Calcium losses would not be significant unless collections were carried out under controlled conditions for periods of at least two weeks. Therefore, mineral balance studies were not attempted in the Gemini program until the first long duration flight was performed, the 14-day Gemini 7 mission. Changes in the excretion of other body constituents were of interest because they demonstrated effects in the body systems under investigation.
Through accurate control and measurement of diet, fluid intake, urine, feces, sweat, and activity, researchers were able to perform complete metabolic balance studies on the two astronauts of Gemini 7. The study of musculoskeletal metabolism required the measurements of the balances of calcium, nitrogen, phosphate, magnesium, sodium, potassium, chloride, and sulfate. Balance can be defined as the amount consumed minus the amount excreted. In addition, urinary excretions of 17-hydroxycorticosteroids, catecholamines, and aldosterone were measured. Estimates of endocrine activity such as adrenocortical hormone activity were measured. Collaboration with the "Bioassays of Body Fluids (M005)" and "Bone Demineralization (M006)" experiments was planned as part of the protocol for this study.
Data collection began 12 days before flight and continued for 10 days. Dietary control was maintained, but collections of excreta had to be interrupted two days prior to lift-off because of the intensity of flight preparations at that time. In-flight data collection was performed during the fourteen days of space flight. Postflight measurements were collected four days during the recovery phase. The diets through all three phases were designed to be similar and constant in elemental content and composition. Since each individual served as his own control for comparison of pre-, in-, and postflight phases, interindividual differences were permitted. During the preflight and postflight phases, the diet was served under supervision. A three-day rotation of menus was allowed for each individual with no additional snacks permitted. Both subjects agreed to drink 2 glasses of milk daily for 5 months preceding the flight to minimize the effects of adjustment on calcium balance.
In-flight dietary menus consisted of prepackaged, cooked foods. Initially it was planned that each crewmember would eat his meals in a predetermined sequence to provide 24-hour consumption rates of each dietary element under investigation. Difficulties in management of food packs in the confined cabin space prevented the meals to be eaten according to the rotation. To minimize the effect of microgravity on calcium balance, calcium intake was maintained in-flight at a level close to that of the preflight phase. The intakes of other elements, notably nitrogen and phosphorous, were considerably reduced during flight. Postflight menus were identical with those during the preflight phase.
During the preflight and postflight phases, 24-hour urine specimens were collected and refrigerated until analyzed. A routine urinalysis was performed, consisting of qualitative tests for sugar, albumin, blood, and a microscopic examination of the urine sediment. Additional tests included total volume, pH, and specific gravity. Special preservatives were provided for some tests.
In-flight urine collection utilized a specially designed urine transport system. The system permitted the total urine volume for each voided sample to be calculated by means of tritium dilution.. A 75 ml aliquot of each void was collected into a plastic sample bag containing a preservative and returned to Earth. As soon as possible after recovery, these samples were frozen for future analysis. Urine was collected continuously for 48 hours after landing. A portion of all urine specimens was shared with the experiment "Bioassays of Body Fluids (M005)."
Urinary excretions from two groups of hormones were measured. The first group, 17-hydroxycorticosteroids, was indicative of long-term stress responses. The second group, catecholamines, indicated short-term or emergency responses. These parameters provided an objective, long-term evaluation of the physiologic cost of space flight. Urinary aldosterone was measured to study the mechanisms associated with sodium excretion. Increases in aldosterone secretion would result in decreased urinary excretion of sodium, and vice versa. Researchers hypothesized that aldosterone secretion would be decreased in space flight resulting in an increased urinary excretion of sodium.
Water and fluid electrolytes were examined to determine the mechanisms associated with weight loss during flight. The rates of urinary excretion of sodium, potassium, and chloride were determined pre-, in-, and postflight.
Fluid intake and output were measured to determine whether weight loss was caused by sweat and imperceptible losses, or by changes in renal function. Fluid intake was ad libitum, but the quantities ingested during the preflight and postflight phases were recorded. The majority of the fluid intake was obtained during meals. In-flight intake was estimated from a water-dispensing device on board the spacecraft; this information was not sufficiently precise to perform calculation of fluid balance data.
Preflight and postflight stool specimens were collected and frozen. In-flight stool collections were made with specially designed defecation bags. Throughout the experiment, the subjects ingested harmless red and blue dye markers to separate individual stool periods. The entire stool sample was stored in the cabin without refrigeration but with a preservative. After flight, stool specimens were frozen and shipped to the laboratories for analysis.
