Abstract
The objective of this study is to propose a method for the design of respiratory mask by considering the depth of facial soft tissue. The air-tightness of a respiratory mask depends on the fit of the interface between the respiratory and the 3D surface of the face. Upon the advent of 3D human scanners, this goal has been realized due to the studies of Yi-Xue Yang and Xiu-Zhen Liao by proposing a mask design method based on the 3D facial surface. It is known that the face covered with different thickness of skin, muscle and other soft tissue, which are subjected to deformation under pressure. Deformation can accommodating the fit of the interface between the mask and the face. The method of this study uses computer tomography images and 3D facial range data to measure the thickness of facial soft tissue on the interface curve. One male and one female was recruited as subjects for CT scan and 3D ficial surface measurement. Upon measurement, an interface curve was extracted using Liao’s method. All CT scan image bounded by the interface were used to measure soft tissue thickness. The thickness was measure as the distance between the skin and the bone on a radial line from the image center. The result shows that the soft tissue thickness on the face range between 2.8mm to 19.5 mm. If the interface curve is divided as mid-nasal point, mid-nasal to subalare, subalare to sublabiale, sublabiale to menton, and menton into five sections, the average thickness of each section the female is: 2.8mm, 6.7mm, 17.7mm, 7.5mm, 5.8mm; and the male is 4.2mm、8.2mm、19.5mm、9.2mm、6.9mm. The study tentatively suggests that the proportion of soft tissue deformation for each section is varying between 30% and 50% due to different tissue composition. If this is the case, then the mask deformation allowance of 10mm~15mm proposed by previous studies can not be achieved solely by the deformation of soft tissue.