PubMed Health⌕ Search

Biomedical subjects

John Smith

Publications and source records attributed to John Smith.

At least 19 recordsLinked to original sources
PubMed2006

Wide-field Fizeau imaging telescope: experimental results.

A nine-aperture, wide-field Fizeau imaging telescope has been built at the Lockheed-Martin Advanced Technology Center. The telescope consists of nine, 125 mm diameter collector telescopes coherently phased and combined to form a diffraction-limited image with a resolution that is consistent with the 610 mm diameter of the telescope. The phased field of view of the array is 1 murad. The measured rms wavefront error is 0.08 waves rms at 635 nm. The telescope is actively controlled to correct for tilt and phasing errors. The control sensing technique is the method known as phase diversity, which extracts wavefront information from a pair of focused and defocused images. The optical design of the telescope and typical performance results are described.

Journal Article↗
PubMed2006

Cryopreservation of economically valuable marine micro-algae in the classes Bacillariophyceae, Chlorophyceae, Cyanophyceae, Dinophyceae, Haptophyceae, Prasinophyceae, and Rhodophyceae.

The ability to routinely cryopreserve micro-algal species reduces costs associated with maintaining large culture collections and reduces the risks of losing particular strains or species through contamination and genetic drift. Cryopreservation is also a useful adjunct in aquaculture hatcheries for strains of micro-algae where the nutritional status may change as a result of continuous sub-culture. In this study, cryopreservation of isolates from seven micro-algal classes was investigated. Successful candidates included the marine dinoflagellates Amphidinium carterae, Amphidinium trulla, and Gymnodinium simplex, and the haptophytes Chrysochromulina simplex, Prymnesium parvum, Prymnesium parvum f. patelliferum, Isochrysis galbana, and Pavlova lutheri. Also successfully cryopreserved were the planktonic diatoms Chaetoceros calcitrans, Chaetoceros muelleri, Chaetoceros sp., and the benthic Nitzschia ovalis, the chlorophyte Chlamydomonas coccoides, the rhodophyte Porphyridium purpureum, the prasinophytes Tetraselmis chuii, and Tetraselmis suecica, and the cyanophytes Raphidiopsis sp., and Aphanizomenon flos-aquae. All species were successfully cryopreserved using 15% Me2SO.

Animals↗
PubMed2006

Left ventricular outflow tract obstruction caused by accessory mitral valve tissue.

This report describes the echocardiographic diagnosis of accessory mitral valve tissue causing left ventricular outflow tract obstruction in a symptomatic man. The accessory tissue was surgically removed and the mitral valve replaced with complete resolution of left ventricular outflow tract gradient and symptoms. The case illustrates the importance of transthoracic and transesophageal echocardiography in the diagnosis and preoperative evaluation of this rare but treatable cause of subaortic valve obstruction.

Humans↗
PubMed2006

Vocal tract resonances and the sound of the Australian didjeridu (yidaki) I. experiment.

The didjeridu, or yidaki, is a simple tube about 1.5 m long, played with the lips, as in a tuba, but mostly producing just a tonal, rhythmic drone sound. The acoustic impedance spectra of performers' vocal tracts were measured while they played and compared with the radiated sound spectra. When the tongue is close to the hard palate, the vocal tract impedance has several maxima in the range 1-3 kHz. These maxima, if sufficiently large, produce minima in the spectral envelope of the sound because the corresponding frequency components of acoustic current in the flow entering the instrument are small. In the ranges between the impedance maxima, the lower impedance of the tract allows relatively large acoustic current components that correspond to strong formants in the radiated sound. Broad, weak formants can also be observed when groups of even or odd harmonics coincide with bore resonances. Schlieren photographs of the jet entering the instrument and high speed video images of the player's lips show that the lips are closed for about half of each cycle, thus generating high levels of upper harmonics of the lip frequency. Examples of the spectra of "circular breathing" and combined playing and vocalization are shown.

Acoustics↗
PubMed2005

HLA-C and killer cell immunoglobulin-like receptor genes in idiopathic bronchiectasis.

