Effects of training flights of combat jet pilots on parameters of airway function, diffusing capacity and systemic oxidative stress, and their association with flight parameters

BACKGROUND

Fighter aircraft pilots are regularly exposed to physiological challenges from high acceleration (Gz) forces, as well as increased breathing pressure and oxygen supply in the support systems. We studied whether effects on the lung and systemic oxidative stress were detectable after real training flights comprising of a wide variety of exposure conditions, and their combinations.

METHODS

Thirty-five pilots of the German Air Force performed 145 flights with the Eurofighter Typhoon. Prior to and after flight lung diffusing capacity for carbon monoxide (DLCO) and nitric oxide (DLNO), alveolar volume (VA), and diffusing capacities per volume (KCO, KNO) were assessed. In addition, the fractional concentration of exhaled nitric oxide (FeNO) was determined, and urine samples for the analysis of molecular species related to 8-hydroxy-2'-deoxyguanosine (8-OHdG) were taken. For statistical analysis, mixed ANOVA models were used.

RESULTS

DLNO, DLCO, KNO, KCO and VA were reduced (p < 0.001) after flights, mean ± SD changes being 2.9 ± 5.0, 3.2 ± 5.2, 1.5 ± 3.7, 1.9 ± 3.7 and 1.4 ± 3.1%, respectively, while FeNO decreased by 11.1% and the ratio of 8-OHdG to creatinine increased by 15.7 ± 37.8%. The reductions of DLNO (DLCO) were smaller (p < 0.001) than those of KNO (KCO). In repeated flights on different days, baseline values were restored. Amongst various flight parameters comprising Gz-forces and/or being indicative of positive pressure breathing and oxygenation support, the combination of long flight duration and high altitude appeared to be linked to greater changes in DLNO and DLCO.

CONCLUSIONS

The pattern of reductions in diffusing capacities suggests effects arising from atelectasis and increased diffusion barrier, without changes in capillary blood volume. The decrease in exhaled endogenous NO suggests bronchial mucosal irritation and/or local oxidative stress, and the increase in urinary oxidized guanosine species suggests systemic oxidative stress. Although changes were small and not clinically relevant, their presence demonstrated physiological effects of real training flights in a modern 4th generation fighter jet.

Ammonia oxidation by novel "Candidatus Nitrosacidococcus urinae" is sensitive to process disturbances at low pH and to iron limitation at neutral pH

Acid-tolerant ammonia-oxidizing bacteria (AOB) can open the door to new applications, such as partial nitritation at low pH. However, they can also be problematic because chemical nitrite oxidation occurs at low pH, leading to the release of harmful nitrogen oxide gases. In this publication, the role of acid-tolerant AOB in urine treatment was explored. On the one hand, the technical feasibility of ammonia oxidation under acidic conditions for source-separated urine with total nitrogen concentrations up to 3.5 g-N L^-1 was investigated. On the other hand, the abundance and growth of acid-tolerant AOB at more neutral pH was explored. Under acidic conditions (pH of 5), ammonia oxidation rates of 500 mg-N L^-1 d^-1 and 10 g-N g-VSS^-1 d^-1 were observed, despite high concentrations of 15 mg-N L^-1 of the AOB-inhibiting compound nitrous acid and low concentration of 0.04 mg-N L^-1 of the substrate ammonia. However, ammonia oxidation under acidic conditions was very sensitive to process disturbances. Even short periods of less than 12 h without oxygen or without influent resulted in a complete cessation of ammonia oxidation with a recovery time of up to two months, which is a problem for low maintenance applications such as decentralized treatment. Furthermore, undesirable nitrogen losses of about 10% were observed. Under acidic conditions, a novel AOB strain was enriched with a relative abundance of up to 80%, for which the name "Candidatus (Ca.) Nitrosacidococcus urinae" is proposed. While Nitrosacidococcus members were present only to a small extent (0.004%) in urine nitrification reactors operated at pH values between 5.8 and 7, acid-tolerant AOB were always enriched during long periods without influent, resulting in an uncontrolled drop in pH to as low as 2.5. Long-term experiments at different pH values showed that the activity of "Ca. Nitrosacidococcus urinae" decreased strongly at a pH of 7, where they were also outcompeted by the acid-sensitive AOB Nitrosomonas halophila. The experiment results showed that the decreased activity of "Ca. Nitrosacidococcus urinae" correlated with the limited availability of dissolved iron at neutral pH.

Crew time and workload in the EDEN ISS greenhouse in Antarctica

The goal of the EDEN ISS project is to research technologies for future greenhouses as a substantial part of planetary surface habitats. In this paper, we investigate crew time and workload needed to operate the space analogue EDEN ISS greenhouse on-site and remotely from the Mission Control Center. Within the almost three years of operation in Antarctica, different vegetable crops were cultivated, which yielded an edible biomass of 646 kg during the experiment phase 2018 and 2019. Operating in such a remote environment, analogue to future planetary missions, both greenhouse systems and remote support capabilities must be carefully developed and assessed to guarantee a reliable and efficient workflow. The investigation of crew time and workload is crucial to optimize processes within the operation of the greenhouse. For the Antarctic winter seasons, 2019 and 2020, as well as the summer season 2019/2020, the workload of the EDEN ISS greenhouse operators was assessed using the NASA Task Load Index. In addition, crew time was measured for the winter season 2019. The participants consisted of on-site operators, who worked inside the EDEN ISS greenhouse in Antarctica and the DLR remote support team, who worked in the Mission Control Center at the DLR Institute of Space Systems in Bremen (Germany). The crew time results show that crew time for the whole experiment phase 2019 required by the on-site operator team 2019 is approximately four times higher than the crew time of the corresponding remote support team without considering planning activities for the next mission. The total crew time for the experiment phase 2019 amounts to 694.5 CM-h or 6.31 CM-h/kg. With the measurements of the experiment phase 2019 it was possible to develop a methodology for crew time categorization for the remote support activities, which facilitates the analysis and increases the comparability of crew time values. In addition, the development of weekly and monthly crew time demand over the experiment phase is presented. The workload investigations indicate that the highest workload is perceived by the remote support team 2019 + 2020, followed by the summer maintenance team 2019/2020. The on-site operator team 2019 and on-site operator team 2020 showed the lowest values. The values presented in this paper indicate the need to minimize crew time as well as workload demands of the operators involved in the operation of future planetary surface greenhouses.

