Engineering topics

Leach, Carolyn S.

Publications and source records attributed to Leach, Carolyn S..

16 records

NASA NTRS1999

Fluid and Electrolyte Nutrition

Studies of fluid and electrolyte homeostasis have been completed since the early human space flight programs, with comprehensive research completed on the Spacelab Life Sciences missions SLS-1 and SLS-2 flights, and more recently on the Mir 18 mission. This work documented the known shifts in fluids, the decrease in total blood volume, and indications of reduced thirst. Data from these flights was used to evaluate the nutritional needs for water, sodium, and potassium. Interpretations of the data are confounded by the inadequate energy intakes routinely observed during space flight. This in turn results in reduced fluid intake, as food provides approximately 70% water intake. Subsequently, body weight, lean body mass, total body water, and total body potassium may decrease. Given these issues, there is evidence to support a minimum required water intake of 2 L per day. Data from previous Shuttle flights indicated that water intake is 2285 +/- 715 ml/day (mean +/- SD, n=26). There are no indications that sodium intake or homeostasis is compromised during space flight. The normal or low aldosterone and urinary sodium levels suggest adequate sodium intake (4047 +/- 902 mg/day, n=26). Because excessive sodium intake is associated with hypercalciuria, the recommended maximum amount of sodium intake during flight is 3500 mg/day (i.e., similar to the Recommended Dietary Allowance, RDA). Potassium metabolism appears to be more complex. Data indicate loss of body potassium related to muscle atrophy and low dietary intake (2407 +/- 548 mg/day, n=26). Although possibly related to measurement error, the elevations in blood potassium suggest alterations in potassium homeostasis. The space RDA for minimum potassium intake is 3500 mg/day. With the documented inadequate intakes, efforts are being made to increase dietary consumption of potassium.

Lane, Helen W.↗

NASA NTRS1992

Duration versus response to space-flight exposure

The duration of human expeditions into space has been as short as a few hours and as long as a year, and although we still need much more information, we can identify some trends indicating effects of flight duration on the physiologic response to space flight. Evidence suggests that after a period of dynamic change that varies for each physiologic system, some physiologic variable stabilize at levels that may differ from those at 1 G. Other variables appear to undergo change from time to time even after months in space, and others have not been observed to reach a plateau. Effects on the neurovestibular system begin very early and certain ones diminish rapidly. Effects of weightlessness on fluid and electrolyte physiology appear to reach a peak after that of neurophysiologic effects. It is possible that the initial responses of these two systems follow a more similar time course than is now apparent. Responses of the cardiovascular system reach a peak that approaches clinical significance after about 3 weeks. The mass of red blood cells is maximally altered after about a month. Bone mineral and lean body mass are lost gradually for at least 6 months, perhaps longer.

Leach, Carolyn S.↗

NASA NTRS1991

Biochemical and hematologic changes after short-term space flight

Clinical laboratory data from blood samples obtained from astronauts before and after 28 flights (average duration = 6 days) of the Space Shuttle were analyzed by the paired t-test and the Wilcoxon signed-rank test and compared with data from the Skylab flights (duration = 28, 56, and 84 days). Angiotensin I and aldosterone were elevated immediately after short-term space flights, but the response of angiotensin I was delayed after Skylab flights. Serum calcium was not elevated after Shuttle flights, but magnesium and uric acid decreased after both Shuttle and Skylab. Creatine phosphokinase in serum was reduced after Shuttle but not Skylab flights, probably because exercises to prevent deconditioning were not performed on the Shuttle. Total cholesterol was unchanged after Shuttle flights, but low density lipoprotein cholesterol increased and high density lipoprotein cholesterol decreased. The concentration of red blood cells was elevated after Shuttle flights and reduced after Skylab flights.

Leach, Carolyn S.↗

NASA NTRS1991

Metabolic changes observed in astronauts

Results of medical experiments with astronauts reveal rapid loss of volume (2 l) from the legs and a transient early increase in left ventricular volume index. These findings indicate that, during space flight, fluid is redistributed from the legs toward the head. In about 2 days, total body water decreases 2 to 3 percent. Increased levels of plasma renin activity and antidiuretic hormone while blood sodium and plasma volume are reduced suggest that space flight-associated factors are influencing the regulatory systems. In addition to fluid and electrolyte loss, Skylab astronauts lost an estimated 0.3 kg of protein. Endocrine factors, including increased cortisol and thyroxine and decreased insulin, are favorable for protein catabolism. The body appears to adapt to weightlessness at some physiologic cost. Readaptation to earth's gravity at landing becomes another physiologic challenge.

