Venous pressure in man during weightlessness.

To determine whether the body fluid shift from the lower limbs toward the head that occurs during spaceflight leads to lasting increases of venous pressure in the upper body, venous pressure and hematocrit measurements were made on four astronauts before flight and 1 and 12 hours after recovery and compared with measurements in space. During the mission the hematocrit was elevated and the venous pressure lowered by 1 to 8 centimeters of water as compared with the preflight data. One hour after landing the hematocrit decreased, indicating a hemodilution, venous pressures were unexpectedly high, and a body weight loss of 4 to 5 percent was observed. Twelve hours later the venous pressures were the lowest recorded during the study. The fluid shift apparently takes place during the first several hours of spaceflight. Thereafter, the pressure in the peripheral veins and the central circulation is lower than that measured before flight.

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 degrees C. We found that water immersion is associated with a reversible increase in total urinary AQP2 excretion.

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.

Effects of dehydration on the vasopressin response to immersion.

Nine healthy volunteers underwent three experimental procedures in random order. The protocols were 4 h of thermal dehydration followed by 2 h of head-out water immersion, 4 h of thermal dehydration followed by 2 h of chair rest, and 6 h of rest in the supine position. Four hours of heat exposure (50 degrees C) resulted in a body weight loss of approximately 3.5%. Plasma osmolality rose by approximately 5 mosmol/kg, mean arterial pressure (MAP) decreased from 85 to 78 mmHg, and body temperature increased from 36.8 to 38.6 degrees C. As a consequence of the combined action of hypertonicity, hypovolemia, hypotension, and hyperthermia, plasma arginine vasopressin (AVP) increased from 2.1 to 8.1 pg/ml after 4 h thermal dehydration. Changes in body weight, plasma osmolality, body temperature, and MAP were similar after either a subsequent 2 h of water immersion or 2 h of chair rest. However, during chair rest plasma AVP remained elevated (8.4 pg/ml), whereas during immersion plasma AVP decreased from 8.1 to 4.7 pg/ml. This was probably due to the central hypervolemia induced by immersion. Our results support the hypothesis that central hypervolemia rather than hypotonicity is the primary stimulus for AVP suppression during water immersion in dehydrated subjects. During the early immersion period hypoosmolality might contribute to the AVP suppression.

Nathan Zuntz (1847-1920)--a German pioneer in high altitude physiology and aviation medicine, Part I: Biography.

Nathan Zuntz (1847-1920) was a key person in the history of high altitude physiology and aviation medicine. As a professor of animal physiology at the Landwirtschaftliche Hochschule (Agricultural University) in Berlin from 1881 until 1918, he carried out laboratory studies on the changes in metabolism at rest and during exercise. To this end he, together with August Julius Geppert, developed the famous "Zuntz-Geppert'schen Respirationsapparat" (Zuntz-Geppert respiratory apparatus) in 1885. In the early 1890's, Zuntz extended his research to the field of high altitude physiology. In view of the variety of questions, and despite considerable methodological problems, Zuntz first studied the effects of lowered PO2 on the human body in a Pneumatischen Kammer (hypobaric chamber). In 1893 the newly completed Capanna Regina Margherita, an international research station at the top of Monte Rosa, Italy (4,500 m), became the site of Zuntz's extensive field studies, where he worked together with his close co-worker Adolf Loewy (1862-1936), the Italian Angelo Mosso (1846-1910), and the Austrian Arnold Durig (1872-1961). For their investigations Zuntz invented the transportable Gasuhr (a gas exchange measuring device). In 1902 Zuntz and the Austrian Hermann von Schroetter (1870-1928) made two balloon ascents up to 5,000 m in Berlin. A synopsis of these studies was published by Zuntz in 1906: his famous book "Höhenklima und Bergwanderungen" (High altitude climate and mountain-touring). A few years later Zuntz undertook further expeditions to the Canary Islands (Pico de Teide), conducting studies in airships and planes until 1914. Zuntz retired in 1916 and died in Berlin on March 22, 1920.

