Biomedical subjects

D L Johnson

Publications and source records attributed to D L Johnson.

At least 55 records · Page 3Linked to original sources

PubMed2000

Rapid search and quantitative analysis of gunshot residue particles in the SEM.

Automated scanning electron microscopy coupled with image analysis and X-ray micro analysis was used to characterize a variety of gunshot residue (GSR) samples. More than 500 rounds of commercially available ammunition and six different types of hand gulls were used in the study of 17 GSR and 19 reference specimens. The individual particle X-ray composition was determined for 12 different elements. Elemental composition of GSR particles was highly variable but consistent with compounds mixed into or associated with a barium oxide matrix. When present in a specimen, GSR could be adequately characterized with automated procedures in less than an hour by restricting analyses to features larger than 2 microm. In "clean" samples, a higher resolution particle search was required to avoid reporting false negatives. Careful control of the back scattered electron signal strength threshold, by reference to a standard, was needed to ensure both time-efficient and accurate analyses. Samples collected from non-shooting subjects. active in a physical environment which contained firearms discharge residue were seen to be easily contaminated by sub-micron GSR particles.

Firearms↗

PubMed2000

Radiographic analysis of femoral tunnel position in anterior cruciate ligament reconstruction.

Successful reconstruction of the anterior cruciate ligament (ACL) depends on anatomic placement of a graft ligament substitute. This study examined the accuracy of a plain radiograph in determining femoral tunnel position during ACL reconstruction. Nine cadaveric distal femurs had six separate tunnels made in each specimen: 12:00 (high position), 1:30 (anatomic position), and 3:00 (low position) in the left femora and 12:00 (high), 10:30 (anatomic), and 9:00 (low) in the right femora. At each position on the clock face, two 9-mm tunnels were drilled, leaving 2 mm (correct) and 12 mm (incorrect) of posterior wall intact. With a radiopaque tunnel dilator in each tunnel, a true lateral radiograph, a 10 degree externally rotated lateral radiograph, and a 10 degree internally rotated lateral radiograph were obtained. All radiographs were analyzed for femoral tunnel placement in the anteroposterior plane with the four-quadrant method described by Harner et al and the ratio method described by Aglietti et al. Statistically significant differences could only be distinguished between anatomic (10:30), anterior (12-mm rim), and posterior (2-mm rim) positions. There were no statistically significant differences for any of the other positions when comparing true laterals to true laterals, true laterals to internal or external oblique views, or when comparing internal and external oblique views. A malpositioned anterior tunnel (12-mm rim posterior), which was "low" at 9:00 or "high" at 12:00 in the notch (malplaced), could not be distinguished reliably from an anatomically correct placed tunnel with a single-plane lateral radiograph.

Analysis of Variance↗

PubMed2000

Effects of resistance form on attachment strength of resin-retained castings.

