# Round Window Reinforcement-Induced Changes in Intracochlear Sound Pressure
## 4 Discussion
### Effect of RWM Reinforcement on the ICSP  
Using cartilage as a reinforcement material, a maximum median (of all samples) \(P_{ST}\) change of 13 dB was identified after the RWM reinforcement (cf. Figure 6). In general, significant RWM reinforcement-induced changes in \(P_{ST}\) were observed only at frequencies below 2 kHz. These results are in good agreement with the corresponding data reported previously by [PERSON] et al. (2018) for one HTB ([PERSON] et al., 2018). The sound pressure in the basal part of the scala vestibule (\(P_{SV}\)) did change considerably less (<3 dB) than in the scala tympani. This behavior indicates that pressure-relieving mechanisms such as the cochlear and vestibular aqueducs prevent a strong increase in \(Z_{C}\) due to the stiffened RWM. The fact that RWM reinforcement did not have a significant influence on the stages velocity (cf. Figure A1, Appendix A) further confirms the relevance of the aqueducs as soon the RWM is reinforced. However, [PERSON] et al. (2018) reported an increase in \(P_{SV}\) of up to 10 dB after stiffening the RWM with a combination of perichondrium, cartilage, and Jeltrate, whereas in our study, we could only observe a pressure increase below 3 dB using cartilage. Nevertheless, it is important to note that the results of [PERSON] et al. (2018) stem from only one HTB sample.  
Considering the individual samples instead of the averaged data, RWM reinforcement-induced changes in \(P_{ST}\) of up to 25 dB but also below 5 dB were observed. We expect that the large variation in the reinforcement effect between individual samples was mainly due to the manipulation of the material during the reinforcement of the RWM. The comparatively small effect of the reinforcement on the ICSP using silicone with the highest material stiffness of the three considered materials confirms our assumption. Using a stiff reinforcement material makes it challenging to firmly attach the material to the 3D curvature of the RWM. In addition, the placement of the material must be conducted with great care to minimize the risk of RWM damage and, hence, loss of the sample.  
To assess the effectiveness of the reinforcement procedure, one would need to quantify the RWM impedance after reinforcement from the simultaneous measurement of the RWM volume velocity and \(P_{ST}\) (\(Z_{RWM}=P_{ST}/U_{RWM}\)). This is difficult to accomplish, mainly due to the opaque nature of the reinforcement material, which prevents the direct interrogation of the RWM motion using the LDV. Estimating the RWM motion from the velocity measurements on the surface of the reinforcement material is inappropriate because of the relatively thick reinforcement material and its uncontrolled interface with the RWM. A better alternative to the reinforcement material used in the present study would be a transparent material that also provides a good binding with the RWM. A transparent hydrogel compound developed by [PERSON] et al. (2018) which directly reacts with biological tissues might be an option for further research. Besides the advantages of a well-controlled interface between the hydrogel and the RWM and direct optical access to the RWM, the hydrogel might also allow for a stepwise increase in RWM stiffness during the curing  
Figure 7: Input cochlea impedance (\(Z_{c}\)) compared to the reference data: (**A**) magnitude of the \(Z_{c}\) and (**B**) respective phase data. The bold black line and the shaded area represent the study data median and the SD, respectively. The literature data are indicated in individual colors.  
process. A reinforcement material with such properties would allow for more repeatable and controllable measurement conditions, which we see as crucial in order to gain a more quantitative knowledge of the RWM reinforcement effect on the cochlear hydrodynamics.