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"P. Galbraith"
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Relative importance of pelagic and sediment respiration in causing hypoxia in a deep estuary
Oxygen depletion in the 100‐m thick bottom layer of the deep Lower St. Lawrence Estuary is currently thought to be principally caused by benthic oxygen demand overcoming turbulent oxygenation from overlying layers, with pelagic respiration playing a secondary role. This conception is revisited with idealized numerical simulations, historical oxygen observations and new turbulence measurements. Results indicate that a dominant sediment oxygen demand, over pelagic, is incompatible with the shape of observed oxygen profiles. It is further argued that to sustain oxygen depletion, the turbulent diffusivity in the bottom waters should be ≪10−4 m2 s−1, consistent with direct measurements but contrary to previous model results. A new model that includes an Arrhenius‐type function for pelagic respiration and a parameterization for turbulence diffusivity is developed. The model demonstrates the importance of the bottom boundary layer in reproducing the shape of oxygen profiles and reproduces to within 14% the observed change in oxygen concentration in the Lower St. Lawrence Estuary. The analysis indicates that turbulent oxygenation represents about 8% of the sum of sediment and pelagic oxygen demand, consistent with the low turbulent oxygenation required to maintain oxygen depletion. However, contrary to previous hypotheses, it is concluded that pelagic oxygen demand needs to be five time larger than sediment oxygen demand to explain hypoxia in the 100‐m thick bottom layer of the Lower St. Lawrence Estuary. Key Points Pelagic oxygen demand (OD) >> sediment OD to explain hypoxia in this estuary Turbulent diffusivity is an order of mag smaller than previously hypothesized The turbulent boundary layer is critical to realistically model oxygen profiles
Journal Article
Rise of the killer plants: investigating the antimicrobial activity of Australian plants to enhance biofilter-mediated pathogen removal
Background
Biofilters are soil-plant based passive stormwater treatment systems which demonstrate promising, although inconsistent, removal of faecal microorganisms. Antimicrobial-producing plants represent a safe, inexpensive yet under-researched biofilter design component that may enhance treatment reliability. The mechanisms underlying plant-mediated microbial removal in biofilters have not been fully elucidated, particularly with respect to antimicrobial production. The aim of this study was therefore to inform biofilter vegetation selection guidelines for optimal pathogen treatment by conducting antimicrobial screening of biofilter-suitable plant species. This involved: (1) selecting native plants suitable for biofilters (17 species) in a Victorian context (southeast Australia); and (2) conducting antimicrobial susceptibility testing of selected plant methanolic extracts (≥ 5 biological replicates/species; 86 total) against reference stormwater faecal bacteria (
Salmonella enterica subsp. enterica
ser. Typhimurium
, Enterococcus faecalis
and
Escherichia coli
).
Results
The present study represents the first report on the inhibitory activity of polar alcoholic extracts from multiple tested species. Extracts of plants in the Myrtaceae family, reputed for their production of antimicrobial oils, demonstrated significantly lower minimum inhibitory concentrations (MICs) than non-myrtaceous candidates (
p
< 0.0001).
Melaleuca fulgens
(median MIC: 8 mg/mL; range: [4–16 mg/mL])
, Callistemon viminalis
(16 mg/mL, [2–16 mg/mL]) and
Leptospermum lanigerum
(8 mg/mL, [4–16 mg/mL]) exhibited the strongest inhibitory activity against the selected bacteria (
p
< 0.05 compared to each tested non-myrtaceous candidate). In contrast, the Australian biofilter gold standard
Carex appressa
demonstrated eight-fold lower activity than the highest performer
M. fulgens
(64 mg/mL, [32–64 mg/mL]).
Conclusion
Our results suggest that myrtaceous plants, particularly
M. fulgens
, may be more effective than the current vegetation gold standard in mediating antibiosis and thus improving pathogen treatment within biofilters. Further investigation of these plants in biofilter contexts is recommended to refine biofilter vegetation selection guidelines.
