1
Nasal Obstruction and Sleep-Disordered Breathing
The link between nasal airway obstruction (NAO) and restless sleep has been known since antiquity: Hippocrates reported an association between poor sleep and nasal polyposis. Case reports and series as early as the 1890s showed an association between the nasal valve and sleep-disordered breathing (SDB). Modern studies report that subjective or objective NAO is a risk factor for SDB. Approximately 15% of patients with SDB also have NAO, and in a prospective population study of almost 5000 patients, self-reported nocturnal congestion was associated with a threefold increased incidence of snoring and daytime sleepiness. Lofaso et al. analyzed cephalometrics, body mass index (BMI), and posterior rhinometry and showed that daytime NAO is an independent risk factor for obstructive sleep apnea (OSA). Others have explored the relationship between NAO and SDB, showing that there is no association between SDB severity and the severity of NAO, although nasal resistance has been associated with snoring severity. McNicholas observed that SDB is more likely to be associated with reversible nasal obstructive disease than chronic obstruction, implying that acute reversible processes (e.g. allergic rhinitis) may have a more severe impact on SDB than static structural problems.
NAO often plays a major role in SDB and its treatment despite variable reports of the association between them. Normal patients have been shown to experience sleep disturbances after acute, complete bilateral NAO, including sleep stage disruption, new-onset snoring, and even mild OSA. One study demonstrated that objective NAO assessed using acoustic rhinometry is associated with optimal titrated nasal continuous positive airway pressure (CPAP) and the Respiratory Disturbance Index (RDI) in patients with a BMI <25.
Mouth breathing has been shown to destabilize the pharyngeal airway and contribute to the development of SDB. Nasal airflow is therefore desired for the treatment of OSA with positive airway pressure therapy, and NAO can interfere with treatment and decrease compliance with therapy. Lafond and Series induced increased nasal resistance in OSA patients with histamine and demonstrated increased airflow limitation using nasal CPAP. Zozula and Rosen emphasized the role of NAO in positive airway pressure therapy tolerance and adherence in their paper reviewing and classifying reasons for CPAP noncompliance.
Four different theories have been proposed to explain the relationship between NAO and SDB ( Table 21.1 ). These will be considered separately after a discussion of nasal anatomy.
| Association Between Nasal Airway Obstruction and Sleep-Disordered Breathing | |
|---|---|
| Theory | Mechanism |
| Starling resistor model | Upstream nasal resistance results in increased negative pressure downstream in the pharyngeal airway |
| Unstable oral breathing | Nasal airway resistance forces an increase in oral breathing fraction, resulting in increased total airway resistance by breathing through an unstable oral airway |
| Nasal-ventilatory reflex | Decreased activation of nasal airflow receptors due to obstruction leads to inhibitory action on muscle tone and minute ventilation |
| Nitric oxide (NO) | Decreased nasal airflow reduces nasal NO production, causing potential perfusion ventilation mismatch, as well as multiple other poorly defined effects on oropharyngeal musculature and arousals |
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Functional Valvular Anatomy
Anatomic models ( Figs. 21.1 and 21.2 ) have shown that inspiratory nasal airflow follows a parabolic curve up through the nostril, across the turbinates, and then downward posteriorly through the nasopharynx. The internal nasal valve area is the narrowest part of the nasal passage and greatest nasal resistance in normal patients. The internal nasal valve is composed of the upper lateral cartilage superiorly, the nasal septum medially, the pyriform aperture inferiorly, and the head of the inferior turbinate posteriorly. Patients with internal nasal valve angles of <10 degrees are more prone to internal nasal valve collapse on inspiration.
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