Biomedical Engineering Reference
In-Depth Information
Fig. 3 Front view of (a) the mean pelvic floor muscle model, and (b) initial position of the fetal
skull in the childbirth simulation.
Beige/light gray
, levator ani;
dark red/dark gray
, obturator
internus;
silver
, pubic bone and fetal skull
series of vertical displacements until the biparietal diameter passed through the LA
orifice. Rotation of the skull was allowed during the descent to minimise the
reaction forces from the LA muscles. The interaction between the LA muscle and
foetal skull was modelled using finite deformation elasticity with additional
constraints to simulate the nonuniform distributions of contact forces between the
two bodies [
24
].
An isotropic exponential constitutive relation was adopted to describe the non-
linear mechanical response of the LA muscles during labour. The material relation
was fitted to the experimental data from uniaxial extension of fresh human PF
specimen reported by Jing et al. with its strain energy density function
C
illustrated
as below.
e
bð
I
1
3
Þ
C ¼
a
½
1
(4)
Where I
1
is the first invariant of right Cauchy-Green deformation tensor,
a
¼
22.1
0.5 [
25
,
26
].
The pubic bones were assumed to be much stiffer than the muscles, with material
coefficients
a
kPa and
b
¼
0.5. Foetal head moulding was not
considered in this work and the mechanical properties of the foetal skull were
assumed to be the same as those of the pubic bones.
¼
22,100,000 kPa and
b
¼
