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Biomedical subjects

A S Smith

Publications and source records attributed to A S Smith.

At least 19 recordsLinked to original sources
PubMed1998

Efficiency of the pTF-FC2 pas poison-antidote stability system in Escherichia coli is affected by the host strain, and antidote degradation requires the lon protease.

The stabilization of a test plasmid by the proteic, poison-antidote plasmid addiction system (pas) of plasmid pTF-FC2 was host strain dependent, with a 100-fold increase in stability in Escherichia coli CSH50, a 2.5-fold increase in E. coli JM105, and no detectable stabilization in E. coli strains JM107 and JM109. The lethality of the PasB toxin was far higher in the E. coli strains in which the pas was most effective. Models for the way in which poison-antidote systems stabilize plasmids require that the antidote have a much higher rate of turnover than that of the toxin. A decrease in host cell death following plasmid loss from an E. coli lon mutant and a decrease in plasmid stability suggested that the Lon protease plays a role in the rate of turnover of PasA antidote.

ATP-Dependent Proteases↗
PubMed1998

Autoregulation of the pTF-FC2 proteic poison-antidote plasmid addiction system (pas) is essential for plasmid stabilization.

The pasABC genes of the proteic plasmid addiction system of broad-host-range plasmid pTF-FC2 were autoregulated. The PasA antidote was able to repress the operon 25-fold on its own, and repression was increased to 100-fold when the PasB toxin was also present. Autoregulation appears to be an essential requirement for pas-mediated plasmid stabilization because when the pas genes were placed behind the isopropyl-beta-D-thiogalactopyranoside (IPTG)-regulated tac promoter, they were unable to stabilize a heterologous test plasmid.

Antidotes↗
PubMed1997

The poison-antidote stability system of the broad-host-range Thiobacillus ferrooxidans plasmid pTF-FC2.

In plasmid pTF-FC2, three small open reading frames (ORFs) are situated between the repB (primase) gene and the repA (helicase) gene of its IncQ-type replicon. Disruption of each of the three ORFs followed by tests for plasmid stability and host cell growth indicated that the ORFs encoded a poison-antidote plasmid stability system. The three genes were named pasA, pasB and pasC (plasmid addiction system), in which PasA is the antidote, PasB the toxin and PasC a protein that appears to enhance the ability of the antidote to neutralize the toxin. Disruption of the pasA gene resulted in two different spontaneous deletions, which inactivated the stability system but did not alter the host range or plasmid copy number. This indicated that the three small ORFs were not involved in plasmid replication. When placed behind a tac promoter, induction of pasB was found to be highly lethal to host cells, which suggests that the Pas system acts by killing plasmid-free host cells rather than by retarding the growth of plasmid-free segregants, as occurs in the ParD system of R1. In spite of this, the presence of the Pas poison-antidote system resulted in a relatively modest threefold stabilization of the pTF-FC2 host replicon and a similar increase in the stabilization of an unstable heterologous R1 plasmid replicon. The Pas system is a poison-antidote plasmid stability module, which appears to have become integrated within the pTF-FC2 replicon module.

Amino Acid Sequence↗
PubMed1996

Applying advanced directives regulations in home care agencies.

As Dombi (1991) indicated, home healthcare agencies see people in their own settings and can be most influential in assisting clients and families to deal with important issues. Furthermore, in receiving care in their homes, clients and their families may be in a more amenable frame of mind to consider such issues. Agencies may find it helpful to identify special resource people who could be accessible to clients and families in enabling them to prepare appropriate documents. In a tape recording that reviews the state of life-sustaining therapy, Wolf (1993) highlighted the importance of seeing the regulations on advance directives as just the beginning of further work and discussion with clients and their families. Home healthcare agencies, in particular, need to do more than just comply with directives related to the Patient Self-Determination Act. Agencies can be in the forefront of identifying needs and concerns of clients and families related to critical life and death decisions and in exploring the ramifications of those decisions. The trend toward developing ethics committees in home healthcare agencies can be a vehicle for further exploration of such issues.

Advance Directives↗
PubMed1995

Development of a measure of medical faculty attitudes toward clinical evaluation of students.

PURPOSE: This research involved the development, and in particular the evaluation of the reliability, of scales to measure medical faculty attitudes toward clinical evaluation (ACE) of medical students. The intent was to create measures that yield reliable data and have practical utility in medical education research and faculty development. METHOD: A systematic, eight-step scale development protocol was used to create the instrument. In early 1993 factor analysis was used on data from 217 clinical faculty at four medical schools to refine the measures. Internal consistency and test-retest reliability analyses were performed. Analyses were also done to determine whether the attitude scores were influenced by such faculty demographic attributes as employing medical school, gender, age, tenure track status, academic rank, or academic department. RESULTS: An initial pool of 52 items was reduced to 30 items based on iterative reliability studies. Factor analysis on the 30 items yielded two scales: (1) Quality of Evaluation Procedures, 12 items, alpha = .81; and (2) Content of Departmental Evaluations, eight items, alpha = .85. Test-retest reliabilities (12 weeks) for the scales were .67 and .74, respectively. Faculty demographics did not influence attitudes about the quality of evaluation procedures. However, family physicians showed a slightly more positive attitude toward the content of departmental evaluations than did physicians in five other medical specialties. CONCLUSION: The goal of developing reliable measures of faculty attitudes toward clinical evaluation of medical students has been achieved. With baseline reliabilities established, future research should assess the validity and utility of the scales, especially in the context of clinical practice examinations.

