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Rapid warming in the Arctic threatens to amplify climate change by releasing the region’s vast stocks of soil carbon to the atmosphere. Increased nutrient availability may exacerbate soil carbon losses by stimulating microbial decomposition or offset them by increasing primary productivity. The outcome of these competing feedbacks remains unclear. Here we present results from a long-term nutrient addition experiment in northern Alaska, United States, coupled with a mechanistic isotope-tracing experiment. We found that soil carbon losses observed during the first 20 years of fertilization were caused by microbial priming and were completely reversed in the subsequent 15 years by shrub expansion which promoted an increasingly efficient carbon–nitrogen economy. Incorporating long-term stoichiometric responses in Earth system models will improve predictions of the magnitude, direction and timing of the Arctic carbon–climate feedback.

Croplands have been the focus of substantial investigation due to their considerable potential for sequestering carbon. Understanding the potential for soil organic carbon (SOC) sequestration and necessary management strategies will be enabled with accurate process‐based models. Accurately representing crop growth and agricultural practices will be critical for realistic SOC modeling. The MEMS 2 model incorporates a current understanding of SOC formation and stabilization, measurable SOC pools, and deep SOC dynamics and is seen as a highly promising tool to inform management intervention for SOC sequestration. Thus far, MEMS 2 has been developed to represent grasslands. In this study, we further developed MEMS 2 to model annual grain crops and common agricultural practices, such as irrigation, fertilization, harvesting, and tillage. Using four Ameriflux sites, we demonstrated an accurate simulation of crop growth and development. Model performance was strong for simulating aboveground biomass (index of agreement [d] range of 0.89–0.98) and green leaf area index (dfrom 0.90 to 0.96) across corn, soybean, and winter wheat. Good agreement with observations was also achieved for net ecosystem CO2exchange (dfrom 0.90 to 0.96), evapotranspiration (dfrom 0.91 to 0.94), and soil temperature (dof 0.96), while discrepancy with the available soil water content data remain (dfrom 0.14 to 0.81 at four depths to 100 cm). While we will continue model testing and improvement, MEMS 2 (version 2.14) has now demonstrated its ability to effectively simulate the growth of common grain crops and practices. The MEMS 2 model was developed to simulate annual crops and agricultural management.Validation showed the MEMS 2 can accurately represent the growth and production of three major crops at four sites.The simulated soil carbon pools were within the range of reported values from field studies.

Within managed ecosystems, such as some livestock grazed grasslands, soil physical, chemical, and biological properties may be severely compromised relative to native grasslands. Conventional grazing (CG) management, commonly referred to as continuous grazing, can affect soil properties and health by reducing soil C stocks and other available nutrients, while creating bare patches in vegetation that may enhance erosion and runoff. In contrast, adaptive multipaddock (AMP) grazing, an intensive form of rotational grazing that moves dense cattle herds quickly over the land followed by rest periods for the regrowth of plants, has been proposed as a regenerative grassland management tool that can improve soil properties such as soil C stocks, soil structure, as well as nutrient and water retention. Our research analyzed soils from 10 grasslands in the southeast United States representing either CG or AMP grazing management. We analyzed the A‐horizons of these soils for physical, chemical, and biological properties considered indicators of soil health across each management type. Chemical soil properties (e.g., cation exchange capacity [CEC], base saturation [BS], electrical conductivity [EC]) were improved where AMP grazing management was implemented. Additionally, farms using AMP grazing management had greater A‐horizon C and N stocks in bulk soils and across multiple soil organic matter (SOM) fractions. No biological indicators measured were affected by the grassland management except potential N mineralization rate, which was lower under AMP. Taken together, these results provide evidence that AMP grazing management could be implemented to regenerate several grassland soil properties across land currently under conventional grazing management. We found improved chemical soil health indicators where AMP grazing was implemented.Greater AMP A‐horizon C and N stocks were apparent across multiple SOM fractions.Biological soil health indicators were largely unaffected by grazing management.Results show that AMP grazing could be used to regenerate grassland soil health.