RATIONALE: In idiopathic bronchiectasis, lung inflammation and chronic bacterial infection lead to progressive lung damage. A possible role for natural killer (NK) cells is suggested by the observation that familial bronchiectasis occurs in a rare group of individuals with impaired HLA class I expression and consequent NK cell dysfunction. OBJECTIVE: Because the HLA-C locus and killer cell immunoglobulin-like receptors (KIRs) are of key importance for NK cell recognition, we analyzed HLA-C/KIR combinations by genotyping patients with idiopathic bronchiectasis. METHODS: Genomic DNA from 96 individuals with idiopathic bronchiectasis and 101 control subjects was analyzed by polymerase chain reaction with sequence-specific primers. High-resolution HLA-C genotyping was performed in addition to KIR analysis. RESULTS: HLA-Cw*03 alleles and, in particular, HLA-C group 1 homozygosity are associated with the presence of bronchiectasis. Analysis of the relationship between HLA-C and KIR genes suggests a shift to activatory NK cell function. CONCLUSION: This is the first demonstration of genetic susceptibility in idiopathic bronchiectasis. The association with HLA-C group 1 homozygosity, and the interplay between HLA-C and KIR genes, argue for a role for NK cells in the progressive lung damage seen in this disease. This will require further investigation using functional studies.

Bronchiectasis↗
PubMed2005

Anti-intercellular adhesion molecule-1 antibodies in sera of heart transplant recipients: a role in endothelial cell activation.

BACKGROUND: Antiendothelial antibodies to non-human leukocyte antigens are made by a subset of heart transplant recipients, but the specificity of such antibodies is undefined. Intercellular adhesion molecule (ICAM)-1 is an abundantly expressed adhesion molecule with polymorphic residues, expressed on the surface of endothelial cells. The hypothesis that ICAM-1 acts as a minor histocompatibility antigen and that anti-ICAM-1 antibodies, directed against polymorphic residues, could be one component of the antiendothelial antibodies found after heart transplantation has been tested. METHODS: Chinese hamster ovary cells were transfected with full-length polymorphic variants of human ICAM-1. The binding of antibodies (immunoglobulin [Ig] G or IgM) to these cells was measured using sera from 50 heart transplant recipients (pretransplant and 1 and 2 years posttransplant) and sera from 20 normal volunteers by flow cytometry. The recipients and donors were genotyped for ICAM-1 polymorphisms. RESULTS: Sixty-eight percent (n=34) of patients made IgM antibodies that bound to ICAM-1. However, it seems unlikely that ICAM-1 is a minor transplantation antigen, because there were no differences in antibody production from recipients matched or mismatched for ICAM-1 alleles. The antibodies bound to mouse endothelial cells that were engineered to overexpress human ICAM-1, and induced a robust activation of the Erk-2 mitogen-activated protein kinase pathway. CONCLUSIONS: Anti-ICAM-1 antibodies are produced after cardiac transplantation, but not to polymorphic residues. Such antibodies may contribute to the endothelial activation by binding to the endothelium, causing activation of proinflammatory signaling pathways.

Adult↗
PubMed2005

Acoustics: the vocal tract and the sound of a didgeridoo.

The Australian didgeridoo (or yidaki in the Yolngu language of northern Australia) is a simple musical instrument that, at the lips of an experienced player, is capable of a spectacular variety of timbres--considerably greater than those that can be coaxed from orchestral instruments, for example. To understand this phenomenon, we simultaneously measured the sound produced by the didgeridoo and the acoustic impedance of the player's vocal tract. We find that the maxima in the envelope of the sound spectrum are associated with minima in the impedance of the vocal tract, as measured just inside the lips. This acoustic effect is similar to the production of vowel sounds made during human speech or singing, although the mechanism is different, and leads to the surprising conclusion that experienced players are subconsciously using their glottis to accentuate the instrument's tonal variation.

Acoustics↗
PubMed2005

Pediatric patient surface doses in neuroangiography.

BACKGROUND: Neuroangiographic techniques (diagnostic and interventional) can be lengthy and complex and can be associated with high radiation entrance skin doses from fluoroscopy and digital subtraction angiography (DSA). OBJECTIVE: To measure entrance surface doses received by pediatric patients undergoing neuroangiographic procedures and to (1) compare these doses with thresholds for deterministic effects, (2) compare these doses with those reported in adults, and (3) to understand the dose relationships among diagnostic and interventional procedures, DSA and fluoroscopy. MATERIALS AND METHODS: A neurobiplane unit with fluoroscopic and DSA capabilities was used for all neuroangiographic procedures. An automated patient dosimeter, installed on both planes of the unit, calculated maximum surface dose. The dosimeter also recorded the number of angiographic frames and the length of fluoroscopy time for each procedure. RESULTS: This retrospective study analyzed entrance surface doses to 100 pediatric patients, 76 of whom underwent neuroangiographic diagnostic procedures and 24 of whom underwent neuroangiographic interventional procedures. The DSA acquisitions ranged from 44 frames to 1,428 frames per procedure and fluoroscopy times ranged from 1.1 to 85.6 min per procedure. The mean surface dose from fluoroscopy was 68.1 mGy (max: 397.1 mGy) in the frontal (PA) plane; in the lateral (LAT) plane, the mean surface dose was 40.9 mGy (max: 418.5 mGy). The mean surface doses from DSA were 263.1 and 126.9 mGy in the frontal and lateral planes, with maximum doses of 924.4 and 410.1 mGy, respectively. Mean fluoroscopy dose rates were 5.4 mGy/min in the PA plane and 4.7 mGy/min in the LAT plane. The DSA largely contributed to the overall procedural surface dose, accounting for 82% of the combined surface dose in the each of the imaging planes. CONCLUSION: The surface dose for each procedure measured in this study was found to be below thresholds for deterministic effects. Interventional procedures consistently yield the highest doses.

