Post-fire stabilization of thaw-affected permafrost terrain in northern Alaska.

In 2007, the Anaktuvuk River fire burned more than 1000 km2 of arctic tundra in northern Alaska, ~ 50% of which occurred in an area with ice-rich syngenetic permafrost (Yedoma). By 2014, widespread degradation of ice wedges was apparent in the Yedoma region. In a 50 km2 area, thaw subsidence was detected across 15% of the land area in repeat airborne LiDAR data acquired in 2009 and 2014. Updating observations with a 2021 airborne LiDAR dataset show that additional thaw subsidence was detected in < 1% of the study area, indicating stabilization of the thaw-affected permafrost terrain. Ground temperature measurements between 2010 and 2015 indicated that the number of near-surface soil thawing-degree-days at the burn site were 3 × greater than at an unburned control site, but by 2022 the number was reduced to 1.3 × greater. Mean annual ground temperature of the near-surface permafrost increased by 0.33 °C/yr in the burn site up to 7-years post-fire, but then cooled by 0.15 °C/yr in the subsequent eight years, while temperatures at the control site remained relatively stable. Permafrost cores collected from ice-wedge troughs (n = 41) and polygon centers (n = 8) revealed the presence of a thaw unconformity, that in most cases was overlain by a recovered permafrost layer that averaged 14.2 cm and 18.3 cm, respectively. Taken together, our observations highlight that the initial degradation of ice-rich permafrost following the Anaktuvuk River tundra fire has been followed by a period of thaw cessation, permafrost aggradation, and terrain stabilization.

Landscape impacts of 3D-seismic surveys in the Arctic National Wildlife Refuge, Alaska.

Although three-dimensional (3D) seismic surveys have improved the success rate of exploratory drilling for oil and gas, the impacts have received little scientific scrutiny, despite affecting more area than any other oil and gas activity. To aid policy-makers and scientists, we reviewed studies of the landscape impacts of 3D-seismic surveys in the Arctic. We analyzed a proposed 3D-seismic program in northeast Alaska, in the northern Arctic National Wildlife Refuge, which includes a grid 63,000 km of seismic trails and additional camp-move trails. Current regulations are not adequate to eliminate impacts from these activities. We address issues related to the high-density of 3D trails compared to 2D methods, with larger crews, more camps, and more vehicles. We focus on consequences to the hilly landscapes, including microtopography, snow, vegetation, hydrology, active layers, and permafrost. Based on studies of 2D-seismic trails created in 1984-1985 in the same area by similar types of vehicles, under similar regulations, approximately 122 km2 would likely sustain direct medium- to high-level disturbance from the proposed exploration, with possibly expanded impacts through permafrost degradation and hydrological connectivity. Strong winds are common, and snow cover necessary to minimize impacts from vehicles is windblown and inadequate to protect much of the area. Studies of 2D-seismic impacts have shown that moist vegetation types, which dominate the area, sustain longer-lasting damage than wet or dry types, and that the heavy vehicles used for mobile camps caused the most damage. The permafrost is ice rich, which combined with the hilly topography, makes it especially susceptible to thermokarst and erosion triggered by winter vehicle traffic. The effects of climate warming will exacerbate the impacts of winter travel due to warmer permafrost and a shift of precipitation from snow to rain. The cumulative impacts of 3D-seismic traffic in tundra areas need to be better assessed, together with the effects of climate change and the industrial development that would likely follow. Current data needs include studies of the impacts of 3D-seismic exploration, better climate records for the Arctic National Wildlife Refuge, especially for wind and snow; and high-resolution maps of topography, ground ice, hydrology, and vegetation.

Very Early Cytomegalovirus Infection After Renal Transplantation: A Single-Center 20-Year Perspective.

