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Biomedical subjects

R L Johnson

Publications and source records attributed to R L Johnson.

At least 181 records · Page 10Linked to original sources
PubMed1992

Biocompatibility of retrograde filling materials in the ferret canine. Amalgam and IRM.

Periapical tissue response to retrograde fillings of amalgam and IRM were compared in the mandibular canine of the adult male ferret. Teeth were cleaned and shaped with a standard technique and obturated with gutta-percha. The root apex was then exposed and retrofillings were placed. The animals were grouped according to observation periods of 5, 10, and 15 weeks. At the proper time the animals were killed and the lower canine tooth along with the surrounding bone was removed. The tissue blocks were examined clinically, radiographed, and prepared for histologic examination. The clinical and radiographic examination indicated both materials to be well tolerated by periapical tissues. Microscopic examination of amalgam specimens showed a decrease in inflammation and the formation of a fibrous capsule over the 15-week period. IRM specimens showed persistent inflammation and slower healing potential.

Alveolar Process↗
PubMed1992

Health and psychosocial issues of individuals with incomplete and resolving spinal cord injuries.

Longitudinal data and clinical experience indicate that a greater proportion of spinal cord injuries result in incomplete or resolving neurological lesions. Although it has been reported that persons with incomplete injuries enjoy better functional outcomes, routine contacts with these individuals indicate that many experience problems and complications strikingly similar to those with complete spinal cord injuries. Thus, to document the issues and needs of these individuals, data from Colorado's population-based spinal cord injury surveillance program were analyzed. Of 330 persons registered since January 1, 1986, 121 (37%) were found to be minimally disabled (Frankel class D or E). Review of medical records and follow up documentation for these individuals indicated that although over 75% were ambulatory and virtually all were physically independent, more than 80% did report problems in one or more areas: 21% had orthopedic issues and 17% faced additional spinal surgery; 16% reported neurological deterioration or increased spasticity; 25% had pain problems; and 16% had bladder difficulties. Other issues included bowel problems, blood pressure abnormalities, skin breakdown, sexual difficulties, depression, and unemployability. Implications for rehabilitation are discussed in the light of these and other findings.

Colorado↗
PubMed1992

Performance measures, blood lactate and plasma ammonia as indicators of overwork in elite junior weightlifters.

The effects of short-term overwork on performance measures, blood lactate, and plasma ammonia concentrations were examined in 28 elite junior weightlifters who participated in a 2 wk high volume resistance training camp. Performance testing (maximum effort vertical jump test and snatch lift) and blood chemistry analyses (ammonia and lactate) were conducted before (T1) and after (T2) 7 d of high volume training (2-3 workouts/d). Blood samples were collected from an antecubital vein at rest, preexercise, 5 min postexercise, and 15 min postexercise at T1 and T2. Results indicated a significant decrease from T1 to T2 in the maximum effort vertical jump test while the snatch lift test yielded no difference across time. Blood lactate and ammonia concentrations were significantly lower at 5 min postexercise at T2 while resting ammonia concentrations were significantly elevated at T2 compared to corresponding measures at T1. These data suggest possible early symptoms of overwork at T2 (decrease in performance of the maximum effort vertical jump test and the elevated resting ammonia concentrations); however, lower 5 min postexercise concentrations of lactate and ammonia at T2 indicated a positive adaptation to the 1 wk high volume resistance training period.

Adolescent↗
PubMed1992

The entrepreneurial physician.

This article draws on the experience of interviews of hundreds of physicians in the last few years. Those at mid-career have deep concerns about what lies ahead for them. A character, Dr. Charles Evans, has been created to describe some of the major possibilities being thought about and explored by physicians who believe their profession is now changing in ways they never had anticipated.

Defensive Medicine↗
PubMed1992

Respiratory muscle blood flow in exercising dogs after pneumonectomy.

In three foxhounds after left pneumonectomy, the relationships of ventilatory work and respiratory muscle (RM) blood flow to ventilation (VE) during steady-state exercise were examined. VE was measured using a specially constructed respiratory mask and a pneumotach; work of breathing was measured by the esophageal balloon technique. Blood flow to RM was measured by the radionuclide-labeled microsphere technique. Lung compliance after pneumonectomy was 55% of that before pneumonectomy; compliance of the thorax was unchanged. O2 uptake (VO2) of RM comprised only 5% of total body VO2 at exercise. At rest, inspiratory muscles received 62% and expiratory muscles 38% of the total O2 delivered to the RM (QO2RM). During exercise, inspiratory muscles received 59% and expiratory muscles 41% of total QO2RM. Blood flow per gram of muscle to the costal diaphragm was significantly higher than that to the crural diaphragm. The diaphragm, parasternals, and posterior cricoarytenoids were the most important inspiratory muscles, and internal intercostals and external obliques were the most important expiratory muscles for exercise. Up to a VE of 120 l/min through one lung, QO2RM constituted only a small fraction of total body VO2 during exercise and maximal vasodilation in the diaphragm was never approached.

