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PubMed1989

Exercise-training protocols for astronauts in microgravity.

The question of the composition of exercise protocols for use by astronauts in microgravity is unresolved. Based on our knowledge of physical working requirements for astronauts during intra- and extravehicular activity and on the findings from bed-rest studies that utilized exercise training as a countermeasure for the reduction of aerobic power, deterioration of muscular strength and endurance, decrements in mood and cognitive performance, and possibly for bone loss, two exercise protocols are proposed. One assumes that, during microgravity, astronaut exercise physiological functions should be maintained at 100% of ground-based levels; the other assumes that maximal aerobic power in flight can be reduced by 10% of the ground-based level. A recommended prescription for in-flight prevention or partial suppression of calcium (bone) loss cannot be written until further research findings are obtained that elucidate the site, the magnitude, and the mechanism of the changes. Hopefully these proposed exercise prescriptions will stimulate further research and discussion resulting in even more efficient protocols that will help ensure the optimal health and well-being of our astronauts.

Exercise↗
PubMed2000

Renal vasopressin receptor expression and function in rats following spaceflight.

It has been suggested there is a decreased renal responsiveness to vasopressin following spaceflight and that this may be the mechanism for the increased urine flow that is observed following return to normal gravity. In the present study, we have therefore measured vasopressin receptor expression and activity in kidneys taken from rats 1 and 14 days following spaceflight of 15 days duration. Measurements of renal vasopressin V(2) and V(1a) receptor mRNA expression by quantitative RT-PCR demonstrated little difference at either 1 day or at 14 days following return from space. Evaluation of (3)H-labeled arginine vasopressin binding to membranes prepared from kidneys indicated that the majority of the vasopressin receptors were V(2) receptors. Furthermore, the data suggested that binding to vasopressin V(2) or V(1a) receptors was unaltered at 1 day and 14 days following spaceflight. Similarly, the ability of vasopressin to stimulate adenylate cyclase suggested no change in vasopressin V(2) receptor activity in these animals. These data suggest that, whatever changes in fluid and electrolyte metabolism are observed following spaceflight, they are not mediated by changes in vasopressin receptor number or vasopressin-induced stimulation of adenylate cyclase.

Animals↗
PubMed2000

Embryonic quail eye development in microgravity.

The US-Russian joint quail embryo project was designed to study the effects of microgravity on development of Japanese quail embryos incubated aboard Mir. For this part of the project, eyes from embryonic days 14 and 16 (E14 and E16) flight embryos were compared with eyes from several groups of ground-based control embryos. Measurements were recorded for eye weights; eye, corneal, and scleral ring diameters; and numbers of bones in scleral ossicle rings. Transparency of E16 corneas was documented, and immunohistochemical staining was performed to observe corneal innervation. In addition, corneal ultrastructure was observed at the electron microscopic level. Except for corneal diameter of E16 flight embryos, compared with that of one of the sets of controls, results reported here indicate that eye development occurred normally in microgravity. Fixation by cracking the shell and placing the egg in paraformaldehyde solution did not adequately preserve corneal nerves or cellular ultrastructure.

Animals↗
PubMed1993

How should human baroreflexes be tested?

A new approach to the study of arterial baroreflexes was developed for use during the National Aeronautics and Space Administration Spacelab Life Sciences-1 Space Shuttle mission. This method holds promise as a means to characterize the vagal limb of human baroreflex responses comprehensively and efficiently.

Adaptation, Physiological↗
PubMed1995

Biological monitoring of iodine, a water disinfectant for long-term space missions.

In order to establish guidelines for exposure of astronauts to iodine, used as a water disinfectant in space, we studied the usefulness of hair, saliva, and urine for biological monitoring in humans and in the human hair/nude mouse model. The monitoring of iodine in patients that received 150 mCi of Na131I (carrier-free) showed similar patterns of elimination for blood, saliva, and urine. The mean correlation coefficient (r) between iodine elimination for blood/saliva was 0.99, for blood/urine, 0.95, and for saliva/urine, 0.97. The absolute value of iodine concentrations in urine revealed marked variability, which was corrected by adjusting for creatinine levels. The autoradiographic studies of human hair demonstrated that iodine is rapidly incorporated into external layers of the hair root and can be removed easily during washing. These data were confirmed after iodine exposure using the human hair/nude mouse model. Hair does not provide satisfactory information about exposure due to unstable incorporation of iodine. The most useful medium for biological monitoring of astronauts exposed to high doses of iodine in drinking water is urine, when adjusted for creatinine, and saliva, if quantitative evaluation of flow rate is provided.

