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1 Clinic of Anaesthesiology and 4 Institute of Surgical Research, University of Munich, 81366 Munich, Germany; 2 Department of Paediatrics, Imperial College School of Medicine, London SW10 9NH, Great Britain; and 3 Institute of Biomedical Problems, Moscow 123007, Russia
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ABSTRACT |
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 TOP
 ABSTRACT
 INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES
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We used venous congestion strain
gauge plethysmography (VCP) to measure the changes in fluid filtration
capacity (Kf), isovolumetric venous pressure
(Pvi), and blood flow in six volunteers before, on the
118th day (D118) of head-down tilt (HDT), and 2 days after remobilization (Post). We hypothesized that 120 days of HDT cause significant micro- and macrovascular changes. We observed a significant increase in Kf from 3.6 ± 0.4 × 10
3 to 5.7 ± 0.9 × 103
ml · min1 · 100 ml1 · mmHg1 (+51.4%;
P < 0.003), which returned to pretilt values (4.0 + 0.4 × 103
ml · min1 · 100 ml1 · mmHg1) after remobilization.
Similarly, Pvi increased from 13.4 ± 2.1 mmHg
to 28.9 ± 2.8 mmHg (+105.8%; P < 0.001) at D118
and was not significantly different at Post (12.4 ± 2.6 mmHg).
Blood flow decreased significantly from 2.3 ± 0.3 to
1.3 ± 0.2 ml · min1 · 100 ml
tissue1 at D118 and was found elevated to 3.4 ± 0.7 ml · min1 · 100 ml tissue1
at Post. We believe that the increased Kf is
caused by a higher microvascular water permeability. Because this may
result in edema formation, it could contribute to the alterations in
fluid homeostasis after exposure to microgravity.
microgravity; fluid filtration capacity; microvascular permeability; head-down tilt
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INTRODUCTION |
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TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES
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COSMONAUTS AND
ASTRONAUTS returning from a prolonged period in microgravity
frequently show orthostatic dysregulation, which can cause
cardiovascular instability and collapse of the subject in response to a
postural challenge (2, 10, 14). A 6° head-down tilt
(HDT) is an established model of simulated weightlessness (18). Profound fluid shifts occur within hours of exposure
to both microgravity and simulated microgravity environments, with an
initial cephalic fluid shift causing relative hypervolemia in the upper
part of the body (9, 22). This was found to be
counteracted by a compensatory fluid loss over the ensuing week,
resulting in a 14-16% reduction in plasma volume
(8). Thereafter, plasma volume remained relatively
constant, and hematocrit stabilized at a lower value as part of the
well-documented space-related anemia (22). The initial
edema, which is always observed in both simulated and true
microgravity, may be due to changes in the forces described by the
Starling equation (16). However, to date, there have been
no reports of systematic investigations into changes in the
microvascular permeability coefficients, the osmotic reflection
coefficient (
), and the hydraulic permeability during microgravity exposure.
We sought to address these questions by using a venous congestion strain gauge plethysmography (VCP) technique and protocol (13) that enables assessment of changes in both microvascular and compliance characteristics of lower limbs. We studied fluid filtration capacity (Kf), an index of microvascular water permeability, and isovolumetric venous pressure (Pvi), which we used to describe the dynamic balance of Starling forces at the microvascular interface. Altered vascular compliance was also thought to be a factor that might contribute to the control of local transvascular forces. Venous compliance has been shown to increase during the first 3-4 wk of HDT (7), as well as after exposure to actual microgravitation (21). However, subsequent studies showed that, after an initial increase in compliance, the value started to decrease after a transient plateau phase when the HDT period was increased to 6 wk (18). We hypothesized that 120 days of continuous 6° HDT causes significant micro- and macrovascular changes, namely an increase in microvascular permeability, a decrease in arterial blood flow, and, contrary to previous reports, also a decrease in venous compliance in the calves of human volunteers.
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METHODS |
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ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES
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The study was approved by the local ethical committee of the Russian Space Agency and the Institute of Biomedical Problems, Moscow, responsible for the medical care of cosmonauts. The experiments were part of a joint research activity of the Russian Space Agency, the European Space Agency, the Japanese Space Agency, and the German Space Agency.