Leach, Carolyn S.↗

NASA NTRS1991

Changes in total body water during spaceflight

Total body water (TBW) changes occurring in humans as a consequence of prolonged exposure to microgravity were measured in five male crewmembers of Space Shuttle missions STS-61C and STS-26. It was found that the inflight mean TBW values were significantly different from the preflight and postflight values, while the preflight TBW values were not significantly different from the postflight values. It was also found that individuals may differ in the rate at which they respond to weightlessness. Of the three crewmen who reported experiencing no symptoms of space motion sickness (SMS), two had not exhibited a decrease of TBW at the time of measurements (24 hrs after launch), while the two crewmen who reported SMS of intermediate severity showed a decrease of several kg by 24 hrs, suggesting that dehydration might be an important factor affecting the rate of TBW decrease.

Leach, Carolyn S.↗

NASA NTRS1991

Flight equipment supporting metabolic experiments on SLS-1

Five experiments in different aspects of human metabolism will be performed on Spacelab Life Sciences-1. Nine items of equipment from the Life Sciences Laboratory Equipment inventory will be used: the rack-mounted centrifuge, the hematocrit centrifuge, the low-gravity centrifuge, a body-mass measurement device, a urine monitoring system, the Spacelab refrigerator/freezer, the Orbiter refrigerator, an in-flight blood collection system, and a pocket voice recorder. In addition, each experiment will require some specialized equipment such as incubators and culture blocks for an immunology experiment, and tracers for a fluid and electrolyte experiment and a hematology experiment. The equipment for these experiments has been developed over many years, in some cases since the Skylab program in the early 1970s, and has been certified for use on the Space Shuttle.

Leach, Carolyn S.↗

NASA NTRS1991

Effects of Weightlessness on Human Fluid and Electrolyte Physiology

The changes that occur in human fluid and electrolyte physiology during the acute and adaptive phases of adaptation to spaceflight are summarized. A number of questions remain to be answered. At a time when plasma volume and extracellular fluid volume are contracted and salt and water intake is unrestricted. ADH does not correct the volume deficit and serum sodium decreases. Change in secretion or activity of a natriuretic factor during spaceflight is one possible explanation. Recent identification of a polypeptide hormone produced in cardiac muscle cells which is natiuretic, is hypotensive, and has an inhibitory effect on renin and aldosterone secretion has renewed interest in the role of a natriuretic factor. The role of this atrial natriuretic factor (ANF) in both long- and short-term variation in extracellular volumes and in the inability of the kidney to bring about an escape from the sodium-retaining state accompanying chronic cardiac dysfunction makes it reasonable to look for a role of ANF in the regulation of sodium during exposure to microgravity. Prostaglandin-E is another hormone that may antagonize the action of ADH. Assays of these hormones will be performed on samples from crew members in the future.

Leach, Carolyn S.↗

NASA NTRS1991

A Systems Approach to the Physiology of Weightlessness

A systems approach to the unraveling of the complex response pattern of the human subjected to weightlessness is presented. The major goal of this research is to obtain an understanding of the role that each of the major components of the human system plays following the transition to and from space. The cornerstone of this approach is the utilization of a variety of mathematical models in order to pose and test alternative hypotheses concerned with the adaptation process. An integrated hypothesis for the human physiological response to weightlessness is developed.

White, Ronald J.↗

NASA NTRS1991

Metabolism and biochemistry in hypogravity

The headward shift of body fluid and increase in stress-related hormones that occur in hypogravity bring about a number of changes in metabolism and biochemistry of the human body. Such alterations may have important effects on health during flight and during a recovery period after return to earth. Body fluid and electrolytes are lost, and blood levels of several hormones that control metabolism are altered during space flight. Increased serum calcium may lead to an increased risk of renal stone formation during flight, and altered drug metabolism could influence the efficacy of therapeutic agents. Orthostatic intolerance and an increased risk of fracturing weakened bones are concerns at landing. It is important to understand biochemistry and metabolism in hypogravity so that clinically important developments can be anticipated and prevented or ameliorated.

