Proceedings of 2004 IEEE/RSJ International Conference on
Intelligent Robots and Systems
September 28 - October 2, 2004, Sendai, Japan
Preliminary design of a childbirth simulator with
haptic feedback
A. Kheddar, C. Devine, M. Brunel, C. Duriez
O. Sibony
Laboratoire Systèmes Complexes
40, rue du Pelvoux
91020, Evry, France
Email: [email protected]
AP-HP, Robert Debré
Service génécologie - obstétrique
75019, Paris, France
Email: [email protected]
Abstract— This paper discusses preliminary design of an
interactive childbirth simulator with haptic feedback. This
exploratory work started following a demand of the obstetrics
and gynecology service of a Parisian hospital. Ideally, the
final system should integrate cases-study database in order
to provide a powerful teaching media by means of best of
the virtual/augmented realities technology in terms of multimodal visualization and display. The difficulty of this new
system lies in the haptic display function allowing to teach
gesture interaction skill to obstetricians/midwifes students.
This paper deals only on the feasibility of such a system.
First, the system is presented and its “nominal ingredients”
described in generic terms. Simple models of women pelvis,
fetus and muscles have been considered. Pilot force feedback
delivery is simulated and experienced; results are discussed.
I. I NTRODUCTION
This work aims to conceive and develop an interactive delivery training and planning simulator with haptic
feedback. There are many motivations and challenges in
realizing such a system. All developments are conducted
together with, and under guidance of, the obstetrical service
of the Robert Debré hospital in Paris and, more recently,
with the similar service of the Evry Hospital. This work
started by a direct demand of the first hospital. Before
starting with the complex issues of this study, this very
pilot work was conducted in order to (i) assess the validity
of the concept, (ii) identify the hard points using simple
design and canonical modules/experiments, and (iii) show
the potential end-users (midwifes/obstetricians students)
what a rough system looks like, since for them, it is difficult
to clearly figure out the interactivity with a simulation. This
approach with its preliminary results are described within
this paper. Since results seem to be very promising we
decided to continue with further developments.
The system will be used as a powerful teaching media
using best of the virtual reality technology in terms of high
fidelity rendering and interactivity. One of the challenging
issues of this system is the integration of haptic interaction
allowing the end-users to learn:
• haptic gestures: the subtle gesture force weighting (or
“dosage”) and the hands placement that accompany
the childbirth process preventing abrupt delivery that
causes vagina’ tissues trauma;
• haptic weighting: when using forceps, vacuums, cesarean or episiotomy interventions;
0-7803-8463-6/04/$20.00 ©2004 IEEE
haptic tact/touch: in birth cases where the baby must
be brought out from the inside fetus (twin or multiple
delivery cases) and for the uterus inspection after the
delivery;
Moreover, there is real challenge in achieving a
biophysically-based simulation of the delivery mechanics
based on actual pregnant women’ clinical data. This system
functionality allows obstetricians to forecast and plan complex delivery cases. It also permits to easily record actual
deliveries to enrich the teaching database.
The paper is organized as fellows; first we describe
in some details the delivery simulator purpose. This is
followed by a section presenting what have been achieved
in canonical modeling for the feasibility study and the validation of the overall system structure. Obtained preliminary
results are presented and discussed. The paper ends with a
conclusion and future work description.
•
II. D ELIVERY SIMULATOR PURPOSE
Different pregnancy checkups specify valuable information concerning the expected childbirth. Indeed, it is known
at an early stage if the pregnant woman will give birth
to one or more babies. Moreover, based on biomedical
data such as pelvimetry and fetus anthropometry (that are
obtained from 2D or 3D ultrasound scan), obstetricians
are able to forecast, with a good likelihood, situations of
natural birth, cesarean, cephalic/breech presentation, etc.
Nevertheless, the obstetrical mechanics is not based on
elementary geometry, kinematics or theoretical dynamics.
Practical enforcement of its taught principles comes mostly
from clinical knowledge. Distinguishing different child presentations, recognizing what causes delay during delivery,
deciding of a reasonable delay before acting... depends on
a skilfully monitoring of the delivery situation. Then, right
gestures, through active touch, restore in few minutes the
normal course of the birth process.
