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In the Arctic, the ground is frozen most of the year. Only the top layer of soil thaws each summer. This frozen ground, called permafrost, contains a lot of frozen water (ice). There are many small lakes in the Arctic, in low spots formed from melted ice. But melting ice does not just create lakes, it can destroy them too. Melting permafrost can create gullies that let the water drain out of a lake. Most lakes in the Arctic are far from where people live, so we watch them using pictures taken from satellites. Recently, we have seen the water drain out of many lakes, which can affect plants and animals. We measure the number and size of drained lakes caused by thawing permafrost to understand how the Arctic is changing.

How do you tell if someone is not well? You take the person’s temperature. If it is too warm, something is not quite right. We care about how the weather and climate are changing in Alaska’s national parks, so we continuously take their temperatures. We have dozens of weather stations in remote locations in the northern Alaska parks that run continuously, powered by the sun. Over the past several years, we found that the air and ground temperatures have been warmer than normal. Plants, animals, and people get used to living in their environments. They thrive within an expected temperature range. Things get out of whack when the environment that organisms are accustomed to changes. In northern Alaska, warming of just a few degrees can cause ice to melt and formerly frozen ground to thaw. Once the ground thaws, the ice changes to water and the landscape changes.

Arctic sea-ice is declining in extent, leaving coastlines exposed to more storm-wave events. There is an urgent need to understand how these changes affect geomorphic processes along Arctic coasts. Here we describe spatial and temporal patterns of shoreline changes along two geomorphologically distinct, storm-wave dominated reaches of the Chukchi Sea coastline over the last 64 years. One study area encompasses the west- to southwest-facing, coarse-clastic shoreline and ice-rich bluffs of Cape Krusenstern (CAKR). The other covers the north-facing, sandy shorelines on barrier islands, ice-rich bluffs, and the Cape Espenberg spit in the Bering Land Bridge National Park (BELA). Both study areas lie within the zone of continuous permafrost, which exists both on and offshore and outcrops as ice-rich bluffs along the BELA coast. We mapped changes in coastal geomorphology over three observation periods: 1950–1980, 1980–2003, and 2003–2014 using aerial and satellite imagery. We then compared these geomorphic changes to changes in sea-ice coverage, which declined ~10 days per decade between 1979 and 2016 in the southern Chukchi Sea. Changes in coastal geomorphology in both BELA and CAKR exhibited high spatial variability over the study period. Between 2003 and 2014, shorelines of barrier islands in BELA exhibited the highest mean rates of change, −1.5 m yr−1, while coarse, clastic barrier beaches in CAKR showed only minimal change. Overall, shorelines in both BELA and CAKR became more dynamic (increasing erosion or increasing accumulation) after ca. 2003, with spatial variability in shoreline changes roughly doubling between the first period of observation (1950–1980) and the last (2003–2014). This increase in coastal dynamism may signal a transitional period leading to new state of geomorphic equilibria along these ice-affected coastlines.

Lakes are an important component of high-latitude regions, providing habitat for fish and wildlife and playing a critical role in biogeochemical and global carbon cycles. High-latitude lakes are sensitive to climate change, in part due to their development within permafrost soils. Considerable heterogeneity exists across arctic and subarctic landscapes, yet little is known about how this landscape variability influences chemical and physical attributes of lakes. We investigated the physical and chemical limnology of 617 lakes in Alaska's boreal forest and boreal-arctic transition zone. We categorized lakes into 10 basin types based on parent material, topography, genesis, and permafrost characteristics. Physical parameters varied across lake basin types, with the deepest lakes occurring in ice-poor glacial deposits and ice-rich terrain, while the shallowest lakes were observed in floodplain deposits and coastal lowlands. Dissolved inorganic nitrogen (N) and phosphorous (P) concentrations were generally low across all landscapes, whereas total N and P were highest in lakes underlain by ice-rich Pleistocene loess. Total N and P concentrations were significantly correlated with chlorophyll a, indicating a possible colimitation of primary productivity in these systems. Base cation concentrations helped elucidate lake basin hydrology and the relative influence of shallow versus deep groundwater inputs to surface water. Using these results, we developed a simple conceptual model for each lake and landscape type based on differences in physical and chemical parameters. Overall, we expect that the vulnerability of lake ecosystems to climate change will vary across lake basin types and will be mediated by spatial patterns in permafrost characteristics and subsurface hydrology.

