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1 Laboratoire de Médecine
Aérospatiale, We measured
upper airway caliber and lung volumes in six normal subjects in the
sitting and supine positions during 20-s periods in normogravity,
hypergravity [1.8 + head-to-foot acceleration (Gz)], and microgravity (~0
Gz) induced by parabolic
flights. Airway caliber and lung volumes were inferred by the acoustic reflection method and inductance plethysmography, respectively. In
subjects in the sitting position, an increase in gravity from 0 to 1.8 +Gz was associated with increases
in the calibers of the retrobasitongue and palatopharyngeal regions
(+20 and +30%, respectively) and with a concomitant 0.5-liter increase
in end-expiratory lung volume (functional residual capacity, FRC). In
subjects in the supine position, no changes in the areas of these
regions were observed, despite significant decreases in FRC from
microgravity to normogravity (
upper airway configuration; weightlessness; hypergravity
THE INFLUENCE of position in normogravity on
respiratory mechanics, including upper airway configuration, has been
investigated extensively. A decrease in upper airway cross-sectional
area and an increase in upper airway resistance were found when human
subjects moved from the upright to the supine position (33). Two
mechanisms have been proposed to explain these effects. The first is
based on the influence of lung volume on upper airway cross-sectional area (5, 28, 29). Lung volume has been shown to decrease in subjects
going from a lying position to a sitting position (1), and this effect
has been suggested as a possible cause of the concomitant change in
upper airway caliber. The second mechanism involves distortion of the
upper airway caused by the effects of gravity on surrounding tissues
(11, 21, 23). Recently, Takasaki et al. (30) suggested that gravity may
have a major influence on upper airway caliber during sleep. To
estimate the contribution of each of these two factors, i.e., change in lung volume and mechanical effect of gravity, we performed a
quantitative evaluation of both lung volume and upper airway area
during the brief periods of weightlessness and of 1.8 + head-to-foot
acceleration (Gz) gravity
encountered inside an aircraft specifically designed for parabolic
flight. Upper airway area was assessed with the noninvasive
two-microphone acoustic reflection method (19). Lung volumes were
inferred by using induction plethysmography. Our study is the first to
demonstrate changes in upper airway area directly ascribable to
gravitational loading and unloading.
Setup
Acoustic reflection method.
Longitudinal airway area profile was inferred by the two-microphone
acoustic reflection method as previously described (19, 20). Briefly, a
tube (30 cm in length, 1.9 cm in diameter) was prepared to accommodate
two flush-mounted piezo-resistive pressure transducers (Endevco model
8510 B-2, Le Pré, Saint Gervais, France) and a horn driver. The
transducers were located 7 cm apart. A mouthpiece was connected to the
end of the wave tube in such way that the distance from the second
microphone to the incisors was 10 cm. The other end of the wave tube
was open to the atmosphere, permitting the subject to breathe
spontaneously. Acoustic impulse was generated by the horn driver, which
was driven via a digital-to-analog converter by a computer-generated
signal. Transducer outputs were fed to an analog-to-digital converter
(14 bits) with a sampling period of 24 µs. Each acoustic pressure
acquisition took ~6 ms. A microcomputer inferred the area-distance
function from the digitized pressure data (Benson Hood Laboratories,
Pembroke, MA).
Airflow.
Airflow was measured using a no. 2 Fleisch pneumotachograph connected
to the wave tube and a differential pressure transducer (Validyne model
DP 45, Northridge, CA). The transducer was placed in an assembly
screwed on the rack holding all of the apparatus to ensure constant
position during flight. Flow signal was electrically zeroed before and
after a series of measurements. Recording of this signal during a
complete parabola revealed no consistent change in transducer output at
zero flow as gravity varied.
Lung volume.
