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At least 145 records · Page 8Linked to original sources
PubMed1983

Sources of error and their correction in the measurement of carbon dioxide elimination using the Siemens-Elema CO2 Analyzer.

The Siemens-Elema CO2 Analyzer 930 allows calculation of carbon dioxide elimination from the instantaneous measurement of expired gas flow (VE) and carbon dioxide fraction (FECO2). VE is measured in the ventilator and FECO2 at the Y-piece. The most important source of error in the measurement of carbon dioxide elimination is rebreathing, which corresponds to about 24 ml of end-expiratory gas per breath with the standard Y-piece and tubing. This problem may be decreased by the use of non-return valves in the Y-piece. Allowance must be made for the effects of intermolecular interaction between carbon dioxide and the carrier gas, as the reading is about 20% greater with nitrous oxide than with oxygen. This problem can be largely circumvented by calibration with appropriate gas mixtures. Errors resulting from analyser delay are small, and are eliminated completely by the inclusion of fast electronic components. Carbon dioxide analysis is linear with air as carrier gas, but slightly alinear with nitrous oxide in oxygen mixtures. This error can be minimized by using calibration gases with a carbon dioxide content close to that of expired gas. The expiratory flow meter is linear if kept in good condition. Variations in temperature and water content of expired gas cause overestimation of mean expired carbon dioxide fraction (FECO2) by a factor of 1.01-1.02. Compressed gas in the tubing causes a small error which may be neglected at normal airway pressures with tubing of low compliance. Carbon dioxide measurement is slightly affected by barometric pressure. During mechanical ventilation of the lungs in 10 patients with air, FECO2 obtained after corrections for known errors agreed well with Scholander analysis of mixed expired gas.

Carbon Dioxide↗
PubMed2004

Variation in scanning line source sensitivity: a significant source of error in simultaneous emission-transmission tomography.

Transmission measurement is recommended in order to accurately correct for attenuation in myocardial single-photon emission tomography (SPET) studies. It is important that transmission studies are artefact-free, otherwise the attenuation-corrected SPET studies may also be affected. An assumption in transmission studies is that the measured transmission in air used as a reference scan is valid for any camera orientation. Variation in transmission source sensitivity (both source efficiency and detector sensitivity) with rotation negates this assumption and can produce errors that result in significant reconstructed artefacts. The aim of this study was to investigate the variation in transmission source sensitivity with a view to defining action thresholds for routine quality control tests. Transmission measurements in air were recorded on two commercial scanning line source installations for the 180 degrees arc normally used in myocardial SPET. Significant variation in transmission source sensitivity was observed on one system (exceeding 30%). Comparison was also made with the reference scan recorded at a different time at a fixed angular location. Both systems demonstrated measurable variation between transmission counts and the corresponding reference scan. A simulation study was undertaken using patient data to determine the influence of transmission sensitivity variation on reconstructed myocardial counts. To maintain reconstructed counts to within 15% of that obtained with artefact-free transmission data, the variation in transmission sensitivity with rotation needed to be within 5%. These results have necessitated the addition of quality control procedures and specific maintenance procedures to attempt rectification of the problem. Variation in transmission source sensitivity with rotation is a potential source of error in attenuation-corrected SPET. Steps should be taken to stabilise transmission source mountings so as to minimise this potential source of error.

Algorithms↗
PubMed1975

[Sources of error in the radioimmunochemical determination of digoxin in serum].

In a study with numerous samples of serum we compared 5 Digoxin RIA and evaluated the reliability of tests by simultaneous determinations. There were found considerable differences in the determinations with the various RIA for the same serum; evident differences also were recorded in the recovery and in the reproducibility of the assays. Among some other sources of error the dependence of temperature and of the duration of the dextran-charcoal separation were observed; therefore, the charcoal incubation is recommendable at 4 degrees C. Each laboratory which is able to perform the determinations of digoxin concentrations in the serum should declare its own range for the therapeutic and toxic levels for the used RIA in collaboration with the clinicians.

Absorption↗
PubMed1987

[Sonographic diagnosis of hip dysplasia. Principles, sources of error and consequences].

