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. 2022 Apr 22;7(3):816-824.
doi: 10.1002/lio2.797. eCollection 2022 Jun.

Evaluation of acoustic changes in and the healing outcomes of rat eardrums with pars tensa and pars flaccida perforations

Yaoqian Liu  1 , Cuiping Wu  1 , Tingting Chen  2 , Qiyue Shen  3 , Yuanping Xiong  4 , Zhengnong Chen  1   5 , Chunyan Li  1   5
Affiliations

Evaluation of acoustic changes in and the healing outcomes of rat eardrums with pars tensa and pars flaccida perforations

Yaoqian Liu et al. Laryngoscope Investig Otolaryngol. .

Abstract

Objectives: To systematically explore the differences in acoustic changes and healing outcomes of tympanic membranes (TMs) with pars flaccida perforation (PFP) and pars tensa perforation (PTP).

Methods: We created PFPs and PTPs of various sizes in Sprague-Dawley rats, and evaluated TM umbo velocity and hearing function using laser Doppler vibrometry and auditory brainstem response (ABR) measurement before and immediately after perforation. Two weeks later, hearing was reevaluated and TMs were investigated by immunohistochemical staining.

Results: Small PFPs and PTPs did not significantly affect umbo velocity and hearing function. Large PFPs increased umbo velocity loss at low frequency (1.5 kHz) and elevated ABR thresholds within 1-2 kHz. Large PTP caused significant velocity loss at low frequencies from 1.5 to 3.5 kHz and threshold elevations at full frequencies (1-2 kHz). Two weeks after the perforation, the hearing function of rats with healed PFPs recovered completely. However, high-frequency hearing loss (16-32 kHz) persisted in rats with healed PTPs. Morphological staining revealed that no increase in the thickness and obvious increase in collagen I level of regenerated par flaccida; regenerated pars tensa exhibited obvious increase in thickness and increased collagen I, while the collagen II regeneration was limited with discontinuous and disordered structure in regenerated pars tensa.

Conclusion: The hearing loss caused by large PFP limits at low frequencies while large PTP can lead to hearing loss at wide range frequencies. PFP and PTP have different functional outcomes after spontaneous healing, which is determined by the discrepant structure reconstruction and collagen regeneration.

Keywords: auditory brainstem response; collagen; pars flaccida perforation; pars tensa perforation; umbo velocity.

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Conflict of interest statement

The authors declare no conflicts of interest.

Figures

FIGURE 1
FIGURE 1
Schematic showing perforation sizes and locations. (A) A TM with a small pars flaccida perforation (PFP)(green). (B) A TM with a small pars tensa perforation (PTP) (green). (C) A TM with a large PFP (red). (D) A TM with a large PTP (red)
FIGURE 2
FIGURE 2
Umbo velocity transfer functions [H(f) values] before and after pars flaccida perforation (PFP) and pars tensa perforation (PTP). (A) Velocity magnitudes in the small PTP, small PFP and control groups. (B) Mean velocity changes caused by a small PTP and small PFP. (C) Velocities magnitudes in the large PTP, large PFP, and control groups. Significant decreases in velocity magnitude were found in the large PTP group at 1.5–3.5 kHz, and in the large PFP group at 1.5 kHz (post hoc test, p < .001). (D) Mean velocity changes in the large PTP and large PFP groups. The error bars (shadow lines) represent for the standard deviation of the mean
FIGURE 3
FIGURE 3
ABR thresholds and threshold shifts measured before and after pars flaccida perforation (PFP) and pars tensa perforation (PTP). (A) ABR thresholds of the small PTP, small PFP, and control groups. (B) ABR threshold shifts of the small PTP and small PFP groups. (C) ABR thresholds of the large PTP, large PFP, and control groups. (D) ABR threshold shifts of the large PTP and large PFP groups. *p < .05. The error bars represent for the standard deviation of the mean
FIGURE 4
FIGURE 4
The recovery of ABR thresholds and TM morphologies after large pars flaccida perforation (PFP) and large pars tensa perforation (PTP). (A) ABR thresholds before, just after, and 2 weeks after large PFP. (B) ABR thresholds before, just after, and 2 weeks after large PTP. *p < .05. The error bars represent for the standard deviation of the mean. (C–F) Hematoxylin–eosin stained images of normal and regenerated pars flaccida (PF) and pars tensa (PT). (G–J) Immunohistochemical staining for collagen I of normal and regenerated PF and PT. (K–N) Immunohistochemical staining for collagen II of normal and regenerated PF and PT. Scale bar = 40 μm. Black arrowhead, proliferative epithelial cells. Black arrows, positive staining for collagen I or collagen I. The top right hand corners of (E), (I), and (M) exhibit local enlarge images of normal PT with scale bar = 10 μm
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