In the past few decades, there has been an evolution in our understanding of soil organic matter (SOM) dynamics from one of inherent biochemical recalcitrance to one deriving from plant‐microbe‐mineral interactions. This shift in understanding has been driven, in part, by influential conceptual frameworks which put forth hypotheses about SOM dynamics. Here, we summarize several focal conceptual frameworks and derive from them six controls related to SOM formation, (de)stabilization, and loss. These include: (a) physical inaccessibility; (b) organo‐mineral and ‐metal stabilization; (c) biodegradability of plant inputs; (d) abiotic environmental factors; (e) biochemical reactivity and diversity; and (f) microbial physiology and morphology. We then review the empirical evidence for these controls, their model representation, and outstanding knowledge gaps. We find relatively strong empirical support and model representation of abiotic environmental factors but disparities between data and models for biochemical reactivity and diversity, organo‐mineral and ‐metal stabilization, and biodegradability of plant inputs, particularly with respect to SOM destabilization for the latter two controls. More empirical research on physical inaccessibility and microbial physiology and morphology is needed to deepen our understanding of these critical SOM controls and improve their model representation. The SOM controls are highly interactive and also present some inconsistencies which may be reconciled by considering methodological limitations or temporal and spatial variation. Future conceptual frameworks must simultaneously refine our understanding of these six SOM controls at various spatial and temporal scales and within a hierarchical structure, while incorporating emerging insights. This will advance our ability to accurately predict SOM dynamics. Soil organic matter, the remains of plants, animals, and microbes in the soil, performs many important functions for humans and ecosystems, providing habitat for animals, nutrients for plants, climate change buffering, and structure for soil animals and human structures. Thus, it is important to understand how soil organic matter is formed, stabilized, and lost. Here, we review conceptual frameworks that have contributed to our understanding of soil organic matter over the past 20 years. We evaluate their support in experiments and also how well represented they are in computer models. We find the least support and representation for controls of soil organic matter associated with properties of microbes and physical barriers between microbes and soil organic matter. These and novel soil organic matter controls require more research for better understanding of soil organic matter functions. Soil organic matter (SOM) research has been advanced by conceptual frameworksConceptual frameworks are associated with different SOM controls with variable empirical support and model representationMicrobial physiology and morphology and physical inaccessibility, as SOM controls, require more empirical work and model representation Soil organic matter (SOM) research has been advanced by conceptual frameworks Conceptual frameworks are associated with different SOM controls with variable empirical support and model representation Microbial physiology and morphology and physical inaccessibility, as SOM controls, require more empirical work and model representation

Objective: To identify perioperative clinical predictors of permanent pacemaker implantation following aortic valve replacement. Design and patients: Prospective cohort study on 276 patients submitted for aortic valve replacement: 267 patients [...]

Soil organic matter (SOM) provides vital services to humanity. Its preservation and further accrual are key to sustain food production and avoid an irreversible climate crisis. Here we present the processes and drivers of SOM formation and persistence within a coherent state-of-the-art framework. We posit that SOM forms via two distinct pathways depending on whether inputs are water soluble and/or easily solubilized entering the soil as dissolved organic matter (DOM), or they are structural. These distinct inputs form mineral-associated organic matter (MAOM), and particulate organic matter (POM), respectively. Both these SOM fractions have plant and microbial components but in different proportions, with MAOM being more highly microbial. SOM persistence will depend on microbial activity inhibition, the degree of its limitation and carbon use efficiency, and microbial access constraints, primarily due to association to minerals and occlusions in fine aggregates. Climate is the overarching control of SOM persistence, also by affecting ecosystem traits, when persistence is driven by microbial activity inhibition or limitation, largely responsible for POM storage. Soil geochemical traits are the overarching control of SOM persistence driven by microbial access constraints, particularly in the subsoil, specifically controlling MAOM storage. SOM affects soil properties (aggregation, porosity, and cation exchange capacity) which in turn determine the soil's capacity for functioning and ability to provide desired outcomes including erosion and flood prevention, plant productivity, and climate mitigation. The specific properties of SOM which influence its contributions to these functions are discussed, with implications for SOM conservation and regeneration to promote desired outcomes.

