J Appl Physiol 104: 938–943, 2008.
First published January 17, 2008; doi:10.1152/japplphysiol.01021.2007.
WISE-2005: tibial and gastrocnemius vein and calf tissue response
to LBNP after a 60-day bed rest with and without countermeasures
P. Arbeille,1 P. Kerbeci,1 L. Mattar,2 J. K. Shoemaker,3 and R. L. Hughson2
1
Unité de Médecine et Physiologie Spatiales (UMPS), Centres Hospitaliers Universitaires Trousseau, Tours, France; 2Faculty
of Applied Health Sciences, University of Waterloo, Waterloo, Ontario; and 3School of Kinesiology, University of Western
Ontario, London, Ontario, Canada
Submitted 26 September 2007; accepted in final form 11 January 2008
leg vein; lower body negative pressure; head-down bed rest; echography; Women International Space Simulation for Exploration 2005
90-day head-down bed rest (HDBR) (5) but there was no
difference between subjects who performed no countermeasures during HDBR and those who performed regular resistive (flywheel) exercise. In the same study, it was observed
that venous plethysmography failed to detect significant
changes (5), confirming that only direct visualization of the
vein and surrounding tissue by echography provides appropriate information on the response of these targets to HDBR
and orthostatic test.
The objectives of the present study were to evaluate the
effect of two countermeasures [exercise ⫹ lower body negative
pressure (LBNP) (Ex-Lb) and nutrition (Nut)] in women participating in a long-duration (60-day) HDBR on the calf vein
CSA and surrounding superficial tissue thickness (STth) at rest
and in response to LBNP of ⫺45 mmHg and to determine the
impact on orthostatic tolerance. It was hypothesized 1) that the
“Ex-Lb” countermeasure combining aerobic and resistive exercise and LBNP (1, 28) would prevent changes in vein and
tissue liquid storage during an LBNP test on HDBR day 55.
Furthermore, it was hypothesized 2) that subjects, regardless of
their countermeasure group, who had the smallest increase in
vein and tissue liquid storage measured during the LBNP test
on day 55 would finish the 10-min tilt test after 60-day HDBR.
Direct visualization and measurement of the vein CSA and
STth by echography during LBNP were used to try to answer
these questions.
METHODS
Women’s International Space Simulation for Exploration
(WISE) Study and Subjects
THE POSSIBLE CONTRIBUTION of the leg veins and surrounding
tissues to orthostatic intolerance has been studied during bed
rest and before and after spaceflight using plethysmographic
(9, 10, 24, 25) or ultrasound methods (3, 5). Blood pooling
in the calf has been proposed as a factor that precipitates the
development of syncope (17). Nevertheless, in some subjects, the increase in calf volume after moving to the
standing position did not correlate with the onset of a
vasovagal syncope (6).
The increase in leg vein cross-sectional area (CSA),
measured by echography, in response to a fluid shift toward
the legs during a stand test was found higher in those unable
to complete a 10-min stand [nonfinishers (NF)] after a
The 60-day at 6° HDBR was organized by the Institute for Space
Physiology and Medicine (MEDES) Space Clinic, located at
Rangueil Hospital, Toulouse, France, in 2005. The experiment was
approved by a French Committee for health (Comité Consultatif de
Protection des Personnes dans la Recherche Biomédicale, MidiPyrénées).
Twenty-four healthy women signed a consent form after having
been informed of the risks and benefits of this long-term bed rest
study. The population were randomly assigned to three groups:
Ex-Lb (n ⫽ 8) and Nut (n ⫽ 8) countermeasure groups and
controls (Con, n ⫽ 8). Ex-Lb subjects performed flywheel (resistance exercise) (1) every third day, and 3– 4 days per week with
interspersed rest days they performed 40 min of treadmill aerobic
exercise within the LBNP chamber with an interval training pattern
(28) followed by 10-min passive LBNP. Nutrition subjects consumed a daily protein supplement during meals corresponding to
Address for reprint requests and other correspondence: P. Arbeille, EFMPUMPS, CHU Trousseau, 37044 Tours, France (e-mail: [email protected]).