This study evaluated the effects of tooth preparation design on resistance to dislodgment of a resin-bonded fixed partial denture (RBFPD). The variations of tooth preparation tested included axial coverage, retentive grooves, and an occlusal rest. Patterns of the tooth preparation designs were prepared and cast in a base metal alloy. Retainer patterns were waxed to refractory casts of metal dies, cast, finished and then bonded to the dies. The complete assemblies were loaded to failure on an Instron mechanical testing machine, and analysis indicated that retainers with occlusal rests were the most resistant. Grooves provided no statistically significant increase in resistance to failure of the cement. Increased axial coverage did not increase resistance to dislodgment. Successful fixed partial dentures (FPDs) depend on cast retainers to resist displacement of the restoration during function. Introduction of resin-bonded restorations opened the possibility of FPDs with minimal reduction of abutments. Specific questions concerning long term success and tooth preparation designs were prominent concerns. The influence of resistance form on overall stability of a restoration was also of particular interest. Buonocore established the foundation for retention of composite resins to acid-pitted enamel. Rochette used this technology to bond perforated cast metal splints to periodontally compromised teeth. A mechanical interlock was created as composite resin engaged these perforations and sustained the cast splint to acid-etched enamel. Howe adapted this design for replacement of anterior teeth by adding porcelain to a metal ceramic framework and then bonding the framework to abutments without tooth preparations. The advantages of these procedures were their conservative nature, esthetics, and ease of rebonding after dislodgment. Livaditis and Thompson adapted the procedure proposed by Tanaka of corrosion-pitting the bonding surface of a base metal alloy. They increased the surface area to be bonded, eliminated the perforations to improve rigidity of the framework, and described tooth preparation modifications of the abutments. They suggested an occlusal rest, establishment of guide planes through axial reduction, and a proximal extension to the facial surface to resist lingual displacement. Simonson, et al., based their anterior tooth preparation design on the configuration suggested by Livaditis which included a slight chamfer finish line plus reduction of the lingual surface to provide a thicker metal framework. Barrack introduced an inlay type tooth preparation for the occlusal rest plus shallow vertical proximal grooves, and Meiers used grooves as an esthetic alternative to proximal extensions. Clinical studies and surveys have identified specific variables involved with success and failure, while in vitro studies have evaluated framework designs, bonding agents, and methods for pitting the metal surface. This study evaluated resistance of RBFPDs to dislodgment of different tooth preparation designs.

Analysis of Variance↗

PubMed2000

Subchondral contusion of the knee caused by axial loading from dashboard impact: detection by magnetic resonance imaging.

We studied the occurrence of "bone bruises" of the knee resulting from dashboard impaction and detected by magnetic resonance imaging (MRI). We chose 21 knees of 20 front seat occupants in head-on motor vehicle collisions. To ensure all knees had received a significant axial load, patients selected had ipsilateral posterior hip dislocations and/or posterior wall acetabular fractures. Anteroposterior and lateral knee radiographs were negative for fracture in all cases. T1-weighted axial and sagittal MRI of each knee with a 1.5-T magnetron scanner revealed signal changes consistent with subchondral microfracture or bone bruise in 8 of the 21 knees. Previous cadaveric, animal, and MRI studies have suggested that such changes may be precursors of posttraumatic osteoarthritis. With the increasing incidence of serious lower extremity injury as a result of motor vehicle accidents, these occult injuries may significantly affect individuals and society.

Accidents, Traffic↗

PubMed1999

Using affinity capillary electrophoresis to study the interaction of the extracellular binding domain of erythropoietin receptor with peptides.

We have shown that affinity capillary electrophoresis (ACE) can be utilized to screen peptides that bind to the extracellular binding domain of the erythropoietin receptor (EBP). The comparison of the cyclic peptides GGTYSCHFGPLTWVCKPQGG (EMP1) GGTYSCHFGPLTAVCKPQGG (EMP13), and LGRKYSCHFGPLTWVCQPAKKD (EMP37) with the linear peptides HFGPLTWV (EMP26) and FMRF as ACE buffer additives were investigated. When EMP1 and EMP37 were the buffer additives, an abrupt change in the electrophoretic mobility of EBP was observed in the electropherogram. When EMP13, EMP26, and FMRF were examined under identical ACE conditions as EMP1 and EMP37, no significant change in the electrophoretic mobility of EBP was observed. These results correlate well with previously reported IC50 competitive binding data; that is, EMP1 and EMP37 bind to EBP while EMP13 and EMP26 bind very weakly. These observations strongly infer that peptide.EBP dimerization were induced by EMP1, and EMP37 but not by EMP13, EMP26 or FMRF. This ACE method provides a rapid tool for the detection of small peptides or drugs that bind to EBP.

Amino Acid Sequence↗

PubMed1999

Shared and unique determinants of the erythropoietin (EPO) receptor are important for binding EPO and EPO mimetic peptide.

