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Biomedical subjects

S M Dunn

Publications and source records attributed to S M Dunn.

At least 109 records · Page 6Linked to original sources
PubMed1993

Voltage-dependent calcium fluxes in skeletal muscle transverse tubule membranes in the range of late afterpotentials.

Calcium flux responses mediated by voltage-dependent calcium channels have been studied in transverse tubule membrane vesicles from rabbit skeletal muscle. Vesicles were loaded with 45Ca2+, and membrane potentials were generated by establishing potassium gradients across the membrane in the presence of valinomycin. After the membranes were polarized to an estimated -80 mV to approximate the resting state of the cell, a significant 45Ca2+ efflux occurred upon subsequent depolarization to -60 mV. The efflux response was modulated by activators and inhibitors of slow, dihydropyridine-sensitive calcium channels, being inhibited by inorganic calcium channel blockers, verapamil, nifedipine, and (-)-SDZ 202-791 and potentiated by the dihydropyridine agonists (+/-)-Bay K8644 and (+)-SDZ 202-791. These results demonstrate that calcium channels in transverse tubule membranes can open to mediate calcium flux in the same range of membrane potential as the late afterpotentials that occur during tetanic contractions of intact muscle fibres.

Animals↗
PubMed1993

General information tapes inhibit recall of the cancer consultation.

PURPOSE: Studies of tape recordings of cancer consultations have produced conflicting results. At the same time, audiotapes containing general information about cancer are poorly evaluated and are distributed to patients in an ad hoc manner. We compared the effects of both interventions on patient satisfaction, psychologic adjustment, and recall of information following their first consultation with a medical oncologist. PATIENTS AND METHODS: Patients (n = 142) were randomized to receive (1) an audiotape of their consultation, (2) an audiotape describing cancer in general terms, or (3) no tape. Recall of information was assessed in a structured interview 4 to 20 days after the consultation. RESULTS: Satisfaction with the consultation increased linearly from no tape to general tape to consultation tape. Satisfaction with the tape itself was higher in patients who received the consultation tape (satisfaction score, 61%) compared with those who received the general tape (43%). Average recall for all groups was 6.4 of the 25 items of information presented, and 2.4 of the six points identified as particularly important by the oncologist. The consultation tape did not improve recall over the no tape control, but the general tape caused a decrease of almost two items in total recall. Spontaneous (ie, unprompted) recall was significantly poorer with the general information tape. Psychologic adjustment to cancer was unaffected. CONCLUSION: We conclude that individual audiotapes have a limited potential to increase recall of information from the oncology consultation. General information tapes about cancer appear to inhibit recall actively.

Adolescent↗
PubMed1993

Cancer by another name: a randomized trial of the effects of euphemism and uncertainty in communicating with cancer patients.

PURPOSE: In this study we tested some assumptions about the use of euphemism in communicating with cancer patients. Does an explicit statement about the diagnosis of cancer cause patients to respond with greater anxiety than when uncertainty or ambiguity is allowed to persist? Do patients believe they cope better with cancer when the diagnosis is explicit? METHODS: A heterogeneous sample of 165 cancer patients completed a new measure of emotional adjustment to cancer using random assignment among four testing variables: agent (self-report v interview), terminology (the words cancer v illness), identification (patient identified v anonymous), and supervision (clinic v home). Internal consistency (Cronbach's alpha) for the 39-item set was 0.74 and face and content validity were determined using the focus-group technique and preliminary factor analysis. After answering the adjustment measures, subjects completed the Spielberger State-Trait Anxiety Inventory (STAI). RESULTS: Overall anxiety levels were significantly lower in the sample than published norms for general medical and surgical patients. Exposure to the word cancer as distinct from illness increased anxiety, but did not alter adjustment scores. Supervision and agent conditions did not affect anxiety, but reported adjustment was poorer in the interview condition compared with the self-report condition. Ambiguous instructions, such as asking patients to complete the questionnaire anonymously but return it in person to staff in the clinic, resulted in poorer adjustment, which was reversed by the consistent instruction to complete the questionnaire anonymously at home and return it by mail. CONCLUSION: Use of the word cancer generated anxiety to levels similar to those reported in general medical and surgical patients, but did not produce any distortion in reported adjustment. However, any ambiguity associated with the conditions under which adjustment is assessed may lead to distortion and an increase in the patient's reported psychologic distress.

Adult↗
PubMed1993

A comparison of two registration techniques for digital subtraction radiography.

