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Biomedical subjects

B Cowan

Publications and source records attributed to B Cowan.

At least 19 recordsLinked to original sources
PubMed2006

Spinodal decomposition in solid isotopic helium mixtures.

We report the first observations of spinodal decomposition in solid helium isotopic mixtures, using NMR measurements. The experiments were performed at a 3He concentration of 50% where the transition proceeds through the critical point. We used an initial pressure such that the system remained solid. Our observations indicate that the transition occurs by the mechanism of spinodal decomposition and we are able to study its evolution in real time.

Journal Article↗
PubMed2005

Visible-laser acceleration of relativistic electrons in a semi-infinite vacuum.

We demonstrate a new particle acceleration mechanism using 800 nm laser radiation to accelerate relativistic electrons in a semi-infinite vacuum. The experimental demonstration is the first of its kind and is a proof of principle for the concept of laser-driven particle acceleration in a structure loaded vacuum. We observed up to 30 keV energy modulation over a distance of 1000 lambda, corresponding to a 40 MeV/m peak gradient. The energy modulation was observed to scale linearly with the laser electric field and showed the expected laser-polarization dependence. Furthermore, as expected, laser acceleration occurred only in the presence of a boundary that limited the laser-electron interaction to a finite distance.

Journal Article↗
PubMed2004

Interfacial friction of thin 3He slabs in the Knudsen limit.

A high precision torsional oscillator has been used to study 3He films of thickness from 100 to 350 nm, in the temperature range 5<T<200 mK. This thickness is much smaller than the viscous penetration depth, and also much smaller than the low temperature inelastic mean-free path of 3He quasiparticles. Such films are observed to decouple from the motion of the oscillator below 60 mK. We interpret the frequency shift and dissipation data in terms of an interfacial friction model.

Journal Article↗
PubMed2004

Validation of the Algase Wandering Scale (Version 2) in a cross cultural sample.

This study examined the psychometric properties of an expanded version of the Algase Wandering Scale (Version 2) (AWS-V2) in a cross-cultural sample. A cross-sectional survey design was used. Study subjects were 172 English-speaking persons with dementia (PWD) from long-term care facilities in the USA, Canada, and Australia. Two or more facility staff rated each subject on the AWS-V2. Demographic and cognitive data (MMSE) were also obtained. Staff provided information on their own knowledge of the subject and of dementia. Separate factor analyses on data from two samples of raters each explained greater than 66% of the variance in AWS-V2 scores and validated four (persistent walking, navigational deficit, eloping behavior, and shadowing) of five factors in the original scale. Items added to create the AWS-V2 strengthened the shadowing subscale, failed to improve the routinized walking subscale, and added a factor, attention shifting as compared to the original AWS. Evidence for validity was found in significant correlations and ANOVAs between the AWS-V2 and most subscales with a single item indicator of wandering and with the MMSE. Evidence of reliability was shown by internal consistency of the AWS-V2 (0.87, 0.88) and its subscales (range 0.88 to 0.66), with Kappa for individual items (17 of 27 greater than 0.4), and ANOVAs comparing ratings across rater groups (nurses, nurse aids, and other staff). Analyses support validity and reliability of the AWS-V2 overall and for persistent walking, spatial disorientation, and eloping behavior subscales. The AWS-V2 and its subscales are an appropriate way to measure wandering as conceptualized within the Need-driven Dementia-compromised Behavior Model in studies of English-speaking subjects. Suggestions for further strengthening the scale and for extending its use to clinical applications are described.

Aged↗
PubMed2002

Management of completely displaced metaphyseal fractures of the distal radius in children. A prospective, randomised controlled trial.

