Computational Fluid and Particle Dynamics (CFPD): An Introduction - Computational Fluid and Particle Dynamics in the Human Respiratory System - page 13

Fig. 1.10 a Lateral view of the nasal cavity and pharynx with nine representative sections. b Shear
force contour. (Image taken from Jeong et al. 2007)
the airflow into the respiratory system. When the mask is placed over the face the new
pressure difference relieves the obstruction in the pharynx, reducing and/or prevent-
ing the apnoeas. Compliance with CPAP has been reported to range between 46 % and
90 % (Krieger 1992; Reeves-Hoche et al. 1994). Up to about 50 % of patients gave
up the treatment because of some minor side effects, such as rhinitis, nasal bridge
sores, discomfort, abdominal bloating, and claustrophobia. One common complaint
made by patients is that the CPAP pressure is too high, leading to the discomfort
(Polo et al. 1994) prior to sleep onset and increased expiratory effort as well.
Computational studies can provide detailed information about the flow charac-
teristics in the pharynx area. For example, numerical measurements inside the nasal
cavity can identify regions of discomfort which can help future designs of CPAP
devices. These measurements allow an evaluation of the CPAP device to determine
whether the effects on the airflow are beneficial for preventing OSA. This can lead
to improved treatment therapy planning, cost-effectiveness of diagnosis and treat-
ment, and patient use of CPAP devices. In addition, CFD studies in the pharyngeal
region can also help in presurgical planning, for irreversible therapies such as tra-
cheostomy or pharyngeal surgery. As an example a study into the flow characteristics
that are produced by obstructive sleep apnea is shown (Jeong et al. 2007) which pro-
vides insight into the pathophysiology of the obstructive sleep apnea (OSA) disease
(Fig. 1.10 ). The results found that the flow in the pharyngeal airway of patients with
OSA comprises a turbulent jet formed by area restriction at the velopharynx—the
region in between the nasopharynx and the oropharynx as shown in Fig. 1.10 . This
turbulent jet causes higher shear and pressure forces in the vicinity of the velopharynx,