Two 24-hour sweat collections of the entire body surface, except the head, were carried out preflight and postflight. After complete washing down the entire skin surface, the subjects donned flight underwear suits and wore these for a continuous 24-hour period. At the end of this period, another washing down was performed. The wash water and the suits were combined and the total fluid concentrated to a volume suitable for analysis. During the in-flight phase, a total 14-day collection was carried out with extraction of the in-flight underwear removed immediately after recovery, combined with wash water of the whole skin surface.
The astronauts engaged in vigorous physical activity daily before and after the flight. In-flight activity consisted of the manual tasks plus an exercise program with a bungee cord exerciser three times a day as part of the "In-flight Exerciser (M003)" experiment.
All preflight and postflight specimens of urine, feces, sweat, and diet were assembled at a provisional laboratory. Aliquots of urine samples were preserved by the addition of appropriate chemicals, frozen and shipped to laboratories associated with this experiment for analysis. Additional aliquots from the same urine samples were preserved with alternate chemicals, frozen and shipped to the laboratories associated with the M005 study. In-flight specimens were recovered from the craft as soon as possible and shipped for analysis to the appropriate laboratory. Specimen preservation and analyses were carried out according to standard techniques of metabolic balance laboratories.
Gemini 7 was the first orbital flight in which an effort was made to obtain physiologic data by collection of excreta in connection with planned controlled studies. It was not possible to carry out what would be considered an ideal experimental protocol due to the many operational and experimental activities required of the astronauts before, during, and after flight. Engineering, training and flight restrictions forced many compromises in the acquisition of physiologic data.
Difficulties were not encountered in obtaining reproducible, accurate collections' values in the preflight and postflight phases. Urinary creatinine values for both subjects were remarkably constant preflight and postflight. In-flight, various problems arose during the collection of urine samples. Due to mechanical difficulties, the in-flight urine transport system did not function wholly effectively. In some cases, variable quantities of urine were lost before the addition of the tritium tracer and therefore estimation of total urine volume could not be determined. In other instances, the inadequate mixing of urine with tracer occurred. In addition, some urine storage bags burst during flight or upon recovery, leading to further loss of urine samples. Urinary creatinine excretions calculated on the basis of recovered samples were extremely variable and low. Such differences between preflight and the in-flight data could not be accounted for on the basis of changes in renal function. The differences were therefore attributed to either losses of urine prior to the addition of tritium or to undiscovered errors in the tritium dilution technique for calculation of volume. Therefore, all in-flight urinary excretion values were corrected on the basis of presumed "true" urinary creatinine excretion. This latter value was calculated as the mean of urinary creatinine excretion of the 10 preflight control days plus the 4 postflight control days for each of the two astronauts.
No difficulties were encountered in the collection of fecal samples preflight, in-flight, or postflight. As part of the preservative technique for the in-flight phase, a lipid soluble dye preservative mixture was added immediately after passage of the stool. The preservation technique led to false estimations of in-flight excretion of stool total lipids.
The urinary calcium excretion did not change significantly during the first seven days of space flight in either subject. However, a definite increase occurred for subject A and persisted during the four days of observation after flight. This persistence of increased urinary calcium excretion after flight was particularly significant and indicated of a true effect of space flight on urinary calcium excretion. The in-flight values for the second week for subject A averaged 23 percent higher than preflight, and for subject B the values were 9 percent higher, the average being a 16 percent increase. The net balance of calcium during flight was distinctly decreased for both crewmembers, due to an increase on fecal calcium in subject B. Dermal losses of calcium, listed as "sweat," were low for both subjects in all phases and slightly higher during the relatively inactive postflight recovery days. The dermal excretion data demonstrated the relative insignificance of loss in magnesium metabolism by this route.
There is approximately 5 to 40% (2 to 15 grams) of skeletal magnesium available for turnover reactions. Urinary magnesium excretion is a function of dietary intake, as well as aldosterone production. No change in urinary excretion of magnesium occurred in the first week of space flight for subject A. Significantly increased amounts of magnesium were excreted in the second week, a pattern similar to that seen in calcium excretion. Starting in-flight and persisting through the four days of the recovery phase, urinary magnesium excretion significantly decreased in both subjects. When the balance data were examined, the increased urinary excretion of magnesium during the in-flight phase was of greater significance because of the reduced dietary intakes. The positive magnesium balance during the postflight period resulted from decreased urinary and fecal excretion, both while dietary intake was increased, suggesting repletion of previous losses. The data for subject B were qualitatively similar but to a lesser degree. The most significant change in magnesium metabolism was the postflight retention.
