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At least 19 recordsLinked to original sources
PubMed2004

Comparison of conventional nighttime with automatic or manual daytime CPAP titration in unselected sleep apnea patients: study of the usefulness of daytime titration studies.

Daytime CPAP titration studies with full polysomnography have been successfully performed in patients with severe sleep apnea-hypopnea syndrome (SAHS). The implementation of daytime studies in unselected SAHS patients could help to reduce the waiting lists for CPAP titrations. The main purpose of this study was to compare the effectiveness of conventional versus manual or automatic daytime CPAP titration in unselected patients with SAHS. Ninety-three consecutive patients with SAHS in whom CPAP was indicated were assigned to conventional titration or to manual or automatic (AutoSet) daytime CPAP titration, after sleep deprivation. The number of valid studies, sleep architecture, final pressure selected and mean pressure in the different sleep stages were compared. Changes in sleepiness (Epworth sleepiness score) and hours of CPAP use were assessed after 3 months of treatment. Four patients did not sleep (3 AutoSet, 1 conventional daytime groups). Sleep latency was shorter during automatic daytime titration whereas REM latency was shorter in daytime studies; the percentage of sleep stages was similar during all types of titration. CPAP requirements were significantly higher during REM sleep in conventional and manual daytime titrations while mean pressure was unchanged throughout sleep stages during AutoSet titration. CPAP pressure selected with conventional or daytime manual titration (7.5(2.2) cm H2O and 7.4(1.5) cm H2O, ns) were significantly lower (P< 0.001) than with AutoSet (9.4(1.6) cm H20. All groups showed similar decrease of sleepiness and hours of use of CPAP at 3 months of follow-up. Automatic and manual daytime PSG studies after sleep deprivation are useful for CPAP titration in unselected patients with SAHS. Pressure selected with AutoSet is significantly higher than with conventional daytime or nighttime titration, although not significant in terms of treatment compliance and symptom improvement.

Adult↗
PubMed2002

Practice parameters for the use of auto-titrating continuous positive airway pressure devices for titrating pressures and treating adult patients with obstructive sleep apnea syndrome. An American Academy of Sleep Medicine report.

Continuous positive airway pressure (CPAP) is used to treat patients with the obstructive sleep apnea syndrome (OSAS). The current standard is for an attendant technician to titrate CPAP during full polysomnography to obtain a fixed single pressure. The patient uses CPAP nightly at this fixed single pressure. Recently, devices using new technology that automatically titrate positive airway pressure (APAP) have become available. Such devices continually adjust pressure, as needed, to maintain airway patency (APAP titration). These adjustments can be made with or without attendant technician intervention. Data obtained during APAP titration can be used to provide a fixed single pressure for subsequent treatment. Alternatively, APAP devices can be used in self-adjusting mode for treatment (APAP treatment). A task force of the Standards of Practice Committee of the American Academy of Sleep Medicine reviewed the available literature. Based on this review, the Standards of Practice Committee developed these practice parameters as a guide to the appropriate use of APAP. Recommendations are as follows: 1) A diagnosis of OSAS must be established by an acceptable method. 2) APAP titration and APAP treatment are not currently recommended for patients with congestive heart failure, significant lung disease (e.g., chronic obstructive pulmonary disease), daytime hypoxemia and respiratory failure from any cause, or prominent nocturnal desaturation other than from OSA (e.g., obesity hypoventilation syndrome). In addition, patients who do not snore (either due to palate surgery or naturally) should not be titrated with an APAP device that relies on vibration or sound in the device's algorithm. 3) APAP devices are not currently recommended for split-night studies since none of the reviewed research studies examined this issue. 4) Certain APAP devices may be used during attended titration to identify by polysomnography a single pressure for use with standard CPAP for treatment of OSA. 5) Once an initial successful attended CPAP or APAP titration has been determined by polysomnography, certain APAP devices may be used in the self-adjusting mode for unattended treatment of patients with OSA. 6) Use of unattended APAP to either initially determine pressures for fixed CPAP or for self-adjusting APAP treatment in CPAP naïve patients is not currently established. 7) Patients being treated with fixed CPAP on the basis of APAP titration or being treated with APAP must be followed to determine treatment effectiveness and safety, and 8) a re-evaluation and, if necessary, a standard attended CPAP titration should be performed if symptoms do not resolve or the CPAP or APAP treatment otherwise appears to lack efficacy.