Sonography of the hip in infants is being increasingly employed. This method of examination involves several specialist disciplines. The more widespread its use, the greater the likelihood of faulty diagnoses if one is not aware of its weak points. Faulty diagnoses are the order of the day if the method is employed by persons whose knowledge has not been updated to latest advances in the field; other sources of error are faulty scanning, unsuitable sonographic equipment and insufficient documentation. Hence, it is mandatory to describe the demands to be made on the equipment according to update standards and to draw up guidelines that will help to avoid quality loss. The criteria for assessing a hip sonogram are defined and the problem of age limit is considered. A review is given of disturbances of normal development of the hip. The possibility of effecting dynamic examination should not mislead one to neglect assessment of the hip joints as precisely as possible by means of an exacting measurement technique. The weak points of the technique of measurement and the valuation of the angles must be known. A review of the literature reveals many problems in hip sonography. A multitude of these problems is unnecessary and can be considered as solved if one would try to match modern quality demands and not be satisfied with a quality standard that is many years old. To achieve best possible hip examination via sonography it will often be necessary to considerably modify principles of general sonography of the soft parts.

Diagnostic Errors↗
PubMed1997

[Abnormal agglutination by reducing surface charge of red cell membrane as source of error in ABO typing and actual cases of incompatible ABO blood transfusion due to various factors].

T activation of red cells results from the effects of microbial sialidase catalysing the cleavage of sialic acid from red cell membrane. Abnormal agglutination may be induced when human-derived antiA,B antibodies containing antiT are used. By the using of mouse-derived antiA,B monoclonal antibodies this type of polyagglutination as source of error could be overcome. Most common cause of ABO mismatch is due to more simple technical or clerical error resulting in transfusion of the wrong blood to the recipient. Three such cases with non-fatal hemolytic transfusion reaction are described.

Adolescent↗
PubMed2002

Identification of the sources of error in allele frequency estimations from pooled DNA indicates an optimal experimental design.

Genotyping costs still preclude analysis of a comprehensive SNP map in thousands of individual subjects in the search for disease susceptibility loci. Allele frequency estimation in DNA pools from cases and controls offers a partial solution, but variance in these estimates will result in some loss of statistical power. However, there has been no systematic attempt to quantify the several sources of error in previous studies. We report an analysis of the magnitude of variance components of each experimental stage in DNA pooling studies, and find that a design based on the formation of numerous small pools of approximately 50 individuals is superior to the formation of fewer, larger pools and the replication of any of the experimental stages. We conclude that this approach may retain an effective sample size greater than 68% of the true sample size, whilst offering a 60-fold reduction in DNA usage and a greater than 30-fold saving in cost, compared to individual genotyping. The possibility of combining pooling with informed selection of haplotype tag SNPs is also considered. In this way further savings in efficiency may be possible by using pooled allele frequency estimates to infer haplotype frequencies and hence, allele frequencies at untyped markers.

Alleles↗
PubMed1977

[The reaction time as a source of error in threshold audiometry (author's transl)].

An investigation of reaction times at the threshold of hearing is described. 96 subjects were classified into two groups of sensorineural hearing loss utilizing Types I and II Bekesy audiometry, and compared with one normal group as control. The results show that reaction times are largely unaffected by the type of hearing loss and test frequency. Increasing age, however, may result in increasing reaction times. These results and possible sources of error are discussed as effecting an exact threshold audiometry.

Adult↗
PubMed1984

On sources of error in the biochemical study of perilymph (guinea-pig).

Contamination of perilymph with other fluids (cerebrospinal fluid, tissue fluid, blood, endolymph) together with sampling, anaesthesia, surgical intervention or food intake of the animals may considerably affect the analytical result. The numerous possible artefacts seem to be the main reason why varying values are given in the literature for the same chemical component of perilymph. This is also partly true of cerebrospinal fluid and blood. The effect of some sources of error on selected chemical components of perilymph, cerebrospinal fluid and blood is briefly summarized.

Anesthesia↗
PubMedDate not supplied

[The reliability and sources of error in basic clinical documentation--a critical report of experiences].

