The nasal cavity is the gateway to the respiratory system and has important physiological functions such as ventilation, humidification, cleansing and filtration, immune defense, and olfaction. In recent years, with the series of studies on upper airway imaging, nasal sinus anatomy, and sleep pathophysiology, abnormal elevated nasal resistance has been found to have important pathophysiological implications. Imaging studies have revealed that most patients with OSAHS have abnormal nasal cavity anatomy, such as deviated nasal septum and enlarged turbinates, which constitute the anatomical basis for elevated nasal resistance. In nasal stenosis, nasal resistance is elevated, negative pressure in the pharyngeal cavity is increased, and collapsibility is increased. Clinical practice has found that elevated nasal resistance is closely related to sleep snoring and sleep apnea, and nasal blockage is a more common symptom in patients with snoring and OSAHS.
The nasal threshold is the narrowest part of the nasal cavity, and it produces about 50% of the total resistance of the upper airway. The elevated hydrostatic pressure in the supine position increases the nasal mucosal vascular congestion, which aggravates nasal obstruction and increases nasal resistance. The pharyngeal cavity is a soft structure compared to the nasal cavity, and its easy collapse makes the cross-sectional area of the pharyngeal cavity likely to vary with nasal resistance. To overcome the increased upper airway resistance caused by nasal stenosis, a compensatory mechanism exists in the physiological state: the diaphragm and external intercostal muscles contract forcefully, increasing negative thoracic pressure and accelerating airflow to ensure a sufficient amount of tidal volume. However, this compensatory mechanism has a negative effect: it increases the negative pressure in the pharyngeal cavity, which increases the attraction in the radial pharyngeal cavity (negative pressure in the lumen) and reduces the effective cross-sectional area of pharyngeal ventilation. Elevated nasal resistance can also induce a costly switch from nasal to oral breathing during sleep. It causes the tongue root to retract, the posterior lingual space to decrease, and the airflow through the mouth to become unstable, vibrating the soft palate and the congested tissue of the pharyngeal cavity and producing snoring.
Based on the above series of studies, Prof. Han Demin et al. proposed the nasal dilation technique. It is a surgical intervention for sleep breathing disorders based on the deepening understanding of the pathophysiological mechanism of sleep breathing disorders and is gradually developed along with the maturation of nasal endoscopic surgery technology, which originates from the surgical intervention of sleep breathing disorders to solve the source factor of nasal obstruction.