Linear and area measurements regarding the airway passage: 1, nasopharynx area; 2, upper pharyngeal width (UPW) at the level of palatal plane; 3, oropharynx 1 area; 4, middle pharyngeal width (MPW) at the level of occlusal plane; 5, oropharynx 2 area; 6, lower pharyngeal width (LPW) at the level of a line connecting cv3ia and hyoid points; 7, SN-CVT angle