Equipment Design↗
PubMed2005

Titration of the bacteriorhodopsin Schiff base involves titration of an additional protein residue.

The retinal protein protonated Schiff base linkage plays a key role in the function of bacteriorhodopsin (bR) as a light-driven proton pump. In the unphotolyzed pigment, the Schiff base (SB) is titrated with a pK(a) of approximately 13, but following light absorption, it experiences a decrease in the pK(a) and undergoes several alterations, including a deprotonation process. We have studied the SB titration using retinal analogues which have intrinsically lower pK(a)'s which allow for SB titrations over a much lower pH range. We found that above pH 9 the channel for the SB titration is perturbed, and the titration rate is considerably reduced. On the basis of studies with several mutants, it is suggested that the protonation state of residue Glu204 is responsible for the channel perturbation. We suggest that above pH 12 a channel for the SB titration is restored probably due to titration of an additional protein residue. The observations may imply that during the bR photocycle and M photointermediate formation the rate of Schiff base protonation from the bulk is decreased. This rate decrease may be due to the deprotonation process of the "proton-releasing complex" which includes Glu204. In contrast, during the lifetime of the O intermediate, the protonated SB is exposed to the bulk. Possible implications for the switch mechanism, and the directionality of the proton movement, are discussed.

Amino Acid Substitution↗
PubMed1985

Generalized theory for two-phase ion-pair and complexometric titrations. II. Two-phase titrations with side reactions.

For the two-phase titration based on ion-pair and metal-complex formation full attention is given to side reactions in both phases. Their significance for the applicability of this type of titration is evaluated. Side reactions in the aqueous phase diminish and in the organic phase promote the 'titratability'. Equations for the calculation of the side reaction coefficients, the titration curve and the selection of the optimal pH and minimal side reaction interference (in the aqueous phase) are presented. Finally a full description is given of the two-phase titration including all parameters determining the 'titratability'. The merits of the developed theory are illustrated by literature examples.

Chemical Phenomena↗
PubMed1992

Electrochemical titration of the cytochrome hemes in the Rhodopseudomonas viridis reaction center. Cyclic equilibrium titrations yield midpoint potentials without evidence for heme cooperativity.

The redox and spectral characteristics of the 4-heme cytochrome c unit of the photochemical reaction center from Rhodopseudomonas viridis were studied by a combination of protein electrochemistry and spectroscopy using an ultra thin-layer spectroelectrochemical cell. Quantitative and reversible reduction of the high-potential and the low-potential hemes was performed in cyclic titrations to record the optical difference spectra in the alpha-band region. The titration of the absorbance from the high-potential hemes can be approximated with a sum of 2 Nernst functions with Em = 0.113 V and Em = 0.175 V. The corresponding titration of the absorbance from the low-potential hemes yielded Em = -0.257 V and Em = -0.175 V (all potentials quoted vs. Ag/AgC1/3 M KCl; add 0.208 V for potentials vs. standard hydrogen electrode). The high-potential hemes equilibrate rapidly and titrate identically for oxidative and reductive titrations. Under identical conditions, the low-potential hemes exhibit a hysteresis, thus indicating much slower equilibration with the applied potential. Cyclic titrations with increasing equilibration periods, however, indicate the disappearance of the hysteresis for equilibration periods approximately twice as long as for the high-potential hemes. We take this as evidence for a slower internal equilibration, but against a cooperativity of the low-potential hemes as observed for other multi-heme cytochromes.

Cytochrome c Group↗
PubMed1995

Microculture virus titration--a simple colourimetric assay for influenza virus titration.

Influenza antigens can be detected by several well established methods. However, when it is important to determine the titre of infective virions, a bioassay should be employed. The standard and the most widely used tests for influenza infectivity are titration carried out in embryonated hen eggs, or the plaque assay employing tissue culture techniques. A simple colourimetric assay for influenza virus detection and titration is described. Samples of allantoic fluid or mice lung homogenates were used to infect MDCK cultures in microplate wells. After an incubation period, the tetrazolium (MTT) colourimetric assay was used to determine cell viability, and when compared to untreated culture control enabled the detection and titration of several influenza strains. When samples were assayed simultaneously in embryonated eggs and by the MCVT method, good correlation in determined titres was obtained. The availability of an additional method for influenza titration allows more flexibility in the choice of titration method according to the specific needs of the study. Furthermore, this method lends itself to full automatization. Similar procedures should also be applicable to titration of other cytopathic viruses.

