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Biomedical subjects

S M Clark

Publications and source records attributed to S M Clark.

At least 55 records · Page 3Linked to original sources
PubMed1993

High-speed parallel separation of DNA restriction fragments using capillary array electrophoresis.

A new method for performing high-speed, high-throughput sizing of DNA has been developed. Samples containing DNA restriction fragments between 70 and 10,000 base pairs in length are electrophoretically separated using capillary arrays in approximately 20 min and detected with high sensitivity using a fluorescence detection system. The separations of phi X174/HaeIII fragments are performed on an array of seven 100-microns i.d., 350-microns o.d. capillaries using replaceable hydroxyethyl-cellulose solutions as the sieving medium. The fragments are fluorescently labeled using ethidium bromide in the running buffer and detected with a laser-excited, confocal-fluorescence scanner. The limit of detection is approximately 1 pg of DNA per band and separations can be detected injecting DNA samples as dilute as 0.1 ng/microliters. Samples were electrokinetically injected from a cassette of microcentrifuge tubes using a format that will facilitate the application of capillary electrophoresis to separations in molecular biology. The feasibility of extending this technique to lower DNA concentrations and to approximately 100 capillary arrays is discussed.

Bacteriophage phi X 174↗
PubMed1993

Intestinal ischemia secondary to thromboangiitis obliterans.

A 38-year-old woman presented with a 10-month history of postprandial abdominal pain and weight loss. She smoked two packs of cigarettes a day, but her history did not indicate diabetes mellitus, hyperlipidemia, or hypercoagulability. A lateral aortogram documented complete occlusion of all three mesenteric arteries but showed no evidence of atherosclerosis, arteritis, or medial fibroplasia. Two retrograde aortomesenteric grafts, one to the superior mesenteric artery and another to the meandering mesenteric artery, utilizing the greater saphenous vein were placed. Pathologic examination of the inferior mesenteric artery demonstrated changes that were considered diagnostic of thromboangiitis obliterans. We found only 10 confirmed cases of thromboangiitis obliterans involving the mesenteric vessels in the English language literature. The present case appears to be the first involving a woman and the only one in which the main trunk of all three mesenteric vessels was involved.

Adult↗
PubMed1993

Biological microscopy: the emergence of digital microscopy.

The past few years have seen a tremendous renaissance in biological optical microscopy, mainly as a result of the application of digital image processing and video imaging techniques. We review recent developments in microscopy that are permitting unprecedented views of biological structure and function.

Animals↗
PubMed1993

Hypersensitive dentin: testing of procedures for mechanical and chemical obliteration of dentinal tubuli.

This study examined by scanning electron microscopy the effect of various mechanical and chemical procedures in obliterating dentinal tubuli. Dentin blocks containing open, cross-sectioned dentinal tubuli were separated into one experimental and one control area. The mechanical treatments consisted of 20 seconds of continuous instrumentation with sharp and dull curets, finely textured inserts for the EVA reciprocating handpiece, metal and plastic inserts for a sonic scaler, and metal inserts for an ultrasonic scaler. Chemical treatments included a light-cured dental resin and active obliterating agents including sodium, stannous and hydrogen fluorides, potassium oxalate, glycerin, ferric oxalate, and potassium nitrate. These substances were applied to the test surfaces for 2 minutes and allowed to dry. One half of the chemically treated specimens were then sprayed with water in order to evaluate the retention of the obliterating agents. The results revealed that among the mechanical treatments, the sharp curet gave the most consistent and complete obliteration of the tubuli. The plastic inserts had no tubular occluding effects. Among the chemical procedures, the light-cured resin resulted in the most complete obliteration of the tubuli, while the fluoride agents and glycerin had no effect. It can be hypothesized that combining instrumentation with a sharp curet causing a heavy smear layer and occlusion of tubuli apertures, followed by application of a light body resin, may prove to be a rational method of desensitizing hypersensitive dentin surfaces. However, this combined treatment should be evaluated in clinical trials.

Curettage↗
PubMed1993

Pain and discomfort levels in patients during root surface debridement with sonic metal or plastic inserts.

