation therapy for prostate cancer are not well characterized, and the potential prognostic significance of serum half-lives and of serum doubling times is unclear. This study was designed to address those issues. METHODS: One hundred fifty-four patients with at least four serial PSA determinations who received external-beam radiation therapy alone were analyzed to determine PSA kinetics and to correlate kinetic parameters with outcome. Nonlinear regression techniques were used to estimate PSA half-lives and doubling times. RESULTS: The PSA data fitted well to exponential models consistent with the hypothesis that PSA kinetics after radiation follow first-order (exponential) kinetics. The mean PSA half-life was 1.9 months (range, 0.5 to 9.2 months). No significant correlation existed between half-life and grade, stage, acid phosphatase level, serum testosterone level, or patient age. A weak correlation between half-life and pretreatment PSA level was observed: patients with low PSA levels tended to have longer half-lives. Half-life did not correlate with disease relapse or with the likelihood of developing a rising PSA profile. PSA doubling time in 37 patients with rising values ranged from 1.6 to 53 months (mean, 12.5 months). Doubling times were significantly longer than half-lives by an average factor of 6.5 and there was no correlation between half-life and subsequent doubling time. Doubling times were longer in low-grade tumors. CONCLUSIONS: Serum kinetics of PSA in particular its rate of fall after radiation provide little, if any, useful clinical information. It is possible that serum kinetics of PSA are related to tumor cell kinetics but such relationships remain speculative. Correlative cell kinetic--PSA kinetic studies are needed to elucidate the mechanisms underlying the changes in PSA level after radiation therapy.

Actuarial Analysis↗

PubMed1978

A new approach in the kinetics of biological transport. The potential of reversible inhibition studies.

Kinetic equations are derived for reversible inhibition of both active and facilitated transport systems for seven common experimental arrangements. It is shown that the unique features of transport kinetics may be exploited to give new kinds of information. It is also shown that that the familiar rules of enzyme kinetics, though often applied to transport, can be seriously misleading. The analysis leads to the following general conclusions: (1) A competitive mechanism frequently gives rise to non-competitive kinetics, depending on the experimental design, but a non-competitive mechanism never produces competitive kinetics. (2) Inhibition studies on exchange diffusion at equilibrium in non-active systems or in the final steady state in active systems are the only unambiguous kinetic tests to distinguish competitive from non-competitive mechanisms. (3) Substrate analogs that are bound to the carrier and transported are readily distinguished by inhibition kinetics from those not transported, even though both may rapidly enter the cell by another route. (4) Even in non-active systems competitive inhibitors commonly have far different affinities for the substrate sites on the two membranes faces: where sufficient non-polarity allows their penetration into the cell, inhibition kinetics readily establish such sideness in their action. (5) Inhibition kinetics of the mixed competitive and non-competitive type result from moderately asymmetrical binding of inhibitor at the substrate site. (6) Asymmetry is a necessary feature of active transport: hence studies of inhibition kinetics should provide important insights into its mechanism.

Binding, Competitive↗

PubMed1986

ATP hydrolysis kinetics of Na,K-ATPase in cataract.

The steady-state kinetics of hydrolysis of Mg2+ ATP by the epithelial Na,K-ATPase of individual human lenses were determined. Among the cataract lens population, four distinct kinetic types were observed: negative kinetic co-operativity. Michaelis-Menten kinetics, positive kinetic co-operativity, and substrate inhibition kinetics. Negative kinetic co-operativity and Michaelis-Menten kinetics were also observed in a group of presumably clear lenses from non-diabetic individuals ages 16-42 years. Substrate inhibition kinetics were found to be prevalent in individuals with mature onset diabetes. Substrate inhibition kinetics were also observed for Na,K-ATPase isolated from lenses which had been incubated in high glucose. It would appear that this modification leads to an inhibition of Na,K-ATPase-dependent K+ influx into these cultured lenses.

Adenosine Triphosphate↗

PubMed2006

Linear and non-linear regression analysis for the sorption kinetics of methylene blue onto activated carbon.

