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- Beard, David J., et al.
(author)
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Considerations and methods for placebo controls in surgical trials (ASPIRE guidelines)
- 2020
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In: The Lancet. - 0140-6736. ; 395:10226, s. 828-838
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Research review (peer-reviewed)abstract
- Placebo comparisons are increasingly being considered for randomised trials assessing the efficacy of surgical interventions. The aim of this Review is to provide a summary of knowledge on placebo controls in surgical trials. A placebo control is a complex type of comparison group in the surgical setting and, although powerful, presents many challenges. This Review outlines what a placebo control entails and present understanding of this tool in the context of surgery. We consider when placebo controls in surgery are acceptable (and when they are desirable) in terms of ethical arguments and regulatory requirements, how a placebo control should be designed, how to identify and mitigate risk for participants in these trials, and how such trials should be done and interpreted. Use of placebo controls is justified in randomised controlled trials of surgical interventions provided there is a strong scientific and ethical rationale. Surgical placebos might be most appropriate when there is poor evidence for the efficacy of the procedure and a justified concern that results of a trial would be associated with high risk of bias, particularly because of the placebo effect. Feasibility work is recommended to optimise the design and implementation of randomised controlled trials. This Review forms an outline for best practice and provides guidance, in the form of the Applying Surgical Placebo in Randomised Evaluations (known as ASPIRE) checklist, for those considering the use of a placebo control in a surgical randomised controlled trial.
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- Beard, David J., et al.
(author)
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Placebo comparator group selection and use in surgical trials : The aspire project including expert workshop
- 2021
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In: Health Technology Assessment. - 1366-5278. ; 25:53
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Journal article (peer-reviewed)abstract
- Background: The use of placebo comparisons for randomised trials assessing the efficacy of surgical interventions is increasingly being considered. However, a placebo control is a complex type of comparison group in the surgical setting and, although powerful, presents many challenges. Objectives: To provide a summary of knowledge on placebo controls in surgical trials and to summarise any recommendations for designers, evaluators and funders of placebo-controlled surgical trials. Design: To carry out a state-of-the-art workshop and produce a corresponding report involving key stakeholders throughout. Setting: A workshop to discuss and summarise the existing knowledge and to develop the new guidelines. Results: To assess what a placebo control entails and to assess the understanding of this tool in the context of surgery is considered, along with when placebo controls in surgery are acceptable (and when they are desirable). We have considered ethics arguments and regulatory requirements, how a placebo control should be designed, how to identify and mitigate risk for participants in these trials, and how such trials should be carried out and interpreted. The use of placebo controls is justified in randomised controlled trials of surgical interventions provided that there is a strong scientific and ethics rationale. Surgical placebos might be most appropriate when there is poor evidence for the efficacy of the procedure and a justified concern that results of a trial would be associated with a high risk of bias, particularly because of the placebo effect. Conclusions: The use of placebo controls is justified in randomised controlled trials of surgical interventions provided that there is a strong scientific and ethics rationale. Feasibility work is recommended to optimise the design and implementation of randomised controlled trials. An outline for best practice was produced in the form of the Applying Surgical Placebo in Randomised Evaluations (ASPIRE) guidelines for those considering the use of a placebo control in a surgical randomised controlled trial. Limitations: Although the workshop participants involved international members, the majority of participants were from the UK. Therefore, although every attempt was made to make the recommendations applicable to all health systems, the guidelines may, unconsciously, be particularly applicable to clinical practice in the UK NHS. Future work: Future work should evaluate the use of the ASPIRE guidelines in making decisions about the use of a placebo-controlled surgical trial. In addition, further work is required on the appropriate nomenclature to adopt in this space.
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- Smith-Martin, Chris M., et al.
(author)
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Hurricanes increase tropical forest vulnerability to drought
- 2022
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In: New Phytologist. - : John Wiley & Sons. - 0028-646X .- 1469-8137. ; 235:3, s. 1005-1017
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Journal article (peer-reviewed)abstract
- Rapid changes in climate and disturbance regimes, including droughts and hurricanes, are likely to influence tropical forests, but our understanding of the compound effects of disturbances on forest ecosystems is extremely limited. Filling this knowledge gap is necessary to elucidate the future of these ecosystems under a changing climate. We examined the relationship between hurricane response (damage, mortality, and resilience) and four hydraulic traits of 13 dominant woody species in a wet tropical forest subject to periodic hurricanes. Species with high resistance to embolisms (low P-50 values) and higher safety margins (SMP50) were more resistant to immediate hurricane mortality and breakage, whereas species with higher hurricane resilience (rapid post-hurricane growth) had high capacitance and P-50 values and low SMP50. During 26 yr of post-hurricane recovery, we found a decrease in community-weighted mean values for traits associated with greater drought resistance (leaf turgor loss point, P-50, SMP50) and an increase in capacitance, which has been linked with lower drought resistance. Hurricane damage favors slow-growing, drought-tolerant species, whereas post-hurricane high resource conditions favor acquisitive, fast-growing but drought-vulnerable species, increasing forest productivity at the expense of drought tolerance and leading to higher overall forest vulnerability to drought.