BACKGROUND: Cytomegalovirus (CMV) infection risk in the first month after transplantation is felt to be minimal; however, the epidemiology has not been specifically investigated, particularly in the modern era of potent immunosuppressive regimens and universal CMV prophylaxis. OBJECTIVE: The aim of this study was to describe the incidence of and risk factors associated with CMV occurring less than 30 days after transplant and evaluate the effect of very early CMV on outcomes. METHODS: Retrospective, single-center study of adult renal transplant (RTX) recipients between January 1, 1994 and December 31, 2014. RESULTS: A total of 5225 patients who received a renal transplant in the study time period were reviewed for the presence of CMV infection occurring less than 30 days after transplant. Of these, only 14 patients demonstrated this finding for an overall incidence of 0.27%. Half of these patients were considered to be at heightened risk due to being a recipient of a non-primary transplant or on chronic immunosuppression. This left seven patients without known risk factors for very early CMV to evaluate. In this group, time from transplant to CMV infection was 13.5 ± 7 days. The majority (57.1%, n = 4) were high-risk serostatus (CMV D+/R-) and occurred in the valganciclovir era (71.4%, n = 5). Lymphocyte-depleting induction predominated (57.1%, n = 4). Average cold ischemic time (CIT) was 19.7 ± 7.7 hours. Three patients had post-operative complications, two required exploratory-laparotomy for hemorrhage. When evaluating outcomes, 43% (n = 3) had subsequent episodes of CMV infection, 28.6% (n = 2) developed rejection, and 28.6% (n = 2) died. Outcomes between patients with CMV infection less than 30 days and those with CMV infection more than 30 days after transplant were not significantly different. CONCLUSIONS: In our review of over 5000 kidney transplants, the incidence of CMV infection in the first 30 days after renal transplant is 0.2%. Notable common patient characteristics include hemorrhage requiring re-operation and prolonged CIT. Outcomes were similar to CMV occurring more than 30 days after transplant. This study should provide the clinician with some reassurance; despite potent immunosuppressive therapy, CMV infection in the first 30 days is unlikely.

Spatiotemporal remote sensing of ecosystem change and causation across Alaska.

Contemporary climate change in Alaska has resulted in amplified rates of press and pulse disturbances that drive ecosystem change with significant consequences for socio-environmental systems. Despite the vulnerability of Arctic and boreal landscapes to change, little has been done to characterize landscape change and associated drivers across northern high-latitude ecosystems. Here we characterize the historical sensitivity of Alaska's ecosystems to environmental change and anthropogenic disturbances using expert knowledge, remote sensing data, and spatiotemporal analyses and modeling. Time-series analysis of moderate-and high-resolution imagery was used to characterize land- and water-surface dynamics across Alaska. Some 430,000 interpretations of ecological and geomorphological change were made using historical air photos and satellite imagery, and corroborate land-surface greening, browning, and wetness/moisture trend parameters derived from peak-growing season Landsat imagery acquired from 1984 to 2015. The time series of change metrics, together with climatic data and maps of landscape characteristics, were incorporated into a modeling framework for mapping and understanding of drivers of change throughout Alaska. According to our analysis, approximately 13% (~174,000 ± 8700 km2 ) of Alaska has experienced directional change in the last 32 years (±95% confidence intervals). At the ecoregions level, substantial increases in remotely sensed vegetation productivity were most pronounced in western and northern foothills of Alaska, which is explained by vegetation growth associated with increasing air temperatures. Significant browning trends were largely the result of recent wildfires in interior Alaska, but browning trends are also driven by increases in evaporative demand and surface-water gains that have predominately occurred over warming permafrost landscapes. Increased rates of photosynthetic activity are associated with stabilization and recovery processes following wildfire, timber harvesting, insect damage, thermokarst, glacial retreat, and lake infilling and drainage events. Our results fill a critical gap in the understanding of historical and potential future trajectories of change in northern high-latitude regions.

Historical and projected trends in landscape drivers affecting carbon dynamics in Alaska.