Batch kinetic experiments were carried out for the sorption of methylene blue onto activated carbon. The experimental kinetics were fitted to the pseudo first-order and pseudo second-order kinetics by linear and a non-linear method. The five different types of Ho pseudo second-order expression have been discussed. A comparison of linear least-squares method and a trial and error non-linear method of estimating the pseudo second-order rate kinetic parameters were examined. The sorption process was found to follow a both pseudo first-order kinetic and pseudo second-order kinetic model. Present investigation showed that it is inappropriate to use a type 1 and type pseudo second-order expressions as proposed by Ho and Blanachard et al. respectively for predicting the kinetic rate constants and the initial sorption rate for the studied system. Three correct possible alternate linear expressions (type 2 to type 4) to better predict the initial sorption rate and kinetic rate constants for the studied system (methylene blue/activated carbon) was proposed. Linear method was found to check only the hypothesis instead of verifying the kinetic model. Non-linear regression method was found to be the more appropriate method to determine the rate kinetic parameters.

Adsorption↗

PubMed2003

The kinetic pathway of folding of barnase.

To search for folding intermediates, we have examined the folding and unfolding kinetics of wild-type barnase and four representative mutants under a wide range of conditions that span two-state and multi-state kinetics. The choice of mutants and conditions provided in-built controls for artifacts that might distort the interpretation of kinetics, such as the non-linearity of kinetic and equilibrium data with concentration of denaturant. We measured unfolding rate constants over a complete range of denaturant concentration by using by 1H/2H-exchange kinetics under conditions that favour folding, conventional stopped-flow methods at higher denaturant concentrations and continuous flow. Under conditions that favour multi-state kinetics, plots of the rate constants for unfolding against denaturant concentration fitted quantitatively to the equation for three-state kinetics, with a sigmoid component for a change of rate determining step, as did the refolding kinetics. The position of the transition state on the reaction pathway, as measured by solvent exposure (the Tanford beta value) also moved with denaturant concentration, fitting quantitatively to the same equations with a change of rate determining step. The sigmoid behaviour disappeared under conditions that favoured two-state kinetics. Those data combined with direct structural observations and simulation support a minimal reaction pathway for the folding of barnase that involves two detectable folding intermediates. The first intermediate, I(1), is the denatured state under physiological conditions, D(Phys), which has native-like topology, is lower in energy than the random-flight denatured state U and is suggested by molecular dynamics simulation of unfolding to be on-pathway. The second intermediate, I(2), is high energy, and is proven by the change in rate determining step in the unfolding kinetics to be on-pathway. The change in rate determining step in unfolding with structure or environment reflects the change in partitioning of this intermediate to products or starting materials.

Bacillus↗

PubMed1999

Multi-enzyme kinetic analysis of glycolipid biosynthesis.

Gangliosides are acidic glycosphingolipids synthesized sequentially by a series of glycosyltransferases acting in parallel biosynthetic pathways. While most glycosyltransferases are highly specific, some, however, may catalyze equivalent steps in each pathway using different gangliosides as substrates (e.g. N-acetylgalactosaminyltransferase, sialyltransferase-IV). A multi-enzyme kinetic analysis was developed on the condition that serial enzymatic reactions operate below substrate saturation. A multi-enzyme kinetic analysis enabled a simultaneous calculation of the Vmax/Km value of each enzyme derived from the equilibrium concentration of the respective substrate. Substrate concentrations [S] were determined by radioactive labelling of gangliosides in intact cells with the precursor sugars [14C]galactose and [14C]glucosamine, followed by high-performance thin-layer chromatography and autoradiography of the radiolabelled glycolipids. On the basis of Michaelis-Menten kinetics, Vmax/Km values were derived from [S] by a system of linear equations. The procedure was used to analyze the development of the glycolipid composition during differentiation of rat gliomaxmurine neuroblastoma (NG108-15) cells. The Vmax/Km values calculated by multi-enzyme kinetic analysis were consistent with the kinetic data obtained with solubilized enzymes. Application of multi-enzyme kinetic analysis to published data on the correlation of enzyme activities with ganglioside levels in various cell lines and tissues indicated the validity of this method for analysis of the glycolipid biosynthesis, in particular, of its initial steps. On the basis of the kinetic analysis, it is suggested that the cell lines can be divided into two groups with respect to the substrate pools of GM3 used by sialyltransferase-II and N-acetylgalactosaminyltransferase-I. The first group encompasses the majority of the neuroblastoma cell lines and the embryonic rat brain where the two enzymes share a common pool of GM3. In the second group, the two enzymes do not compete for the same pool of GM3, indicating a different subcellular localization of CMP-NeuAc:GM3 alpha2-8-sialyltransferase and UDP-N-acetylgalactosaminyl:GM3 N-acetylgalactosaminyltransferase. In this study, the theory of a multi-enzyme kinetic analysis is discussed and its application to analysis of the glycolipid biosynthesis in neuroblastoma cells is demonstrated. A multi-enzyme kinetic analysis can be applied to other biosynthetic pathways and provides the advantage of analyzing kinetic data with intact cells or tissue samples.

