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PubMed1993

Dissociation of achromatic and chromatic processing of spatial form and temporal modulation by the titration method.

Using a titration method to attempt to silence the achromatic contrast subsystem, we tested the assumption that an equiluminant chromatic pattern does not stimulate the physiological achromatic contrast subsystem. We also examined the question whether contrast threshold is entirely or even partially determined by the chromatic contrast subsystem at equiluminance. We report a method for demonstrating when contrast threshold is entirely determined by the chromatic contrast subsystem.

Adult↗
PubMed1995

CPAP titration for sleep apnea using a split-night protocol.

We studied 107 patients with sleep-disordered breathing to confirm the effectiveness of continuous positive airway pressure (CPAP) titration using a split-night protocol. Patients spent two consecutive nights in our laboratory with complete polysomnography. On the first night, we applied a split-night protocol; the first half of the night was used as a baseline (B), and after a diagnosis was made, CPAP was applied during the second half of the night (SN). On the second night (2N), patients spent the entire night on CPAP to confirm the effectiveness of CPAP treatment. The SN and 2N both revealed a significant reduction in arousal index (37.8 +/- 27.9 on B, 13.2 +/- 12.1 on SN, 11.4 +/- 8.0 on 2N, values are mean +/- SD, p < 0.001), apnea hypopnea index (AHI) (23.6 +/- 26.3/h on B, 3.0 +/- 3.7/h on SN, 2.4 +/- 2.6/h on 2N, p < 0.001), percent total sleep time below 90% SaO2 (21.0 +/- 27.2% on B, 8.2 +/- 13.8% on SN, 4.9 +/- 10.2% on 2N, p < 0.001), and percent total sleep time below 80% SaO2 (1.1 +/- 3.8% on B, 0.0 +/- 0.1% on SN, 0.1 +/- 0.5% on 2N, p < 0.001). There were no significant differences between the SN and the 2N for these measurements. Final CPAP pressure was significantly lower at the end of the SN when compared with the 2N (8.8 +/- 2.7 cm H2O on SN, vs 10.3 +/- 2.8 cm H2O on 2N, p < 0.001). When patients were divided into three groups (AHI < 20, n = 69; 20 < AHI < 40, n = 18; AHI > 40, n = 20), the final CPAP pressure was different only in the group with AHI < 20 (8.1 +/- 2.3 cm H2O on SN, 9.6 +/- 2.3 cm H2O on 2N, p < 0.001). We conclude that a split-night protocol may be sufficient to determine the effective CPAP pressure, especially in patients with an AHI > 20.

Female↗
PubMed1984

Titration of PEEP by the arterial minus end-tidal carbon dioxide gradient.

It was shown in dogs that intrapulmonary physiologic shunt (Qsp/Qt), arterial oxygen tension (PaO2), total static respiratory compliance (CT), oxygen delivery (O2AV), cardiac output (Qt), and arterial minus end-tidal carbon dioxide gradient (PaCO2-PetCO2) undergo statistically significant deterioration when oleic acid is injected into the pulmonary artery. Positive end-expiratory pressure (PEEP) therapy reduced Qsp/Qt and PaCO2-PetCO2 gradient and increased PaO2. The CT did not show any consistent pattern of improvement with the application of PEEP. The Qt and the O2AV progressively decreased as PEEP was increased. The application of additional PEEP beyond that which minimized the PaCO2-PetCO2 gradient produced a statistically significant increase in the PaCO2-PetCO2 gradient, but this was not reflected by concomitant changes in Qsp/Qt or PaO2 in spite of a further decrease in Qt. Thus, the PaCO2-PetCO2 gradient may be a more sensitive indicator of excessive PEEP than is Qst/Qt or PaO2, since it should be smallest when there is maximal recruitment of perfused or functional gas units without overdistention of alveolar areas contributing to dead space. Also, the use of the PaCO2-PetCO2 gradient permits the rapid titration of PEEP without the need for a pulmonary artery catheter.

Animals↗
PubMed2005

Isolation, propagation, and titration of human immunodeficiency virus type 1 from peripheral blood of infected individuals.

HIV-1 can be isolated from peripheral blood mononuclear cells and is easily propagated on primary cells in vitro. Here we describe the method for bulk isolation of the HIV-1 quasispecies and a limiting dilution virus isolation protocol by which single coexisting clones can be obtained. In addition, methods for propagation and titration of HIV-1 are provided.

HIV Infections↗
PubMed2005

Isothermal titration calorimetry.