Nathan Zuntz (1847-1920)--a German pioneer in high altitude physiology and aviation medicine, Part II: Scientific work.

For over 52 years, the work of Nathan Zuntz (1847-1920) covered an amazingly wide spectrum of research fields; metabolism, nutrition, respiration, blood gases, exercise, and high altitude physiology were the main themes. Zuntz achieved fame for his invention of the Zuntz-Geppert respiratory apparatus in 1886 and the first Laufband (treadmill) in 1889. To this experimental setup Zuntz later added an X-ray apparatus in 1914 to determine the changes in heart volume during exercise. Moreover, he constructed a climate chamber to study exercise under varying and sometimes extreme climates. For field studies Zuntz invented a transportable Gasuhr (dry gas measuring device). Zuntz was the first to describe the difference between laboratory data gained in a hypobaric chamber and the measurements at high altitude. He found that the barometric formula is not applicable in the field. Two balloon expeditions in 1902 by Zuntz and his pupil, v. Schroetter, marked the step from terrestrial physiology towards aviation medicine. An outline of the development of scientific aviation in Berlin from 1880-1918 elucidates how closely the aviation union, army, and scientific departments were connected with and dependent upon each other. In cooperation with these institutions Zuntz and v. Schroetter constructed an oxygen supply system and planned a pressure cabin for extreme altitudes above 10,000 m, a forerunner of modern systems in aviation and astronautics. In 1912, Zuntz and v. Schroetter each published papers on aviation medicine, both publications internationally unique in style and extent. Zuntz's work in its empirical approach was the counterpart to the established formal mathematical-physical reductionism of the German Physiological Society.(ABSTRACT TRUNCATED AT 250 WORDS)

Hormonal changes during a 20-week confinement.

BACKGROUND: When the European Space Agency planned the EUROMIR'95 long-duration flight with a European astronaut on board the Russian orbital MIR station, it organized simultaneously a ground simulation, called the Human Behaviour Study, of this manned space mission. The ground simulation was a confinement experiment, and this paper describes the changes in volume-regulating hormones that occurred during and after 20 weeks of confinement. METHODS: In a normobaric diving chamber, 3 subjects were confined for 135 d. Arterial pressure, plasma concentrations of blood volume-regulating hormones (active renin and arginine-vasopressin), and urinary variables (aldosterone, arginine-vasopressin, and metabolites of catecholamines) were measured before, during, and after confinement. RESULTS: Arterial pressure was increased from week 1 until week 15 of confinement, while heart rate was elevated from week 6 until the end of the simulation. Plasma active renin was elevated throughout the confinement (after week 6). Urine volume increased transitively on the first 2 d of confinement. CONCLUSIONS: The results obtained during this long-term confinement experiment have major importance regarding concerns about spaceflight and bed rest data, because we observed hormonal changes during the experiment that normally are assigned to the fluid shift that occurs in weightlessness or in the head-down tilt position (i.e., an increase of renin, an increase of urinary volume during the first two days, and a decreased urinary cyclic guanosine monophosphate.

Current views and future programs in cardiovascular physiology in space.

The volume shift of 2000 cm3 from the lower to the upper part of the human body during weightlessness gave rise to theoretical and practical questions which are addressed in this communication. The analysis revealed that the mobilized fluid reduced the interstitial fluid of the lower extremities by 40%. Applying the current ideas in the field of interstitial tissue physiology to these problems, one must conclude that the fluid displacement can only be brought about by a change of the interstitial tissue compliance. Based on the observations made by the astronauts and on our working hypothesis, a method was proposed to follow the fluid migration and to measure the tissue compliance in man. Results are reported from experiments under terrestrial conditions. They show that the tissue compliance indeed can be modulated. Applying the method in space can eventually help to clarify several concepts in terrestrial physiology.

Differences in the autonomic reactivity pattern to psychological load in patients with hypertension and rheumatic diseases.