Animals↗
PubMed1988

Cultural systems for growing potatoes in space.

Higher plants are being evaluated for life support to provide needed food, oxygen and water as well as removal of carbon dioxide from the atmosphere. The successful utilization of plants in space will require the development of not only highly productive growing systems but also highly efficient bioregenerative systems. It will be necessary to recycle all inedible plant parts and all human wastes so that the entire complement of elemental compounds can be reused. Potatoes have been proposed as one of the desirable crops because they are 1) extremely productive, yielding more than 100 metric tons per hectare from field plantings, 2) the edible tubers are high in digestible starch (70%) and protein (10%) on a dry weight basis, 3) up to 80% of the total plant production is in tubers and thus edible, 4) the plants are easily propagated either from tubers or from tissue culture plantlets, 5) the tubers can be utilized with a minimum of processing, and 6) potatoes can be prepared in a variety of different forms for the human diet (Tibbitts et al., 1982). However potatoes have a growth pattern that complicates the development of growing the plants in controlled systems. Tubers are borne on underground stems that are botanically termed 'rhizomes', but in common usage termed 'stolons'. The stolons must be maintained in a dark, moist area with sufficient provision for enlargement of tubers. Stems rapidly terminate in flowers forcing extensive branching and spreading of plants so that individual plants will cover 0.2 m2 or more area. Thus the growing system must be developed to provide an area that is darkened for tuber and root growth and of sufficient size for plant spread. A system developed for growing potatoes, or any plants, in space will have certain requirements that must be met to make them a useful part of a life support system. The system must 1) be constructed of materials, and involve media, that can be reused for many successive cycles of plant growth, 2) involve a minimum quantity of media, 3) contain media that is essentially inert and not oxidize or degrade with use, 4) utilize a recirculating nutrient solution to permit regulation of pH and nutrient concentrations, and 5) be capable of complete automation of all planting, maintenance and harvesting procedures.

Ecological Systems, Closed↗
PubMed1999

Short-arm (1.9 m) +2.2 Gz acceleration: isotonic exercise load-O2 uptake relationship.

BACKGROUND: The deconditioning syndrome from prolonged bed rest (BR) or spaceflight includes decreases in maximal oxygen uptake (VO2max), muscular strength and endurance, and orthostatic tolerance. In addition to exercise training as a countermeasure, +Gz (head-to-foot) acceleration training on 1.8-2.0 m centrifuges can ameliorate the orthostatic and acceleration intolerances induced by BR and immersion deconditioning. PURPOSE: Study A was designed to determine the magnitude and linearity of the heart rate (HR) response to human-powered centrifuge (HPC) acceleration with supine exercise vs. passive (no exercise) acceleration. Study B was designed to test the hypothesis that moderate +Gz acceleration during exercise will not affect the respective normal linear relationships between exercise load and VO2max, HR, and pulmonary ventilation (VEBTPS). Study C: To determine if these physiological responses from the HPC runs (exercise + on-platform acceleration) will be similar to those from the exercise + off-platform acceleration responses. METHODS: In Study A, four men and two women (31-62 yr) were tested supine during exercise + acceleration and only passive acceleration at 100% [maximal acceleration (rpm) = Amax] and at 25%, 50%, and 75% of Amax. In Studies B and C, seven men (33+/-SD 7 yr) exercised supine on the HPC that has two opposing on-platform exercise stations. A VO2max test and submaximal exercise runs occurred under three conditions: (EX) exercise (on-platform cycle at 42%, 61%, 89% and 100% VO2max) with no acceleration; (HPC) exercise + acceleration via the chain drive at 25%,50%, and 100% Gzmax (35%, 72% and 100% VO2max); and (EXA) exercise (on-platform cycle at 42%, 61%, 89%, and 100% VO2max) with acceleration performed via the off-platform cycle operator at +2.2+/-0.2 Gz [50% of max (rpm) G]. RESULTS: Study A: Mean (+/-SE) Amax was 43.7+/-1.3 rpm (mean = +3.9+/-0.2, range = 3.3 to 4.9 Gz). Amax run time for exercise +acceleration was 50-70 s, and 40-70 s for passive acceleration. Regression of X HR on Gz levels indicated explained variances (r2) of 0.88 (exercise) and 0.96 (passive). The mean exercise HR of 107+/-4 (25%), to 189+/-13 (100%) bpm were 43-50 bpm higher (p < 0.05) than comparable passive HR of 64+/-2 to 142+/-22 bpm, respectively. Study B: There were no significant differences in VO2, HR or VEBTPS at the submaximal or maximal levels between the EX and EXA runs. Mean (+/-SE) VO2max for EX was 2.86+/-0.12 L x min(-1)(35+/-2 ml x min(-1) x kg(-1)) and for EXA was 3.09+/-0.14 L x min(-1) (37+/-2 ml-min(-1) x kg(-1)). Study C: There were no significant differences in the essentially linear relationships between the HPC and EXA data for VO2 (p = 0.45), HR (p < 0.08), VEBTPS (p = 0.28), or the RE (p = 0.15) when the exercise load was % VO2max. CONCLUSION: Addition of + 2.2 Gz acceleration does not significantly influence levels of oxygen uptake, heart rate, or pulmonary ventilation during submaximal or maximal cycle ergometer leg exercise on a short-arm centrifuge.