Animals↗
PubMed2004

Long-range nature of the interactions between titratable groups in Bacillus agaradhaerens family 11 xylanase: pH titration of B. agaradhaerens xylanase.

Xylanase from Bacillus agaradhaerens belongs to a large group of glycosyl hydrolases which catalyze the degradation of xylan. The protonation behavior of titratable groups of the uniformly (15)N- and (13)C-labeled xylanase was investigated by multinuclear NMR spectroscopy. A total of 224 chemical shift titration curves corresponding to (1)H, (13)C, and (15)N resonances revealed pK(a) values for all aspartic and glutamic acid residues, as well as for the C-terminal carboxylate and histidine residues. Most of the titratable groups exhibit a complex titration behavior, which is most likely due to the mutual interactions with other neighboring groups or due to an unusual local microenvironment. Subsite -1 containing the catalytic dyad shows a long-range interaction over 9 A with Asp21 via two hydrogen bonds with Asn45 as the mediator. This result illuminates the pivotal role of the conserved position 45 among family 11 endoxylanases, determining an alkaline pH optimum by asparagine residues or an acidic pH optimum by an aspartate. The asymmetric interactions of neighboring tryptophan side chains with respect to the catalytic dyad can be comprehended as a result of hydrogen bonding and aromatic stacking. Most of the chemical shift-pH profiles of the backbone amides exhibit biphasic behavior with two distinct inflection points, which correspond to the pK(a) values of the nearby acidic side chains. However, the alternation of both positive and negative slopes of individual amide titration curves is interpreted as a consequence of a simultaneous reorganization of side chain conformational space at pH approximately 6 and/or an overall change in the hydrogen network in the substrate binding cleft.

Aspartic Acid↗
PubMed1997

pH titration of native and unfolded beta-trypsin: evaluation of the delta delta G0 titration and the carboxyl pK values.

The stabilizing free energy of beta-trypsin was determined by hydrogen ion titration. In the pH range from 3.0 to 7.0, the change in free energy difference for the stabilization of the native protein relative to the unfolded one (delta delta G0 titration) was 9.51 +/- 0.06 kcal/mol. An isoelectric point of 10.0 was determined, allowing us to calculate the Tanford and Kirkwood electrostatic factor w. This factor presented a nonlinear behavior and indicated more than one type of titratable carboxyl groups in beta-trypsin. In fact, one class of carboxyl group with a pK = 3.91 +/- 0.01 and another one with a pK = 4.63 +/- 0.03 were also found by hydrogen ion titration of the protein in the folded state.

Enzyme Stability↗
PubMedDate not supplied

Reliable pKw values from potentiometric titrations: the striking effect of the titration final added volume.

Errors affecting the estimation of the ionic product of water from the potentiometric titration of weak acids have been analysed. A Fortran programme has been developed in order to simulate experimental titration data sets. This programme allows one to isolate experimental error sources and analyse their effect upon the final fitted equilibrium constant. pKw dependence with titration final added volume and the pK value of the weak acid, predicted with the simulation programme are coincident with experimental data, suggesting that obtaining reliable pKw values entails using experimental data of titrations up to a sufficiently large hydroxyl concentration which depends on the value of pK.

Environmental Monitoring↗
PubMed2003

[Large-scale real-time titration of green-fluorescence-protein-marked recombinant retrovirus: comparison with standard titration method].