We have shown previously that Phe93 in the extracellular domain of the erythropoietin (EPO) receptor (EPOR) is crucial for binding EPO. Substitution of Phe93 with alanine resulted in a dramatic decrease in EPO binding to the Escherichia coli-expressed extracellular domain of the EPOR (EPO-binding protein or EBP) and no detectable binding to full-length mutant receptor expressed in COS cells. Remarkably, Phe93 forms extensive contacts with a peptide ligand in the crystal structure of the EBP bound to an EPO-mimetic peptide (EMP1), suggesting that Phe93 is also important for EMP1 binding. We used alanine substitution of EBP residues that contact EMP1 in the crystal structure to investigate the function of these residues in both EMP1 and EPO binding. The three largest hydrophobic contacts at Phe93, Met150, and Phe205 and a hydrogen bonding interaction at Thr151 were examined. Our results indicate that Phe93 and Phe205 are important for both EPO and EMP1 binding, Met150 is not important for EPO binding but is critical for EMP1 binding, and Thr151 is not important for binding either ligand. Thus, Phe93 and Phe205 are important binding determinants for both EPO and EMP1, even though these ligands share no sequence or structural homology, suggesting that these residues may represent a minimum epitope on the EPOR for productive ligand binding.

Circular Dichroism↗

PubMed1999

A TATA element is required for tRNA promoter activity and confers TATA-binding protein responsiveness in Drosophila Schneider-2 cells.

In contrast to yeast and mammalian systems, which depend principally on internal promoter elements for tRNA gene transcription, insect systems require additional upstream sequences. To understand the function of the upstream sequences, we have asked whether the Bombyx mori tRNACAla and tRNASGAla genes, which are absolutely dependent on these sequences in vitro, also require them for transcription in vivo. We introduced wild-type and mutant versions of the Bombyx tRNAAla genes into Drosophila Schneider-2 cells and found that the tRNACAla gene is efficiently transcribed and that its transcription depends strongly on the distal segment of its upstream promoter. In contrast, the tRNASGAla gene is inefficiently transcribed, and this inefficiency results from lack of a specific sequence within the distal tRNACAla upstream promoter. This sequence, 5'-TTTATAT-3', is sufficient to increase the activity of the tRNASGAla promoter to that of the tRNACAla promoter. Moreover, promoters containing the 5'-TTTATAT-3' element are stimulated by increased levels of cellular TATA-binding protein. Together these results indicate that, in insect cells, a TATA-like element is specifically required to form functional TATA-binding protein-containing complexes that promote efficient transcription of tRNA genes.

Animals↗

PubMed1999

Crystallographic evidence for preformed dimers of erythropoietin receptor before ligand activation.

Erythropoietin receptor (EPOR) is thought to be activated by ligand-induced homodimerization. However, structures of agonist and antagonist peptide complexes of EPOR, as well as an EPO-EPOR complex, have shown that the actual dimer configuration is critical for the biological response and signal efficiency. The crystal structure of the extracellular domain of EPOR in its unliganded form at 2.4 angstrom resolution has revealed a dimer in which the individual membrane-spanning and intracellular domains would be too far apart to permit phosphorylation by JAK2. This unliganded EPOR dimer is formed from self-association of the same key binding site residues that interact with EPO-mimetic peptide and EPO ligands. This model for a preformed dimer on the cell surface provides insights into the organization, activation, and plasticity of recognition of hematopoietic cell surface receptors.

Cell Membrane↗

PubMed1999

Hamstring extensibility and transverse plane knee control relationship in athletic women.

