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Biomedical subjects

L J Walker

Publications and source records attributed to L J Walker.

33 records · Page 2Linked to original sources
PubMed1987

Successful treatment by doxycycline of endocarditis caused by ornithosis.

The case of a 59 year old man with ornithosis endocarditis and a history of contact with pheasants is reported. Treatment with oxytetracycline was not tolerated and so doxycycline was substituted. Over the two year follow up the patient's clinical condition and serial echocardiographic appearances improved and Chlamydia psittaci complement fixation titres returned to normal. Valve replacement was not required.

Doxycycline↗
PubMed1986

Reduced cellular immunity to varicella zoster virus during treatment for acute lymphoblastic leukemia of childhood: in vitro studies of possible mechanisms.

To determine the effect of antileukemic therapy on preexisting immunity to varicella zoster virus, we studied 20 children with acute lymphoblastic leukemia maintained in complete continuous remission for greater than 1 year. Cellular immunity was tested by lymphocyte proliferation in response to varicella antigen. Antiviral antibody was measured using the fluorescent antibody to membrane antigen technique. Reduced lymphocyte proliferation was found in 9 of 16 seropositive patients when compared to an age-related control group. On the other hand, antibody titers in patients receiving chemotherapy remained positive and were essentially unchanged from pretreatment values. Shingles occurred in two of nine children with diminished and none of seven patients with normal cellular immunity, suggesting that proliferative responses to varicella antigen may have predicative value in identifying patients at risk for viral reactivation. Additional studies were done to determine if defective antigen presentation or reduced lymphocyte responder-cell frequency could account for the subnormal proliferative responses. Intact presentation of varicella antigens by patient mononuclear cells to parental, virus-specific T-cell blasts suggested that antigen processing was not defective. However, varicella-specific responder-cell frequencies measured by limiting dilution analysis were found to be depressed in most patients, including some with normal proliferative responses. Our findings indicate that therapy for acute lymphoblastic leukemia in children can be associated with depressed cell-mediated immunity to varicella zoster virus even though patients remain seropositive. Further studies suggest that while monocyte-mediated antigen presentation remains intact, virus-specific lymphocyte numbers decline and probably contribute to decreased cellular immunity to varicella zoster virus in children being treated for leukemia.

Adult↗
PubMed1985

Intravenous catheter-associated fungemia due to Candida rugosa.

We report a case of intravenous catheter-associated fungemia caused by Candida rugosa; this is the first report of such an infection in a human. Multiple cultures of blood taken over a 24-h period and of the intravenous catheter tip were positive for this unusual isolate. The patient was treated with intravenous amphotericin B and made an uneventful recovery. Intravenous cannulae and other intravascular devices are well recognized as potential sites of intravascular infection by a variety of microorganisms, including several Candida species; however, fungemia caused by C. rugosa has not been reported.

Amphotericin B↗
PubMed1984

Free and total putrescine in cerebrospinal fluid quantified by reversed-phase liquid chromatography.

This is a simple, rapid, sensitive method for routine quantification of the polyamine putrescine (1,4-diaminobutane) in cerebrospinal fluid. Sample preparation involves protein precipitation, acid hydrolysis for 18 h (if total putrescine is to be measured), pre-column derivatization with o-phthalaldehyde, and extraction into acetonitrile. The derivative is separated and quantified by "high-performance" liquid chromatography on a reversed-phase C18 radial-compression column. A single chromatographic run takes less than 18 min. Putrescine concentrations as low as 50 nmol/L in cerebrospinal fluid can be detected.

Chemical Precipitation↗
PubMedDate not supplied

Parent and peer contexts for children's moral reasoning development.

This study addressed the polarization among theoretical perspectives in moral psychology regarding the relative significance of parents and peers in children's developing moral maturity. The sample was composed of 60 target children from late childhood and midadolescence, 60 parents, and 60 friends who participated in parent/child and friend/child dyadic discussions of a series of moral conflicts. The quality of parents' and friends' verbal interactions, ego functioning, and level of moral reasoning in these discussions was used to predict the rate of children's moral reasoning development over a 4-year longitudinal interval. Results revealed that interactions with both parents and peers were predictive of children's development but that these two types of relationships influence development in rather different ways. Implications of the findings for the understanding of these socialization agents' roles in moral development are discussed.

Adolescent↗
PubMedDate not supplied

Bacteriocidal properties of platelet concentrates.

Platelet concentrates were contaminated with predetermined numbers of bacteria isolated from patients. Staphylococcus epidermidis and Pseudomonas aeruginosa organisms were killed if the number introduced was less than 10(3). When 10(4) through 10(6) organisms were added, their growth was depressed for 24 hours and then slowly resumed. If more than 10(7) organisms were used, a slow and progressive growth occurred. After the concentrates were contaminated with Staphylocoecus aureus, slow progressive growth occurred regardless of the size of the inoculum. Cultures taken from sample phlebotomies performed on a few donors showed that the number and type of organisms released into the blood during the venepuncture are such that they could usually, but not always, be inactivated by the bacteriocidal property of the platelet packs. This bacteriocidal property will usually allow the platelet packs to be stored at room temperature for considerable amounts of time with relative safety. Bacterial growth will normally occur only when the number of organisms introduced during the venepuncture is quite large, and growth will usually occur during the first 24 hours.

Blood Bactericidal Activity↗
PubMedDate not supplied

Possible neuronal refractory or recovery artifacts associated with recording the mismatch negativity response.

The mismatch negativity (MMN) is an event-related potential that involves a negative voltage shift of baseline electroencephalographic (EEG) activity in the approximate latency window of the N1 and P2 cortical potentials in response to new or novel sounds. The MMN is present at birth and has been hypothesized to serve as an automatic preconscious detector of changes in the auditory environment. Research paradigms used to extract the MMN response from EEG activity have a potential problem related to neuronal refractoriness or recovery. Both N1 and P2 are known to increase in amplitude with longer interstimulus intervals (ISIs). The MMN extraction procedures involve mathematical subtraction of waveforms elicited by standard sounds (with short ISIs) from those recorded to rare deviant sounds (with longer ISIs). Any ISI-dependent amplitude changes in N1 and/or P2 could therefore alter the morphology of the resulting difference wave and lead to misinterpretation of the nature of the underlying MMN generators. We tested 12 young females and found that the MMN can be influenced by ISI-dependent refractory effects that may modify the waveform morphology. This has important clinical implications since the MMN is being investigated as an assessment tool.

Adult↗