Tidal volume (VT) was
calculated by integration of the flow signal. The flow calibration was
obtained before takeoff by passing the volume of a 1-liter syringe
through the pneumotachograph at different speeds. The gain was then
adjusted (offline) to match the volume of the integrated flow signal to
the known volume of the syringe. Thoracic and abdominal movements were
measured using an inductance plethysmograph (Respitrace Ambulatory
Monitoring, Ardsley, NY). Before takeoff, the bands were positioned
around the thorax at the level of the nipples and around the abdomen at
the level of the umbilicus. The bands were firmly secured to the skin
by tape. The plethysmograph was calibrated against the integrated
pneumotachograph signal at 1 +Gz with subjects in the sitting position as described by Sackner et al. (26) during an ~5-min
period of natural breathing. The volumetric sums of thoracic and
abdominal displacements were matched to obtain changes in
end-expiratory lung volume (functional residual capacity, FRC).
Gravity acceleration.
Gz acceleration was continuously
measured using the Gz
accelerometer (±20 m/s2
accelerometer JT21-46, SFIM, Massy-Palaiseau, France) currently used in French Flight Test Centers.
Protocol
Subjects.
Six healthy adults [5 men and 1 woman, age 38 ± 6 (SD) yr, height 174 ± 5 cm, and weight 71 ± 11 kg]
volunteered for this study. The experimental protocol was approved by
the human ethics committee of our institution. All subjects underwent
preliminary medical examinations before participation, according to
National Aeronautics and Space Administration (NASA) class III
specifications (13). They had become familiarized with functional
respiratory tests. Furthermore, five of them had prior experience with
parabolic flights.
Parabola.
Periods of weightlessness of 20-25 s were obtained by flying a
NASA KC135 aircraft along parabolic trajectories. The flight lasted
~2.5 h and included six series of five parabolas. Each parabola
included the following steps: 1)
steady 1 +Gz in horizontal trajectory at ~8,000 m; 2) ~20-s
period of hypergravity (~1.8 +Gz, pull-up at +45° of
incidence in an ascendant trajectory); 3) parabolic trajectory (20- to 25-s
period of weightlessness, ~0
Gz); and
4) ~20-s period with an
acceleration of ~1.8 +Gz
(recovery trajectory; Fig. 1). In parabolic
flight, whatever the gravity (1 or 1.8 +Gz), the gravitational force is
applied perpendicularly to the longitudinal axis of the plane in a
top-to-deck direction (Fig. 1). The five parabolas within a series were
separated by steady-state periods of 90 s at normogravity. Between two
consecutive series of parabolas, duration of the 1 +Gz period was ~5 min.
ABSTRACT
Top
Abstract
Introduction
Materials & Methods
Results
Discussion
References
0.6 liter) and from microgravity
to hypergravity (0.5 liter). Laryngeal narrowing also occurred
in both positions (about 15%) when gravity increased from 0 to
1.8 +Gz. We concluded that
variation in lung volume is insufficient to explain all upper airway
caliber variation but that direct gravity effects on tissues surrounding the upper airway should be taken into account.
INTRODUCTION
Top
Abstract
Introduction
Materials & Methods
Results
Discussion
References
MATERIALS AND METHODS
Top
Abstract
Introduction
Materials & Methods
Results
Discussion
References
View larger version (12K):
[in a new window]
Fig. 1.
Schematic trajectory of plane during a parabola. This trajectory
induces variations in apparent gravity in a perpendicular direction to
deck of plane. GZ, head-to-foot acceleration.
Data recording and data analysis. While acoustic pressure data were being recorded on one microcomputer, flow, rib cage and abdominal displacements, acoustic pulse, and Gz acceleration signals were simultaneously sampled at a rate of 128 Hz and stored in the hard drive of another microcomputer by use of Acknowledge software and device (Biopac Systems, Santa Barbara, CA; Fig. 2). Data recordings were composed of consecutive periods of 105 s, including the duration of the entire parabola (~65 s) plus periods of ~20 s before and after the parabola. During these 105-s periods, acoustic pulses were run at a rate of ~1 Hz.