As is the case for many medical specialties, theoretical
obstetrics is taught thanks to manuals and books and
practical obstetrics from actual situations’ observations and
dissections. Before reaching an acceptable skill, considerable hours of practicing are needed. Nevertheless, in
the contrary of other medical specialties such as surgery
training, obstetrics can not benefit from cadavers. Nowadays, the childbirth process is learned thanks to mothers
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Fig. 1.
Example of a commercially available childbirth simulator.
parts and babies mannequins based simulators allowing
direct touch and manual exploration. These equipments
with other means and simulators dedicated to students
training have been developed in recent years and most of
them are commercially available (see the figure 11 ). Among
the available obstetrics teaching simulator, we denote:
• simple 3D illustrations allowing students to learn cervical fading steps and different fetus positions within
its amniotic bag, and within the pelvis cavity during
the delivery phase;
• 3D flexible material representing realistic anatomical
parts used in training: vaginal cavity inspections,
cervix (i.e. neck of the womb)’s dilatation estimate;
fontanels and sutures palpations, actual fetus’ position
evaluation, etc;
• complete women’s torso mannequin and fetus made
with flexible and rigid vinyl respectively. This “realistic” setup is used to simulate both cephalic and
breech delivery cases. Additional syringes are used to
reproduce blooding and the amniotic liquid;
• advanced delivery simulator composed of an anthropomorphic women pelvis, an anatomically accurate backbone and fontanel’s on fetal baby/babies,
soft vulva inserts for episiotomy exercises, umbilical
cords... It allows training on: episiotomy, cesarean,
fetus’s parts touching, etc;
• episiotomy dedicated simulators that allows one to
perform different incisions and sutures and to develop
surgical techniques compatible with the required time
constraint;
Although very useful, these simulators are not adjustable
or variably controllable. They are far from representing
all the complex cases that may occur in actual delivery
situations. Indeed, even if the experienced doctors (ie.
the teachers) can see if the users’ gestures are adequate
to some situations, they can not monitor the subtlety of
the touch process and, more peculiarly, the hand’s force
weighting. Reversely, the students can not experience a
realistic response behavior subsequent to their gesture.
Moreover, the very fact is that, mostly, each delivery is
a unique case study. Indeed, obstetricians and midwifes
reported that they face a considerable number of different
cases.
1 Courtesy
of http://www.3bscientific.com/
The right applied gestures is gained from a long practicing experience. Thus, novice midwifes and obstetricians
knowing mostly theoretical aspects, will master the actual
gesture subtlety only after a long confirmed practice. Even
if the experienced doctor guides as best as possible, novice
doctors and midwifes develop apprehensions during the
first clinical enforcements. This situation is negative for
the pregnant women which feels this inexperience causing
additional stress that influences the normal events’ course.
In particular delivery cases (eg. the twin delivery case) the
task is as difficult as the risk is high; in this cases, the
experienced midwife and doctor takes immediately in hand
the control of the situation.
For the previously cited reasons (and others of less trivial
explanations), there is an interest in building an interactive
simulator, based on advanced virtual and augmented reality
techniques. We emphasize that this demand come from
the medical obstetrical service of a Parisian hospital. We
did not made a questionnaire neither assess quantitatively
this demand. The scientific challenge was a sufficient
motivation. Indeed, in many medical fields, such as surgery
training, interactive simulators based on augmented and
virtual reality techniques have demonstrated their benefit
for similar objectives. Moreover, some of these simulators have been adapted to serve as efficient assistance in
mastering novel biomedical techniques and technologies.
Obstetrician and midwifes are helping for its realization.
The system design brings into light additional needs.
Indeed some of the system functionalities may concern the
possibility to study, to forecast and to plan difficult cases
at an early stage. This could be made possible thanks to
a modeling module that links actual clinical data obtained
from the pregnant women to the simulator’ 3D models.