Animals↗
PubMed1992

Cardiopulmonary adaptations to pneumonectomy in dogs. I. Maximal exercise performance.

Maximal exercise performance was evaluated in four adult foxhounds after right pneumonectomy (removal of 58% of lung) and compared with that in seven sham-operated control dogs 6 mo after surgery. Maximal O2 uptake (ml O2.min-1.kg-1) was 142.9 +/- 1.9 in the sham group and 123.0 +/- 3.8 in the pneumonectomy group, a reduction of 14% (P less than 0.001). Maximal stroke volume (ml/kg) was 2.59 +/- 0.10 in the sham group and 1.99 +/- 0.05 in the pneumonectomy group, a reduction of 23% (P less than 0.005). Lung diffusing capacity (DL(CO)) (ml.min-1.Torr-1.kg-1) reached 2.27 +/- 0.08 in the combined lungs of the sham group and 1.67 +/- 0.07 in the remaining lung of the pneumonectomy group (P less than 0.001). In the pneumonectomy group, DL(CO) of the left lung was 76% greater than that in the left lung of controls. Blood lactate concentration and hematocrit were significantly higher at exercise in the pneumonectomy group. We conclude that, in dogs after resection of 58% of lung, O2 uptake, cardiac output, stroke volume, and DL(CO) at maximal exercise were restricted. However, the magnitude of overall impairment was surprisingly small, indicating a remarkable ability to compensate for the loss of one lung. This compensation was achieved through the recruitment of reserves in DL(CO) in the remaining lung, the development of exercise-induced polycythemia, and the maintenance of a relatively large stroke volume in the face of an increased pulmonary vascular resistance.

Animals↗
PubMed1992

The philosophy of administrative fellowships.

The administrative fellowship, which has its roots in the origins of health administration education, had gone by the wayside as the programs became more oriented to the university setting, rather than the practice setting. The author makes the case that restoring the administrative fellowship to the standard course of study would close the gap he sees between practice and academia. He then states that opportunities to learn on the job in fields such as hospital consulting have dwindled and that administrative fellowships would help program graduates get the exposure to problems and the decision-making skills necessary to be competitive in the job market.

Consultants↗
PubMed1992

Sexual behaviors of African-American male college students and the risk of HIV infection.

A survey of the rates of sexually transmitted diseases and protective sexual behaviors among a population of African-American male college students demonstrates that although monogamy, avoidance of casual sexual activity, and the avoidance of the use of drugs and alcohol during sexual activity tends to decrease the risk of exposure to human immunodeficiency virus, consistent condom use is the only sexually related behavior that is significantly protective.

Acquired Immunodeficiency Syndrome↗
PubMed1992

Effect of musculoskeletal development on the prediction of body density in females.

The purpose of this study was to determine if musculoskeletal development had a significant effect on the prediction of body density in females. Subjects consisted of 156 females aged 17 to 44 years. Subjects were divided into three groups on the basis of musculoskeletal development as determined by the Heath-Carter Anthropometric Somatotype mesomorphy rating. Anthropometric measurements included eight skinfold measures (tricep, subscapula, chest, midaxillary, abdomen, suprailiac, thigh, and calf), body diameters of the humerus and femur, and circumferences at five locations (waist, forearm, upper arm, calf, and gluteal). Residual lung volume was determined by the closed circuit oxygen dilution method prior to the measurement of body density by hydrostatic weighing. A regression equation was developed to predict body density from the sum of seven skinfolds, sum of seven skinfolds squared, age, and mesomorphy rating. A similar regression equation was developed using the sum of three skinfolds, sum of three skinfolds squared, and the other variables. Results indicated that mesomorphy rating did not contribute significantly to the prediction of body density in females. It was concluded that musculoskeletal development did not have a significant effect on the prediction of body density in females.

Adolescent↗
PubMed1991

Characterization of retinal and hippocampal L-AP4 receptors using conformationally constrained AP4 analogues.