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Statistics
Data were analyzed using a one-way ANOVA [supine position at 0, 1, and 2 +Gz (SU0G, SU1G, and SU2G, respectively), and sitting position at 0, 1, and 2 +Gz (SI0G, SI1G, and SI2G, respectively)]. Because gravity and posture are not independent variables (modifying posture results in a 90° change in inertial force exerted on the body), use of two-way ANOVA would not have been appropriate. The significance level was set at P = 0.05. Post hoc comparisons were performed using a Newman-Keuls test to look for statistically significant differences in physiological responses to the changes in situations.| |
RESULTS |
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Abstract
Introduction
Materials & Methods
Results
Discussion
References
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VT
Significant changes in VT occurred in subjects in the sitting position between 0 Gz and the other gravity levels (0.12 liter between SI0G and SI1G,
P < 0.05; 0.1 liter between
SI0G and SI2G, P < 0.05). Changing
in normogravity from the sitting to supine position did not produce
significant variation of VT
(P > 0.05). In the supine position,
significant changes were observed only between 0 and 2 +Gz (0.08 liter,
P < 0.05; Fig.
5A).
However, the 0.17-liter variation observed between SI0G and SU0G, which cannot be explained inasmuch as these two situations are equivalent in
terms of gravity, suggests that no relevant change in
VT was observed in our study.
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FRC
For each subject, the mean values obtained in sitting positions in normogravity (SI1G) were chosen as the baseline values (Fig. 5B). In the sitting position, FRC increased by 0.5 liter (P < 0.05) from microgravity to hypergravity (0.2 liter SI0G and 0.3 liter
SI2G). Changing from the sitting to supine position at 1 +Gz produced a decrease in FRC of
~1.1 liter (P < 0.05). In the
supine position, the value increased at 0 and 2 +Gz (0.64 and 0.17 liter,
respectively; P < 0.05). The
0.26-liter variation observed between the two equivalent situations of
microgravity (SI0G and SU0G) is not explainable. It suggests that
differences between SU1G and SU2G (0.17 liter) are meaningless.
Mean Area of Palatopharyngeal Region
Relative changes in mean area of the palatopharyngeal are shown in Fig. 6A. For all subjects, the value obtained in the sitting position in normogravity (SI1G) was chosen as the baseline. The values obtained in SI0G, SU0G, and SU2G were statistically similar. These three situations resulted in a 15% (P < 0.05) decrease in the mean area of the palatopharyngeal region compared with baseline. SU1G also induced an ~20% (P < 0.05) decrease in the mean area of the palatopharyngeal region. By contrast, hypergravity in the sitting posture induced a 15% expansion of the mean palatopharyngeal area. Interestingly, changes in FRC and the palatopharyngeal region mean area occurred in the same direction.
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Mean Area of Retrobasitongue Region
Relative changes in mean area of the retrobasitongue region are shown in Fig. 6B. In the sitting position, the mean area of the retrobasitongue region increased with Gz, and a concomitant increase in FRC was also seen. Compared with SI1G (baseline), lying down induced a significant decrease of ~2-5% (P < 0.05) in the area in all gravity conditions. In the supine position, the evolution vs. gravity of this area seemed to be in opposition with the evolution of the FRC; an increase in FRC corresponded to a decrease in the area of the retrobasitongue region and vice versa. Differences between SU1G and SU2G and between SU0G and SU2G were not significant, and there was a slight difference between SU0G and SU1G (2.5% of baseline value).Mean Area of Laryngeal Region
Relative changes in mean area of the laryngeal region are shown in Fig. 6C. In the supine and sitting positions, the mean area of the laryngeal region decreased as Gz increased. This decrease was more marked in the supine posture, reaching 17% at 2 +Gz vs. baseline (SI1G). Changes in laryngeal region area occurred in the opposite direction from changes in FRC in the sitting position and also in the supine position at 0 Gz (SU0G) only.Mean Total Area of Upper Airways
Relative changes in mean area of the total area of upper airways are shown in Fig. 6D. Compared with the baseline situation (SI1G), this total area decreased by 4% (P < 0.05) in microgravity (SI0G) and increased by 2% (P < 0.05) in hypergravity (SI2G). Changing from the sitting to supine position in normogravity (SU1G) induced an 11% decrease in mean total upper airway area (P < 0.05). In the supine position compared with normogravity, the mean total area was higher by 5.5% (P < 0.05) in microgravity (SU0G) and lower by 4% (P < 0.05) in hypergravity (SU2G).| |
DISCUSSION |
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Top
Abstract
Introduction
Materials & Methods
Results
Discussion
References
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We found two main effects of gravity on upper airway configuration. First, mean laryngeal region area increased as gravity decreased in both positions. Second, when gravity increased, mean areas of the palatopharyngeal and retrobasitongue regions increased in the sitting position but exhibited only minor variations in the supine position.
