Hanns-Christian Gunga

Biology of the sauropod dinosaurs: the evolution of gigantism

The herbivorous sauropod dinosaurs of the Jurassic and Cretaceous periods were the largest terrestrial animals ever, surpassing the largest herbivorous mammals by an order of magnitude in body mass. Several evolutionary lineages among Sauropoda produced giants with body masses in excess of 50 metric tonnes by conservative estimates. With body mass increase driven by the selective advantages of large body size, animal lineages will increase in body size until they reach the limit determined by the interplay of bauplan, biology, and resource availability. There is no evidence, however, that resource availability and global physicochemical parameters were different enough in the Mesozoic to have led to sauropod gigantism.

Differential expression of nitric oxide synthases (NOS 1-3) in human skeletal muscle following exercise countermeasure during 12 weeks of bed rest

Adaptive changes of major body systems in astronauts during spaceflight can be simulated by strict anti‐orthostatic head‐down tilt (HDT) bed rest (BR), a ground‐based microgravity (μG) model that provides a meaningful opportunity to study atrophy mechanisms and possible countermeasures under controlled experimental conditions. As nitric oxide (NO) signaling is linked to muscle activity, we investigated altered expression of the three major isoforms of nitric oxide synthase (NOS 1–3) at cellular compartments during prolonged HDT BR without (control group) and with resistance exercise interventions (exercise group) using a flywheel ergometer (FWE). Atrophy detected in mixed (fast–slow) m. vastus lateralis (VL) and slow‐type m. soleus (SOL) myofiber Types I and II (minus 35–40% of myofiber cross‐sectional area) was prevented by FWE training. Concomitant to muscle atrophy, reduced NOS 1 protein and immunostaining was found in VL not in SOL biopsies. In trained VL, NOS 1 protein and immunostaining at myofibers II were significantly increased at the end of BR. Exercise altered NOS 2/caveolin 3 co‐immunostaining patterns of subsarcolemmal focal accumulations in VL or SOL myofibers, which suggests reorganization of sarcolemmal microdomains. In trained VL, increased capillary‐ to‐fiber (C/F) ratio and NOS 3 protein content were documented. Activity‐linked NO signaling may be widespread in skeletal muscle cellular compartments that may be directly or indirectly impacted by adequate exercise countermeasure protocols to offset the negative effects induced by disuse, immobilization, or extended exposure to microgravity.

Erythropoietin production during flights with pressurised aircrafts.

416 Vol 348 • August 10, 1996 SIR—James emphasises the importance of hypoxia as a risk factor for older passengers engaged in long-haul air travel. A cabin altitude of 8000 ft (2438 m), which is equivalent to a cabin ambient pressure of 75·8 kPa, is regarded as the maximum acceptable cabin altitude of modern airliners cruising at altitudes up to 43 000 ft (13 106 m). We have measured oxygen saturation of haemoglobin (SaO 2 ; ear pulse-oximetry) in 15 resting healthy individuals seated in a hypobaric chamber with an inside ambient pressure of 75·8 kPa. Mean SaO 2 was 90% (SD 1·9; range 85–93) after 30 min of exposure. There is considerable interindividual variation in the responses to a lowered partial O 2 pressure. Responses to hypoxic hypoxia include an increase in pulmonary ventilation, which is evident even at 6600 ft (2012 m). However, immobility, cramped seating conditions, and drowsiness might hinder proper respiratory activities. Moreover, the lower ambient pressure in the cabin leads to gastrointestinal distension, which might limit downward movements of the diaphragm. In those who were dozing off in our hypobaric chamber we found much lower SaO 2 levels (80%) at cabin altitudes of 8000 ft (2438 m). when they were stimulated to respire properly, SaO 2 levels increased substantially. Therefore, if airlines’ advice on routine in-flight exercise were also to address proper pulmonary ventilation, both important hypoxia and venous thrombosis might be prevented. For older people, these exercises should not be too strenuous, because strenuous activities might lower their SaO 2 even further. Airlines’ advice should also include recommendations on adequate fluid intake, because the low relative humidity in the cabin could lead to dehydration. The cabin relative humidity from outside fresh air is less than 1%. Moisture from passengers and crew will cause it to increase, depending on the passenger load factor, ventilation rate, temperature, and pressure. During 16 long-haul flights (Boeing 747–400) we found cabin values ranged between 7 and 14% (mean 10%), which is in accord with studies in other types of aircraft, We undertook a pilot study, in which six healthy people were exposed for 8 h to a simulated altitude of 8000 ft and relative humidity of 8–10% and were instructed to drink 2 L in that time. Compared with the control condition (sea level; relative humidity 30–40%), we found an increase of mean plasma osmolality, mean urine osmolality, and urine specific gravity, indicating dehydration. Because dehydration is a risk factor in long-haul air travel, airlines should instruct passengers to take adequate fluids, while avoiding alcohol (diuretic action, cellular dehydration, drowsiness) and carbonated beverages (gastrointestinal distension).