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.
938
8750-7587/08 $8.00 Copyright © 2008 the American Physiological Society
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Arbeille P, Kerbeci P, Mattar L, Shoemaker JK, Hughson RL.
WISE-2005: tibial and gastrocnemius vein and calf tissue response to
LBNP after a 60-day bed rest with and without countermeasures.
J Appl Physiol 104: 938–943, 2008. First published January 17, 2008;
doi:10.1152/japplphysiol.01021.2007.—The objective of this study
was to quantify by echography the changes in the intramuscular
[gastrocnemius (Gast)] and nonintramuscular [posterior tibial (Tib)]
calf veins cross-sectional area (CSA) and the superficial tissue thickness (STth) in response to lower body negative pressure (LBNP) after
60-day head-down bed rest (HDBR). Twenty-four healthy women
(25– 40 yr) were divided into three groups: control (Con), treadmillLBNP and flywheel (Ex-Lb), nutrition (Nut; protein supplement). All
underwent a LBNP (0 and ⫺45 mmHg) before and on day 55 of
HDBR. Subjects were identified as finisher (F) or nonfinisher (NF) of
a 10-min tilt test after 60 days of HDBR. There were no differences
in resting CSA of the Tib and Gast veins on HDBR day 55 compared
with pre-HDBR for the Ex-Lb, Con and Nut, or the F groups;
however, for NF both the Tib and Gast vein CSA at rest were
significantly smaller after HDBR. At ⫺45 mmHg LBNP, Tib and
Gast CSAs were not significantly different from before HDBR in all
groups (Ex-Lb, Con, Nut, F, NF). However, percent change in CSA of
both veins from rest to ⫺45 mmHg LBNP was significantly greater in
the Con and Nut groups compared with Ex-Lb, and also NF compared
with F. Similarly, the percent increase in STth on going from rest to
⫺45 mmHg was higher after HDBR in the Con and Nut groups
compared with Ex-Lb, as well as NF compared with F. These results
showed that the Ex-Lb countermeasure minimized the bed rest effect
on leg vein capacitance (CSA percent change) and STth increase
during LBNP, whereas Nut had no effect and that higher leg vein and
superficial tissue capacitance were associated with reduced orthostatic
tolerance.
EFFECT OF LBNP ON LEG VEIN AND TISSUE AFTER BED REST
0.6 g 䡠 kg⫺1 䡠 day⫺1, i.e., between 30 and 40 g of additional protein
per day.
LBNP
Subjects were placed in a supine position then instrumented with
the calf echographic probe. They were studied at rest and at ⫺45
mmHg LBNP for 3 min.
Echographic Parameters
Measurement Schedule
LBNP test. The vein CSA and STth parameters were measured
pre-HDBR and after 55-day HDBR on the subject supine at 0 mmHg
and at LBNP ⫺45 mmHg.
Orthostatic tolerance test. Orthostatic tolerance was evaluated by
comparing the ability to complete a 10-min 80° head-up tilt test before
HDBR and as the very first upright activity after 60-day HDBR. All
subjects completed the 10-min test pre-HDBR, whereas in the postHDBR test, two of eight Ex-Lb (25%), five of eight Con (63%), and
six of eight Nut (75%) subjects failed to complete the full 10-min tilt
test. Based on these results, we further subdivided the subjects as F
and NF of the 10-min tilt test for additional comparison of the
hypothesis that completion of the 10-min tilt test was related to
smaller increases in vein and tissue liquid storage during LBNP at
HDBR day 55 compared with NF.
Statistical Analysis
Values are expressed as means ⫾ SD , and changes were considered statistically significant for P ⬍ 0.05. Data were analyzed using
nonparametric tests because of the number of subjects. Comparisons
between the Ex-Lb, Con, and Nut groups, and between F and NF
subjects, were made using the Mann-Whitney test for unpaired variables. Two periods within the same group were compared using the
Wilcoxon test for paired data.