The investigations were performed on six healthy 25- to 42-yr-old male volunteers (age 30.8 ± 7.5 yr, weight 79.5 ± 7.1 kg, height 180.7 ± 5.2 cm; means ± SE) who gave written, informed consent. Subjects were selected from more than 300 volunteers after an extended physical examination procedure as used by the Russian Space Agency before entering a volunteer into the cosmonaut training program.
All subjects were under permanent medical supervision during the 6-mo period encompassing the 120-day test. After the control period of 7 days, all subjects were placed on a modified hospital bed, which sustained 6° HDT. This position was strictly maintained throughout the 120 days, including sleep, food intake, and daily hygiene, with the exception of a few experiments requiring an upright position. VCP measurements were conducted 7 days before the start of the HDT, on the 118th day of the 120-day HDT, and 2 days after remobilization.
VCP. We used a computer-assisted strain gauge plethysmography technique and a small cumulative pressure step protocol to determine Kf from the relationship between congestion cuff pressure and fluid filtration into the limb (13). The studies were bilateral and the strain gauges (measurement accuracy < 5 µm) fixed onto the limbs at a site of known circumference. The gauges were then pre-tensioned such that the calibration procedure, comprising application of cumulative, known, small (~2 mm) increases and decreases in length, gave a uniform and repeatable signal. The gauges were then rebalanced in the Wheatstone bridge circuit at this ideal tension. After an equilibration period of 15 min, the venous congestion cuff, placed around the thigh, was inflated by using six to eight small (8.0-mmHg) cumulative pressure steps. The highest congestion pressure used did not exceed the subjects' diastolic blood pressure.
Determination of Kf and venous compliance.
Kf and venous compliance were determined by
using the method previously described by Gamble et al.
(13). When cuff pressure is increased, by small cumulative
steps, to a value in excess of the subject's existing venous pressure
at the level of the strain gauge, a rapid volume change is recorded,
which achieves a steady-state value [asymptotic volume (Va)]
at each pressure. Va reflects filling of the compliant vessels of the
limb. Each compliance response to a small pressure step can, typically,
be described by an exponential function, with a time constant <13 s
(4, 13). Once the congestion pressure also exceeds the value required to induce net fluid filtration, the volume increase comprises two components: the rapid initial compliance function together with a slow, steady-state volume change attributable to fluid
filtration. The analysis program uses an exponential fitting routine,
which allows us to distinguish between the two components. When the
vascular compliance data are plotted with respect to applied pressure,
a curvilinear relationship is usually seen, which reflects the
compliance of the low-pressure vessels and the surrounding tissue. The
relationship between cuff pressure and fluid filtration is linear, once
the existing balance of the Starling forces is exceeded. The slope of
this function is the Kf, and the intercept
represents the Pvi, the cuff pressure that has to be
applied to induce net fluid filtration into the tissue (13). This pressure intercept, which is the product of the
and plasma colloid osmotic pressure, is equivalent to the effective osmotic pressure at the microvascular interface in the calf.
a) to the limb was determined from the
initial slope of the volume response to a large pressure step (>33
mmHg). Blood flow was routinely measured before and then after
completion of the small cumulative pressure step protocol (12).
Brachial arterial blood pressure and heart rate, oxygen saturation,
end-tidal CO2, respiration rate, skin temperature, and room
temperature were measured every 2 min throughout the protocol by using
a Siemens SC 9000 monitor (Siemens, Munich, Germany) to ensure a
comparable physiological state at the different measurement points. At
the end of the study, all data were saved to disk for subsequent
off-line analysis.
Measurements were obtained 7 days before (D0) and on the 118th day of
6° HDT (D118) as well as 2 days after remobilization (Post).
Statistical analysis.
Data are given as mean values ± SE. We obtained bilateral
measurements of Kf, Pvi, and
a, of which the mean value was taken as an individual data point
for each subject.