Modern climate change in Alaska has resulted in widespread thawing of permafrost, increased fire activity, and extensive changes in vegetation characteristics that have significant consequences for socioecological systems. Despite observations of the heightened sensitivity of these systems to change, there has not been a comprehensive assessment of factors that drive ecosystem changes throughout Alaska. Here we present research that improves our understanding of the main drivers of the spatiotemporal patterns of carbon dynamics using in situ observations, remote sensing data, and an array of modeling techniques. In the last 60 yr, Alaska has seen a large increase in mean annual air temperature (1.7°C), with the greatest warming occurring over winter and spring. Warming trends are projected to continue throughout the 21st century and will likely result in landscape-level changes to ecosystem structure and function. Wetlands, mainly bogs and fens, which are currently estimated to cover 12.5% of the landscape, strongly influence exchange of methane between Alaska's ecosystems and the atmosphere and are expected to be affected by thawing permafrost and shifts in hydrology. Simulations suggest the current proportion of near-surface (within 1 m) and deep (within 5 m) permafrost extent will be reduced by 9-74% and 33-55% by the end of the 21st century, respectively. Since 2000, an average of 678 595 ha/yr was burned, more than twice the annual average during 1950-1999. The largest increase in fire activity is projected for the boreal forest, which could result in a reduction in late-successional spruce forest (8-44%) and an increase in early-successional deciduous forest (25-113%) that would mediate future fire activity and weaken permafrost stability in the region. Climate warming will also affect vegetation communities across arctic regions, where the coverage of deciduous forest could increase (223-620%), shrub tundra may increase (4-21%), and graminoid tundra might decrease (10-24%). This study sheds light on the sensitivity of Alaska's ecosystems to change that has the potential to significantly affect local and regional carbon balance, but more research is needed to improve estimates of land-surface and subsurface properties, and to better account for ecosystem dynamics affected by a myriad of biophysical factors and interactions.

Long-term recovery patterns of arctic tundra after winter seismic exploration.

In response to the increasing global demand for energy, oil exploration and development are expanding into frontier areas of the Arctic, where slow-growing tundra vegetation and the underlying permafrost soils are very sensitive to disturbance. The creation of vehicle trails on the tundra from seismic exploration for oil has accelerated in the past decade, and the cumulative impact represents a geographic footprint that covers a greater extent of Alaska's North Slope tundra than all other direct human impacts combined. Seismic exploration for oil and gas was conducted on the coastal plain of the Arctic National Wildlife Refuge, Alaska, USA, in the winters of 1984 and 1985. This study documents recovery of vegetation and permafrost soils over a two-decade period after vehicle traffic on snow-covered tundra. Paired permanent vegetation plots (disturbed vs. reference) were monitored six times from 1984 to 2002. Data were collected on percent vegetative cover by plant species and on soil and ground ice characteristics. We developed Bayesian hierarchical models, with temporally and spatially autocorrelated errors, to analyze the effects of vegetation type and initial disturbance levels on recovery patterns of the different plant growth forms as well as soil thaw depth. Plant community composition was altered on the trails by species-specific responses to initial disturbance and subsequent changes in substrate. Long-term changes included increased cover of graminoids and decreased cover of evergreen shrubs and mosses. Trails with low levels of initial disturbance usually improved well over time, whereas those with medium to high levels of initial disturbance recovered slowly. Trails on ice-poor, gravel substrates of riparian areas recovered better than those on ice-rich loamy soils of the uplands, even after severe initial damage. Recovery to pre-disturbance communities was not possible where trail subsidence occurred due to thawing of ground ice. Previous studies of disturbance from winter seismic vehicles in the Arctic predicted short-term and mostly aesthetic impacts, but we found that severe impacts to tundra vegetation persisted for two decades after disturbance under some conditions. We recommend management approaches that should be used to prevent persistent tundra damage.

Pressure rinsing of coronary stents immediately before implantation reduces inflammation and neointimal hyperplasia.

