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133 records · Page 8Linked to original sources
PubMed1989

Indexes to the reassociation and stability of solution DNA hybrids.

The computation, assumptions, and properties of DNA-hybrid stability and reassociation indexes were reviewed. Different methods of computing the same index typically yielded similar values. However, because dissociation curves change from asymmetric to symmetric as increasingly divergent DNAs are compared, adequate determination of mode required fitting a complex function. Delta Tm, delta mode, and delta T50H correlated well up to ca. 12, and all were found to be useful indexes of genomic similarity in that range. They also exhibited similar levels of error, even though T50H comprises a percent reassociation component with relatively large variance. At greater distances, the delta Tm scale became markedly compressed because of the boundary imposed by the temperature of hybrid formation (incubation temperature). Though not compressed or technically limited by it, delta mode and delta T50H could not be extrapolated with certainty below the incubation temperature. Among theoretical problems discussed: Tm and mode index an increasingly small percentage of the genome as the extent of reassociation decreases, and they may compare different genomic segments as DNAs become highly diverged. T50H relies upon the assumptions that all sequences evolve at a constant rate and that reassociation behavior is the same among all sequences regardless of their extent of divergence. Tm and T50H may be biased by self-hybridization of repetitive elements or cross-hybridization of paralogous sequences. Delta mode is free of such biases as long as the genomes under comparison are not too diverged. No index was found to be best in all circumstances.

Algorithms↗
PubMed1991

Classification of vertebral fractures.

Although it is a cardinal feature of involutional osteoporosis, there is often disagreement on what constitutes a vertebral fracture. We measured vertebrae T4-L5 in 52 healthy women to develop a normal range (mean +/- 3 SD) for vertebral shape and used these data to assess the prevalence of vertebral fractures. We classified vertebral fractures by type of deformity (wedge, biconcavity, or compression) and further by the degree of deformity (grades 1 and 2). In 195 postmenopausal women who were an age-stratified random sample of the Rochester population (ages 47-94), 40 (21%) had vertebral fractures (mean, 2 per person). There was a similar number of compression and wedge fractures, and grade 2 fractures were as common as grade 1. In a referral sample of 74 women with suspected osteoporosis, 62 (84%) had vertebral fractures (mean, 3.3 per person). Wedge fractures were most common, and grade 2 fractures were more common than grade 1. The distribution of type and grade of fractures differed between the two patient groups (P less than 0.01). Bone mineral density of the lumbar spine was related to mean fracture grade (r = -0.33, P less than 0.05) and to fracture number (r = -0.57, P less than 0.001) but not to fracture type. We conclude that a comprehensive approach is required in describing vertebral fractures. Using this approach we found distortion in the fracture characteristics of women referred to an osteoporosis clinic compared to women in the community.

Aged↗
PubMed1988

Data compression: 8-dimensional flow cytometric data processing with 28K addressable computer memory.

A method of data analysis for flow cytometry is presented which enables up to eight-dimensional data to be handled by a microcomputer with 28K addressable plus a further 32K non-addressable memory. The multi-parameter coordinates are coded into single numbers using a minimal modification of the array vector mapping equation. These code numbers, each of which corresponds to a given set of coordinates, and then ranked in ascending order according to magnitude and the frequency of each code number is found. Following this step the code is then decoded by integer arithmetic into its original coordinates which are then packed, together with the frequency, into two, three or four 16-bit words depending on the dimensionality of the data set. A five-dimensional data set is used as the illustration. Three regions were set on one two-dimensional data space and the five mono-dimensional histograms, plus a different bivariate distribution, were extracted in a single pass through the processed data file. In addition to considerable space saving the technique has two further attributes, namely, increased speed with which the user can appreciate multiparameter data and the ability to analyse such data sets with a microcomputer.

Algorithms↗
PubMed1992

Treatment of iatrogenic femoral artery injuries with ultrasound-guided compression.

Iatrogenic injuries of the groin are becoming more common after increasingly sophisticated vascular intervention. These injuries are accurately detected by duplex and color Doppler ultrasonography. Recent treatment of these lesions by ultrasound-guided compression repair (UGCR) has been described. During a 1-year period we identified 18 femoral artery injuries, including 17 pseudoaneurysms and one arteriovenous fistula. Three of the pseudoaneurysms thrombosed spontaneously before attempted treatment. The remaining 15 lesions underwent a trial of UGCR. Successful closure was accomplished in 10 patients (56%). Seven of these lesions were successfully treated during the initial session, and thrombosis was accomplished after repeat compression in three additional lesions. Three patients who were given anticoagulants had a failed UGCR, but their pseudoaneurysms thrombosed after administration of anticoagulants was discontinued. Two patients had failed UGCR and required operation. Seven (88%) of eight patients who were not given anticoagulants were successfully treated. In contrast only two (29%) of seven patients given therapeutic doses of anticoagulant medication were successfully treated by the technique. There was no statistical difference between mean pseudoaneurysm diameter, mean width and length of pseudoaneurysm neck, or depth of pseudoaneurysm neck from skin surface in patients in whom successful initial closure was achieved when compared with those patients in whom the initial attempt failed. UGCR is a safe, simple, noninvasive technique that can be used to treat many femoral artery injuries that traditionally were treated with surgery. The technique can be applied by any laboratory that has the necessary ultrasonography equipment and is currently the method of choice for treating uncomplicated iatrogenic femoral artery injuries at our institution.

