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Vol. 83, Issue 5, 1531-1537, 1997
Department of Electronics, Microelectronics and Telecommunications, Laboratory of Movement Biomechanics, Chest Service, Erasme University Hospital, and Biomedical Physics Laboratory, Free University of Brussels, 1070 Brussels, Belgium
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
APPENDIX
ACKNOWLEDGEMENTS
FOOTNOTES
REFERENCES
ABSTRACT 
De Groote, A., M. Wantier, G. Cheron, M. Estenne, and M. Paiva. Chest wall motion during tidal breathing. J. Appl. Physiol. 83(5): 1531-1537, 1997.
We have used an automatic
motion analyzer, the ELITE system, to study changes in
chest wall configuration during resting breathing in five normal,
seated subjects. Two television cameras were used to record the
x-y-z displacements of 36 markers positioned circumferentially
at the level of the third (S1) and fifth
(S2) costal cartilage, corresponding to the lung-apposed
rib cage; midway between the xyphoid process and the
costal margin (S3), corresponding to the abdomen-apposed
rib cage; and at the level of the umbilicus (S4).
Recordings of different subsets of markers were made by submitting the
subject to five successive rotations of 45-90°. Each recording
lasted 30 s, and three-dimensional displacements of markers were
analyzed with the Matlab software. At spontaneous end expiration,
sections S1-3 were elliptical but S4 was
more circular. Tidal changes in chest wall dimensions were consistent
among subjects. For S1-2, changes during inspiration
occurred primarily in the cranial and ventral directions and averaged
3-5 mm; displacements in the lateral direction were smaller
(1-2 mm). On the other hand, changes at the level of
S4 occurred almost exclusively in the ventral direction. In
addition, both compartments showed a ventral displacement of their
dorsal aspect that was not accounted for by flexion of the spine. We
conclude that, in normal subjects breathing at rest in the seated
posture, displacements of the rib cage during inspiration are in the
cranial, lateral outward, and ventral directions but that expansion of
the abdomen is confined to the ventral direction.
rib cage; respiratory muscles; abdomen; mechanics; shape
INTRODUCTION SINCE THE WORK of Konno and Mead (8), the chest
wall has been considered as a structure with two compartments, the rib cage and the abdomen. Distinct displacements of each part have been
measured with magnetometers (9) and inductive plethysmography (Respitrace) (10), but three-dimensional (3D) motion within each
compartment has not been analyzed in detail because the information provided by the Respitrace was limited to changes in a single rib cage
or abdominal cross section and magnetometers did not provide
simultaneous measurements for more than three or four diameters. In
1985, Ferrigno et al. (6) described a new method enabling the analysis
of 3D movements of a large number of markers fixed on the chest wall.
The method was validated in 12 healthy subjects in a study in which
inspired volumes were computed from geometric reconstructions and were
compared with spirometric data (5). In present work, we have analyzed
with the same technique detailed movements of points located on the rib
cage and the abdomen during quiet breathing. The aim of the study was
to assess respiratory changes in the 3D configuration of the chest wall
and to provide normative data for seated subjects.
MATERIALS AND METHODS Chest wall motion was studied by using an automatic motion analyzer,
the ELITE system (5). This system records the position of markers
(hemispheres coated with reflective paper) placed on an object in
motion by using television cameras that have different viewpoints. The
system supplies the acquisition of two-dimensional frames for each
camera and then computes 3D coordinates of each marker as a function of
time. It also provides algorithms that filter the noisy biological
signals (4, 6). In addition to these measurements, respiratory changes
in rib cage and abdomen cross section were measured using inductive
plethysmography.
