High Ventilation Rates Research Articles

External validation of a prognostic model for intensive care unit mortality: a retrospective study using the Ontario Critical Care Information System.

PurposeTo externally validate an intensive care unit (ICU) mortality prediction model that was created using the Ontario Critical Care Information System (CCIS), which includes the Multiple Organ Dysfunction Score (MODS).MethodsWe applied the Transparent Reporting of a multivariable prediction model for Individual Prognosis Or Diagnosis (TRIPOD) recommendations to a prospective longitudinal cohort of patients discharged between 1 July 2015 and 31 December 31 2016 from 90 adult level-3 critical care units in Ontario. We used multivariable logistic regression with measures of discrimination, calibration-in-the-large, calibration slope, and flexible calibration plots to compare prediction model performance of the entire data set and for each ICU subtype.ResultsAmong 121,201 CCIS records with ICU mortality of 11.3%, the C-statistic for the validation data set was 0.805. The C-statistic ranged from 0.775 to 0.846 among the ICU subtypes. After intercept recalibration to adjust the baseline risk, the mean predicted risk of death matched actual ICU mortality. The calibration slope was close to 1 with all CCIS data and ICU subtypes of cardiovascular and community hospitals with low ventilation rates. Calibration slopes significantly less than 1 were found for ICUs in teaching hospitals and community hospitals with high ventilation rates whereas coronary care units had a calibration slope significantly higher than 1. Calibration plots revealed over-prediction in high risk groups to a varying degree across all cohorts.ConclusionsA risk prediction model primarily based on the MODS shows reproducibility and transportability after intercept recalibration. Risk adjusting models that use existing and feasible data collection can support performance measurement at the individual ICU level.Electronic supplementary materialThe online version of this article (10.1007/s12630-020-01686-5) contains supplementary material, which is available to authorized users.

Exercise in Sub-zero Temperatures and Airway Health: Implications for Athletes With Special Focus on Heat-and-Moisture-Exchanging Breathing Devices.

Asthma is highly prevalent among winter endurance athletes. This “occupational disease” of cross-country skiers, among others, was acknowledged during the 1990s, with the pathogenesis attributed to repeated and prolonged exposure to cold, dry air combined with high rates of ventilation during exercise. Nevertheless, more than 25 years later, the prevalence of asthma among Scandinavian cross-country skiers is unchanged, and prevention remains a primary concern for sports physicians. Heat-and-moisture-exchanging breathing devices (HMEs) prevent exercise-induced bronchoconstriction in subjects with pre-existing disease and may have potential as a preventative intervention for healthy athletes undertaking training and competition in winter endurance sports. Herein we firstly provide an overview of the influence of temperature and humidity on airway health and the implications for athletes training and competing in sub-zero temperatures. We thereafter describe the properties and effects of HMEs, identify gaps in current understanding, and suggest avenues for future research.

Modelling Cyclists’ Multi-Exposure to Air and Noise Pollution with Low-Cost Sensors—The Case of Paris

Cyclists are particularly exposed to air and noise pollution because of their higher ventilation rate and their proximity to traffic. However, few studies have investigated their multi-exposure and have taken into account its real complexity in building statistical models (nonlinearity, pseudo replication, autocorrelation, etc.). We propose here to model cyclists’ exposure to air and noise pollution simultaneously in Paris (France). Specifically, the purpose of this study is to develop a methodology based on an extensive mobile data collection using low-cost sensors to determine which factors of the urban micro-scale environment contribute to cyclists’ multi-exposure and to what extent. To this end, we developed a conceptual framework to define cyclists’ multi-exposure and applied it to a multivariate generalized additive model with mixed effects and temporal autocorrelation. The results show that it is possible to reduce cyclists’ multi-exposure by adapting the planning and development practices of cycling infrastructure, and that this reduction can be substantial for noise exposure.

