![]() ![]() Thus, the association of peak pressure of the UEHPZ with location of the TP may hold only at very low levels of arousal and excitability and a fixed head position. It is possible that the very relaxed conditions and the fixed position of the head in these experiments 2, 3, 4, 8 resulted in very low states of activation of the CP compared to the TP. 2, 3, 4, 8 It has been found that UES tone 13, 14, 15, 16 and CP electromyography ( EMG) 1 but not TP EMG 1 are very variable and change greatly with the state of arousal, excitability, and head position (see Functions of the Upper Esophageal Sphincter, below). Therefore, the point of highest intraluminal pressure need not correspond with the most active muscle.Īnother problem with the conclusion that the IPC is the main muscle of the UEHPZ is that all the investigations that associated peak pressure of the UEHPZ with location of specific muscles were recorded with the subject at rest in a fixed head position. ![]() For example, the pressure of the UEHPZ may peak in the region of the IPC because of higher passive forces of the IPC and lower compliance of the IPC muscle or pharyngeal wall, rather than a stronger contraction of the IPC muscle itself. Therefore, although peak intraluminal pressure is recorded at the IPC, it is unknown which component of the region of the IPC accounted for this peak pressure. The pressure recorded intraluminally is the sum of all external forces and is related to active and passive forces of the muscles as well as the compliance of the surrounding structures. ( Source: Adapted from Goyal et al., 12 with permission of Springer Science and Business Media.) A, arytenoid AEF, aryepiglottic fold CC, cricoid cartilage ESO, esophagus IPC, inferior pharyngeal constrictor PE, pharyngoesophageal TR, tracheal ring VC, vocal cord. Note that the peak pressures of the UEHPZ in humans at rest with the head fixed in all three studies coincides with the lower border of the IPC.
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