Adolescent↗
PubMed2005

Lack of adult-type salivary cortisol circadian rhythm in hospitalized preterm infants.

BACKGROUND/AIMS: Knowledge of the presence or absence of cortisol (F) circadian rhythm in preterm infants is important for the interpretation of F measurements made in samples taken for both clinical and research purposes. Little is known about its emergence in very preterm infants. This study examines circadian rhythm in F secretion in hospitalized infants born before 30 weeks' gestation. METHODS DESIGN: Prospective longitudinal observational study. SUBJECTS: 11 infants admitted consecutively and born before 30 completed weeks of gestation. MEASUREMENTS: F was measured by highly specific radioimmunoassay on morning and evening saliva samples gathered at weekly intervals until discharged home. Circadian rhythm was defined as > or =40% reduction from morning to evening level. RESULTS: For all data, the median salivary F was 10.3 nmol/l (range <0.5-372.8). F levels were highest in the first 3 weeks of life. No infants displayed classical circadian rhythm for 4 weeks or more prior to being discharged from hospital. The other infants showed randomly distributed morning and evening F values with a trend in 4 infants towards periods of consistently higher evening than morning values. CONCLUSION: Adult-type F circadian rhythm is rarely evident in hospitalized preterm infants born before 30 weeks' gestation.

Circadian Rhythm↗
PubMed2005

Student-selected components in the undergraduate medical curriculum: a multi-institutional consensus on assessable key tasks.

This paper describes further progress by the Northern Universities SSC Consortium in achieving consensus on the contribution of the Student Selected Components (SSCs) to undergraduate medical courses. Following the identification of common purposes and outcomes, the group has matched these to assessable key tasks which students may undertake in order to demonstrate competence on a range of attributes not normally fully assessed in the core curriculum. In some schools, SSCs may be the predominant route through which students gain exposure to research methods and reflective practice. In addition to opportunities to acquire knowledge and skills outside the core curriculum, SSCs can contribute towards enhancement of core skills. SSCs may also contribute to the overall longitudinal assessment of personal and professional development. The potential role of portfolios in maximizing student learning from SSCs is discussed, and future areas for development identified.

Choice Behavior↗
PubMed2005

Array analysis of simian varicella virus gene transcription in productively infected cells in tissue culture.

Simian varicella virus (SVV) is a neurotropic alphaherpesvirus of monkeys that is a model for varicella pathogenesis and latency. Like human varicella-zoster virus (VZV), SVV causes chicken pox (varicella), becomes latent in ganglia along the entire neuraxis, and reactivates to produce shingles (zoster). We developed macroarrays to determine the extent of viral transcription from all 70 predicted SVV open reading frames (ORFs) in infected cells in tissue culture. Cloned fragments (200 to 400 bp) from the 5' and 3' ends of each ORF were PCR amplified, quantitated, spotted onto nylon membranes, and fixed by UV cross-linking. Using a cDNA probe prepared from poly(A)+ RNA extracted from SVV-infected Vero cells at the height of the cytopathic effect (3 days after infection) and chemiluminescence for detection, transcripts corresponding to all SVV ORFs were identified. The abundance of each SVV transcript was compared with that previously demonstrated for VZV in infected tissue culture cells.

Animals↗
PubMed2004

The role of coronary angiography in acute type A aortic dissection.

