Engineering topics

Leach, C. S.

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

At least 19 records

NASA NTRS1998

Collagen cross-link excretion during space flight and bed rest

Extended exposure to weightlessness results in bone loss. However, little information exists as to the precise nature or time course of this bone loss. Bone resorption results in the release of collagen breakdown products, including N-telopeptide and the pyridinium (PYD) cross-links, pyridinoline and deoxypyridinoline. Urinary pyridinoline and deoxypyridinoline are known to increase during bed rest. We assessed excretion of PYD cross-links and N-telopeptide before, during, and after long (28-day, 59-day, and 84-day) Skylab missions, as well as during short (14-day) and long (119-day) bed-rest studies. During space flight, the urinary cross-link excretion level was twice those observed before flight. Urinary excretion levels of the collagen breakdown products were also 40-50% higher, during short and long bed rest, than before. These results clearly show that the changes in bone metabolism associated with space flight involve increased resorption. The rate of response (i.e. within days to weeks) suggests that alterations in bone metabolism are an early effect of weightlessness. These studies are important for a better understanding of bone metabolism in space crews and in those who are bedridden.

NASA Center JSC↗

NASA NTRS1997

Regulation of body fluid volume and electrolyte concentrations in spaceflight

Despite a number of difficulties in performing experiments during weightlessness, a great deal of information has been obtained concerning the effects of spaceflight on the regulation of body fluid and electrolytes. Many paradoxes and questions remain, however. Although body mass, extracellular fluid volume, and plasma volume are reduced during spaceflight and remain so at landing, the changes in total body water are comparatively small. Serum or plasma sodium and osmolality have generally been unchanged or reduced during the spaceflight, and fluid intake is substantially reduced, especially during the first of flight. The diuresis that was predicted to be caused by weightlessness, has only rarely been observed as an increased urine volume. What has been well established by now, is the occurrence of a relative diuresis, where fluid intake decreases more than urine volume does. Urinary excretion of electrolytes has been variable during spaceflight, but retention of fluid and electrolytes at landing has been consistently observed. The glomerular filtration rate was significantly elevated during the SLS missions, and water and electrolyte loading tests have indicated that renal function is altered during readaptation to Earth's gravity. Endocrine control of fluid volumes and electrolyte concentrations may be altered during weightlessness, but levels of hormones in body fluids do not conform to predictions based on early hypotheses. Antidiuretic hormone is not suppressed, though its level is highly variable and its secretion may be affected by space motion sickness and environmental factors. Plasma renin activity and aldosterone are generally elevated at landing, consistent with sodium retention, but inflight levels have been variable. Salt intake may be an important factor influencing the levels of these hormones. The circadian rhythm of cortisol has undoubtedly contributed to its variability, and little is known yet about the influence of spaceflight on circadian rhythms. Atrial natriuretic peptide does not seem to play an important role in the control of natriuresis during spaceflight. Inflight activity of the sympathetic nervous system, assessed by measuring catecholamines and their metabolites and precursors in body fluids, generally seems to be no greater than on Earth, but this system is usually activated at landing. Collaborative experiments on the Mir and the International Space Station should provide more of the data needed from long-term flights, and perhaps help to resolve some of the discrepancies between U.S. and Russian data. The use of alternative methods that are easier to execute during spaceflight, such as collection of saliva instead of blood and urine, should permit more thorough study of circadian rhythms and rapid hormone changes in weightlessness. More investigations of dietary intake of fluid and electrolytes must be performed to understand regulatory processes. Additional hormones that may participate in these processes, such as other natriuretic hormones, should be determined during and after spaceflight. Alterations in body fluid volume and blood electrolyte concentrations during spaceflight have important consequences for readaptation to the 1-G environment. The current assessment of fluid and electrolyte status during weightlessness and at landing and our still incomplete understanding of the processes of adaptation to weightlessness and readaptation to Earth's gravity have resulted in the development of countermeasures that are only partly successful in reducing the postflight orthostatic intolerance experienced by astronauts and cosmonauts. More complete knowledge of these processes can be expected to produce countermeasures that are even more successful, as well as expand our comprehension of the range of adaptability of human physiologic processes.

