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Biomedical subjects

M J Johnson

Publications and source records attributed to M J Johnson.

At least 127 records · Page 7Linked to original sources

Strategies for infant auditory brain stem response assessment.

The use of auditory brain stem response (ABR) represents a new dimension in auditory and neurological pediatric assessment. Because the ABR may be altered by stimulus and procedural variables, the lack of an established standard has reduced its clinical efficiency. This paper describes a suggested ABR protocol for infants. Included are stimulus and electrode considerations, measurement criteria, and procedures. In addition, ABR results are presented from 125 newborns ranging between 40 and 49 weeks gestational age. The effects of age and intensity on latency and amplitude are discussed.

Audiometry↗

Isolated arthroscopic meniscal repair: a long-term outcome study (more than 10 years).

A single surgeon's consecutive series of 50 arthroscopically repaired meniscal tears in 48 patients was retrospectively reviewed. None of these patients had concomitant ligament damage to the knee. The average follow-up period was 10 years, 9 months. Criteria for clinical success included 1) history of pain of grade 1 or less and absence of locking, catching, or giving way; 2) a physical examination demonstrating no significant effusion and a painless and negative jump sign; and 3) no subsequent surgical procedures on the repaired meniscus. Patient satisfaction was quite high, although clinical confirmation was possible in only 38 knees, indicating a clinical success rate of 76%. Bilateral standing radiographs were obtained on these 38 operated knees and were evaluated using Fairbank's classification. Evaluation of the radiographs revealed that 8% of the operated knees had minimal joint changes, as compared with 3% in the contralateral, nonoperated knee. This study demonstrates that arthroscopic meniscal repair in knees with isolated meniscal tears has the potential for a long-term successful clinical and radiographic outcome.

Adolescent↗

Simplified method for detecting tritium contamination in plants and soil.

Cost-effective methods are needed to identify the presence and distribution of tritium near radioactive waste disposal and other contaminated sites. The objectives of this study were to (i) develop a simplified sample preparation method for determining tritium contamination in plants and (ii) determine if plant data could be used as an indicator of soil contamination. The method entailed collection and solar distillation of plant water from foliage, followed by filtration and adsorption of scintillation-interfering constituents on a graphite-based solid phase extraction (SPE) column. The method was evaluated using samples of creosote bush [Larrea tridentata (Sessé & Moc. ex DC.) Coville], an evergreen shrub, near a radioactive disposal area in the Mojave Desert. Laboratory tests showed that a 2-g SPE column was necessary and sufficient for accurate determination of known tritium concentrations in plant water. Comparisons of tritium concentrations in plant water determined with the solar distillation-SPE method and the standard (and more laborious) toluene-extraction method showed no significant difference between methods. Tritium concentrations in plant water and in water vapor of root-zone soil also showed no significant difference between methods. Thus, the solar distillation-SPE method provides a simple and cost-effective way to identify plant and soil contamination. The method is of sufficient accuracy to facilitate collection of plume-scale data and optimize placement of more sophisticated (and costly) monitoring equipment at contaminated sites. Although work to date has focused on one desert plant, the approach may be transferable to other species and environments after site-specific experiments.

Cost-Benefit Analysis↗