Palatopharyngeal Region, Retrobasitongue Region, and Laryngeal Region Mean Areas
Supine posture. In the supine position, the decrease in the mean total area of the upper airways seen as gravity increased was entirely due to a decrease in the mean area of the laryngeal region, since the mean areas of the palatopharyngeal and retrobasitongue regions remained virtually unchanged (Fig. 6). Moreover, the reduction in the area of the laryngeal region that occurred as gravity increased was more pronounced in the supine than in the sitting position, suggesting that it may contribute to the increase in upper airway resistance known to occur when body position changes from sitting to lying down (18). Because this decrease in laryngeal area between normogravity and hypergravity occurred in the absence of any decrease in FRC, it can be concluded that it was dependent primarily on gravity. Indeed, in terms of upper airway narrowing due to lying down, position effects have been shown to be more important than lung volume effects (11, 16). In normal subjects, gravity effects are known to make a much larger contribution to the increase in upper airway resistance seen during sleep than the relative atonia of upper airway muscle (30). Similarly, at sea level, gravity forces that cause the soft palate and tongue to fall back in the supine posture would narrow upper airways in all its length. For instance, some studies (11, 16) reported that passage from the sitting to supine position resulted in a pharyngeal area decrease of ~20%. In exploring the hypothesis that upper airway area decreases in the supine position, we were surprised that only small changes occurred in the retrobasitongue region compared with the changes in palatopharyngeal region. The contrast between the decrease in the mean laryngeal region area and the absence of any noticeable change in the retrobasitongue region may be ascribable to a difference in the amount of upper airway dilator muscles between these two regions. Almost all of the muscles in the retrobasitongue region are dilators, and the mean area of the retrobasitongue region depends on the activity of the dilator muscles of the tongue. Contrary to others (30), we studied our subjects during wakefulness, a state in which subtle neuromuscular mechanisms may maintain the retrobasitongue region open (4), thus potentially counteracting the effects of gravity. This assumption is supported by the fact that dilator muscle activity increases significantly when position is changed from upright to supine (27). In contrast, the larynx is semirigid due to its cartilaginous components, and there is only one dilator muscle in the laryngeal region (cricoarytenoid muscle). Reflex regulation of caliber is less important than in the retrobasitongue region. In our study, a decrease in laryngeal section with the increase in gravity was observed. We can assume that the anterior wall of the larynx moved downward to the posterior wall, thus reducing the laryngeal airway section. In the supine position, FRC changes were of little relevance to variations in upper airway patency, since the palatopharyngeal and retrobasitongue region areas remained constant despite FRC changes, and the laryngeal region area failed to mirror variations in FRC (Figs. 5 and 6).
Sitting posture.