In a prospective, randomised controlled trial, 68 children who had a completely displaced metaphyseal fracture of the distal radius were treated either by manipulation (MUA) and application of an above-elbow cast alone or by the additional insertion of a percutaneous Kirschner (K-) wire. Full radiological follow-up to union was obtained in 65 children and 56 returned for clinical evaluation three months after injury. Maintenance of reduction was significantly better in the K-wire group and fewer follow-up radiographs were required. There was no significant difference in the clinical outcome measured three months after injury. Seven of 33 patients in the MUA group had to undergo a second procedure because of an unacceptable position compared with none of the 35 in the K-wire group (chi-squared test, p < 0.01). One patient in the K-wire group required exploration for recovery of a migrated wire. We conclude that the use of a percutaneous K-wire to augment the reduction of the fracture in children who have a completely displaced metaphyseal fracture of the distal radius is a safe and reliable way of maintaining alignment of the fracture.

Adolescent↗
PubMed2001

An investigation of 2 techniques for optimizing joint surface congruency using multiple cylindrical osteochondral autografts.

PURPOSE: To compare 2 techniques for optimizing joint congruency for miniature osteochondral autografting in the knee: intrinsic postoperative forces acting on overdrilled autografts protruding from the femur versus alignment by a surgeon at the time of grafting. TYPE OF STUDY: Controlled animal model experiment. METHODS: A full-thickness cartilage defect was created on the weight-bearing surface of the medial femoral condyle of 13 mature sheep. Three 4.5 x 10 mm cylindrical autografts were inserted into 14-mm deep recipient holes such that the grafts were held in place by side-wall friction alone. One treatment group received grafts that were delivered flush with the surrounding cartilage and the second group received grafts that were left 2-mm proud of the joint surface. RESULTS: Three months postoperatively, the proud grafts had been repositioned by weight bearing but perigraft fissuring and fibroplasia, and subchondral cavitations were serious complications. It is suspected that these complications were caused by excessive motion between the graft and recipient site in the proud grafts. CONCLUSIONS: Grafts should be delivered flush with the joint surface when performing osteochondral transfers to avoid graft micromotion and the consequent interference with graft integration and function.

Animals↗
PubMed1999

Extension of the elbow and supracondylar fractures in children.

We tested the hypothesis that children who sustain a supracondylar fracture have a greater range of elbow hyperextension than those with a fracture of the distal radius. Three observers made 358 measurements in 183 children (114 boys and 69 girls). There were 119 fractures of the distal radius and 64 supracondylar fractures. Initially, the group with a supracondylar fracture appeared to have extension 1.7 degrees greater than that of the group with fracture of the distal radius. On average, there was a maximum variation of 3 degrees between observers. After allowing for age, gender and observer, there was no significant difference between the groups. Our study had greater than 80% power to detect a difference in hyperextension of 2 degrees at the 5% level with the above observer variability. When age and gender are taken into account, any variation in the amount of hyperextension at the elbow is not sufficient to explain the occurrence of a supracondylar fracture.

Adolescent↗
PubMed1996

Elafin, a serine elastase inhibitor, attenuates post-cardiac transplant coronary arteriopathy and reduces myocardial necrosis in rabbits afer heterotopic cardiac transplantation.

We have related experimentally induced post-cardiac transplant coronary arteriopathy to increased elastolytic activity, IL-1beta, fibronectin-mediated inflammatory and smooth muscle cell (SMC) migration, and SMC proliferation. Since our in vitro studies show that a serine elastase releases SMC mitogens and facilitates IL-lbeta induction of fibronectin, we hypothesized that administration in vivo of the specific serine elastase inhibitor, elafin, would decrease the post-cardiac transplant coronary arteriopathy. Cholesterol-fed rabbits underwent a heterotopic cardiac transplant without immunosuppression and received elafin (1.79 mg/kg per d continuous infusion after a 9 mg bolus, n = 6) or vehicle (n = 6). 1 wk later, hearts were harvested for morphometric, immunohistochemical, and biochemical analyses. A > 70% decrease in the total number of coronary arteries with intimal thickening in elafin-treated compared to control donor hearts (P < 0.002) was associated with reduced vascular elastolytic activity judged by fewer breaks in the internal elastic lamina (P < 0.03), less accumulation of immunoreactive fibronectin (P < 0.02), and reduced cell proliferation quantified by proliferating cell nuclear antigen (P < 0.0001). Despite myocardial lymphocytic infiltration, wet weight of elafin-treated donor hearts was reduced by 50% compared to untreated controls (P < 0.002) and associated with relative preservation of myocyte integrity, instead of extensive myocardial necrosis (P < 0.004). This protective effect correlated with decreased myocardial elastolytic activity (P < 0.0001) and inflammatory cell proliferation (P < 0.0001) and with an elafin-inhibitable elastase in lymphocytes. Serine elastase activity thus appears an important therapeutic target for post-cardiac transplant coronary arteriopathy and myocardial necrosis induced by rejection.