The study was designed to evaluate whether root surface debridement with a sonic scaler plastic insert would cause less pain and discomfort to patients than an ordinary, probe-shaped metal sonic insert. One quadrant in each of 23 patients was debrided with each insert. Blood pressure, mean arterial pressure, and heart rate were monitored before, during, and immediately after each treatment. Pain was also evaluated on a visual analogue scale (VAS) after each treatment, as well as 2 weeks later following pain-provoking stimuli. Blood pressure, mean arterial pressure, and heart rate did not reveal any differences between quadrants treated with plastic or metal inserts. Heart rate had a weak, positive association with treatment time. The VAS gave a higher pain score for the plastic (30.8) than for the metal insert (24.4), but this difference was not statistically significant (P = 0.055). Following pain-provoking stimuli at the 2-week follow-up visit, quadrants debrided with the metal insert (31.3) scored significantly lower (less pain) (P < 0.01) on the VAS than quadrants treated with the plastic insert (30.7). It is concluded that the sonic metal insert caused less pain and discomfort to the patients due to its superior accessibility and water spray cooling. The significant difference between metal and plastic tip debrided quadrants at the follow-up visit was probably caused by the smearing effect of the metal insert with partial closure of the dentin tubule orifices.

Adult↗
PubMed1993

Strategic sensemaking and organizational performance: linkages among scanning, interpretation, action, and outcomes.

This study investigated the strategic "sensemaking" processes of scanning, interpretation, and action and how those activities are linked to organizational performance. Using path analyses on data from 156 hospitals, we tested the direct and indirect effects among these sensemaking processes and performance outcomes and developed a model of their relationships. In a more general sense, the research represents an attempt to provide insight not only into relationships between cognition and action, but also into the links between those fundamental processes and organizational performance outcomes.

Adult↗
PubMed1993

Computer-assisted search of medical literature.

Computers now offer physicians a wide range of time-saving and cost-effective means of user-friendly access to medical literature. This article describes different methods of using the computer to find information on a subject, focusing on end-user services that provide access to MEDLINE. The different systems available and their respective advantages and disadvantages are described. Use of electronic bulletin boards, Internet and online publishing in medicine also are addressed.

MEDLINE↗
PubMed1992

Root dentin morphology after different modes of citric acid and tetracycline hydrochloride conditioning.

The purpose of this study was to assess the effect of citric acid and tetracycline HCl application to dentin surfaces by a "passive dripping" or an "active burnishing" technique. Twenty dentin blocks were prepared from freshly extracted non-diseased human impacted third molars. The blocks were root planed and randomly assigned to two groups for treatment with either citric acid or tetracycline HCl. The duration of treatment was 30, 60, 120, or 240 seconds. Control blocks were treated with distilled water. After treatment the blocks were processed for observation and measurements in the scanning electron microscope (SEM). Application of either of the acid solutions resulted in removal of the smear layer. Measurements indicated a time dependent increase in the mean dentinal tubule orifice diameter ranging from 1.05 microns in control specimens to 3.18 microns after 4 minutes treatment (citric acid group). The increase in tubule diameter was significantly greater (P less than or equal to 0.01) for both citric acid treatment modalities than tetracycline HCl treatment. There was also a time dependent increase in the depth of penetration as measured by a trumpeting of the tubule profiles, and this penetration was significantly greater (P less than or equal to 0.01) after citric acid treatments. Passive or active application of the acids did not seem to have any major impact on the measurements or on the surface morphology. It was concluded that citric acid causes more extensive changes than tetracycline HCl and that the mode of application of the agent is probably not critical.

Acid Etching, Dental↗
PubMed1992

Innominate artery compression of the trachea. Treatment by reimplantation of the innominate artery.

