Biomedical subjects

Ryan D Wilson

Publications and source records attributed to Ryan D Wilson.

4 recordsLinked to original sources

PubMed2006

A comparison of empiric to physician-tailored programming of implantable cardioverter-defibrillators: results from the prospective randomized multicenter EMPIRIC trial.

OBJECTIVES: The purpose of this randomized study was to determine whether a strategically chosen standardized set of programmable settings is at least as effective as physician-tailored choices, as measured by the shock-related morbidity of implantable cardioverter-defibrillator (ICD) therapy. BACKGROUND: Programming of ventricular tachyarrhythmia (ventricular tachycardia [VT] or ventricular fibrillation [VF]) detection and therapy for ICDs is complex, requires many choices by highly trained physicians, and directly influences the frequency of shocks and patient morbidity. METHODS: A total of 900 ICD patients were randomly assigned to standardized (EMPIRIC, n = 445) or physician-tailored (TAILORED, n = 455) VT/VF programming and followed for 1 year. RESULTS: The primary end point was met: the adjusted percentages of both VT/VF (22.3% vs. 28.7%) and supraventricular tachycardia or other non-VT/VF event episodes (11.9% vs. 26.1%) that resulted in a shock were non-inferior and lower in the EMPIRIC arm compared to the TAILORED arm. The time to first all-cause shock was non-inferior in the EMPIRIC arm (hazard ratio = 0.95, 90% confidence interval 0.74 to 1.23, non-inferiority p = 0.0016). The EMPIRIC trial had a significant reduction of patients with 5 or more shocks for all-cause (3.8% vs. 7.0%, p = 0.039) and true VT/VF (0.9% vs. 3.3%, p = 0.018). There were no significant differences in total mortality, syncope, emergency room visits, or unscheduled outpatient visits. Unscheduled hospitalizations occurred significantly less often (p = 0.001) in the EMPIRIC arm. CONCLUSIONS: Standardized empiric ICD programming for VT/VF settings is at least as effective as patient-specific, physician-tailored programming, as measured by many clinical outcomes. Simplified and pre-specified ICD programming is possible without an increase in shock-related morbidity.

Aged↗

PubMed2004

Challenges in monitoring the natural attenuation of spatially variable plumes.

Monitored natural attenuation may be applied as a risk-based remediation strategy if it can be established that contaminants are or will be reduced to some acceptable level at or before a compliance point. Contaminant attenuation is often attributed to intrinsic biodegradation, which in some circumstances may occur only at the plume fringes where electron acceptors from the surrounding uncontaminated zones mix by dispersion and diffusion with the plume. However, due to the common spatial and temporal variability exhibited by many plumes, the centreline monitoring approaches advocated in many natural attenuation protocols may be unable to detect natural attenuation occurring primarily by fringe processes. Snapshot data from a multilevel sampling well transect across an MTBE plume at Vandenberg Air Force Base, CA, USA, illustrate the difficulty of centreline monitoring and the challenge of providing sufficient detail to detect attenuation processes that may be occurring primarily at plume fringes. In a study of a phenols plume in Wolverhampton, UK, high-resolution multilevel wells demonstrated that the key biodegradation processes were restricted spatially to the upper fringe of the plume and were rate-limited by transverse dispersion and diffusion of electron acceptors into the plume. Thus the overall extent of biodegradation was considerably less than suggested by a plume-scale analysis of total electron acceptor and contaminant budgets. These examples indicate that more robust and cost-effective MNA assessments can be obtained using monitoring strategies that focus on the location of key biodegradation processes.

Aerobiosis↗

PubMed2002

Carbon and hydrogen isotopic fractionation during biodegradation of methyl tert-butyl ether.

Carbon and hydrogen isotopic fractionation during aerobic biodegradation of MTBE by a bacterial pure culture (PM1) and a mixed consortia from Vandenberg Air Force Base (VAFB) were studied in order to assess the relative merits of stable carbon versus hydrogen isotopic analysis as an indicator of biodegradation. Carbon isotopic enrichment in residual MTBE of up to 8.1/1000 was observed at 99.7% biodegradation. Carbon fractionation was reproducible in the PM1 and VAFB experiments, yielding similar enrichment factors (epsilon) of -2.0/1000 +/- 0.1/1000 to -2.4/1000 +/- 0.3/1000 for replicates in the PM1 experiment and -1.5/1000 +/- 0.1/1000 to -1.8/1000 +/- 0.1/1000 for replicates in the VAFB experiment. Hydrogen isotopic fractionation was highly reproducible for the PM1 pure cultures, with epsilon values of -33/1000 +/- 5/1000 to -37/1000 +/- 4/1000 for replicate samples. In the VAFB microcosms, there was considerably more variability in epsilon values, with values of -29/1000 +/- 4/1000 and -66/1000 +/- 3/1000 measured for duplicate sample bottles. Despite this variability, hydrogen isotopic fractionation always resulted in 2H enrichment of the residual MTBE of >80/1000 at 90% biodegradation. The reproducible carbon fractionation suggests that compound-specific carbon isotope analysis may be used to estimate the extent of biodegradation at contaminated sites. Conversely, the large hydrogen isotopic fractionation documented during biodegradation of MTBE suggests that compound-specific hydrogen isotope analysis offers the most conclusive means of identifying in-situ biodegradation at contaminated sites.

Bacteria↗

PubMed2002

In situ MTBE biodegradation supported by diffusive oxygen release.

Microcosm studies with sediments from Vandenberg Air Force Base, CA, suggest that native aerobic methyl tert-butyl ether (MTBE)-degrading microorganisms can be stimulated to degrade MTBE. In a series of field experiments, dissolved oxygen has been released into the anaerobic MTBE plume by diffusion through the walls of oxygen-pressurized polymeric tubing placed in contact with the flowing groundwater. MTBE concentrations were decreased from several hundred to less than 10 microg/L during passage through the induced aerobic zone, due apparently to in situ biodegradation: abiotic MTBE loss mechanisms were insignificant. Lag time for initiation of degradation was less than 2 months, and the apparent pseudo-first-order degradation rate was 5.3 day(-1). Additional MTBE was added in steps to raise the influent concentration to a maximum of 2.1 mg/L. With each step, MTBE was degraded within the preestablished aerobic treatment zone at rates ranging from 4.4 to 8.6 day(-1). Excess dissolved oxygen suggested that even higher MTBE concentrations could have been treated. Continued flow through the treatment zone was repeatedly confirmed through tracer and other tests. These and others' results suggest that it is possible to create permeable in situ treatment zones solely by releasing oxygen to support native microbial degradation of MTBE.

Bacteria, Anaerobic↗