As a ground-based reference study to a space experiment, a complex psychophysiological test battery (heart rate, blood pressure, skin conductance, finger temperature, forearm electromyogram during psychological loading task solving) was developed and first applied on two cohorts of subjects with different blood pressure levels at rest (53 hypertensive patients, and 30 normal controls). The data describing autonomic reactivity could be differentiated by cluster analysis into four Autonomic Outlet Types (AOT). The method was subsequently applied to 20 patients with systemic Lupus erythematosus and 13 subjects with rheumatoid arthritis to work out a discriminant function for classifying and testing it's validity. The AOT classification of all subjects showed a significant correlation with the different types of diseases.

Changes in the autonomic reactivity pattern to psychological load under long-term microgravity--twelve men during 6-month spaceflights.

A complex psychophysiological test battery was applied to twelve subjects during long-term spaceflights. This experiment was designed to assess the psychophysiological reactivity to acute psychological stressors. A set of noninvasive physiological measurements (electrocardiogram, electromyogram, blood pressure, skin conductance, peripheral skin temperature) was used to describe the reactivity of the autonomic nervous system and the cardiovascular system to an induced series of changes between mental activity load and quiet relaxation. It could be shown that under space conditions the subjects react differently than on earth. On the basis of significantly lower heart rates we concluded that an extended parasympathetic cardial influence is present during later periods of long-term space flights. The peripheral skin conductance reactivity, however, indicated a tendency to higher peripheral sympathetic tonus under microgravity. Assuming individually different pathways of sympathetic-parasympathetic traffic under psychological stress, the whole set of data could be classified into autonomic outlet types (AOT) based on clinical reference data. Most of the subjects changed their AOT during flight. After flight the subjects eventually fell back into their pre-flight patterns, but seven of twelve subjects showed a significantly different autonomic system reactivity at least once after landing that was similar to that of hypertensive patients, indicating an extended sympathetic overshoot directly post-flight. In conclusion it is assumed that sympathetic effects in one measurement do not exclude less sympathetic or even parasympathetic effects in others during adaptation to extreme environments.

Feeding patterns of endurance athletes.

Feeding pattern was studied in 13 long distance runners, eight cyclists and eight sedentary men. The timing of the food and fluid intakes, the kind and the amount of food and fluids taken, the body weight (BW), and the exercise schedules were recorded on 3 or 4 successive days under ad libitum conditions of feeding and drinking. The subjects remained in energy and water balance, since the BW measured in the morning during the observation periods did not change significantly. The total caloric intake was 13 876 kJ per day in the runners and 26 282 kJ per day in the cyclists, exceeding the estimated basic metabolic rate by 103% and 250% respectively. The total water intakes were 33 and 36 ml . kg-1 . 24 h-1. The athletes consistently showed a nibbling pattern, characterized by frequent eating and drinking (average 8-10 per day). In the runners 63% of eating and drinking were synchronized, in the cyclists only 49% (p less than 0.01). In both groups drinking occurred most frequently in the morning, at noontime and in the evening. After 8 p.m. 45% of the total daily fluid intake occurred. In all likelihood the fluid intake followed an underlying circadian rhythm. The total intake frequency was determined by the total caloric needs.

Sex-dependent changes in plasma globulins in women and men exposed to heat stress.

Healthy, sedentary women and men, aged 20 to 30 years, were exposed to the same degree of intermittent heat stress in a sauna bath. Blood samples were taken immediately before and at various intervals after heat exposure. The concentrations and intravascular masses of IgG, IgA, IgM, alpha1-antitrypsin, transferrin and alpha2-macroglobulin were determined by the radial immunodiffusion technique and by the measurement of plasma volume. Losses in body weight and plasma volume were lower in women than in men. The globulin concentrations increased significantly in both sexes after heat exposure. The sum of the masses of individual globulins increased only in women, a change interpreted as globulin shifts from the interstitial into the vascular space. Whereas it is unlikely that sex-dependent differences in these shifts are due to changes in vascular permeability, it seems that the protein composition of the lymphatic fluid entering the vascular space plays an important role in these shifts.