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RESULTS |
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TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES
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The baseline hemodynamic data obtained in the supine position,
which are given in Table 1, show that no
significant changes in heart rate; systolic, mean, and diastolic blood
pressure; or respiration rate and oxygen saturation were seen at the
three stages of the study. End-tidal CO2, however, was
significantly lower after 118 days HDT (Table 1).
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VCP.
After 118 days of HDT, there was a significant reduction in calf
circumference (P < 0.001; RmA). However, after only 2 days of remobilization, the calf circumference had returned to a value that was not significantly different from the pre-HDT control value
(Table 2). Limb a decreased
significantly from 2.3 ± 0.3 to 1.3 ± 0.2 ml · min1 · 100 ml tissue1
at D118 and was found elevated to 3.4 ± 0.7 ml · min1 · 100 ml tissue1
2 days after remobilization (Fig. 1).
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3 to 5.7 ± 0.9 × 103 ml · min1 · 100 ml1 · mmHg1 (+51.4%;
P < 0.003) at D118 which decreased to 4.0 ± 0.4 × 103 ml · min1 · 100 ml1 · mmHg1 2 days after
remobilization (Fig. 3).
Pvi also increased from a value of 13.4 ± 2.1 mmHg
before HDT to 28.9 ± 2.8 mmHg (+105.8%; P < 0.001) at D118 and decreased to 12.4 ± 2.6 mmHg at 2 days post-HDT (Fig. 4). Thus,
within 2 days of remobilization, both Kf and
Pvi values were not significantly different from the D0 control values.
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a, and Pvi at any of the time points measured.
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DISCUSSION |
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ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES
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Our data showed that, after 118 days, HDT steady-state peripheral arterial blood flow and venous compliance were decreased and both Kf and Pvi were elevated. However, all measured parameters showed an almost complete restitution 2 days after the return from simulated microgravity.
Kf and Pvi.
Kf, the filtration capacity, is the product of
the total surface area available for fluid filtration per 100 ml soft
tissue and the permeability of the microvessels per unit surface
area. It describes the increase in fluid filtration after a local
elevation of microvascular hydrostatic pressure induced by a venous
congestion pressure cuff (13). Pvi is the
equilibrium pressure at the microvascular interface, which has to be
exceeded to achieve net fluid filtration. It is equivalent to the
product of plasma colloid osmotic pressure and the coefficient ()
that describes the effective microvascular permeability to proteins.
The relationship between these parameters is described by the Starling
equation (20)
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(1) |
the colloid osmotic (oncotic) pressures, and the subscripts c and t
the intraluminal and interstitial microvascular environments, respectively. In the light of Eq. 1, the higher
Kf values found on the 118th day, in the present
study, could be caused by 1) an increased microvascular
permeability to water (filtration coefficient, Kf), 2) an increased surface area
available for fluid filtration, or 3) a decreased lymphatic flow.
By contrast, the observed changes in Pvi could be
attributed to 1) a decrease in microvascular permeability to
proteins, i.e., an increase in the protein reflection coefficient ()
or 2) either a systemic or a local increase in plasma
oncotic pressure.
Leach et al. (17) used increased microvascular
permeability to water to explain the discrepancy in the fluid balance
of astronauts after their exposure to microgravity environments. Many
factors have been shown to cause such changes, in particular free
oxygen radicals, activated leukocytes or thrombocytes, and a variety of
mediators like tumor necrosis factor-
and interleukins. The data
from this study presented by Chouker et al. (3) confirms this hypothesis, and we believe, in agreement with Leach et al., that
an increased permeability to water is the most likely cause of the
observed increased Kf. Other mechanisms,
however, also have to be considered.
Because Kf is the product of the mean
permeability per unit surface area and the total surface area available
for filtration, an increase in the available area is a theoretical
cause for the higher Kf after 118 days. In an
earlier publication (11), our laboratory provided evidence
that, in healthy supine controls, the microvascular surface area
available for filtration assessment was not influenced by challenges
giving rise to extremes of vasomotor control. We deduced that, in
healthy controls, the whole microvascular surface was available for
assessment using this technique. Studies have shown that, after 30 days
of HDT, leg volume decreased by 9.9%; half of this could be attributed
to the muscle compartment (7, 15). Nuclear magnetic
resonance investigations corroborated these observations, showing a
decrease in muscle mass of 8.2 ± 1.2% in control subjects,
compared with only 5.8 ± 1.5% in a group using countermeasures.
