Spatial distribution of sequential ventilation during mechanical ventilation of the uninjured lung: an argument for cyclical airway collapse and expansion

<p>Abstract</p> <p>Background</p> <p>Ventilator-induced lung injury (VILI) is a recognized complication of mechanical ventilation. Although the specific mechanism by which mechanical ventilation causes lung injury remains an active area of study, the application of positive end expiratory pressure (PEEP) reduces its severity. We have previously reported that VILI is spatially heterogeneous with the most severe injury in the dorsal-caudal lung. This regional injury heterogeneity was abolished by the application of PEEP = 8 cm H₂O. We hypothesized that the spatial distribution of lung injury correlates with areas in which cyclical airway collapse and recruitment occurs.</p> <p>Methods</p> <p>To test this hypothesis, rabbits were mechanically ventilated in the supine posture, and regional ventilation distribution was measured under four conditions: tidal volumes (V_T) of 6 and 12 ml/kg with PEEP levels of 0 and 8 cm H₂O.</p> <p>Results</p> <p>We found that relative ventilation was sequentially redistributed towards dorsal-caudal lung with increasing tidal volume. This sequential ventilation redistribution was abolished with the addition of PEEP.</p> <p>Conclusions</p> <p>These results suggest that cyclical airway collapse and recruitment is regionally heterogeneous and spatially correlated with areas most susceptible to VILI.</p

Proglacial lake sediment records reveal Holocene climate changes in the Venezuelan Andes

Lake sediment records from the Cordillera de Mérida in the northern Venezuelan Andes document the history of local glacial variability and climate changes during the Holocene (∼12 ka to the present). The valleys that contain these lakes have similar bedrock compositions and hypsometries, but have different headwall elevations and aspects, which makes them useful for investigating the magnitude of past glaciations. There was widespread glacial retreat in the Venezuelan Andes during the early Holocene, after which most watersheds remained ice free, and thus far only valleys with headwalls higher than ∼4400 m asl contain evidence of glaciation during the last ∼10 ka. There was a pronounced shift in sediment composition for the Montos (headwall: ∼4750 m asl) and Los Anteojos (headwall: ∼4400 m asl) records during the middle Holocene from ∼8.0 to 7.7 ka when conditions appear to have become ice free and drier. There is tentative evidence that the glacier in the Mucubají valley (headwall: ∼4609 m asl) advanced from ∼8.1 to 6.6 ka and then retreated during the latter stages of the middle Holocene. Clastic sediment accumulation in other nearby lake basins was either low or decreased throughout most of the middle Holocene as watersheds stabilized under warmer and/or drier conditions. In the Montos record, there was another major shift in sediment composition that occurred from ∼6.5 to 5.7 ka, similar to other regional records that suggest conditions were drier during this period. Overall, the late Holocene was a period of warmer and wetter conditions with ice extent at a minimum in the northern tropical Andes. There were also punctuated decadal to multi-centennial periods of higher clastic sediment accumulation during the last ∼4 ka, likely in response to periods of cooling and/or local precipitation changes. In watersheds with headwalls above 4600 m asl, there is evidence of glacial advances during the Little Ice Age (∼0.6–0.1 ka). The pattern of glacial variability is generally similar in both the northern and southern tropics during the Little Ice Age, suggesting that ice margins in both regions were responding to colder and wetter conditions during the latest Holocene. The observed pattern of Holocene climate variability in the Venezuelan Andes cannot be explained by insolation forcing alone, and tropical ocean influences were likely associated with the observed glacial and lake level changes

Quantification of uncertainties in fossil leaf aleoaltimetry: does leaf size matter?

The utility of multivariate foliar physiognomy, specifically the Climate Leaf Analysis Multivariate Program (CLAMP), to yield reliable estimates of enthalpy and hence paleoelevation has been demonstrated by comparison with other proxies, yet concerns have arisen regarding uncertainties arising from 1) apparent ambiguities in the scoring regime and 2) the way leaf size is scored. Regarding 1) scoring ambiguities are examined by reporting on scoring tests with novice users and inter-laboratory comparisons. The uncertainties were found to be less than those arising from the statistical methodology underpinning CLAMP. In respect of 2) the effect of removing all size data both from modern test sites and fossil data was tested. Specifically the effect of removing leaf size data from the 15 Ma Namling data set from south central Tibet, was investigated. Removal of all size data from modern sites demonstrated that size data contributes little to estimates of MAT (Mean Annual Temperature) and enthalpy. Similarly the removal of leaf size information from the Namling data set alone, but with calibration unchanged, and from both the Namling site and calibration sites, this time with recalibration, still yield paleoelevation estimates that have been independently matched by oxygen isotope techniques. Moreover the removal of all leaf size information results in only small increases in uncertainty (± 52 m)

Spatial analysis of lung, colorectal, and breast cancer on Cape Cod: An application of generalized additive models to case-control data