Soil carbon sequestration is seen as an effective means to draw down atmospheric CO2, but at the same time warming may accelerate the loss of extant soil carbon, so an accurate estimation of soil carbon stocks and their vulnerability to climate change is required. Here we demonstrate how separating soil carbon into particulate and mineral-associated organic matter (POM and MAOM, respectively) aids in the understanding of its vulnerability to climate change and identification of carbon sequestration strategies. By coupling European-wide databases with soil organic matter physical fractionation, we assessed the current geographical distribution of mineral topsoil carbon in POM and MAOM by land cover using a machine-learning approach. Further, using observed climate relationships, we projected the vulnerability of carbon in POM and MAOM to future climate change. Arable and coniferous forest soils contain the largest and most vulnerable carbon stocks when cumulated at the European scale. Although we show a lower carbon loss from mineral topsoils with climate change (2.5 ± 1.2 PgC by 2080) than those in some previous predictions, we urge the implementation of coniferous forest management practices that increase plant inputs to soils to offset POM losses, and the adoption of best management practices to avert the loss of and to build up both POM and MAOM in arable soils.

Pyrogenic carbon (PyC), the product of incomplete biomass combustion, is a key component of soil organic carbon (SOC) because it can persist in soils for centuries to millennia. Quantifying PyC across large spatial scales remains a significant challenge in constraining the global carbon cycle. We measured PyC in topsoils across Europe using molecular marker (benzene polycarboxylic acids, BPCA) and spectroscopic techniques (Diffuse Reflectance Infrared Fourier Transform Spectroscopy, DRIFTS). We developed a calibration between BPCA and DRIFTS, but the calibration was less reliable (Y -variance explained=0.62) than previous reports due to low soil PyC content and heterogeneity of soil matrices. Thus, we performed multiple regressions to identify drivers of PyC distribution using only the measured BPCA data. PyC content varied widely among soils, contributing 0–24% of SOC. Organic carbon was the strongest predictor of soil PyC content, but mean annual temperature, clay, and cation exchange capacity also emerged as predictors. PyC contributes a smaller proportion of SOC in European soils compared to other geographic regions. Comparing soil PyC measurements to PyC production rates in high latitude and Mediterranean regions suggests that transport, degradation, and recombustion are important mechanisms regulating soil PyC accumulation.

Soil organic carbon (SOC) stores a large portion of terrestrial C, yet the mechanisms that affect its formation efficiency under different residue management in irrigated systems are still not well understood. No‐till (NT) increases SOC concentrations in topsoil compared with conventional tillage (CT) but there is uncertainty surrounding the stability of these gains in irrigated systems. We investigated the effect of NT and CT residue management on CO2loss and SOC formation by applying isotopically (13C) labeled residues on the surface or incorporated in the mineral soil of disturbed (i.e., CT) or undisturbed (i.e., NT) soil in a semiarid, NT, sprinkler‐irrigated, continuous corn (Zea maysL.) field. We measured residue‐derived C in CO2, bulk soil, dissolved organic C, particulate organic matter (POM), and silt‐ and clay‐sized mineral‐associated organic matter (MAOM) fractions. Twelve months after residue addition, soils with surface‐applied residue produced 19% more CO2and formed 41% less SOC than residue‐incorporated soils. Across all treatments, 62% of residue‐derived C was recovered in POM, and 38% in the MAOM fractions. Residue‐derived bulk soil C formation was more efficient when the residue was incorporated (0.60) rather than surface‐applied (0.42), suggesting that mixing and burial of residue within the soil matrix is a key pathway of SOC formation. During the growing season, surface residue under NT management in irrigated systems is particularly vulnerable to decomposition and will require additional conservation strategies to generate long‐term C sequestration.

Effective land-based solutions to climate change mitigation require actions that maximize soil carbon storage without generating surplus nitrogen. Land management for carbon sequestration is most often informed by bulk soil carbon inventories, without considering the form in which carbon is stored, its capacity, persistency and nitrogen demand. Here, we present coupling of European-wide databases with soil organic matter physical fractionation to determine continental-scale forest and grassland topsoil carbon and nitrogen stocks and their distribution between mineral-associated and particulate organic matter pools. Grasslands and arbuscular mycorrhizal forests store more soil carbon in mineral-associated organic carbon, which is more persistent but has a higher nitrogen demand and saturates. Ectomycorrhizal forests store more carbon in particulate organic matter, which is more vulnerable to disturbance but has a lower nitrogen demand and can potentially accumulate indefinitely. The share of carbon between mineral-associated and particulate organic matter and the ratio between carbon and nitrogen affect soil carbon stocks and mediate the effects of other variables on soil carbon stocks. Understanding the physical distribution of organic matter in pools of mineral-associated versus particulate organic matter can inform land management for nitrogen-efficient carbon sequestration, which should be driven by the inherent soil carbon capacity and nitrogen availability in ecosystems.