Plasma volume, albumin and globulin concentrations and their intravascular masses. A comparative study in endurance athletes and sedentary subjects.

Plasma volume, hematocrit, intravascular protein concentration, colloid osmotic pressure and the intravascular mass of proteins were measured in 49 sedentary subjects and 40 endurance athletes (long-, middle distance runners, cyclists). The plasma volume in sedentary subjects was 42.7(35.8-51.7) ml/kg body weight (BW) as compared to 54.6(46.7-65.9) ml/kg BW in athletes. The protein concentrations were 71.0 (66.5-77.1) g/l in sedentary subjects and 69.0 (64.8-75.2) g/l in athletes. The respective numbers for the hematocrit were 44.6 (40.1-49.25)% and 42.8 (38.2-49.6)%, for the colloid osmotic pressure 38.0 (36.0-40.5) cm H2O (n=35) and 30.0 (25.0-34.4) cm H2O (n=31), for the intravascular mass of proteins 3.09 (2.45-4.01) g/kg BW and 3.75 (3.31-4.67) g/kg BW. All differences were statistically significant at least on the 5% level. The physiological consequences for athletes of having a lower hematocrit and lower protein concentration but a higher intravascular mass of proteins (+22%) for their waterbalance as well as for their dietary protein intake are discussed. Endurance exercise stimulates mainly the synthesis of albumin and globulins produced by the liver resulting in an expansion of the PV. The protein synthesis of the RES does not seem to respond to exercise stimulus.

Fluid control mechanisms after exercise dehydration.

Since the osmocontrol- (osmolality), the renin-angiotensin-(PRA), and the volume control-(central venous pressure, CVP) systems are involved in the maintainance of the salt-water balance, we investigated the pattern of these parameters in the recovery period after exercise dehydration in 13 well trained long-distance runners. On average, after exercise the athletes had lost 3.1% of their body weight (BW). After eating and drinking the BW was still 1.3% below control value, indicative of continuing deficits. Plasma osmolality increased, however, from an average value of 286-290 mosmol/kg after exercise as well as postprandially, but the change was not significant. PRA-Levels rose significantly from 0.167-0.599 ng/ml . h after exercise and decreased to 0.333 ng/ml . h postprandially. CVP was significantly altered after exercise (-3.5 cm H20) as well as postprandially (-2.4 cm H20). The results suggest that the salt-water balance is maintained by the interplay of all the three systems. In conflicting situations, however, as when intercompartmental water- and solute-shifts take place during the recovery period, the volume control system triggered off by the CVP is the dominant corrective response to the prevailing deficits.U

Oxygen uptake in whole-body vibration exercise: influence of vibration frequency, amplitude, and external load.

Vibration exercise (VbX) is a new type of physical training to increase muscle power. The present study was designed to assess the influence of whole-body VbX on metabolic power. Specific oxygen uptake (sVO(2)) was assessed, testing the hypotheses that sVO(2) increases with the frequency of vibration (tested in 10 males) and with the amplitude (tested in 8 males), and that the VbX-related increase in sVO(2) is enhanced by increased muscle force (tested in 8 males). With a vibration amplitude of 5 mm, a linear increase in sVO(2) was found from frequencies 18 to 34 Hz (p < 0.01). Each vibration cycle evoked an oxygen consumption of approximately 2.5 micro l x kg(-1). At a vibration frequency of 26 Hz, sVO(2) increased more than proportionally with amplitudes from 2.5 to 7.5 mm. With an additional load of 40 % of the lean body mass attached to the waist, sVO(2) likewise increased significantly. A further increase was observed when the load was applied to the shoulders. The present findings indicate that metabolic power in whole-body VbX can be parametrically controlled by frequency and amplitude, and by application of additional loads. These results further substantiate the view that VbX enhances muscular metabolic power, and thus muscle activity.