Animals↗

PubMed2006

Measurements of kinetic parameters in a microfluidic reactor.

Continuous flow microfluidic reactors that use immobilized components of enzymatic reactions present special challenges in interpretation of kinetic data. This study evaluates the difference between mass-transfer effects and reduced efficiencies of an enzyme reaction. The kinetic properties of immobilized alkaline phosphatase (AP) were measured by the dephosphorylation of 6,8-difluoro-4-methylumbelliferyl/phosphate to a fluorescent 6,8-difluoro-4-methylumbelliferone. A glass microfluidic chip with an in-channel weir was created for the capture of solid silica microbeads functionalized with enzyme. The input substrate concentrations and flow rates across the bed were varied to probe the flow-dependent transport and kinetic properties of the reaction in the microreactor bed. Unlike previous reactors, substrate was titrated directly over the fixed enzyme bed by controlling the air pressure over the chip reservoirs. The reactor explored substrate conversions from near zero to 100%. The average bed porosity, residence time, and bed resistance were measured with dye pulses. A simple criterion was derived to evaluate the importance of flow-dependent mass-transfer resistances when using microreactors for calculating kinetic rate constants. In the absence of mass-transfer resistances, the Michaelis-Menten kinetic parameters are shown to be flow independent and are appropriately predicted using low substrate conversion data. A comparison of the kinetic parameters with those obtained using solution-phase enzymatic reactions shows a significant decrease in enzyme activity in the immobilized conformation. The immobilized Km of AP is approximately 6 times greater while the kcat is reduced by approximately 28 times. Contradictions found in literature on the evaluation of Michaelis-Menten kinetic parameters for immobilized enzymes in microfluidic reactors are addressed. When product molecules occupy a significant number of enzymatic sites or modify the enzyme activity, the assumed Michaelis-Menten mechanism can no longer be valid. Under these conditions, the calculations of "apparent" kinetic rate constants, based on Michaelis-Menten kinetics, can superficially show a dependence on flow rate conditions even in the absence of mass-transfer resistances. High substrate conversions are shown to depend on flow rate. A kinetic model based on known mechanisms of the alkaline phosphatase enzyme reaction is tested to predict the measurements for high substrate conversion. The study provides a basis for appropriate use of mass-transfer and reaction arguments in successful application of enzymatic microreactors.

Adsorption↗

PubMed2001

Myofilament kinetics in isometric twitch dynamics.

To better understand the relationship between kinetic processes of contraction and the dynamic features of an isometric twitch, studies were conducted using a mathematical model that included: (1) kinetics of cross bridge (XB) cycling; (2) kinetics of thin filament regulatory processes; (3) serial and feedback interactions between these two kinetic processes; and (4) time course of calcium activation. Isometric twitch wave forms were predicted, morphometric features of the predicted twitch wave form were evaluated, and sensitivities of wave form morphometric features to model kinetic parameters were assessed. Initially, the impulse response of the XB cycle alone was analyzed with the findings that dynamic constants of the twitch transient were much faster than turnover number of steady-state XB cycling, and, although speed and duration of the twitch wave form were sensitive to XB cycle kinetic constants. parameters of wave shape were not. When thin filament regulatory unit (RU) kinetics were added to XB cycle kinetics, the system impulse response was slowed with only little effect on wave shape. When cooperative neighbor interactions between RU and XB were added, twitch wave shape (as well as amplitude, speed and duration) proved to be sensitive to variation in cooperativity. Importantly, persistence and shape of the falling phase could be strongly modified. When kinetic coefficients of XB attachment were made to depend on sarcomere length, changes in wave shape occurred that did not occur when only sliding filament mechanisms were operative. Indeed, the force-length relationship proved to be highly sensitive to length-dependent XB attachment in combination with cooperative interactions. These model findings are the basis of hypotheses for the role of specific kinetic events of contraction in generating twitch wave form features.

