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At least 253 records · Page 14Linked to original sources
PubMed1990

Inhomogeneous deformation as a source of error in strain measurements derived from implanted markers in the canine left ventricle.

This article quantifies the errors inherent in the measurement of myocardial strain in the canine left ventricle when the motion of four radiopaque marker beads is used to determine this strain. These errors are introduced because the strain is strongly inhomogeneous and only an averaged value of this strain can be determined by measuring the displacements of four points with finite separation. In this work, the error in the principal strains has been estimated by modeling the primary deformation components of the left ventricle and comparing the true strains obtained from these models with the strains computed according to the protocol typically used in experimental studies to determine strain from the motion of marker beads. Both a cylindrical and a spherical model of the left ventricle are used. For the cylindrical model, it is found that the traditional tetrahedra used may give errors as high as 20% in the maximum principal strain. A six-marker prism is found to give more consistent results, underestimating the maximum principal strain, which is in the radial direction, by no more than 8% in almost all cases. The spherical model, having double curvature, gives larger errors. In both models, the error in the other two principal strains was usually less than 5%. Furthermore, the principal strain directions were correct to within 6 degrees.

Animals↗
PubMed1987

Sources of error in measurement of children's blood pressure in a large epidemiologic study: Bogalusa Heart Study.

Accurate and reliable measurement of blood pressure is essential in the determination of early hypertensive disease. Multiple blood pressure measures were determined by well trained field observers on a large number of children representing a total pediatric community. Changes in children's blood pressure levels with multiple measurements, as well as differences between field observers, were examined. A random effects analysis of variance model was used to determine specific contributors to blood pressure variability in an epidemiologic survey of children. Observer differences were found to be the largest preventable contributor to blood pressure variation. In addition, systolic blood pressure levels decreased approx. 2.5 mmHg from the first to the third blood pressure station. More than 86% of systolic blood pressure readings and 90% of diastolic blood pressure readings by two different observers on the same child were within 15 mmHg. These data emphasize the importance of both adequate training of field observers and the use of replicate blood pressure measurements by multiple observers to determine blood pressure levels accurately in an epidemiologic survey.

Adolescent↗
PubMed1975

Disturbance of hapten-antibody equilibria by ammonium sulphate solutions. A source of error in antibody affinity determinations.

The affinity of anti-hapten antibody can be conveniently measured by precipitating immune complexes with ammonium sulphate. The method has, however, not proved very reproducible. Here is described one variable difficult to control in the assay: the ammonium sulphate was found to cause dissociation of ligands from hapten (NIP)--antibody complexes. The reason was the volume increase caused by addition of ammonium sulphate. The study suggested that in the calculation of the free hapten concentration the final volume during precipitation should be used. The precipitate should not be washed when hapten binding capacities are measured.

Ammonium Sulfate↗
PubMed1980

A source of error in equilibrium dialysis.

Equilibrium dialysis is often used to study the binding of steroids to proteins. With this technique it is customary to determine the percent bound and unbound steroid in the sample, the affinity constant for the steroid-protein binding reaction, and the concentration of binding sites on the protein. Investigators have used many different ratios of dialysis buffer to sample volumes in their experiments assuming that the equilibrium in the post-dialysis sample was the same as existed before dialysis. Chemical equilibrium expressions for the system before and after dialysis indicate that during dialysis the concentration of steroid in the sample decreases resulting in a new equilibrium in which the percent bound and unbound are different from the original sample. The magnitude of the difference between the pre- and post-dialysis systems is proportional to the ratio of dialysis buffer to sample volumes. Accurate values for the affinity constant and binding site can be obtained only if this change in the equilibrium is considered.

Carrier Proteins↗
PubMed1992

Methodologic sources of errors in image and flow cytometric DNA assessments of the malignancy potential of prostatic carcinoma.

Considerable controversy exists about the value of using cytometric assessments of nuclear DNA ploidy patterns from neoplastic parenchymal cells of prostatic carcinomas as a supplement to conventional clinicopathologic data in an assessment of malignancy potential in neoplastic disease. To a great extent, the controversy is of methodologic origin. By revealing common pitfalls in this kind of DNA cytometry and by suggesting means to avoid or at least to reduce them, a realistic assessment can ultimately be made of the prognostic values of this technique: (1) the results of DNA assessments using flow cytometry and image cytometry should be combined (advantages and disadvantages with the two techniques outbalance each other); (2) the cytometric DNA ploidy pattern must always be correlated with results of histopathologic assessments and clinical data; (3) a standardization of DNA histograms obtained by means of both flow DNA cytometry and image DNA cytometry must be made with precise definitions of "diploidy," "tetraploidy," and "aneuploidy"; (4) the subjective component in classifying DNA histograms can be reduced by means of a computerized evaluation technique; (5) the degree of intratumoral variation in DNA ploidy patterns of neoplastic cell nuclei must be established by means of assessments of multiple biopsy specimens from widely different parts of a carcinoma; and (6) foci of a previously poor recognized neuroendocrine phenotype of neoplastic parenchymal cells are ubiquitous in prostatic carcinomas, particularly in anaplastic adenocarcinomas. Today, the DNA ploidy pattern of this phenotype can be assessed by means of a new image DNA cytometry technique.

DNA, Neoplasm↗
PubMed1982

Catheter as source of error in urodynamic study.

The effect of introducing a fine catheter on the urethral wall was studied by electromyography in rabbits. On introducing the catheter, increased electrical activity in the form of biphasic potentials was recorded from the external sphincter and bladder neck. This indicates active muscular contraction of these regions. The biphasic potentials persisted for about four minutes and then became less frequent and lower in voltage until they disappeared completely after fourteen minutes. We conclude that in urodynamic studies one must wait for at least fifteen minutes after catheter introduction before recording the results.

Animals↗
PubMed1994

Sources of errors in different single-electrode voltage-clamp techniques: a computer simulation study.

The use of voltage clamp with a single electrode has been useful in estimating kinetic parameters for a number of ionic whole-cell currents. There are two main types of such a technique: discontinuous voltage clamp (dSEVC) (Brennecke and Lindemann, 1974), and continuous voltage clamp (cSEVC) (Hamill et al., 1981). We have studied, by means of computer simulations, the performance of both types of clamp on estimating activation kinetics parameters of a typical neuronal Ca2+ current. Deviations from the theoretical values are shown to be sensitive on both set-up and cell properties. Both types of clamp are shown to lose voltage control when either access resistance or absolute membrane conductance are increased. In contrast, changes in membrane capacitance affect differently to the estimates obtained by the two types of clamp. Cell size is also shown to affect cSEVC performance but not that of dSEVC. The nature and magnitude of errors obtained by using both types of clamp in different situations are discussed.

Amplifiers, Electronic↗
PubMed1984

Sources of error in the registration of oral cancer.

The names of 102 patients with histologically confirmed squamous cell carcinoma of the oral cavity were checked against Cancer Registry data for the Trent Region. The study was carried out to determine the accuracy of site recording and the failure rate of registration. Although 94 of the patients were registered, 38 per cent of these were incorrectly coded with respect to site. The way in which such errors may occur is discussed and the procedure for registration of oral cancer is explained.

Carcinoma, Squamous Cell↗