Since 1. 1. 1985, computer-aided basic medical documentation has been routine at the University Orthopedic Clinic in Friedrichsheim, near Frankfurt. In addition to data on patient's histories, all data needed to satisfy the criteria of the Federal Directive on Operating Cost Rates are gathered. The diagnoses are stored in clear text, in a modified Eichler code, and according to ICD 9. Conversion from the Eichler code to ICD 9 is almost fully automated. In a study covering 100 hospitalized cases the following findings were obtained relating to sources of error and reliability: Without any additional in-house plausibility checks, the rate of error in the ID code, created by coding family name, date of birth, and sex, was 7%. In clear text all diagnoses except one and all forms of therapy were correctly reproduced as contained in the medical report. On the other hand, 7% of the conversions into the Eichler code contained errors. The reason for the difference in the quality of data is pointed out. In some of the other surveys, e.g., of infection rates, the rates of error were very high; most errors had been caused by the ward physicians. Data quality is enhanced by exploitation of routine process data when these control administrative procedures or are used for communication between physicians, since they then become relevant to actions and decisions and hence have to be reliable, regardless of documentation purposes.

Bone Diseases↗
PubMed1983

[Radioimmunoassay and its problems: quality, sources of error and quality control of in vitro procedures for thyroid diagnosis].

A review is made of methodical aspects of the performance of radioimmunoassays with special regard to the determination of T3, T4, TSH and free thyroxine. The quality of the analytical systems is determined by specificity, sensitivity, correctness and accuracy. To ensure quality, guidelines are given for the procedure of obtaining test samples as well as for the transport and storage; furthermore, the dependence of the results on the employed method is documented. For determination of the normal range particular emphasis has to be given to the methodical details, regional differences and the age of the patients. To ensure quality, the most frequent sources of error have to be known. These are listed for the determination of thyroid hormones, TSH, thyroxine-binding globulin, thyroglobulin and for the T3U-test; a critical review of the methods is added. Suggestions are given for the systematic internal control of quality; a method for continuous control by a computer program is presented.

Female↗
PubMed1998

Catheter deadspace: a source of error during tonometry.

Tonometry of PCO2 is a promising method for assessing the oxygen supply to demand ratio of the gastrointestinal mucosa in critically ill patients. A balloon-tipped tonometer is introduced into the stomach or sigmoid colon, and saline is instilled into the balloon. After a time to allow partial equilibration with intraluminal PCO2, saline is aspirated and PCO2 is measured. Intermittent instillation and aspiration of saline allows serial PCO2 measurements, provided correction factors are used to calculate the PCO2 value expected at full equilibration from the PCO2 values measured after short dwell times. The technique is not yet widely applied, partly because of methodological controversies. We evaluated the role of the catheter deadspace as a source of error during PCO2 tonometry. The increase in PCO2 in sigmoid-type tonometers with a normal length (normal tonometer (NT)) and in those with a 50% increase in length and thus deadspace (extended tonometer (ET)), in a saline bath at a PCO2 of 4.8 kPa was assessed. Saline dwell times were 10, 20, 30, 45, 60 and 90 min and the time-dependent PCO2 increase was determined at deadspace PCO2 values of approximately 4.0 and 8.0 kPa following contamination of the catheter deadspace after immersion in saline baths at PCO2 values of 4.8 and 9.6 kPa, respectively, before each measurement cycle. In another experiment, the tonometer was rinsed between measurement cycles to remove deadspace saline containing carbon dioxide and to obviate contamination of instilled saline. PCO2 was measured in a blood-gas analyser, taking into account measurement bias in saline. Failure to remove deadspace saline between measurement cycles resulted in an overestimation of 10% and 6% for the NT and 16% and 10% for the ET, at saline dwell times of 10 and 20 min, respectively, at a deadspace PCO2 of approximately 4.0 kPa. At a deadspace PCO2 of approximately 8.0 kPa, PCO2 was overestimated by 17%, 11% and 5% for the NT and 31%, 20% and 11% for the ET, at dwell times of 10, 20 and 30 min, respectively. Rinsing the NT/ET resulted in accurate assessment of PCO2 at all dwell times, but the dwell time-dependent increase in PCO2 was slightly slower in the ET, particularly at 10 min, after a sink effect of the increased deadspace. Hence, a previously unrecognized deadspace effect caused error during PCO2 tonometry, particularly with short dwell times. This potentially large error can be avoided by rinsing the tonometer before each measurement cycle, allowing accurate PCO2 tonometry even at 10-min saline dwell times, provided that correction factors are used that are specific for catheter size. These findings may help to widen the clinical applicability of tonometry.