Analysis of Variance↗
PubMed1995

Parallel and spiral flow patterns of vertebral artery contributions to the basilar artery.

PURPOSE: To demonstrate that the in vivo flow from individual vertebral arteries can be imaged and tracked in the basilar artery by use of saturation planes with three-dimensional time of flight MR angiography. METHODS: Twenty volunteers were studied with intracranial three-dimensional time of flight angiography MR. The MR angiography was repeated with saturation of the individual vertebral arteries. Flow voids and signal intensity within the basilar and posterior cerebral arteries were evaluated for flow patterns. RESULTS: Of 15 volunteers with a "normal" vertebrobasilar anatomy, 80% demonstrated a pattern of flow within the basilar artery in which the contributing vertebral components remained ipisilateral. This pattern was called "parallel." A "spiral" pattern of rotation of the contributing vertebral components was found in 20% of studies. The inflow to the posterior cerebral arteries could be identified from specific vertebral contributions and was related to the size-dominance of the vertebral artery. CONCLUSION: There is nonadmixture of vertebral artery flows of variable duration within the basilar artery; at least two patterns of flow can be described within the basilar artery. The method presented is a simple technique for determining vertebral artery flow components with routine software and without secondary data manipulation.

Adult↗
PubMed1994

Time-of-flight intracranial MR venography: evaluation of the sequential oblique section technique.

PURPOSE: To implement a time-of-flight MR angiographic technique using the oblique acquisition of thin gradient-echo sections to evaluate the intracranial venous system, and to assess the feasibility of application of this technique in a routine clinical setting. METHODS: The MR angiographic technique consisted of a two-dimensional gradient-echo technique with sequential overlapped sections obtained with an oblique orientation, angled from the sagittal toward the coronal plane. Parameters were evaluated during 41 measurements in 21 healthy volunteers with the section orientation varying from direct sagittal to direct coronal, followed by 64 examinations in 53 patients with an angle of obliquity of 15 degrees to 20 degrees from the sagittal toward the coronal plane. Confirmation of MR venographic findings was through correlation with clinical data and imaging studies. RESULTS: The volunteer data demonstrated optimal visibility of the smaller midline structures with an angle of obliquity of 15 degrees or greater. Patient examinations with this angle demonstrated sinus obstruction or thrombosis (n = 11), sinus compression (n = 2), and apparent sinus stenosis (n = 1). CONCLUSIONS: Oblique-acquisition time-of-flight MR venography seems to provide a rapid, robust technique for intracranial venous examination and can be applied as a useful adjunct to parenchymal MR in the evaluation of suspected venoocclusive disease. This oblique technique demonstrated improved vessel contrast over direct sagittal acquisition, required significantly fewer sections and thus a shorter acquisition time than direct coronal acquisition, and was applied without difficulty in the vast majority of patients in the clinical setting.

Adolescent↗
PubMed1994

Short versus long echo time for cranial MR angiography in children and adults.

PURPOSE: To evaluate the ability of short-echo-time (TE) versus long-TE three-dimensional time-of-flight MR angiography sequences to decrease phase-related signal loss and refocus signal from blood in intracranial MR angiography of adults and children. METHODS: We evaluated 3-D time-of-flight cranial MR angiography in 33 cases (18 children and 15 adults) using two sequences. The longer-echo reference sequence had a TE of 8.0 milliseconds and a field echo of 6.5 milliseconds; the shorter-echo sequence had a TE of 5.1 and a field echo of 4.2 milliseconds. Repetition time, flip angle, and matrix were constant. The bandwidth for the longer-echo sequence was 130 Hz, 195 Hz for the shorter-echo sequence. RESULTS: The greatest improvement in diagnostic images was for children; significant and mildly improved signal recovery was demonstrated in 15 and 2 cases, respectively, of a total of 18 studies. This allowed improved diagnostic assessment. However, in the adult group significantly and mildly improved signal recovery were present in only 2 and 6 cases, respectively, of a total of 15 studies. In the group of children and adults combined, decreased lumen definition and peripheral vessel visibility were present in 24 and 30 of 33 cases, respectively, because of higher signal from background tissue when the shorter-TE field-echo sequence was used and, hence, reduced vascular contrast. CONCLUSION: The use of a short-field-echo/TE sequence is therefore recommended as the initial study in children but as a secondary examination in areas of abnormality in adults. This study illustrates the improved signal recovery from phase-related sources and improved visibility of intracranial stenosis in children with the use of a short-echo sequence. In adults, the short-echo sequence should not be used for the initial screening but reserved for secondary evaluation.

