ABSTRACT
Objective To study the flow characteristics of the upper airway and force dynamics of the soft palate and uvula in a representative male OSAHS (obstructive sleep apnea hypopnea syndrome) patient during normal respiration. Methods A CT image-based reliable geometry model of the upper airway was established. Numerical simulation boundary conditions were determined by clinical data of sleep monitoring, and the low-Reynolds number turbulence model was adopted to calculate the flow movement during a complete respiration period. Results The flow characteristics of the upper airway were obviously different in the breathing process of OSAHS patient. During inspiration, the maximum velocity of airflow in the upper airway reached 9.808 m/s, and the maximum negative pressure of airflow reached -78.856 Pa. Backflow districts were found at top of the nasal cavity. The maximum pressure on the soft palate was -10.884 Pa, and that on the uvula was -51.946 Pa. The maximum shear stress on the soft palate and uvula was 78 and 311 mPa, respectively. During expiration, the maximum velocity of airflow in the upper airway was 10.330 m/s, and the maximum negative pressure was -51.921 Pa. Backflow was observed to appear both at the oropharynx and top of the nasal cavity. Specifically, clockwise backflow was remarkable at the oropharynx. The maximum pressure on the soft palate was 2.603 Pa, and that on the uvula was -18.222 Pa. The maximum shear stress on the soft palate and uvula was 51 and 508 mPa, respectively. Conclusions Oropharynx is most likely to collapse in the upper airway. Numerical simulation on the respiratory cycle can capture the salient backflow features of the flow field in the upper airway. The backflow in the upper airway directly affects the forces on the soft palate and uvula and the breathing fluency of OSAHS patients.
ABSTRACT
Objective To study the modeling method of rat model and the air flow characteristicwith its upper stenosis-airway. Methods Thirty-two 3-month old rats were randomly divided into two groups: the control group and the model group. For the model group, sodium hyaluronte of 0.1 mL was injected into mucosa of the soft palate and uvula in each rat under the anesthetic state. After feeding under the same condition for 3 months, CT scans and respiratory experimental examinations were performed on the two groups, respectively. The computational fluid dynamic (CFD) method was then employed to simulate the airflow in their upper airway. The flow characteristics were compared between the control rat and the model rat. Results (1) The minimum cross-sectional area of pharyngeal in the model group was reduced remarkably than that of the control group, showing that the airway of the model rats was significantly narrower than that of the control rats (P<0.05). (2) The model rats became breathless, and their respiratory period became unsteady. The breath intensity of the model rat on the pharynx fluctuated more rapidly. (3) The maximum wall shear stress on the pharynx of the control rat was scattered at the respiratory phase while it was concentrated for the model rat. Conclusions The injection of sodium hyaluronte into mucosa of the soft palate and the uvula can induced the narrowness of the upper airway in the model rat, which is similar to patients with obstructive sleep apnea-hypopnea syndrome (OSAHS) in pathology. The narrowness of the upper airway can cause dyspnea and extend respiratory period. The shear stress on the pharynx of the upper stenosis-airway induces stronger damage to the pharynx tissue, especially to the soft palate and uvula, which aggravates reconstruction of the pharynx tissue.