Table 1.
Overview of studies involving animal models investigating the role of the tensor veli palatine muscle in Eustachian tube opening
| Authors | Year | Aim(s) of the study | Subjects | Characteristics age/weight (range) | Results | Conclusion(s) |
|---|---|---|---|---|---|---|
| Honjo et al. [22] | 1979 | Identify muscle responsible for tubal opening using EMG and electrical muscle stimulation. | 12 dogs | NR/NR | Stimulation of TVP resulted in drop of pressure in middle ear space, whereas LVP stimulation did not affect pressure. | (1) TVP is the only active tubal dilator in dogs (2) LVP has no effect in ET dilation |
| Cantekin et al. [23] | 1979 | Verify results of previous studies showing the TVP as only tubal dilator. | 5 juvenile macaque monkeys | NR/2.5–4 kg | (1) Stimulation of mandibular nerve produced a pressure-flow drop in ET similar as recorded during swallowinga. (2) Pressure-flow drops were no longer observed following TVP transection. |
(1) TVP is the only active tubal dilator in rhesus monkeys. (2) Mandibular nerve innervates the TVP |
| Honjo et al. [24] | 1980 | Examining (1) synergistic action between TVP and LVP and (2) ET opening process using contrast fluid and cineradiographic analysis while stimulating the muscles. | 4 macaque monkeys | NR/4–10.5 kg | (1) TVP stimulation resulted in drop of tympanal pressure, while LVP stimulation did not affect pressure. (2) LVP stimulation caused inward movement of the torus tubarius and thus widening of the pharyngeal orifice. TVP stimulation opened the proximal part of the ET through outward displacement of the lateral tubal wall. |
(1) TVP is the sole ET opener. (2) LVP dilates the ET only at its pharyngeal orifice, while the TVP opens the ET by pulling the lateral wall outwards. |
| Cantekinet al. [25] | 1980 | Examining the effects of surgical TVP procedures (excision, transection, transposition) on ET function and ME status. | 22 juvenile and adult macaque monkeys | NR/2–6 kg | (1) TVP excision caused chronic OME and complete tubal dysfunction. (2) TVP transection lead to abnormal ME pressure, effusion, or both with a transient, recurrent or chronic character. The ET was initially dysfunctional, however slowly regained function. (3) TVP transposition had initially similar effects as transection, though ME pathology and ET function improved more rapidly. |
Surgical manipulations of the TVP created a functional ET obstruction; the severity of ET dysfunction depended on the performed surgical procedure with excision being the most harmful. |
| Casselbrant et al. [26] | 1988 | Investigate the effects of TVP paralysis (using botulinum toxin Ab) on ET function and ME status. | 8 adult macaque monkeys | NR/5–9 kg | 10/12 examined ears develop flat tympanograms within 8–30 days indicating middle ear effusion (confirmed in 7 ears by tympanoscentesis). Tympanograms required 13–32 days to normalize. | Injecting botulinum toxin A into the TVP creates reversible functional ET obstruction which became evident as high-negative pressure followed by middle ear effusion. |
| Ghadiali et al. [27] | 2003 | Investigate the effects of TVP paralysis (using botulinum toxin Ab) on ET tissue dynamics. | 12 macaque monkeys | NR/2–4 kg | Loss of TVP muscle tone and stiffness resulted in significant decrease of ET opening pressure, increased ET compliance and reduced ET viscoelasticity. | Paralysis of TVP by botulinum toxin results in decreased function due to alterations of ET mechanical properties. |
ET Eustachian tube, EMG electromyography, TVP tensor veli palatini muscle, LVP levator veli palatini muscle, ME middle ear, OME otitis media with effusion, NR not reported
aSwallowing was induced by pharyngeal stimulation
bBotulinum toxin A is known for its paralyzing effects by working on acetylcholine release at the neuromuscular junctions