RESULTS
Vein CSA at Rest
There was no significant change in the CSA of the Tib and
Gast veins at rest on HDBR day 55 compared with pre-HDBR
in any of Ex-Lb, Con, and Nut (Fig. 2). Only when considering
the NF group was there a significant decrease in resting CSA
[Tib: from 0.33 ⫾ 0.07 to 0.28 ⫾ 0.06 cm2 (P ⬍ 0.05), Gast:
from 0.083 ⫾ 0.021 to 0.066 ⫾ 0.018 (P ⬍ 0.05)]. The number
of subjects within each group that decreased the resting Tib
CSA on HDBR day 55 relative to pre-HDBR was three, four,
and five for the Ex-Lb, Con, and Nut groups (38, 50, and 63%),
respectively. For the 11 F subjects, only 3 had a decrease in
resting CSA (27%), whereas for the 13 NF subjects, 9 had a
decrease in CSA (69%). The proportion of subjects that reduced their Gast vein CSA at rest, was 13, 86, and 57% for
Ex-Lb, Co, and Nut, respectively, and it was 36 and 70% and
for F and NF, respectively.
Vein CSA during ⫺45 mmHg LBNP. The absolute Tib and
Gast vein CSA during ⫺45 mmHg LBNP (maximal vein size)
did not differ between pre-HDBR and HDBR day 55 for any of
Ex-Lb, Con, or Nut groups (Fig. 2). Similarly, there was no
difference in the CSA during ⫺45 mmHg on HDBR day 55
relative to pre-HDBR for the F or NF groups. The number of
subjects within each group that increased their Tib CSA on
HDBR day 55 relative to pre-HDBR was two of eight for
Ex-Lb, five of eight for Con, and four of eight for Nut (25%;
63%; 50%). Of the 11 F subjects, only 4 had an increase in Tib
CSA on HDBR day 55 (36%), while 7 of 13 NF subjects (54%)
had an increase in absolute Tib CSA. The proportion of
subjects that increased their Gast vein CSA at LBNP ⫺45
mmHg was 38, 43, and 71% for the Ex-Lb, Co, and Nut
groups, respectively, and it was 45 and 60% for the F and NF
groups, respectively.
As a consequence of the smaller starting Tib or Gast CSA at
rest for some individuals on the HDBR day 55 testing, or the
higher maximal CSA reached at ⫺45 mmHg, the percent
increase from rest to ⫺45 mmHg LBNP was significantly
greater at HDBR day 55 for the Con and Nut groups as well as
for the NF group (Fig. 3). The proportion of subjects within
each group that showed a greater CSA percent increase at
HDBR day 55 for the Tib vein was 50% Ex-Lb, 75% Con, and
88% Nut, and for the Gast vein the proportion was 25% Ex-Lb
and 86% Con and Nut. Of the 13 NF subjects, 11 (85%) had a
greater percentage increase in Tib CSA after HDBR, whereas
only 5 of the 11 F subjects (45%) had a greater percent
increase. Also 70% of the NF subjects and 55% of the F had a
greater percent increase in Gast vein CSA after HDBR.
STth
Fig. 1. Anatomic view of the calf area investigated, and echographic view
showing the gastrocnemius vein (V) cross-sectional area and the superficial
tissue thickness (STth).
J Appl Physiol • VOL
Between the pre-HDBR to HDBR day 55 session the absolute STth at rest did not differ for any group, whereas the
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The calf veins and tissue were investigated using a 7.5-MHz
ultrasound “T-shaped probe” attached to the upper posterior level of
the left calf by an adhesive patch, and connected to the echograph by
a 2-m-long cable (Logic book GE France). The ultrasound probe was
placed, to visualize in a transverse cross section the upper part of the
posterior tibial vein (Tib) and one or two gastrocnemius veins (Gast)
depending on the subject’s anatomy. Echographic views were digitized and recorded continuously during the LBNP test and processed
on a program designed by our laboratory (Fig. 1). The contours of the
Tib and Gast veins were outlined on the images, and the vein CSA
was expressed in centimeters squared.
