α-Amido Trifluoromethyl Xanthates: A New Class of RAFT/MADIX Agents.

Xanthates have long been described as poor RAFT/MADIX agents for styrene polymerization. Through the determination of chain transfer constants to xanthates, this work demonstrated beneficial capto-dative substituent effects for the leaving group of a new series of α-amido trifluoromethyl xanthates, with the best effect observed with trifluoroacetyl group. The previously observed Z-group activation with a O-trifluoroethyl group compared to the O-ethyl counterpart was quantitatively established with Cex = 2.7 (3-4 fold increase) using the SEC peak resolution method. This study further confirmed the advantageous incorporation of trifluoromethyl substituents to activate xanthates in radical chain transfer processes and contributed to identify the most reactive xanthate reported to date for RAFT/MADIX polymerization of styrene.

Microfabrication-based engineering of biomimetic dentin-like constructs to simulate dental aging.

Human dentin is a highly organized dental tissue displaying a complex microarchitecture consisting of micrometer-sized tubules encased in a mineralized type-I collagen matrix. As such, it serves as an important substrate for the adhesion of microbial colonizers and oral biofilm formation in the context of dental caries disease, including root caries in the elderly. Despite this issue, there remains a current lack of effective biomimetic in vitro dentin models that facilitate the study of oral microbial adhesion by considering the surface architecture at the micro- and nanoscales. Therefore, the aim of this study was to develop a novel in vitro microfabricated biomimetic dentin surface that simulates the complex surface microarchitecture of exposed dentin. For this, a combination of soft lithography microfabrication and biomaterial science approaches were employed to construct a micropitted PDMS substrate functionalized with mineralized type-I collagen. These dentin analogs were subsequently glycated with methylglyoxal (MGO) to simulate dentin matrix aging in vitro and analyzed utilizing an interdisciplinary array of techniques including atomic force microscopy (AFM), elemental analysis, and electron microscopy. AFM force-mapping demonstrated that the nanomechanical properties of the biomimetic constructs were within the expected biological parameters, and that mineralization was mostly predominated by hydroxyapatite deposition. Finally, dual-species biofilms of Streptococcus mutans and Candida albicans were grown and characterized on the biofunctionalized PDMS microchips, demonstrating biofilm-specific morphologic characteristics and confirming the suitability of this model for the study of early biofilm formation under controlled conditions. Overall, we expect that this novel biomimetic dentin model could serve as an in vitro platform to study oral biofilm formation or dentin-biomaterial bonding in the laboratory without the need for animal or human tooth samples in the future.

An assessment tool to improve rural groundwater access: Integrating hydrogeological modelling with socio-technical factors.

Sustainable exploitation of groundwater resources for drinking water provision in rural communities in sub-Sahara Africa remains elusive due to the limited knowledge of these hydrogeological systems. This is exacerbated by poor maintenance of existing infrastructure, limited technical capacity, the socio-economic characteristics of the area and poor governance. Assessing the likelihood of a given individual user experiencing water shortage calls for an interdisciplinary approach. After a preliminary multifactorial analysis incorporating a range of variables from technical to societal, it was found that most of the overall risk of water shortage for an individual household could be attributed to three factors; (1) Proximity, specified as the distance to the closest supply well (determined by geographical parameters), (2) Availability of good quality water in the wells (determined by hydrogeological understanding and modelling), and (3) Sustainability (determined by socio-technical and socio-economic parameters). In the latter case, a distinction was made between hardware functionality- the water point's performance considering a sufficient yield and reliability through time- and software functionality, based on a combination of socioeconomic data from surveys and analysed using Multiple Factor Analysis (MFA). All three factors are eventually mapped onto indicators in the range of [0-1] and then represented in a Geographical Information System based on the partition of the entire spatial domain (e.g., counties, villages, and neighbourhoods). The three indicators are then combined in a final index based on the product of the three factors, thus mapping time-dependent overall risk and allowing the assessment of temporal risk-evolution scenarios. The methodology is applied to Kwale County, Kenya, where community handpumps and groundwater points comprise the main water supply system. Apart from mapping the present situation, the methodology is finally used to assess the impact of future climate scenarios.

Exploring the biocapacitance in M3C-based biosensors for the assessment of microbial activity and organic matter.