In the sitting position, increasing gravity was associated with
increases in FRC and retrobasitongue and palatopharyngeal mean areas
and with a decrease in laryngeal region mean area. Mean total upper
airway area increased with gravity. The dilating effect of gravity on
the retrobasitongue and palatopharyngeal regions may be ascribable to
the FRC changes seen in our study in agreement with previous studies
(9, 10, 22). Also, many studies in humans subjected to hypergravity
found that blood volume decreased in the upper part of the body and
increased in the lower part (6-8, 14). Thus blood volume in the
palatopharyngeal and retrobasitongue regions probably decreases with
increasing gravity. In the sitting position, an increase in gravity
from 0 to 2 +Gz may significantly
increase the size of the upper airways as a result of substantial
reductions in the volume of blood surrounding the upper airways.
Shepard et al. (29) have reported that a decrease in blood volume may
increase upper airway size. Because the tongue is a well-vascularized
region, this mechanism would explain size increases in the
palatopharyngeal and retrobasitongue regions but not in the laryngeal
region. We found that laryngeal region area decreased as gravity
increased (+10% of baseline at 0 Gz to 10% of baseline at 2 +Gz). In a previous study of
subjects in the sitting position, Beydon et al. (2) found that, after topical anesthesia, the epiglottis could drop onto the vocal cords, resulting in complete airway obstruction. A similar phenomenon may be
part of the explanation of our observation. Further studies are
required to confirm this assumption. Indeed, in our study, the subjects
were not anesthetized, and the tone of the cricoarytenoid muscle would
be able to limit the obstruction in hypergravity.
End-Expiratory Lung Volume
Sitting posture.
When normogravity was used as the reference, a decrease in FRC has been
reported in microgravity in the sitting (9, 22) and standing positions
(10). By contrast, an increase in FRC in microgravity has been observed
compared with supine position in normogravity (10). Our results are in
agreement with these findings. When subjects assumed the sitting
position, we found a decrease in FRC by 0.17 liter, which is
closed to the decrease in FRC (0.25 ± 0.03 liter) reported
by Edyvean et al. (9) in microgravity during parabolic flight. Paiva et
al. (22) reported a more pronounced decrease in FRC (0.4 ± 0.07 liter), which could be explained by the fact that their subjects'
shoulders were securely taped to the back support, tending to reduce
inspiratory capacity maneuvers and possibly the expansion of the rib
cage during normal tidal breathing. The reduction in FRC reported by
these studies and ours can be attributed to changes in respiratory
mechanics, i.e., to a cranial shift of the diaphragm-abdominal
compartment related to the gravitational unloading of the abdomen. On
the other hand, it is known that changes in thoracic volumes measured by Respitrace include trunk blood volume modifications. We were unable
to assess the possible microgravity-related increase in intrathoracic
blood volume. However, by measuring FRC and thoracoabdominal volume
(Vw), Paiva et al. (22) could detect whether any changes in
intrathoracic blood volume occurred during the brief periods of
microgravity. Because the decrease in Vw did not differ from that in
FRC, these data suggest that there was no increase in intrathoracic
blood volume. Moreover, because, in studies in parabolic flight such as
ours, measurements are made during very brief periods of microgravity,
which are bracketed by 2-G exposures, there may not have been time for
blood volume shifts, since it has been shown that the increase in
thoracic blood volume is time dependent (10, 31). We can therefore
assume that, in our study, the decrease in FRC at microgravity is
purely due to changes in respiratory mechanics.
Supine posture. We found that FRC at normogravity or hypergravity is lower than FRC measured in microgravity. This finding is consistent with a previous observation (32) showing that, in normogravity, changing from sitting to supine posture, i.e., introducing the gravity component oriented from belly to back, induces a decrease in cross-sectional area of the abdomen and thus a shift of the diaphragm in the cranial direction and a decrease in FRC.