Actin Cytoskeleton↗

PubMed2005

Processing of kinetic boundaries in macaque V4.

We used gratings and shapes defined by relative motion to study selectivity for static kinetic boundaries in macaque V4 neurons. Kinetic gratings were generated by random pixels moving in opposite directions in the neighboring bars, either parallel to the orientation of the boundary (parallel kinetic grating) or perpendicular to the boundary (orthogonal kinetic grating). Neurons were also tested with static, luminance defined gratings to establish cue invariance. In addition, we used eight shapes defined either by relative motion or by luminance contrast, as used previously to test cue invariance in the infero-temporal (IT) cortex. A sizeable fraction (10-20%) of the V4 neurons responded selectively to kinetic patterns. Most neurons selective for kinetic contours had receptive fields (RFs) within the central 10 degrees of the visual field. Neurons selective for the orientation of kinetic gratings were defined as having similar orientation preferences for the two types of kinetic gratings, and the vast majority of these neurons also retained the same orientation preference for luminance defined gratings. Also, kinetic shape selective neurons had similar shape preferences when the shape was defined by relative motion or by luminance contrast, showing a cue-invariant form processing in V4. Although shape selectivity was weaker in V4 than what has been reported in the IT cortex, cue invariance was similar in the two areas, suggesting that invariance for luminance and motion cues of IT originates in V4. The neurons selective for kinetic patterns tended to be clustered within dorsal V4.

Animals↗

PubMed2002

Metaanalysis of input/output kinetics in lactating dairy cows.

The kinetics of dry matter intake, raw milk yield, milk fat yield, and body weight of 140 treatment groups of cows reported in 37 articles published between 1959 and 1999 were collected in a database. The majority of these experiments were performed with Holstein-Friesian cows (primiparous: n = 51, multiparous: n = 89). Animals were fed with forages and concentrates, offered separately (n = 98) or as a total mixed ration (n = 42). Empty body weight was calculated assuming that an increase of 1 kg in dry matter intake corresponded to an increase of 4 kg in gastrointestinal tract content. Each kinetic, denoted Y, was fitted with the model proposed by Grossman (1999) for raw milk yield. This model allowed the partitioning of the kinetic into three stages (early, middle, and late stages of lactation), each characterized by its own linear tendency. Kinetics were therefore summarized with parameter estimates of the model: the plateau value of Y in middle stage, the slopes of Y in early and late stages, and the weeks of start and end of the middle stage. The following additional variables were also calculated: the total increase of Y in early stage, the extrapolated value of Y at calving, and the persistency of Y defined as the duration of the middle stage. Variability of these parameters for each kinetic across treatment groups was examined through mixed models including the year of publication as covariate, parity as a fixed between-group factor, and trial as a random factor. Correlations between parameters within a Y-kinetic and between different Y-kinetics were calculated by parity group and feed allocation system. Finally we propose predictive models which emphasized (1) the effect of empty body weight at calving on the depletion of empty body weight in early lactation, (2) the incidence of the kinetic of dry matter intake on the kinetic of raw milk yield in middle and late stages of lactation, and (3) the relationships between the kinetics of raw milk yield and milk fat yield in middle and late stages of lactation.

Animal Nutritional Physiological Phenomena↗

PubMed1993

A method to study complex enzyme kinetics involving numerical analysis of enzymatic schemes. The mannitol permease of Escherichia coli as an example.

An analysis of complex kinetic mechanisms is proposed that consists of two steps, (i) building of an kinetic scheme from experimental data other than steady-state kinetics and (ii) numerical simulation and analysis of the kinetics of the proposed scheme in relation to the experimental kinetics. Procedures are introduced to deal with large numbers of enzymatic states and rate constants, and numerical tools are defined to support the analysis of the scheme. The approach is explored by taking the mannitol permease of Escherichia coli as an example. This enzyme catalyzes both the transport of mannitol across the cytoplasmic membrane and the phosphorylation of mannitol. The challenge is to deduce the transport properties of this dimeric enzyme from the phosphorylation kinetics. It is concluded that (i) the steady-state kinetic behavior is largely consistent with the proposed catalytic cycle of the monomeric subunit, (ii) the kinetics provide no direct support but also do not disprove a coupled translocation of the binding sites on the two monomeric subunits. The approach reveals the need for further experimentation where the implementation of experimental results in the scheme conflict with the experimental kinetics and where specific experimental characteristics do not show up in the simulations of the proposed kinetic scheme.