NASA Discipline Number 18-10↗

NASA NTRS1994

Short-term space flight on nitrogenous compounds, lipoproteins, and serum proteins

Biochemical variables in blood were measured in venous blood samples from 38 to 72 Space Shuttle astronauts before and immediately after flights of 2 to 11 days. Mean pre- and postflight values were compared using the paired t-test or the Wilcoxon signed-rank test. The largest change in serum enzymes was a 21% increase (P = .0014) in gamma-glutamyl-transpeptidase, which may have been related to stress. The median value of apolipoprotein (apo) A-I decreased from 152 to 127 mg/dL (P < .0001), but the change in apo B (77 to 73 mg/dL) was not statistically significant, and the mean apo A-I/apo B ratio remained well above 1.5. A decrease in dietary fat and cholesterol intake during shuttle missions may have been a cause of the change in apo A-I. Twelve of the 16 nonenzyme serum proteins measured were significantly elevated (P < .05), possibly because of hemoconcentration and increased protein catabolism. The 56% increase in haptoglobin may be related to release of suppressed erythropoiesis at landing.

Blood Proteins/analysis/metabolism↗

NASA NTRS1992

Changes in renal function and fluid and electrolyte regulation in space flight

The cephalad fluid redistribution resulting from weightlessness has a number of physiologic consequences. Plasma volume is reduced soon after weightlessness is reached, and red blood cell mass reduction follows. Plasma atrial natriuretic peptide, which inhibits aldosterone secretion, was elevated during space flight while plasma aldosterone was below preflight levels. Serum sodium was also reduced and potassium was elevated. Antidiuretic hormone (ADH) was markedly elevated at almost all measurement times in the first eight days of flight, but plasma volume did not return to preflight levels.

Leach, C. S.↗

NASA NTRS1992

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 approximately 28, 59, 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. Reticulocyte count was decreased after both short- and long-term flights, indicating that a reduction in red blood cell mass is probably more closely related to suppression of red cell production than to an increase in destruction of erythrocytes. Serum ferritin and number of platelets were also elevated after Shuttle flights. In determining the reasons for postflight differences between the shorter and longer flights, it is important to consider not only duration but also countermeasures, differences between spacecraft, and procedures for landing and egress.

NASA Program Flight↗

NASA NTRS1990

Extended Duration Orbiter Medical Project

The Extended Duration Orbiter (EDO) program addresses a need for more time to perform experiments and other tasks during Space Shuttle missions. As a part of this program, the Extended Duration Orbiter Medical Project (EDOMP) has been instituted to obtain information about physiologic effects of extending mission duration and the effectiveness of countermeasures against factors that might compromise crew health, safety, or performance on extended-duration missions. Only those investigations that address and characterize operational problems, develop countermeasures, or evaluate the effectiveness of countermeasures will be pursued. The EDOMP investigations will include flight-associated Detailed Supplementary Objectives as well as ground-based studies simulating the influence of microgravity. Investigator teams have been formed in the following areas: biomedical physiology, cardiovascular and fluid/electrolyte physiology, environmental health, muscle and exercise physiology, and neurophysiology. Major operational questions must be answered in each of these areas, and investigations have been designed to answer them. The EDO program will proceed only after countermeasures have been shown to be effective in preventing or mitigating the adverse changes they have been designed to attenuate. The program is underway and will continue on each Shuttle flight as the manifest builds toward a 16-day orbital flight.

Leach, C. S.↗

NASA NTRS1990

Medical considerations for extending human presence in space

The prospects for extending the length of time that humans can safely remain in space depend partly on resolution of a number of medical issues. Physiologic effects of weightlessness that may affect health during flight include loss of body fluid, functional alterations in the cardiovascular system, loss of red blood cells and bone mineral, compromised immune system function, and neurosensory disturbances. Some of the physiologic adaptations to weightlessness contribute to difficulties with readaptation to Earth's gravity. These include cardiovascular deconditioning and loss of body fluids and electrolytes; red blood cell mass; muscle mass, strength, and endurance; and bone mineral. Potentially harmful factors in space flight that are not related to weightlessness include radiation, altered circadian rhythms and rest/work cycles, and the closed, isolated environment of the spacecraft. There is no evidence that space flight has long-term effects on humans, except that bone mass lost during flight may not be replaced, and radiation damage is cumulative. However, the number of people who have spent several months or longer in space is still small. Only carefully-planned experiments in space preceded by thorough ground-based studies can provide the information needed to increase the amount of time humans can safely spend in space.

Review, Tutorial↗

NASA NTRS1990

Metabolic consequences of fluid shifts induced by microgravity

The effects of fluid redistribution induced by weightlessness on the fluid and electrolyte regulation, the maintenance of optimum nutritional status, and on pharmacodynamics (i.e., the absorption, distribution, and elimination of pharmacologic agents) are examined on the basis of published data on flights aboard Skylab and Space Shuttle. Data are presented on changes in plasma osmolarity and the content of antinuclear factor, serum glucose, and the salivary scopolamine concentrations after oral administration before and during space flights.