The distance between the superficial Gastrocnemius muscle aponeurosis and the skin was measured at the level of the Gast vein and
called “superficial tissue thickness” (STth) (Fig. 1).
CSA at rest and maximal CSA at LBNP ⫺45 mmHg, and the
percent changes in CSA and STth from 0 to LBNP ⫺45 mmHg, were
analyzed according to the countermeasure used and considering the
fact that the subject finished [finisher (F)] or not (NF) the post-HDBR
10-min tilt test. The percent change in Tib and Gast CSA and STth
from LBNP 0 to ⫺45 mmHg was considered to be proportional to the
vein and tissue capacity to stow liquid (capacitance).
939
940
EFFECT OF LBNP ON LEG VEIN AND TISSUE AFTER BED REST
maximal thickness at ⫺45 mmHg LBNP was significantly
higher in the Con and Nut groups (P ⬍ 0.05), and it approached significance in the NF group (P ⫽ 0.07) (Fig. 4).
However, the percent increase in STth on going from rest to
⫺45 mmHg LBNP was significantly greater on HDBR day 55
compared with pre-HDBR in the Con and Nut groups as well
as in the NF group (Fig. 5).
The number of subjects within each group with a greater
percent increase of STth (from 0 to ⫺45 mmHg) on HDBR day
55 relative to pre-HDBR was two of eight for Ex-Lb, five of
eight for Con, and six of eight for Nut (25; 63, and 75%). Of
the 11 F subjects, only 1 had a greater percentage increase in
STth on HDBR day 55 (9%), whereas 12 of 13 NF subjects
(92%) had a greater percent increase in STth.
DISCUSSION
In the present study, the percent changes in leg vein CSA
and STth from rest to ⫺45 mmHg LBNP were significantly
greater after HDBR in the Con and Nut groups but not in the
Ex-Lb group. These data supported our first hypothesis that the
Ex-Lb countermeasure would prevent changes in liquid storage
in the veins and tissues of the lower leg after bed rest. To
examine our second hypothesis, subjects were classified as F or
NF of the post-HDBR tilt test to determine whether those
subjects with the smallest increases in leg vein CSA and STth
measured during LBNP in the last week of bed rest would be
most tolerant of the upright posture after long-duration HDBR.
J Appl Physiol • VOL
Results from this analysis supported the second hypothesis.
Overall, our results support the conclusions of some previous
research that bed rest caused increased leg compliance (10, 17,
23, 24) but contrast with other research (6, 7, 15, 29, 34).
Differences in methodology (ultrasound imaging vs. occlusion
plethysmography) as well as different durations of HDBR
might account for the contrasting conclusions as our present
findings in women after 55-day HDBR were similar to those in
men at the conclusion of 90-day HDBR (5).
Previously, Convertino et al. (10) concluded that the increased leg compliance after HDBR contributed to orthostatic
intolerance. On the other hand, Melchior and Fortney (29)
reported no relationship between leg vein compliance and
orthostatic tolerance. Subsequently, Fu et al. (15) observed that
those most likely to faint after HDBR had increased leg vein
compliance in pre-HDBR testing but that the increase in
compliance with HDBR was not related to a change in tolerance. More recently and contrary to most published studies,
Bleeker et al. (7) reported a reduction in leg vein compliance
and an increase in leg vein resistance after HDBR but the
change in orthostatic tolerance was not related to leg vascular
conductance. Xiao et al. (34) also reported findings that conflicted with previous studies as their subjects with higher
values of leg vein compliance in the pre-HDBR testing were
more, not less, tolerant in the orthostatic position after HDBR.
