The NASA atomic oxygen effects test program

The NASA Atomic Oxygen Effects Test Program was established to compare the low earth orbital simulation characteristics of existing atomic oxygen test facilities and utilize the collective data from a multitude of simulation facilities to promote understanding of mechanisms and erosion yield dependence upon energy, flux, metastables, charge, and environmental species. Four materials chosen for this evaluation include Kapton HN polyimide, FEP Teflon, polyethylene, and graphite single crystals. The conditions and results of atomic oxygen exposure of these materials is reported by the participating organizations and then assembled to identify degrees of dependency of erosion yields that may not be observable from any single atomic oxygen low earth orbital simulation facility. To date, the program includes 30 test facilities. Characteristics of the participating test facilities and results to date are reported

Inhibiting Glutathione Metabolism in Lung Lining Fluid as a Strategy to Augment Antioxidant Defense

Glutathione is abundant in the lining fluid that bathes the gas exchange surface of the lung. On the one hand glutathione in this extracellular pool functions in antioxidant defense to protect cells and proteins in the alveolar space from oxidant injury; on the other hand, it functions as a source of cysteine to maintain cellular glutathione and protein synthesis. These seemingly opposing functions are regulated through metabolism by gamma-glutamyl transferase (GGT, EC 2.3.2.2). Even under normal physiologic conditions, lung lining fluid (LLF) contains a concentrated pool of GGT activity exceeding that of whole lung by about 7-fold and indicating increased turnover of glutathione at the epithelial surface of the lung. With oxidant stress LLF GGT activity is amplified even further as glutathione turnover is accelerated to meet the increased demands of cells for cysteine. Mouse models of GGT deficiency confirmed this biological role of LLF GGT activity and revealed the robust expansiveness and antioxidant capacity of the LLF glutathione pool in the absence of metabolism. Acivicin, an irreversible inhibitor of GGT, can be utilized to augment LLF fluid glutathione content in normal mice and novel GGT inhibitors have now been defined that provide advantages over acivicin. Inhibiting LLF GGT activity is a novel strategy to selectively augment the extracellular LLF glutathione pool. The enhanced antioxidant capacity can maintain lung epithelial cell integrity and barrier function under oxidant stress

Oxidation and protection of fiberglass-epoxy composite masts for photovoltaic arrays in the low Earth orbital environment

Fiberglass-epoxy composites are considered for use as structural members for the mast of the space station solar array panel. The low Earth orbital environment in which space station is to operate is composed mainly of atomic oxygen, which has been shown to cause erosion of many organic materials and some metals. Ground based testing in a plasma asher was performed to determine the extent of degradation of fiberglass-epoxy composites when exposed to a simulated atomic oxygen environment. During exposure, the epoxy at the surface of the composite was oxidized, exposing individual glass fibers which could easily be removed. Several methods of protecting the composite were evaluated in an atomic oxygen environment and with thermal cycling and flexing. The protection techniques evaluated to date include an aluminum braid covering, an indium-tin eutectic and a silicone based paint. The open aluminum braid offered little protection while the CV-1144 coating offered some initial protection against atomic oxygen, but appears to develop cracks which accelerate degradation when flexed. Coatings such as the In-Sn eutectic may provide adequate protection by containing the glass fibers even though mass loss still occurs

Development and prospective validation of a model for predicting weaning in chronic ventilator dependent patients

BACKGROUND: Approximately ten percent of patients placed on mechanical ventilation during acute illness will require long-term ventilator support. Unfortunately, despite rehabilitation, some will never be liberated from the ventilator. A method of predicting weaning outcomes for these patients could help conserve resources and minimize frustrating failed weaning attempts for this population. The objective of this investigation was to identify predictors of weaning outcome for patients admitted to a chronic ventilator unit (CVU). METHODS: This was a retrospective analysis with prospective validation. The study setting was a 25 bed CVU within a rehabilitation hospital. The training group consisted of 43 patients referred to our facility for weaning after > 3 weeks of mechanical ventilation. A multivariate model to predict weaning outcome was constructed in this group and applied to a prospective group of 31 patients followed during an 18-month period. RESULTS: A modified Glasgow Coma Scale (GCS) and the presence of sustained spontaneous respirations (SSR), defined as the presence of 2 breaths recorded above the ventilator settings on four occasions, were highly predictive of weaning success within six months of CVU admission. Patients with a modified GCS ≥ 8 were 6.5 times more likely to wean than those with a modified GCS < 8 (95% confidence interval 1.6–26.3) and those with SSR were 25.5 times more likely to wean than those without SSR (95% confidence interval 4.3–51.9). CONCLUSIONS: In our population of CVU patients, simple parameters that were available on admission and did not directly reflect cardiopulmonary function were useful predictors of weaning outcome

Perinatal Lung Development: The Lung at Birth

The successful transition from liquid to air breathing at birth is essential in mammalian lung development and the primary biological role of the hypothalamic-pituitary-adrenal axis. At this moment, the lung experiences a major environmental change in oxygen tension as the fluid that filled this organ in utero (pO2 ∼26) is rapidly replaced with ambient air during the first few breaths (pO2 ∼150). This change induces oxidant stress in the lung which is balanced by antioxidant genes that are induced in the late gestational fetal lung to protect against injury. These antioxidant genes impact distinct antioxidant molecules, including glutathione, which can regulate the level of redox stress in lung cells. Cells, such as the alveolar macrophage, are central for host defense and surfactant homeostasis at the newly established air-liquid surface. Yet they are prone to dysfunction with excessive oxidant stress and the newborn lung is susceptible to infection. And yet the rise in alveolar oxygen tension can also serve as a physiologic redox signal that initiates expression of genes that regulate postnatal lung development. Taken together, birth can be viewed as a natural experiment with hyperoxia where the birth process itself serves as an integrator for that level of redox stress that limits lung injury while activating genes required for postnatal lung development