We monitored the growth of 22 retrogressive thaw slumps (RTS), dramatic erosion features associated with thaw of permafrost, in the Noatak Valley of northern Alaska using high-resolution structure-from-motion digital photogrammetry. We created time-series of 3–6 Digital Elevation Models (DEMs) and orthophoto mosaics during the time period from 2010–2016 at each slump, using high-resolution digital single-lens reflex (SLR) photographs taken from airplanes or helicopters. DEMs created using airborne GPS camera locations were adequate to detect elevations changes as small as 10 to 15 cm. Measurements made on these DEMs and orthophotographs showed slump growth rates of up to 38 m yr−1, with the fastest rates on slumps with scarps of moderate height (1 to 4 m) exposing Pleistocene glacial ice. Most of the slumps grew at constant or declining rates during the study, apparently as a result of the slumps encountering more gentle topography as they expanded upslope. Sedimentation was predominantly on the slump floor within 40 m of the active scarp, and the zone of accumulation migrated upslope with the scarp, away from adjacent water bodies. This study demonstrates that low-cost cameras coupled with airborne GPS and no ground control are suitable for monitoring geomorphic change on the order of decimeters and are a powerful tool for monitoring in remote settings.

Climate warming affects arctic and boreal ecosystems by interacting with numerous biophysical factors across heterogeneous landscapes. To assess potential effects of warming on diverse local-scale ecosystems (ecotypes) across northwest Alaska, we compiled data on historical areal changes over the last 25–50 years. Based on historical rates of change relative to time and temperature, we developed three state-transition models to project future changes in area for 60 ecotypes involving 243 potential transitions during three 30-year periods (ending 2040, 2070, 2100). The time model, assuming changes over the past 30 years continue at the same rate, projected a net change, or directional shift, of 6 % by 2100. The temperature model, using past rates of change relative to the past increase in regional mean annual air temperatures (1 °C/30 year), projected a net change of 17 % in response to expected warming of 2, 4, and 6 °C at the end of the three periods. A rate-adjusted temperature model, which adjusted transition rates (±50 %) based on assigned feedbacks associated with 23 biophysical drivers, estimated a net change of 13 %, with 33 ecotypes gaining and 23 ecotypes losing area. Major drivers included shrub and tree expansion, fire, succession, and thermokarst. Overall, projected changes will be modest over the next century even though climate warming increased transition rates up to 9 fold. The strength of this state-transition modeling is that it used a large dataset of past changes to provide a comprehensive assessment of likely future changes associated with numerous drivers affecting the full diversity of ecosystems across a broad region.

We sampled shrub canopy volume (height times area) and environmental factors (soil wetness, soil depth of thaw, soil pH, mean July air temperature, and typical date of spring snow loss) on 471 plots across five National Park Service units in northern Alaska. Our goal was to determine the environments where tall shrubs thrive and use this information to predict the location of future shrub expansion. The study area covers over 80,000 km2 and has mostly tundra vegetation. Large canopy volumes were uncommon, with volumes over 0.5 m3/m2 present on just 8% of plots. Shrub canopy volumes were highest where mean July temperatures were above 10.5°C and on weakly acid to neutral soils (pH of 6 to 7) with deep summer thaw (>80 cm) and good drainage. On many sites, flooding helped maintain favorable soil conditions for shrub growth. Canopy volumes were highest where the typical snow loss date was near 20 May; these represent sites that are neither strongly wind-scoured in the winter nor late to melt from deep snowdrifts. Individual species varied widely in the canopy volumes they attained and their response to the environmental factors. Betula sp. shrubs were the most common and quite tolerant of soil acidity, cold July temperatures, and shallow thaw depths, but they did not form high-volume canopies under these conditions. Alnus viridis formed the largest canopies and was tolerant of soil acidity down to about pH 5, but required more summer warmth (over 12°C) than the other species. The Salix species varied widely from S. pulchra, tolerant of wet and moderately acid soils, to S. alaxensis, requiring well-drained soils with near neutral pH. Nearly half of the land area in ARCN has mean July temperatures of 10.5 to 12.5°C, where 2°C of warming would bring temperatures into the range needed for all of the potential tall shrub species to form large canopies. However, limitations in the other environmental factors would probably prevent the formation of large shrub canopies on at least half of the land area with newly favorable temperatures after 2°C of warming.