Biomechanics based planning algorithms could be designed
to simulate the delivery process based on tunable external
parameters given by obstetricians. Then, the simulator runtime interactively animate the childbirth process according
to various parameters to assess for risky manipulations.
This module is of prime interest for obstetricians. To
conceive specific biophysically-based animation, critical
factors (such as pelvimetry, fetus anthropometry -size and
shape- and contraction forces) will be taken into account
together with an integrated deformable model describing
interactions (including specific collision tracking, reaction
force and haptics computations).
III. M ODELING
This section deals with geometric modeling of the main
virtual parts involved in the childbirth process, namely: the
women’s parts (pelvis and pelvis’ muscles) and the fetus.
The animation process is also presented.
A. Women’s parts
To have a truthful simulation of the childbirth process,
it is necessary to correctly build the women’s pelvis and
the pelvis’ muscles.
Pelvis’ data acquisition can be obtained from medical
imaging techniques (CT scan, MRI...). Then modeling the
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women’s pelvis can be achieved by two different methods:
– In the first method, mesh construction is carried out from
the obtained volume data (voxels). After different processing levels, a set of points are obtained form which triangle
meshes are constructed (eg. Delaunay’s triangulation). This
technique is used for the more general purpose of 3D
reconstruction from volume data and peculiarly in the medical field. Many refinements have been proposed to enhance
robustness. In [10][11][12] different 3D reconstruction
methods and algorithms have been proposed. Surprisingly,
a women pelvis has been chosen as an implementation
instance.
– The second modeling method is to parametrically model
off-line a “generic” virtual pelvis. Indeed, in obstetrics,
there are specific pelvis’ measurements/parameters that
could be obtained from a direct volume data processing.
Based on these pelvis’ characterizing measures, a morphism is processed to draw the “generic” pelvis so that
it matches the actual geometrical measures. Although the
final obtained virtual pelvis may (and more likely will) be
different from the actual one, the critical pelvis’ parts are
the same (namely the circumferences of the maternal inlet
and the mid-pelvis).
We recall that the goal of this preliminary study is to
show the feasibility of the childbirth simulator. We choose
the free software developed by the INRIA2 allowing to
construct the virtual pelvis directly from medical imaging
data.
Conclusion 1: The women pelvis modeling is not problematic and do not constitute a difficult issue.
The other important part of the system is the geometric
and dynamic modeling of the women pelvis’ muscles. In
this study, we focused on the four main muscles of the
pelvis/vagina which form the major obstacle for the fetus
during the delivery process. There are three types of human
muscles: the “soft” muscles, the cardiac muscles and the
skeletal muscles. The pelvis’s muscles, as about 90% of
the human muscles, are “skeletal type” muscles.
Fig. 2. Pelvis’ muscle FEM deformation. Poisson and Young modulus
are obtained from actual biomechanical data. Up is the rest position
(wireframe and textured muscle). Down is the deforming position.
The mechanical properties of living tissues (including
muscles) have been thoroughly studied by Fung [4]. Considering a first order approximation, the pelvis’ muscles
2 http://www-sop.inria.fr/prisme/
behave as an elastic material having a linear deformation
when a constrain is applied on it. The muscle’s characteristics are: the Poisson coefficient ν = 0.4 and the
Young modulus E = 7.105 . The pelvis’ muscles are shaped
in a simple geometry. In this first implementation, the
deformation’s behavior is related to the constrained applied
forces thanks to a Finite Element Method (FEM) [18].
The figure 2 illustrates the FEM modeling behavior of
one of the four main pelvis’s muscles. In the left part of
the figure a wireframe model is shown whereas in the right
part, the same muscle is shown in solid textured frame. The
muscle is attached to the pelvis through specific extremal
nodes. In this example, a deformation force is applied at
the center of the muscle with a direction pointing to the
up of the figure. The first line of the figure 2 shows the
muscle in a rest position whereas the second line of the
figure shows the muscle during the deformation.