Animals↗
PubMed1996

Hormone replacement therapy in breast cancer survivors: a cohort study.

OBJECTIVE: Our purpose was to measure any adverse effect (if one exists) of hormone replacement therapy administered to breast cancer survivors. STUDY DESIGN: Forty-one patients from a group of 77 patients who received hormone replacement therapy after therapy for breast cancer were matched with 82 comparison patients not receiving hormone replacement therapy. Both groups were taken from the same population on the basis of cancer registry of the Cancer Surveillance Program of Orange County and were compared with regard to survival results. RESULTS: An analysis of survival time and disease-free time revealed no statistically significant difference between the two groups. CONCLUSIONS: No obvious adverse effect of hormone replacement therapy could be shown in this pilot study. A case is made for a prospective randomized trial.

Adult↗
PubMed1995

Replacement therapy for breast cancer survivors. A pilot study.

BACKGROUND: Traditionally, breast cancer survivors were not considered as candidates for hormone replacement therapy (HRT) because of the possibility that an occult metastatic site of disease might be activated, thus negatively influencing the outcome for the patient. METHODS: A retrospective review of 77 breast cancer survivors who have taken HRT was conducted. RESULTS: Seven recurrences were reported among the 77 patients studied in-depth, with correlations to stage, age, and node and receptor status. There have been no recurrences among the 33 additional patients who were placed on the study after the completion of this analysis. CONCLUSIONS: No significant adverse outcome was detected in this group of breast cancer survivors receiving HRT. Given the established benefits of HRT, a reappraisal of this subject is necessary, and a prospective randomized trial is essential.

Adult↗
PubMed1992

Accuracy of coagulation studies performed on blood samples obtained from arterial cannulae.

We have assessed the accuracy of coagulation studies in blood obtained from intra-arterial cannulae. Paired samples were studied in blood from 39 patients receiving intensive care; one sample was obtained by venepuncture and the other from an intra-arterial cannula after the apparatus deadspace plus 5 ml of blood had been discarded. Activated partial thromboplastin time (APTT) (with thromboplastin routinely used in our laboratory), prothrombin time (PT), thrombin time (TT), fibrinogen and heparin assays were measured on each sample. In 37 sample pairs, APTT was measured also using a different thromboplastin. The median difference between the sample pairs was 5.5 s for APTT (P = 0.032) and 1.0 s (P = 0.048) for TT, the times for arterial cannula samples being longer. There was no significant difference between arterial cannula and venepuncture samples for PT or fibrinogen concentration. Heparin assays revealed heparin contamination in samples obtained from arterial cannulae in 15 of 30 patients not receiving heparin. It is concluded that, when coagulation studies are performed using the techniques used routinely in our laboratory, a blood sample from an arterial cannula may give clinically misleading information because of contamination with small amounts of heparin, and that separate venepuncture is recommended.

Blood Coagulation Tests↗
PubMed1987

Brain metabolism after electroshock seizure in the neonatal dog: a [31P]NMR study.

In vivo [31P] nuclear magnetic resonance (NMR) spectroscopy disclosed that a 10 second electroshock seizure in oxygenated neonatal dogs produced prolonged alteration of brain phosphocreatine (PCr), inorganic phosphate (Pi), and lactate. The slow return of these metabolites to baseline may be related to lower endogenous stores of high energy phosphates, or less developed pathways for their regeneration.

Adenosine Triphosphate↗