The impact of ventilation rate on the fungal and bacterial ecology of home indoor air

The following study explores how measured ventilation rates influence bacterial and fungal community structure and concentrations in the indoor air of homes ventilated by leakage-based airflow. The dynamics of bacterial and fungal communities were quantified from homes within the Cherokee Nation in North Eastern, Oklahoma, USA, where seasonal air exchange rates (AERs) were measured, and seasonal outdoor and indoor air, floor dust, and settled dust samples were collected. Quantitative PCR (qPCR) and DNA amplicon sequencing were paired with a mass balance model to determine if high and low ventilation rate regimes impacted bacterial and fungal concentration and community structure, and to estimate the relative contributions of microbiota to indoor air from infiltration of outdoor air (ventilation) versus indoor emissions. For indoor PM10 and settled dusts samples, comparative analyses of microbial communities revealed no significant bacterial or fungal community differences between samples taken from homes dichotomized into high (average high AER = 0.56 hr−1) and low (average low AER = 0.16 hr−1) AER regimes (p > 0.1 for all), suggesting that ventilation was not a significant factor controlling bacterial and fungal concentrations and ecologies in the indoor air of these homes. A comparison between indoor emissions (typically due to occupancy and resuspension) and ventilation (infiltration of outdoor air) as a source of bacteria and fungi indicates that indoor emissions are the dominant source of particulate matter, bacteria, and fungi, accounting for ~94% indoor air PM10, ~97% of indoor air bacteria, and ~91% of indoor air fungi. Thus, indoor emission sources must be controlled to significantly impact human bacterial and fungal (allergen) exposure in the indoor air of these residential environments.

미세먼지와 프로스포츠

Exposure to ambient particulate matter may cause acute and chronic harmful health effects. Since athletes have higher ventilation rates during their competition or training, the quantity of inhaled pollutants is likely to be increased. In addition, if their competition is held in high particulate matter conditions, the sports officials and even spectators can also be affected by the air pollutants. However, there has been no procedures and standards for readjusting athletic training or competition schedule in high particulate matter conditions in Korea. Therefore, the present review focuses on an overview of particulate matter and its deleterious effects on athletic performance and health. Also, we report on current situation related to Korean professional sports events which were held in high particulate matter conditions. We expect our research to offer relevant information for developing policies related to particulate matter and professional sports.

Concentration and size distribution of particulate matter in a new aviary system for laying hens in China

ABSTRACTParticulate matter (PM) from poultry production facilities may strongly affect the health of animals and workers in the houses, and PM emitted to the ambient air is an important pollution source to the surrounding areas. Aviary system is considered as a welfare friendly production system for laying hens. However, its air quality is typically worse as compared with conventional cage systems, because of the higher PM concentration of indoor air and other airborne contaminants. Furthermore, PM’s physical property, which has a direct impact on the penetration depth into the lungs of the birds and humans, is largely unknown for the aviary system. Therefore, a systematic method was utilized to investigate the characteristics of particles in the aviary house with large cage aviary unit system (LCAU) in Beijing, China. For the field measurements, three measuring locations were selected with two inside and one outside the house with LCAU to continuously monitor PM concentrations and collect the samples for particle size distribution (PSD) analysis. Results showed that PM2.5, PM10, and total suspended particulate (TSP) concentrations averaged at 0.037 ± 0.025 mg/m3, 0.42 ± 0.10 mg/m3, and 1.92 ± 1.91 mg/m3, respectively. Particle concentrations increased from October to December due to less ventilation as the weather got colder, and were generally affected by stocking density, ventilation rate, birds’ activities, and housing system. Meanwhile, indoor PM2.5 concentration was easily impacted by the ambient air quality. Mass median diameter (MMD) and mass geometric standard deviation (MGSD) of the TSP during the measurement were 18.92 ± 7.08 μm and 3.11 ± 0.31, respectively. Count median diameter (CMD) and count geometric standard deviation (CGSD) were 1.94 ± 0.14 μm and 1.48 ± 0.08, respectively. Results indicated that the aviary system can attain a good indoor condition by suitable system design and environment control strategy.Implications: Indoor PM2.5 concentration of the layer house can be significantly affected by ambient air quality when the air quality index (AQI) was larger than 100. PM2.5 and PM10 concentrations of the layer house with a LCAU system were comparable to the cage system. TSP concentration was higher, and PM size was larger than most of the cage system. System design, larger space volume, and higher ventilation rate were the main influence factors. Good indoor environment of the aviary system can be achieved through the reasonable design of the production system and appropriate environment control strategy.