Surfactants effect on aeroponics and important mass balances of regenerative life support system - Lettuce case study

In order to be able to permanently settle other celestial bodies, it is necessary to create an efficient and closed life support system. Such a system will allow high autonomy and significantly reduce operating costs in a future colony. Grey water is a major waste stream in terms of the water volume generated by colonists, and its reuse is necessary. One possibility is to reuse it in aeroponic cultivation without treatment, which will in turn reduce its transported mass. The article focuses on water, carbon and other elements (N, P, K, Ca, Mg, Na) that are included in the mass balance of part of a life support system containing the aeroponic cultivation of lettuce that is supplied with clean water and water contaminated with one surfactant, crewmembers and a urine nitrification reactor. Three surfactants (Sodium Laureth Sulfate (SLES), Sodium Dodecylbenzene Sulfonate (SDBS), Sodium Methyl Cocoyl Taurate (SMCT)) in two concentrations, reflecting concentrated and diluted grey water, were tested. The growth of lettuce exposed to low concentrations (ca. 0.07 g·L-1) of surfactants has a moderate (SLES, SMCT) or no (SDBS) impact on the mass of grown plant. Exposition to high concentrations (>1.0 g·L-1) led to the complete failure of cultivation (SDBS, SMCT) or to very limited growth (SLES). In all cases, exposition to surfactants in low concentrations causes differences in the mineral composition of lettuce. In most cases, crops cultivated on water containing surfactants were characterized by a decreased harvest index (the ratio of edible biomass to total biomass). For the most cultivations the relative mass balances of water, C, N, P and K were generally unaffected by surfactants, while for Ca, Mg and Na, noticeable differences occurred. The data provided in the paper gives clues about which surfactant could be used in a future extraterrestrial colony.

An overview of blackwater data collection from space life support systems and its comparison to a terrestrial wastewater dataset

Extraterrestrial colonization is a certain eventuality that would be nearly impossible without the efficient and robust resources of recovering life support systems. Knowledge of inputs is necessary for the development of such systems, especially for the first stages of design such as mass balancing and the selection of unitary processes. One of the most important inputs is blackwater, as this stream is the most polluted and rich in resources and needs to be treated and reused. In the paper, data from space missions and terrestrial sources concerning the flows, concentrations and loads in urine and feces are compared and analyzed. It is shown that results obtained during space missions are scarce and for many parameters no information is available. It is also shown how gravity influences the elemental composition of urine and feces. In contrast, data from terrestrial sources are abundant. The presented analysis shows that data from space and terrestrial systems are convergent for many parameters and that the available terrestrial data for those parameters can be used for mass balancing and unitary process selection without a high risk.

A urine-fuelled soil-based bioregenerative life support system for long-term and long-distance manned space missions

A soil-based cropping unit fuelled with human urine for long-term manned space missions was investigated with the aim to analyze whether a closed-loop nutrient cycle from human liquid wastes was achievable. Its ecohydrology and biogeochemistry were analysed in microgravity with the use of an advanced computational tool. Urine from the crew was used to supply primary (N, P, and K) and secondary (S, Ca and Mg) nutrients to wheat and soybean plants in the controlled cropping unit. Breakdown of urine compounds into primary and secondary nutrients as well as byproduct gases, adsorbed, and uptake fractions were tracked over a period of 20 years. Results suggested that human urine could satisfy the demand of at least 3 to 4 out of 6 nutrients with an offset in pH and salinity tolerable by plants. It was therefore inferred that a urine-fuelled life support system can introduce a number of advantages including: (1) recycling of liquids wastes and production of food; (2) forgiveness of neglect as compared to engineered electro-mechanical systems that may fail under unexpected or unplanned conditions; and (3) reduction of supply and waste loads during space missions.

Prospects for using a full-scale installation for wet combustion of organic wastes in closed life support systems

The issue of recycling organic wastes in closed life support systems (CLSS) includes both fundamental aspects of environmental safety of the recycled products and their effective involvement in material cycles and technical aspects related to the structure of the system and the crew's demands. This study estimates the effectiveness of wet combustion of different amounts of organic wastes in hydrogen peroxide under application of an alternating current electric field. The study also addresses the possibility of controlling the process automatically. The results show that processing of greater amounts of wastes reduces specific power consumption and shortens the duration of the process, without significantly affecting the level of oxidation of the products. An automatic control system for a semi-commercial installation has been constructed and tested experimentally. The solution of mineralized human wastes prepared in the automatically controlled process in this installation was successfully used to grow radish plants, with the main production parameters being similar to those of the control.

The effects of the frequency and waveform of the activating current on physicochemical oxidation of organic wastes

The study describes the process of organic waste mineralization in an H2O2 aqueous medium activated by alternating current, which is intended to enhance the cycling rates in closed life support systems (CLSS) for space missions. The focus of this study is the relationship between the energy consumption and duration of the process and oxidation level of organic wastes on the one hand and the frequency and waveform of the electric current activating H2O2 decomposition, on the other. Energy consumption and duration of the complete waste mineralization process have been reduced by about 17-18%. A physical model of the process and the applicability of the results for both space and terrestrial purposes have been discussed.