Erythropoietin regulations in humans under different environmental and experimental conditions

In the adult human, the kidney is the main organ for the production and release of erythropoietin (EPO). EPO is stimulating erythropoiesis by increasing the proliferation, differentiation and maturation of the erythroid precursors. In the last decades, enormous efforts were made in the purification, molecular encoding and description of the EPO gene. This led to an incredible increase in the understanding of the EPO-feedback-regulation loop at a molecular level, especially the oxygen-dependent EPO gene expression, a key function in the regulation loop. However, studies in humans at a systemic level are still very scanty. Therefore, it is the purpose of the present review to report on the main recent investigations on EPO production and release in humans under different environmental and experimental conditions, including: (i) studies on EPO circadian, monthly and even annual variations, (ii) studies in connection with short-, medium- and long-term exercise at sea-level which will be followed (iii) by studies performed at moderate and high altitude.

Vascular endothelial growth factor in exercising humans under different environmental conditions

Abstract It was the aim of this study to investigate the time course of changes in the serum concentrations of vascular endothelial growth factor (VEGF) during a regular survival training programme combined with food and fluid deprivation and during a high altitude marathon run. We studied soldiers of the Austrian Special Forces performing survival training at sea-level and marathon runners of the Posta Atletica who crossed the border between Chile and Argentina at altitudes up to 4722 m. Baseline data collected before the 1-week of survival training showed that the soldiers had normal VEGF [n=8, 246.7 (SD 118.5) pg · ml−1] serum concentrations which remained unchanged during the course of the study. Before the high altitude marathon the subjects showed normal VEGF serum concentrations [178 (SD 84.5) pg · ml−1]. After the run VEGF concentrations were found to be significantly decreased [41.0 (SD 41.6) pg · ml−1, P < 0.01]. It was concluded that prolonged physical stress during normobaric-normoxia did not alter the VEGF concentrations whereas during severe hypobaric-hypoxia decreased VEGF serum concentrations were measured, at least temporarily, after prolonged physical exercise which might have been due to changes in production, release, removal and/or binding of circulating VEGF.

Improvement of metabolic syndrome markers through altitude specific hiking vacations

To study the influence of a 3-week hiking vacation at moderate (1700 m) and low altitude (LA) (200 m) on key-markers of the metabolic syndrome, 71 male volunteers (age 36–66 yr old) with the metabolic syndrome [according to the National Cholesterol Education Program’s Adult Treatment Panel III (NCEP-ATP III) — or World Health Organization (WHO) — definition] participated in the study and were randomly assigned into a moderate altitude (MA) group (1700 m, no. 36) and a low altitude (LA) group (200 m, no. 35). The 3-week vacation program included 12 moderate-intensity guided hiking tours [4 times/week, 55–65% heart rate maximum (HRmax)] with a total exercise time of 29 h plus moderate recreational activities. Both study groups had a comparable and balanced nutrition with no specific dietary restrictions. Anthropometric, metabolic and cardiovascular parameters were measured 10–14 days before vacation, several times during the 3-week vacation, 7–10 days and 6–8 weeks after return. All participants tolerated the vacation without any adverse effects. Body weight, body fat, waist-circumference, fasting glucose, total cholesterol, LDL-cholesterol (LDL-C), plasma fibrinogen, resting systolic and diastolic blood pressure were significantly decreased over time in both study groups. In the LA group, fasting insulin and homeostasis model assessment (HOMA)-index were significantly decreased one week after return. Relative cycle ergometry performance was significantly increased after return compared to baseline. In both study groups, waist-to-hip ratio (WHR), 2-h oral glucose tolerance test (OGTT), HDL-cholesterol (HDL-C), and triglycerides remained unchanged. The 3-week vacation intervention at moderate and LA had a positive influence on all key-markers of the metabolic syndrome. No clinically relevant differences could be detected between the study groups. A hiking vacation at moderate and LA can be recommended for people with stable, controlled metabolic and cardiovascular risk factors.