Aim To understand the similarities and differences between the taiga floras of far north-eastern Asia and north-western North America in the light of their Tertiary and Quaternary histories. Does the taiga flora follow the tundra pattern (Asian–American commonality of species as a result of continuity through the Quaternary), the temperate forest pattern (distinct species because of late Tertiary disjunction), a combination of these two patterns, or some pattern unique to the taiga? Location The taiga regions of interior Alaska and the Yukon in North America (the ‘Alaskan taiga’), and the Kolyma and eastern Indigirka River basins in Russia (the ‘Kolyma taiga’). The study areas include both forested and unforested habitats below elevational treeline. The two regions have similar climate and topography and were linked via the Bering Land Bridge in the Tertiary and for several extended periods during Quaternary cold periods. Methods Systematic comparison of the vascular floras of the two regions from published sources; and review of palaeoecological literature for the region. Results Of the 796 species found in the study areas, 27% occur only in the Alaskan taiga, 35% occur only in the Kolyma taiga, and 38% occur in both the regions. The following subsets of species show a high proportion of species in common between the study areas (subsets are not mutually exclusive): plants that occur on the tundra and the taiga, non-flowering plants, abundant taiga understory plants, and wetland and aquatic plants. A lower proportion of shared plants was noted for warm, south-facing steppe communities. No tree species are common to both areas. Main conclusions The Bering Strait region in the Quaternary has acted as a biogeographical filter for taiga plants. Significant divergence between northeast Asia and northwest North America has developed among the more southerly ranging fraction of the flora (e.g. trees), while the more cosmopolitan and the most cold-adapted elements of the taiga flora are common to both areas. Many plants in the former group have been disjunct between Asia and North America for millions of years, while many plants in the latter group have probably maintained continuity between the study areas via the Bering Land Bridge through much of the late Tertiary and Quaternary periods. Repeated extirpation of the less cold-adapted species from both study areas during Pleistocene cold periods has probably enhanced floristic differences between the two regions.

Background Endocardial mapping using standard electrode catheters is often technically limited in ventricular tachycardia and constitutes a major obstacle to successful ablation. We wished to examine the utility of a basket-shaped multielectrode mapping catheter (MMC) in the mapping and ablation of ventricular tachycardia. Methods and Results This study of sustained monomorphic ventricular tachycardia (SMVT) was conducted in two phases in the postinfarction pig model. In the first phase, the utility of the MMC in providing adequate localization of potential ablation site(s) of SMVT by different techniques (presystolic potentials, pace mapping, and concealed entrainment) was assessed in 21 pigs. In the second phase, ablation of induced SMVT was attempted in 10 pigs. Mapping of SMVT was performed after percutaneous introduction of the MMC to the LV. Comprehensive mapping was performed in 90 episodes of SMVT and required 2.0 to 25 seconds. Diastolic potentials were recorded during 86 episodes; good or identical pace maps (≥9 of 12 paced surface ECG leads identical to ventricular tachycardia surface ECG leads) were obtained in 25 of 31 maps, and entrainment was achieved during 28 of 42 SMVTs. In 10 pigs, 10 SMVTs were recorded at least twice and were considered for radiofrequency ablation. An 8-mm tip ablation catheter was advanced to potential ablation sites with a specially designed “homing” device, requiring a median time of 120 seconds. In these 10 pigs, either identical pace map (≥11 of 12, 6 SMVTs) or concealed entrainment (4 SMVTs) guided the ablation procedure. After ablation, 8 of 10 SMVTs were rendered noninducible, while 2 pigs died during energy application of degeneration of SMVT to ventricular fibrillation. Conclusions The MMC allows rapid, comprehensive, and reliable endocardial mapping during SMVTs, which facilitates successful ablation in the porcine post–myocardial infarction model.

