Units of measure in clinical information systems.
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The authors surveyed existing standard codes for units of measures, such as ISO 2955, ANSI X3.50, and Health Level 7's ISO+. Because these standards specify only the character representation of units, the authors developed a semantic model for units based on dimensional analysis. Through this model, conversion between units and calculations with dimensioned quantities become as simple as calculating with numbers. All atomic symbols for prefixes and units are defined in one small table. Huge permutated conversion tables are not required. This method is also simple enough to be widely implementable in today's information systems. To promote the application of the method the authors provide an open-source implementation of this method in JAVA. All existing code standards for units, however, are incomplete for practical use and require substantial changes to correct their many ambiguities. The authors therefore developed a code for units that is much more complete and free from ambiguities. (+info)
Unit conversion as a source of misclassification in US birthweight data.
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OBJECTIVES: This study explains why frequency polygons for US birthweights in 100-g weight classes appear spiky compared with their European counterparts. METHODS: A probability model is used to describe how unit conversion can induce misclassification. Birthweights from the United States and Norway are used to illustrate that misclassification operates in grouped US data. RESULTS: Spikiness represents misclassification that arises when measured birthweights are rounded to the nearer ounce, converted to grams, and then grouped into weight classes. Misclassification is ameliorated, not eliminated, with 200-g weight classes. CONCLUSIONS: Possible biases from misclassification should be carefully evaluated when fitting statistical models to grouped US birthweights. (+info)
Sizes of components in frog skeletal muscle measured by methods of stereology.
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Stereological techniques of point and intersection counting were used to measure morphological parameters from light and electron micrographs of frog skeletal muscle. Results for sartorius muscle are as follows: myofibrils comprise 83% of fiber volume; their surface to volume ratio is 3.8 mum-1. Mitochondria comprise 1.6% of fiber volume. Transverse tubules comprise 0.32% of fiber volume, and their surface area per volume of fiber is 0.22 mum-1. Terminal cisternae of the sarcoplasmic reticulum comprise 4.1% of fiber volume; their surface area per volume of fiber is 0.54 mum-1. Longitudinal sarcoplasmic reticullum comprises 5.0% of fiber volume, and its surface area per volume of fiber is 1.48 mum-1. Longitudinal bridges between terminal cisternae on either side of a Z disk were observed infrequently; they make up only 0.035% of fiber volume and their surface area per volume of fiber is 0.009 mum-1. T-SR junction occurs over 67% of the surface of transverse tubules and over 27% of the surface of terminal cisternae. The surface to volume ratio of the caveolae is 48 mum-1; caveolae may increase the sarcolemmal surface area by 47%. Essentially the same results were obtained from semitendinosus fibers. (+info)
The tortuous road to the adoption of katal for the expression of catalytic activity by the General Conference on Weights and Measures.
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BACKGROUND: The "unit" for "enzymic activity" (U = 1 micromol/min) was recommended by the International Union of Biochemistry and Molecular Biology (IUB) in 1961 and is widely used in medical laboratory reports. The general trend in metrology, however, is toward global standardization through defining units coherent with the International System of Units (SI). APPROACH: Several proposals were advanced from the IFCC, International Union of Pure and Applied Chemistry, and IUB regarding the definition for enzymic activity as well as the terms for kind-of-quantity, units, symbol, and dimension. In 1977, international agreement was reached between these bodies and WHO that "catalytic activity" (z), of a catalyst in a given system is defined by the rate of conversion in a measuring system (in mol/s) and expressed in "katal" (symbol, kat; equal to 1 mol/s). The katal is invariant of the measurement procedure, but the numerical quantity value is not. Gaining support for the katal from the final arbiter, the General Conference on Weights and Measures, was slow, but Resolution 12 of 1999 adopted the katal (symbol, kat) as a special name and symbol for the SI-derived unit, mol/s, used in measuring catalytic activity. CONCLUSIONS: Laboratory results for amounts of catalysts, including enzymes, measured by their catalytic activity can now officially be expressed in katals and are traceable to the SI provided that the specified indicator reaction reflects first-order kinetics. The conversion from "unit" is: 1 U = 16.667 x 10(-9) kat. Further derived quantities have coherent units such as kat/L, kat/kg, and kat/kat = 1. (+info)
Positron ranges obtained from biomedically important positron-emitting radionuclides.
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Positron ranges were obtained experimentally for several nuclides used in scintigraphic imaging. The nuclides examined were 13C, 13N, 15O, 18F, 68Ga, and 82Rb. The results are discussed with respect to the ultimate spatial resolution obrained in a scintigraphic image. (+info)
A randomized trial of assessment of efficacy of leukapheresis volumes, 8 liters vs 12 liters.