BACKGROUND: The availability of geographic information from cancer and birth defect registries has increased public demands for investigation of perceived disease clusters. Many neighborhood-level cluster investigations are methodologically problematic, while maps made from registry data often ignore latency and many known risk factors. Population-based case-control and cohort studies provide a stronger foundation for spatial epidemiology because potential confounders and disease latency can be addressed. METHODS: We investigated the association between residence and colorectal, lung, and breast cancer on upper Cape Cod, Massachusetts (USA) using extensive data on covariates and residential history from two case-control studies for 1983–1993. We generated maps using generalized additive models, smoothing on longitude and latitude while adjusting for covariates. The resulting continuous surface estimates disease rates relative to the whole study area. We used permutation tests to examine the overall importance of location in the model and identify areas of increased and decreased risk. RESULTS: Maps of colorectal cancer were relatively flat. Assuming 15 years of latency, lung cancer was significantly elevated just northeast of the Massachusetts Military Reservation, although the result did not hold when we restricted to residences of longest duration. Earlier non-spatial epidemiology had found a weak association between lung cancer and proximity to gun and mortar positions on the reservation. Breast cancer hot spots tended to increase in magnitude as we increased latency and adjusted for covariates, indicating that confounders were partly hiding these areas. Significant breast cancer hot spots were located near known groundwater plumes and the Massachusetts Military Reservation. DISCUSSION: Spatial epidemiology of population-based case-control studies addresses many methodological criticisms of cluster studies and generates new exposure hypotheses. Our results provide evidence for spatial clustering of breast cancer on upper Cape Cod. The analysis suggests further investigation of the potential association between breast cancer and pollution plumes based on detailed exposure modeling

Onset of the aerobic nitrogen cycle during the Great Oxidation Event

The rise of oxygen on the early Earth (about 2.4 billion years ago)1 caused a reorganization of marine nutrient cycles2, 3, including that of nitrogen, which is important for controlling global primary productivity. However, current geochemical records4 lack the temporal resolution to address the nature and timing of the biogeochemical response to oxygenation directly. Here we couple records of ocean redox chemistry with nitrogen isotope (15N/14N) values from approximately 2.31-billion-year-old shales5 of the Rooihoogte and Timeball Hill formations in South Africa, deposited during the early stages of the first rise in atmospheric oxygen on the Earth (the Great Oxidation Event)6. Our data fill a gap of about 400 million years in the temporal 15N/14N record4 and provide evidence for the emergence of a pervasive aerobic marine nitrogen cycle. The interpretation of our nitrogen isotope data in the context of iron speciation and carbon isotope data suggests biogeochemical cycling across a dynamic redox boundary, with primary productivity fuelled by chemoautotrophic production and a nitrogen cycle dominated by nitrogen loss processes using newly available marine oxidants. This chemostratigraphic trend constrains the onset of widespread nitrate availability associated with ocean oxygenation. The rise of marine nitrate could have allowed for the rapid diversification and proliferation of nitrate-using cyanobacteria and, potentially, eukaryotic phytoplankton

A novel palaeoaltimetry proxy based on spore and pollen wall chemistry

Understanding the uplift history and the evolution of high altitude plateaux is of major interest to a wide range of geoscientists and has implications for many disparate fields. Currently the majority of palaeoaltimetry proxies are based on detecting a physical change in climate in response to uplift, making the relationship between uplift and climate difficult to decipher. Furthermore, current palaeoaltimetry proxies have a low degree of precision with errors typically greater than 1 km. This makes the calculation of uplift histories and the identification of the mechanisms responsible for uplift difficult to determine. Here we report on advances in both instrumentation and our understanding of the biogeochemical structure of sporopollenin that are leading to the establishment of a new proxy to track changes in the flux of UV-B radiation over geological time. The UV-B proxy is based on quantifying changes in the concentration of UV-B absorbing compounds (UACs) found in the spores and pollen grains of land plants, with the relative abundances of UACs increasing on exposure to elevated UV-B radiation. Given the physical relationship between altitude and UV-B radiation we suggest that the analysis of sporopollenin chemistry, specifically changes in the concentration of UACs, may offer the basis for the first climate independent palaeoaltimetry proxy. Owing to the ubiquity of spores and pollen in the fossil record our proposed proxy has the potential to enable the reconstruction of the uplift history of high altitude plateaux at unprecedented levels of fidelity, both spatially and temporally

Spatio-temporal trends of mortality in small areas of Southern Spain

Background: Most mortality atlases show static maps from count data aggregated over time. This procedure has several methodological problems and serious limitations for decision making in Public Health. The evaluation of health outcomes, including mortality, should be approached from a dynamic time perspective that is specific for each gender and age group. At the moment, researches in Spain do not provide a dynamic image of the population’s mortality status from a spatio-temporal point of view. The aim of this paper is to describe the spatial distribution of mortality from all causes in small areas of Andalusia (Southern Spain) and evolution over time from 1981 to 2006. Methods: A small-area ecological study was devised using the municipality as the unit for analysis. Two spatiotemporal hierarchical Bayesian models were estimated for each age group and gender. One of these was used to estimate the specific mortality rate, together with its time trends, and the other to estimate the specific rate ratio for each municipality compared with Spain as a whole. Results: More than 97% of the municipalities showed a diminishing or flat mortality trend in all gender and age groups. In 2006, over 95% of municipalities showed male and female mortality specific rates similar or significantly lower than Spanish rates for all age groups below 65. Systematically, municipalities in Western Andalusia showed significant male and female mortality excess from 1981 to 2006 only in age groups over 65. Conclusions: The study shows a dynamic geographical distribution of mortality, with a different pattern for each year, gender and age group. This information will contribute towards a reflection on the past, present and future of mortality in Andalusia.Ye