Conversely the echographic direct measurement of the calf
vein CSA demonstrated a higher capacity of the vein to expand
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Fig. 2. Tibial (Tib) and gastrocnemius (Gast)
vein cross-sectional area at rest and at ⫺45
mmHg lower body negative pressure (LBNP)
(⫺45) pre-head-down bed rest (HDBR) and
HDBR day 55 (55d) for the 5 groups: exercise ⫹ LBNP (Ex-Lb), control (Con), nutrition
(Nut), finishers (F), and nonfinishers (NF). *Significant difference between cross-sectional area
mean value at rest for NF only, P ⬍ 0.05. There
was no significant difference between mean
cross-sectional area value at LBNP ⫺45 mmHg
in each group.
EFFECT OF LBNP ON LEG VEIN AND TISSUE AFTER BED REST
941
Fig. 5. Percent change of the STth (%STth) between rest (LBNP ⫽ 0
mmHg) and LBNP ⫺45 mmHg pre-HDBR and HDBR day 55. *%STth in
the Con and Nut groups is significantly higher than in the Ex-Lb group,
*P ⬍ 0.05. %STth increase is higher in NF of the post-HDBR tilt test
compared with F, P ⬍ 0.05.
at the end of the bed rest in the nontolerant subjects, which is
not in agreement with many (7, 15, 29, 34) but not all (10) of
the plethysmographic results which did not see any difference
between tolerant and nontolerant subjects.
The plethysmographic method measures the whole calf CSA
change, but it never measures vein CSA. We have demonstrated that the higher capacity for the vein to expand its CSA
is related to the fact that the calf vein CSA at rest decreased or
that the maximal CSA at LBNP ⫺45 mmHg became higher at
the end of the bed rest. Moreover, plethysmography was used
to measure the calf compliance in response to a gradual
pressure-controlled occlusion of the whole venous network.
Conversely, the echography was used to measure the vein CSA
Fig. 4. Superficial tissue thickness (STth) at rest and at ⫺45 mmHg LBNP
pre-HDBR and HDBR day 55 for the 5 groups: Ex-Lb, Con, Nut, F, and NF.
There was no significant difference between mean value at rest at HDBR day
55 and pre-HDBR. *Mean STth value at LBNP ⫺45 mmHg significantly
higher at HDBR day 55 compared with pre-HDBR in Con and Nut groups,
P ⬍ 0.05.
J Appl Physiol • VOL
Tib and Gast Vein CSA at Rest
At HDBR day 55, the Tib and Gast vein CSA at rest were
significantly reduced compared with pre-HDBR in 70% of the
NF subjects, suggesting that the vein size at rest is one the
major parameters for evaluating the vein deconditioning.
Several factors could have contributed to the reduction of
resting vein CSA. A reduction in venous flow might be anticipated with the inactivity of bed rest and the absence of
increased cardiac output and sympathetic stimulation in relation with exercise or postural change. Previous studies focused
on the flow changes in the lower limbs in relation to the
antiorthostatic position have proposed that reductions in perfusion pressure and in demand for blood flow with reduced
activity could result in structural and functional changes in the
vasculature. Hindlimb suspension in the rat caused changes in
vessel wall dimensions, reduced capillary density, reduced
sympathetic perivascular nervous fiber density, and functional
changes in rat limb arterial vessels (11, 12, 26, 35). In support
of this, other authors have reported that 1) reduction in flow
contributed to reduce arterial CSA and that such response was
endothelium dependent (22), 2) reduction in CSA in the soleus
muscle was associated with decrement in muscle perfusion
(27), and 3) imbalance between sympathetic vasoconstrictor
traffic and nitric oxide release might contribute to increased
vascular resistance and reduced flow (20). Although the structure of the vein is not similar to that of the arteries, we may
suggest that a similar disadaptative process could result in
structural alterations of the veins with the chronic changes in
distending pressure and flow stimulus while in the head-down
position. These structural and functional changes could contribute to increase the relative stowage of blood in the veins
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Fig. 3. Percent change of the Tib and Gast vein cross-sectional area between
rest (LBNP ⫽ 0) and LBNP-45 mmHg (0 – 45) (vein capacitance), pre-HDBR,
and at HDBR day 55. *The vein distension (capacitance) in the Con and Nut
groups is significantly higher than in the Ex-Lb group, P ⬍ 0.05. *There is a
higher increase in vein distension (capacitance) in NF of the post-HDBR tilt
test compared with F, P ⬍ 0.05.
