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PubMed2003

Dimensional analysis revisited.

The applicability of dimensional analysis (DA) is discussed in relation to the metabolic scaling laws. The evolution of different theories of biological similarity has shown that the calculated reduced exponents (b) of Huxley's allometric equation are closely correlated with the numerical values obtained from the statistical analysis of empirical data. Body mass and body weight are not equivalent as biological reference systems, since in accordance to Newton's second law, the former has a dimension of a mass, while the latter should be dimensionally considered as a force (W = MLT-2). This distinction affects the coefficients of the mass exponent (alpha). This difference is of paramount importance in microgravity conditions (spaceflight) and of buoyancy during the fetal life in mammals. Furthermore, the coefficients (beta) of the length dimension, and (gamma) of the time dimension do not vary when mass or weight are utilized as reference systems. Consequently, the "specific metabolic time," that results from the ratio of basal oxygen consumption and body mass or body weight yields the "biological meaning" of the time dimension, which is of fractal nature.

Animals↗
PubMedDate not supplied

The reluctant entrepreneur.

Unlike a lot of corporate executives, Ken Veit never longed to be his own boss. But after 30 years on the fast track, he lost his high-powered job at one of the world's largest insurance companies and was forced to take an entrepreneurial leap of faith. In 1989, Veit signed a franchise agreement to own and operate a Cartoon Corner store in a mall in Scottsdale, Arizona. Cartoon Corner was based on the Disney store idea, but it carried hundreds of products featuring cartoon characters from every movie studio. Most important, Cartoon Corner offered extensive training and an elaborate management support system for its franchisees. The company planned to franchise 100 stores over the next few years, then go public. If all went well, its young executives claimed, the Cartoon Corner chain would build a market valuation of up to $100 million by the mid-1990s. In addition, the mall, which was in the planning stages when Veit signed on, was supposed to become a new kind of entertainment mall, with seven movie theaters, a space-flight simulator, and a shark-filled aquarium. It had all sounded too good to be true--and it was. Despite Veit's careful forecasting, he suffered a series of unexpected catastrophes. The mall failed to keep its promises. The franchisor lost its venture capital. The Gulf War dried up retail traffic. But it was too late to back out. Veit went forward on his own, truly alone for the first time in his life. When the mall and his store finally opened in May 1991, they did so in the midst of a recession. Despite the inspirational stories of other former executives, Veit has learned that the life of an entrepreneur is not all it's cracked up to be. As he notes, "I began with well-above-average experience, a proven concept, and excellent capitalization, yet in my case, personal bankruptcy remains a distinct possibility."

Arizona↗
PubMed2000

Effects of gender on the autonomic modulation of the cardiovascular responses to lower body negative pressure.

BACKGROUND: The cardiovascular responses to submaximal lower body negative pressure (LBNP) appear to differ between genders, but the underlying mechanisms are uncertain. HYPOTHESIS: These differences are due to differences in the autonomic modulation of the cardiovascular system. METHODS: There were 14 women and 13 men who underwent LBNP to -50 mmHg in 10 mmHg increments of 6 min each. Heart rate (HR), stroke volume (SV), BP, forearm blood flow and R-R interval data were acquired. Spectral analysis of the R-R interval data was used to assess autonomic modulation with the low frequency component (LF) set at 0.04 to 0.15 Hz and the high frequency component (HF) at 0.15 to 0.4 Hz. RESULTS: The responses to LBNP to -40 mmHg did not differ between groups. LBNP of -50 mmHg evoked greater HR increases in the women than the men (7.2 +/- 1.0 vs. 3.8 +/- 1.1 bpm; p < 0.05), while SV, cardiac output and total peripheral conductance decreased more (-15 +/- 2 vs. -8 +/- 2 ml x beat(-1); -0.668 +/- 0.131 vs. -0.1778 +/- 0.124 L x min(-1); -0.009 +/- 0.002 vs. -0.004 +/- 0.001 units; p < 0.05). Normalized HF, an indicator of the vagal influence on HR variability, declined below rest at -40 mmHg while the LF/HF ratio, an indicator of sympathetic neural modulation of HR variability, increased above rest at -40 mmHg. These responses did not differ significantly between groups. CONCLUSIONS: These results suggest that gender differences in the cardiovascular responses to LBNP are not due to gross differences in modulation of the autonomic nervous systems.

Adult↗
PubMed2000

[Effect of 120 days head-down tilt (HDT) on characteristics of tendinous reflexes].