OBJECTIVE: To compare large-scale real-time titration method (LaSRT) with standard titration method by flow cytometry (FACS) for determining the titers of green-fluorescence-protein (GFP)-marked recombinant retrovirus. METHODS: (1) Standard titration method: NIH3T3 cells were inoculated at 2x10(5) /well in 6-well plate, and after cell culture for 12 h, 0.5 ml, 50 microl and 5 microl GFP-marked recombinant retrovirus (n=3) were respectively used to infect the cells, with the final concentration of polybrene being 8 microg/ml. Forty-eight hours later, the cells were treated with trypsin and assayed for the positive rate of GFP by means of FACS. When the positive rate was lower than 10%, the titer was calculated according to the equation: virus titer (TU/ml) =2x10(5)xGFP positive rate/volume of virus stock solution used. (2) LaSRT method: The cells were inoculated at 5,000 cells/well in a 96-well plate, and after cell culture for 12 h, 90 microl/well complete culture medium was used with 8 microg/ml polybrene and 10% newborn bovine serum, 10 microl virus was added into the first well, and ten-fold dilution of the previous virus-containing solution was performed before the virus was added into the next well (8 wells in each group, altogether 3 groups). Forty-eight hours later, inverted fluorescence microscope was used to observe the fluorescence-positive cells in each well. The virus titer was calculated according to the equation: virus titer (TU/ml) =mx10(n+1), where n is the serial number of the reference well, and m the number of positive cells. (3) LaSRT was used to study the influence of freezing/thawing on the titers of recombinant retroviruses. RESULTS: The virus titer obtained with standard method by FACS was (1.54+/-0.38)x10(6) TU/ml, and that of LaSRT was (1.33+/-0.57)x10(6) TU/ml (P>0.05). After one cycle of freezing/thawing, the virus titer dropped to (18.1+/-9.9)% (n=7). CONCLUSION: LaSRT is more rapid and convenient as well as easier to determine the virus titer compared with standard method, and no significant difference is found between the two titration methods.

Animals↗
PubMed1985

Generalized theory for two-phase ion-pair and complexometric titrations. I. Two-phase titrations without side reactions.

A systematic theoretical treatment of the two-phase titration based on ion-pair and metal-complex formation is presented. Equations for the titration curve, accuracy, equivalence point and choice of the indicator are derived. Much attention is paid to the parameters determining the 'titratability' viz. extraction constant, distribution constant, phase volume ratio and the concentration of the analyte. Special attention is given to the role of intermediate ion-pair and metal-complex formation in the aqueous phase. The ion-pair formation in aqueous solution is examined closer by means of the relationship between the association constant in water, the degree of dissociation of the ion pair (alpha) and the concentration of the counter ion. The merits of this theoretical treatment are illustrated with literature examples.

Chemical Phenomena↗
PubMed2005

Standardization of a neutralizing anti-vaccinia antibodies titration method: an essential step for titration of vaccinia immunoglobulins and smallpox vaccines evaluation.

The possibility of mass population vaccination with smallpox vaccine implies the development of anti-vaccinia immunoglobulins for the treatment of severe side effects following vaccination. We have chosen to develop and validate the "gold standard method" (plaque reduction neutralization assay) to titrate neutralizing anti-vaccinia antibodies in two different French laboratories belonging to the Department of Defense (CRSSA) and to the French Health Products Safety Agency (Afssaps). The results of precision, linearity and accuracy of the method led to consider the method as validated. In parallel, we have prepared and lyophilized a pool of anti-vaccinia plasma samples issued from a unique donor and qualified this preparation versus the first British standard to use it as an in-house standard with a titer of 25 international units (IU). This work will allow to titrate, in IU, sera from vaccinated persons in order (i) to titrate purified anti-vaccinia immunoglobulin preparations for vaccine severe side effect treatments; (ii) to investigate the level of neutralizing antibodies in the general population; and (iii) to investigate clinical trials of new generation smallpox vaccines. In the future, this will allow comparability of studies on either smallpox vaccines or on the serological status of the population.

Animals↗
PubMed1975

Titration of tetanus antitoxin by passive hemagglutination. I. Titration of guinea-pig antitoxins at various periods of immunization.

An improved technique for passive hemagglutination (HA) for titration of tetanus antitoxin was described. The use of highly purified tetanus toxoid and of improved diluent increased the specificity and reproducibility of the test. Several hundreds of specimens of guinea-pig serum taken at various stages of immunization were titrated by HA and toxin neutralization (NT) in mice. The ratio of HA to NT titers varied significantly depending on the immunization stage; higher at early stages and lower at later stages. The high HA/NT ratio was not due to the IgM antitoxin, which is very rare in guinea pigs. The variation in discrepancy between HA and NT titers decreased considerably by grouping the serum specimens with respect to the stage of immunization. Thus, it is possible to predict the in vivo titer of a tetanus antitoxin accurately enough for clinical study. The HA test may be useful as an alternative method for titrating tetanus antitoxin in the field trials. Moreover, it can be used for the study of characteristics of antitoxins.

Animals↗