OBJECTIVES: In recent years, non-invasive methods have replaced angiography in the diagnosis of aortic dissection. Angiography maybe used to evaluate coexisting coronary artery disease (CAD), which can delay surgery and increase the risk of rupture. We set out to examine the role of angiography in acute aortic dissection. METHODS: A retrospective analysis of patients who underwent repair of acute aortic dissection between January 1992 and June 2002 was conducted. The effect of angiography on the need for concomitant coronary artery surgery (CABG), delay to surgery and outcome were analysed. RESULTS: Seventy-four patients were identified. Initial diagnosis was established by non-invasive techniques. Twenty-three patients (31%) underwent angiography (Group I) in three this was unsuccessful. Three in Group I and four in the non-angiography group (Group II, n=51) had history of angina. One patient in Group I underwent concomitant CABG compared to seven in Group II. The patient who underwent CABG in Group I; and four out of seven in Group II died (NS). Patients who underwent concomitant CABG had a significantly higher mortality rate (P=0.04). Mortality in Group I was 35% (n=8) and in Group II was 29% (n=15) (NS). Mortality rate was also significantly higher in patients who presented with syncope (P=0.01) or hypotension (P=0.04). Median transfer time from arrival at our centre to the operating room was 5 h in Group I and 1.5 h in Group II (P<0.001). Mortality rate was higher in patients who took longer to transfer to the operating room, but this did not reach statistical significance. CONCLUSIONS: We have shown that coronary angiography did not affect the occurrence of CABG and was not associated with improved hospital survival. Furthermore, there is a considerable delay to surgery caused by angiography. Therefore in this setting coronary angiography is not recommended.

Acute Disease↗
PubMed2004

Student-selected components in the undergraduate medical curriculum: a multi-institutional consensus on purpose.

Student-selected components (SSCs) are an established part of undergraduate medical curricula in the UK. Implementation has been against a background of differing educational approaches to curricular change, together with a lack of clarity about their purpose, relationship with the core curriculum and contribution to overall assessment. This has resulted in a diversity of programmes with perceived differing importance between medical schools. This paper documents the approach used by a consortium of medical schools with diverse curricula to develop consensus on the educational purpose and learning outcomes of SSCs. Agreement on common purposes and outcomes was achieved, and consensus documents are reported. These may be valuable for other medical schools implementing any form of student-selected project work. This work will now be the starting point for further work on producing recommendations for assessment of SSCs, which will be applicable across different medical schools.

Choice Behavior↗
PubMed2004

Vocal tract resonances in singing: the soprano voice.

The vocal tract resonances of trained soprano singers were measured while they sang a range of vowels softly at different pitches. The measurements were made by broad band acoustic excitation at the mouth, which allowed the resonances of the tract to be measured simultaneously with and independently from the harmonics of the voice. At low pitch, when the lowest resonance frequency R1 exceeded f0, the values of the first two resonances R1 and R2 varied little with frequency and had values consistent with normal speech. At higher pitches, however, when fo exceeded the value of R1 observed at low pitch, R1 increased with f0 so that R1 was approximately equal to f0. R2 also increased over this high pitch range, probably as an incidental consequence of the tuning of R1. R3 increased slightly but systematically, across the whole pitch range measured. There was no evidence that any resonances are tuned close to harmonics of the pitch frequency except for R1 at high pitch. The variations in R1 and R2 at high pitch mean that vowels move, converge, and overlap their positions on the vocal plane (R2,R1) to an extent that implies loss of intelligibility.

Acoustics↗
PubMed2004

Management of patients undergoing coronary artery bypass graft surgery with mild to moderate aortic stenosis.

BACKGROUND AND AIM OF THE STUDY: The management of patients undergoing coronary artery bypass graft (CABG) surgery with mild to moderate aortic stenosis (AS) remains controversial. The study aim was to examine the outcome in patients with mild to moderate AS undergoing CABG. METHODS: A retrospective analysis was carried out of 200 patients with coronary artery disease requiring CABG and with a peak AS gradient < 40 mmHg measured by Doppler echocardiography, between 1990 and 2000. Among patients, 154 underwent isolated CABG (group A) and 46 CABG + aortic valve replacement (AVR) (group B). RESULTS: Mortality was 2.6% (n = 4) in group A and 6.5% (n = 3) in group B (p = NS). The median AS gradients were 34 and 40 mmHg, respectively. Thirty patients (20%) in group A were in NYHA class III-IV compared to 20 (44%) in group B (p = 0.002). There was no significant difference in postoperative complications. The mean intensive care unit stay was 2.3 and 2.2 days, respectively (p = NS); median postoperative stay was 6 and 8 days, respectively (p = 0.02). During the median follow up period of 4.2 years no patient in group A required AVR. Nine late deaths occurred in group B, none of which was cardiac-related. CONCLUSION: Morbidity and mortality in patients who underwent combined surgery was comparable with that in patients who had isolated CABG. However, none of the patients who underwent only CABG required AVR during the follow up period. It is concluded that patients with mild AS at the time of CABG should not undergo AVR. It is possible that a cut-off AS gradient > 40 mmHg should be considered for combined surgery.

Aged↗