In our experiments, the ELITE system was calibrated for a working
volume of 60 cm × 60 cm × 40 cm. We estimated the resolution to be
0.1 mm by measuring the signal-to-noise ratio while the system was
recording the position of a static marker. For the volume studied, the
ELITE manufacturers give a precision better than We studied five healthy male subjects of whom two were highly trained
in respiratory maneuvers (Table 1). The
subjects were studied while seated on a rotating stool with the lower
portion of the dorsal spine resting against a support. They were asked
to maintain the same position during the acquisitions and to breathe
quietly through a pneumotachograph by using a mouthpiece and a
noseclip. No particular instruction regarding the breathing pattern was
given. We positioned a total of 36 (or 37) markers (Fig. 1) by using
the projection of a grid on the body with a
slide projector. The markers were attached around the chest wall at the
level of the third (S1) and fifth (S2)
costal cartilage, corresponding to the lung-apposed rib cage; midway
between the xyphoid process and the costal margin (S3),
corresponding to the abdomen-apposed rib cage; and at the level of the
umbilicus (S4). Markers that were in front of the spine
were fixed on the support. Each section, S1,
S2, S3, and S4, was perpendicular
to the craniocaudal axis of the body and was described by eight
markers. The markers of sections S2 and S4 were
fixed on the rib cage and abdomen Respitrace bands, respectively.
Comparison between movements of the markers and changes in rib cage and
abdominal cross section will form the basis of another study.
Because our Elite system included only two television cameras, we
recorded motion of different subsets of markers during six successive
acquisitions. Between two acquisitions, the orientation of the subject
relative to the cameras was modified by rotating the stool (Fig.
2) [angle of rotation (
Flow at the mouth was recorded with a Lilly-type pneumotachograph and a
Validyne differential pressure transducer. Volume was obtained by flow
integration, and calibration was made by means of a 1-liter syringe.
The flow signal was recorded on an eight-channel tape recorder,
digitized at a frequency of 50 Hz with an analog-digital card, and
synchronized with the ELITE data.
mm. We have
recorded the displacements of a marker positioned with a micrometer and
have calculated a precision better than 1/2 mm.
Table 1.
Physical characteristics of subjects
Subject
Age, yr
Height, m
Weight, kg
MP
52
1.72
70
NP
29
1.86
77
OV
25
1.76
70
VA
39
1.77
65
WP
28
1.76
56
Mean ± SD
34.60 ± 9.89
1.77 ± 0.05
67.6 ± 6.95
Fig. 1.
Schematic view of ventral and dorsal aspects of the chest wall in 1 subject showing positioning of markers (
), Respitrace bands (hatched
areas), and spine support. x, y, and z,
Laterolateral, craniocaudal, and dorsoventral axes, respectively.
[View Larger Version of this Image (30K GIF file)]
) = 0, 45, 135, 180, 225, and 315°]. Data were recorded at a rate
of 50 Hz during periods of 30 s. When movements of the ventral part of
the body were recorded ( = 0, 45, and 315°), the subjects'
hands were positioned behind the back. When movements of the dorsal
part of the body were recorded ( = 135, 180, and 225°), the
hands were placed on the knees (Fig. 1).
Fig. 2.
Schematic view of subject positioned on rotating stool with his spine
resting on a support (C). Cameras were placed 150 cm (A) from the
subject and were spaced 128 cm (B) apart. x
yz, Relative
axis system with respect to cameras; , angle of rotation between
absolute axis system xyz and xyz; t, translation
vector between the 2 axis systems; o and o, origins.
[View Larger Version of this Image (10K GIF file)]
yz of the cameras (Fig. 2), we applied a rotation ()
around its origin (o) to express data in an intermediate system. This
system was parallel to the absolute system xyz of the subject
( = 0°) but did not share the same origin (o and o in Fig. 2).
Therefore we chose the marker placed on the support as the
characteristic point in each system, and we made a translation (t) to
merge the origins of the two systems. For some acquisitions, the
position of this characteristic marker had been actually recorded
( = 135, 180, and 225°), but for others ( = 0, 45, and
315°), it was located by using the position of the marker placed on
the sternum and the distance between this marker and the one placed on
the support.
RESULTS
= 0°; *, data
for = 45°; 
, data for = 135°, 
, data for = 180°; encircled crossed plus, data for = 225°; +, data for
315°.
