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Biomedical subjects

C A Burns

Publications and source records attributed to C A Burns.

At least 19 recordsLinked to original sources
PubMed2006

Excitations of lithium ammonia complexes studied by inelastic x-ray scattering.

We have carried out high-resolution inelastic x-ray scattering measurements of the excitations of lithium dissolved in ammonia. The incident x-ray energy was 21.6 keV and the resolution was about 2 meV. Several different excitations are observed in the energy range of 0-60 meV (0-500 cm(-1)). In addition to acoustic phonons at low energies, we see excitations that are associated with vibrations of Li(NH3)4+ complexes. We examined these excitations as a function of momentum transfer, lithium concentration, temperature, and state of the system (solid versus liquid). Data are compared with Hartree-Fock and density-functional theory calculations of the excitations of this complex, which agree well with the measured excitation energies.

Journal Article↗
PubMed2003

Synthesis, permeability and biocompatibility of tricomponent membranes containing polyethylene glycol, polydimethylsiloxane and polypentamethylcyclopentasiloxane domains.

The synthesis of "smart" tricomponent amphiphilic membranes containing poly(ethylene glycol) (PEG), polydimethylsiloxane (PDMS) and polypentamethylcyclopentasiloxane (PD(5)) domains is described. Contact angle hysteresis indicates that in air, the surfaces of such PEG/PD(5)/PDMS membranes are enriched by the hydrophobic components, PDMS and PD(5), while in water, the surfaces are rich in the hydrophilic PEG. The oxygen permeability of a series of membranes with varying M(c,hydrophilic) (M(n,PEG)=4600, 10,000 and 20,000 g/mol) and varying PEG/PD(5)/PDMS compositions was studied. Oxygen permeability increased with the amount of PDMS in the membrane. The molecular weight cut-off (MWCO) ranges and permeability coefficients of insulin through a series of PEG/PD(5)/PDMS(=29/14/57) membranes with varying M(c,hydrophilic) were determined. Insulin permeability is directly related to M(c,hydrophilic) of the membrane. MWCO studies show that the membranes are semipermeable to, i.e., allow the transport of smaller proteins such as insulin (M(n)=5733 g/mol, R(s)=1.34 nm) and cytochrome c (M(n)=12,400 g/mol, R(s)=1.63 nm), but are barriers to larger proteins such as albumin (M(n)=66,000 g/mol, R(s)=3.62 nm). Implantation of representative membranes in rats showed them to be biocompatible. According to these studies, PEG/PD(5)/PDMS membranes may be suitable for biological applications, e.g., immunoisolation of cells.

Animals↗
PubMed2002

Electronic interactions in the expanded metal compound Li-NH3.

Inelastic x-ray scattering was used to measure the plasmon as a function of electron density in liquid lithium ammonia as well as the low temperature solid phase. As the electronic density is lowered, electronic correlation effects cause the random-phase approximation (RPA) to break down, requiring more advanced theoretical treatments. The deviation from RPA becomes greatest at the lowest electronic densities. We also see evidence for decreased electronic screening as shown by an increase in the strength of the pseudopotential at lower concentrations. Plasmon behavior in the solid is similar to that of the heavier alkali metals, but surprisingly different than in the liquid.

Journal Article↗
PubMed2002

Resonant inelastic x-ray scattering study of charge excitations in La(2)CuO(4).

We report a resonant inelastic x-ray scattering study of the dispersion relations of charge-transfer excitations in insulating La(2)CuO(4).. These data reveal two peaks, both of which show two-dimensional characteristics. The lowest energy excitation has a gap energy of approximately 2.2 eV at the zone enter, and a dispersion of approximately 1 eV. The spectral weight of this mode becomes dramatically smaller around (pi, pi). The second peak shows a smaller dispersion ( approximately 0.5 eV) with a zone-center energy of approximately 3.9 eV. We argue that these are both highly dispersive exciton modes damped by the presence of the electron-hole continuum.

Journal Article↗
PubMed2001

Evidence for an instability near twice the fermi wave vector in the low electronic density liquid metal Li(NH3)4.

We report high-resolution inelastic x-ray scattering measurements in the metallic liquid Li(NH3)4, which to a good approximation can be treated as a dilute alkali metal. We see a well-defined excitation out to large momentum transfers. This excitation shows a strong softening at wave vectors near the first peak in the structure factor, which occurs near twice the Fermi momentum.

Journal Article↗
PubMed1998

Using scientific evidence to improve hospital library services: Southern Chapter/Medical Library Association journal usage study.

BACKGROUND: Journal usage studies, which are useful for budget management and for evaluating collection performance relative to library use, have generally described a single library or subject discipline. The Southern Chapter/Medical Library Association (SC/MLA) study has examined journal usage at the aggregate data level with the long-term goal of developing hospital library benchmarks for journal use. METHODS: Thirty-six SC/MLA hospital libraries, categorized for the study by size as small, medium, or large, reported current journal title use centrally for a one-year period following standardized data collection procedures. Institutional and aggregate data were analyzed for the average annual frequency of use, average costs per use and non-use, and average percent of non-used titles. Permutation F-type tests were used to measure difference among the three hospital groups. RESULTS: Averages were reported for each data set analysis. Statistical tests indicated no significant differences between the hospital groups, suggesting that benchmarks can be derived applying to all types of hospital libraries. The unanticipated lack of commonality among heavily used titles pointed to a need for uniquely tailored collections. CONCLUSION: Although the small sample size precluded definitive results, the study's findings constituted a baseline of data that can be compared against future studies.