The 0.17-liter increase in FRC observed from SU1G to SU2G appears irrelevant, since this variation is lower than the variation observed between the two equivalent situations of microgravity (SI0G and SU0G). Such an increase is probably due to the extreme conditions of the parabolic flights. In addition, a 0.17-liter variation in FRC represents ~5% of the FRC normal value (24). This suggests that such a variation is relatively irrelevant from the clinical point of view.VT
No relevant changes in VT were observed in the study (Fig. 5) regardless of gravity or posture. Stability of VT values with changes in gravity has previously been reported for the sitting (22) and standing (9) positions during parabolic flight. Here, we extended these results to the supine position. This finding was expected, since VT is known to remain constant from the upright to the supine position in normogravity and to be controlled by a reflex originating in muscular mechanoreceptors (17).We were surprised that no changes in upper airway cross-sectional area occurred during the breathing cycle. However, stability of upper airway geometry throughout the breathing cycle has been reported in previous studies using the acoustic reflective method (3, 12, 15, 25). One possible explanation for this phenomenon may be the small variations in lung volume observed during quiet breathing in comparison to total lung volume. If total lung volume is assumed to 5-6 liters in an adult, the variations observed in our study were never higher than 15% of the total lung volume.
In summary, we observed an increase in palatopharyngeal and retrobasitongue areas with increasing gravity in the sitting position only, whereas the laryngeal region area decreased in both positions. In the sitting position, the increase in mean area of the palatopharyngeal and retrobasitongue regions may be related to 1) increases in end-expiratory lung volume and 2) decreases in blood volume due to a mechanical hydrostatic effect of gravity. In the supine position, the area of the palatopharyngeal and retrobasitongue regions remained unchanged; a dilator muscle reflex probably inhibits the narrowing effect of gravity in these regions. In the sitting position, narrowing of the larynx with gravity could be linked to downward displacement of the epiglottis. In the supine position, the laryngeal section decreased with increasing gravity, probably as a result of direct mechanical effects of gravity on this semirigid structure.
The variations observed in all of the upper airway regions in the supine position and in the laryngeal region in the sitting position were apparently independent from lung volume variations. Variations in lung volume were clearly insufficient to explain most of the variations in upper airway areas observed in this study. Other mechanisms, such as gravity effects on tissues surrounding the upper airways and/or on the blood volume in these tissues, must have been operative.
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ACKNOWLEDGEMENTS |
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We are grateful to A. Bacchi and B. Malbec, Flight Test Center, Brétigny-sur-Orge, France, for their assistance with this study.
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FOOTNOTES |
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This work was supported by Centre National d'Etudes Spatiales, Toulouse, France.
Address for reprint requests: B. Louis, Faculté de Médecine, Institut National de la Santé et de la Recherche Médicale U492, 8 Ave. du Général Sarrail, 94010 Créteil Cedex, France.
Received 19 May 1997; accepted in final form 26 January 1998.
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REFERENCES |
|---|
|
Top
Abstract
Introduction
Materials & Methods
Results
Discussion
References
|
|---|
1.
Agostoni, E.,
and
R. E. Hyatt.
Static behavior of the respiratory system.
In: Handbook of Physiology. The Respiratory System. Mechanics of Breathing. Bethesda, MD: Am. Physiol. Soc., 1986, sect. 3, vol. III, pt. 1, chapt. 9, p. 113-130.
2.
Beydon, L.,
A. M. Lorino,
F. Verra,
M. Labroue,
P. Catoire,
F. Lofaso,
and
F. Bonnet.
Topical upper airway anaesthesia with lidocaine increases airway resistance by impairing glottic function.
Intensive Care Med.
21:
920-926,
1995[Medline].
3.
Brooks, L. J.,
R. G. Castille,
G. M. Glass,
N. T. Griscombe,
M. E. B. Wohl,
and
J. J. Fredberg.
Reproducibility and accuracy of airway area by acoustic reflection.
J. Appl. Physiol.
57:
777-787,
1984
4.
Brouillette, R. T.,
and
B. T. Thach.
A neuromuscular mechanism maintaining extrathoracic airway patency.
J. Appl. Physiol.
46:
772-779,
1979
5.