Permafrost thaw is projected to restructure the connectivity of surface and subsurface flow paths, influencing export dynamics of dissolved organic matter (DOM) through Arctic watersheds. Resulting shifts in flow path exchange between both soil horizons (organic‐mineral) and landscape positions (hillslope‐riparian) could alter DOM mobility and molecular‐level patterns in chemical composition. Using conservative tracers, we found relatively rapid lateral flows occurred across a headwater Arctic tundra hillslope, as well as along the mineral‐permafrost interface. While pore waters collected from the organic horizon were associated with plant‐derived molecules, those collected from permafrost‐influenced mineral horizons had a microbial origin, as determined by fluorescence spectroscopy. Using high‐resolution nuclear magnetic resonance spectroscopy, we found that riparian DOM had greater structural diversity than hillslope DOM, suggesting riparian soils could supply a diverse array of compounds to surface waters if terrestrial‐aquatic connectivity increases with warming. In combination, these results suggest that integrating DOM mobilization with its chemical and spatial heterogeneity can help predict how permafrost loss will structure ecosystem metabolism and carbon‐climate feedbacks in Arctic catchments with similar topographic features. Permafrost thaw restructures subsurface flow paths and mobilizes dissolved organic matter transport within Arctic catchmentsDissolved organic matter transport is appreciable at the permafrost‐mineral interface, potentially reducing the terrestrial carbon sinkThe structural diversity of dissolved organic matter increases downslope and is greatest along the mineral‐permafrost interface

Pyrogenic carbon (PyC) constitutes a significant fraction of organic carbon in most soils. However, PyC soil stocks are generally smaller than what is expected from estimates of PyC produced from fire and decomposition losses, implying that other processes cause PyC loss from soils. Surface erosion has been previously suggested as one such process. To address this, following a large wildfire in the Rocky Mountains (CO, USA), we tracked PyC from the litter layer and soil, through eroded, suspended, and dissolved solids to alluvial deposits along riversides. We separated deposited sediment into high- and low-density fractions to identify preferential forms of PyC transport and quantified PyC in all samples and density fractions using benzene polycarboxylic acid markers. A few months after the fire, PyC had yet to move vertically into the mineral soil and remained in the organic layer or had been transported off site by rainfall driven overland flow. During major storm events PyC was associated with suspended sediments in river water and later identified in low-density riverbank deposits. Flows from an unusually long-duration and high magnitude rainstorm either removed or buried the riverbank sediments approximately 1?year after their deposition. We conclude that PyC redistributes after wildfire in patterns that are consistent with erosion and deposition of low-density sediments. A more complete understanding of PyC dynamics requires attention to the interaction of post fire precipitation patterns and geomorphological features that control surface erosion and deposition throughout the watershed. Surface erosion is a major loss pathway of PyC from burned mountain soilsPyC is transported primarily with the low-density organic fraction of sedimentsPyC can accumulate for millennia in alluvial deposits of burned watersheds

Soil organic matter is the largest terrestrial carbon pool. The pool size depends on the balance between formation of soil organic matter from decomposition of plant litter and its mineralization to inorganic carbon. Knowledge of soil organic matter formation remains limited and current C numerical models assume that stable soil organic matter is formed primarily from recalcitrant plant litter. However, labile components of plant litter could also form mineral-stabilized soil organic matter. Here we followed the decomposition of isotopically labelled above-ground litter and its incorporation into soil organic matter over three years in a grassland in Kansas, USA, and used laboratory incubations to determine the decay rates and pool structure of litter-derived organic matter. Early in decomposition, soil organic matter formed when non-structural compounds were lost from litter. Soil organic matter also formed at the end of decomposition, when both non-structural and structural compounds were lost at similar rates. We conclude that two pathways yield soil organic matter efficiently. A dissolved organic matter–microbial path occurs early in decomposition when litter loses mostly non-structural compounds, which are incorporated into microbial biomass at high rates, resulting in efficient soil organic matter formation. An equally efficient physical-transfer path occurs when litter fragments move into soil.