Reliable monitoring of microbial and water quality parameters in freshwater ecosystems (either natural or human-made) is of capital importance for improving both the management of water resources and the assessment of microbially-driven bio-geo-chemical processes. In this context, bioelectrochemical systems (BES), such as microbial three-cell electrodes (M3C), are very promising devices for their use as biosensors. However, current experiences on the use of BES-based devices for biosensing purposes are almost exclusively limited to water-saturated environments. This limitation hampers the use of this technology for a wider range of applications where the biosensor may work discontinuously (such as discontinuously saturated ecosystems). Discontinuous operation of M3C-based biosensors creates an electric current peak immediately after the reconnection of the system due to electron accumulation, in a process known as biocapacitance. The present work aimed at quantifying the bioindication potential of biocapacitance for the assessment of key ecosystem parameters such as microbial metabolic activity and biomass, as well as organic matter concentration. Significant linear regression coefficients (R2 > 0.9) were found for all combinations of parameters tested. Moreover, for most of the ecological parameters assessed, an electric charge accumulation of 1-5 min (biocapacitance elapsed time) and discharge of 5 min was enough to get reliable information. In conclusion, we have demonstrated for the first time that biocapacitance in M3C-based biosensors can be used as a proxy parameter for the assessment of microbial activity, microbial biomass and organic matter concentration in a model nature-based ecosystem.

Role of Soil Biofilms in Clogging and Fate of Pharmaceuticals: A Laboratory-Scale Column Experiment.

Contamination of groundwater with pharmaceutical active compounds (PhACs) increased over the last decades. Potential pathways of PhACs to groundwater include techniques such as irrigation, managed aquifer recharge, or bank filtration as well as natural processes such as losing streams of PhACs-loaded source waters. Usually, these systems are characterized by redox-active zones, where microorganisms grow and become immobilized by the formation of biofilms, structures that colonize the pore space and decrease the infiltration capacities, a phenomenon known as bioclogging. The goal of this work is to gain a deeper understanding of the influence of soil biofilms on hydraulic conductivity reduction and the fate of PhACs in the subsurface. For this purpose, we selected three PhACs with different physicochemical properties (carbamazepine, diclofenac, and metoprolol) and performed batch and column experiments using a natural soil, as it is and with the organic matter removed, under different biological conditions. We observed enhanced sorption and biodegradation for all PhACs in the system with higher biological activity. Bioclogging was more prevalent in the absence of organic matter. Our results differ from works using artificial porous media and thus reveal the importance of utilizing natural soils with organic matter in studies designed to assess the role of soil biofilms in bioclogging and the fate of PhACs in soils.

Simulating degradation of organic compounds accounting for the growth of microorganisms (Monod kinetics) in a fully Lagrangian framework.

Biologically mediated degradation of organic compounds in porous media is a complex mathematical problem, described by a non-linear differential equation. The organic compound gets in contact with the biomass, and an enzyme-catalysed reaction takes place. The net result is that part of the parent compound degrades into some daughter product, while some of the organic carbon is used for microbial growth. The rate of biomass growth in the presence of a limiting nutrient supply is usually modelled with the experimentally derived Monod equation, i.e., it is proportional to the actual existing biomass multiplied by a factor that is non-linear in terms of available organic matter. This non-linearity in the degradation equation implies a strong difficulty in directly implementing a numerical solution within a fully Lagrangian framework, and thus, numerical solutions have traditionally been sought in either an Eulerian, or else an Eulerian-Lagrangian framework. Here we pursue a fully Lagrangian solution to the problem. First, the Monod empirical equation is formulated as the outcome of a two-step reaction; while the approach is less general than other derivations existing in the literature based on a full understanding of the thermodynamics of the process, it allows two things: 1) providing some physical meaning to the actual parameters in the Monod equation, and more interestingly, 2) formulating a methodology for the solution of the degradation equation incorporating Monod kinetics by means of a particle tracking formulation. For the latter purpose, both reactants and biomass are represented by particles, and their location at any given time is represented by a kernel that accounts for the uncertainty in the actual physical location. By solving the reaction equation in a kernel framework, we can reproduce the Monod kinetics and, as a particular result in the case no biomass growth is allowed, the Michaelis-Menten kinetics. The methodology proposed is then successfully applied to reproduce two studies of microbially induced degradation of organic compounds in porous media, first, the observed kinetics of Pseudomonas putida F1 in batch reactors while growing on benzene, toluene and phenol, and second, the column study of carbon tetrachloride biodegradation by the denitrifying bacterium Pseudomonas Stutzeri KC.