Acceleration↗
PubMed1993

Body position and volume status as determinants of cardiovascular responses to transition into microgravity in parabolic flight.

The condition of microgravity during spaceflight imposes a new challenge to the cardiovascular system and to its homeostatic mechanisms. Initial fluids shifts from the dependent parts to the upper parts of the body are supposed to induce a plethora of effects which eventually lead to the well-known puffy faces and chicken legs' of astronauts. At the same time some 2-3 kgs. in fluid is lost in urine and by diminished uptake. For research into these longer-term effects of spaceflight extensive physiologic experiments are required in space. In view of the high cost and the logistic problems related to space-research much work is done in simulation experiments like bedrest or head down tilt studies. For the very initial effects of micro-G parabolic flight can be used. In parabolic flights we have addressed the question of immediate cardiovascular effects of the transition into microgravity. Since a parabola will last for not more than some 25 seconds, one may expect to observe mainly changes in the outflow of the autonomic nervous system, reflecting in blood pressure and heart rate as easily measurable parameters. Such changes can be expected to be caused by the sudden disappearance of hydrostatic effects and the shifts of fluid from pools where it is kept under the influence of gravity. Hydrostatic effects will play a role in the position of the baroreceptors with respect to the heart: in the upright position the carotid sinuses are some 25 cm above heart level, consequently they observe a lower pressure than that at the heart. When this effect disappears in micro-G a suddenly increased pressure will be observed and the baroreflex is called into action. On the venous side blood will rush to the right atrium when it is no longer pulled down in the compliant vessels of the abdomen and legs. This may be expected to lead to increased pressures on the low-pressure side of the heart. Apart from changes in filling of the left heart this may lead to autonomic nervous effects on systemic blood pressure and heart rate as well.

Adult↗
PubMed1989

Potential utilization of algal protein concentrate as a food ingredient in space habitats.

Green alga Scenedesmus obliquus was studied as one of the potential sources of macronutrients in a space habitat. Algal protein concentrate (70.5% protein) was incorporated into a variety of food products such as bran muffins, fettuccine (spinach noodle imitation) and chocolate chip cookies. Food products containing 20 to 40% of incorporated algal proteins were considered. In the sensory analysis the greenish color of the bran muffins and cookies was not found to be objectional. The mild spinachy flavor (algae flavor) was less detectable in chocolate chip cookies than in bran muffins. The color and taste of the algae noodles were found to be pleasant and compared well with commercially available spinach noodles. Commercially available spray-dried Spirulina algae was also incorporated so the products can be compared with those containing Scenedesmus obliquus concentrate. Food products containing commercial algae had a dark green color and a "burnt after taste" and were less acceptable to the panelists.

Biomass↗
PubMed1990

[Life on Mars].

Explore the source record for details and available documents.

Antarctic Regions↗
PubMed1989

Growing plant in space.