Biochar (BC) application to agricultural soils could potentially sequester recalcitrant C, increase N retention, increase water holding capacity, and decrease greenhouse gas (GHG) emissions. Biochar addition to soils can alter soil N cycling and in some cases decrease extractable mineral N (NO3−and NH4+) and N2O emissions. These benefits are not uniformly observed across varying soil types, N fertilization, and BC properties. To determine the effects of BC addition on N retention and GHG flux, we added two sizes (>250 and <250 µm) of oak‐derived BC (10% w/w) to two soils (aridic Argiustoll and aquic Haplustoll) with and without N fertilizer and measured extractable NO3−and NH4+and GHG efflux (N2O, CO2, and CH4) in a 123‐d laboratory incubation. Biochar had no effect on NO3−, NH4+, or N2O in the unfertilized treatments of either soil. Biochar decreased cumulative extractable NO3−in N fertilized treatments by 8% but had mixed effects on NH4+. Greenhouse gas efflux differed substantially between the two soils, but generally with N fertilizer BC addition decreased N2O 3 to 60%, increased CO210 to 21%, and increased CH4emissions 5 to 72%. Soil pH and total treatment N (soil + fertilizer + BC) predicted soil N2O flux well across these two different soils. Expressed as CO2equivalents, BC significantly reduced GHG emissions only in the N‐fertilized silt loam by decreasing N2O flux. In unfertilized soils, CO2was the dominant GHG component, and the direction of the flux was mediated by positive or negative BC effects on soil CO2flux. On the basis of our data, the use of BC appears to be an effective management strategy to reduce N leaching and GHG emissions, particularly in neutral to acidic soils with high N content.

High-resolution diode laser spectroscopy in the near-infrared region is applied to the accurate measurement of soil respiration. In particular, the use of a diode-laser-based spectrometer has allowed the implementation, for the first time, of a static accumulation method capable of measuring soil respiration from continuous measurements of CO2concentrations, with minor perturbation on soil respiration as well as on CO2transport and emission. The system has been tested in a laboratory experiment by detection of CO2production from sandy matrices, inoculated with active soil microbes and supplied with different amounts of decomposable plant material. Respiration rates of all samples were then retrieved using a diffusion model. The results of the laboratory tests are in agreement with those expected on the basis of sample composition. Examples of operation with real soil samples are also reported. We discuss the possible field application of the system, in conjunction with closed static soil chambers.

Objective Postoperative respiratory failure is a frequent and serious complication in patients with type A acute aortic dissection. Experimental evidence suggests that pulmonary artery perfusion using hypothermic protective solutions helps prevent lung injury. The aim of this pilot prospective study was to evaluate the effect of pulmonary artery flushing during selective cerebral perfusion (SCP) on lung function.Methods Twenty patients referred for acute type A aortic dissection, who were free from preoperative respiratory dysfunction, were assigned prospectively and alternately to two treatment groups. Pulmonary flushing was performed during SCP in group P (10 patients), while conventional Kazui technique was applied in group N (10 patients). Lung perfusion consisted of single-shot hypothermic pulmonary artery flush with Celsior. Lung function was evaluated by intubation time, scoring of chest radiograms at 12 hours after CPB, and PaO2/FiO2assessed from immediately before surgery to 72 hours after termination of cardiopulmonary bypass.Results Incidence of pre, intra and post operative determinants of lung dysfunction proved homogeneous in both groups. Lung oxygenation function showed a marked post operative decline followed by a slow improvement in both groups. Analysis of respiratory ratios did not disclose significant differences even though the flushed group had a better performance in all study patients. The incidence of prolonged ventilator support (longer than 72 hours) (30% vs 20%, p=NS) and severity of x-ray pulmonary infiltrate score were comparable (mean score 1.7±0.71 vs 1.6±0.68, p=NS).Conclusions Pulmonary artery flushing with Celsior solution does not seem to provide an effective preservation of lung function.