Isothermal titration calorimetry is an ideal technique for measuring biological binding interactions. It does not rely on the presence of chromophores or fluorophores, nor does it require an enzymatic assay. Because the technique relies only on the detection of a heat effect upon binding, it can be used to measure the binding constant, K, the enthalpy of binding, DeltaH degrees and the stoichiometry, or number of binding sites, n. This chapter describes instrumentation, experimental design, and the theoretical underpinnings necessary to run and analyze a calorimetric binding experiment.

Calorimetry↗
PubMed2006

Theoretical description of the ion transport across nanopores with titratable fixed charges: analogies between ion channels and synthetic pores.

Recently developed nanometer-sized synthetic pores display several properties so far believed to be distinctive features of a large variety of biological wide ion channels. Thus conductance in the pS-nS range, pH-dependent ion selectivity, fluctuations of current between open and closed states, flux inhibition caused by protons or divalent cations, current rectification, and the ability to perform selective macromolecule sizing and counting are found in synthetic and biological channels alike. Despite other differences such as pore size and geometry, the similarities open a new field for exploring specific technological applications via the chemical modification of synthetic pores with biological molecules. This article reviews some of the basic concepts and theories relevant to ion transport in nanopores with titratable charges stressing the analogies between synthetic pores and biological ion channels. The ultimate goal is to show that continuum theories may account for the essential features of these systems. A simple electrodiffusion model and its comparison with experimental results are chosen as a case study.

Ion Channels↗
PubMed1975

The mechanism of the increase in the activity of liver alkaline phosphatase in experimental cholestasis: measurement of an increased enzyme concentration by immunochemical titration.

Alkaline phosphatase (EC 3.1.3.1) activity increases 5-15 fold in the livers of rats, following bile duct ligation. The mechanism of this increase has been the subject of numerous investigations. In HeLa cells the synthesis of a different phosphatase enzyme protein with higher catalytic activity has been postulated. After preparing an antiserum against rat liver phosphatase, we compared the phosphatase protein concentration in normal and cholestatic livers by immunochemical titration. Our results clearly indicate that the elevation of enzyme activity is due to an increased accumulation of enzyme protein.

Alkaline Phosphatase↗
PubMed1985

Laser nephelometric equivalence point titration for the measurements of specific proteins in turbid biological fluids.

A reliable, sensitive and specific laser nephelometric (LN) assay for the quantitative measurement of specific proteins in body fluids by equivalence point titration is described. The method is relatively free from interference encountered in conventional LN assays, e.g. unspecific background scatter, antigen excess, and the inhibition of complex formation by high ionic strength and salt concentration, low pH and elevated urea concentrations. It can be applied to turbid body fluids containing relatively small amounts of antigen. A serial dilution of the antigen preparation (human urinary albumin in the present work) is incubated with a fixed amount of highly diluted specific antiserum. The antigen concentration is determined by estimation of the equivalence point on the LN immunoprecipitation curve and comparison of this position with that on a standard curve. The data presented show good correlation with values obtained by radioimmunoassay (p less than or equal to 1 X 10(-5);log (LNET) = 0.956 log (RIA) - 0.03; n = 50).

Adjuvants, Pharmaceutic↗
PubMed2005

Titration behavior of residues at the entrance of the D-pathway of cytochrome c oxidase from paracoccus denitrificans investigated by continuum electrostatic calculations.

Continuum electrostatic calculations were employed to investigate the titration curves of the fully oxidized state of wild type and several variants of cytochrome c oxidase from Paracoccus denitrificans (N131D, N131C, N131V, and D124N) for different values of the dielectric constant of the protein. The effects of the mutations at the entrance of the D-proton transfer pathway were found to be quite localized to their immediate surroundings. The results can be well interpreted in the light of the available biochemical and structural data and help understanding the effects of mutations on proton conductivity. The mutations of aspartic acid Asp-I-124 to a neutral residue resulted in a decreased pK(a) value of His-I-28 suggesting that the mutation of His-I-28 may have a significant influence on the coupling of electron and proton transfer in cytochrome c oxidase. We also investigated the effect of the mutations N131D, N131C, and N131V on the residue Glu-I-278 in terms of its pK(a) value and electrostatic interaction energies.

Amino Acid Substitution↗
PubMed2005

Dissecting homo-heptamer thermodynamics by isothermal titration calorimetry: entropy-driven assembly of co-chaperonin protein 10.

