Fig 1.
Top view of the decompression model.
This model was created to evaluate the decompression effect based on the opening angle of the facial nerve canal in facial nerve decompression surgery. A tracheal tube with an inner diameter of 6.0 mm and an outer diameter of 8.2 mm (Shiley™, with TaperGuard™ cuff and stylet, Product No. 18760S; Medtronic Japan Co., Ltd.) was used to simulate the facial nerve. The canal model was positioned over the cuff portion of the tube. The photograph shows a top view of the entire model.
Fig 2.
Facial nerve canal models created for each opening angle.
A Opening angle: 0°. B Opening angle: 30°. C Opening angle: 60°. D Opening angle: 90°. E Opening angle: 120°. F Opening angle: 150°. G Opening angle: 180°. The facial nerve canal was simulated by covering a standard anesthesia circuit (1.5 m, DAR Breathing System, Product No. 300P14347, Certification No. 220AABZX00156000) with a 7-mm-thick layer of clay. The clay-covered section was assumed to represent the nerve canal, and external cuts were made at predetermined angles to create seven models with opening angles ranging from 0° (A) to 180° (G). Each photograph shows a top view of the corresponding model.
Fig 3.
A. Top view of the decompression model with injected colored solution.
The pressure inside the facial nerve canal was measured using a colored solution prepared by dissolving 0.1 g of red food coloring in 100 mL of normal saline. A volume of 6.6 mL of this solution was injected into the tracheal tube (simulating the nerve) to replicate internal pressure. In this model, the injection volume into the cuff was standardized at 6.6 mL. B. Cross-sectional view showing compression by the nerve canal model at an opening angle of 0°. Colored solution was injected into the tracheal tube simulating the nerve, and the entire outer surface was covered with the canal model to reproduce a constricted state at an opening angle of 0°. The image shows a lateral cross-sectional view of the model, in which the tracheal tube (representing the nerve) is seen to be circumferentially compressed by the canal. The red area represents the colored solution injected to simulate internal pressure.
Fig 4.
Decompression model during internal pressure measurement using the VBM Cuff Control Inflator.
For each model with a different opening angle, internal pressure within the tracheal tube was measured using a VBM Cuff Control Inflator (VBM Medizintechnik GmbH, Germany; measurement range: 0–120 cm H₂O). The photograph shows a top-down view of the model with the colored solution injected, while the pressure gauge is connected to measure internal pressure.
Table 1.
Mean internal pressure ± standard deviation (cm H₂O) for each release angle.
Fig 5.
Relationship between the degree of canal opening and internal pressure.
The vertical axis represents intraneural pressure (cm H₂O), and the horizontal axis indicates the degree of canal opening (0° to 180°), including the no-compression condition. A decreasing trend in intraneural pressure was observed with increasing degrees of canal opening. Notably, a marked reduction in pressure was seen between 0° and 30°, and pressures at 150° and beyond were comparable to those of the no-compression condition. Error bars indicate standard deviations (SD). The mean ± SD values were as follows: 0°, 45.1 ± 2.6; 30°, 36.0 ± 2.1; 60°, 35.0 ± 2.3; 90°, 33.3 ± 2.8; 120°, 32.4 ± 1.9; 150°, 28.8 ± 1.9; 180°, 29.1 ± 1.3; and no compression, 28.9 ± 1.7 cm H₂O.