Background Perioperative management of post-infarction left ventricular free wall rupture (LVFWR) is not clearly standardized and surgical repair is the only therapeutic option. Role of off-pump surgery and stabilization with perioperative intraaortic balloon pumping (IABP) were here analysed.Methods Seven patients underwent surgery for LVFWR between 1990 and 2002. Clinical picture included electromechanical dissociation (3 patients) and sudden hypotension (4 patients). Except in one patient who was reanimated through femoro-femoral cardiopulmonary bypass, off-pump repair through on-lay patching technique was always performed. IABP was employed in the immediate postoperative period in five cases.Results A satisfactory hemodynamic state was restored in all cases and there were no reoperations for bleeding or rerupture. Hospital survival was 100%. One patient underwent successful surgical myocardial revascularization two months after LVFWR. Two patients died at follow-up. The survivors present with good NYHA and CCS functional classes.Conclusions When the anatomy of the LVFWR is favourable, off-pump external patching repair proves a good choice. Postoperative IABP provides satisfactory hemodynamic support.

This study aimed to assess whether low doses of albumin in the priming solution for cardiopulmonary bypass (CPB) reduce postoperative bleeding.Three-hundred and seventy-seven patients undergoing CPB were retrospectively assigned to group A (154 patients, CPB primed with 20 ml/kg Ringer Lactate solution + 0.75mg/kg albumin 20%) and group B (223 patients with 20 ml/kg Ringer Lactate).A significant difference was found in terms of reoperations for bleeding (group A 0/154 versus group B 9/223; P=0.033). The mean number of blood derivatives transfused per patient was higher in group B than in group A (p <0.001). Platelet count after CPB was higher in group A than in group B (175±52×103/µl versus 131±70×103/µl; P=0.045). The amount of postoperative bleeding was 525ml versus 680ml at 24hrs (p <0.001), 819ml versus 1102ml at 48hrs, (p <0.001), 963ml versus 1294ml at 72hrs, (p <0.045) (group A versus group B respectively). Crystalloid priming with low-dose albumin reduces postoperative bleeding.

In this prospective trial the results of preoperative and intraoperative IABP in coronary artery bypass graft (CABG) patients with low left ventricular ejection fraction (LVEF) were compared. Sixty CABG patients with preoperative LVEF =0.30 were enrolled: in group A patients (n=30) IABP was started within 2 hours preoperatively; in group B (n=30) it was instituted intraoperatively before weaning from cardiopulmonary bypass. Cardiac performance was assessed through Swan-Ganz catheter monitoring and daily echocardiography. Hospital survival, length of IABP support, intubation, ICU and hospital stay, need for postoperative inotropic drugs and incidence of myocardial infarction were compared between the two groups.Survival in group A patients proved significantly higher (P=0.047). Cardiac performance after myocardial revascularization improved in both groups with significantly better outcomes in group A patients (p<0.001). Doses of inotropic drugs (dobutamine, enoximone) were lower in group A (P=0.001; P=0.004) and duration shorter (p<0.001; p<0.001). No major IABP-related complication was observed.

Results after isolated aortic valve replacement with bileaflet prostheses in patients over 70 years old were reviewed.One-hundred-twenty-eight elderly patients were operated on between January 1988 and January 2000. Patients with associated heart disease were excluded from the study. Preoperative data, early and late postoperative mortality, all valve related complications and data concerning anticoagulation status were recorded.Hospital mortality was 9.3%. Mean follow-up time was 60.98±2.23 months. Twelve-year actuarial survival was 69.6±0.08%. Valve related and anticoagulation related complication rates (0.8% and 1.6% respectively) and actuarial freedom (99±0.009 both) were low, as well as the mean interval between consecutive INR checks (18.39±1.90 days) and the mean INR value (2.17±0.135). Late echocardiographic results showed low postoperative mean transprosthetic gradients (15.48±0.94).Bileaftlet prostheses in the elderly can achieve excellent results with a low incidence of anticoagulation related complications and low risk of reoperation. Older age can no longer be considered a contraindication to bileaftlet prosthesis implant.