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It is logical to expect that large-volume leukapheresis may be able to collect adequate numbers of PBSC with fewer procedures. To date, there is no agreement on the optimal volume of leukapheresis. Therefore, in this study we compared 8 l volume with 12 l and assessed whether a 50% increase in the blood volume processed would decrease the number of leukaphereses each patient needed to collect > or =2.5 x 10(6) CD34(+) cells/kg in normal mobilizers. PBSC mobilization was done with cyclophosphamide etoposide followed by rhG-CSF in all patients. Forty patients were randomized to undergo 8 l leukaphereses (n = 20 patients) or 12 l leukaphereses (n = 20). The median numbers of leukaphereses required in order to collect > or =2.5 x 10(6) CD34(+) cells/kg in patients processed with 8 l and 12 l were 1 (range 1-5) and 1 (1-4), respectively (P = 0.50). The median number of total nucleated cells (TNC) collected per patient was greater for the 12 l group (7.47 x 10(8)/kg vs 3.90 x 10(8)/kg, P < 0.001), as was the median number of total mononuclear cells (TMNC) (4.26 x 10(8)/kg vs 2.16 x 10(8)/kg, P < 0.001), whereas there was no difference between the two groups for the median number of CD34(+)cells collected per patient (8.94 x 10(6)/kg vs 8.60 x 10(6)/kg, P = 0.85). The TNCs and TMNCs collected per leukapheresis were again greater for the 12 l group (3.64 x 10(8)/kg vs 1.91 x 10(8)/kg, P = 0.001 and 2.17 x 10(8)/kg vs 0.88 x 10(8)/kg, P < 0.001), whereas there was no difference between the two groups for the median number of CD34(+) cells collected per leukapheresis (3.98 x 10(6)/kg vs 3.26 x 10(6)/kg, P = 0.90). This study showed that there is no difference between 8 l and 12 l volumes in regard to collected CD34(+) cells/kg and also the use of a 12 l leukapheresis volume did not decrease the number of leukaphereses performed compared with a 8 l leukapheresis volume. In fact, the use of the larger leukapheresis volume had the disadvantage of adding 60 min to the time the patient was on the machine. (+info)
Ultrasound biomicroscopic dimensions of the anterior chamber in angle-closure glaucoma patients.
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In order to evaluate the morphologic types of appositional angle-closure glaucoma, biometric measurements were made in angle-closure glaucoma patients using Ultrasound biomicroscopy (UBM). Twenty-six patients with primary angle-closure glaucoma and 21 cataract patients with as a control group were examined. The angle-closure glaucomatous eyes were classified as type B in which the angle closure started at the bottom of the angle and type S in which the angle closure occurred in the vicinity of Schwalbe's line. The trabecular-ciliary process distance (TCPD, type B; 873.20+/-86.77 microm, type S; 832.52+/-82.96 microm, control; 1233.50+/-73.01 microm, p = 0.000) and the angle opening distance (AOD500, type B; 89.75+/-63.27 microm, type S; 88.85+/-72.95 microm, control; 304.40+/-104.30 microm, p = 0.000) were significantly shorter in patients with angle closure vice control group. No significant difference were noted in the three groups of patients in regards to iris thickness or ciliary process-iris angle. In this study, we have demonstrated that there are two types of appositional angle-closure and have shown the forward rotation of the ciliary process without changes of the ciliary process-iris angle in cases of angle-closure glaucoma. (+info)
Interocular comparison of nerve fiber layer thickness and its relation with optic disc size in normal subjects.
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We conducted an investigation of the relation between RNFL thickness and optic disc size along with an interocular comparison of optic disc size, RNFL thickness, and RNFL density in healthy subjects. A total of 64 normal eyes from 32 Korean volunteers were enrolled in this study. A GDx Nerve Fiber Analyzer with software version 2.0.09 was used to image all subjects. Optic disc size was measured by pi x (horizontal radius) x (vertical radius). The RNFL density of each quadrant was calculated by dividing each quadrant integral by the total integral. Optic disc size was positively correlated with the total RNFL thickness (r = 0.615, p < 0.01). Optic disc size and RNFL density were inversely related in the superior quadrant (r = -0.248, p < 0.05). There was a significant positive correlation between optic disc size and RNFL density in the nasal quadrant (r = 0.439, p < 0.01) and the temporal quadrant to a certain degree. A significant positive correlation was found between the right and left eyes in terms of total RNFL thickness in and that of each quadrant. Interocular RNFL density was positively correlated in both the temporal and nasal quadrants. These findings must be considered when one evaluates and compares RNFL measurements between two eyes as is often the case where both eyes are usually affected in the course of glaucomatous RNFL damage. (+info)