Allometry of visceral organs in living amniotes and its implications for sauropod dinosaurs

Allometric equations are often used to extrapolate traits in animals for which only body mass estimates are known, such as dinosaurs. One important decision can be whether these equations should be based on mammal, bird or reptile data. To address whether this choice will have a relevant influence on reconstructions, we compared allometric equations for birds and mammals from the literature to those for reptiles derived from both published and hitherto unpublished data. Organs studied included the heart, kidneys, liver and gut, as well as gut contents. While the available data indicate that gut content mass does not differ between the clades, the organ masses for reptiles are generally lower than those for mammals and birds. In particular, gut tissue mass is significantly lower in reptiles. When applying the results in the reconstruction of a sauropod dinosaur, the estimated volume of the coelomic cavity greatly exceeds the estimated volume of the combined organ masses, irrespective of the allometric equation used. Therefore, substantial deviation of sauropod organ allometry from that of the extant vertebrates can be allowed conceptually. Extrapolations of retention times from estimated gut contents mass and food intake do not suggest digestive constraints on sauropod dinosaur body size.

Bed rest and cognition: effects on executive functioning and reaction time

INTRODUCTION Executive functions are high-order aspects of cognition heavily dependent upon the prefrontal cortex. Both prefrontal cortex activity and executive function task performance are enhanced by participation in aerobic physical activity, suggesting that a lack of such activity during the bed rest model of prolonged weightlessness might induce executive function deficits. METHODS Twenty-four healthy males (ages 21-45 yr) undertook 60 d of head-down bed rest (-6 degrees) for the 2nd Berlin Bed Rest Study (BBR2-2). Three executive function tasks (Iowa Gambling Task, working memory, and flanker) and a reaction time task were administered before, during, and after bed rest. RESULTS Iowa Gambling Task scores were significantly worse during bed rest (1.7 +/- 6.9) than in other sessions (24.3 +/- 7.8). Effects on working memory and flanker task performance were less obvious, requiring practice effects to be considered. Reaction time was significantly slower after bed rest (569 +/- 42 ms) than in earlier tests (529 +/- 45 ms). There was also significantly less intrasubject variability in reaction time after bed rest, consistent with more efficient executive functioning at this stage. DISCUSSION Our results provide some evidence for a detrimental effect of bed rest on executive functioning. Whether this stems from a lack of aerobic physical activity and/or changes in the prefrontal cortex remains to be determined. Cognitive effects of bed rest could have implications for the planned human exploration of Mars, and for medical and lifestyle conditions with inadequate levels of aerobic physical activity.

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.

Blood volume regulating hormones response during two space related simulation protocols: Four-week confinement and head-down bed-rest

The volume of regulating hormones (renin, aldosterone, arginine vasopressin and atrial natriuretic factor), electrolytes and creatinine concentrations, and blood pressure were measured in two different four-week experimental protocols: respectively -6 degrees head-down bed-rest (5 subjects) and confinement (6 subjects). We observed a significant increase (P < 0.01 at D2 vs D-5) of systolic blood pressure during confinement and a different level of response for some hormones, especially for arginine vasopressin (300% increase during confinement instead of 50% during bed-rest). The renin-angiotensin-aldosterone system was enhanced during confinement and head-down bed-rest. In both conditions, we obtained a similar pattern of response for blood volume regulating hormones. During confinement, two main factors were inactivity and stress activation of the sympathetic nervous system. In the bed-rest study the response is principally due to the fluid shift and blood volume adaptation but it is not possible to exclude the role of inactivity and stress.