Adolescent↗
PubMed1991

Disc herniation in cervical fracture subluxation.

Previous reports of computed tomographic scan with contrast myelography in cervical spinal cord injury have shown a rate of disc herniation of less than 5%. We hypothesized that injuries associated with forces adequate to cause bone or ligamentous injury in the region of the disc space could be associated with higher and more significant rates of disc herniation. Thirty-seven consecutive traumatic midcervical fracture subluxations were reviewed. Fracture subluxation was defined by fracture of the facet joints, pedicles, or vertebral bodies or more than 3.5 mm subluxation from C2-C3 to C7-T1. Reduction was achieved in 97% and was not associated with neurological deterioration. On the basis of plain films, tomograms, and plain computed tomographic scans, the injuries were classified as flexion dislocation, flexion compression, compression burst, or extension injuries. Twenty-five computed tomographic scans with contrast myelograms and one magnetic resonance imaging scan were obtained. All patients with partial neurological deficits were studied. A herniated disc was defined as that which deformed the thecal sac and/or nerve roots. Retrospectively, a neuroradiologist reviewed the studies for the presence of herniated disc. Disc herniation was seen at the level of injury in 9 (35%) patients and not seen in other patients. Forty-seven percent of the patients with partial deficits had herniated discs. Herniated disc was seen most frequently in flexion dislocation and flexion compression injuries. Three patients (20%) with partial deficits underwent discectomy. Patients with partial spinal cord injury and discectomy, on average, improved more than other patients with partial spinal cord injury.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

A "PICA communicating artery" aneurysm: case report.

We present an unusual case of an aneurysm of the distal posterior inferior cerebellar artery (PICA). The aneurysm was associated with a unilateral PICA that supplied both cerebellar hemispheres and arose from an anastomotic vessel to the contralateral circulation, a branch of the contralateral PICA. Such an aneurysm has not been reported previously. The associated of vascular anomalies with aneurysms of the PICA is discussed.

Cerebellum↗
PubMed1991

MR of infectious and inflammatory diseases of the spine.

Magnetic resonance imaging is the study of choice in the evaluation of infectious and inflammatory disease of the spinal cord and spinal column. Not only is the multiplanar imaging a distinct advantage over other modalities, but direct visualization of the soft tissues, including the spinal cord, paraspinal musculature, and disk, is present. The sensitivity of MR, to evaluate infectious processes of the spine, especially when used with gadolinium, has been well documented. This article is an overview of the pathophysiology and MR appearance of various types of inflammation and infection of the spine. Subjects covered include disk space infections, epidural abscess, meningitis, arachnoiditis, and inflammatory mimics of disk space infections. Suggested imaging protocols are stated.

Bacterial Infections↗
PubMed1991

Velocity quantification in magnetic resonance imaging.

A variety of methods has been developed for quantitating flow in vivo. These are usually based on the principles of velocity-phase or TOF information. The former allows a point-by-point 2D image of velocity, but also has other manifestations involving real-time 1D projections or 1D projections with 1D velocity information (flow zeugmatography). The TOF methods use the in-flow of unsaturated spins into a saturated region (for example) to estimate flow. The concepts, features, and clinical applications of these and other techniques are reviewed in this article.

Blood Flow Velocity↗
PubMed1991

Infectious and inflammatory processes of the spine.

Infectious and inflammatory processes of the spinal column are discussed, including disc space infection, osteomyelitis, epidural abscess, arachnoiditis, and rheumatoid arthritis. The relative sensitivity and specificity of various imaging modalities, as well as the imaging characteristics and utility of these various modalities are given. Emphasis is placed on the use of magnetic resonance imaging.

Arachnoiditis↗
PubMed1990

Dermal grafts of the temporomandibular joint: postoperative appearance on MR images.

Complications may follow meniscectomy and placement of an allogenic implant in temporomandibular joint (TMJ) dysfunction. To characterize the anatomy of autogenous dermal grafts for repair and repositioning of the meniscus, the authors performed T1-weighted magnetic resonance (MR) imaging of 20 TMJs in 10 patients 6-23 months after surgery that was considered successful. MR imaging did not enable detection of the dermal grafts. Comparison of preoperative and postoperative MR images revealed little, if any, change in meniscal position. MR images of 20 menisci revealed anterior displacement (n = 11), normal position (n = 4), focal areas of increased signal intensity (n = 4), fragmentation (n = 2), and suboptimal visualization (n = 5). MR images of 20 condyles revealed normal features (n = 11), erosions (n = 2), early avascular necrosis (AVN) or subchondral cysts (n = 2), AVN (n = 3), an osteophyte (n = 1), and loss of bone (n = 2). One TMJ demonstrated increased soft tissue in the bilaminar zone.

Adolescent↗