In this first muscle model, we experienced tetrahedral
and parallelepiped (cubic) elements. Each muscle is composed by 54 elements and 112 nodes. The mass and the
inertia effects of each element are negligible in the face of
the muscle stiffness effect. The elements assembly leads to
the well knows FEM equation (in its linear form):
KU = F
(1)
where K is the FEM stiffness matrix that is computed and
inverted off-line (since linear deformation), U is the vector
of nodes’ displacements, and F is the vectore of nodes’
applied external forces.
The obtained muscle’s simulated deformation seems to
behave as an actual muscle. However, there are still investigations that must be undertaken to validate the simulation.
Namely, by confronting the simulation behavior to true
vagina tissue deformation. We stress however, that this is
not a trivial task and there is a great lack of information
concerning this issue. But, in any case, actual physiological
data are a matter of mesh and geometry refinements with
Poisson coefficient and Young modulus adaptation. These
adjustments would be difficult to make if a simple massspring based modeling is chosen instead of FEM. The
deformation computation (O(n2 )) takes less than 0.1msec,
which allows us to perform real-time animation.
Conclusion 2: Modeling vagina tissues/muscles is not a
hard issue. There is also important work in the literature
that has been done in human muscle modeling: model
characterization and parameters identification. We believe
that this part will not bring difficulties. There is however a
thankless work in designing a realistic looking positioning
and muscles attachments between the skin and the pelvis.
B. The fetus
The other important item to be modeled is the fetus.
For fetal modeling, we adopted a methodology that uses
a generic model of the fetus. The fetus is considered as
an articulated parameterized multi-body system, see the
figure 3.
The lengths and circumferences of the upper/lower
limbs, the front/back legs and the fetal abdomen do not
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space during each fetus’ member independent motion.
Indeed, no triangle meshes’ discontinuity arises when the
fetus is animated. The actual fetus model is composed by
approximately 2000 triangles, the fetus skeleton forms five
serial chains with a total of 19 degrees of freedom.
The interaction between the fetus and its surrounding
environment is made through contact forces determined
from a dedicated collision topology tracking algorithm.
These forces induce torques on the fetus’ joints modifying
its skeletal posture. Since the fetus mass is negligible
in the face of muscular stress and abdominal forces, the
joints are modeled as a passive spring/damping mechanism
of stiffness K and damping coefficient B. Considering a
single joint, an applied torque T~ will produce a rotation of
same direction to the torque with amplitude q, such that:
30cm
9.5cm
K(q − q0 ) + B q̇ + |T~ | = 0
Biparital = 95mm
Fig. 3. Snapshot of the fetus modeler/visualizer and obstetrical fetus
measures.
need to be very precise (mean data are chosen as values).
Indeed, the major delivery effort and difficulty arises during
the head’s release (which, in normal delivery cases, comes
out first). The fetus head is also parameterized according
to obstetrical standard measures, see the figure 3.
The virtual head’s geometry is fitted to match the actual fetal clinical data. A visualization interface is being
developed to allow interactive simulation and adjustments
of the fetal modeling process, see the figure 3 (up picture).
The fetus is considered as an articulated multi-body system
described by a hierarchical serial links starting from the
abdomen (chosen to be the local reference frame). The
joints are set with degrees of freedom as same as the real
fetus (but only the more pertinent degrees of freedom are
taken into account). The initial joint space position of the
fetus is not supposed to be the position taken inside the
women, but the born one. This rest position is illustrated
in the figure 3. Inside the women abdomen the fetus
undergoes a special folding position.
The fetus joints are supposed to be passive springdampers actuators, and the folding position is obtained
under the abdomen’ space constraints and/or the ultrasound obtained one. When the fetus is delivered, it goes
back to its “initial” rest state since no constraints are
applied on its parts. These passive joint actuators are
mandatory, they just allow to not animate the fetus from
an external system controller.
The fetus animation is skeleton driven and the triangle
meshes, that are near the joints, are made deformable (by
simple interpolation). This is to hide the induced empty
(2)
q0 is the initial value vector. When a force F~ is applied, it
influences the related joint and the rest of the kinematics’
chain. The projection of forces into equivalent torques on
the joint space is made simply through on-line Jacobian
computation. Indeed the applied torque (equation 2) is
replace by K(~q − ~q0 ) + B ~q̇ + J(q)t F~ = ~0.