Respiratory movements during tidal breathing. Figure 4A (section S1, axial projection) and Fig. 4B (sections S1-S4, frontal projection) show for one representative subject (VA) the positions of the markers at the beginning and at the end of selected inspirations. The tidal vector is amplified by a factor of 10. The orthogonal scale refers to the anthropometric dimensions of the body, and the 3-mm scale refers to the amplitude of respiratory movements. Figure 4 illustrates that, although obtained during successive acquisitions with the subject in different orientations, the position of the markers did not show too much scatter.
, Beginning of inspiration; X, end of
inspiration; arrows = mean tidal vectors. See text for discussion.
To study the variability in amplitude and direction of tidal vectors between subjects, we represented all vectors in Figs. 5, A-D, and 6; in Figs. 5 and 6, tidal vectors from all subjects were merged to have the same origin. The scales are the same as in Fig. 4. We observed that markers on the rib cage (Fig. 5, A, B, C: S1, S2, S3, respectively) moved mainly in the ventral and cranial direction during inspiration. Lateral movements were small for all markers and, as expected, were negligible for markers positioned on the mediosagittal line (navel, sternum). For the abdomen (Fig. 5D: S4), the largest movements were in the ventral direction. Lateral and craniocaudal movements were small. The navel did not present any lateral movement. Markers placed on the support did not move. Finally, markers on the dorsal aspect of the rib cage and abdomen presented movements that predominated in the ventral direction.
Table 2 summarizes average displacements of the seven markers of sections S2 and S4 and of the two markers fixed on the support. It also provides information relative to individual trends and level of statistical significance for group data. We considered separately the markers placed on the mediosagittal line and on the ventral, lateral, or dorsal portions of the chest. Changes in the left and right side of the body were averaged. Table 2 also gives the number of respirations used for each measurement. We observed that displacements of the ventral and lateral parts of the rib cage during inspiration occurred primarily in the cranial and ventral directions and averaged 3-5 mm. Displacements in the lateral outward direction were smaller (1-2 mm). For the abdomen, displacements predominated in the ventral direction and were more pronounced for the ventral part. The dorsal parts of the rib cage and abdomen also showed significant movements, in particular in the ventral direction.
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DISCUSSION
) that describes the
orientation of the subject with respect to the cameras was measured by
reference to a mark on the stool with a precision of ~3°. Taking
into account that the angle of the subject could slightly differ from
the angle of the stool, we estimated that the global precision was
5°. Finally, to visualize lateral markers, we had to make
measurements with the arms either on the knees or behind the back. This
postural change could also be responsible for small modifications in
marker position. Results shown in Fig. 3 suggest, however, that the
errors of the method were small.
Configuration at end expiration.
It is shown in Fig. 3 for subject VA that, at end expiration,
the ratio between the dorsoventral and transverse diameters was smaller
for the rib cage than for the abdomen. A similar observation was made
in the other subjects, indicating that, in the seated posture, the
abdominal cross section is closer to a circle than the rib cage cross
section. This finding is consistent with previous studies of chest wall
shape obtained by using magnetometers in normal humans (13).
Respiratory movements during tidal breathing.
Measurements of rib cage and abdominal dimensions have been previously
obtained by Konno and Mead (8) using pairs of linear differential
transducers and by Wade (14) and Agostoni et al. (2) using
mercury-in-rubber transducers. They studied how the dorsoventral and
transverse diameters or the circumference of the rib cage and abdomen
changed during various respiratory maneuvers in the upright
and/or the supine posture (1). In the present study, geometric
displacements of several markers fixed on the chest wall were measured
with the subjects in the seated posture and during quiet breathing.
This study differs from earlier works in that the 3D displacement of
each marker was computed, which allowed us to assess changes in the 3D
configuration of the chest wall during breathing.