In the past, the absence of useful 2-amino-4-phosphonobutanoic acid (AP4) analogues has hampered the pharmacological study and comparison of different systems which are sensitive to L-AP4. Several conformationally constrained AP4 analogues have now been synthesized: (E)- and (Z)-1-amino-3-phosphonocyclopentanecarboxylic acid [(E)- and (Z)-cyclopentyl AP4], and (E)- and (Z)-1-amino-3-phosphonocyclohexanecarboxylic acid [(E)- and (Z)-cyclohexyl AP4], and the recently synthesized cyclopropyl analogues (E)- and (Z)-2-amino-2,3-methano-4-phosphonobutanoic acid [(E)- and (Z)-cyclopropyl AP4]. Therefore, we have examined and report here the pharmacology of two retinal and two hippocampal L-AP4 sensitive systems using these analogues. In addition, the pharmacology of two kainic acid/alpha-amino-3-hydroxy-5-methylisoxazole-4- propionic acid (KAIN/AMPA) pathways and one N-methyl-D-aspartate (NMDA) hippocampal pathway was examined. We found that the rank order potency of the L-AP4 sensitive systems were similar though not identical. The KAIN/AMPA and NMDA systems had a quite different rank order of potencies than the L-AP4 systems. These data suggest that the L-AP4 receptors in these different systems are structurally similar to each other and differ from both KAIN/AMPA and NMDA receptors.

Aminobutyrates↗
PubMed1991

Overexpression of the cAMP receptor 1 in growing Dictyostelium cells.

cAR1, the cAMP receptor expressed normally during the early aggregation stage of the Dictyostelium developmental program, has been expressed during the growth stage, when only low amounts of endogenous receptors are present. Transformants expressing cAR1 have 7-40 times over growth stage and 3-5-fold over aggregation stage levels of endogenous receptors. The high amounts of cAR1 protein expressed constitutively throughout early development did not drastically disrupt the developmental program; the onset of aggregation was delayed by 1-3 h, and then subsequent stages proceeded normally. The affinity of the expressed cAR1 was similar to that of the endogenous receptors in aggregation stage cells when measured either in phosphate buffer (two affinity states with Kd's of approximately 30 and 300 nM) or in 3 M ammonium sulfate (one affinity state with a Kd of 2-3 nM). When expressed during growth, cAR1 did not appear to couple to its normal effectors since these cells failed to carry out chemotaxis or to elevate cGMP or cAMP levels when stimulated with cAMP. However, cAMP stimulated phosphorylation, and loss of ligand binding of cAR1 did occur. Like aggregation stage control cells, the cAR1 protein shifted in apparent molecular mass from 40 to 43 kDa and became highly phosphorylated when exposed to cAMP. In addition, the number of surface cAMP binding sites in cAR1 cells was reduced by over 80% during prolonged cAMP stimulation. These results define a useful system to express altered cAR1 proteins and examine their regulatory functions.

Cyclic AMP↗
PubMed1991

On the anisotropy of the canine diaphragmatic central tendon.

We studied the mechanical and anatomical anisotropy of the canine diaphragmatic central tendon (CT). Dumb-bell-shaped strips with effective dimensions of 10 x 2 mm (length x width) were cut from different regions of the canine diaphragmatic CT in two different orientations relative to the direction of neighboring muscle fibers. Specimens sampled with their long axial dimension oriented parallel to the neighboring muscle fibers were named Group-1 and those sampled with an orientation perpendicular to the neighboring muscle fibers were named Group-2. Results from one-dimensional stress-strain and tensile failure strength tests revealed that the CT is a nonlinear, inelastic, and anisotropic material. Group-1 specimens were found to have a higher stiffness, higher failure strength and higher strain energy density at failure than Group-2 specimens. Polarized microscopy showed that multiple sheets of collagen fiber bundles formed an orthogonal network in the tendon. Collagen fiber bundles along Group-1 direction formed parallel trajectory lines connecting the neighboring costal and crural muscles; bundles along Group-2 direction were observed to orient 90 degrees away. At the central apex region of the CT, collagen bundles of Group-1 formed a fan-like trajectory pattern. This collagen network architecture was compared favorably to the trajectories of an approximated principal stress field in the CT due to simulated contractile forces from its adjacent costal and crural muscles. These combined results suggest a structure-function relationship for the anatomical and mechanical anisotropy in the canine diaphragmatic CT.

Animals↗
PubMed1991

Estimation of diffusion limitation after pneumonectomy from carbon monoxide diffusing capacity.