Binding Sites↗

PubMed2002

Complexities in ETS-domain transcription factor function and regulation: lessons from the TCF (ternary complex factor) subfamily. The Colworth Medal Lecture.

The ETS-domain transcription factor family can be divided into a series of subfamilies. Elk-1 represents the founding member of the ternary complex factor (TCF) subfamily. By focusing on the TCF subfamily, we can demonstrate the complexities that exist in the function and regulation of ETS-domain transcription factors. This article focuses on Elk-1 in detail and summarizes the functions of other TCFs. The key themes covered include the domain structure of the TCFs, the mechanisms of complex formation with serum response factor, regulation of TCFs by mitogen-activated protein kinase cascades, and transcriptional regulatory properties of the TCFs. Finally, the emerging role of the TCFs in vivo is discussed. A picture is developing indicating that, while these proteins exhibit significant sequence and functional conservation, key differences in their structure and regulation are being identified which may relate to unique functions of these proteins in vivo.

Amino Acid Sequence↗

PubMed2001

[Evaluation of extensive visual field defects with computer-assisted kinetic perimetry].

BACKGROUND: Conventional kinetic perimetry is of especial use in case of advanced scotoma. However, examiner dependency is a major drawback. Purpose of this study was to evaluate the clinical feasibility and intraindividual scatter of computer-assisted kinetic perimetry in monitoring advanced visual field defects of various origins. METHODS: Examinations were carried out with the Tuebingen Computer Campimeter (background lumincance 10 cd/m2). In an initial session, the localization of the scotoma border is estimated with conventional manual kinetic perimetry. In the subsequent computer assisted kinetic mode, an individually adjusted set of vectors is designed. Each vector crosses the manually assessed visual field defect border almost perpendicularly, starting approximately 3 degrees within the scotoma. Each individual set of vectors can be stored and recalled for follow-up. Stimuli move along these vectors with identical characteristics as in manual kinetic perimetry. Stimulus presentations are repeated six times in a randomized order. Patients' responses are recorded and additionally corrected for mean individual reaction time. A "local kinetic threshold" (mean) and a related parameter for dispersion (standard deviation) are assessed. RESULTS: Four subjects with advanced visual field loss of various origin (retinitis pigmentosa, vigabatrin-associated visual field defect, glaucomatous nerve fibre layer defect, and postgeniculate visual pathway defect) participated in this study. Maximal difference between manual-kinetic and automated kinetic thresholds reaches from 1.7 degrees to 5 degrees. Local scatter (standard deviation) of kinetic threshold, assessed by computer-assisted perimetry, varies between 0.1 degree and 3.0 degrees. CONCLUSION: Computer assisted kinetic perimetry is a new, useful, examiner-independent, reliable method for effective evaluation and monitoring of advanced visual field loss.

Adult↗

PubMed2004

Open versus closed kinetic chain exercises in patellofemoral pain: a 5-year prospective randomized study.

BACKGROUND: Today, no clinical studies have been undertaken to examine the long-term effects of an open kinetic chain or closed kinetic chain program. HYPOTHESIS: The long-term follow-up results after a conservative exercise protocol are significantly worse than the short-term results. The long-term effect of closed kinetic chain training is significantly better compared to the effect of open kinetic chain training. STUDY DESIGN: Prospective randomized clinical trial. METHODS: Sixty patients were randomized into a 5-week conservative program, consisting of only closed kinetic chain exercises or only open kinetic chain exercises. Assessment of muscular characteristics, subjective symptoms, and functional performance was evaluated in this study at the time of initial physical examination, at the end of the treatment period, and 5 years later. RESULTS: At the 5-year follow-up, both groups demonstrated maintenance of good subjective and functional outcomes achieved immediately after the conservative treatment. No significant difference between both groups was observed at the 5-year follow-up for the majority of the examined parameters. However, on 3 of the 18 visual analog scales, the open kinetic chain group showed significantly less complaints compared to the closed kinetic chain group. CONCLUSIONS: On the basis of these results, the authors conclude that both open kinetic chain and closed kinetic chain programs lead to an equal long-term good functional outcome.

Adolescent↗