These changes correlated well with observations on venous
distensibility that were made on the same subjects (18). It is now well established that calf muscle mass decreases in both real
as well as simulated weightlessness, and the significant reduction in
calf circumference during exposure to HDT and hypokinesia found in this
study is in good agreement with previous reports. With respect to the
changes in Kf, however, it is noteworthy that in
animal experiments the number of capillaries decreased in skeletal muscle during the exposure to microgravity (15). Thus the
surface area available for fluid filtration decreases, resulting in a lower measured Kf. With this in mind, the
increased Kf at the 118th day can therefore not
be explained by the changes in surface area but most likely represent
an underestimation of the true increase in microvascular permeability.
Because no morphometric data are currently available on the change in
the actual number of microvessels perfused in humans after exposure to
microgravity, more experiments are needed to confirm this hypothesis.
A decrease in lymphatic flow is another mechanism that might contribute
to the measured increased net fluid flux, as described by
Kf. The basic limb lymph flow during rest is
known to be very low indeed. Moreover, the changes that might occur in
response to factors that could upregulate it, like the application of a venous congestion pressure, may take hours to reach a new steady state
(1). Although unlikely, the contribution of a reduced lymphatic flow to the measured increase in Kf
has to be considered and could in part explain the rapid normalization
of the Kf value after remobilization.
Pvi.
There have been no direct measurements of the plasma protein
permeability coefficient during prolonged exposure to either real
or simulated microgravity environments. In the present study, venous
plasma oncotic pressure was not measured. Hsieh et al. (16), however, showed that plasma oncotic pressure
increased from 23 to 30 mmHg after 14 days of 6° HDT. Because we have
previously shown that an increased plasma oncotic pressure causes a
similar change in Pvi (5), we believe that
this may be the main cause for the elevated Pvi found at
D118. Moreover, we have postulated that high values of Pvi
may be associated with factors giving rise to a simultaneous decrease
in microvascular plasma flow and an increase in the filtration force of
the hydrostatic pressure of the intraluminal environment. Such
changes might be brought about by venular leukocyte-endothelial
interaction, leading to a flow-limited exchange, which results in a
high local oncotic pressure (6) and hence a high
Pvi.
Venous compliance. There have been a number of studies on the changes in venous compliance after periods of 6° HDT. It has been shown that compliance increases during the first weeks of both HDT and actual weightlessness (7, 19). Louisy et al. (19) investigated the venous outflow dynamics after 41 days of HDT. They found that, after an increase in venous compliance by 67% of the prebedrest value, the compliance decreased after the 26th day of HDT to a value that was only slightly higher than that obtained pretilt. Louisy et al. suggested that studies on longer periods of HDT were necessary to clarify the late changes in venous compliance that they had observed. We did not investigate the early changes in venous compliance; our data, however, support the contention that the late decrease in venous compliance described by Louisy et al. continues, and, on the 118th day, venous distensibility is in fact reduced compared with control values. Louisy et al., using an optoelectronic sensor, also showed that leg volume decreased rapidly within 24 h of imposing HDT and continued to decrease in the ensuing 3 wk to a 13% reduction on the 41st day of HDT. They speculated that the initial change in leg volume may be due to a cephalic intravascular fluid shift followed by changes in interstitial and later intracellular fluid volume. The decrease in leg volume only correlated with the changes in venous compliance during the first phase of the study period (up to day 28). This observation supports our contention that there may be a time-related change in venous compliance during simulated microgravity. Orthostatic intolerance after prolonged exposure to microgravity has been frequently attributed to the increase in venous compliance (7, 19). Our observation and those of Louisy et al., however, suggest that this may not be the case for periods of more than 40 days. After this period, other mechanisms, like the cardiovascular deconditioning syndrome or the suggested reduction in venous smooth muscle tone, may play a more important role (19).
