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Biomedical subjects

C S Leach

Publications and source records attributed to C S Leach.

At least 37 records · Page 2Linked to original sources
PubMed1984

Serum erythropoietin titers during prolonged bedrest; relevance to the "anaemia" of space flight.

The overall objective of these studies was to test the hypothesis that the suppression of erythropoiesis, which occurs during both spaceflight and bedrest, was mediated by reduction in circulating levels of erythropoietin. In each of two 7-day studies, groups of subjects were exposed to either horizontal or 6 degrees head-down tilt bedrest and no evidence was obtained to suggest that the erythropoietic effects were dependent on the angle of recumbency. An additional study involved six men who were exposed to horizontal bedrest for 28 days. Serum erythropoietin titers were not significantly depressed in any of the subjects but total red cell volume was decreased. Absolute increases in red cell numbers and reductions in plasma volume both elevate the haematocrit, but our data suggest that the mechanism of erythrosuppression in these two instances may be different.

Adult↗
PubMed1983

Quantitation of tissue loss during prolonged space flight.

An analysis of data from the three Skylab missions was performed to assess the lean body mass (LBM) and fat components of inflight body weight loss. Six methods for determining LBM were employed based on changes in total body water, total body potassium, nitrogen balance, potassium balance, and stereophotometric-body density. Those based solely on body potassium, and potassium and nitrogen balances (when expressed as shifts from preflight control), consistently overestimated LBM loss unless appropriate corrections were made. The average results from the various methods indicated that of a mean inflight total body weight loss of 2.7 +/- 0.3 kg (SD) for all nine crewmembers, more than half (1.5 +/- 0.3 kg) can be attributed to loss of LBM (including 1.1 kg body water), the remainder (1.2 +/- 0.3 kg) being derived from fat stores. The reduction of LBM appeared to be complete after the first month of flight and thereafter was largely independent of mission duration, diet, and exercise.

Adipose Tissue↗
PubMed1983

The endocrine and metabolic responses to space flight.

The absence of hydrostatic forces, which results in body fluid shifts, and the absence of deformation forces on normally load-bearing tissues, appear to cause the principal disturbances found during and after space flight in the cardiovascular, fluid and electrolyte, erythropoietic, musculoskeletal, and metabolic systems. These alterations produce reduced body fluid volume, reduced musculoskeletal mass, and alterations in basal metabolism, resulting in the following consistent findings of space flight: weight loss, altered body composition, decreased orthostatic tolerance, and a compromised ability to deal with physical activity after returning from a space-flight environment. Specific changes include alterations in hydration status, resulting in a relative dehydration, loss of body calcium stores with a concomitant increase in urinary hydroxyproline, skeletal muscular atrophy, and a negative energy balance after prolonged space flight. Numerous endocrine changes have been determined during space flight, but more sensitive assay developed recently will allow careful determination of other hormone levels, and measurement of some of the primary changes that occur during the first hours of space flight. These results will be integrated into a working systems model of the physiologic response to weightlessness.

Atrophy↗
PubMed1983

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.

Aerospace Medicine↗
PubMed1983

Concepts for NASA longitudinal health studies.

Clinical data collected from a 15-year study of the homogeneous 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 heterogeneous 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.

Aerospace Medicine↗
PubMed1982

A systems approach to the physiology of weightlessness.

This paper presents a systems approach to the unraveling of the complex response pattern of the human subjected to the challenge of weightlessness. 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.

Adaptation, Physiological↗
PubMed1980

Is the weight loss of hyperbaric habitation a disorder of osmoregulation?

To examine the weight loss of hyperbaric helium-oxygen habitation, we measured the exchange of liquids and calories in six men who lived in this atmosphere for 32 d. The maximum pressure was 49.5 ATA. The men lost 3.7-10.1 kg, in spite of warm ambient (31-32 degrees C) temperatures and adequate calories (2,737 kcal/d) provided for the sedentary ways of chamber living. Weight loss and a calculated fluid deficit were accompanied by significant hemoconcentration, shown by increases in serum proteins. These changes were followed by a rise in urinary aldosterone and vasopressin, but not thirst. Weight loss in hyperbaric atmospheres is probably multifactorial, but our data suggests an uncoupling of normal osmoregulation may have occurred in the present set of subjects. This may have been due to altered lung mechanics, increased catecholamines, or effects of high pressure on cellular responses to vasopressin.

Aldosterone↗
PubMed1979

A review of the consequences of fluid and electrolyte shifts in weightlessness.

This review describes the renal-endocrine mechanisms related to the early losses of fluid-electrolytes from the body during weightlessness as well as their contribution to longer term adaptation of fluid-electrolyte balance. The hypotheses presented were generated by a systematic analysis of body fluid and renal dynamics observed under conditions of actual and simulated spaceflight. These have increased our understanding of the effects of acute headward fluid shifts on renal excretion, the factors promoting excess sodium excretion and the regulation of extracellular fluid composition.

Adaptation, Physiological↗
PubMed1979

A study of metabolic balance in crewmembers of Skylab IV.