Journal Article
Patient perspectives on engagement in decision-making in early management of non-ST elevation acute coronary syndrome: a qualitative study
Background
Surveys of patients suggest many want to be actively involved in treatment decisions for acute coronary syndromes. However, patient experiences of their engagement and participation in early phase decision-making have not been well described.
Methods
We performed a patient led qualitative study to explore patient experiences with decision-making processes when admitted to hospital with non-ST elevation acute coronary syndrome. Trained patient-researchers conducted the study via a three-phase approach using focus groups and semi-structured interviews and employing grounded theory methodology.
Results
Twenty patients discharged within one year of a non-ST elevation acute coronary syndrome participated in the study. Several common themes emerged. First, patients characterized the admission and early treatment of ACS as a rapidly unfolding process where they had little control. Participants felt they played a passive role in early phase decision-making. Furthermore, participants described feeling reduced capacity for decision-making owing to fear and mental stress from acute illness, and therefore most but not all participants were relieved that expert clinicians made decisions for them. Finally, once past the emergent phase of care, participants wanted to retake a more active role in their treatment and follow-up plans.
Conclusions
Patients admitted with ACS often do not take an active role in initial clinical decisions, and are satisfied to allow the medical team to direct early phase care. These results provide important insight relevant to designing patient-centered interventions in ACS and other urgent care situations.
Journal Article
Impact of clinical presentation and presence of coronary sclerosis on long-term outcome of patients with non-obstructive coronary artery disease
Background
Non-obstructive coronary artery disease (NOCAD) is a common finding on coronary angiography. Our goal was to evaluate the long-term prognosis of NOCAD patients with stable angina (SA).
Methods
The study cohort consisted of 7478 NOCAD patients with normal EF (≥ 50%), and SA who underwent coronary angiography between 1995 and 2012. We compared NOCAD patients (stenosis< 50%) with 10,906 patients with stable obstructive CAD (≥ 50%). The primary endpoint was all-cause mortality. Secondary endpoints included repeat angiography, progressive CAD, and PCI. A second comparison group consisted of 7344 patients with NOCAD presenting with an ACS. Rates of all-cause mortality of NOCAD ACS patients were compared to NOCAD SA patients.
Results
Median follow-up time was 6.5 years. NOCAD patients had a lower risk of all-cause mortality compared to CAD patients (HR CAD vs. NOCAD 1.33 (1.19–1.49);
p
< 0.001). This was driven by patients with normal coronary arteries (HR CAD vs. normal 1.63 (1.36–1.94),
p
< 0.001), whereas patients with minimal disease (> 0% and < 50%) were at similar risk as CAD patients (HR CAD vs. minimal 1.08 (0.99–1.29),
p
= 0.06). In NOCAD patients, the strongest predictors of all-cause mortality were age and minimal disease. SA patients with NOCAD had low rates of repeat angiography (7.3%), future CAD (2.3%) and PCI (1.7%). NOCAD ACS patients had a 41% increase in all-cause mortality risk compared to NOCAD SA patients (HR 1.41 (1.25–1.6),
p
< 0.001).
Conclusions
This study underlines the importance of minimal CAD, as it is not a benign disease entity and portends a similar risk as stable obstructive CAD.
Journal Article
Interior versus boundary mixing of a cold intermediate layer
The relative importance of interior versus boundary mixing is examined for the erosion of the cold intermediate layer (CIL) of the Gulf of St. Lawrence. Based on 18 years of historical temperature profiles, the seasonal erosion of the core temperature, thickness and heat content of the CIL are, respectively, min = 0.24 ± 0.04°C mo−1, min = −11 ± 2 m mo−1 and = 0.59 ± 0.09 MJ m−3 mo−1. These erosion rates are remarkably well reproduced with a one–dimensional vertical diffusion model fed with turbulent diffusivities inferred from 892 microstructure casts. This suggests that the CIL is principally eroded by vertical diffusion processes. The CIL erosion is best reproduced by mean turbulent kinetic energy dissipation rate and eddy diffusivity coefficient of ε ≃ 2 × 10−8 W kg−1 and K ≃ 4 × 10−5 m2 s−1, respectively. It is also suggested that while boundary mixing may be significant it may not dominate CIL erosion. Interior mixing alone accounts for about 70% of this diffusivity with the remainder being attributed to boundary mixing. The latter result is in accordance with recent studies that suggest that boundary mixing is not the principal mixing agent in coastal seas. Key Points Vertical mixing is the main mixing agent for the erosion of a CIL Interior mixing is the principal contributor to the erosion Boundary mixing plays a secondary but significant role in the mixing budget
Journal Article
Kaplan–Meier methods yielded misleading results in competing risk scenarios
Time-to-event curves are routinely presented in the medical literature. The most widely used method is the Kaplan–Meier (K-M) method, but this analysis approach may not be appropriate when an analysis focuses on time-to-first event in scenarios where there are competing events. We compared K-M methods applying various censoring approaches with the lesser-known “cumulative incidence competing risks” (CICR) method in an analysis of competing events.