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| 5. |
- Smith-Martin, Chris M., et al.
(author)
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Hydraulic traits are not robust predictors of tree species stem growth during a severe drought in a wet tropical forest
- 2023
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In: Functional Ecology. - : British Ecological Society. - 0269-8463 .- 1365-2435. ; 37:2, s. 447-460
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Journal article (peer-reviewed)abstract
- 1. Severe droughts have led to lower plant growth and high mortality in many ecosystems worldwide, including tropical forests. Drought vulnerability differs among species, but there is limited consensus on the nature and degree of this variation in tropical forest communities. Understanding species-level vulnerability to drought requires examination of hydraulic traits since these reflect the different strategies species employ for surviving drought.2. Here, we examined hydraulic traits and growth reductions during a severe drought for 12 common woody species in a wet tropical forest community in Puerto Rico to ask: Q1. To what extent can hydraulic traits predict growth declines during drought? We expected that species with more hydraulically vulnerable xylem and narrower safety margins (SMP50) would grow less during drought. Q2. How does species successional association relate to the levels of vulnerability to drought and hydraulic strategies? We predicted that early- and mid-successional species would exhibit more acquisitive strategies, making them more susceptible to drought than shade-tolerant species. Q3. What are the different hydraulic strategies employed by species and are there trade-offs between drought avoidance and drought tolerance? We anticipated that species with greater water storage capacity would have leaves that lose turgor at higher xylem water potential and be less resistant to embolism forming in their xylem (P-50).3. We found a large range of variation in hydraulic traits across species; however, they did not closely capture the magnitude of growth declines during drought. Among larger trees (& GE;10 cm diameter at breast height-DBH), some tree species with high xylem embolism vulnerability (P-50) and risk of hydraulic failure (SMP50) experienced substantial growth declines during drought, but this pattern was not consistent across species. We found a trade-off among species between drought avoidance (capacitance) and drought tolerating (P-50) in this tropical forest community. Hydraulic strategies did not align with successional associations. Instead, some of the more drought-vulnerable species were shade-tolerant dominants in the community, suggesting that a drying climate could lead to shifts in long-term forest composition and function in Puerto Rico and the Caribbean. Read the free Plain Language Summary for this article on the Journal blog.
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| 6. |
- Zieminska, Kasia, et al.
(author)
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Shifts in wood anatomical traits after a major hurricane
- 2023
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In: Functional Ecology. - : John Wiley & Sons. - 0269-8463 .- 1365-2435. ; 37:12, s. 3000-3014
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Journal article (peer-reviewed)abstract
- 1. Trait variation across individuals and species influences the resistance and resilience of ecosystems to disturbance, and the ability of individuals to capitalize on postdisturbance conditions. In trees, the anatomical structure of xylem directly affects plant function and, consequently, it is a valuable lens through which to understand resistance and resilience to disturbance.2. To determine how hurricanes affect wood anatomy of tropical trees, we characterized a set of anatomical traits in wood produced before and after a major hurricane for 65 individuals of 10 Puerto Rican tree species. We quantified variation at different scales (among and within species, and within individuals) and determined trait shifts between the pre- and posthurricane periods. We also assessed correlations between traits and growth rates.3. While the majority of anatomical trait variation occurred among species, we also observed substantial variation within species and individuals. Within individuals, we found significant shifts for some traits that generally reflected increased hydraulic conductivity in the posthurricane period. We found weak evidence for an association between individual xylem anatomical traits and diameter growth rates.4. Ultimately, within-individual variation of xylem anatomical traits observed in our study could be related to posthurricane recovery and overall growth (e.g. canopy filling). Other factors, however, likely decouple a relationship between xylem anatomy and diameter growth. While adjustments of wood anatomy may enable individual trees to capitalize on favourable postdisturbance conditions, these may also influence their future responses or vulnerability to subsequent disturbances.
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