Clustering of educational building load data for defining healthy and energy-efficient management solutions of integrated HVAC systems

The COVID-19 pandemic is changing the way individuals, worldwide, feel about staying in public indoor spaces. A strict control of indoor air quality and of people’s presence in buildings will be the new normal, to ensure a healthy and safe environment. Higher ventilation rates with fresh air are expected to be a requirement, especially in educational buildings, due to their high crowding index and social importance. Yet, in this framework, an increased use of primary energy may be overlooked. This paper offers a methodology to efficiently manage complex HVAC systems in educational buildings, concurrently considering the fundamental goals of occupants’ health and energy sustainability. The proposed fourstep procedure includes: dynamic simulation of the building, to generate synthetic energy loads; clustering of the energy data, to identify and predict typical building use profiles; day-ahead planning of energy dispatch, to optimize energy efficiency; dynamic adjustment of air changes, to guarantee a safe indoor air quality. Clustering and forecasting energy needs are expected to become particularly effective in a highly regulated context. The technique has been tested on two university classroom buildings, considering pre-lockdown attendance. This notwithstanding, quality and significance of the obtained thermal energy clusters push towards a benchmark post-pandemic application.

A field study of the individual and combined effect of ventilation rate and lighting conditions on pupils’ performance

A field lab study was conducted to determine how much the indoor climate parameters, ventilation and lighting, influence children's academic abilities. The study involved 92 children, aged 10–12 years, who over four weeks answered a questionnaire and three different performance tests, which measured their processing speed, concentration, logical reasoning and math solving abilities. An experimental design was constructed to test the effect of changing the lighting from constant warm light with a maintained correlated colour temperature average of 2900 K and lighting level of 450 lux to a dynamic cool light of 4900 K and 750 lux. The change was tested at both low (3.9 l/s per person) and high ventilation rate (10.6 l/s per person). The results showed that processing speed (6.6%, P < 0.001), concentration (8.3%, P < 0.001) and math skills (11.8%, P < 0.006), improved the most in the combined scenario with high ventilation rate and dynamic cool lighting. The logical reasoning test did not show any significant changes. The questionnaire results of the pupils' perception of the indoor environment suggested that they were satisfied in general, but the indoor environmental changes had only very limited effect on how they perceived the classroom. The combination of dynamic lighting and increased ventilation rate indicated a boosted positive impact on the speed and concentration of the children which means that future renovations would benefit from a holistic design including both of these factors.

Outcome and prognostic factors of Pneumocystis jirovecii pneumonia in immunocompromised adults: a prospective observational study

BackgroundPneumocystis jirovecii pneumonia (PJP) remains a severe disease associated with high rates of invasive mechanical ventilation (MV) and mortality. The objectives of this study were to assess early risk factors for severe PJP and 90-day mortality, including the broncho-alveolar lavage fluid cytology profiles at diagnosis.MethodsWe prospectively enrolled all patients meeting pre-defined diagnostic criteria for PJP admitted at Nantes university hospital, France, from January 2012 to January 2017. Diagnostic criteria for PJP were typical clinical features with microbiological confirmation of P. jirovecii cysts by direct examination or a positive specific quantitative real-time polymerase chain reaction (PCR) assay. Severe PJP was defined as hypoxemic acute respiratory failure requiring high-flow nasal oxygen with at least 50% FiO2, non-invasive ventilation, or MV.ResultsOf 2446 respiratory samples investigated during the study period, 514 from 430 patients were positive for P. jirovecii. Of these 430 patients, 107 met criteria for PJP and were included in the study, 53 (49.5%) patients had severe PJP, including 30 who required MV. All patients were immunocompromised with haematological malignancy ranking first (n = 37, 35%), followed by solid organ transplantation (n = 27, 25%), HIV-infection (n = 21, 20%), systemic diseases (n = 13, 12%), solid tumors (n = 12, 11%) and primary immunodeficiency (n = 6, 8%). By multivariate analysis, factors independently associated with severity were older age (OR, 3.36; 95% CI 1.4–8.5; p < 0.05), a P. jirovecii microscopy-positive result from bronchoalveolar lavage (BAL) (OR, 1.3; 95% CI 1.54–9.3; p < 0.05); and absence of a BAL fluid alveolitis profile (OR, 3.2; 95% CI 1.27–8.8; p < 0.04). The 90-day mortality rate was 27%, increasing to 50% in the severe PJP group. Factors independently associated with 90-day mortality were worse SOFA score on day 1 (OR, 1.05; 95% CI 1.02–1.09; p < 0.001) whereas alveolitis at BAL was protective (OR, 0.79; 95% CI 0.65–0.96; p < 0.05). In the subgroup of HIV-negative patients, similar findings were obtained, then viral co-infection were independently associated with higher 90-day mortality (OR, 1.25; 95% CI 1.02–1.55; p < 0.05).ConclusionsOlder age and P. jirovecii oocysts at microscopic examination of BAL were independently associated with severe PJP. Both initial PJP severity as evaluated by the SOFA score and viral co-infection predicted 90-day mortality. Alveolitis at BAL examination was associated with less severe PJP. The pathophysiological mechanism underlying this observation deserves further investigation.