Background Identification of critical areas within the ventricular tachycardia circuit is a prerequisite for catheter ablation. Currently, mapping during ventricular tachycardia, usually performed with standard catheters, is difficult and time-consuming and can be used only in patients with hemodynamically stable tachycardia. Methods and Results A total of 43 pigs underwent closed-chest induction of myocardial infarction. A basket-shaped catheter carrying 64 electrodes was deployed in the left ventricle during normal sinus rhythm. Unipolar pacing at 3 mA was successful in 78% of the basket catheter electrodes, demonstrating good electrode-tissue contact. Hemodynamic and echocardiographic measurements did not reveal any significant interference with myocardial or valvular function during or after catheter deployment. One hundred eighteen episodes of monomorphic ventricular tachycardia were induced in 28 pigs through right ventricular stimulation, 81 of which were mapped and analyzed. Ventricular tachycardia mapping was rapid, requiring only several beats and Conclusions The multielectrode catheter enables rapid and safe percutaneous endocardial mapping of ventricular tachycardia in the swine model. Exploration of the clinical potential of the multielectrode catheter seems warranted.

This study analyzed the influence of electrode geometry, tissue-electrode angle, and blood flow on current density and temperature distribution, lesion size, and power requirements during radio-frequency ablation. The authors used validated three-dimensional finite element models to perform these analyses. They found that the use of an electrically insulating layer over the junction between electrode and catheter body reduced the chances of charring and coagulation. The use of a thermistor at the tip of the ablation electrodes did not affect the current density distribution. For longer electrodes, the lateral current density decreased more slowly with distance from the electrode surface. The authors analyzed the effects of three tissue-electrode angles: 0, 45, and 90/spl deg/. More power was needed to reach a maximal tissue temperature of 95/spl deg/C after 120 s when the electrode-tissue angle was 45/spl deg/. Consequently, the lesions were larger and deeper for a tissue-electrode angle of 45/spl deg/ than for 0 and 90/spl deg/. The lesion depth, volume, and required power increased with blood flow rate regardless of the tissue-electrode angle. The significant changes in power with the tissue-electrode angle suggest that it is safer and more efficient to ablate using temperature-controlled RF generators. The maximal temperature was reached at locations within the tissue, a fraction of a millimeter away from the electrode surface. These locations did not always coincide with the local current density maxima. The locations of these hottest spots and the difference between their temperature and the temperature read by a sensor placed at the electrode tip changed with blood flow rate and tissue-electrode angle. >

Quaking aspen (Populus tremuloides Michx.) is a valuable species that is declining in the Blue Mountains of northeastern Oregon. This publication is a compilation of over 20 years of aspen management experience by USDA Forest Service workers in the Blue Mountains. It includes a summary of aspen biology and occurrence in the Blue Mountains, and a discussion of aspen conservation and management techniques such as fencing, conifer removal, and artificial propagation. Local data on bird use of aspen stands, insects and diseases in aspen, and genetic studies of aspen are also included. An aspen community classification developed from over 200 sample plots is presented, with plant species composition and cover, environment and soils, and management considerations.

Late Pleistocene Beringia had herb-dominated vegetation with abundant grasses (Poaceae), and it was inhabited by an impressive assemblage of large grazing mammals. This paper reconstructs the list of most probable late Pleistocene Beringian lowland grass species from biogeographical evidence. Late Pleistocene eolian sediments and buried soils indicate that large areas of the Beringian lowlands had nutrient-rich, silty soils that occurred over ice-rich permafrost but were generally not waterlogged. A list of likely grasses was compiled from all species that have been recorded on similar fine-grained, mesic-to-dry lowland soils (i.e., presumed refugia) and are distributed at least sporadically across the whole region today. Grasses from 13 genera met these criteria, including most of the taxa that have been identified as late Pleistocene fossils from the study area. Most of these grasses are high-latitude species of genera that are also common in temperate latitudes (e.g., Elymus , Festuca , and Poa ). This diverse group of plants has a wide range of adaptations today, suggesting that grasses would have been available to occupy a variety of habitats through Pleistocene climatic fluctuations. Among these grasses are a number of highly productive forage species.

