Hormonal regulation during a 60-day confinement (ESA-EXEMSI'92) in humans

EXEMSI'92 was a 60-day isolation and confinement experiment with an international crew. During this second experiment of the European Space Agency (the first one was a 28-day confinement with 6 men: ISEMSI'90), blood volume regulating hormones and water balance were studied. During ISEMSI'90, stress level was elevated as shown by specific markers and we observed some interesting results which have been already observed before, during bed-rest experiments. Thus, our conclusion was that some of the physiological effects observed during bed rest could be the consequence of the "confinement effect" and/or stress imposed to the subjects during such experiments. The aim of the present physiological study was: 1/to define the origin of the blood pressure increase seen during ISEMSI'90; 2/ to study the blood volume regulating hormones (ANP, renin, aldosterone) variations; 3/ to determine the dehydration level by measuring the total body water with the doubly labeled water (DLW) method and fluid balance in general.     

Changes of 25-OH-Vitamin D during Overwintering at the German Antarctic Stations Neumayer II and III

Purpose

Humans in Antarctica face different environmental challenges, such as low ultra-violet radiation, which is crucial for vitamin D production in humans. Therefore we assessed changes in 25-OH-vitamin D serum concentration during 13 months of overwintering at the German Stations Neumayer II and III (2007–2012). We hypothesized that (i) 25-OH-vitamin D serum concentration would significantly decrease, (ii) changes would be affected by age, gender, baseline (i.e. pre-overwintering) fat mass, baseline 25-OH-vitamin D serum concentration, and station residence, and (iii) our results would not differ from similar previous studies in comparable high latitudes.

Materials & Methods

25-OH-vitamin D serum concentrations were determined before, after, and monthly during the campaigns from venous blood samples of n = 43 participants (28 men, 15 women). Baseline fat mass was determined via bio impedance analysis and body plethysmography. Data were analyzed for change over time, dependency on independent parameters, and after categorization for sufficiency (>50nmol/l), insufficiency (25-50nmol/l), and deficiency (<25nmol/l). Results were compared with data from similar previous studies.

Results

We found a significant decrease of 25-OH-vitamin D with dependency on month. Age, gender, fat mass, and station residence had no influence. Only baseline 25-OH-vitamin D serum concentrations significantly affected subsequent 25-OH-vitamin D values.

Conclusions

Overwinterings at the Antarctic German research stations Neumayer II and III are associated with a decrease in 25-OH-vitamin D serum concentrations, unaffected by age, gender, baseline fat mass, and station residence. Higher baseline vitamin D serum concentrations might protect from subsequent deficiencies. Residence at the Neumayer Stations may lead to lower vitamin D serum concentrations than found in other comparable high latitudes.     

Effects of a 60-day confinement on the blood pressure, hormonal responses and body fluids of a mixed crew

During the EXEMSI experiment, an international crew of 4 subjects (1 woman and 3 men) was confined for 60 days in a normobaric diving chamber (with 1060 mbar atmospheric pressure) to simulate life in a space station and to assess the effects of confinement on psychological and physiological factors. Blood pressure and blood volume regulating hormones (atrial natriuretic peptide, renin, aldosterone) and urine data (24-h urine outputs, ionogram) were measured before (BDC: baseline data collection), during (D: day) and after (R: recovery) confinement. We also measured energy expenditure and total body water, 14 days before, and after 27 days of confinement, by the double-labeled water method. We found a marked increase in 24-h urine output during most of the confinement in the men and the woman. Body weight (-1.8 +/- 0.9 kg) and energy expenditure (-1064 +/- 143 kcal/d, p<0.01) decreased in the 3 men. The total body water (TBW) decreased by 1.5 +/- 1.2 l in the men. Stress was not indicated by plasma and urine catecholamines but plasma growth hormone was elevated on D2 (p<0.01 vs. BDC) in the men. This study shows that confinement conditions can modify body fluid (increases in 24-h urine outputs and TBW changes) and energetic metabolisms.     