A registry containing data on 21,624 patients undergoing cardiac catheterization was analyzed. Time to coronary artery bypass grafting (CABG) was assessed in an analysis for which percutaneous coronary intervention and death were competing events. Time-to-CABG curves were calculated using the “K-M censor all method,” “K-M censor death only method,” “K-M ignore all method,” and the CICR method.
One-year CABG rates calculated for the K-M “censor all,” “censor death only,” and “ignore all” methods were 28.8%, 22.8%, and 22.4%, respectively compared to the “actual” rate of 20.8%. For the CICR method, the corresponding 1-year rate was identical to the “actual” rate.
In situations with competing risks, and where an analysis focuses on first events, the CICR method is most appropriate, as K-M methods will tend to overestimate event rates.
Journal Article
Turbulent nitrate fluxes in the Amundsen Gulf during ice-covered conditions
Turbulence and nitrate measurements collected in the Amundsen Gulf during ice‐covered conditions in fall 2007 are combined to provide mean vertical profiles of eddy diffusivity and diffusive nitrate fluxes . The mean diffusivity (with 95% confidence intervals) was maximum near the uppermost sampling depth (10 m) with max = 3(2, 5) × 10−3 m2 s−1 and decreased exponentially to a depth of ∼50 m, below which it was roughly constant at the background value b = 3(2, 5) × 10−6 m2 s−1. The nitracline, centered around 62 m depth, was subject to an eddy diffusivity close to the background value b and the mean diffusive nitrate flux across the nitracline was nit = 0.12(0.075, 0.20) mmol m−2 d−1. These observations are compared with other regions and the role of vertical mixing on primary production in the Amundsen Gulf is discussed. Key Points The average turbulent nitrate flux through the nitracline was 0.5 mmol/m3/d Parameterization for the depth‐dependence of the turbulent diffusivity is given Turbulent mixing may have contributed to 60% of total nitrate uptake
Journal Article
Coronary dominance and prognosis of patients with acute coronary syndrome
A number of studies have identified the number of diseased vessels to be an important determinant of survival in patients with acute coronary syndrome (ACS). It is unknown if coronary dominance has an impact on prognosis of these patients. We hypothesized that the prognosis of patients with ACS with left dominance (LD) would be worse than that of patients with right or mixed dominance.
The study population consisted of 27289 patients whose primary indication for cardiac catheterization was ACS. The patients were divided into 3 groups according to coronary dominance. The mean duration of follow-up was 3.5 years (range 1-6.5 years). A Cox proportional hazards analysis was used to compare survival by dominance, adjusting for age, sex, diagnosis, comorbidities, severity of coronary disease, and ejection fraction.
The rates and patterns of revascularization among patients with significant coronary disease were similar between the groups. At the end of follow-up, patients with LD had a significantly higher mortality (hazard ratio 1.18, 95% CI 1.05-1.34; adjusted hazard ratio 1.13, CI 1.00-1.28). The mortality of patients with mixed and right dominance was similar.
In patients with ACS, LD is a significant and independent predictor of increased long-term mortality. Further research is needed to determine mechanisms of increased mortality in patients with LD and measures that can be taken to improve the outcome of patients with left-dominant circulation.
Journal Article