Biomedical subjects

John A Barnard

Publications and source records attributed to John A Barnard.

5 recordsLinked to original sources

PubMed2006

Dendrimer pattern formation in evaporating drops.

The redistribution of organic solutes during drop evaporation is a nanoscale self-assembly process with relevance to technologies ranging from inkjet printing of organic displays to synthesis of biosmart interfaces for sensing and screening. We have used solutions of dendrimer molecules with incrementally varying terminal site chemistry to explore whether the condensed dendrimer patterns resulting from microdroplet evaporation sensitively depend on, and are characteristic of, the surface chemistry of the solute molecules. This hypothesis has been experimentally confirmed by comparing the behavior of microdroplets of G4, G4-25%C12, and G4-50%C12 dendrimers dissolved in pentanol and deposited on mica substrates. For the dilute concentration studied here, the presence of periodically 'scalloped' dendrimer rings is ubiquitous. The instability wavelength of the scalloped rings is found to be proportional to the width of the ring, similar to observations of the rim instability in dewetting holes. The effect of dendrimer surface chemistry is obvious in the detailed structure of the self-assembled rings. G4 rings are diffuse and disordered with no evidence for layered growth. G4-25%C12 exhibits highly ordered ring structures and the onset of monomolecular terracing. G4-50%C12 exhibits highly periodic scallops and very distinct monomolecular height terraced growth of the rings with flat terraces and sharply defined steps. On the basis of these results, it is likely that the morphology of condensed molecule-based ring patterns formed by evaporation of microdroplets on surfaces can be used as a 'fingerprint' to identify, for example, solute molecule surface chemistry and concentration and function as a sensor for a variety of biochemical events.

Journal Article↗

PubMed2004

Gastrointestinal polyps and polyp syndromes in adolescents.

Although gastrointestinal polyps are more common in the first decade of life than during adolescence, underlying genetic polyposis syndromes are more likely in adolescents. In the past decade, the discovery of gene defects associated with polyposis syndromes has improved classification of these disorders, assisted in the stratification of cancer risk, and permitted more precise diagnosis. Genetic testing is now clinically available for the gene defects that occur in familial adenomatous polyposis coli, Peutz-Jeghers syndrome, Cowden syndrome, and juvenile polyposis syndrome. This review outlines clinical features, genetics, and management strategies for the major polyposis syndromes that affect adolescents.

Adenomatous Polyposis Coli↗

PubMed2002

Removal of esophageal foreign bodies in the pediatric ED: is ketamine an option?

The objective of the study was to evaluate our experience with esophageal foreign body (EFB) removal comparing the use of ketamine-midazolam (K-M) and fentanyl-midazolam (F-M) in the emergency department (ED), to admission and general anesthesia (GA) in the operating room (OR). A retrospective review of all children undergoing EFB removal at our institution during a 2-year period was conducted. A total of 93 patients were identified: K-M 57/93 (61.2%), F-M 28/93 (30.1%), GA 5/93 (5.4%), and 3/93 (3.2%) by other means. Mean procedure durations were 4.8 min for K-M and 7.0 min for F-M. Mean lengths of stay (LOS) for ED procedures were 3.6 hrs for K-M and 5.7 hrs for F-M, versus 17.7 hrs if admitted. Transient hypoxemia occurred in 10.7% of K-M and 15.4% of F-M. Removal of EFBs in the ED may obviate the need for admission. In our experience, the use of K-M is associated with fewer airway complications, shorter removal times, and an overall shorter LOS.

Anesthesia Department, Hospital↗

PubMed2002

Children's knowledge, anticipatory anxiety, procedural distress, and recall of esophagogastroduodenoscopy.

BACKGROUND: This study evaluates the relations among children's knowledge of esophagogastroduodenoscopy (EGD) and anticipatory anxiety, procedural distress, and the nature of postprocedural recall and evaluations. METHODS: One hundred patients, aged 8 to 17 years, completed self-report measures of knowledge and anxiety before EGD. Parents completed a self-report measure assessing how they prepared their children. Nurses and trained observers completed observational ratings of distress. Children's recall and evaluation of the procedure were assessed by self-report 1 hour after the procedure and by telephone that evening. RESULTS: Most children knew about the major components of EGD. Children with greater knowledge experienced less distress and reported that they would be less anxious and upset when undergoing future EGDs. Children with greater anticipatory anxiety exhibited more procedural distress. Children's distress varied by the phase of the procedure. Children who were more distressed during intravenous line insertion experienced greater distress during esophageal intubation and the endoscopic examination. Approximately 20% of patients reported at least some memory of the procedure even at the end of the day. Children with greater recall reported greater aversion and a more negative attitude toward future EGDs. CONCLUSIONS: This study provides information about children's distress during EGD and the effects of conscious sedation on patients' memories and attitudes toward future procedures. The study indicates that preparation before EGD may reduce patient distress.

Adolescent↗

PubMed2002

Gastrointestinal polyps and polyposis syndromes in children.

Gastrointestinal polyps are common during childhood and most often present with painless rectal bleeding. Most polyps occur as isolated colonic lesions and are not harbingers of an underlying genetic disorder, nor do they bestow a risk of gastrointestinal cancer. The astute pediatrician must be aware, however, that occasionally polyps may occur in the context of a genetic polyposis disorder characterized by an increase in the life-time risk of cancer in the gastrointestinal tract and other organ systems. This review outlines the major polyposis syndromes affecting children and highlights associated findings that might clue the alert physician to an underlying diagnosis. Recent developments in the understanding of the genetics of each disorder are emphasized.

Adenomatous Polyposis Coli↗