Biomedical Engineering Reference
In-Depth Information
3 Results and Discussion
3.1 Statistical Shape Analysis
The first two mode shapes collectively accounted for approximately 70% of the
total variation in the sample population, calculated as the ratio between the individ-
ual variance and the total cumulative variance. The first mode shape explained 45%
of the total variation, primarily describing the LA thickness and its span in the
anterior-posterior direction. The arms of the iliococcygeus decreased in length with
addition of this mode. The second mode shape described a combination of the axial
span of the PF muscles and the span of the iliococcygeus arms (Fig.
4
).
3.2 Effects of PF Shape on Childbirth Mechanics
The modified mean and four PCA-derived models were used to illustrate effects of
the primary shape variations on the mechanics of vaginal childbirth. Nodal
parameters of the derived models were calculated by linearly combining the
population mean with one standard deviation of the shape modes.
Forces required for delivery of the foetal head were calculated for the five cases
at different descent displacements of the foetal head, by adding all reaction forces
from the PF. The forces were normalised with respect to the peak value for the case
of the mean model, as illustrated in Fig.
5a
. The first shape mode primarily
influenced the magnitude of the peak reaction force, since addition of one standard
deviation of the mode to the mean gave the highest normalised peak force among all
Fig. 4 The two most predominant shape variations across the sample population. The
top panels
illustrate the (mean-1
) PF models; the
central panels
show the mean PF models, and the
right
panels
show the (mean + 1
s
s
) PF model.
s
, standard deviation