Cintron, N. M.↗

NASA NTRS1989

Human factors and productivity on Space Station Freedom

Three main facets of man systems are investigated with reference to the Space Station Freedom program: specific hardware systems that focus on the human element; requirements definition for man-systems integration; and crew interface and operations analysis. Three key criteria have been identified for selecting individuals to constitute the human system or crew for Space Station Freedom missions: aptitude for mission specific skills, motivation, and sensitivity to self and others. Integration of the human system into the complex engineering and science systems planned on Space Station Freedom will require the close collaboration of engineers, physicians, psychologists, and human factors experts. Ground-based research and experiments on the KC-135 aircraft are providing information about how human systems will function on a space station and how to design other systems to interact with the crew. A laboratory for further research will be provided onboard Space Station Freedom.

Leach, C. S.↗

NASA NTRS1988

Medical considerations for extending human presence in space

The medical factors affecting the duration of manned space missions are reviewed. Topics addressed include the effects of weightlessness on body fluids, the cardiovascular system, red blood cells, the musculoskeletal system, the immune system, and the nervous system and the problems encountered in readaptation to normal gravity for each of these systems. Also discussed are the effects of radiation exposure, altered circadian rhythms, and closed environments. Plans for in-flight health care on the International Space Station are briefly outlined.

Leach, C. S.↗

NASA NTRS1988

The endocrine system in space flight

A trial natriuretic factor (ANF), a hormone recently shown to regulate sodium and water excretion, has been measured in blood specimens obtained during flight. After 30 or 42 h of weightlessness, mean ANF was elevated. After 175 or 180 h, ANF has increased by 59 percent, and it changed little between that time and soon after landing. There is probably an increase in ANF early inflight associated with the fluid shift, followed by a compensatory decrease in blood volume. Increased renal blood flow may cause the later ANF decrease. Erythropoietin (Ep), a hormone involved in the control of red blood cell proudction, was measured in blood samples taken during the first Spacelab mission and was significantly decreased on the second day of flight, suggesting also an increase in renal blood flow. Spacelab-2 investigators report that the active vitamin D metabolite 1 alpha, 25-dihydroxyvitamin D-3 increased early in the flight, indicating that a stimulus for increased bone resorption occurs by 30 h after launch.

Leach, C. S.↗

NASA NTRS1986

The regulation of fluid and electrolyte metabolism in weightlessness

Endocrine and biochemical changes in astronauts caused by weightlessness are discussed. Translocation of fluid from the extremities to the head and chest at the onset of weightlessness is thought to lead to the establishment of a lower blood volume as an adaptation to microgravity. Results of Skylab experiments indicate that several other regulatory systems have lower homeostatic set points during space flight. Inflight blood samples from three Spacelab flights show increased antidiuretic hormone throughout these short flights and decreased aldosterone and cortisol after 3 days. Results help to explain blood hypoosmolality and hyponatremia but do not explain what happens between the onset of weightlessness and hormone changes. Other factors such as natriuretic peptides and changes in renal function are being studied to elucidate the physiologic adaptation mechanisms.

Leach, C. S.↗

NASA NTRS1985

Fluid and electrolyte control in simulated and actual spaceflight

Effects of microgravity on body fluid distribution and electrolyte and hormonal levels of astronauts have been studied since the early manned space missions. Bedrested subjects have been used as controls to separate effects of microgravity from those of hypokinesia. These investigations have led to documentation of the physiological effects of spaceflight and to a unified theory of response to microgravity. During flight, crewmembers have decreased thirst and a net loss of body water, sodium, and potassium. These changes seem to be initiated by passive transfer of extracellular fluid resulting in increased central venous pressure (CVP), to which the homeostatic mechanisms respond. A new equilibrium state is maintained during flight; it does not change in response to negative calcium and nitrogen balances during flight. On reexposure to gravity, profound water and salt retention occurs to replete extracellular fluid. Attempts to avoid cardiac deconditioning by repleting water and salt before leaving microgravity have somewhat ameliorated postural hypotension but have had little effect on CVP, cardiac chamber size or electrolyte dynamics.