OBJECTIVES: This study evaluates whether rinsing stents with high pressure immediately before implantation minimizes stent-induced inflammation and neointimal formation. BACKGROUND: Several reports indicate that manual stent manipulation before implantation results in foreign body contamination and increased neointimal hyperplasia. METHODS: A stent-cleaning chamber was developed to rinse stents at a sustained hydrodynamic pressure of 4 atm for 10 s. Commercial pre-mounted stents were examined with different levels of manipulation: 1) untouched stents: no stent manipulation before implantation; 2) handled stents: manual stent re-crimping on the balloon; 3) rinsed stents: pressure-rinsed with the stent-cleaning chamber. In vitro surface analysis was evaluated by scanning electron microscopy. Neointimal hyperplasia and inflammation around stent struts were also assessed in the pig in-stent restenosis model. RESULTS: In vitro analysis revealed fewer contaminants on rinsed stents compared with untouched (p = 0.01) and handled stents (p < 0.001). In vivo, neointimal thickness, neointimal area and vessel percent stenosis were significantly reduced in rinsed, compared with not-rinsed, stents (p = 0.002, p = 0.007, p = 0.008 respectively). In addition, a significant reduction in the inflammatory infiltrate around struts was observed in untouched, compared with handled, stents (p = 0.04) and in rinsed, compared with not-rinsed, stents (p < 0.001). Regression analysis accounting for injury and neointimal thickness showed significant differences in slopes between "handled + not-rinsed" and "handled + rinsed" stents (p = 0.004), and between "untouched + not-rinsed" and "untouched + rinsed stents" (p = 0.037). CONCLUSIONS: Rinsing stents under high pressure immediately before coronary implantation results in less inflammation around struts and thinner neointima at 28 days in this pig model.

Neointimal thickening after severe coronary artery injury is limited by a short-term administration of a factor Xa inhibitor. Results in a porcine model.

BACKGROUND: Fibrin- and platelet-rich thrombus formations occur as the initial event after percutaneous transluminal coronary angioplasty. We therefore tested the hypothesis that short-term administration of the recombinant tick anticoagulant peptide (rTAP), a factor Xa inhibitor, would reduce the thickness of neointima at 28 days after injury in a porcine coronary balloon angioplasty model. METHODS AND RESULTS: Continuous intravenous infusion of rTAP (average dose, 194 micrograms . kg-1 . min-1) or placebo (vehicle only) was given to the study pigs for 60 hours. The goal of anticoagulation was to maintain the activated clotting time at 200 seconds. A central venous catheter was inserted 2 days before the procedure. On the day of coronary injury, the animals were administered boluses of rTAP (6.5 mg) and then underwent injury with an oversized metallic coil by standard methods in the right, circumflex, or left anterior descending coronary artery. No significant difference in vascular injury between rTAP and vehicle control was observed after euthanasia at 28 days. Significantly less neointimal thickening occurred in the rTAP-treated animals (thickness, mean +/-SD: 0.30 +/-0.08 mm) compared with the control (0.48 +/- 0.12 mm, P< .001). CONCLUSIONS: The specific factor Xa inhibitor rTAP, when given in fully anticoagulant doses for a short duration after coronary artery injury in the porcine model, resulted in a long-term decrease in neointimal thickness. These results implicate thrombin generation in neointimal formation and suggest that administration of a potent antithrombotic for several days immediately after the procedure may influence the long-term outcome of the coronary injury with a decrease in neointimal formation.

The effects of lovastatin on neointimal hyperplasia following injury in a porcine coronary artery model.

