Seasonality of Radon-222 near the surface at King Sejong Station (62°S), Antarctic Peninsula, and the role of atmospheric circulation based on observations and CAM-Chem model

We examined the seasonal cycle of radon concentration observed at King Sejong Station (KSG, 62°S), Antarctic Peninsula, during the period 2013-2016. The distribution of monthly radon concentration was found to be highly positively skewed from March through October (austral autumn to spring) due to large numbers of short-lived periods of high radon concentration. The global atmospheric chemistry model (CAM-Chem), which includes all global terrestrial sources of radon except for those in Antarctica, well reproduces the observed seasonal cycle of monthly-mean radon concentration at KSG. Further offline experiments suggest that uncertainties in radon emissions over South America and the Southern Ocean should be improved for the simulations of radon in Antarctica. The results demonstrate that seasonally varying transport of radon in the boundary layer from South America substantially affects the seasonality of monthly mean radon concentration at KSG. The composite analyses further reveal that high radon events at KSG are the result of a distinct east-west dipole-like structure associated with surface cyclonic circulation over the Bellingshausen Sea and anticyclonic circulation in the Weddell Sea. This atmospheric pattern provides favorable conditions for radon transport into KSG from the northwest. The relationship between radon concentration at KSG and climate variability is also discussed in this study.

Radon-222 related influence on ambient gamma dose

Ambient gamma dose, radon, and rainfall have been monitored in southern Bucharest, Romania, from 2010 to 2016. The seasonal cycle of background ambient gamma dose peaked between July and October (100-105 nSv h^-1), with minimum values in February (75-80 nSv h^-1), the time of maximum snow cover. Based on 10 m a.g.l. radon concentrations, the ambient gamma dose increased by around 1 nSv h^-1 for every 5 Bq m^-3 increase in radon. Radon variability attributable to diurnal changes in atmospheric mixing contributed less than 15 nSv h^-1 to the overall variability in ambient gamma dose, a factor of 4 more than synoptic timescale changes in air mass fetch. By contrast, precipitation-related enhancements of the ambient gamma dose were 15-80 nSv h^-1. To facilitate routine analysis, and account in part for occasional equipment failure, an automated method for identifying precipitation spikes in the ambient gamma dose was developed. Lastly, a simple model for predicting rainfall-related enhancement of the ambient gamma dose is tested against rainfall observations from events of contrasting duration and intensity. Results are also compared with those from previously published models of simple and complex formulation. Generally, the model performed very well. When simulations underestimated observations the absolute difference was typically less than the natural variability in ambient gamma dose arising from atmospheric mixing influences. Consequently, combined use of the automated event detection method and the simple model of this study could enable the ambient gamma dose "attention limit" (which indicates a potential radiological emergency) to be reduced from 200 to 400% above background to 25-50%.

The Impact of Boreal Forest Fire on Climate Warming

We report measurements and analysis of a boreal forest fire, integrating the effects of greenhouse gases, aerosols, black carbon deposition on snow and sea ice, and postfire changes in surface albedo. The net effect of all agents was to increase radiative forcing during the first year (34 +/- 31 Watts per square meter of burned area), but to decrease radiative forcing when averaged over an 80-year fire cycle (-2.3 +/- 2.2 Watts per square meter) because multidecadal increases in surface albedo had a larger impact than fire-emitted greenhouse gases. This result implies that future increases in boreal fire may not accelerate climate warming.

Ground based radon-222 observations and their application to atmospheric studies

The aim of this paper is to review recent trends in the application of ground based radon observations to atmospheric research. In spite of over four decades of atmospheric radon monitoring, only in the past decade has the potential of this passive tracer been realised through a series of atmospheric model evaluation studies. Firstly, the key operational requirements for baseline radon detectors are briefly discussed, including lower limit of detection and response time. Then, current radon-related benchmarks for the evaluation of regional and global models are reviewed, with particular consideration given to the implications of data availability, resolution, site location and model spatial/temporal resolution. An 8-year subset of radon observations from the Cape Grim Baseline Air Pollution Station is used to suggest new benchmarks that exploit long-term data sets. Lastly an overview is presented of a technique that uses radon to estimate regional fluxes of climatically sensitive gases, with specific examples for CO2, CH4 and N2O.