Changes in arterial blood flow after 118 days of 6° HDT.
In a 41-day HDT study, Louisy and co-workers (19) showed
that arterial blood flow decreased from 2.1 to 1.1 ml · min1 · 100 ml tissue1
on the 40th day to reach a significantly higher value of 2.8 ml · min1 · 100 ml tissue1 on the third day of
remobilization. We also found a reduction in arterial blood flow after
118 days of HDT; moreover, the values reached a significantly higher
level after the volunteers had resumed normal daily activity. The
absolute values obtained in both studies were comparable but low with
respect to previous reported values in healthy volunteers
(12). We suspect that remaining immobile in a 6° HDT for
118 days results not only in muscular atrophy but also in a
downregulation of the skeletal muscle blood flow of the leg.
Because we found no obvious correlation between the changes in
Kf and blood flow, we assume that the changes in
the macro- and microcirculation occur independently from each other.
Limitations of the study. In this study, no representative control group was included. This was due to the extreme nature of the study but limits the results because the observed changes in microvascular parameters could also be due to alterations in the experimental conditions over time. Although great care was undertaken to not change the study environment and conditions, this could, however, not be wholly excluded because of the length of the study period.
In summary, the present study provides evidence that profound microcirculatory changes occur during simulated microgravity. The increase in Kf and Pvi, as well as the decrease in venous compliance, may play a role in the fluid shift and the orthostatic dysregulation encountered after exposure to microgravity. In addition, because cosmonauts and astronauts are exposed to a high radiation load, which is known to increase microvascular permeability, the routine measurement of the permeability values characterized by Kf and seems a
valuable procedure for the assessment of the microcirculatory risks
associated with these procedures. This appears to be of even greater
relevance in view of long-term missions planned both by the NASA and
the Russian Space Agency.
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ACKNOWLEDGEMENTS |
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This study was supported by Deutsches Zentrum für Luft- und Raumfahrt Grant 50-WB9654 and by Siemens AG, Germany.
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FOOTNOTES |
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Address for reprint requests and other correspondence: F. Christ, Clinic of Anaesthesiology, Ludwig Maximilians Univ. Munich, 81366 Munich, Germany (E-mail: frank.christ{at}ana.med.uni-muenchen.de).
The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
Received 15 April 2001; accepted in final form 27 July 2001.
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REFERENCES |
|---|
|
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES
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|---|
1.
Aukland, K,
and
Reed RK.
Interstitial-lymphatic mechanisms in the control of extracellular fluid volume.
Physiol Rev
73:
1-78,
1993
2.
Buckey, JC, Jr,
Lane LD,
Levine BD,
Watenpaugh DE,
Wright SJ,
Moore WE,
Gaffney FA,
and
Blomqvist CG.
Orthostatic intolerance after spaceflight.
J Appl Physiol
81:
7-18,
1996
3.
Chouker, A,
Thiel M,
Baranov V,
Meshkov D,
Kotov A,
Peter K,
Messmer K,
and
Christ F.
Simulated microgravity, psychic stress, and immune cells in men: observations during 120-day 6° HDT.
J Appl Physiol
90:
1736-1743,
2001
4.
Christ, F,
Gamble J,
Baschnegger H,
and
Gartside IB.
Relationship between venous pressure and tissue volume during venous congestion plethysmography in man.
J Physiol (Lond)
503:
463-467,
1997[ISI].
5.
Christ, F,
Gamble J,
Raithel P,
Steckmeier B,
and
Messmer K.
Perioperative Veränderungen der Flüssigkeitsfiltrationskapazität bei gefässchirurgischen Patienten.
Anästhesist
48:
9-18,
1999[Medline].
6.
Christ, F,
Gartside IB,
Kox WJ,
and
Gamble J.
The assessment of the microcirculatory effects of dobutamine using mercury in Silastic strain gauge plethysmography in man.
Postgrad Med J
67, Suppl1:
S42-S50,
1991.
7.
Convertino, VA,
Doerr DF,
Mathes KL,
Stein SL,
and
Buchanan P.
Changes in volume, muscle compartment and compliance of the lower extremities in man following 30 days of exposure to simulated microgravity.