Benchmarking↗
PubMed1996

Home use of a functional electrical stimulation system for standing and mobility in adolescents with spinal cord injury.

OBJECTIVE: Functional electrical stimulation (FES) is a technology that may allow some patients with spinal cord injury (SCI) to integrate standing and upright mobility with wheelchair mobility. The purpose of this study was to document the patterns of home and community use of a FES system for standing and mobility. DESIGN: A telephone questionnaire was administered every 1 to 4 weeks for a minimum of 1 year. An interview was given at the end of the study to probe the motivators and barriers to home use. SETTING: Training for use of the FES system was performed in an inpatient pediatric rehabilitation setting. Data collection began after the subjects were discharged to home. PARTICIPANTS: Five adolescents with complete, thoracic-level SCI. INTERVENTION: Subjects participated in a program of FES exercise followed by training in basic mobility skills such as standing transfers, maneuvering, level ambulation, one-handed and reaching activities, and stair ascent/descent. MAIN OUTCOME MEASURE: The frequency with which the FES system was used at home and the activities for which it was utilized were documented. Motivators and barriers to FES home use were examined. RESULTS: Subjects donned the FES system on the average once every 3 to 4 days. Between 51% and 84% of the times donned, the system was used for exercise. The remaining times it was used for standing activities, most commonly reaching, one-handed tasks, and standing for exercise. "Motivators" included being able to do things that would otherwise be difficult, perceiving a healthful benefit or a sense of well-being from standing and exercise, and feeling an obligation to stand as a participant in a research study. "Barriers" to FES use included not finding time to use the system, having difficulty seeing opportunities to stand, and being reluctant to wear the FES system all day.

Activities of Daily Living↗
PubMed1993

Doppler echocardiographic assessment of an impedance-based dual-chamber rate-responsive pacemaker.

Rate-responsive pacing allows patients with chronotropic incompetence to achieve more physiologic heart rate responses to exercise. One sensor currently being investigated uses impedance-derived measurements of changes in right ventricular stroke volume to alter the pacing rate. Correlation of pacemaker-derived measurements of stroke volume with an accepted method of stroke volume measurement has not been performed. The relative changes in impedance-derived stroke volume were compared in 10 patients with an impedance-based dual-chamber rate-responsive pacemaker (Precept DR, Cardiac Pacemakers, Inc.) with simultaneous Doppler echocardiographic measurements of right and left ventricular stroke volume. These comparisons were made during pacing at 2 heart rates (70 and 100 beats/min) and 3 AV intervals (150, 200 and 250 ms) while in a supine resting state, during lower body negative pressure to -30 mm Hg, and while performing 25% maximal handgrip. Pacemaker-derived stroke volume decreased by 7 to 11% and Doppler time-velocity integral measurements decreased by 14 to 19% in response to an increase in pacing rate (p = NS). There was also no significant difference by either technique in the mean stroke volume change when the atrioventricular interval was varied. Both techniques detected a decrease in stroke volume during lower body negative pressure, ranging from -7 to -20% by pacemaker, and -17 to -38% by Doppler. Overall, the pacemaker stroke volume measurements responded in an appropriate direction to each intervention, signaling the pacemaker's ability to detect directional change in stroke volume. The Precept DR may aid in the programming of parameters such as atrioventricular interval and heart rate by allowing for optimization of stroke volume in individual patients.

Adult↗
PubMed1992

Transesophageal echocardiography to assess mitral valve function and flow during cardiopulmonary resuscitation.

This study further defines the mechanism of blood flow during closed-chest compression using transesophageal Doppler echocardiography. Although the echocardiographic demonstration of mitral valve closure during closed-chest compression has been used as evidence of direct cardiac compression, mitral valve closure has also been documented to occur during resuscitation by selectively increasing intrathoracic pressure. Transesophageal Doppler echocardiography was used to assess mitral valve position and flow in 17 adult patients undergoing cardiopulmonary resuscitation with a mechanical piston compression device. Left and right ventricular fractional shortening, mitral valve position with chest compression, timing and magnitude of transmitral flow, and anteroposterior chest diameter were recorded. In 12 patients (group I), the mitral valve closed during the down-stroke of chest compression; in the remaining 5 (group II), it opened further. Peak transmitral flow occurred during the release phase and was significantly higher (p < 0.05) in group I (39.5 +/- 9.3 cm/s) than the peak flow in group II (21.3 +/- 5.9 cm/s), which occurred during the downstroke of chest compression. Left ventricular fractional shortening inversely correlated (r = -0.68; p = 0.02) with the anteroposterior chest diameter, but did not correlate with peak transmitral flow (r = 0.34; p = not significant). It is concluded that the mitral valve closes during the downstroke of chest compression in most adult patients during resuscitation. The absence of a relation between mitral valve flow and left ventricular fractional shortening supports the hypothesis that other factors such as nonuniform increases in intrathoracic pressure cause the mitral valve to open or close during chest compression.