Carbon Dioxide↗
PubMed2003

Identification of a potent antibacterial factor isolated from bronchoalveolar lavage fluid: guanidine, N-[3-[(aminoiminomethyl)amino]propyl]-N-dodecyl-, a potential source of error in the analysis of antibacterial agents.

The widespread use of antibiotics in modern society has encouraged the search for new antibacterial compounds. In this laboratory investigations are being made to identify and characterise novel antibacterial peptides. With this in mind, the antibacterial properties of human bronchoalveolar lavage (BAL) fluid from sarcoidosis patients is being investigated. In this communication we report on the identification and characterisation of a highly active non-peptide antibacterial compound isolated from BAL fluid. The structure of this active compound was elucidated by high-resolution accurate mass and tandem mass spectrometry to be guanidine, N-[3-[(aminoiminomethyl)amino]propyl]-N-dodecyl-. This compound does not appear to be endogenous, and its presence in BAL fluid extracts presents a potential source of error in analysis of antibacterial agents. The biological effects of guanidine, N-[3-[(aminoiminomethyl)amino]propyl]-N-dodecyl- have not previously been described in the literature.

Anti-Bacterial Agents↗
PubMed1986

Heterophilic antibody as a source of error in immunoassay.

We describe our experience with a young woman believed to be hypothyroid and menopausal because of erroneously elevated TSH, LH, and FSH estimates. These errors were found to be due to the presence of antibodies to rabbit IgG in the patient's blood. We found that antibody-limited assays for TSH, LH, and FSH using antisera raised in rabbits were affected by this problem unless rabbit IgG was included, whereas antibody-excess assays were not. These problems were most simply detected by observing inappropriate results when measurements were made in dilutions of the patient's serum. The presence of endogenous antibody directed against antibodies used in immunoassays is a significant potential source of error requiring awareness on the part of both the clinician caring for such patients and the clinical laboratory making the measurements.

Adult↗
PubMed1999

Sources of errors in the quantitative analysis of food carotenoids by HPLC.

Several factors render carotenoid determination inherently difficult. Thus, in spite of advances in analytical instrumentation, discrepancies in quantitative results on carotenoids can be encountered in the international literature. A good part of the errors comes from the pre-chromatographic steps such as: sampling scheme that does not yield samples representative of the food lots under investigation; sample preparation which does not maintain representativity and guarantee homogeneity of the analytical sample; incomplete extraction; physical losses of carotenoids during the various steps, especially during partition or washing and by adsorption to glass walls of containers; isomerization and oxidation of carotenoids during analysis. On the other hand, although currently considered the method of choice for carotenoids, high performance liquid chromatography (HPLC) is subject to various sources of errors, such as: incompatibility of the injection solvent and the mobile phase, resulting in distorted or split peaks; erroneous identification; unavailability, impurity and instability of carotenoid standards; quantification of highly overlapping peaks; low recovery from the HPLC column; errors in the preparation of standard solutions and in the calibration procedure; calculation errors. Illustrations of the possible errors in the quantification of carotenoids by HPLC are presented.

Carotenoids↗
PubMed1998

Demonstration of a possible source of error with an electric pulp tester.

The purpose of this study was to determine whether electrical current can travel between adjacent teeth through contacting interproximal amalgam restorations. Twenty-two extracted human premolars were restored with class II amalgam restorations. They were then mounted in pairs in self-curing resin, simulating adjacent teeth. Only their restorations were allowed to contact. An electrical multimeter was used to supply electrical current and to measure any current passing through the mounted teeth. One current measurement was made from the buccal enamel of a tooth to the occlusal surface of the filling in that tooth. A second measurement was made from the buccal enamel of the same tooth to the occlusal surface of the adjacent filling. These two measurements were made for all 11 trials. Statistically, all current that entered the first tooth passed to the adjacent tooth. This finding suggests a potential source of error when using an electric pulp tester.