Burger, C. D.,
A. W. W. Stanson,
B. K. K. Daniels,
I. P. F. Sheedy,
and
J. W. Shepard, Jr.
Fast-CT evaluation of the effect of lung volume on upper airway size and function in normal men.
Am. Rev. Respir. Dis.
146:
335-339,
1992[Medline].
6.
Burns, J. W.,
and
U. I. Balldin.
Assisted positive-pressure breathing for augmentation of acceleration tolerance time.
Aviat. Space Environ. Med.
59:
225-233,
1988[Medline].
7.
Burton, R. R.,
and
R. W. Krutz.
Gz tolerance and protection associated with anti-G suit concepts.
Aviat. Space Environ. Med.
46:
119-124,
1984.
8.
Clère, J. M., D. Lejeune, D. Tran-Cong-Chi, H. Marotte, and J. L. Poirier. Effect of different
schedules of assisted positive pressure breathing on G-level tolerance.
Ann. SAFE Symp. 26th Yoncalla OR 1988,
p. 76-79.
9.
Edyvean, J.,
M. Estenne,
M. Paiva,
and
L. A. Engel.
Lung and chest wall mechanics in microgravity.
J. Appl. Physiol.
71:
1956-1966,
1991
10.
Elliott, A. R.,
G. K. Prisk,
H. J. B. Guy,
and
J. B. West.
Lung volume during sustained microgravity on Spacelab SLS-1.
J. Appl. Physiol.
77:
2005-2014,
1994
11.
Fouke, J. M.,
and
K. P. Strohl.
Effect of position and lung volume on upper airway geometry.
J. Appl. Physiol.
63:
375-380,
1987
12.
Fredberg, J. J.,
M. E. B. Wohl,
G. M. Glass,
and
H. L. Dorkin.
Airway area by acoustic reflection measured at the mouth.
J. Appl. Physiol.
48:
749-758,
1980
13.
Gonfalone, A.,
and
V. Pletser.
Medical and physiological training certificates.
In: Microgravity During Parabolic Flights with Caravelle ESA. Users' Guide. Noordwijk, Netherlands: Eur. Space Res. Technol. Ctr., 1989, p. 52.
14.
Goodman, L. S.,
W. D. Fraser,
K. N. Ackles,
D. Mohn,
and
M. Pecaric.
Effect of extending G-suit coverage on cardiovascular responses to positive pressure breathing.
Aviat. Space Environ. Med.
64:
1101-1107,
1993[Medline].
15.
Hoffstein, V.,
and
J. J. Fredberg.
The acoustic reflection technique for non-invasive assessment of upper airway area.
Eur. Respir. J.
4:
602-611,
1991[Abstract].
16.
Jan, M. A.,
I. Marshall,
and
N. J. Douglas.
Effect of posture on upper airway dimensions in normal human.
Am. J. Respir. Crit. Care Med.
149:
145-148,
1994[Abstract].
17.
Kinnear, W.,
T. Higenbottam,
D. Shaw,
J. Wallwork,
and
M. Estenne.
Ventilatory compensation for changes in posture after human heart-lung transplantation.
Respir. Physiol.
77:
78-88,
1989.
18.
Lorino, A. M.,
G. Atlan,
H. Lorino,
D. Zanditenas,
and
A. Harf.
Influence of posture on mechanical parameters derived from respiratory impedance.
Eur. Respir. J.
5:
1118-1122,
1992[Abstract].
19.
Louis, B.,
G. M. Glass,
and
J. J. Fredberg.
Pulmonary airway area by the two-microphones acoustic reflection method.
J. Appl. Physiol.
76:
2234-2240,
1994
20.
Louis, B.,
G. M. Glass,
B. Kresen,
and
J. J. Fredberg.
Airway area by acoustic reflection: the two-microphone method.
J. Biomech. Eng.
115:
278-285,
1993[Medline].
21.