Time dynamics of variations in the spinal reflex mechanisms was evaluated during 120-d HDT (-6 degrees). Already within the first days in HDT the knee and Achilles reflexes were noted to sharply become easy to fulfil, the conclusion made from a significant drop of thresholds, an appreciable rise of amplitudes of reflex responses and an expansion of the range of stimulations. However, dynamics of these variations was diverse. The abrupt drop of reflex thresholds determined already on HDT day 2 was persistent throughout the experiment, whereas maximal rise of the tendon reflex amplitude was seen on the initial phase of HDT (days 15-30). Later on, a clear-cut downward trend of the electromyographic amplitude was observed. The experimental data suggest that hyperreflexia during HDT is one of the manifestations of partial deafferentation of the motoneuron pool due to diminution of the proprioceptive afflux. At the same time, hyperactivity of the reflex mechanisms is masked by the peripheral muscular effects of the same factor, i.e. HDT.

Adult↗
PubMed2000

[Some mechanisms of modeling the hydrostatic component of hemodynamics in microgravity].

Proposed is a modified method to counteract the headword redistribution of local blood volumes in microgravity by discrete or combined exposure to respiration at negative pressure (RNP) and lower body negative pressure (LBNP). Physically and physiologically substantiated levels of the barometric influences on the central and peripheral hemodynamics to approximate the normal gradients of blood hydrostatic pressure along the body axis are given. Discrete RNP applied to test-subjects during HDT was shown to return the cerebral and cervical hemodynamic parameters to levels determined in horizontal position. Combination of RNP and LBNP had additive character as it advantaged the recovery of values characteristic of the orthostatic position. There are technical possibilities to integrate the LBNP and RNP devices for the benefit of scientific, certification, predictive, and training objectives of space biomedicine.

Adaptation, Physiological↗
PubMed2000

[Experience of selecting test-subjects for extended model studies].

Methodical approaches to selection and results of examination of test-subjects (aged 18 to 50 yr) volunteered to participate in extended model studies were reviewed. General and age-specific morbidity was analyzed. Various diseases (163 nosologic forms) were found in 94.3% of candidates. This fact raises concern since the age group of 18-50 represents the main employable cohort of population. Given rare visits of this age group to policlinic, the health service personnel should concentrate attention on prophylactic medical examination of "no-complaint" patients.

Adolescent↗
PubMed2000

[Pharmacological prophylaxis of vestibulo-autonomous syndrome (motion sickness) in model investigations].

The authors summarize results of multiyear investigations at the Institute of Biomedical Problems of induced motion sickness and development of prophylactic medicaments representing various classes of biologically active substances (choline blocking agents, sympathomimetics, antihistamines etc.) prescribed singularly or in an combination based on the knowledge of MS-provoking inter-receptor interactions and therapeutic effects of drugs.

Adult↗
PubMed2001

Parasympathetic activity during parabolic flight, effect of LBNP during microgravity.

BACKGROUND/HYPOTHESIS: During parabolic flight, in the standing position, changes are partly due to an acute shift in fluid between the lower extremities, the head and the thorax (Vaïda P, et al. J Appl Physiol 1997; 82:1091-7; and Bailliart O, et al. J Appl Physiol 1998; 85:2100-5). We hypothesized that modifications of parasympathetic activity associated with changes in hydrostatic pressure gradients induced by changes in gravity could be detected by analysis of short time periods. METHODS: We assessed heart rate variability (HRV) in 11 healthy volunteers by indices of temporal analysis (NN, SDNN, RMSSD) and normalized indices such as coefficients of variation CV-SDNN and CV-RMSSD and ratio SDNN/RMSSD. A lower body negative pressure (LBNP) at -50 mm Hg was randomly applied during the microgravity phase (0 Gz) to counteract the lack of hydrostatic pressure in the lower part of the body. RESULTS: NN, CV-SDNN and CV-RMSSD decreased during hypergravity phases and increased during microgravity and during early normogravity (1 Gz) period at the end of parabolas. With LBNP changes are less pronounced at 0 Gz and in the 1 Gz post parabolic period. CONCLUSION: We concluded that parasympathetic nervous activity is recordable by temporal analysis of HRV during short periods of time. LBNP applied during 0 Gz phase reduced the parasympathetic activation at 0 Gz and post parabolic 1 Gz.

Adult↗
PubMed2000

Antiorthostatic suspension for 14 days does not diminish the oxidative response of neutrophils in mice.

The effects of long-term spaceflight on inflammatory responses have not been well-studied in either humans or animals. It is thus important to determine if the functions of immune and inflammatory cells are altered in models of spaceflight. One such animal model is antiorthostatic suspension (AOS), in which the experimental animal is subjected to a head-down tilt that mimics both the stress and the cephalad fluid shift experienced in spaceflight. A previous study reported that the peritoneal neutrophils from mice experiencing AOS generated less superoxide than unsuspended controls. We expanded on this study using several different stimuli and measuring the oxidative response of murine neutrophils in a variety of ways. These responses included the rate, lag period, and dose/response characteristics for superoxide generation, FACS analysis with dihydrodichlorofluorescein as a substrate, and a chemiluminescence response with luminol as a substrate. We also examined phagocytosis of three different microorganisms. While some effects of orthostatic suspension (attributable to the stress of the apparatus) were observed, no clear effects of AOS on oxidative function of the peritoneal neutrophils were seen.