Innate antipredator behavior can promote infection in fish even in the absence of predators

AbstractNatural enemies—predators and parasites—largely shape the dynamics of ecosystems. It is known that antipredator and antiparasite defense can be mutually conflicting, however consequences of this trade-off for the regulation of infection burden in animals are still poorly understood. We hypothesize that even in the absence of cues from predators, innate antipredator behavior (“ghost of predation past”) interferes with defense against parasites and can enhance the infection risk. As a case study, we explore interactions between a commercial species, the rainbow trout Oncorhynchus mykiss, and its parasite, the trematode eye-fluke Diplostomum pseudospathaceum. Fish–parasite interactions were tested in compartmentalized tanks where shelters and parasites were presented in different combinations providing various conditions for microhabitat choice and territorial behavior. Shelters were attractive and contestable despite the absence of predators and presence of parasites. The individuals fighting for shelters acquired more than twice the number of cercariae as compared to those in infected shelter-free compartments. Most infected were subordinate fish with a higher ventilation rate. Fish possessing shelters were less vulnerable to parasites than fighting fish. Grouping reduced the infection load, although less efficiently than sheltering. Our data demonstrate that the innate antipredator behavior can undermine antiparasite tactics of the fish and result in higher infection rates. Using our empirical results, we construct a mathematical model which predicts that enriching the environment in fish farming will be beneficial only when a large number of shelters is provided. Using insufficient number of shelters will increase the parasite burden in the fish.

Ventilation Rates and Pediatric In-Hospital Cardiac Arrest Survival Outcomes*

The objective of this study was to associate ventilation rates during in-hospital cardiopulmonary resuscitation with 1) arterial blood pressure during cardiopulmonary resuscitation and 2) survival outcomes. Prospective, multicenter observational study. Pediatric and pediatric cardiac ICUs of the Collaborative Pediatric Critical Care Research Network. Intubated children (≥ 37 wk gestation and < 19 yr old) who received at least 1 minute of cardiopulmonary resuscitation. None. Arterial blood pressure and ventilation rate (breaths/min) were manually extracted from arterial line and capnogram waveforms. Guideline rate was defined as 10 ± 2 breaths/min; high ventilation rate as greater than or equal to 30 breaths/min in children less than 1 year old, and greater than or equal to 25 breaths/min in older children. The primary outcome was survival to hospital discharge. Regression models using Firth penalized likelihood assessed the association between ventilation rates and outcomes. Ventilation rates were available for 52 events (47 patients). More than half of patients (30/47; 64%) were less than 1 year old. Eighteen patients (38%) survived to discharge. Median event-level average ventilation rate was 29.8 breaths/min (interquartile range, 23.8-35.7). No event-level average ventilation rate was within guidelines; 30 events (58%) had high ventilation rates. The only significant association between ventilation rate and arterial blood pressure occurred in children 1 year old or older and was present for systolic blood pressure only (-17.8 mm Hg/10 breaths/min; 95% CI, -27.6 to -8.1; p < 0.01). High ventilation rates were associated with a higher odds of survival to discharge (odds ratio, 4.73; p = 0.029). This association was stable after individually controlling for location (adjusted odds ratio, 5.97; p = 0.022), initial rhythm (adjusted odds ratio, 3.87; p = 0.066), and time of day (adjusted odds ratio, 4.12; p = 0.049). In this multicenter cohort, ventilation rates exceeding guidelines were common. Among the range of rates delivered, higher rates were associated with improved survival to hospital discharge.