Leach, C. S.↗

NASA NTRS1985

Endocrine and fluid metabolism in males and females of different ages after bedrest, acceleration and lower body negative pressure

Space shuttle flight simulations were conducted to determine the effects of weightlessness, lower body negative pressure (LBNP), and acceleration of fluid and electrolyte excretion and the hormones that control it. Measurements were made on male and female subjects of different ages before and after bedrest. After admission to a controlled environment, groups of 6 to 14 subjects in the age ranges 25 to 35, 35 to 45, 45 to 55 to 65 years were exposed to +3 G sub z for 15 minutes (G1) and to LBNP (LBNP1) on different days. On 3 days during this prebedrest period, no tests were conducted. Six days of bedrest followed, and the G sub z (G2) and LBNP (LBNP2) tests were run again. Hormones, electrolytes, and other parameters were measured in 24-hour urine pools throughout the experiment. During bedrest, cortisol and aldosterone excretion increased. Urine volume decreased, and specific gravity and osmolality increased. Urinary electrolytes were statistically unchanged from levels during the non-stress control period. During G2, cortisol increased significantly over its control and bedrest levels. Urine volume, sodium, and chloride were significantly lower; specific gravity and osmolality were higher during the control period or bedrest. The retention of fluids and electrolytes after +G sub z may at least partially explain decreased urine volume and increased osmolality observed during bedrest in this study. There were some who indicated that space flight would not affect the fluid and electrolyte metabolism of females or older males any more severely than it has affected that of male astronauts.

Leach, C. S.↗

NASA NTRS1985

Spacelab 1 hematology experiment (INS103): Influence of space flight on erythrokinetics in man

An experiment conducted on the 10-day Spacelab 1 mission aboard the ninth Space Shuttle flight in November to December 1983 was designed to measure factors involved in the control of erythrocyte turnover that might be altered during weightlessness. Blood samples were collected before, during, and after the flight. Immediately after landing, red cell mass showed a mean decrease of 9.3 percent in the four astronauts. Neither hyperoxia nor an increase in blood phosphate was a cause of 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. Erythropoietin levels decreased during and after flight, but preflight levels were high and the decrease was not significant. The space flight-induced decrease in red cell mass may result from a failure of erythropoiesis to replace cells destroyed by the spleen soon after weightlessness is attained.

Leach, C. S.↗

NASA NTRS1984

Influence of spaceflight on erythrokinetics in man

It has been found in connection with American and Soviet manned space missions that a reduction in the circulating red blood cell mass (RCM) is a result of the effect of space flight on the human hematological system. An experiment conducted during the 10-day Spacelab 1 mission in November 1983 was designed to measure factors involved in the control of erythrokinetics which might be altered after exposure to microgravity. In this experiment a decrement in RCM approximately equal to that observed in crewmen returning from Apollo flights of similar duration (7) was measured. Erythropoietin decreased in flight in all crew members. The lack of significant change in erythropoietin with a significant decrease in reticulocyte number and a decrease of about 1 percent per day in mean RCM suggests that inhibition of erythropoiesis ms not the primary or only cause of the inflight RCM reduction.

Leach, C. S.↗

NASA NTRS1983

Medical results from STS 1-4 - Analysis of body fluids

Venous blood was drawn from the eight crewmembers of Space Shuttle flights STS-1 through STS-4 three times before lift-off and twice after landing, and the characteristics of biochemical blood components were evaluated. Twenty-four-hour urine pools were collected 30 d before flight and on landing day or day 4 after landing, and electrolytes, selected hormones and other components were measured. The results indicated that, although fluid and electrolyte loss occur during space flight, conservation of these substances is begun almost immediately upon cessation of weightlessness. Enzyme and hormone measurements indicated that landing may have caused some stress on crewmembers.

Leach, C. S.↗

NASA NTRS1983

Concepts for NASA longitudinal health studies

Clinical data collected from a 15-year study of the homogenous group of pre-Shuttle astronauts have revealed no significant long-term effects from spaceflight. The current hypothesis suggests that repeated exposures to the space environment in the Shuttle era will similarly have no long-term health effects. However, a much more heterogenous group of astronauts and non-astronaut scientists will fly in Shuttle, and data on this group's adaptation to the space environment and readaptation to earth are currently sparse. In addition, very little information is available concerning the short- and long-term medical consequences of long duration exposure to space and subsequent readaptation to the earth environment. In this paper, retrospective clinical information on astronauts is reviewed and concepts for conducting epidemiological studies examining long-term health effects of spaceflight on humans, including associated occupational risks factors, are presented.

Nicogossian, A. E.↗