OBJECTIVE: To assess the effectiveness of lovastatin, an HMGCoA reductase inhibitor, in the inhibition of coronary arterial restenosis post-balloon angioplasty. DESIGN: Randomized single-blind study comparing the degree of restenosis in a control and lovastatin group of animals with similar degree of arterial injury. ANIMALS: Seventeen domestic cross-bred pigs received either oral lovastatin (11 animals) or no lovastatin (six animals). INTERVENTIONS: The pigs received 20 mg of oral lovastatin twice daily or no drug. All pigs received acetylsalicylic acid and verapamil preprocedure. One or more coronary arteries were injured by deployment of tantalum wire stents delivered on oversized percutaneous transluminal coronary angioplasty balloons. The balloons were intentionally overexpanded to create arterial injury. The animals were sacrificed at 28 days. The arteries were cross-sectioned and evaluated blindly by quantitative histomorphometry. The amounts of arterial injury and neointimal thickening were quantitated. A series of linear regression models was used to control for the degree of injury. MAIN RESULTS: The reduction of neointimal thickness for the lovastatin group compared with the control animals was 0.08 mm, a statistically significant result (P < 0.05). CONCLUSIONS: Although lovastatin produced a statistically significant decrease in neointimal thickness post-balloon angioplasty, when extrapolated to angiographical end-points, the differences would not be clinically significant. These data suggest that lovastatin may be of marginal use in humans for limiting restenosis.

Polymeric stenting in the porcine coronary artery model: differential outcome of exogenous fibrin sleeves versus polyurethane-coated stents.

OBJECTIVES: In a porcine coronary model, fibrin film soaked for 3 h in heparin was used as a circumferential coating on a tantalum stent to assess the effect of this naturally occurring biopolymer on arterial healing. The results were compared with those obtained with medical grade polyurethane-coated stainless steel stents. BACKGROUND: Thrombus plays an important role in healing after arterial injury and may affect the development of neointimal hyperplasia. Manipulation of the initial thrombus may alter the healing response. To study this, we placed a template of fibrin in a porcine coronary artery restenosis model. METHODS: Thirty-four fibrin film stents were delivered in 20 swine. Oversizing was avoided, to prevent deep arterial injury, by placement of optimally sized stents. Initial patency of the stented vessel was confirmed by angiography. RESULTS: Three fibrin-stented swine died within 48 h; in each, the stent was occluded with a fibrin/red blood cell mass. In two of these three, a portion of the exogenous fibrin had become detached from the stent and partially occluded the lumen. Of the remaining 31 stents, all were patent at elective sacrifice at 28 days. Eighty-four percent had a diameter stenosis < 50%, and the mean (+/- SD) diameter stenosis was 32.3 +/- 13%. There was no evidence of significant foreign-body giant-cell reaction. These results contrasted with the medical grade polyurethane-coated stents placed according to the same protocol without oversizing. Twelve of these stents were placed; six swine died of thrombotic occlusion within the 1st 48 h. At elective sacrifice at 28 days, the remaining polyurethane-coated stents were occluded by marked neointimal hyperplasia. CONCLUSIONS: Fibrin film-coated stents seem promising as a template for modifying the local response to arterial injury and for potentially decreasing restenosis rates.

Differential neointimal response to coronary artery injury in pigs and dogs. Implications for restenosis models.

Neointimal hyperplasia occurs in the coronary arteries after percutaneous revascularization procedures and is a reparative response that frequently causes recurrent stenosis. Prior animal studies have shown that neointimal tissue thickness is proportional to the depth of arterial injury. Because animal models are increasingly used to test therapeutic strategies against restenosis, the purpose of this study was to evaluate the degree of neointimal thickening formed in the coronary arteries of pigs compared with dogs in response to severe injury. Fourteen coronary arteries in six mongrel dogs and 18 coronary arteries in nine pigs underwent severe arterial injury using tantalum metal coils delivered on oversized angioplasty balloons. Animals were killed after 4 weeks, and all coronary arteries were pressure perfusion fixed. Mean histological injury scores and neointimal thicknesses for dogs were 1.9 +/- 0.3 and 0.30 +/- 0.11, respectively, compared with 2.1 +/- 0.7 and 0.71 +/- 0.36 for pigs. Thus, there was significantly less neointimal thickening in dogs compared with pigs (P < .001) despite no differences in injury (P = NS). The neointimal thickening differences translated into significantly different percent area stenoses: 55 +/- 24% for pigs versus 27 +/- 13% for dogs (P < .001). Linear regression modeled neointimal thickness versus injury assessed by an ordinal injury score proportional to the depth of injury for each species. This analysis confirmed the differences across multiple injury levels. The slope of the regression line for dogs was small, suggesting that no relation may exist between injury and neointimal thickness in this species. The pig may be a more appropriate model for the study of the genesis of stenosing neointima.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of angiotensin converting enzyme inhibition on neointimal proliferation in a porcine coronary injury model.