Blood Flow Velocity↗
PubMed1992

Coronary aneurysms: a case report and review.

This case report describes a large coronary aneurysm and poses questions regarding management. The discussion that follows addresses what is known about the natural history of and options for management of coronary aneurysms.

Aged↗
PubMed1989

Structure of (20R)-20,21-epoxy-19-norpregna-1,3,5(10)-triene-3,17 beta-diol.

C20H26O3, Mr = 314.4, orthorhombic, P2(1)2(1)2(1), a = 10.25 (1), b = 25.36 (2), c = 13.11 (1) A, V = 3410.14 A3, Z = 8, Dx = 1.225 g cm-3, lambda(Mo K alpha) = 0.71069 A, mu = 0.45 cm-1, F(000) = 1352, T = 293 K. The structure was solved by direct methods and refined to R = 0.051 for 2384 reflections with F/signa(F) greater than 5. Both the crystallographically independent molecules are in one 20R configuration and confirm predictions based on mechanistic and stereochemical arguments. In the crystal lattice the molecules form a two-dimensional network of hydrogen bonds approximately perpendicular to c.

Antineoplastic Agents↗
PubMed1985

The association of Streptococcus bovis fecal carriage and colon neoplasia: possible relationship with polyps and their premalignant potential.

We designed a study to evaluate the fecal carrier rate of Streptococcus bovis in patients with endoscopically proven colonic polyps. Benign polyps (n = 63), i.e., hyperplastic, inflammatory, and juvenile, had a similar fecal carrier rate as the normal control colons. Colons with polyps that are at increased risk for malignant degeneration (n = 62), i.e., tubulovillous and villous adenomas, and colons with carcinoma (n = 18), had a statistically significant increase (p less than 0.05) in the fecal carrier rate for S. bovis over the benign colon group. Overall, the incidence of S. bovis carriage in all colons with polyps was intermediary between normal colons and colons with carcinoma although the numbers did not achieve statistical significance.

Adenoma↗
PubMed1982

Comparison fo agglutinin titers for Streptococcus mutans in tears, saliva, and serum.

The agglutinin titers for three Streptococcus mutans serotypes (AHT, BHT, and 10449, representing serotypes a, b, and c, respectively) were measured in the saliva, tears, and serum of 19 human subjects. Naturally occurring S. mutans agglutinins were routinely present in all fluids tested in the absence of overt local stimulation by antigen. The immunoglobulin A nature of this secretory agglutinin activity was suggested by blocking with alpha heavy-chain-specific antiserum and by the demonstration of S. mutans-reactive immunoglobulin A in the saliva and tears by indirect immunofluorescence. This finding is consistent with stimulation and antigen commitment of immunoglobulin A precursor lymphocytes at remote sites and subsequent homing to the lacrimal system. The relationship of anti-AHT agglutinins to anti-10449 agglutinins differed among the body fluids tested. The tears had more agglutinins for strain AHT than for strain 10449, whereas the reverse was true for saliva and serum. A possible explanation is local antigen-driven expansion of AHT-reactive committed lymphocytes in the lacrimal tissues.

Adult↗
PubMed1982

Immunoglobulin A antibody levels in human tears, saliva, and serum.

The presence and level of immunoglobulin A (IgA) antibodies to the oral microorganism Streptococcus mutans were determined in human tears, parotid saliva, and serum by a modified, indirect enzyme-linked immunosorbent assay. IgA antibodies were found in the tears of all 15 subjects, although S. mutans is a nonocular bacterium. The IgA antibody levels in tears and saliva were not significantly different. This finding suggests that the level of IgA antibody activity per volume is independent of the naturally occurring site of the antigen, and that local stimulation does not cause a significant difference in the antibody level per volume of secretion between exocrine sites. Much higher levels of IgA antibody were present in serum, suggesting that after oral ingestion of antigen both the systemic and exocrine systems are stimulated. IgG antibodies to S. mutans were also found in human tears, saliva, and serum. No relationship between serum levels and tear and saliva levels was found for either IgA or IgG antibodies. Thus the antibodies in tears and saliva did not appear to have leaked from serum. We conclude that there may be remote regulation of both the ocular and the parotid IgA and IgG antibody systems.

Antibodies, Bacterial↗
PubMed1982

The effects of silica and fly ash dust inhalation on alveolar macrophage effector cell function.

Inhalation of silica was found to cause significant enhancement of alveolar macrophage antibody-dependent cell-mediated cytotoxicity (ADCC) after 14, 42, and 70 days of exposure, while similar treatment using fly ash resulted in significant suppression of ADCC after 42 days of exposure. Both silica and fly ash inhalation depressed the ability of alveolar macrophages from BCG-primed and BCG-rechallenged animals to mediate tumor cell lysis. Fly ash exposure also significantly suppressed the ability of BCG-activated macrophages to lyse target cells by the ADCC mechanism.

Adjuvants, Immunologic↗