Effect of tensor veli palatini muscle paralysis on eustachian tube mechanics

Several physiological functions, such as regulating middle ear (ME) pressure and clearing ME fluid into the nasopharynx, require an opening of the collapsed eustachian tube (ET). The ability to perform these functions has been related to several mechanical properties of the ET: opening pressure (Popen), compliance (ETC), and hysteresis (eta). These global properties may be influenced by the mechanics of the surrounding tissue and/or the mucosa-air interface. In this study, we investigated the influence of tissue mechanics by paralyzing the right tensor veli palatini (TVP) muscle in 12 cynomolgus monkeys via botulinum toxin injection. A previously developed modified forced-response protocol was used to measure Popen, ETC, and eta under normal conditions and after muscle paralysis. The loss of muscle tone and/or stiffness resulted in a significant decrease in Popen (p < .01) and a significant increase in ETC (p < .01). In addition, muscle paralysis reduced the viscoelastic properties of the TVP muscle and therefore resulted in a significant decrease in eta (p < .05). A comparison with previous measurements on the influence of surface tension mechanics indicates that the ET's compliance is primarily determined by tissue elastic properties. The ET hysteresis, however, is equally affected by viscoelastic tissue properties and surface tension hysteretic properties. Knowledge of how these physical components affect the global mechanical environment may lead to improved treatments for ET dysfunction that target the underlying mechanical abnormality.