We found that the pattern of marker displacements during tidal
breathing was similar in the five subjects of the study. The rib cage
was invariably displaced in the cranial direction during inspiration
and showed an outward motion of its ventral and lateral aspects. Based
on the anatomy of the ribs' articulations with the vertebral bodies,
cranial motion of a rib is expected to be accompanied by a ventral and
a lateral component, but the amplitude of these two components should
differ in the upper vs. the lower portion of the rib cage. In the upper
portion of the cage, the rib neck axes are almost parallel to the
frontal plane of the body. Consequently, when the upper ribs move
cranially in inspiration, their ventral ends move ventrally but their
lateral displacement is small (the so-called "pump-handle"
motion). In contrast, the axes of the necks of the lower ribs are
oriented dorsally. Therefore, elevation of these ribs in inspiration is
accompanied by a significant lateral expansion (the so-called
"bucket-handle" motion) (11, 12, 15). In the present study, we
did not find such a difference between the upper and lower portions of
the rib cage; as shown in Fig. 5, A-C, there was no
clear-cut difference in the relative amplitude of the ventral and
lateral displacements measured at the level of the third costal
cartilage (S1) and midway between the xyphoid process and
the costal margin (S3). This observation can be best
explained by the fact that the orientation of the rib neck axes changes
significantly between ribs 1-2 and 3-4 but is
very similar for all ribs located caudally to ribs 3-4
(7).
In contrast to the rib cage, markers placed on the abdomen did not show
any cranial motion during inspiration, and lateral movements were
small. In fact, motion of the ventral and lateral aspects of the
abdominal wall was primarily in the ventral direction such that the
abdomen became more circular during inspiration. This deformation can
be explained by the fact that skeletal structures constrain the abdomen
laterally and restrict its lateral expansion during breathing.
Markers placed on the dorsal aspect of the rib cage and abdomen also
moved during inspiration. Although motion in the cranial and lateral
directions was small in magnitude and was not present in all subjects,
motion in the ventral direction was substantial and was invariably
present. This motion, which has not been reported previously, is not
easy to explain. We do not think that it may be artifactual in nature
and represent a skin motion artifact because sliding of markers around
the elliptical perimeter of the rib cage and abdomen would be expected
to produce a predominant displacement in the lateral, rather than in
the ventral, direction. Similarly, involuntary flexion of the spine may
be discarded because markers placed on the spine did not move
(APPENDIX).
Alternatively, we suggest that the ventral displacement of the dorsal
aspect of the chest wall observed here might be related to a ventral
displacement of the center of gravity of the body during inspiration.
Because the ventral aspect of the rib cage and of the abdomen moves
outward during inspiration, the center of gravity of both compartments
is expected to be displaced ventrally. If unopposed by contraction of
paraspinal muscles, this alteration should result, in turn, in a
ventral displacement of the trunk. Because in the present experiments
the position of the spine was fixed, only the dorsal aspects of the rib
cage and abdomen located laterally to the spine were allowed to move
ventrally.
In summary, we have shown that, in normal subjects breathing at rest in
the seated posture, displacements of the rib cage during inspiration
are in the cranial, lateral, and ventral directions but that expansion
of the abdomen is confined to the ventral direction. We have also
demonstrated that the dorsal aspects of the two compartments move
ventrally during inspiration.
ACKNOWLEDGEMENTS
The authors acknowledge Pierre Mathys and Jean-Louis Van Eck for critical review and helpful suggestions on the manuscript. The authors also express their thanks to Alain Van Muylem for the statistical analysis and help during the experiments.
FOOTNOTES
Address for reprint requests: M. Paiva, Biomedical Physics Laboratory, cp 613, Route de Lennik, 808, 1070 Brussels, Belgium.
Received 21 February 1996; accepted in final form 27 June 1997.
APPENDIX
We made a specific experiment to verify the motionlessness of the spine in two subjects (MP and VA). We used an excavated support that allowed us to place four markers directly on the spine; one marker was fixed to the support, and 10 additional markers were attached to the rib cage and abdomen (Fig. 7A). Recordings of 30-s duration were performed on three occasions in the two subjects and showed that displacements of the markers fixed on the spine and on the support were of the order of magnitude of the noise (Fig. 7B). On the other hand, markers fixed to the dorsal aspect of the chest wall showed a significant ventral motion during inspiration (Fig. 7B).
) and excavated support used
during specific experiment performed to study movements of spine
(APPENDIX). B: lung volume and dorsoventral
movements for markers (nos. 1-15) are shown as a function of time.
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