Adult↗
PubMed1991

Review of arterial thoracic outlet syndrome with a report of five new instances.

Arterial damage, causing ischemia of the limb, occurs in less than 5 per cent of all instances of thoracic outlet syndrome. Arterial complications are usually associated with cervical ribs or rudimentary first ribs, but 12 per cent have occurred in patients with no osseous abnormality. The physiopathologic factors begin with compression of the subclavian artery which, in most patients, produces stenosis, poststenotic dilatation, formation of aneurysms and mural thrombosis. In other patients, aneurysms do not form, but the compression still causes stenosis, intimal injury and mural thrombosis. With either scenario, distal embolization can occur and produce signs and symptoms of ischemia that can limb-threatening. In this study, more than 200 patients reported previously and five additional sides in four patients were reviewed. Treatment depends upon the condition of the patient at presentation. Those with osseous abnormalities and no aneurysm or symptoms are not treated, while those with poststenotic dilatation or small aneurysms undergo rib resection only. Aneurysms more than twice the arterial diameter, intimal injury or mural thrombus are indications to resect, replace or bypass the subclavian artery. Patients who have had distal embolization and severe ischemic symptoms require, in addition to the aforementioned, distal thromboembolectomy, dorsal sympathectomy or both. Good results from treatment have been reported in 84 per cent of the 137 patients reported since 1970; 3 per cent required amputation and 3 per cent had cerebral emboli. Because the severe arterial complications were primarily the result of delayed therapy, they can best be avoided by early recognition, diagnosis and treatment.

Adult↗
PubMed1988

Modelling the phase equilibria in two-component membranes of phospholipids with different acyl-chain lengths.

A phenomenological model is proposed to describe the membrane phase equilibria in binary mixtures of saturated phospholipids with different acyl-chain lengths. The model is formulated in terms of thermodynamic and thermomechanic properties of the pure lipid bilayers, specifically the chain-melting transition temperature and enthalpy, the hydrophobic bilayer thickness, and the lateral area compressibility modulus. The model is studied using a regular solution theory made up of a set of interaction parameters which directly identify that part of the lipid-lipid interaction which is due to hydrophobic mismatch of saturated chains of different lengths. It is then found that there is effectively a single universal interaction parameter which, in the full composition range, describes the phase equilibria in mixtures of DMPC/DPPC, DPPC/DSPC, DMPC/DSPC, and DLPC/DSPC, in excellent agreement with experimental measurements. The model is used to predict the variation with temperature and composition of the specific heat, as well as of the average membrane thickness and area in each of the phases. Given the value of the universal interaction parameter, the model is then used to predict the phase diagrams of binary mixtures of phospholipids with different polar head groups, e.g., DPPC/DPPE, DMPC/DPPE and DMPE/DSPC. By comparison with experimental results for these mixtures, it is shown that difference in acyl-chain lengths gives the major contribution to deviation from ideal mixing. Application of the model to mixtures with non-saturated lipids is also discussed.

Algorithms↗
PubMed1990

Electrocardiographic ambulatory monitoring with a real-time analysis system.

The analysis of records collected during long-term ambulatory electrocardiographic monitoring has traditionally involved the review of massive data, either manually or with the aid of interactive scanning computers. Many factors complicate this analysis, including the use of analog tape for storage of electrocardiographic waveforms, the need to analyze 100,000 waveforms from an average 24-hour study, and the need to deal with an interface that compresses 24 hours of data into as little as 6 minutes on a screen. Today, the computer incorporated in the monitor can scrutinize each cardiac cycle in real time. The system produces a statistical report based on every heart beat and also performs data reduction and storage of electrocardiograph samples. To assess real-time analysis we examined data collected from the Circadian CircaMed ambulatory electrocardiography system. We found that it could detect and quantify simple or complex ventricular ectopic beats, brady- or tachyarrhythmic events, and ST-segment deviation. One hundred fifty patients 21 to 85 years old with symptoms or clinical finding suggestive of ischemia, cardiac arrhythmia, or conductive defects were referred to our electrocardiography laboratory for ambulatory monitoring. The results demonstrate that this system can detect the full range of cardiac disease found with the traditional method. Of the 150 patients, ambulatory electrocardiographic tests were positive in 93 (62%). In addition, we developed a methodology for lead placement when using two bipolar leads, as is typical for ambulatory electrocardiography. We present a procedure for determining the optimum lead placement that is based on the patient's history and a 12-lead electrocardiogram.

Adult↗