Leach, Carolyn S.↗

NASA NTRS1991

Effects of weightlessness on human fluid and electrolyte physiology

Skylab and Spacelab data on changes occurring in human fluid and electrolyte physiology during the acute and adaptive phases of adaptation to spaceflight are summarized. The combined results for all three Spacelab studies show that hyponatremia developed within 20 h after the onset of weightlessness and continued throughout the flights, and hypokalemia developed by 40 h. Antidiuretic hormone was increased in plasma throughout the flights. Aldosterone decreased by 40 h, but after 7 days it had reached preflight levels.

Leach, Carolyn S.↗

NASA NTRS1991

A systems approach to the physiology of weightlessness

A general systems approach to conducting and analyzing research on the human adaptation to weightlessness is presented. The research is aimed at clarifying the role that each of the major components of the human system plays following the transition to and from space. The approach utilizes a variety of mathematical models in order to pose and test alternative hypotheses concerned with the adaptation process. Certain aspects of the problem of fluid and electrolyte shifts in weightlessnes are considered, and an integrated hypothesis based on numerical simulation studies and experimental data is presented.

White, Ronald J.↗

NASA NTRS1989

Biochemical correlates of neurosensory changes in weightlessness

The possible existence of a relationship between space motion sickness and chemical and biochemical variables measured in body fluids is studied. Clinical chemistry and endocrine measurements from blood and urine samples taken before and after Space Shuttle flights were analyzed along with the occurrence of SMS during flight and provocative testing before flight. Significant positive correlations were observed with serum chloride and significant negative correlations with serum phosphate, serum uric acid, and plasma thyroid stimulating hormone.

Leach, Carolyn S.↗

NASA NTRS1988

Cholesterol in serum lipoprotein fractions after spaceflight

Results are reported from blood-lipid measurements obtained from 125 Space Shuttle crew members before and after space flight. The data are presented in tables and discussed in detail. The main differences noted between preflight and postflight values are a 12.8-percent decrease in high-density lipoproteins on postflight day 1 and significant decreases in total cholesterol and both high- and low-density lipoproteins later in the 23-day postflight period.

Leach, Carolyn S.↗

NASA NTRS1988

Hematology and biochemical findings of Spacelab 1 flight

The changes in erythropoiesis in astronauts caused by weightlessness was experimentally studied during the Spacelab 1 flight. Immediately after landing showed a mean decrease of 9,3 percent in the four astronauts. Neither hyperoxia nor an increase in blood phosphate caused the decrease. Red cell survival time and iron incorporation postflight were not significantly different from their preflight levels. Serum haptoglobin did not decrease, indicating that intravascular hemolysis was not a major cause of red cell mass change. An increase in serum ferritin after the second day of flight may have been caused by red cell breakdown early in flight. The space flight-induced decrease in red cell mass may result from a failure of erythropoesis to replace cells destroyed by the spleen soon after weightlessness is attained.

Leach, Carolyn S.↗

NASA NTRS1987

Fluid control mechanisms in weightlessness

Experiments performed on Space Shuttle flights have emphasized study of the earliest effects of the cephalad fluid shift resulting from microgravity. Analysis of one subject's urine collected during flight showed that a sharp increase in antidiuretic hormone occurred within 2 h of launch, followed by an increase in cortisol excretion. Although this subject had symptoms of the space adaptation syndrome (SAS), inflight data from Spacelab missions suggested that these transient changes were not caused by SAS. Unpaired t-tests and Mann-Whitney tests showed that before and after flight, plasma thyroxine and urine osmolality were significantly higher in Shuttle crewmembers who exhibited more severe symptoms of SAS than in asymptomatic crewmembers.

Leach, Carolyn S.↗

NASA NTRS1987

Spacelab Life Sciences 1 and 2 scientific research objectives

The pressurized Spacelab module was designed and built to allow investigators to conduct research in space in an environment approximating that of a ground-based laboratory. It is configured to allow multiple investigations employing both human and nonhuman subjects. This flexability is exemplified by the SLS-1, SLS-2, and SLS-3 experiment complement. A total of 21 experiments are scheduled for these missions; the areas to be investigated are renal/endocrine function, cardiovascular/cardiopulmonary function, hematology, immunology, metabolic activity of muscle, Ca metabolism, the vestibular system, and general biology. A plan for integration of measurements will allow each investigator to use data from other experiments. The experiments make up a scientifically balanced payload that addresses fundamental biomedical problems associated with space flight and provides the first opportunity to study the acute effects of weightlessness in a comprehensive, interrelated fashion.

Leach, Carolyn S.↗