Animals↗
PubMed1995

Living in space: results from Biosphere 2's initial closure, an early testbed for closed ecological systems on Mars.

The following summary of results from the first 2-year closure experiment (September 26, 1991 to September 26, 1993) in Biosphere 2 is excerpted from a chapter written by William Dempster and myself for a book, Strategies for Mars, edited by Carol Stoker and Carter Emmart of NASA Ames Research Center. The book will be published later this year by Krieger Publishers. It brings together a number of the most striking initial results, including food production and nutrition; ecosystem changes; oxygen and carbon dioxide dynamics; and the human role and response to living in a small, recycling life support system. The references cited are useful as a guide to currently available articles in journals. Hopefully, the next year will see a proliferation of papers presenting more data from the first 2 years of Biosphere 2's operation. There was a wealth of data collected during the closure and by teams of researchers who had access to the facility during the 5-month transition period following the departure of the first crew and the commencement of the second closure experiment in March, 1994.

Agriculture↗
PubMed1996

Choosing plants to be grown in a Controlled Environment Life Support System (CELSS) based upon attractive vegetarian diets.

Space explorers on the Moon, Mars, or even in a space craft might grow plants in a CELSS to remove CO2 and provide O2 and food. Selection of crops to be studied has been rather arbitrary but should be based on plants that can provide a balanced and attractive, mostly vegetarian diet. Additional selection criteria include ease of growth in artificial environments and sufficient variety provided over long intervals. This article is based on a workshop convened to study vegetarian diets for use in a CELSS. Participants included nutritional scientists, practicing vegetarians, and interested employees of the Johnson Space Center. It was concluded that diets meeting the criteria could be formulated, and a list of suitable crops was compiled.

Crops, Agricultural↗
PubMed1995

Growing super-dwarf wheat in Svet on Mir.

In cooperation with Russian colleagues, we will carry out three experiments with a super-dwarf cultivar of wheat in the plant growth chamber Svet on the Russian Space Station Mir: an early test of the root module and other instruments (July-August, 1995), a seed-to-seed experiment (1996), and a third planting that will be harvested after about 35 days, frozen, and returned to Earth for chemical analysis (1996). Plants will be photographed, sampled,and chemically fixed at intervals during the first two plantings. Instrumentation has been constructed to measure CO2, water vapor, air temperatures, infrared leaf temperatures, oxygen, pressure, irradiance levels, and moisture in the root module substrate (Balkanine). The primary objective of this equipment is to allow controllers to eliminate plant environmental stresses, leading to vigorous plant growth in microgravity. We are testing sampling and analysis techniques and growing plants in ground versions of Svet in Moscow and in Svet mockups in Utah: 12 chambers in two temperature-controlled rooms, with two compartments in each chamber (two temperatures, four CO2 concentrations, and three photoperiods in a current experiment).

Air Conditioning↗
PubMed1998

Bioregenerative [correction of bioregnerative] life support: not a picnic.

If humans are to live permanently in space, regenerative life support systems are an enabling technology and must replace the picnic approach of taking all supplies required for each mission. These systems are classified by technologies as either physical/chemical or bioregenerative. Both of these system-types can recycle water, remove carbon dioxide, produce oxygen, and recover essential elements from waste products. Bioregenerative can also produce food, thus, making it essential if humans are to exist in space independent of earth. A solely bioregenerative life support system includes plants as a biomass production module and microbial organisms in bioreactors as a resource recovery module. In the Advanced Life Support Program, bioregenerative life support systems are being investigated through a research and technology development project which includes large scale testing as part of the Breadboard Project and human tests conducted in the soon to be constructed BioPlex facility. Research and technology development efforts are directed toward optimizing biomass productivity in controlled chambers by developing light weight, energy efficient, and automated systems; recycling liquid and solid wastes; baselining the operation of bioreactors; determining system microbial stability; assessing chemical contamination; and building models required for long term system operations. The program will include space flight studies in the near future to determine if these life support technologies will function in microgravity. When a bioregenerative system is finally incorporated into a mission, the conversion from a picnic and resupply mentality to permanent recycling and independence from earth will be complete.

Biofilms↗
PubMed1997

Group structure and its development in an isolated and confined environment.

An Antarctic winter-over has been regarded as one of the analogue situations in long-term space flight, especially from the aspect of prolonged isolation and a confined environment. Thus, Antarctic winter-overs at research stations offer us a unique opportunity to observe the dynamics of group and individual behavior. This research examines group structure and its development during long-term isolation and confinement in an Antarctic research station using direct, quantitative observations.

Adaptation, Psychological↗