Biomedical Engineering Reference
In-Depth Information
Fig. 7.23
CAD-model of the final prototype
During testing, the minimum and maximum membrane pressure was adjusted
such that the T-bars were horizontally levelled and not contacting the guiding
mechanism. Adjustment of the membrane (over) pressure was not possible since
the resolution of the employed barometer was above 10 mbar. For pressure
mapping the I
NTERFACE
F
ORCE
X-
SENSOR
M
AT
(81 9 203 cm) was used including
the software package X3 M
EDICAL
V6.0.
7.1.7.2 Pressure Mapping Measurements Involving
Foam Material S
AF
6060
The pressure mapping images in Fig.
7.24
illustrate a strong influence of body
position on the maximum interface contact pressure stress. The body of the female
volunteer, Fig.
7.24
a, was not centered on the mattress but positioned to the left.
This placed more load on the left T-bars, pushing the right T-bar upwards, leading
to a maximum interface contact pressure of 36.4 mmHg at a membrane internal air
pressure of 12 mbar (cf. colour grid with mean pressure values). Figure
7.24
b
shows a membrane internal air pressure of 20 mbar and the volunteer was placed
on the right side, showing a contrary effect to that described previously. Inter-
estingly, almost doubling membrane internal air pressure from 12 to 20 mbar,
resulted
in
only
a
marginal
increase
of
mean
interface
contact
pressure,
i.e. 31.3 mmHg compared to 32.1 mmHg.
Figure
7.25
shows the contact pressure distribution for the male volunteer
with a minimum and maximum membrane pressure of 10 and 22 mbar. Again,
the body position strongly influenced the contact pressure values. In contrast to
the female volunteer, increasing the membrane internal air pressure by factor
2.2-22 mbar caused a 2 mmHg decrease of mean interface contact pressure.
This may have been caused by repositioning of the volunteer during mea-
surement (cf. the sensor numbers) and/or by the viscoelastic behaviour of the
mattress foam material. As observed for the female volunteer, doubling the
membrane internal air pressure only resulted in a marginal increase of mean
contact pressure.