Background Catheter ablation with radiofrequency energy is feasible in a limited subset of patients with ventricular tachycardia. The purpose of this study was to evaluate a technique for mapping and ablation of ventricular myocardium with the use of transcatheter subendocardial infusion. Methods and Results A needle-tipped deflectable electrode catheter was used to deliver reagents to endocardial target sites. This was equipped with two central lumens to allow sequential administration of mapping and ablation injectants with minimal admixture. The mapping injectant consisted of a mixture of lidocaine, iohexal, and glycerin; the ablation injectant contained ethanol, iohexal, and glycerin. Infusion of the mapping injectant (1 cm 3 over 3 or 5 seconds, n=14) produced a stain on fluoroscopy and increased local capture threshold by 61%. No lesions resulted from mapping infusions. Infusion of the ethanol-containing injectant (n=48) produced discrete lesions, with a mean volume ranging from 0.6 to 1.5 cm 3 . There was a direct relationship between infusion volume, infusion duration, and resultant lesion volume. Fibrosis in a region of healed myocardial infarction did not impair diffusion of the injectant or affect lesion dimensions. Microscopic analysis of chronic lesions showed a sharply demarcated border zone between fibrotic and normal myocardium. Conclusions Transcatheter subendocardial infusion can be used to reversibly impair local excitability and mark an injection site fluoroscopically. Subendocardial injection of ethanol can predictably ablate a large volume of ventricular myocardium. Additional study of this system in an arrhythmia model will help to define its potential for mapping and ablation of hypotensive ventricular tachycardia.

Minimum squared error (MinSE) testing protocols and a MinSE estimator are presented which accurately estimate the voltage that defibrillates 95% of the time (the ED95). The MinSE experimental procedures, presented in the form of lookup tables, detail the response to successful and unsuccessful trials. The lookup tables also show the ED95 estimates calculated from the observed results using the MinSE estimator. Two assumptions are required to develop the look-up tables: 1) the dose-response curve, chosen using a statistical analysis of a retrospective sample, and 2) the distribution of the ED95's in the population. The MinSE estimator and experimental procedure are examined in a prospective study of five dogs (19-25 kg, heart weights 139.3-236.9 gm) using nonthoracotomy implantable defibrillator electrodes and a biphasic defibrillation waveform (3.5 ms first phase, 2.0 ms second phase). Employing an ED95 population distribution assumption applicable to most implantable defibrillator electrodes and waveforms, e.g., the ED95 is between 0.0 and 800.0 V, the measured rms error was 15% of the mean measured ED95 for the MinSE, four test shock, ED95 estimates. If the protocols are designed with an ED95 population distribution assumption for animals of the same species and size, and defibrillation is constrained to one electrode configuration and waveform, the estimates improve by 3.8%. Using techniques from the Bayesian statistics literature, the MinSE approach can be extended to a variety of defibrillation parameter estimation problems.

A bistatic active ultrasonic sensor is used to detect and identify an insect attracted to a pheromone lure in the beam intersection. The ultrasound beam is a continuous waveform (CW) of approximately 200 kHz to avoid detection by the insect auditory system, which is very sensitive near 40 kHz and below to detect predatory bats. Both amplitude modulation (AM) and frequency modulation (FM) of the CW beam are examined. The reflection factor of the wing material is measured using ultrasonic pulses. The near‐field interference nulls of the transmitting beam are modeled and measured to ensure that the lure is not placed in one of these zones. While good AM and FM signals are seen in the received waveform, the pivoting and flapping motions of the wings along with the insect movements create a complex pulse‐train like waveform. This is seen to be inherently due to the narrow beam‐width for the transducers and a lack of nonspecular scattering from the moving wings. The data show that a simple AM detector can be us...

The present invention provides ultrasound-guided ablation catheters and methods for their use. In one embodiment, a tissue ablation apparatus (2) includes a flexible elongate body (12) having proximal (14) and distal (12) ends. A plurality of spaced-apart electrodes (24) are operably attached to the flexible body near the distal end. A plurality of transducer elements (28) are disposed between at least some of the electrodes. Transducers assist the physician in determining whether or not the ablation elements are in contact with the tissue to be ablated.