The dental radiograph is a diagnostic tool that is used to view internal structures without any invasive procedures. A difference radiograph, i.e. one showing the changes that occurred over time, is the best tool for diagnosing slow or small changes. The difficulty in creating a meaningful difference radiograph, or its digital image, is that the imaging geometry of the image pair must be identical. This paper addresses the problem of reproducing imaging geometry. A new technique for registering digital images of radiographs based on the correspondence of 3D anatomical structures (such as root apices and the cemento-enamel junction) was compared with a registration method using occlusal stents. In a pilot study of 30 volunteers, difference images were created by three different registration techniques (no registration, mathematical methods and occlusal stents). The standard deviations of the difference images were used to compare the registration techniques. The results show that this new mathematical technique applied to digital images of radiographs can be used to establish correspondence between pairs of clinical images taken at different projection angles and to produce reconstructed images comparable with images taken with occlusal stents.

Adult↗
PubMed1993

Bleeding complications in the patient with cardiac disease following thrombolytic and anticoagulant therapies.

Thrombolytic and anticoagulant therapies are used frequently in the cardiac patient. Bleeding complications and other coagulation defects, such as heparin-induced thrombocytopenia (HITP), can occur following the administration of these drugs. Nurses caring for the cardiac patient need to be aware of the potential for bleeding and know how to safely and effectively care for the patient who experiences a bleeding event.

Anticoagulants↗
PubMed1993

Digital radiology. Facts and fictions.

Dental digital radiology is a rapidly changing field. The advantages and disadvantages are presented with an understanding that attention to fundamentals is paramount. The message for the near future is cautious optimism.

Bicuspid↗
PubMed1992

Low-affinity binding sites for 1,4-dihydropyridines in skeletal muscle transverse tubule membranes revealed by changes in the fluorescence of felodipine.

The fluorescence changes accompanying the binding of the fluorescent calcium channel antagonist, felodipine, to transverse tubule membranes from rabbit skeletal muscle have been used to characterize low-affinity binding sites for 1,4-dihydropyridine derivatives in these preparations. In competition experiments, felodipine inhibited the high-affinity binding of (+)-[3H]PN200-110 to transverse tubule membranes with an apparent Ki of 5 +/- 2 nM. Binding of felodipine to additional low-affinity sites resulted in a large, saturable (Kd = 6 +/- 2 microM) increase in its fluorescence which could be excited either directly (380 nm) or indirectly via energy transfer from membrane protein (290 nm). The observed fluorescence enhancement was competitively inhibited by other 1,4-dihydropyridines with inhibition constants of 3-21 microM but was unaffected by the structurally unrelated calcium channel antagonists, diltiazem and verapamil, or by Ca2+, Cd2+, and La3+. Both high- and low-affinity binding sites appear to be localized in the transverse tubular system, since the magnitude of the observed fluorescence enhancement was higher in these membranes than in microsomal preparations and was directly proportional to the density of high-affinity sites for (+)-[3H]PN200-110. Furthermore, both high- and low-affinity sites appear to be conformationally coupled since, over the same concentration range that the fluorescence changes were observed, felodipine accelerated the rate of dissociation of [3H]PN200-110 previously bound to its high-affinity sites. Similar behavior has previously been reported for other 1,4-dihydropyridines [Dunn, S. M. J., & Bladen, C. (1991) Biochemistry 30, 5716-5721].(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Diagnosing periapical bone lesions on radiographs by means of texture analysis.

Trabecular pattern, the radiographic projection of trabecular bone, is a repeated structure that appears in a dental radiograph. Texture analysis, the computer image analysis of repeated patterns, is a technique that can be used to automate the diagnosis of periapical lesions with the detection of the absence of the texture that corresponds to the trabecular bone. The purpose of this study was to determine whether it is feasible to use texture analysis to identify the presence of the trabecular pattern in radiographs and to detect a periapical bone lesion based on a local absence of this pattern. Thirty-two mandibular periapical films, 16 with and 16 without periapical lesions, were used in this study. Texture analysis was carried out on the digital images of these radiographs. In the 16 films with lesions, they were all correctly identified, and no lesions were found in the 16 films without lesions. This result is based on the a prior knowledge of the user about the localization of the disease. Locating periapical regions without user interaction is a goal for future research.

Alveolar Process↗
PubMed1992

A scale for the measurement of quality of life in adults with asthma.

