Jjj. Dirckx et al., VOLUME DISPLACEMENT OF THE GERBIL EARDRUM PARS FLACCIDA AS A FUNCTIONOF MIDDLE-EAR PRESSURE, Hearing research, 118(1-2), 1998, pp. 35-46
The pars flaccida (PF) is a small region of the eardrum, with elastici
ty and histology completely different from the rest of the membrane, w
hich has often been attributed a pressure regulating function for the
middle ear (ME). In this paper, the Volume displacement of the PF as a
function of ME pressure is discussed. The deformation of the PF was m
easured in vitro in five Mongolian gerbil ears, by means of an opto-el
ectronic moire interferometer. Volume displacement was determined at s
mall intervals in three sequential pressure cycles, in the range of +/
- 0.4 kPa, +/- 2 kPa, and again +/- 0.4 kPa. The displacement was foun
d to be a highly non-linear function of pressure, with a strong increa
se up to 0.4 kPa ME over-or underpressure and remaining nearly unchang
ed for pressures beyond 0.4 kPa. In all animals, maximal volume displa
cement was less than 0.5 mu l, or 0.2% of total ME air volume. Clear h
ysteresis was found between the deformations at the same pressure leve
l in the increasing and decreasing parts of the pressure cycles. Membr
ane behavior in the first 0.4 kPa pressure cycle was significantly dif
ferent from that in the second 0.4 kPa cycle, which followed the 2 kPa
pressure cycle. The results indicate that the ME pressure change regu
lation function of the PF is limited to very small pressure changes of
a few hundred Pa around ambient pressure, and that larger ME pressure
s cause at least short-term changes in the membrane's behavior. (C) 19
98 Elsevier Science B.V.