Soils at the crests of moraines are commonly used to estimate the relative ages of moraines. However, for various pedologic and geomorphic reasons, soil development at crest sites may not truly reflect the time since moraine formation; for example, some crest soils on moraines of greatly different age are similar in morphology and development. Soil catena data for soils at several sites aligned downslope from the crest can greatly improve on the usefulness of soil data for estimating moraine ages. For this purpose, the authors use the weighted mean catena profile development index, which condenses field data for all of the soils in each catena into a single value.

Four methods of protecting the heart during implantation were compared. All hearts were arrested in situ by perfusing 4° C cardioplegic solution into the aortic root and were stored by a nonperfused cold storage technique for 5 hours at 4° C. The hearts were then transplanted orthotopically with the use of topical iced slush alone or with infusions of either blood cardioplegic solution or one of two crystalloid cardioplegic solutions after each atrial anastomosis. Five dog hearts were included in each group. Biopsy samples to test for adenylates were taken before the arrest, at the end of storage, before cross-clamp removal, and 3.5 hours after cross-clamp removal. The dogs were removed from cardiopulmonary bypass, and with the chest open, left ventricular function curves were measured at 1, 2, and 3 hours after cross-clamp removal. At 3.5 hours of reperfusion time, a full-width section was obtained from the left ventricle for measurement of tissue sodium and water content No differences in tissue water, sodium, or potassium content were found among the groups. Left ventricular function was significantly better in the blood cardioplegia group than in any other groups. Adenosine triphosphate levels were significantly reduced 3.5 hours after reperfusion in the crystalloid cardioplegia groups but were not significantly depressed at any other measurement time. Excellent early graft function was observed after crystalloid cardioplegic arrest and blood cardioplegic reperfusion during graft implantation.

Heart and kidney allografts showed markedly prolonged survival in unrelated mongrel dogs following total lymphoid irradiation (TLI) and donor bone marrow without any other immunosuppression. In every animal the heart survived longer than the kidney; genetic disparity was ruled out, since the heart and kidney from the same donor were placed into one recipient. Placing the kidney allograft in the abdomen with the bone marrow given intraperitoneally doubled kidney survival over placement in the neck, but heart survival was equally prolonged in the abdomen or neck. Splenectomy before TLI or after TLI, but just before transplantation, almost completely eliminated the prolonged survival of both heart and kidney allografts. Thus there is suggestive evidence from the work of Slavin and his colleagues and from our study that TLI plus bone marrow from the donor may be valuable for transplantation in man, particularly heart transplantation.

A computerized fluoroscopy system has been developed on the basis of real-time digital processing of x-ray transmission data from traditional image-intensified fluoroscopy equipment. High-quality visualization of any part of the arterial system is obtained following intravenous injection of 0.5 to 0.75 ml/kg of iodinated contrast materials. This report describes the use of this technique to evaluate the aortic arch, left ventricular function, and coronary artery bypass graft patency. Fifty intravenous studies were performed in 25 patients. Among 20 patients with coronary artery bypass grafts, computerized fluoroscopy correctly identified 11 of 15 patent grafts and 11 of 11 occluded grafts as confirmed by standard coronary arteriography in 11 of these patients. Unlike computerized tomography, our technique gives a longitudinal view of the bypass graft much like direct coronary angiography. Aortic arch studies included demonstration of a right aortic arch with a small left subclavian artery, a coarctation, and a normal aortic arch in a trauma patient with a wide mediastinum. Segmental wall motion abnormalities were clearly identified by a modification of the technique which produces a negative outline on the ventriculogram in dyskinetic segments. Ejection fractions may be calculated by determining the amount of iodine in the ventricle in systole and diastole. This technique may also be used to evaluate carotid disease and peripheral vascular disease in patients undergoing coronary artery bypass procedures. Computerized fluoroscopy, therefore, allows evaluation of the entire cardiovascular system by the relatively noninvasive technique of intravenous angiography.