A 20-item self-administered questionnaire with Likert scale responses was developed to measure quality of life in adult subjects with asthma. A total scale score together with subscale scores for breathlessness, mood disturbance, social disruption and concerns for health were calculated by addition of item scores. Items for the scale were selected by principal components analysis of the responses of 283 subjects to a preliminary pool of 69 items. In 58 subjects with stable asthma, good short term test-retest reliability was demonstrated with the intraclass correlation coefficient for the total scale being 0.80. The questionnaire was internally consistent in a sample of outpatients (Cronbach's alpha 0.92 in 77 subjects) and in a community sample with asthma (Cronbach's alpha 0.94 in 87 subjects). Weak correlations in the expected direction were seen with three medical markers of asthma severity. This supports the construct validity of the questionnaire and emphasizes that quality of life represents a separate dimension of asthma.

Adult↗
PubMed1992

Recognizing invariant geometric structure in dental radiographs.

The dental radiograph is a non-invasive tool that is used to view internal structures for the diagnosis of caries, periapical lesions and periodontal disease. The requirement for a standardized image is most prominent in periodontal disease since the diagnosis is best done with a difference radiograph. The difficulty is that exact registration for subtraction requires exact reproduction of imaging geometry. A new model of imaging geometry, based on the correspondence of 3D structures, to describe the radiograph formation process is presented. The experimental results show that 3D measurements can be made in dental radiographs (P < 0.01) with up to 16-mm translation errors and angulation errors of up to 32 degrees.

Algorithms↗
PubMed1992

An introduction to model-based imaging.

The purpose of this paper is to clarify the distinction between the recognition of form, i.e. pattern recognition, and the interpretation of visual scenes, i.e. image understanding. Pattern recognition is part of image understanding, but the latter also includes cognitive tasks such as learning and inference. The key to developing image-understanding systems is to concentrate on the representation and use of models. This paper is a brief outline of the components of a model-based image-understanding system. First, the notions of iconic, categorical and symbolic knowledge are described. Although they appear to be disparate, the common notion is that the image understanding is based on recognizing concepts and not recognizing form. Next, the notion of a concept is defined, followed by representation techniques and control strategies for using concepts. Last, an example is given of an image-understanding system that learns to recognize concepts such as radiographic projections of teeth in panoramic radiographs.

Expert Systems↗
PubMed1991

Functional reconstitution of a GABAA receptor purified from bovine brain.

The GABAA/benzodiazepine receptor has been solubilized from bovine brain membranes and purified by benzodiazepine affinity chromatography. Polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate revealed two major protein species of 53 and 56 kDa. The purified protein has been reconstituted, in a functionally active form, into phospholipid vesicles. Chloride flux responses of the reconstituted preparations were investigated in stopped-flow experiments by monitoring fluorescence changes of a chloride-sensitive dye trapped within the vesicles. Flux was rapidly stimulated by muscimol and this response was potentiated by diazepam and blocked by desensitization of the receptor and by preincubation with the channel blocker, picrotoxin.

Animals↗
PubMed1991

Kinetics of binding of dihydropyridine calcium channel ligands to skeletal muscle membranes: evidence for low-affinity sites and for the involvement of G proteins.

Detailed kinetic studies of the binding of the calcium channel antagonist (+)-[3H]PN200-110 to membrane preparations from rabbit skeletal muscle have demonstrated that, in addition to the high-affinity sites (Kd = 0.30 +/- 0.05 nM) that are readily measured in equilibrium and kinetic experiments, there are also dihydropyridine binding sites with much lower affinities. These sites were detected by the ability of micromolar concentrations of several dihydropyridines to accelerate the rate of dissociation of (+)-[3H]-PN200-110 from its high-affinity sites. The observed increase in rate was dependent on the concentration of competing ligand, and half-maximal effects occurred at approximately 10 microM for the agonist (+/-)-Bay K8644 and for the antagonists nifedipine, (+/-)-nitrendipine, and (+)-PN200-110. The low-affinity sites appear to be stereospecific since (-)-PN200-110 (1-200 microM) did not affect the dissociation rate. The possible involvement of guanine nucleotide binding proteins in dihydropyridine binding has been investigated by studying the effects of guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S) and guanosine 5'-O-(2-thiodiphosphate) (GDP beta S) on binding parameters. At a concentration of 10 microM, neither GTP gamma S nor GDP beta S significantly affected the binding of dihydropyridines to their high-affinity sites. GTP gamma S did, however, increase the ability of (+/-)-Bay K8644, but not of (+/-)-nitrendipine, to accelerate the rate of dissociation of tightly bound (+)-[3H]PN200-110. GDP beta S did not affect the dose dependence of either the agonist or the antagonist.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