Conclusion 3: A more refined model of the fetus can
possibly be achieved. However, we believe that the difficult
problem of this part is to model the fetus’s head deformation under constraints. Indeed, the fetus head undergoes deformations during the delivery and to our best knowledge,
there is no previous work in modeling this phenomenon.
C. Biophysically-based animation and computer haptics
The muscles are attached to the pelvis and the fetus
put into the uterus cavity. Now one needs to simulate the
delivery process. The fetus is put into a highly constrained
environment, and is under the influence of multiple forces.
For a normal childbirth, two operations are necessary: the
outbreak of the cervix (neck of the womb) that allows the
fetus eviction out of the uterus, and to work the pelvis’s
way up. Before the eviction mechanism occurs, the only
forces that act on the fetus are the uterus contractions. They
are: involuntary; progressive in frequency (from 2 to 5mn)
in intensity, and in duration (from 15sec to 1mn); total
(they propagate to the whole uterus); subjectively painful,
palpable and efficient.
F2
F1
Fig. 4.
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Applied forces during the delivery process.
When the delivery starts the fetus’ eviction/drop, the
only propulsive force is the uterus contraction. Contraction
force transmits its strength through the pressure increase in
the amniotic liquid trapped behind the fetus. This process
could be likely considered as an hydraulic actuator [1] (see
force F1 in the figure 4).
During the final extricating phase, additional forces are
added to the uterus contractions: the expulsion forces
that repulse the uterus downwards through an increase
of the intra-abdominal pressure of about 3 to 5cmHg
[6]. This pressure is comparable to a pneumatic actuator
[1] (see F2 in the figure 4): closed glottis, in a forced
inspiration, the effort repulses the diaphragm downwards.
Since the abdominal muscles are contracted, they prevent
the abdomen expansion. Consequently the intra-abdominal
pressure increases and flushes the uterus.
The main issue of the system is indubitably the design
of the simulation engine that takes into account all these
forces and the external constrained forces due to the Pelvis
and the vagina tissues/muscles. In another paper [2] of
this conference, a real-time formalism for the computation
of deformable objects deformation with haptic feedback
is proposed. Although the application concerns industry
virtual prototyping, is applies for this system but in taking
into account the multi-body and skeletal-driven specificities
of fetus. External interaction forces must also include the
user hand that will interact with the fetus (when it starts
to come out) and with the vagina tissues.
Conclusion 4: This part is actually the sensitive issue
and the bottleneck of the entire system. Specific collision tracking and biophysically-based modeling must be
designed. If theoretically solutions and practical real-time
implementation algorithms seem to emerge, it remains the
complicated problem of how to tune adequately the simulation parameters? and how they link to actual physiological
and clinical ones? what parameters to consider? how to set
friction parameters?... are still very open questions.
IV. P RELIMINARY EXPERIMENTS
We have conducted preliminary experiments in order to
assess actual needs and requirements (a sort of a draft
mock-up) that help the obstetricians to see what would
the final system looks like.
A virtual hand, representing the user is added to the
simulated women pelvis, muscles and fetus. We recall that
this preliminary study aims to show the feasibility of the
concept. Consequently, the virtual models are somehow
simplistic and the haptic interface is taken to be the
PHANToM Desktop from Sensable technologies3 . The
PHANToM’ stylus is attached to the right hand major
phalanx in such a way the PHANToM’s terminal point
fits in the ‘center’ of the inside palm. Consequently, the
virtual hand is animated by the actual one and the reaction
forces are applied normal to the user hand’s palm. During
the simulation process, the virtual hand interacts with the
fetus’ head to prevent an abrupt childbirth through a subtle
force weighting on the fetus’ head. Collision detection and
force feedback are computed from the GHOST library.
Fig. 5.
Fetus progression under different applied forces. The fetus
trajectory follows a parameterized path (λ).
The fetus motion is the aggregate of the contraction
forces, the constraint forces and the user applied forces.