Hearts preserved for 2 hours at 15 degrees C were evaluated for maximum function with the use of an isolated working dog heart subjected to stress. We determined left ventricular function by controlling aortic flow resistance and flow into the left atrium. Groups studied were hypothermia alone (H), hypothermia with a modified extracellular solution (H + DKS), hypothermia with a modified Collins solution (H + C), six periods of 20 minutes of hypoxic hypothermia followed by 10 minutes of blood reperfusion (H20 + R10) and blood cardiplegia (BC). Hypothermia alone for 1 hour was also evaluated. Functions were studied for 2 1/2 hours following reperfusion by determining Starling's curves for each heart. Our data show that H alone gave adequate myocardial protection for only 1 hour but not for 2 hours. H20 + R10 was better than H, but function was depressed. Use of H + C provided protection equal to H20 + R10, but the hearts recovered function slowly. Only hearts preserved by H + DKS and BC for 2 hours had normal function. Hearts from all groups except H + DKS and BC became edematous. Excellent function was obtained with DKS or BC following 2 hours of ischemia at 15 degrees C. Initial clinical use of BC supported these laboratory findings.

A retrospective analysis of 38 patients undergoing cardiac catheterization with the diagnoses of hypothyroidism and chest pain revealed 23 to be euthyroid while receiving replacement therapy and 15 to be hypothyroid. Cardiac index was significantly reduced (p less than 0.01) in hypothyroid and euthyroid patients with thyroxine values between 4 and 7 micrograms/dl (2.8 +/- 0.7 and 3.0 +/- 0.9 L/min/m2, respectively), compared to euthyroid patients with thyroxine values greater than 7 micrograms/dl with or without coronary artery disease (4.0 +/- 1.2 and 4.0 +/- 0.7 L/min/m2, respectively). Ten hypothyroid patients underwent coronary artery bypass. There were no deaths, and only one patient required prolonged postoperative intubation. With a mean follow-up of 36 months, there have been no myocardial infarctions and one late death, which occurred at 7 years secondary to stroke. We conclude that preoperative thyroid replacement therapy is theoretically dangerous and may not significantly improve hemodynamics until full replacement is achieved. Coronary bypass grafting can be performed safely despite hypothyroidism with excellent early results.

Reperfusion conditions significantly affect recovery following global myocardial ischemia. Using an isolated dog heart model, we investigated the effect of initial (first 10 minutes) reperfusion temperature and pressure on the metabolic and functional recovery of the preserved heart. Four groups of five or six dogs each underwent 2 hours of ischemic cardioplegic arrest at 15 degrees C following single-dose crystalloid cardioplegia. Hearts were initially reperfused at 37 degrees C (high temperature) or 28 degrees C (low temperature) and at 50 mm Hg (low pressure) or 80 mm Hg (high pressure), giving four groups: (1) high-temperature, high-pressure; (2) high-temperature, low-pressure; (3) low-temperature, high-pressure; and (4) low-temperature, low-pressure. Septal temperatures were continuously recorded. Ventricular function curves 1 and 2 hours following reperfusion were significantly depressed in the high-temperature, high-pressure group (70%, p less than 0.01, and 83%, p less than 0.02) and the low-temperature, high-pressure group (78%, p less than 0.03, and 85%, p less than 0.03) but were normal in the low-temperature, low-pressure and the high-temperature, low-pressure groups. All groups showed edema 1/2 hour after reperfusion as measured by water and sodium content in myocardial biopsy specimens but only the high-temperature, high-pressure and the low-temperature, high-pressure groups showed persistent edema at 3 hours (3.95 +/- 0.2 ml H2O/gm dry weight, p less than 0.03 and 3.99 +/- 0.16 ml/gm, p less than 0.02, respectively). Only low-temperature, high-pressure reperfusion resulted in statistically significant reductions in adenosine triphosphate (ATP) 1/2 hour and 2 hours following reperfusion (a 15% reduction from baseline). Maximum rewarming rates were measured for each group. High-temperature, high-pressure = 2 degrees C per second; low-temperature, high-pressure = 1 degree C per second; high-temperature, low-pressure = 0.75 degrees C per second; and low-temperature, low-pressure = 0.4 degrees C per second. High-pressure reperfusion following global myocardial ischemia results in rapid rewarming and is associated with prolonged myocardial edema, depressed ATP levels, and delayed functional recovery. Therefore, we employ 10 minutes of low-pressure reperfusion in our patients undergoing potassium cardioplegic arrest.