Bicuspid↗
PubMed1996

Sources of error in estimation of laryngeal airway resistance in persons with spasmodic dysphonia.

Estimation of laryngeal airway resistance is a noninvasive method that has proven useful in the study of people with normal and some types of disordered voices. We were interested in examining more closely the application of this method to persons with spasmodic dysphonia (SD), a voice disorder sometimes associated with fluctuating airflow. We speculated unstable airflow could affect the estimation of subglottal pressure and laryngeal airway resistance. Oral pressure and airflow were collected from 10 subjects with SD and 10 control subjects during repetition of /pi/. The coefficient of variation (COV) of airflow during vowel production was calculated to quantify stability of airflow. The results indicated that although some SD subjects produced steady flows during the syllable repetition task, others exhibited substantially varying flows. Inability on the part of the subject to attain steady flows could compromise the usefulness of a midpoint measure of airflow and/or estimation of subglottal pressure, resulting in sources of error in estimation of laryngeal airway resistance. As a result, of the 10 subjects with SD in this study, laryngeal airway resistance could not be estimated in 6 subjects with unsteady flows. Laryngeal airway resistance was estimated in 4 SD subjects who produced steady airflow. Two of these subjects exhibited high laryngeal airway resistance; the others exhibited normal laryngeal airway resistance.

Adult↗
PubMed2002

Biliary and total extrarenal clearance of inulin and iohexol in pigs. A source of error when determining gfr as body clearance.

Biliary clearance, total extrarenal clearance, body and renal clearance of inulin and iohexol were determined in 11 normal and 11 nephrectomized pigs. The biliary clearance of inulin, calculated as biliary excretion divided by the plasma concentration, was 0.04 and 0.01 ml min(-1) 10 kg(-1) and of iohexol 0.21 and 0.1 ml min(-1) 10 kg(-1), in normal, respectively, nephrectomized pigs (p < 0.05). The extrarenal clearance of inulin, calculated as body minus renal clearance, was 2.7 and 0.7 ml min(-1) 10 kg(-1) and of iohexol 3.7 and 0.7 ml min(-1) 10 kg(-1) in normal, respectively, nephrectomized pigs (p < 0.05). Some hours after injection of the markers their plasma concentrations were much higher in the nephrectomized pigs. This higher plasma concentration was not matched by an equally higher biliary excretion and therefore biliary clearance decreased. The smaller total extrarenal clearance in nephrectomized pigs, i.e. the overestimation of GFR when calculated as body clearance, indicates that this source of error decreases with decreasing renal function.

Animals↗
PubMed2001

Variability in doses obtained from a multi-dose ophthalmic solution: a potential source of error in the assessment of compliance.

BACKGROUND: Assessment of compliance with prescribed therapy is an important aspect of patient management that can be overlooked. Compliance with topical ophthalmic medications is frequently assessed without knowledge of doses obtained per bottle. METHOD: Thirty-three normal subjects who agreed to participate were asked to instill one drop of Refresh Tears in each eye twice daily until a 3-ml bottle was empty. Each subject was also asked to record the date and time of each drop instillation using a calendar log sheet. On enrollment, the subjects were required to demonstrate proper drop instillation technique. With the use of the log sheets, doses obtained and administrations missed by each subject were tabulated. The 'expected count' per bottle was determined by counting the drops in Refresh Tears under laboratory conditions. RESULTS: Of the 26 subjects, who completed the study, the mean (SD) number of doses reportedly obtained was 63.7 +/- 17.1 (range = 26 to 110). The mean number of drops counted per bottle was 63.5 +/- 1.0 (range = 62 to 65). CONCLUSIONS: The range of doses reportedly obtained per bottle was quite large. This variability could represent a significant source of error if patient compliance is assessed by how long a bottle lasts.

Adolescent↗