Monitoring of Sodium Balance during Long-Term Isolation of Humans in a Ground-Based Space Station Model

According to the generally accepted view, sodium accumulation in the human body takes place in the extracellular space and is accompanied by an increase in the rate of fluid retention and body weight gain. However, this view was revised in recent studies, which demonstrated that sodium could be accumulated in the human body without expansion of the extracellular space. Sodium exchange and its effect on body weight (BW) were investigated in long-term balance studies. Three apparently healthy volunteer subjects were confined for 135 days to a ground-based model of the main unit of the Mir space station, where they were exposed to model conditions similar to conditions of actual long-term spaceflight. The daily balance of sodium and its contribution to BW changes were studied. During the period of observation, the subjects accumulated 2.973–7.324 mmol of sodium and gained 5.1–9.3 kg. Initially, there was a positive correlation between changes in the total body sodium and the BW, which reflected sodium-dependent extracellular space expansion. However, by the end of the period of isolation, the relative rate of body weight gain was lower than the relative rate of gain in the total body sodium, which suggested that sodium accumulated in an osmotically inactive form. The fact that sodium accumulated without BW gain suggests that isolation of healthy subjects in a hermetically sealed enclosure stimulates sodium accumulation in the body in an osmotically inactive form. The sodium-storing processes activated under these conditions might be localized in bone, connective tissue (skin), or cartilage. Rhythmic variation in the net sodium balance was observed and attributed to oscillations of renal excretion of aldosterone. It is obvious that the depot of osmotically inactive sodium should be taken into account in studies of cardiovascular system function and in pathophysiological approaches to edematous syndrome and hypertension.     

Enhanced slow caudad fluid shifts in orthostatic intolerance after 24-h bed-rest

To evaluate mechanisms of late orthostatic intolerance, slow fluid shifts along the body axis were studied during deconditioning by 24-h bed-rest and during 13-min upright tilts before and after this manoeuvre. In 11 healthy male subjects the fluid volumes of a thorax and a calf segment (impedance plethysmography) as well as tissue thickness at the forehead and the tibia (miniature ultrasonic plethysmograph) were recorded. Cardiovascular performance was monitored by recording heart rate (electrocardiogram), brachial and finger arterial pressure (by the Riva Rocci method and by the Finapres technique) as well as stroke volume (by impedance cardiography). Bed-rest led to a cephalad fluid shift with a mean interstitial leg dehydration of 2.2 ml·-100 ml^–1 with no changes in body mass and plasma volume. No syncope during the tilt occurred before bed-rest, while after bed-rest 8 subjects fainted between min 2.1 and 9.0 of the tilt. Bed-rest resulted in an augmented initial heart rate response to tilting which was similar in all subjects. In later orthostasis, bed-rest caused two- to threefold faster caudad fluid shifts with higher calf filtration rates in fainters (prior to hypotension) than in nonfainters. Through bed-rest the estimated extravasation within 10 min into general lower body tissue spaces increased by 192 ml in (late) fainters as opposed to only 23 ml in nonfainters. It was concluded that contributing factors to orthostatic intolerance may be slow transcapillary fluid shifts which are easily underestimated and whose quantity and time course call for further investigation after various deconditioning manoeuvres. In particular, the postflight fluid shifts in astronauts who will have markedly dehydrated legs, may impose a circulatory stress which needs to be evaluated. In general, the filtration rate in relevant areas appears to be an integrative and easily determined parameter, reflecting hormonal and neurogenic vascular as well as local interstitial control of the Starling forces.     

Influence of prolonged physical exercise on the erythropoietin concentration in blood

Erythropoietin (EPO) and red blood cells were studied in 15 well-trained men before and several times after a marathon run. Changes in red blood cells reflected changes of plasma volume. Immediately after the run, red blood cells were increased due to haemoconcentration, whereas 31 h later the values were decreased due to haemodilution. The EPO concentration was increased 3 h, and more impressive 31 h, after the run. This long-lasting increase in EPO concentration after the marathon run would seem to be responsible for the increased red blood cell mass in long distance runners.     

Water immersion is associated with an increase in aquaporin-2 excretion in healthy volunteers

Here, we report the alterations in renal water handling in healthy volunteers during a 6 h thermoneutral water immersion at 34 to 36 °C. We found that water immersion is associated with a reversible increase in total urinary AQP2 excretion.