Fig 1.
STL model of a nasal cavity and nasopharynx.
Fig 2.
Digital unstructured grid models.
Fig 3.
CFD computational domain of the nasal cavity, the nasopharynx, and a box-shaped closed space in front of the nostrils.
Fig 4.
Airflow and velocity distributions in the nasal cavity and nasopharynx under 10 cmH2O CPAP (left panel).
Velocity distributions in the nasal cavity and nasopharynx (right panel). Velocity contour mappings are shown in a colored distribution. Red streamlines indicate high velocity, and blue streamlines indicate low velocity, implying impaired airflow. Inspiratory airflow on the narrowed side became a rapid stream, as fast as 32.7 m/s. In contrast, the velocity on the normal side was 7.6 m/s. Airflow was not able to disperse across the entire cross-sectional area and thus became a concentrated, rapidly moving stream. Turbulence in front of the nostrils was seen. X-axis: distance from the nostrils; Y-axis: velocity (V, m/s) (right panel).
Fig 5.
Caudal views comparing airflow and velocity contours with CPAP.
Same patient as Fig 4.
Fig 6.
Inspiratory static pressure distribution (10 cmH2O, 889 ml/s).
The pressure drop was 102460 − 101935 = 525 Pa = 5.35 cmH2O. Same patient as Fig 4.
Table 1.
Summary of CFD results under 10 cmH2O CPAP.
Fig 7.
Scatter plot of maximum velocity versus inspiratory pressure loss coefficient (Cp).
The nasal obstruction and control groups were separated by a velocity threshold of 13.5 m/s and Cp threshold of approximately 10.0. r = 0.776, p<0.001. Blue squares: patients with nasal obstruction; red squares: controls.
Fig 8.
Scatter plot of relative cross-sectional area at the nostril versus inspiratory pressure loss coefficient (Cp).
Note that the Cp thresholds were independent of the cross-sectional area at the nostrils. The longitudinal axis is the same Cp as Fig 7.