Phosphate is present in the body as the principle anion in bone salt, as well as in protein and in soluble forms. Urinary excretion of phosphate is a function of dietary intake, bone salt turnover (45% of urinary calcium values), and of muscle metabolism (6.8% of urinary nitrogen excretion values). In addition, carbohydrate metabolism may influence shifts of phosphate among body compartments. The data obtained for subject A demonstrated an increase in urinary phosphate over the first nine days of space flight, occurring during the time when dietary phosphate was half that of the preflight control values. Thereafter, despite relatively constant dietary intake, urinary excretion dropped to control values. Despite decreased fecal excretion, the balances became more negative during the flight and returned to the control levels after flight. Similar results were observed for subject B.
Urinary sulfate is derived primarily from protein catabolism (approximately 7% of urinary nitrogen). Fecal sulfate is usually constant over a wide range of intake values. The sulfate excretion data for subject A showed a slight fall in the urinary excretion during flight, and rose to slightly above control values during the postflight period. Since the curtailment of in-flight dietary intake was marked, these changes in excretion resulted in negative balance during flight, and returned to preflight control balance levels postflight. Similar results were observed for astronaut B.
Fecal nitrogen is relatively constant over a wide range of dietary intakes in any individual. Urinary nitrogen reflects dietary intake and protein metabolism. In both subjects A and B, urinary nitrogen fell during flight and returned to preflight values postflight. Dietary nitrogen was significantly less during flight with the resulting in a negative nitrogen balance.
Urinary nitrogen and sulfate were less in flight than in the preflight phase for both subjects. The excretions did not fall as much as would have been expected from the decrease in dietary intake of these two elements. This observation indicated the loss of a modest but measurable amount of muscle tissue.
Urinary sodium is a function of dietary intake, aldosterone activity, and glucocorticoid secretion. Intake restriction produces secondary hyperaldosteronism with reduction of urinary sodium excretion. Fecal losses of sodium usually are small and relatively constant. In subject A, despite the decrease in dietary sodium, there was an increased natriuresis during the first week of flight with a return to preflight control values during the second week. A significant retention was observed in the early postflight period. Conversely, subject B demonstrated no changes in sodium excretion during the first part of the space flight, a slight increase thereafter and then marked retention postflight.
Epinephrine excretion and, more variably, norepinephrine excretion, were greatest on the two days of greatest predicted "stress," the day of "lift-off" and the day of landing. In subject B, catecholamine excretion approximated this pattern, but the values were not significantly different from the preflight values. The excretion of 17-hydroxycorticosteroids, which is regarded as representing chronic adaptation to stress, was surprisingly low during the entire flight phase. In both subjects, this measurement was elevated on the day of landing. The few values for urinary aldosterone obtained were elevated during and immediately following flight.
Urinary excretion of potassium reflects protein metabolism, aldosterone secretion, and glucocorticoid action. The variability in response seen with subjects A and B may have been due to variations in endocrine responses. Subject A showed an initial decrease in urinary potassium as a result of space flight in the presence of a marked decrease in dietary potassium. During the second week, potassium excretion increased (which correlated with the simultaneous decrease in urinary sodium). Immediately postflight potassium excretion decreased to preflight values as the dietary intake was increased. Subject B showed only a slight decrease in urinary potassium the first week of flight despite restricted dietary intake. During the second week, potassium excretion decreased further and then returned to preflight values during the recovery phase.
Chloride metabolism is controlled primarily by renal excretion following the excretion of cations. Since sodium forms the largest proportion of renal cations, chloride control depends chiefly on the control of sodium. Subject B showed a pattern of chloride excretion parallel to that of sodium excretion. Subject A, on the other hand, excreted chloride in parallel with potassium. The reason for this discrepancy was not apparent. Balances of chloride were not calculated because of technical difficulties in measuring dietary chloride.
No apparent difficulties were noted in the collection and estimation of sweat losses during any phases of the study. Sweat was a significant route of loss for sodium, potassium, and chloride in this study. Sweat loss balances of calcium, magnesium, sulfate, phosphate, and nitrogen were insignificant in all three phases of the experiment.
The changes in calcium metabolism and other factors were moderate enough to support (from the metabolic viewpoint) the decision that a voyage to and from the Moon would be medically safe. The time involved would be no more (in fact, less) than the time involved on the Gemini 7 mission. However, for future long duration flights, it was evident that additional in-flight metabolic observations were needed for the assessment of physiological safety and performance of astronauts. Researchers hoped such studies would result in more reliable information for accurate prediction of mineral and other metabolic changes in long-duration space flight. This in turn would result in predictive or protective measures.
Despite inadequacies, researchers believed that the experiment was of value in that it represented the first effort to obtain information on possible metabolic changes in humans during space flight. In addition, the experiences lead to the better planning of subsequent studies to obtain more conclusive data.
|Mission||Launch/Start Date||Landing/End Date||Duration|
|Gemini 7||12/04/1965||12/18/1965||14 days|