Simulations on non-healthy indoor humidity by ventilation rates in nearly zero energy residential buildings in China

Indoor humidity can be easily overlooked when discussing building ventilation. However, evidences have shown that moisture-related consequences on health are increasingly common both in China and worldwide. In addition, there is an ongoing debate on what the adequate ventilation rates (VRs) should be for nearly zero energy buildings (NZEBs). Therefore, the effects of VRs for NZEBs in China, on moist environment, are investigated using EnergyPlus in this paper. More than 1100 residential settings have been analysed with different VRs in five major cities, representing all climate zones, in China. Three generally-agreed humidity levels have been adopted as the thresholds to reduce habitability of microbes. The results indicate that, first, humidity risk decrease with higher VRs in all zones except for some southern regions, and most cities would be free of moisture issues under current VR requirements (∼8 L/s). Second, indoor spaces feature, 1) small per capita area; 2) the ground or top floor; 3) small window-wall ratio and 4) north-orientation, are more prone to risk of high humidity.

Effect of inspiration cycle and ventilation rate on heat exchange in human respiratory airways.

A transient three dimensional (3D) theoretical axisymmetric model is developed for heat exchange across the human respiratory tract during inspiration phase and applied to study the changes in the airway temperature and velocity profile for varying ventilation rates and inhalation temperatures. A multi-compartment approach is used to study the same to avoid the airway scaling problem from micro to nano scale. This analysis also includes the role of water evaporation in mucus and non perfused tissue layers and the role of capillary bed in thermal variations during respiration. The results of heat transfer in airway and mucus layer depend on the local morphological parameters. The results are compared with the case of hypothetical regular geometry to show the significance of local morphology. The location where the inhaled air gets saturated with the body core temperature is computed to estimate the saturation distance of air. The complete analysis is made for two breathing cycles with different inhalation to exhalation ratios. The results indicate that decreasing the ventilation rate and increasing the respiration cycle can avoid the deep penetration of heat into the tract and consequently tissue thermal injury can be avoided. We have also explained numerically the role of mucus layer in avoiding tissue injury in intra-thoracic airways. We have also observed a significant difference in results for high ventilation rates between the cases of actual (cast replica) and regular airway geometry. The numerical results are in good adjustment with existing experimental data and thus validate our approach.

Design and thermal evaluation of a social housing model conceived with bioclimatic principles and recycled aggregates

The present work discloses the design and thermal evaluation of single-family houses adapted with bioclimatic principles to tropical climates – the Vila Sustentável complex. The architectural layout of each 2-bedroom unit embraces accessibility measures and bioclimatic strategies for energy-efficiency. The envelope embodies an innovative approach: the full replacement of natural aggregates by processed steelmaking slag in all cement-based composites (mortars, concretes and concrete blocks). These building elements were characterized physically and thermally. Subsequently, the thermal performance of the buildings was evaluated through an energy simulation using the software EnergyPlus. Results indicated that the stack effect designed in the living room promotes high ventilation rates with no energy consumption. The building elements produced with steel slag presented better thermal performance than the conventional ones, due to the high thermal inertia and low thermal conductivity of the slag. In this sense, the passive strategies proposed are replicable and energy-efficient alternatives for tropical countries.