Improved right heart function with a compliant inflow artificial lung in series with the pulmonary circulation

BACKGROUND

We previously reported a 50% incidence of immediate right heart failure using a rigidly housed, noncompliant inflow artificial lung in series with the pulmonary circulation in a healthy ovine survival model. Three device modifications resulted: (1) an inflow cannula compliance chamber, (2) an inlet blood flow separator, and (3) modification of the artificial lung outlet geometry, all to reduce resistance and mimic the compliance of the pulmonary vascular bed.

METHODS

In 7 sheep, arterial grafts were anastomosed end-to-side to the proximal and distal main pulmonary artery, with the paracorporeal artificial lung interposed. A pulmonary artery snare between anastomoses diverted full pulmonary blood flow through the artificial lung for up to 72 hours.

RESULTS

Six of 7 sheep exhibited good cardiac function throughout the test period: mean central venous pressure was 6.8 mm Hg (range, 4 to 11 mm Hg), mean cardiac output, 4.17 +/- 0.12 L/min (range, 2.4 to 6.3 L/min); before and after device mean pulmonary arterial pressure, 21.8 and 18.5 mm Hg, and left atrial pressure, 10.8 mm Hg.

CONCLUSIONS

This modified artificial lung prototype with an inflow compliance chamber, blood flow separator, and modified outlet geometry has greatly improved cardiac function and initial survival in our healthy ovine model.

Hemolytic potential of hydrodynamic cavitation

The purpose of this study was to determine the hemolytic potentials of discrete bubble cavitation and attached cavitation. To generate controlled cavitation events, a venturigeometry hydrodynamic device, called a Cavitation Susceptibility Meter (CSM), was constructed. A comparison between the hemolytic potential of discrete bubble cavitation and attached cavitation was investigated with a single-pass flow apparatus and a recirculating flow apparatus, both utilizing the CSM. An analytical model, based on spherical bubble dynamics, was developed for predicting the hemolysis caused by discrete bubble cavitation. Experimentally, discrete bubble cavitation did not correlate with a measurable increase in plasma-free hemoglobin (PFHb), as predicted by the analytical model. However, attached cavitation did result in significant PFHb generation. The rate of PFHb generation scaled inversely with the Cavitation number at a constant flow rate, suggesting that the size of the attached cavity was the dominant hemolytic factor.

Determination of the in vivo cavitation nuclei characteristics of blood

Cavitation has been documented in the in vitro testing of blood-handling devices. To predict whether cavitation will occur clinically, the nuclei content of blood and the threshold pressure for activation of the in situ nuclei must be characterized. A single-pass flow apparatus is described for determining the nuclei characteristics of blood. The flow apparatus consists of a syringe pump and a venturi-geometry hydrodynamic device, called a cavitation susceptibility meter (CSM). Blood is accelerated through the throat of the CSM, thus exposing the nuclei in the blood to a well-defined pressure profile. The apparatus was used in an ex vivo sheep model for the determination of the in vivo nuclei characteristics of blood. The active nuclei concentration of in vivo blood was measured to be at most 2.7 nuclei per liter of plasma at a minimum throat pressure of -1610 mm Hg gauge (i.e., tension of 900 mm Hg). At this pressure, bubble stability theory predicts the active nuclei to have a radius on the order of 0.3 microm. Based on these results, in vitro studies to determine the cavitation potential of blood-handling devices must utilize test fluids that contain a minimum nuclei size distribution and concentration. It cannot be assumed that in vivo blood is nuclei rich, such that it will cavitate at or near vapor pressure.