McEvoy, R. D.,
D. J. Sharp,
and
A. T. Thornton.
The effect of posture on obstructive sleep apnea.
Am. Rev. Respir. Dis.
133:
662-666,
1986[Medline].
22.
Paiva, M.,
M. Estenne,
and
L. A. Engel.
Lung volumes, chest wall configuration, and pattern of breathing in microgravity.
J. Appl. Physiol.
67:
1542-1550,
1989
23.
Phillips, B. A.,
J. Okeson,
D. Paesani,
and
R. Gilmore.
Effect of sleep position on sleep apnea and parafunctional activity.
Chest
90:
424-429,
1986
24.
Quanjer, P.,
G. Tammeling,
J. Cotes,
O. Pedersen,
R. Peslin,
and
J. Yernault.
Lung volumes and forced ventilatory flows. Standardization of lung function tests.
Eur. Respir. J.
16:
5-40,
1993.
25.
Rubistein, I.,
P. A. MacClean,
R. Boucher,
M. Zamel,
and
J. J. Fredberg.
Effect of the mouthpiece, noseclips, and head position on airway area measured by acoustic reflections.
J. Appl. Physiol.
63:
1469-1474,
1987
26.
Sackner, M. A.,
H. Watson,
A. S. Belsito,
D. Feinerman,
M. Suarez,
G. Gonzalez,
F. Bizousky,
and
B. Krieger.
Calibration of respiratory inductive plethysmography during natural breathing.
J. Appl. Physiol.
66:
410-420,
1989
27.
Sauerland, E. K.,
and
R. M. Harper.
The human tongue during sleep: electromyographics activity on the genioglossus muscle.
Exp. Neurol.
51:
160-170,
1976[Medline].
28.
Schwab, R. J.,
W. B. Gefter,
E. A. Hoffman,
K. B. Gupta,
and
A. I. Pack.
Dynamic upper airway imaging during awake respiration in normal subjects and patients with sleep disordered breathing.
Am. Rev. Respir. Dis.
148:
1385-1400,
1993[Medline].
29.
Shepard, J. W.,
A. W. Stanson,
P. F. Sheedy,
and
P. R. Westbrook.
Fast-CT evaluation of the upper airway during wakefulness in patients with obstructive sleep apnea.
Prog. Clin. Biol. Res.
345:
273-279,
1990[Medline].
30.
Takasaki, Y.,
K. Kamio,
M. Okamoto,
Y. Ohta,
and
H. Yamabayashi.
Changes in diaphragmatic EMG activity during sleep in space.
Am. Rev. Respir. Dis.
148:
612-617,
1993[Medline].
31.
Tenney, S. M.
Fluid volume redistribution and thoracic volumes changes during recumbency.
J. Appl. Physiol.
14:
129-132,
1959
32.
Vellody, V. P.,
M. Nassery,
W. S. Druz,
and
J. T. Sharp.
Effects of body position change on thoracoadominal motion.
J. Appl. Physiol.
45:
581-589,
1978
33.
Yildirim, N.,
M. F. Fitzpatrick,
K. F. Whyte,
R. Jalley,
A. J. Wightman,
and
N. J. Douglas.
The effect of posture on upper airway dimensions in normal subjects and in patients with the sleep-apnea/hypopnea syndrome.
Am. Rev. Respir. Dis.
144:
845-847,
1991[Medline].
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FRC;
B) as functions of gravity and
position. SI0G, SI1G, and SI2G, sitting position in microgravity,
normogravity, and hypergravity, respectively. SU0G, SU1G, and SU2G,
supine position in microgravity, normogravity, and hypergravity,
respectively. Values are means ± SE. For
VT, significant differences
(P < 0.05) occurred only between 0 and 1 or 2 +Gz in sitting position
and between 0 and 2 +Gz in supine
position. For FRC, there are significant differences
(P < 0.05) between all position and
gravity conditions. * Situation significantly different from baseline
value (SI1G).