Simple Newton’s law
P dynamics are applied to this first
experiment, that is
F = mλ̈, explicit numerical integrations provide the fetus position at each simulation loop.
We assume that the contraction forces are dominant and
that the fetus is constrained on a precomputed path. A
mean contraction induces a pressure of about 5cmHg(4) .
The pressure acts on the largest fetal section perpendicular
to the pressure axle of the uterus. This section is the area
of the abdominal circumference, ∼85cm2 . Consequently,
the fetus is propelled with a force of 56N during the pelvis
excavation descent, [6]). The extrication force increases the
pressure from 3 to 5cmHg on a 300cm2 surface [6]; this
corresponds to additional forces of 120 to 200N. The total
applied force on the fetus is approximately 156 to 256N
per contraction. These forces are the delivery ones and not
the ones to be rendered to the users. Simulation of a hapticgesture-guided delivery is illustrated (at different scales) on
the figure 5. One can notice the λ ∈ [0, 1] progression in
function of the contraction forces (that are supposed to be
nicely periodic) and operator applied forces.
The figure 6 shows snapshots of the animated virtual
childbirth process. The fetus is placed in a space corresponding to its approximate position inside the uterus. A
virtual hand, representing the midwife’s or obstetrician’s
one, is animated through position and orientation data
obtained directly from the PHANToM. The fetus is propelled under contraction forces. The four important pelvis’
muscles, making up the major obstruction that prevents
from fetus outing, has been fixed to appropriate pelvis
locations. Obstruction forces are considered to be the main
constraint forces, in this demonstration case, they have
been computed through a penalty based method. A more
refined algorithms will be applied to compute interaction
4A
3 http://www.sensable.com/
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pressure of 1cmHg is equivalent to 1.33kPa.
V. C ONCLUSIONS AND FUTURE WORK
Fig. 6. Different steps in an actual interactive delivery simulation with
force feedback.
forces between deformable bodies including friction and a
truthful biophysical behavior [2].
Another functionality that may offer the developed
system is to allow on-line interactive path design. This
functionality is requested by the obstetricians. In this case
only the fetus head is represented. The fetus’ head fellows
a predefined path that can be adjusted interactively. The
fetal progression path is defined as a parameterized Bézier
curve with four control points. User can add additional
control points, change the position of the control points
and vary the curve parameters in real time. The figure 7
illustrates a fetal head progression through a predefined
path. In the final simulator design, this trajectory is also
generated thanks to less constraint path planning algorithm
to study potential problems that may occur during the
delivery process.
Fig. 7.
path.
Different steps in a fetal head progression through a predefined
Conclusion 5: From this preliminary study, we come up
with the following points:
• the system design is feasible and we will work toward
its realization under obstetricians/midwifes guidance;
• the PHANToM device is not adequate and it appears
clearly from the experiments that a new dedicated
haptic device must be conceived;
• mixing the visualization and haptic spaces is necessary in this application;
• lack of clinical data and obstetrical bio-mechanical
models, namely to tune and set the values of various
parameters is clearly problematic;
• it will be difficult to compare the simulation behavior
to the real process because ethic law prohibits obtaining data in-situ (ie. on-line during a delivery case).
The first objective of this work was to demonstrate the
feasibility and the usefulness of an interactive childbirth
simulator. Obstetrical gesture seems to be complex and
difficult to master; a lot of practice is necessary. It comes
under experience of practicing and requires haptic sensory
skill. Up to date, to our best knowledge, we are the
first to propose using virtual reality haptics in obstetrics
and childbirth training. To fulfill preliminary investigations
requirements, we show the feasibility of each components
of the proposed system. All the achieved subsystems show
that the project is viable.
Further investigations are concerned with the refinement
of all the developed modules. We are now working actively
to realize a realistic interactive simulation based on realtime collision tracking algorithms and biophysically-based
animation of all existing tissues. As for the haptic interface,
the PHANToM appears to be limited and the conception
of a novel dedicated interface, including tactile feedback
is in the way. In the near future, we hope to complete this
interactive childbirth simulator.
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