Athletic women are at particular risk for sustaining a non-contact anterior cruciate ligament (ACL) injury. The hamstrings are vital to providing dynamic knee motion control in the sagittal and transverse planes during running stance, and some have suggested this function is enhanced when they are less extensible. This study attempted to determine the correlational relationships between hamstring extensibility and transverse plane knee kinematics and from these data to describe the dynamic transverse plane knee motion control capabilities of the hamstrings. Twenty normal athletic women (mean +/- SD; aged 21 +/- 1.6 years; height 163.3 +/- 5.7 cm; weight 60.1 +/- 3.6 kg) were evaluated for active hamstring extensibility and transverse plane knee kinematic relationships during crossover-cut stance phase. Following crossover-cut training (3 weeks) using the left (preferred) lower extremity as the stance limb, hamstring extensibility was measured. Following this, subjects were fitted with 9 retroreflective markers denoting the local segmental coordinate systems (3 markers each) of the left foot, leg and thigh. Kinematic (3-dimensional, four phase-locked cameras, 200 Hz) knee and ankle data were sampled and analyzed. Descriptive statistics and Pearson correlations between hamstring extensibility and knee and ankle kinematic variables were calculated. Statistical significance was set at P < or = 0.05 with Bonferroni adjustments. Hamstring extensibility (12 degrees +/- 8 degrees terminal extension) revealed low but significant positive correlations with tibial external rotation (6 degrees +/- 10.7 degrees) at heelstrike (19.3 degrees +/- 8.5 degrees knee flexion) (r = 0.62, P = 0.004) and tibial internal rotation (-13 degrees +/- 8.4 degrees) at peak knee flexion (57.8 degrees +/- 9.3 degrees) following heelstrike (r = 0.47, P = 0.01). Increased hamstring extensibility resulted in increased tibial external rotation at heelstrike and decreased tibial internal rotation at peak knee flexion. Increased hamstring extensibility may improve knee extensor efficiency at heelstrike by enabling greater tibial external rotation and protect the ACL at peak knee flexion by decreasing the tibial internal rotation magnitude.

Adult↗

PubMed1999

Meniscal allograft transplantation.

Meniscal allograft transplantation remains an investigational procedure. Loss of native meniscal function has been consistently shown to result in the development and progression of degenerative joint disease. Allograft reconstruction is a technically feasible and reproducible procedure in both animals and humans with demonstrated incorporation of the transplanted graft with host tissue. However, the ultimate success or failure of the meniscal reconstruction cannot be judged solely on demonstration of allograft incorporation. Success must be measured by the prevention or deceleration of the progression of degenerative changes in the knee that has undergone meniscectomy or by the additional stability the reconstruction provides to the knee. To date the long-term viability and function of the meniscal allograft transplant remains unknown.

Animals↗

PubMed1999

Technical pitfalls of anterior cruciate ligament surgery.

Anterior cruciate ligament (ACL) reconstruction is extremely common. Although the number of primary reconstructions is increasing, failures and revision procedures continue to occur at approximately the same frequency. ACL reconstruction is a technically difficult procedure, and many failures can be attributed to surgical error. This article addresses the causes for failure of primary ACL reconstruction that lie within the surgeon's control. Preoperative assessment, surgical technique, and rehabilitation are addressed.

Anterior Cruciate Ligament↗

PubMed1999

An anatomic evaluation of T-Fix suture device placement for arthroscopic all-inside meniscal repair.

This investigation documented the locations of endoscopically applied T-Fix suture devices (Acufex Microsurgical, Mansfield, MA) placed in six fresh-frozen cadaveric knees (age, 60 to 72 years) in relationship to the joint capsule, and adjacent neurovascular and musculotendinous structures. Five T-Fix devices were placed in the posterior meniscal regions at approximately 20 degree intervals. Gross dissection enabled T-Fix bar and suture placement identification. Fifty total devices were placed (23 medially and 27 laterally). Lateral: None of the devices penetrated more superficially than the deepest capsular layer (layer III). Six of the 27 devices placed at the posterior horn of the lateral meniscus pierced the popliteus tendon. None of the bars pierced the lateral collateral ligament (layer III). All devices placed at the posterolateral knee were outside the arcuate ligament (layer III) but inside the fabellofibular ligament (layer II). Medial: Seven of the 23 devices pierced the deep medial collateral ligament (MCL, layer III), and 4 pierced the superficial MCL (layer II). Three devices pierced the sartorius tendon (layer I) and one pierced the gracilis tendon (layer II). None of the medial devices created a plicating effect on the posterior capsule. None of the devices were placed near neurovascular structures. Devices placed within the posterior meniscal horns had a > or =1.5-cm buffer zone from the popliteal neurovascular bundle. Most bars (36 of 50) were anchored to the capsular layer (layer III) after piercing the meniscocapsular junction (layer II). T-Fix devices simulating arthroscopic all-inside meniscal repair provided well-positioned, solid suture anchorage through the junction with no neurovascular involvement. Care needs to be taken when placing lateral (popliteus muscle) and medial (gracilis, sartorius tendons and superficial MCL) devices to avoid possible soft tissue tenodesis.