Optimizing the Surface Structural and Morphological Properties of Silk Thin Films via Ultra-Short Laser Texturing for Creation of Muscle Cell Matrix Model.

Temporary scaffolds that mimic the extracellular matrix's structure and provide a stable substratum for the natural growth of cells are an innovative trend in the field of tissue engineering. The aim of this study is to obtain and design porous 2D fibroin-based cell matrices by femtosecond laser-induced microstructuring for future applications in muscle tissue engineering. Ultra-fast laser treatment is a non-contact method, which generates controlled porosity-the creation of micro/nanostructures on the surface of the biopolymer that can strongly affect cell behavior, while the control over its surface characteristics has the potential of directing the growth of future muscle tissue in the desired direction. The laser structured 2D thin film matrices from silk were characterized by means of SEM, EDX, AFM, FTIR, Micro-Raman, XRD, and 3D-roughness analyses. A WCA evaluation and initial experiments with murine C2C12 myoblasts cells were also performed. The results show that by varying the laser parameters, a different structuring degree can be achieved through the initial lifting and ejection of the material around the area of laser interaction to generate porous channels with varying widths and depths. The proper optimization of the applied laser parameters can significantly improve the bioactive properties of the investigated 2D model of a muscle cell matrix.

Power assisted MFC-based biosensor for continuous assessment of microbial activity and biomass in freshwater ecosystems.

Microbial activity and biomass are important factors that determine nutrient and carbon fluxes in freshwater ecosystems and, therefore are also related to both water quality and climate change induced stressors. This study aimed at assessing the feasibility of a power assisted Microbial Fuel Cell (MFC)-based biosensors for the continuous monitoring of microbial activity and biomass concentrations in saturated freshwater ecosystems. For this purpose, four lab-scale reactors were constructed and operated for 30 weeks. Reactors were fed with four different organic matter concentrations to promote a suite of microbial activity and biomass conditions. The reactors consisted of 3.8 L PVC vessels filled with 23 extractable gravel- sockets, used for microbial activity and biomass assessment, and 1 MFC granular-graphite socket, for biosensing assessment. Microbial activity was determined by the ATP content and the hydrolytic enzymatic activity, and the biomass content was assessed as the volatile solids attached to the gravel. Very significant linear relationships could be established between the parameters studied and the current density produced by the MFC with a very short detection time: 10 min for the ATP content (R2 = 0.88) and 1 h for the enzymatic activity (R2 = 0.78) and biomass (R2 = 0.74). Moreover, the power assisted MFC-based biosensing tool demonstrated to be functional after a long operation time and under a wide range of organic loading conditions. Overall, the results highlight the feasibility to develop a power assisted MFC-based biosensor for on-line monitoring of the microbial activity and biomass of a given ecosystem (either natural or artificial) even in remote locations.

Microbial activity enhancement in constructed wetlands operated as bioelectrochemical systems.

Treatment wetlands (TW) operated as bioelectrochemical systems (BES-TW) provide a higher degree of treatment than conventional TW. Yet, the fundamental processes or mechanisms for the envisaged better performance of BES-TW over conventional TW remains poorly understood. This work aimed to determine to which extent microbial activity enhancement could be the reason behind this treatment performance increase. To this purpose, pilot-scale horizontal sub-surface flow BES-TW operated under three different configurations were continuously fed with real urban wastewater. BES-TW were evaluated for COD and ammonia removal efficiency, and two techniques of microbial activity assessment were applied. Configurations, tested in duplicate, were: control TWs without electrodes (C-TW), TWs operated as microbial fuel cells (MFC-TW), and TWs operated as microbial electrolysis cells (MEC-TW). Microbial activity was assessed by measuring the enzymatic activity (EA) (FDA hydrolysis technique) and the aerobic activity (AA) (estimated through respirometry). Results showed that BES-TW outperformed C-TW in terms of both microbial activity enhancement and contaminants removal efficiency, especially in the case of MEC-TW. More precisely, this configuration showed an average improvement of 17%, and 56% in COD removal and EA efficiencies, respectively, compared to C-TW. Regarding AA activity, although MEC-TW seemed to outperform the rest of the configurations, differences were not statistically significant. This work demonstrates that TWs operated as BES increase the overall enzymatic activity of the treatment bed and this, in turn, is the leading cause to a higher degree of treatment performance.