Multiple ablation technologies are used to provide atrial fibrillation therapy during cardiac surgery. A rigorous search was performed to identify all peer-reviewed papers that provided clinical outcome data following ablation therapy. A META analysis showed significant differences in clinical outcome by ablation technology: clinicians, using temperature-controlled RF power delivery, achieved higher rates of normal sinus rhythm at follow-up, and patients ablated with microwave ablation had lower rates of normal sinus rhythm than the average of all ablation-treated patients. Permanent pacemaker implantation rates were higher than average for patients treated with microwave or argon-based cryoablation technologies, but were lower than the average for patients treated using temperature-controlled RF.

On the plains of central North America and western Siberia, soil carbon storage and cover by organic soils are highest in the region with mean annual soil temperatures near 0° C, and generally decrease to the north and south. The location of this large soil carbon sink in the boreal and subarctic is probably due in part to the low heat availability in the soil as compared to the air in these regions. The thermal advantage of the air environment gives green plants a metabolic advantage over decomposers in the soil, which favors soil carbon accumulation. The thermal advantage of the air environment relative to the soil is greatest where mean annual soil temperatures are near or a few degrees below the lower limit of biological activity for cold-adapted soil organisms and plants, i.e. near 0° C., Dans les plaines du centre de l'Amérique du Nord et de la Sibérie occidentale, l'accumulation du carbone organique dans le sol et l'étendue des sols tourbeux sont maximales là où les températures annuelles moyennes du sol sont près de 0° C et diminuent généralement vers le nord et le sud. La présence de ce grand bassin de carbone dans les régions boréale et subarctique est probablement le résultat d'une faible provision de chaleur dans le sol comparativement à celle de l'air. Cela procure à l'air un « avantage thermique » qui permet le métabolisme des plantes vertes, contrairement à la très faible capacité de décomposition des microorganismes présents dans le sol, ce qui favorise l'accumulation du carbone. Cet « avantage thermique » de l'air est maximal là où les températures moyennes annuelles du sol sont près ou à quelques degrés sous la limite inférieure de l'activité biologique des organismes adaptés au froid et des plantes, soit près de 0° C., In den Ebenen von Zentral-Nordamerika und West-Sibirien wird eine maximale Akkumulation und Ausdehnung von organischem Kohlenstoff im Boden da erreicht, wo die durchschnittlichen jährlichen Bodentemperaturen um die 0° C sind, und sie nimmt im Allgemeinen nach Norden und Süden ab. Das Vorhandensein dieses breiten Kohlenstoff-Beckens in dem borealen und subarktischen Gebiet ist wahrscheinlich auf das geringe Wärme-Vorkommen im Boden im Vergleich zu der Luft zurückzuführen. Der "thermische Vorteil" der Luftumgebung begünstigt den Stoffwechsel der grünen Pflanzen gegenüber den Zersetzungsprozessen in der Erde, was die Kohlenstoffakkumulation im Boden begünstigt. Der "thermische Vorteil" der Luftumgebung im Verhältnis zum Boden ist da am größten, wo durchschnittliche jährliche Bodentemperaturen nahe bei oder einige Grad unter der unteren Grenze der biologischen Aktivität von an Kälte angepassten Boden-Organismen und Pflanzen sind, d.h. nahe bei 0 °C.

The genesis of flark-and-string mire patterns oriented perpendicular to the slope can be simulated by a simple stochastic model which presumes 1) that hummocks impede the flow of water across a mire surface more than do hollows, and 2) that as the water table is lowered the probability of hummock formation increases and the probability of hollow formation decreases. The model suggests that a critical minimum surface slope of the mire is required to produce this type of patterning. Furthermore, the supply of water to the mire must be sufficient to prevent the mire surface from being dominated by hummock-level conditions. The geographic distribution of patterned mires appears to be in agreement with the conditions for their formation that are suggested by the model.