Aged↗

PubMed1999

The radiographic position of medial and lateral meniscal horns as a basis for meniscal reconstruction.

This investigation attempted to determine the radiographic position of human meniscal horn bony insertion sites. This information would prove vital for anatomically correct osseous tunnel placement necessary for the restoration of a functional meniscus after reconstructive surgery. The native bony insertion sites of the medial and lateral meniscus in 13 fresh-frozen human cadaver knees were radiographically examined. After insertion site outline with 22-gauge fine wire, anteroposterior and lateral radiographs were obtained. Radiographic landmarks were then described in detail. Each meniscal horn was found to have a distinct bony insertion site with characteristic and consistent radiographic landmarks defining its margins. Using an arthroscopic guide, 3/32-inch fine wires were drilled into the center of the lateral (5 specimens) and medial (5 specimens) meniscal horns to validate these locations and to establish the clinical usefulness of these measures. Improved understanding of meniscal horn insertion site locations should improve osseous tunnel placements during meniscal transplantation. In the presence of a properly sized allograft, anatomically correct tunnel placement increases the likelihood of restoring normal meniscal function.

Arthroscopy↗

PubMed1999

New epoetin molecules and novel therapeutic approaches.

Erythropoietin (EPO) is a 34 kDa protein that is the primary regulator of red blood cell production. EPO facilitates its effect by binding to the cell surface EPO receptor which initiates the JAK-STAT signal transduction cascade. The search for small mimetic molecules of EPO has led to the discovery of a family of peptides that demonstrate EPO mimetic activity. A member of this peptide family, EMP1 (EPO mimetic peptide 1), was used to solve the crystal structure of the soluble EPO receptor in complex with this peptide. The structure revealed a 2:2 stoichiometry of receptor to peptide, with each peptide contacting both receptor molecules in a symmetrical fashion. The potency of the EMPs could be improved through the covalent dimerization of two peptide molecules. Further investigations of EMP EPO receptor complex structures revealed the formation of a non-productive receptor dimer using an inactive peptide. An alternative approach towards the identification of an EPO-like mimetic is to target an intracellular signalling molecule such as haematopoietic cell phosphatase (HCP), also known as SHP1. Inhibiting HCP causes responsive cells to be hypersensitive to EPO. The cloned HCP protein has been utilized in screening assays to identify small molecule inhibitors of HCP.

Amino Acid Sequence↗

PubMed1999

Cerebral blood flow changes associated with attribution of emotional valence to pleasant, unpleasant, and neutral visual stimuli in a PET study of normal subjects.

OBJECTIVE: To assist in the development of a model for the psychopathology of emotions, the present study sought to identify the neural circuits associated with the evaluation of visual stimuli for emotional valence. METHOD: Seventeen healthy individuals were shown three sets of emotionally laden pictures carrying pleasant, unpleasant, and neutral content. While subjects evaluated the picture set for emotional valence, regional cerebral blood flow was measured with the use of [15O] water positron emission tomography. Subjective ratings of the emotional valence of the picture sets were recorded. Data were analyzed by comparing the images acquired during the neutral condition with the unpleasant and pleasant image sets and the unpleasant and pleasant conditions with each other. RESULTS: Processing of pleasant stimuli was associated with increased blood flow in the dorsal-lateral, orbital, and medial frontal cortex relative to the unpleasant condition and in the cingulate, precuneus, and visual cortex relative to the neutral condition. Evaluation of unpleasant stimuli activated the amygdala, visual cortex, and cerebellum relative to the pleasant condition and the nucleus accumbens, precuneus, and visual cortex relative to the neutral condition. CONCLUSIONS: Observing and assigning emotional value to unpleasant stimuli produced activations in subcortical limbic regions, whereas evaluation of pleasant stimuli produced activations in cortical limbic areas. These findings are consistent with the notion of a subcortical and archaic danger recognition system and a system detecting pleasantness in events and situations that is phylogenetically younger, involving primarily the prefrontal cortex.