Impact of compost reactive layer on hydraulic transport and C & N cycles: Biogeochemical modeling of infiltration column experiments.

Managed Aquifer Recharge (MAR) is a key strategy to increase freshwater resources in many regions facing water scarcity. MAR issues are related to both quantity and quality of the infiltrating water. In most countries, very high quality of the infiltrating water is required, to limit the impact on the aquifer geochemistry. In this paper, the possibility of injecting water of lower quality in the aquifer and letting the biogeochemical reactions take place in order to enhance its quality is explored. Here, we present the fate of nutrients (C, N) in the biogeochemical system of a reactive barrier formed by mixture of different proportions of sand and compost, supplied with treated wastewater to mimic MAR. An integrated conceptual model involving the nutrient cycles and biomass dynamics (auto- and heterotrophic) was developed, and then tested with a number of solute transport experiments in columns with different compost fraction in the column filling. The model incorporated both saturation and inhibition processes (regarding the nutrients and their byproducts) to provide a comprehensive picture of the nutrient dynamics within the column. The model developed (three if considering the 3 column setups) allowed to discriminate the processes that govern the fate of nutrients in relation with the compost enhancing long-term nutrient degradation, yet hindering hydraulic parameters that affect infiltration rates.

Enhanced BMP-2-Mediated Bone Repair Using an Anisotropic Silk Fibroin Scaffold Coated with Bone-like Apatite.

The repair of large bone defects remains challenging and often requires graft material due to limited availability of autologous bone. In clinical settings, collagen sponges loaded with excessive amounts of bone morphogenetic protein 2 (rhBMP-2) are occasionally used for the treatment of bone non-unions, increasing the risk of adverse events. Therefore, strategies to reduce rhBMP-2 dosage are desirable. Silk scaffolds show great promise due to their favorable biocompatibility and their utility for various biofabrication methods. For this study, we generated silk scaffolds with axially aligned pores, which were subsequently treated with 10× simulated body fluid (SBF) to generate an apatitic calcium phosphate coating. Using a rat femoral critical sized defect model (CSD) we evaluated if the resulting scaffold allows the reduction of BMP-2 dosage to promote efficient bone repair by providing appropriate guidance cues. Highly porous, anisotropic silk scaffolds were produced, demonstrating good cytocompatibility in vitro and treatment with 10× SBF resulted in efficient surface coating. In vivo, the coated silk scaffolds loaded with a low dose of rhBMP-2 demonstrated significantly improved bone regeneration when compared to the unmineralized scaffold. Overall, our findings show that this simple and cost-efficient technique yields scaffolds that enhance rhBMP-2 mediated bone healing.

The Experience of COPD Patients in Lockdown Due to the COVID-19 Pandemic.

Purpose: On March 16, 2020, the Spanish government declared a state of alarm due to the rapid spread of coronavirus disease 2019 (COVID-19). Patients with chronic obstructive pulmonary disease (COPD) were restricted to remain confined at home, and medical visits were cancelled for 3 months. The impact of this lockdown on the manifestations of COPD and the quality-of-life of these patients has not been explored. Patients and Methods: One hundred patients with COPD were interviewed by telephone from May 2-18, 2020. The interviews included questions about the lockdown, missed medical appointments, fears of the disease, possible COVID-19 infection, and exacerbations of COPD suffered during this period and their management. In addition, the COPD Assessment Test, the Hospital Anxiety and Depression, and the 5-Dimension Euro Quality-of-Life questionnaires were administered. Results: Sixty-four (64%) patients claimed to have strictly complied with the lockdown, and only 42 (42%) stated they had left home at least once during lockdown. Only one patient (1%) was hospitalized due to COVID-19, and 13 (13%) patients presented an exacerbation of COPD self-managed at home with no admissions due to exacerbation of COPD during this period. A medical consultation or complementary test was cancelled in 90% of the patients, but 61% had a medical telephone visit with a high degree of satisfaction (mean 9.3/10). Most patients declared that their feeling regarding lung disease and general health was similar or even better during lockdown (82% and 81%, respectively). Conclusion: Our results indicate that in general lockdown had a low impact on COPD patients. Only one patient was affected by COVID-19, but moderate exacerbations of COPD were not infrequent. Although many medical visits and test were cancelled, patients were very satisfied with the medical telephone visits.