The standard treatment of innominate artery compression of the trachea has been innominate artery suspension, but the syndrome can recur when this technique is used. From October 1985 until March 1991, 29 infants and children were treated for this syndrome by innominate artery reimplantation. In all patients severe anterior vascular compression of the trachea was demonstrated preoperatively by bronchoscopy and in 17 the diagnosis was confirmed by magnetic resonance imaging scanning. Indications for operation included apneic episodes in 17 (58.6%), severe stridor in seven (24.1%), recurrent bronchopulmonary infections in four (13.8%), and exercise-induced stridor in one (3.4%). Through a median sternotomy, the innominate artery was reimplanted more proximally on the ascending aorta and to the right of the trachea. In this new position, the innominate artery no longer crosses the trachea anteriorly, and the anatomic cause of tracheal obstruction is completely eliminated. There were no early or late deaths, and 27 of the 29 patients (93%) had complete resolution of symptoms. Partial resolution of symptoms was seen in two patients (7%). Reimplantation of the innominate artery offers a unique method by which the anatomic cause of tracheal compression is eliminated. It is a safe and effective means of treating symptomatic compression of the trachea by the innominate artery.

Adolescent↗
PubMed1991

Parasitization of humans in West Virginia by Ixodes cookei (Acari: Ixodidae), a potential vector of Lyme borreliosis.

In 32 collections, two larvae, 33 nymphs, and one adult female Ixodes cookei Packard were collected from humans in West Virginia from August 1987 to May 1990. Most were attached. The ticks were found in 14 counties and were the most abundant Ixodes found biting humans. One nymphal I. cookei was removed from the left axilla of a 39-yr-old woman who lives and works in Monongalia and Marion counties, W. Va. The bite was the center of an expanding erythematous lesion reaching 4 cm in diameter, clearing centrally, and typical of erythema migrans. This association and the near absence of Ixodes dammini Spielman, Clifford, Piesman & Corwin from the state suggests the possibility that I. cookei may be an important vector of Lyme borreliosis in West Virginia. In five separate collections, five nymphal Ixodes dentatus Marx were removed from humans in four counties, implicating this species as a potential minor vector of Lyme borreliosis in West Virginia.

Adult↗
PubMed1990

Early adolescent age and gender differences in patterns of emotional self-disclosure to parents and friends.

This study explored adolescent age and gender differences in patterns of emotional self-disclosure to parents and friends. The sample consisted of 174 junior high school students between the ages of 12 and 15. Results revealed that females exhibited greater emotional self-disclosure to parents and peers than did males, and that emotional self-disclosure to friends was greatest among older adolescents. In addition, while younger adolescents preferred to disclose information about their emotional state to parents, older adolescents chose friends. Exploratory hierarchical regression analyses revealed that emotional disclosure to parents was most strongly associated with adolescent perceptions of the openness of family communication, family cohesion, and satisfaction with family relationships. Emotional disclosure to friends was associated with adolescent self-esteem in the peer context and identity development. The results are discussed in terms of the complementary socializing processes that may operate within the contexts of family and friends.

Adolescent↗
PubMed1988

A novel instrument for separating large DNA molecules with pulsed homogeneous electric fields.

A new instrument has been developed for the electrophoretic separation of large DNA molecules that can independently regulate the voltage of each of 24 electrodes and allow the magnitude, orientation, homogeneity, and duration of the electric field to be precisely controlled. Each parameter can be varied at any time during the electrophoretic process. Thus distinct sets of conditions can be combined to optimize the separation of various fragment sizes in a single run. Independent control of electrode voltage allows all of the fields to be generated with electrodes arranged in a closed contour, independent of a particular geometry. This device increases both the resolution in any size range and the speed of separation, especially for DNA molecules larger than 3 megabases.

DNA↗
PubMed1988

Optimized conditions for pulsed field gel electrophoretic separations of DNA.

Quantitative measurement of DNA migration in gel electrophoresis requires precisely controlled homogeneous electric fields. A new electrophoresis system has allowed us to explore several parameters governing DNA migration during homogeneous field pulsed field gel (PFG) electrophoresis. Migration was measured at different switch times, temperatures, agarose concentrations, and voltage gradients. Conditions which increase DNA velocities permit separation over a wider size range, but reduce resolution. We have also varied the angle between the alternating electric fields. Reorientation angles between 105 degrees and 165 degrees give equivalent resolution, despite significant differences in DNA velocity. Separation of DNA fragments from 50 to greater than 7000 kilobases (Kb) can easily be optimized for speed and resolution based on conditions we describe.

Chromosomes↗