Assessment of endovascular stent-graft treatment for diseases of the descending thoracic aorta as a valid and effective alternative to surgery.

This retrospective chart review study aimed to evaluate whether a more aggressive staged approach can reduce morbidity and mortality following post-cardiotomy deep sternal wound infection.

Although new models of bileaflet valves with improved orifice have been devised, aortic valve replacement with 19mm prostheses still raises concerns about long term effects of residual transprosthetic gradient.We reviewed our experience with 19 mm standard model St Jude prostheses in 68 patients operated on between January 1983 and December 1995. Clinical late assessment was performed to evaluate the incidence of valve related complications. Postoperative echocardiography was performed to evaluate hemodynamic performance of the prostheses.Mean body surface area was 1.66±0.14m2. Late postoperative peak gradient was 53.85±7.16 mmHg; mean gradient was 34.80±5.55 mm Hg; effective orifice area was 1.93±0.05 cm2. Thirteen-year actuarial survival has been 90.89 ± 0.6%; thirteen-year freedom from embolism 89.41 ± 0.7% and freedom from hemorrhage 98.25 ± 0.02%. No case of prosthetic endocarditis, thrombosis, or reoperation was observed during follow-up.

A new model of surgical injury for the induction and development of stenosis in common rat carotids is described. This model differs from balloon angioplasty or vein graft systems currently applied on animals to develop stenosis, since it involves the entire vessel wall layers and mimics the injury occurring during arterial grafts, endarterectomy or organ transplantation. At different times following arterial damage, the pattern of expression of genes already known to be involved in the proliferation, differentiation, and apoptosis of smooth muscle cells (c-myc, Angiotensin II receptor 1, Bcl-2 and Bax α), as well as of Rb and Rb2 genes, whose pattern of expression after arterial injury has not yet been reported, was analyzed by semi-quantitative reverse transcription-polymerase chain reaction technique. Histological and histochemical analysis on carotid sections shows the morphological changes which occurred 30 days after surgical injury in the vessel wall. Molecular and histological data demonstrate that this model of surgical injury induces neointimal proliferation in about 30% of rats. In about 70% of the remaining rats, it induces the processes responsible for negative remodelling, namely the significant accumulation of extracellular matrix and fibers and disorganization of arterial tunics. This model is therefore available for further studies on the expression of genes involved in the arterial stenotic process, as well as for testing drugs aimed at limiting this recurrent pathophysiological phenomenon. J. Cell. Physiol. 186:307–313, 2001. © 2001 Wiley-Liss, Inc.

To evaluate whether perioperative bacteria identification in blood and/or in valve cultures can predict early and late outcome of surgery for infective endocarditis, a retrospective study was performed.

Although many studies in medical literature are comparing percutaneous trans-septal mitral commissurotomy (PTMC) and open mitral commissurotomy (OMC), very few long-term comparative follow-ups are available.

Atrial fibrillation (AF) is the most frequently encountered arrhythmic complication associated with coronary surgery. The aim of this paper was then to identify the clinical predictors of post-CABG AF occurrence.

Three perennial grass species, perennial ryegrass (Lolium perenneL.), colonial bentgrass (Agrostis capillarisL.), and sheep fescue (Festuca ovinaL.), were grown at two CO2concentrations (350 and 700 μL L−1) and under two N regimes: one with a minor addition of 8 kg N ha−1and one with an addition of ≈278 kg N ha−1, both labeled with 15N. The effects of elevated CO2on 15N and N uptake and dynamics in the plant–soil systems were determined after 32 and 55 d, with close attention to the rhizosphere. Total N uptake by the plants was not affected by elevated CO2, compared with ambient CO2, independent of N treatment and grass species. A clear decrease from 1.77 at ambient CO2to 1.25 at elevated CO2was observed in the shoot/root (S/R) ratio of N, resulting from a significant decrease of the N concentration in shoots, and an unchanged root N concentration. At 700 μL L−1CO2, N concentration in the shoots decreased from 12.9 to 9.9 g kg−1, even at the low N supply, whereas the slight decrease in root N concentration for plants grown at elevated CO2(7.9 vs. 7.3 g kg−1) was not significantly different. The relative increase of 15N found in the rhizosphere soil microbial biomass (SMB) and the rhizosphere soil residue under elevated CO2was too small to affect plant growth, even in the low N treatment. The total amount of 15N recovered in the plants was not affected by the CO2treatment. Although at the second harvest slightly more 15N was found in the plants than at the first harvest, probably due to turnover of the SMB, no interaction with CO2was observed. This shows that the fertilizer 15N had not been immobilized to a larger extent or for a longer time by the SMB at elevated CO2than under ambient CO2, even independent of N level and grass species. No evidence was found that under elevated CO2substantial amounts of N had been immobilized by the SMB, nor that mineralization of native soil organic matter (SOM) had been stimulated by an increased supply of substrate to the SMB. We conclude that elevated CO2has the potential to induce significant changes in plant N nutrition, modifying N allocation and tissue quality within perennial grasses, but that these effects appear to be independent of the SMB.