In three foxhounds, diffusing capacity for carbon monoxide (DLCO) was reduced by 25-30% after left pneumonectomy. Based on previous morphometric data in animals and physiologic data in humans, this reduction should not result in any impairment in gas exchange. However, experimental evidence indicates that diffusion limitation develops during exercise after pneumonectomy. Our objective is to determine whether this diffusion limitation to gas exchange can be predicted from physiologic measurements of DLCO. DLCO measured by the rebreathing technique was translated into diffusing capacity for O2 (DLO2) using an average conversion factor for canids obtained morphometrically (Weibel et al., Respir. Physiol. 54: 173-188, 1983). Arterial O2 saturation (SaO2) at various intensities of steady state exercise was calculated from DLO2 and measured values of O2 consumption, alveolar PO2, hemoglobin and arterial pH, and compared to observed SaO2. After pneumonectomy, SaO2 declined progressively with increasing exercise load. In all dogs, the observed pattern of arterial O2 saturation could be predicted from DLCO measured at similar work loads. The relationship between predicted (Pr) and observed (Ob) SaO2 is: SaO2(Pr) = 22.73 + 0.77SaO2(Ob), r = 0.92. The slope is significantly less than 1.0 (P less than 0.005), indicating that other factors must also contribute to arterial desaturation. We conclude that physiologic measurement of DLCO is a meaningful indicator of diffusion limitation to gas exchange. In the foxhound, a modest reduction in DLCO significantly impairs O2 transport during exercise; but other gas exchange abnormalities, e.g. ventilation perfusion inhomogeneity, must also develop.

Animals↗
PubMed1991

Depression in inner city adolescents attending an adolescent medicine clinic.

Interviews of 70 healthy inner city adolescents attending an adolescent medicine clinic, using the Diagnostic Interview for Children and Adolescents (DICA), revealed that 13% met criteria for current major depressive disorder. Lifetime diagnoses of major depression were found in 30% of the subjects, with many describing recurrent episodes and chronic residual symptoms. Depression in inner city adolescents represents a serious problem that may be best first detected in a medical setting.

Adolescent↗
PubMed1991

HIV-relevant sexual behavior among a healthy inner-city heterosexual adolescent population in an endemic area of HIV.

The AIDS crisis has devastated segments of the population including the gay community and those who use intravenous drugs. HIV has spread to other groups including prostitutes and those with other sexually transmitted diseases. We have been studying adolescents in a major Northeast city where there is a major HIV/AIDS epidemic. Despite high levels of AIDS related knowledge, these adolescents reported high levels of sex risk behaviors. In addition, our data suggests that even moderate alcohol or marijuana use predicts high risk sexual behaviors. These data indicate the urgent need to develop prevention strategies for the spread of HIV among inner-city youth based upon relevant predictors of risk behaviors. The coupling of HIV in inner-city populations with a high frequency of risk behaviors in adolescents demands an immediate public health response.

Adolescent↗
PubMed1991

Synthesis of the 2-amino-4-phosphonobutanoic acid analogues (E)- and (Z)-2-amino-2,3-methano-4-phosphonobutanoic acid and their evaluation as inhibitors of hippocampal excitatory neurotransmission.

The cyclopropyl compounds (Z)- and (E)-2-amino-2,3-methano-4-phosphonobutanoic acid, 5 and 6, respectively, were prepared as constrained analogues of 2-amino-4-phosphonobutanoic acid (AP4), a selective glutamate receptor ligand. A Horner-Emmons reaction of trimethyl N-(benzyloxycarbonyl)phosphonoglycinate with 2-(diethoxyphosphinyl)acetaldehyde gave the protected dehydroamino acids 9 and 10, which were individually subjected to the following sequence of reactions: cycloaddition of diazomethane, photoelimination of N2, and acid hydrolysis, to give 5 and 6, respectively. Extracellular recording techniques were used to evaluate the abilities of 5 and 6 to block evoked synaptic transmission in specific neuronal pathways of the rat hippocampal slice. In the lateral perforant path (LPP) 5 and 6 were equipotent and possessed IC50 values of 18 and 17 microM, respectively. In the medial perforant path (MPP), 6 (IC50 = 81 microM) was much more potent than 5 (IC50 = 1580 microM). In paired pulse experiments which differentiate presynaptic and postsynaptic inhibition, 5 and 6 enhanced the second response to the same extent as L-AP4, suggesting a presynaptic site of action for these compounds. In contrast, the cyclopentyl AP4 analogues 3 and 4 enhanced the second response to a lesser extent. It was concluded that the biologically active conformation of AP4 in the LPP is different than in the MPP. In order to explain the same potency of 5 and 6 in the LPP, it was postulated that the two analogues assume a conformation that allows their functional groups to occupy the same relative place in space. Molecular modeling showed that the best overlap was achieved when the alpha C-beta C-gamma C-P dihedral angle for 5 was in the range of 130 degrees to 180 degrees and that of 6 was in the range of -130 degrees to -180 degrees. The results suggest that the bioactive conformation of AP4 in the LPP is an extended one.

Aminobutyrates↗
PubMed1991

Whose child is this? Assessment and treatment of children in foster care.

Clinicians who treat children in foster care must continually balance the development and therapeutic needs of the foster child with the expectations of a complex network of caretakers and professionals with whom the child interacts. A model that integrates individual and systemic issues in the assessment and treatment of children in foster care is proposed.

Adaptation, Psychological↗