Experimental analysis of a PCM integrated solar chimney under laboratory conditions

The objective of this work is to experimentally investigate the impact of integrating a Phase Change Material (PCM) on the performance of two different laboratory solar chimney prototypes, rendering it a viable option for yearlong use. It has been stated that solar chimneys can provide constant ventilation and increase air quality in a building. This study aims to provide a different approach in means of improving the current performance of solar chimneys as, nowadays, it is mostly pursued through the modification of the inclination, the air gap size or the inlet/outlet dimensions. The solar chimney prototype mainly analysed in this work is built with 2 cm plywood plates with a thermal conductivity of 0.15 W/mK with a volume of 3.50×1.00×0.30 m. After a 6 h charge period, a mean ventilation rate above 70 m3/h can be achieved with a relative low gain of 550 W/m2 provided by a series of 7 halogen lamps directed towards an effective collector area of 3.00 m2. The results obtained in this work show that PCM integration provides a higher ventilation rate and a slower decrease during ventilation only phases (6 h discharge), where the halogen lamps do not provide any energy to the solar chimney. Overall, the implementation of paraffinic PCMs in solar chimneys could be an economically viable option for hybrid design solutions to create a healthy indoor environment within residential buildings through renewable solar energy.

Impact of 'synchronous' and 'asynchronous' CPR modality on quality bundles and outcome in out-of-hospital cardiac arrest patients.

During cardiopulmonary resuscitation (CPR), the need to interrupt chest compressions to provide synchronous ventilations prevents blood flow continuity, reducing the possibility to ensure high-quality CPR bundles of care and, thus, having a potentially negative impact on perfusion and patient outcome. Contemporaneous asynchronous chest compressions and ventilations may avoid these potentially negative effects. Only a few studies measured the CPR quality metrics during synchronous and asynchronous CPR modality and its relation to patient outcome. A prospective observational study was conducted on 285 consecutive adult patients with out-of-hospital cardiac arrest treated by EMS teams over a 30-month period. Ventilation rate, chest compression fraction (i.e. cardiac arrest time spent delivering uninterrupted chest compressions compared to total cardiac arrest time) and chest compression rate per minute were collected in real time by defibrillators and analysed through a dedicated software (electrical cardiac activity through the ECG, chest compression and ventilations through the transthoracic impedance) during synchronous and asynchronous CPR modalities. During asynchronous CPR modality, higher ventilation rate and chest compression fraction (p < 0.001), and lower chest compression rate per minute (p < 0.001) were ensured, being all cited metrics more adherent to the high-quality CPR bundles. Ventilation rate provided during the whole CPR was an independent predictor for a good neurological outcome (OR 3.795, p = 0.005). Asynchronous chest compression and ventilation ensured the most adequate chest compression fraction, uninterrupted chest compression rate and ventilation rate.

Study of natural ventilation in a Gothic multi-tunnel greenhouse designed to produce rose (Rosa spp.) in the high-Andean tropic

In tropical regions the production of ornamentals is developed exclusively in naturally ventilated plastic greenhouses, which sometimes leads to inappropriate microclimates with high temperatures and humidity that limit the productive development of plants. The aim of this work was to study air flows, temperature distribution and relative humidity inside an alternative greenhouse designed to produce rose (Rosa spp.). Three configurations of ventilation, side ventilation (SV), roof ventilation (RC) and combined roof and side ventilation (RSV) were analyzed. The methodological development was based on the use of a previously validated CFD-2D numerical simulation model, which showed an adequate fit between the measured and simulated data, obtaining MAE and RMSE values for temperature and relative humidity of 0.44 and 0.47 °C, 3.99% and 4.04% respectively. The results obtained for the predominant climatic conditions of the study region showed that the highest ventilation rates were obtained for RSV, with values of 0.044 and 0.182 m3 m-2s-1, this ventilation efficiency propitiated the generation of a homogeneous microclimate, with temperature and relative humidity values adequate to produce rose (Rosa spp).

