Increased core body temperature in astronauts during long-duration space missions.

Humans' core body temperature (CBT) is strictly controlled within a narrow range. Various studies dealt with the impact of physical activity, clothing, and environmental factors on CBT regulation under terrestrial conditions. However, the effects of weightlessness on human thermoregulation are not well understood. Specifically, studies, investigating the effects of long-duration spaceflight on CBT at rest and during exercise are clearly lacking. We here show that during exercise CBT rises higher and faster in space than on Earth. Moreover, we observed for the first time a sustained increased astronauts' CBT also under resting conditions. This increase of about 1 °C developed gradually over 2.5 months and was associated with augmented concentrations of interleukin-1 receptor antagonist, a key anti-inflammatory protein. Since even minor increases in CBT can impair physical and cognitive performance, both findings have a considerable impact on astronauts' health and well-being during future long-term spaceflights. Moreover, our findings also pinpoint crucial physiological challenges for spacefaring civilizations, and raise questions about the assumption of a thermoregulatory set point in humans, and our evolutionary ability to adapt to climate changes on Earth.

Leg edema formation and venous blood flow velocity during a simulated long-haul flight.

INTRODUCTION: Long-distance traveling in a sitting position may be associated with an increased incidence for venous thromboembolism. As major contributing factors immobility and compression of leg veins are discussed. At present no studies have been performed measuring the time course of lower limb blood flow, leg volume and leg tissue thickness during a long-haul flight. MATERIALS AND METHODS: We measured limb volumes (plethysmographic method), lower leg tissue thickness and lower limb venous hemodynamics before, during and after 10 h sitting in modern aircraft chairs under normobaric hypoxia in healthy volunteers (n=12). RESULTS: Lower leg volume was already significantly increased after 4 h sitting (+109 ml) reaching its maximum after 10 h (+145 ml). These changes were accompanied by an increased body weight, total body water, extracellular water and tissue thickness of the tibia. No significant changes were measured for leg vessel cross-section diameters and maximal flow velocities in superficial femoral veins. After 10 h sitting core temperature, overall surface temperature and skin temperatures in front of the tibia were significantly increased. All parameters returned to baseline one day after sitting. CONCLUSIONS: Prolonged sitting in modern aircraft seats is associated with a remarkable fluid accumulation in the lower legs which mainly occurred during the first hours. These fluid shifts were independent of lower limb venous hemodynamics and vessel cross-sectional diameters.

Formation of edema and fluid shifts during a long-haul flight.

BACKGROUND: More than 1.5 billion passengers travel by aircraft every year. Leg edema, as a sign of venous stasis, is a well-known problem among passengers during and after long-haul flights. Until now, no studies have been done on the development of leg edema and fluid shifts under real flight conditions. The aim of our study was to evaluate edema formation in the leg and to investigate possible fluid shifts to the interstitial space under real flight conditions. METHODS: Twenty participants, 10 without risk and 10 with moderate risk for venous thrombosis, were selected. They flew from Vienna to Washington, flight time 9 h, and returned 2 days later. Investigations were done 48 h before the flight, between the fifth and eighth flight hour on board to Washington and back to Vienna, immediately after arrival in Vienna, and 1 and 3 days after arrival. Plethysmographic measurements were carried out using an optoelectronic scanner system (Perometer). Thickness of the skin was measured at the forehead and in front of the tibia. RESULTS: There were no differences in all measurements between both groups. The volume of the leg increased from 8242 +/- 1420 mL to 8496 +/- 1474 mL after the flight (p <.001). Volume accumulation was distributed to the lower leg as well as to the thigh. Skin thickness in front of the tibia increased significantly during the flight (p <.05), and remained elevated 1 day after arrival. CONCLUSION: We have demonstrated that long-haul flights induce significant fluid accumulation in the lower extremity, involving the lower leg and thigh. This increase in tissue thickness was maintained for some days after the flights.

Austrian Moderate Altitude Study (AMAS 2000) - fluid shifts, erythropoiesis, and angiogenesis in patients with metabolic syndrome at moderate altitude (congruent with 1700 m).

It was hypothesized that subjects with metabolic syndrome (hypertension, obesity, hyperlipidemia, diabetes mellitus): (1) develop measurable peripheral edema at moderate altitude and (2) might show differences on erythropoiesis, iron status and vascular endothelial growth factor (VEGF) in comparison to healthy subjects during and after a long-term stay (3-week exposure) at moderate altitude (congruent with 1700 m). Twenty-two male subjects with metabolic syndrome were selected. Baseline investigations (t1) were performed in Innsbruck (500 m). All participants were transferred by bus to 1700 m (Alps) and remained there for 3 weeks with examinations on day 1 (after the first night at altitude, t2), day 4 (t3), day 9 (t4) and day 19 (t5). After returning to Innsbruck, post-altitude examinations were conducted after 7-10 days (t6) and 6-7 weeks (t7), respectively. Body mass was decreased from t1 to t7 (P<0.01). Total body water was decreased at t2 (P<0.01), returned to control level (t3, t4), and was found elevated at t7 (P<0.01). Lean body mass did not change, but body fat decreased during the study (P<0.01). Tissue thickness at the forehead decreased during and after altitude exposure (P<0.01), whereas tissue thickness at the tibia did not alter. Erythropoietin (EPO) was elevated as early as t2 and remained increased until t5. Reticulocyte count was increased at t3 and remained above pre-altitude values. VEGF levels were unchanged. After a 3-week exposure to moderate altitude, patients with metabolic syndrome had reduced their body mass, mainly because of a reduction in body fat. The moderate altitude was found to stimulate erythropoiesis in these patients but this was not sufficient to increase serum VEGF concentration.