Coupling Flow, Heat, and Reactive Transport Modeling to Reproduce In Situ Redox Potential Evolution: Application to an Infiltration Pond.

Redox potential (Eh) measurements are widely used as indicators of the dominant reduction-oxidation reactions occurring underground. Yet, Eh data are mostly used in qualitative terms, as actual values cannot be used to distinguish uniquely the dominant redox processes at a sampling point and should therefore be combined with a detailed geochemical characterization of water samples. In this work, we have intensively characterized the redox potential of the first meter of soil in an infiltration pond recharged with river water using a set of in situ sensors measuring every 12 min during a 1 year period. This large amount of data combined with hydrogeochemical campaigns allowed developing a reactive transport model capable of reproducing the redox potential in space and time together with the site hydrochemistry. Our results showed that redox processes were mainly driven by the amount of sedimentary organic matter in the system as well as by seasonal variation of temperature. As a subsidiary result, our work emphasizes the need to use a fully coupled model of flow, heat transport, solute transport, and the geochemical reaction network to fully reproduce the Eh observations in the topsoil.

What are the main factors influencing the presence of faecal bacteria pollution in groundwater systems in developing countries?

Groundwater is the major source of drinking water in most rural areas in developing countries. This resource is threatened by the potential presence of faecal bacteria coming from a variety of sources and pollution paths, the former including septic tanks, landfills, and crop irrigation with untreated, or insufficiently treated, sewage effluent. Accurately assessing the microbiological safety of water resources is essential to reduce diseases caused by waterborne faecal exposure. The objective of this study is to discern which are the most significant sanitary, hydrogeological, geochemical, and physical variables influencing the presence of faecal bacterial pollution in groundwater by means of statistical multivariate analyses. The concentration of Escherichia coli was measured in a number of waterpoints of different types in a rural area located in the coast of Kenya, assessing both a dry and a wet season. The results from the analyses reaffirm that the design of the well and their maintenance, the distance to latrines, and the geological structure of the waterpoints are the most significant variables affecting the presence of E. coli. Most notably, the presence of faecal bacteria in the study area correlates negatively with the concentration of ion Na+ (being an indirect indicator of fast recharge in the study site), and also negatively with the length of the water column inside the well.

Effect of fluid dynamics on decellularization efficacy and mechanical properties of blood vessels.

Decellularization of blood vessels is a promising approach to generate native biomaterials for replacement of diseased vessels. The decellularization process affects the mechanical properties of the vascular graft and thus can have a negative impact for in vivo functionality. The aim of this study was to determine how detergents under different fluid dynamics affects decellularization efficacy and mechanical properties of the vascular graft. We applied a protocol utilizing 1% TritonX, 1% Tributyl phosphate (TnBP) and DNase on porcine vena cava. The detergents were applied to the vessels under different conditions; static, agitation and perfusion with 3 different perfusion rates (25, 100 and 400 mL/min). The decellularized grafts were analyzed with histological, immunohistochemical and mechanical tests. We found that decellularization efficacy was equal in all groups, however the luminal ultrastructure of the static group showed remnant cell debris and the 400 mL/min perfusion group showed local damage and tearing of the luminal surface. The mechanical stiffness and maximum tensile strength were not influenced by the detergent application method. In conclusion, our results indicate that agitation or low-velocity perfusion with detergents are preferable methods for blood vessel decellularization.

Are dominant microbial sub-surface communities affected by water quality and soil characteristics?

Subsurface microorganisms must deal with quite extreme environmental conditions. The lack of light, oxygen, and potentially nutrients are the main environmental stresses faced by subsurface microbial communities. Likewise, environmental disruptions providing an unbalanced positive input of nutrients force microorganisms to adapt to varying conditions, visible in the changes in microbial community diversity. In order to test microbial community adaptation to environmental changes, we performed a study in a surface Managed Aquifer Recharge facility, consisting of a settlement basin (two-day residence time) and an infiltration pond. Data on groundwater hydrochemistry, soil texture, and microbial characterization was compiled from surface water, groundwater, and soil samples at two distinct recharge operation conditions. Multivariate statistics by means of Principal Component Analysis (PCA) was the technique used to map the relevant dimensionality reduced combinations of input variables that properly describe the system behavior. The methodology selected allows including variables of different nature and displaying very different range values. Strong differences in the microbial assemblage under recharge conditions were found, coupled to hydrochemistry and grain-size distribution variables. Also, some microbial groups displayed correlations with either carbon or nitrogen cycles, especially showing abundant populations of denitrifying bacteria in groundwater. A significant correlation was found between Methylotenera mobilis and the concentrations of NO3 and SO4, and also between Vogesella indigofera and the presence of DOC in the infiltrating water. Also, microbial communities present at the bottom of the pond correlated with representative descriptors of soil grain size distribution.