Influence of prolonged physical exercise on plasma volume, plasma proteins, electrolytes, and fluid-regulating hormones.

Fluid-regulating hormones [arginine vasopressin (AVP) and aldosterone] as well as electrolytes, plasma volume (PV), and plasma proteins were studied in 16 well-trained male amateur runners (mean age 31.8 years) before t0), immediately after (t1), and 60 min (t2) and 22 h (t3) after a marathon run. Immediately after the run PV was significantly decreased by 12.1%, whereas the concentration of plasma proteins increased by 13.9%, sodium by 5.8 mMol.l-1, and potassium by 0.58 mMol.l-1, respectively. Aldosterone increased by 1089 pg/ml and AVP by 9.0 pg/ml. PV was significantly increased 22 h after the run by 10.6% (P less than 0.001) and plasma proteins were increased by 1.0% (P greater than 0.05), whereas aldosterone and AVP as well as electrolytes returned to control values. At t1, and particularly at t2 and t3, the total plasma protein concentration increased much more than could have been expected from changes of PV. It is suggested that this phenomenon was caused by an influx of proteins into the vascular space. This might also be the reason for the expanded PV especially in the longer recovery period at t3. The volume-regulating hormones (AVP and aldosterone) may play an important role during and immediately after the run but not in the longer recovery period (t2 and t3).

Body weight and body composition during sixty days of isolation.

The aim of this study was to find the mechanisms leading to the weight changes that have frequently been observed during isolation and in spaceflight. Isolation studies with small groups impose limitations on the measurements that can be performed to simple, noninvasive methods. In this study the simple parameters of body weight and body composition, along with sodium and potassium excretion, were determined in three males and one female subject before, during and after 60 days of isolation. Our assumption was that application of these simple methods might provide valuable information, when measurements are done on a daily basis and when the pre- and post-isolation periods are taken into account. Three subjects gained weight before isolation, while one lost weight. All four subjects gradually lost weight during isolation, 1-4% of their weight on the first day of isolation. During the first post-isolation week weight remained stable. During isolation one subject lost body fat, whereas another lost body water and lean body mass, but gained body fat. The urinary electrolyte excretion pattern reflected the changes in body composition: sodium loss coincided with a decrease of total body water, and potassium loss with a decrease of lean body mass. The Bioelectrical Impedance Analysis method, used in defining changes in body composition, provided data in good agreement with those obtained with the double-labeled water method. The results reported here are in agreement with observations reported by other investigators with respect to the body weight changes and the body composition. However, it is still not understood why some subjects lose fat and others gain fat under identical conditions. Psychological factors may be involved in these individual differences. Two further points have become clear from these studies: (1) the pre- and post-isolation periods should be taken into account, (2) urinary electrolyte excretion must be seen in the context of changes in body composition, not only in the context of kidney function.

Tissue compliance in superficial tissues along body axis in man.

A previously described miniature plethysmograph which allowed the measurement of tissue volumes in superficial tissues was enclosed in a small plexiglass chamber and attached to the frontal area, sternum, dorsum and the tibia. The tissues interposed between bone and skin underneath the chamber were exposed to pressures between +/- 3 and +/- 15 mmHg in order to test tissue deformability. The pressure application induced within the first 5 s a fast component of tissue deformation comprising between 75-90% of the total deformation followed by a slow component which lasted till the end of the pressure application. The highest deformability was found in the tissues of the sternum and dorsum whereas the stiffest tissues were in the pretibial area. Assuming the tissue deformation is due to a translocation of fluid into or out of the pressurized tissue, the tissue compliance was calculated. This calculated tissue compliance was 19.2 ml . 1,000 ml-1 . mmHg-1 in the sternum and 6.4 ml . 1,000 ml-1 . mmHg-1 (P < 0.01) in the pretibial area applying a pressure of +/- 3 mmHg. The differences observed are due to the morphological arrangement of the tissue fibres which in turn have to counteract the gravity forces to which the tissues are usually exposed during upright standing.