Normally, isothermal titration calorimetry (ITC) is used to study binding reactions between two different biomolecules. Self-association processes leading to homo-oligomeric complexes have usually not been studied by ITC; instead, methods such as spectroscopy and analytical ultracentrifugation, which only provide affinity and Gibbs-free energy (i.e., K(D) and DeltaG), are employed. We here demonstrate that complete thermodynamic descriptions (i.e., K(D), DeltaG, DeltaH, and DeltaS) for self-associating systems can be obtained by ITC-dilution experiments upon proper analysis. We use this approach to probe the dissociation (and thus association) equilibrium for the heptameric co-chaperonin proteins 10 (cpn10) from Aquifex aeolicus (Aacpn10-del25) and human mitochondria (hmcpn10). We find that the midpoints for the heptamer-monomer equilibrium occur at 0.51 +/- 0.03 microM and 3.5 +/- 0.1 microM total monomer concentration (25 degrees C), for Aacpn10-del25 and hmcpn10, respectively. For both proteins, association involves endothermic enthalpy and positive entropy changes; thus, the reactions are driven by the entropy increase. This is in accord with the release of ordered water molecules and, for the thermophilic variant, a relaxation of monomer-tertiary structure when the heptamers form.

Bacteria↗
PubMed2006

Exact analysis of heterotropic interactions in proteins: Characterization of cooperative ligand binding by isothermal titration calorimetry.

Intramolecular interaction networks in proteins are responsible for heterotropic ligand binding cooperativity, a biologically important, widespread phenomenon in nature (e.g., signaling transduction cascades, enzymatic cofactors, enzymatic allosteric activators or inhibitors, gene transcription, or repression). The cooperative binding of two (or more) different ligands to a macromolecule is the underlying principle. To date, heterotropic effects have been studied mainly kinetically in enzymatic systems. Until now, approximate approaches have been employed for studying equilibrium heterotropic ligand binding effects, except in two special cases in which an exact analysis was developed: independent binding (no cooperativity) and competitive binding (maximal negative cooperativity). The exact analysis and methodology for characterizing ligand binding cooperativity interactions in the general case (any degree of cooperativity) using isothermal titration calorimetry are presented in this work. Intramolecular interaction pathways within the allosteric macromolecule can be identified and characterized using this methodology. As an example, the thermodynamic characterization of the binding interaction between ferredoxin-NADP+ reductase and its three substrates, NADP+, ferredoxin, and flavodoxin, as well as the characterization of their binding cooperativity interaction, is presented.

Algorithms↗
PubMed1994

Treatment of Graves' disease by carbimazole: high dose with thyroxine compared to titration dose.

A comparative study of high-dose (HD, carbimazole 60 mg plus thyroxine 100-150 micrograms daily) and titration-dose (TD) regimens of carbimazole was carried out in 70 patients with Graves' disease, the patients being assigned randomly to one or other regimen. The treatment was given for 1 year and follow-up was for 2 years after stopping treatment. In both groups, recurrence of hyperthyroidism occurred, most commonly during the first 6 months (35% of HD and 44% of TD). By 2 years after stopping treatment, recurrence had occurred in 50% of the HD and 66% of the TD group. The differences were not significant. Thyroid antibodies, serum thyroglobulin and pertechnetate uptake fell similarly in both groups during treatment. Cigarette smoking was similar in both the groups and did not influence the frequency of relapse. In both HD and TD groups, when relapsing patients were examined according to whether they relapsed early (within 6 months or less) or late it was found that those who relapsed late were, in respect of goitre size, pertechnetate uptake and presence of detectable plasma TSH, similar to the patients who did not relapse at all. In conclusion, the changes in the measured variables and the progress of the patients was similar whether treated by the HD or TD regimen.

Adult↗
PubMed2001

Determination by fluorimetric titration of the ionization constants of ciprofloxacin in solution and in the presence of liposomes.

A fluorescence titration method was applied for the determination of pKa of ciprofloxacin (CPX) in solution. Values of 6.18 +/- 0.05 and 8.76 +/- 0.03 were obtained for pKa1 and pKa2, respectively. The method was used to determine the ionization constants in the presence of liposomes of dipalmitoylphosphatidylcholine (DPPC) and DPPC with 10 mol% of dipalmitoylphosphatidylglycerol. A dependence on the surface charge of liposomes was found which supported the existence of a basic electrostatic interaction between CPX and the phospholipid bilayer. Both pK values for the N-4 butyl-piperazinyl derivative (BCPX) of the parent compound were also determined in solution and in the presence of liposomes. The competition of both drugs for the same binding site as 1-anilino-8-naphtalene sulfonate demonstrate that the interaction is governed by electrostatic forces.