Extreme negative pressure does not cause erythrocyte damage in flowing blood

In extracorporeal circulation, negative pressure is thought to be a source of hemolysis. This study was designed to investigate the effects of extreme negative pressure on flowing blood. The study model was pipe flow. The hemolysis generated by negative pressure driven flow was compared with that generated by positive pressure driven flow of equal magnitude to control for the hemolytic effect of shear stress. A series of pressures (720, 600, 500, -500, -600, and -720 mm Hg; n = 8) was tested for pipe diameters of 0.04 and 0.16 cm, with a length-to-diameter ratio of 500. The pressure difference across the pipe (deltaP) was equal to the magnitude of the applied pressure. The hemolysis was quantified by the modified index of hemolysis (MIH). For both pipe diameters, MIH was found to not depend on the deltaP or the blood collection day (multiple regression analysis, p = 0.50 and p = 0.63, respectively). There was no statistically significant difference between the MIH for equal deltaP generated by positive or negative pressure (p = 0.50) for both pipe diameters tested. MIH did depend upon the pipe diameter, with 0.04 cm having higher MIH at all pressures (p = 0.0003). Thus, negative pressure is not a significant hemolytic factor in flowing blood.

Partial liquid ventilation improves gas exchange and increases EELV in acute lung injury

Gas exchange is improved during partial liquid ventilation with perfluorocarbon in animal models of acute lung injury. The specific mechanisms are unproved. We measured end-expiratory lung volume (EELV) by null-point body plethysmography in anesthetized sheep. Measurements of gas exchange and EELV were made before and after acute lung injury was induced with intravenous oleic acid to decrease EELV and worsen gas exchange. Measurements of gas exchange and EELV were again performed after partial liquid ventilation with 30 ml/kg of perfluorocarbon and compared with gas-ventilated controls. Oxygenation was significantly improved during partial liquid ventilation, and EELV (composite of gas and liquid) was significantly increased, compared with preliquid ventilation values and gas-ventilated controls. We conclude that partial liquid ventilation may directly recruit consolidated alveoli in the lung-injured sheep and that this may be one mechanism whereby gas exchange is improved.

Effects of static pressure on red blood cells on removal of the air interface

Previous studies investigated the effects of pressure on red blood cells, but did not address the presence of an air interface. It has been established that an air interface promotes damage to blood. This study was designed to allow for the isolation of the blood-air interface during pressurization. Fresh human blood was divided into 2 ml samples in polypropylene tubes and exposed to either negative or positive pressure for 5 min at 37 degrees C. The plasma free hemoglobin was measured and compared to controls (0 mmHg) exposed to the same environment. This procedure was duplicated with a 1 ml layer of mineral oil on each sample, to remove the air interface. The sample size for each pressure was 15. Results from this study demonstrate that blood is resistant to positive pressures (1,000 mmHg), even on removal of the air interface. However, hemolysis previously attributed to negative pressures was not seen when the air interface was removed by mineral oil. Removal of the air interface halted cavitation, which occurred at pressures equal to or below -680 mmHg in the presence of the air interface. It is the authors' belief that hemolysis is not correlated with negative pressure, but rather with the susceptibility of blood to cavitation.

Measuring functional residual capacity in normal and oleic acid-injured lungs

Functional residual capacity (FRC) is an important oxygen reserve that is often depleted in acute respiratory failure. Recent interest in the mechanisms of liquid ventilation and limited experience in measuring FRC in paralyzed, mechanically ventilated, normal and lung-injured animal models have mandated development of accurate laboratory techniques. Eight sheep, from 17 to 27 kg, were anesthetized and instrumented to provide a tracheostomy, a pulmonary artery catheter, and carotid arterial line. They were randomized to two groups, one of which received 0.07 ml/kg of intravenous oleic acid to induce lung injury. Gas ventilation of both groups was identical except for respiratory rate, which was adjusted to normalize PaCO2. FRC was measured in duplicate by both helium dilution (HD) and body plethysmography (BP). When measurements were completed, the animals were euthanized and their endotracheal tubes clamped at end expiration. The lungs were then removed and their water displacement (WD) FRC values were measured. FRC was the difference between WD and tissue weight assuming 1 ml = 1g. Pearson's correlation coefficient (R(2)) was calculated. During in vitro measurement of test lungs, HD had an R(2) value of 0.99 and BP had an R(2) value of 0.98. When compared to WD, in vivo measurement of FRC by HD had an R(2) value of 0.94 while the value for BP was 0.97. In conclusion, both HD and BP are accurate methods of determining FRC in an uninjured and injured lung model when compared to postmortem WD. Documenting changes in FRC will aid in elucidating the mechanisms of alternative ventilatory techniques.