changes for evaluating the capacity of the vein to stow blood
volume under a passive fluid shift. During a previous 90-day
HDBR, the calf volume filling measured by plethysmography
during a stand test tended to increase in the NF subjects,
whereas the percent increase in calf vein CSA (capacitance)
was significantly higher in NF (5). The 90-day HDBR study
during which we performed at the same time both the echographic and plethysmographic measurements confirmed that
these two methods do not measure the same thing and that
plethysmography provides a very indirect approach of what
happens at the vein and tissue levels.
942
EFFECT OF LBNP ON LEG VEIN AND TISSUE AFTER BED REST
after HDBR, reducing venous return, and increase the risk of
orthostatic intolerance.
Nevertheless the HDBR position and Ex-Lb countermeasure had a more limited impact on the vein size than
expected because only 50 –75% of the non-Ex-Lb subjects
reduced their calf vein CSA and 13–38% of the Ex-Lb
subjects still reduced it.
Maximal Tib and Gast Vein CSA at ⫺45 mmHg LBNP
Tib and Gast CSA Relative Change From
0 to ⫺45 mmHg (Vein Capacitance)
The proportion of subjects reducing their CSA at rest or
increasing their maximal vein CSA at LBNP ⫺45 mmHg at
HDBR day 55 was found to be higher inside the Con and Nut
and NF groups compared with the Ex-Lb or F groups. This
may explain why the relative change in CSA from 0 to ⫺45
mmHg LBNP (vein capacitance) was higher in these three
groups, whereas no significant change in the minimal vein
CSA or maximal CSA average value was evidenced between
these groups.
Finally the combined Ex-Lb countermeasure that prevented
cardiac volume decrease was found to prevent CSA reduction
and make smaller the relative change in CSA during LBNP,
while probably keeping unchanged the flow volume into the
leg veins at rest.
Calf STth Change From 0 to ⫺45 mmHg LBNP
(Tissue Capacitance)
The absolute values of STth measured at rest were not
significantly different from pre-HDBR to day 55 of HDBR for
any group. With application of ⫺45 mmHg LBNP, there was
J Appl Physiol • VOL
Conclusion
The higher amount of liquid stowed both into the main veins
and into the superficial tissue areas as observed in the NF group
during LBNP, probably contributed to the reduction in orthostatic tolerance. The exercise countermeasure (aerobic exercise
in LBNP ⫹ resistive) had a protective effect against vein and
skin tissue increased stowage and contributed to reduce the
disadaptation of these targets and to maintain the adequate
level of orthostatic tolerance while the nutrition countermeasure had no effect.
ACKNOWLEDGMENTS
The study WISE-2005 was sponsored by the European Space Agency
(ESA), the National Aeronautics and Space Administration of the USA, the
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The maximal CSA of both the Tib and Gast veins reached at
LBNP 45 mmHg, was not significantly affected by HDBR or
by the exercise ⫹ LBNP and nutrition countermeasures because only 50 – 63% of the non-Ex-Lb subjects increased
maximal CSA, whereas 25% of the Ex-Lb subjects increased
maximal CSA. Moreover the maximal CSA was not significantly different for the Tib (nonintramuscular) and the Gast
(muscular) vein whether the subject experienced or not leg
muscle atrophy as measured by MRI (33). Thus the maximal
calf vein CSA did not depend on the muscle environment.