Aviat Space Environ Med
60:
653-658,
1989[Medline].
8.
Convertino, VA,
Engelke KA,
Ludwig DA,
and
Doerr DF.
Restoration of plasma volume after 16 days of head-down tilt induced by a single bout of maximal exercise.
Am J Physiol Regulatory Integrative Comp Physiol
270:
R3-R10,
1996
9.
Fortney, SM,
Hyatt KH,
Davis JE,
and
Vogel JM.
Changes in body fluid compartments during a 28-day bed rest.
Aviat Space Environ Med
62:
97-104,
1991[Medline].
10.
Fritsch Yelle, JM,
Whitson PA,
Bondar RL,
and
Brown TE.
Subnormal norepinephrine release relates to presyncope in astronauts after spaceflight.
J Appl Physiol
81:
2134-2141,
1996
11.
Gamble, J,
Christ F,
and
Gartside IB.
Human calf pre-capillary resistance decreases in response to small cumulative increases in venous congestion pressure.
J Physiol (Lond)
507:
611-617,
1998
12.
Christ, F,
Gamble J,
Baranov V,
Kotov A,
Gartside IB,
Nehring I,
and
Messmer K.
Microvascular fluid filtration capacity (Kf) and blood flow during various degrees of tilt.
Eur J Med Res
4:
264-270,
1999[Medline].
13.
Gamble, J,
Gartside IB,
and
Christ F.
A reassessment of mercury in Silastic strain gauge plethysmography for the microvascular permeability assessment in man.
J Physiol (Lond)
464:
407-422,
1993
14.
Grigoriev, AI,
and
Egorov AD.
Physiological aspects of adaptation of main human body systems during and after spaceflights.
In: Advances in Space Biology and Medicine. Stamford, CT: JAI Press, 1992, p. 43-82.
15.
Hikida, RS,
Gollnick PD,
Dudley GA,
Convertino VA,
and
Buchanan P.
Structural and metabolic characteristics of human skeletal muscle following 30 days of simulated microgravity.
Aviat Space Environ Med
60:
664-670,
1989[Medline].
16.
Hsieh, ST,
Ballard RE,
Murthy G,
Hargens AR,
and
Convertino VA.
Plasma colloid osmotic pressure increases in humans during simulated microgravity.
Aviat Space Environ Med
69:
23-26,
1998[Medline].
17.
Leach, CS,
Alfrey CP,
Suki WN,
Leonard JI,
Rambaut PC,
Inners LD,
Smith SM,
Lane HW,
and
Krauhs JM.
Regulation of body fluid compartments during short-term spaceflight.
J Appl Physiol
81:
105-116,
1996
18.
Louisy, F,
Berry P,
Marini JF,
Guell A,
and
Guezennec CY.
Characteristics of the venous hemodynamics of the leg under simulated weightlessness: effects of physical exercise as countermeasure.
Aviat Space Environ Med
66:
542-549,
1995[Medline].
19.
Louisy, F,
Schroiff P,
and
Guell A.
Changes in leg vein filling and emptying characteristics and leg volumes during long-term head-down bed rest.
J Appl Physiol
82:
1726-1733,
1997
20.
Pappenheimer, JR,
and
Soto-Rivera A.
Effective osmotic pressure of the plasma proteins and other quantities associated with the capillary circulation in the hindlimbs of cats and dogs.
Am J Physiol
152:
471-491,
1948.
21.
Thornton, WE,
Hedge V,
Coleman E,
Uri JJ,
and
Moore TP.
Changes in leg volume during microgravity simulation.
Aviat Space Environ Med
63:
789-794,
1992[Medline].
22.
Udden, MM,
Driscoll TB,
Pickett MH,
Leach Huntoon CS,
and
Alfrey CP.
Decreased production of red blood cells in human subjects exposed to microgravity.
J Lab Clin Med
125:
442-449,
1995[ISI][Medline].
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, Individual data; 
and error
bars, means ± SE obtained before (D0) and after 118 days (D118)
of 6° head-down tilt (HDT) and 2 days after remobilization (Post).