High temperature radiator materials for applications in the low Earth orbital environment

Radiators must be constructed of materials which have high emittance in order to efficiently radiate heat from high temperature space power systems. In addition, if these radiators are to be used for applications in the low Earth orbital environment, they must not be detrimentally affected by exposure to atomic oxygen. Four materials selected as candidate radiator materials (304 stainless steel, copper, titanium-6% aluminum-4% vanadium (Ti-6%Al-4%V), and niobium-1% zirconium (Nb-1%Zr)) were surface modified by acid etching, heat treating, abrading, sputter texturing, electrochemical etching, and combinations of the above in order to improve their emittance. Combination treatment techniques with heat treating as the second treatment provided about a factor of two improvement in emittance for 304 stainless steel, Ti-6%Al-4%V, and Nb-1%Zr. A factor of three improvement in emittance occurred for discharge chamber sputter textured copper. Exposure to atomic oxygen in an RF plasma asher did not significantly change the emittance of those samples that had been heat treated as part of their texturing process. An evaluation of oxygen penetration is needed to understand how oxidation affects the mechanical properties of these materials when heat treated

Atomic oxygen effects on materials

Understanding of the basic processes of atomic oxygen interaction is currently at a very elementary level. However, measurement of erosion yields, surface morphology, and optical properties for low fluences have brought about much progress in the past decade. Understanding the mechanisms and those factors that are important for proper simulation of low Earth orbit is at a much lower level of understanding. The ability to use laboratory simulations with confidence to quantifiably address the functional performance and durability of materials in low Earth orbit will be necessary to assure long-term survivability to the natural space environment

Births: Final Data for 2006

Objectives—This report presents 2006 data on U.S. births according to a wide variety of characteristics. Data are presented for maternal demographic characteristics including age, live-birth order, race, Hispanic origin, marital status, and educational attainment; maternal lifestyle and health characteristics (medical risk factors, weight gain, and tobacco use); medical care utilization by pregnant women (prenatal care, obstetric procedures, characteristics of labor and/or delivery, attendant at birth, and method of delivery); and infant characteristics (period of gestation, birthweight, Apgar score, congenital anomalies, and multiple births). Also presented are birth and fertility rates by age, live-birth order, race, Hispanic origin, and marital status. Selected data by mother’s state of residence are shown, as well as data on month and day of birth, sex ratio, and age of father. Trends in fertility patterns and maternal and infant characteristics are described and interpreted. Methods—Descriptive tabulations of data reported on the birth certificates of the 4.3 million births that occurred in 2006 are presented. Denominators for population-based rates are postcensal estimates derived from the U.S. 2000 census. Results—In 2006, births and fertility rates increased for most states, age groups, and race and Hispanic origin groups. A total of 4,265,555 births were registered in the United States in 2006, 3 percent more than in 2005, and the largest number of births in more than four decades. The crude birth rate was 14.2, up slightly from the previous year; the general fertility rate was 68.5, up 3 percent. Birth rates increased for women in nearly all age groups, with the largest increases for teenagers and for women aged 20–24 and 40–44 years. Teenage childbearing increased, interrupting the 14-year decline from 1991– 2005. The mean age at first birth for U.S. women was down in 2006, to 25.0 years. The total fertility rate increased to 2,100.5 births per 1,000 women. All measures of unmarried childbearing reached record levels in 2006. Women were less likely to receive timely prenatal care in 2006. The cesarean delivery rate climbed to 31.1 percent, another all-time high. Preterm and low birth weight rates continued to rise; the twin birth rate was unchanged for the second consecutive year; the rate of triplet and higher order multiple births declined 5 percent

Births: Final Data for 2006

Objectives—This report presents 2006 data on U.S. births according to a wide variety of characteristics. Data are presented for maternal demographic characteristics including age, live-birth order, race, Hispanic origin, marital status, and educational attainment; maternal lifestyle and health characteristics (medical risk factors, weight gain, and tobacco use); medical care utilization by pregnant women (prenatal care, obstetric procedures, characteristics of labor and/or delivery, attendant at birth, and method of delivery); and infant characteristics (period of gestation, birthweight, Apgar score, congenital anomalies, and multiple births). Also presented are birth and fertility rates by age, live-birth order, race, Hispanic origin, and marital status. Selected data by mother’s state of residence are shown, as well as data on month and day of birth, sex ratio, and age of father. Trends in fertility patterns and maternal and infant characteristics are described and interpreted. Methods—Descriptive tabulations of data reported on the birth certificates of the 4.3 million births that occurred in 2006 are presented. Denominators for population-based rates are postcensal estimates derived from the U.S. 2000 census. Results—In 2006, births and fertility rates increased for most states, age groups, and race and Hispanic origin groups. A total of 4,265,555 births were registered in the United States in 2006, 3 percent more than in 2005, and the largest number of births in more than four decades. The crude birth rate was 14.2, up slightly from the previous year; the general fertility rate was 68.5, up 3 percent. Birth rates increased for women in nearly all age groups, with the largest increases for teenagers and for women aged 20–24 and 40–44 years. Teenage childbearing increased, interrupting the 14-year decline from 1991– 2005. The mean age at first birth for U.S. women was down in 2006, to 25.0 years. The total fertility rate increased to 2,100.5 births per 1,000 women. All measures of unmarried childbearing reached record levels in 2006. Women were less likely to receive timely prenatal care in 2006. The cesarean delivery rate climbed to 31.1 percent, another all-time high. Preterm and low birth weight rates continued to rise; the twin birth rate was unchanged for the second consecutive year; the rate of triplet and higher order multiple births declined 5 percent