Future studies focused on the effect of the bed rest on the
vein wall structure and capacity to respond to vasoactive drugs
and flow pressure might be necessary to better understand the
changes in vessel area and capacitance and the possible role of
the sympathetic nervous system on the vein response to fluid
shift. Purdy et al. (30) reported no significant effect of rat
hindlimb suspension on maximal vein response to norepinephrine (jugular and femoral). Moreover, Halliwill et al. (16)
specifically studied calf veins and demonstrated no effects of
sympathetic activation on calf venous compliance in humans.
This observation is in agreement with the fact that the maximal
expansion of the vein (at LBNP ⫺45 mmHg) does not change
significantly, whereas the arterial vasoconstriction is significantly reduced by bed rest (2, 4, 18, 31, 32). This should be in
relation with the fact that the vein wall is anatomically much
less complex and respond much more like a passive system
compared with the artery that is directly and strongly regulated
by the sympathetic system.
a small increase in STth after HDBR, but the difference was
not significant, probably due to the relatively small sample size
in each group. These results were not similar to those obtained
in a 7-day HDBR on men on which a significant decrease in
STth was found (⬃3– 6%) (13) and with spaceflight data (21).
Methodological differences between studies might have accounted for the contrasting findings because the previous
studies examined the anterior part of the Tib bone were the skin
thickness is regular but very thin, whereas we did our measurements on the posterior part of the calf were the skin
thickness is higher but less regular. There was however, a
significant increase in relative change in STth (from 0 to ⫺45
mmHg LBNP) after HDBR that reflected a greater fluid stowage in this tissue in the Con, Nut and NF groups, but not in the
Ex-Lb and F groups. The proportion of subjects with a higher
increase in STth at HDBR day 55 was more important in Con
and Nut compared with Ex-Lb (63, 75, vs. 25%, respectively)
and in NF compared with F (92 vs. 9%, respectively). Thus
HDBR contributed to increase the superficial tissue capacity to
stow liquid, whereas the Ex-Lb countermeasure efficiently
prevented such disadaptation. On the other hand, the higher
amount of liquid stowed into the superficial tissue areas as
observed in almost all the NF subjects might have contributed
to the reduction in orthostatic tolerance in this group.
Other studies also using the ultrasound method reported an
increase in superficial tissue thickness of comparable range.
The superficial tissue was found to increase by ⬃11.6% when
a subject moves from supine to 30° head-up tilt (14). On
patients during hemodialysis echographic skin measurements
showed a decrease in tibial tissue thickness of 12.8% in men
and 23.9% in women (19). This confirmed the huge capacity of
the skin compartment to stow liquid and suggested that this
response to fluid shift could be of different amplitude in men
and women.
Increased capillary permeability, caused by leg dehydration,
extravascular pressure and loss of muscle mass, has been
reported during previous bed rest periods or at the end of
spaceflight (8). These modifications in capillary permeability
may explain the greater calf volume filling measured by plethysmography and the higher superficial tissue capacitance observed in intolerant subjects by echography in the present
study. It is nevertheless difficult to evaluate the relative contribution of tissue filtration and secondary vein filling to the
changes in calf volume, because the vein CSA is small compared with the calf CSA and the identification of the distal vein
network problematic.
EFFECT OF LBNP ON LEG VEIN AND TISSUE AFTER BED REST
Canadian Space Agency (CSA), and the French Centre National d’Etudes
Spatiales (CNES), which has been the “Promoteur” of the study according to
French law. The head-down bed rest has been managed by MEDES (Institute
for Space Physiology and Medicine in Toulouse, France). The authors are
grateful for the outstanding contributions of the 24 WISE women who
committed themselves to the success of this study. The authors thank the
sonographer technicians D. Greaves, M. Porcher, V. Moreau, and J. L. Boulay
for their outstanding contribution to the data collection and processing and the
MEDES staff for excellent support throughout the study.
GRANTS
This research was supported by CSA Contract 9F007-033004/001/ST (to
R. L. Hughson and J. K. Shoemaker) and by CNES Grant 4800000367 (to
P. Arbeille).
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