Adult↗

PubMed1999

Cerebral blood flow and personality: a positron emission tomography study.

OBJECTIVE: This study sought to describe brain regions associated with the personality dimension of introversion/extraversion. METHOD: Measures of cerebral blood flow (CBF) were obtained from 18 healthy subjects by means of [150]H20 positron emission tomography. Correlations of regional CBF with introversion/extraversion were calculated, and a three-dimensional map of those correlations was generated. RESULTS: Overall, introversion was associated with increased blood flow in the frontal lobes and in the anterior thalamus. Regions in the anterior cingulate gyrus, the temporal lobes, and the posterior thalamus were found to be correlated with extraversion. CONCLUSIONS: The findings of the study lend support to the notion that introversion is associated with increased activity in frontal lobe regions. Moreover, the study suggests that individual differences in introversion and extraversion are related to differences in a fronto-striato-thalamic circuit.

Adult↗

PubMed1999

Adult smoking in the home environment and children's IQ.

In a sample of 3- and 5-yr.-old children, smoking in the home was found to be significantly and inversely related to IQ. Children of normal birth weight and without neurological impairment had been enrolled in a longitudinal study of child development. Analyses were conducted with sex, ethnicity, socioeconomic status, educational stimulation in the home, day care, and mother's intelligence controlled. Significant results were obtained for scores on the Peabody Picture Vocabulary Test-Revised at age three years and on the major Stanford-Binet Fourth Edition scales at ages three and five years. All effects were for the mother, not the father, smoking in the home.

Adult↗

PubMed1999

Relationship between ankle invertor H-reflexes and acute swelling induced by inversion ankle sprain.

STUDY DESIGN: Single group, post-test design using the uninvolved lower extremity as the experimental control. OBJECTIVES: To determine relationships between ankle swelling and flexor digitorum longus and peroneus longus H-reflex amplitude and latency. BACKGROUND: Primary capsuloligamentous injury, neural injury, and joint effusion and swelling may contribute to H-reflex changes following inversion ankle sprain. The relationship between ankle swelling and invertor or evertor H-reflexes has not been reported. METHODS AND MEASURES: Fifteen subjects with acute grade I or II inversion ankle sprains (mean +/- SD) 6.5 +/- 3 days after onset participated in this study. Swelling was estimated using a tape measure and the figure-of-eight girth assessment method. H-reflexes were determined using standard techniques. Paired t-tests were used to compare mean differences in ankle girth (swelling) and ankle invertor or evertor H-reflex amplitude and latency between the involved and uninvolved limbs. Pearson product moment correlations were used to assess relationships between swelling and H-reflex variables. RESULTS: Involved limb ankle girth was increased with respect to the uninvolved limb (1.5 +/- 0.9 cm) and the involved ankle flexor digitorum longus latency was delayed (0.72 +/- 0.7 ms). There was a moderate positive association (r = 0.73) between the latency delay in the involved ankle flexor digitorum longus and swelling. There were no significant differences in H-reflex amplitude and peroneus longus latency between ankles. CONCLUSIONS: Grade I or II inversion sprains and the related swelling appear to delay involved ankle flexor digitorum longus latency to a greater extent than peroneus longus latency. Clinicians need to direct greater attention to the ankle invertors when designing and implementing ankle rehabilitation programs, particularly during the swelling management phase of treatment.

Acute Disease↗