To assess the effectiveness of angiotensin converting enzyme inhibition in a proliferative porcine coronary restenosis model, 35 animals received orally administered trandolapril (10 mg) or captopril (200 mg) or no drug (control group) for 6 days before and 28 days after injury by oversized metallic coils in one or more coronary arteries. Twenty arterial lesions in the trandolapril group, 17 in the captopril group, and 18 in the control group were evaluated. There was no significant difference in neointimal thickness or percentage luminal area stenosis for the groups as a whole. However, in quantitative comparisons in which vessel injury score was used as a covariate, the fractional increase in mean neointimal thickness per unit of injury was significantly less for the trandolapril group (p = 0.019) but not for the captopril group when compared with control animals. In this model, neointimal proliferation from arterial injury was inhibited by angiotensin converting enzyme inhibition with trandolapril but only modestly. Such an effect may not be clinically significant.

Coronary restenosis: prospects for solution and new perspectives from a porcine model.

Coronary restenosis, a major unresolved problem for percutaneous coronary revascularization procedures, has thus far been resistant to all therapeutic strategies. In part, ineffective treatment or prevention of coronary restenosis may be due to reliance on a conceptualization of the restenosis process that incompletely reflects the pathophysiologic factors associated with neointimal formation after arterial injury. In a porcine coronary restenosis model, three stages of neointimal growth after arterial injury have been identified: an early thrombotic stage, with platelets, fibrin, and erythrocytes; a cellular recruitment stage, with endothelialization and an infiltration by lymphocytes and monocytes; and a proliferative stage, in which smooth muscle cells migrate into and proliferate within the fibrin-rich degenerating thrombus. Evaluation of basic mechanisms responsible for neointimal formation has been possible with this model. In particular, a direct relationship exists between the depth of arterial injury and subsequent neointimal thickness. This relationship can be used for investigating the efficacy of new therapies. Treatment strategies for restenosis should be directed toward interference with the cellular or humoral events that lead to neointimal formation, with the specific goal of decreasing the neointimal volume. These strategies may include delivery of drugs to the site of arterial injury to limit the amount of early mural thrombus or decreasing subsequent cellular recruitment and proliferation as well as synthesis of extracellular matrix.

Prediction of atmospherically induced wave-front degradations.

Accurate prediction of the short-term future behavior of atmospherically distorted wave fronts would permit the elimination of delays inherent in current adaptive-optics systems. It is shown by using astronomical image data that atmospherically induced wave-front distortions as represented by time series of wave-front tips and tilts measured in the visible and piston values measured in the infrared are predictable to a degree that would be useful in an adaptive-optics system. Adaptive linear predictors as well as predictors based on the back-propagation neural network are employed in this study.

Evidence of a chaotic attractor in star-wander data.

The observed motion of stellar-image centroids is shown to have a chaotic attractor with a correlation dimension of ~6. The existence of a chaotic attractor in star wander, or equivalently in wave-front tilts, indicates that the atmospheric processes that cause image degradation may be more accurately described as chaotic, not so random as is usually assumed. This new result has important implications for the accurate modeling of atmospheric processes, the operation of adaptive optics systems, and the processing of stellar images.