Space agencies in several countries are planning for the culture of plants in long duration space bases. The challenge of developing crop production procedures suitable for space projects will result in a new approach of problems we may meet today or in the near future in our common production systems. You may keep in mind subjects as: minimizing wastes or pollution problems, saving materials, introductions robotic helps. Discussion between scientists involved with food production for space programmes and protected horticultural cultivation may open new perspectives.

Crops, Agricultural↗
PubMed1995

Transduction of mechanical strain in bone.

One physiologic consequence of extended periods of weightlessness is the rapid loss of bone mass associated with skeletal unloading. Conversely, mechanical loading has been shown to increase bone formation and stimulate osteoblastic function. The mechanisms underlying mechanotransduction, or how the osteoblast senses and converts biophysical stimuli into cellular responses has yet to be determined. For non-innervated mechanosensitive cells like the osteoblast, mechanotransduction can be divided into four distinct phases: 1) mechanocoupling, or the characteristics of the mechanical force applied to the osteoblast, 2) biochemical coupling, or the mechanism through which mechanical strain is transduced into a cellular biochemical signal, 3) transmission of signal from sensor to effector cell and 4) the effector cell response. This review examines the characteristics of the mechanical strain encountered by osteoblasts, possible biochemical coupling mechanisms, and how the osteoblast responds to mechanical strain. Differences in osteoblastic responses to mechanical strain are discussed in relation to the types of strain encountered and the possible transduction pathways involved.

Animals↗
PubMed1989

The resources of Mars for human settlement.

Spacecraft exploration of Mars has shown that the essential resources necessary for life support are present on the martian surface. The key life-support compounds O2, N2, and H2O are available on Mars. The soil could be used as radiation shielding and could provide many useful industrial and construction materials. Compounds with high chemical energy, such as rocket fuels, can be manufactured in-situ on Mars. Solar power, and possibly wind power, are available and practical on Mars. Preliminary engineering studies indicate that fairly autonomous processes can be designed to extract and stockpile Martian consumables. The ability to utilize these materials in support of a human exploration effort allows missions that are more robust and economical than would otherwise be possible.

Atmosphere↗
PubMed1989

Multiplex gas chromatography: an alternative concept for gas chromatographic analysis of planetary atmospheres.

Gas chromatography (GC) is a powerful technique for analyzing gaseous mixtures. Applied to the earth's atmosphere, GC can be used to determine the permanent gases--such as carbon dioxide, nitrogen, and oxygen--and to analyze organic pollutants in air. The U.S. National Aeronautics and Space Administration (NASA) has used GC in spacecraft missions to Mars (the Viking Biology Gas Exchange Experiment [GEX] and the Viking Gas Chromatograph-Mass Spectrometer [GC-MS]) and to Venus (the Pioneer Venus Gas Chromatograph [PVGC] on board the Pioneer Venus sounder probe) for determining the atmospheric constituents of these two planets. Even though conventional GC was very useful in the Viking and Pioneer missions, spacecraft constraints and limitations intrinsic to the technique prevented the collection of more samples. With the Venus probe, for instance, each measurement took a relatively long time to complete (10 min), and successive samples could not be introduced until the previous samples had left the column. Therefore, while the probe descended through the Venusian atmosphere, only three samples were acquired at widely separated altitudes. With the Viking mission, the sampling rate was not a serious problem because samples were acquired over a period of one year. However, the detection limit was a major disadvantage. The GC-MS could not detect simple hydrocarbons and simple alcohols below 0.1 ppm, and the GEX could not detect them below 1 ppm. For more complex molecules, the detection limits were at the parts-per-billion level for both instruments. Finally, in both the Viking and Pioneer missions, the relatively slow rate of data acquisition limited the number of analyses, and consequently, the amount of information returned. Similar constraints are expected in future NASA missions. For instance, gas chromatographic instrumentation is being developed to collect and analyze organic gases and aerosols in the atmosphere of Titan (one of Saturn's satellites). The Titan-Cassini entry probe, which is being jointly planned by NASA and the European Space Agency (ESA), might be launched as early as 1994. As in the Pioneer mission, limited time--perhaps only 3-4 h--will be available for the completion of all analyses while the probe descends through the atmosphere. A conventional GC or GC-MS system would be able to analyze no more than two aerosol and two gas samples during the probe's descent. Conventional GC also is limited by the sensitivity of the detector and by the sample volume. For the Titan mission, the sensitivity problems will be worse because the atmospheric pressure at the time of instrument deployment is expected to be < 3 torr. Consequently, the sample volume might not be large enough to satisfy the detector sensitivity requirements. Because of such limitations, alternative GC analysis techniques have been investigated for future NASA missions. Multiplex gas chromatography has been investigated as a possible candidate for chemical analysis within a spacecraft or other restricted environment, and chemical modulators have been developed and used when needed with this technique to reduce the size and weight of the instrumentation. Also, several new multiplex techniques have been developed for use in specific applications.