A simple contaminant fate and transport modelling tool for management and risk assessment of groundwater pollution from contaminated sites.

Contaminated sites pose a significant threat to groundwater resources. The resources that can be allocated by water regulators for site investigation and cleanup are limited compared to the large number of contaminated sites. Numerical transport models of individual sites require large amounts of data and are labor intensive to set up, and thus they are likely to be too expensive to be useful in the management of thousands of contaminated sites. Therefore, simple tools based on analytical solutions of contaminant transport models are widely used to assess (at an early stage) whether a site might pose a threat to groundwater. We present a tool consisting of five different models, representing common geological settings, contaminant pathways, and transport processes. The tool employs a simplified approach for preliminary, conservative, fast and inexpensive estimation of the contamination levels of aquifers. This is useful for risk assessment applications or to select and prioritize the sites, which should be targeted for further investigation. The tool is based on steady-state semi-analytical models simulating different contaminant transport scenarios from the source to downstream groundwater, and includes both unsaturated and saturated transport processes. The models combine existing analytical solutions from the literature for vertical (from the source to the top of the aquifer) and horizontal (within the aquifer) transport. The effect of net recharge causing a downward migration and an increase of vertical dispersion and dilution of the plume is also considered. Finally, we illustrate the application of the tool for a preliminary assessment of two contaminated sites in Denmark and compare the model results with field data. The comparison shows that a first preliminary assessment with conservative, and often non-site specific parameter selection, is qualitatively consistent with broad trends in observations and provides a conservative estimate of contamination.

How whole-body vibration can help our COPD patients. Physiological changes at different vibration frequencies.

OBJECTIVE: Evaluate cardiac, metabolic, and ventilatory changes during a training session with whole-body vibration training (WBVT) with 3 different frequencies in patients with chronic obstructive pulmonary disease (COPD). METHODS: This was a prospective, interventional trial in outpatients with severe COPD. Participants performed 3 vertical WBVT sessions once a week using frequencies of 35, 25 Hz and no vibration in squatting position (isometric). Cardiac, metabolic, and ventilator parameters were monitored during the sessions using an ergospirometer. Changes in oxygen pulse response (VO2/HR) at the different frequencies were the primary outcome of the study. RESULTS: Thirty-two male patients with a mean forced expiratory volume in 1 second of 39.7% completed the study. Compared to the reference of 35 Hz, VO2/HR at no vibration was 10.7% lower (P=0.005); however, no statistically significant differences were observed on comparing the frequencies of 35 and 25 Hz. The median oxygen uptake (VO2) at 25 Hz and no vibration was 9.43% and 13.9% lower, respectively, compared to that obtained at 35 Hz (both comparisons P<0.0001). The median expiratory volume without vibration was 9.43% lower than the VO2 at the end of the assessment at 35 Hz vibration (P=0.002). CONCLUSION: Vertical WBVT training sessions show greater cardiac, metabolic, and respiratory responses compared with the squat position. On comparing the 2 frequencies used, we observed that the frequency of 35 Hz provides higher cardiorespiratory adaptation.

Ischiocrural Strength May Be a Better Prognostic Marker Than Quadriceps Strength in COPD.

It is well known that chronic obstructive pulmonary disease (COPD) patients present with muscle dysfunction that may not correlate with the degree of severity of airflow obstruction. Historically, the strength deficit of the knee extensor musculature (quadriceps) has been described as an independent factor of mortality in COPD. We present the results of a retrospective study with longitudinal follow-up of 60 patients with severe COPD followed for 7 years. During follow-up 22 patients died, mainly of respiratory cause. We have observed that the strength of knee flexor muscles (ischiocrural) and dominant handgrip were independent predictors of mortality in severe COPD patients. However, knee extensor strength (quadriceps) was not an independent predictor of mortality. This is the first study which highlights the importance of knee flexor musculature as a prognostic factor in COPD.