Fifteen collaborating centers in eight countries present their pooled experience with the new Bicarbon bileaflet valve.

The adherence of bacterial cells to valvular prostheses has been studied. Bacteria were selected on the. basis of their surface features (fimbriae, hydrophobicity and specific receptors). It was found that only strains having fimbriae and high cell surface hydrophobicity adhered to bioprostheses, while they did not adhere to metallic prostheses to any significant extent. Adherence to bioprostheses depended on the exposure time and it was affected by the saline concentration of the suspension medium. Furthermore, different bacterial binding capacity was observed for bioprostheses from different companies.

Despite the achievements of third generation mechanical cardiac valve prostheses, conservative procedures are still considered the best surgical option for rheumatic mitral valve stenosis. To compare long-term results of open mitral commissurotomy (Group A) and mitral valve replacement with bileaflet prostheses (Group B) a 15-year follow-up study was carried out.

The effect of elevated atmospheric CO2 and nutrient supply on elemental composition and decomposition rates of tree leaf litter was studied using litters derived from birch (Betula pendula Roth.) plants grown under two levels of atmospheric CO2 (ambient and ambient +250 ppm) and two nutrient regimes in solar domes. CO2 and nutrient treatments affected the chemical composition of leaves, both independently and interactively. The elevated CO2 and unfertilized soil regime significantly enhanced lignin/N and C/N ratios of birch leaves. Decomposition was studied using field litter-bags, and marked differences were observed in the decomposition rates of litters derived from the two treatments, with the highest weight remaining being associated with litter derived from the enhanced CO2 and unfertilized regime. Highly significant correlations were shown between birch litter decomposition rates and lignin/N and C/N ratios. It can be concluded, from this study, that at levels of atmospheric CO2 predicted for the middle of the next century a deterioration of litter quality will result in decreased decomposition rates, leading to reduction of nutrient mineralization and increased C storage in forest ecosystems. However, such conclusions are difficult to generalize, since tree responses to elevated CO2 depend on soil nutritional status.

Five clinical cases were treated with the implantation of an apical-aortic conduit.Two adult patients were affected by obstructive myocardiopathy associated to subaortic membrane in one case, and three children by different forms of aortic stenosis (subaortic tunnel in one case; subaortic tunnel associated to severe coartation of the thoracic aorta in one case; aortic annulus hypoplasia in one case).A double outlet left ventricle has been created in all cases by implanting a composite prosthesis between the apex of the left ventricle and the aorta. The extracardiac conduit consisted of an apical curved connector and a valved dacron tubular prosthesis. The site of implantation was the supraceliac abdominal aorta in three cases and the ascending aorta in two cases.All patients survived the operation and one late mortality was observed for cerebral bleeding. The surviving patients have been restudied with satisfactory data.

Atrial septal defect transcatheter occlusion techniques have become a reliable alternative to surgical procedures. Possible complications can derive from unfavorable anatomy of the defect and over-dimensioning of the device. We describe the first case ever reported of anterior mitral leaflet perforation caused by an atrial septal occluder. The diagnosis was performed by conventional echocardiography and 3 dimensions helped for a more accurate anatomic definition. Device removal, atrial septal defect closure, and repair of the mitral tear were then successfully performed.