A metabolic balance study was conducted on the three crewmembers of the 84-day Skylab IV earth orbital mission. Dietary intake was controlled, monitored, and kept very nearly constant for a period commencing 21 days prior to flight, throughout flight, and for a period of 18 days postflight. Within the first 30 days of flight urine calcium rose to a level approx. 100% above preflight levels and remained elevated for the remainder of the flight. Fecal calcium excretion increased more slowly but continued to accelerate throughout the flight and did not return to baseline levels during the postflight period. Urinary nitrogen increased to 25-30% above preflight levels within one month following launch and thereafter gradually subsided toward control values. The overall losses of calcium averaged approx. 200 mg per day throughout the mission while nitrogen losses averaged 590 mg. Various other indices of musculoskeletal deterioration are discussed and correlated. The parallelism between the effects of weightlessness and bed rest is reviewed. It is noted, that no evidence is yet available as to the identity of the initial biological response to the absence of gravity.

Adaptation, Physiological↗
PubMed1979

Amino aciduria in weightlessness.

Urinary excretion of amino acids by the 9 Skylab crewmen was studied as an indicator of the metabolic effects caused by exposure to the space flight environment. Intake was consistent in quality and quantity throughout the 28, 59 and 84-day flights for each of the crewmen and complete collections were accomplished. The results indicated an increased excretion in most amino acids during the first month of flight which remained elevated in the second and third months but to a lesser extent. Additional indications of change in muscle and skeletal metabolism were observed. These results point to the desirability of obtaining additional indices of alterations in protein synthetic processes in conjunction with future space flights.

Adaptation, Physiological↗
PubMed1978

Stress levels of ambulance paramedics and fire fighters.

Responses to Rahe and job stress questionnaires and urinary concentrations of cortisols and catecholamines served to indicate work related stress in 56 fire fighters and 67 paramedics. Although the average Rahe test scores, indicative of stress arising from life events, were comparable, those of the job stress test were statistically significantly higher for the paramedics. The paramedics felt their jobs more exhausting, less satisfying and requiring too much responsibility. For the paramedics, statistically significant higher levels of epinephrine and elevated levels of norepinephrine were found for the work as compared to the off day. For fire fighters, higher levels of cortisol and norepinephrine evident on the off day rather than the work day apparently reflect the relatively light work load experienced during the span of urine collections.

Adult↗
PubMed1978

Evaporative water loss in man in a gravity-free environment.

Daily evaporative water losses (EWL) during the three Skylab missions were measured indirectly using mass and water-balance techniques. The mean daily values of EWL for the nine crew members who averaged 1 h of daily exercise were: preflight 1,750 +/- 37 (SE) ml or 970 +/- 20 ml/m2 and inflight 1,560 +/- 26 ml or 860 +/- 14 ml/m2. Although it was expected the EWL would increase in the hypobaric environment of Skylab (one-third atmosphere). an average decrease from preflight sealevel conditions of 11% was measured. The results suggest that weightlessness decreased sweat losses during exercise and possibly reduced insensible skin losses as well. The weightlessness environment apparently promotes the formation of an observed sweat film on the skin surface during exercise by reducing convective flow and sweat drippage, resulting in high levels of skin wettedness that favor sweat suppression.

Body Water↗
PubMed1977

Space motion sickness medications: interference with biomedical parameters.

The possibility that drugs administered to Skylab 3 (SL-3) and 4 (SL-4) crewmen for space motion sickness may have interfered with their biomedical evaluation in space was investigated. Healthy volunteers received combinations of Scopolamine/Dexedrine for four days in regimens similar to those used in these missions. Urine samples, heart rate, body temperature, mood and performance were analyzed for drug-related changes. Twenty-four hour urine samples were analyzed by the same procedures as those used to analyze the flight samples. Hormone concentrations determined included cortisol, epinephrine, norepinephrine, aldosterone and antidiuretic hormone (ADH). In addition, volume, specific gravity, osmolarity, sodium (Na), potassium (K), calcium (Ca), magnesium (Mg), chloride (Cl), inorganic phosphate, uric acid and creatinine were measured. Performance was not affected by the Scopolamine/Dexedrine. The drug combination increased daily mean heart rate (HR) significantly in all the subjects and daily mean rectal temperature (RT) in some of the subjects. A 2-4 hr phase shift in the HR circadian rhythm was also observed which indicates that internal circadian synchrony was disturbed by the drugs. Psychological and subjective evaluation indicated that the subjects could usually identify which days they were given the drugs by an increase in tension and anxiety, decreased patience, restlessness, decreased appetite, difficulty in sleeping and feelings of increased heart rate and body temperature. Urinary electrolytes were not changed significantly by the drug, but marked and significant changes occurred in urine volume and hormone excretion patterns. Scopolamine/Dexedrine caused consistent elevations in urinary cortisol and epinephrine and a transient elevation in ADH. Norepinephrine excretion was decreased, but there was no significant change in aldosterone excretion or in 24 hr urine volume. A comparison of these findings with the first four days of inflight data from the SL-3 and SL-4 missions leads to the conclusion that the dramatic increases in aldosterone excretion during the first three days of spaceflight probably can be directly attributed to weightlessness, whereas the antimotion sickness medication could have substantially contributed to the early increased excretion of epinephrine and cortisol during these missions.

Adult↗