Inpatient outcome of solid tumor associated tumor lysis syndrome.

e18185 Background: Tumor lysis syndrome (TLS) is a constellation of metabolic disturbances that can occur in virtually any malignancy, though it is more common in hematological malignancies given their high tumor burden and growth index. While TLS can occur in patients with solid tumors, the clinical behavior and outcome of solid tumor associated-TLS (STA-TLS) is not well characterized. Methods: We used the national inpatient sample to identify patients with STA-TLS (utilizing the ICD10 code E883; and ICD9 code 27788), from year 2010 through year 2016. Patients with both hematological malignancy and solid tumor, and patients without a cancer diagnosis were excluded. Results: A total of 11,733 patients were identified using the above criteria, of which 2117 (18.0%) had STA-TLS. The median age at admission was 63 years and 940 (44.4%) STA-TLS patients were females. The most common primary cancer sites were lung (26.8%), breast (4.2%), and colon (3.7%). Patients with STA-TLS were more likely to receive mechanical ventilation and less likely to receive red blood cell or platelet transfusion compared to those with hematological malignancies ( Table). STA-TLS was also associated with a significantly higher inpatient mortality rate and shorter length of stay than TLS in hematological malignancies ( P &lt; 0.001). No statistically significant difference was found in the requirement of dialysis, transfusion of plasma, and cardiac arrest rates. Conclusions: STA-TLS is rare with an inferior outcome than TLS in hematological malignancies evident by a higher mechanical ventilation and mortality rate. Future studies should identify factors that impact management and outcome of STA-TLS. [Table: see text]

Winter Upper-Ocean Stability and Ice–Ocean Feedbacks in the Sea Ice–Covered Southern Ocean

AbstractIn this study, under-ice ocean data from profiling floats, instrumented seals, and shipboard casts are used to assess wintertime upper-ocean stability and heat availability in the sea ice–covered Southern Ocean. This analysis reveals that the southern Weddell Sea, which features a weak upper-ocean stratification and relatively strong thermocline, is preconditioned for exceptionally high rates of winter ventilation. This preconditioning also facilitates a strong negative feedback to winter ice growth. Idealized experiments with a 1D ice–ocean model show that the entrainment of heat into the mixed layer of this region can maintain a near-constant ice thickness over much of winter. However, this quasi-equilibrium is attained when the pycnocline is thin and supports a large temperature gradient. We find that the surface stress imparted by a powerful storm may upset this balance and lead to substantial ice melt. This response can be greatly amplified when coincident with anomalous thermocline shoaling. In more strongly stratified regions, such as near the sea ice edge of the major gyres, winter ice growth is weakly limited by the entrainment of heat into the mixed layer. Thus, the thermodynamic coupling between winter sea ice growth and ocean ventilation has significant regional variability. This regionality will influence the response of the Southern Ocean ice–ocean system to future changes in ocean stratification and surface forcing.

Continuous exercise induces airway epithelium damage while a matched-intensity and volume intermittent exercise does not

BackgroundWhile continuous exercise (CE) induces greater ventilation ( dot{V} E) when compared to intermittent exercise (IE), little is known of the consequences on airway damage. Our aim was to investigate markers of epithelial cell damage – i.e. serum levels of CC16 and of the CC16/SP-D ratio - during and following a bout of CE and IE of matched work.MethodsSixteen healthy young adults performed a 30-min continuous (CE) and a 60-min intermittent exercise (IE; 1-min work: 1-min rest) on separate occasions in a random order. Intensity was set at 70% of their maximum work rate (WRmax). Heart rate (HR) and dot{V} E were measured throughout both tests. Blood samples were taken at rest, after the 10th min of the warm-up, at the end of both exercises, half way through IE (matched time but 50% work done for IE) as well as 30- and 60-min post-exercise. Lactate and CC16 and SP-D were determined.ResultsMean dot{V} E was higher for CE compared to IE (85 ± 17 l.min− 1 vs 50 ± 8 l.min− 1, respectively; P < 0.001). Serum-based markers of epithelial cell damage remained unchanged during IE. Interaction of test × time was observed for SP-D (P = 0.02), CC16 (μg.l− 1) (P = 0.006) and CC16/SP-D ratio (P = 0.03). Maximum delta CC16/SP-D was significantly correlated with mean dot{V} E sustained (r = 0.83, P < 0.001) during CE but not during IE.ConclusionThe 30-min CE performed at 70% WRmax induced mild airway damage, while a time- or work-matched IE did not. The extent of the damage during CE was associated with the higher ventilation rate.