Atmosphere↗
PubMed1990

A review of interstellar rocketry fundamentals.

To reach even the nearest stars in a human lifetime requires a ship speed that is a substantial fraction of the speed of light. This means an enormous kinetic energy investment in the ship and suggests that maximizing the efficiency may be more important than minimizing the mass ratio. This paper develops the pertinent relativistic rocket equations and finds the conditions for high kinematic efficiency. Using the limiting efficiency of 100%, the minimum energy needed for one-way and for round trip voyages, and to explore all "good" suns out to a given distance, using pre-fueled rockets, is determined. Savings due to refueling the rocket (and reloading propellant) at the destination and in flight are both somewhat greater than 2:1.

Mathematics↗
PubMed2002

Compression under a mechanical counter pressure space suit glove.

BACKGROUND: Current gas-pressurized space suits are bulky stiff shells severely limiting astronaut function and capability. A mechanical counter pressure (MCP) space suit in the form of a tight elastic garment could dramatically improve extravehicular activity (EVA) dexterity, but also be advantageous in safety, cost, mass and volume. The purpose of this study was to verify that a prototype MCP glove exerts the design compression of 200 mmHg, a pressure similar to the current NASA EVA suit. METHODS: Seven male subjects donned a pressure measurement array and MCP glove on the right hand, which was placed into a partial vacuum chamber. Average compression was recorded on the palm, the bottom of the middle finger, the top of the middle finger and the dorsum of the hand at pressures of 760 (ambient), 660 and 580 mmHg. The vacuum chamber was used to simulate the pressure difference between the low breathing pressure of the current NASA space suits (approximately 200 mmHg) and an unprotected hand in space. RESULTS: At ambient conditions, the MCP glove compressed the dorsum of the hand at 203.5 +/- 22.7 mmHg, the bottom of the middle finger at 179.4 +/- 16.0 mmHg, and the top of the middle finger at 183.8 +/- 22.6 mmHg. The palm compression was significantly lower (59.6 +/- 18.8 mmHg, p<0.001). There was no significant change in glove compression with the chamber pressure reductions. CONCLUSIONS: The MCP glove compressed the dorsum of the hand and middle finger at the design pressure.

Adult↗
PubMed2004

Ethylene production throughout growth and development of plants.

Ethylene production by 10 or 20 m2 stands of wheat, soybean, lettuce, potato, and tomato was monitored throughout growth and development in an atmospherically closed plant chamber. Chamber ethylene levels varied among species and rose during periods of canopy expansion and rapid growth for all species. Following this, ethylene levels either declined during seed fill and maturation for wheat and soybean, or remained relatively constant for potato and tomato (during flowering and early fruit development). Lettuce plants were harvested during rapid growth and peak ethylene production. Chamber ethylene levels increased rapidly during tomato ripening, reaching concentrations about 10 times that measured during vegetative growth. The highest ethylene production rates during vegetative growth ranged from 1.6 to 2.5 nmol m-2 d-1 during rapid growth of lettuce and wheat stands, or about 0.3 to 0.5 nmol g-1 fresh weight per hour. Estimates of stand ethylene production during tomato ripening showed that rates reached 43 nmol m-2 d-1 in one study and 93 nmol m-2 d-1 in a second study with higher lighting, or about 50x that of the rate during vegetative growth of tomato. In a related test with potato, the photoperiod was extended from 12 to 24 hours (continuous light) at 58 days after planting (to increase tuber yield), but this change in the environment caused a sharp increase in ethylene production from the basal rate of 0.4 to 6.2 nmol m-2 d-1. Following this, the photoperiod was changed back to 12 h at 61 days and ethylene levels decreased. The results suggest three separate categories of ethylene production were observed with whole stands of plants: 1) production during rapid vegetative growth, 2) production during climacteric fruit ripening, and 3) production from environmental stress.

Biomass↗