Anti-Infective Agents↗
PubMedDate not supplied

Hyperimmune antirabies sera titration by standard mouse neutralization and counterimmunoelectrophoresis tests, comparing results of different laboratories.

To determine the rabies antibody level of twenty-four hyperimmune equine sera, Standard Mouse Neutralization (SMN) and Couterimmunoelectrophoresis (CIE) tests were carried out, both at the Instituto Butantan (IB) and Instituto Panamericano de Proteccíon de Alimentos y Zoonosis (INPPAZ). Statistical analysis has shown a correlation (r) of 0.9317 between the SMN and CIE performed at the IB, while at the INPPAZ it scored 0.974. Comparison of CIE data of both laboratories yielded a correlation of 0.845. The CIE technique has shown to be a sensitive and efficient as the SMN in titrating antirabies hyperimmune equine sera. Based on CIE results, a simple, rapid and inexpensive technique, titers of sera antibody can be rellably estimated in SMN test.

Animals↗
PubMed2004

In situ enzyme immunoassay for titration of a Brazilian hepatitis A virus strain (HAF-203).

Hepatitis A virus (HAV) replicates relatively slowly in cell culture without a cytopathic effect, a fact that limits the use of tissue culture assays. The radioimmunofocus assay is the standard method for HAV titration, although it is labor intensive and requires the use of radioisotopes. A simple, rapid and objective infectivity assay based on an in situ enzyme immunoassay (EIA) is described here for a Brazilian cell culture-adapted HAV strain (HAF-203). The assay uses a peroxidase-labeled polyclonal antibody to fixed monolayers as an indicator of infection. EIA may be completed within 7 days using serial 5-fold dilutions of the virus, yielding a titer of 5.024 log 50% tissue culture infective dose (TCID50)/ml for HAF-203. This technique had a detection limit of 1.1 log TCID50/ml and the specificity was demonstrated by detecting no reaction on the columns of uninfected wells. The reproducibility (with intra- and inter-assay coefficients of variation ranging from 1.9 to 3.8% and from 3.5 to 9.9%, respectively) and quantitation of the assay were demonstrated by close agreement in virus infectivity titers among different assays of the same amount of virus and between assays of different amounts of virus. Furthermore, this assay does not require the use of radiolabeled antibodies. We describe here an efficient EIA that is highly reproducible and that could be used to monitor HAV growth in cell culture and to determine the quantity of HAV antigen needed for diagnostic assays. This is the first report of the infectious titer of the Brazilian cell culture-adapted HAV strain (HAF-203).

Hepatitis A virus↗
PubMed2001

Titration of subcutaneously administered eprinomectin against mature and immature nematodes in cattle.

Eprinomectin has been approved for use as a topically applied endectocide for beef and dairy cattle. To determine if eprinomectin has utility as an injectable anthelmintic, it was titrated at 0.05, 0.1, and 0.2 mg/kg s.c. against adult (Trial 1) and at 0.05, 0.1, 0.14, and 0.2 mg/kg s.c. against immature (Trial 2) stages of lung and gastrointestinal nematodes in cattle. In Trial 1, every dose of subcutaneously delivered eprinomectin showed maximal or near-maximal (> or = 99%) efficacy against Haemonchus placei, Ostertagia ostertagi, Trichostrongylus axei, T colubriformis, Cooperia punctata, Nematodirus helvetianus, Oesophagostomum radiatum, and Dictyocaulus viviparus. Adult C. oncophora was the only exception. However, even against this species, the lowest dose of 0.05 mg/kg showed 93% efficacy, and the efficacious dose necessary to kill 95% (ED95) of adults was 0.056 mg/kg. In Trial 2, every dose of subcutaneously delivered eprinomectin showed maximal or near-maximal (> or = 99%) efficacy against the immature stages of all of the above species of endoparasites. As a result, ED95 values could not be calculated. Consequently, the exquisite potency against endoparasites through parenteral administration suggests that eprinomectin may also have potential utility as an injectable product for cattle.

Age Factors↗
PubMed1963

A titration schedule on a treadmill.

A technique is presented utilizing a titration schedule to measure performance decrement as a function of continuing heavy muscular exertion. A treadmill is equipped with a reversible motor controlling the velocity control of the treadmill itself. This provides a constant acceleration of the treadmill unless a subject-controlled, spring loaded switch is depressed. If this switch is depressed, the treadmill decelerates at a constant rate. A subject is instructed to walk at maximum rate at all times, controlling the velocity of the treadmill with the switch. A performance record is obtained from a tachometer-generator on the treadmill delivering current to a recorder.

Journal Article↗