The nasal airway serves as the primary entry point of air and oxygen into the body. It serves critical functions, such as providing a physical barrier against external irritants and pathogens and warming and humidifying incoming air.¹ Consequently, disorders of the nose and nasal cavity may lead to pathological downstream effects by impacting the normal physiological functions of the nose. In fact, the unified airway theory posits that inflammatory conditions that affect the nasal cavity or paranasal sinuses, such as chronic rhinosinusitis, allergic rhinitis and aspirin-exacerbated respiratory disease, are closely linked to increased prevalence of respiratory disorders, such as asthma and bronchiectasis.^2–5

The impact of purely anatomical abnormalities of the nose on the respiratory system as a whole is understudied. The most common anatomical abnormalities of the nasal cavity are deviated nasal septum (DNS), turbinate hypertrophy, internal and external nasal valve collapse and concha bullosa, all of which may lead to chronic and fixed nasal obstruction. Surgical correction of nasal airway obstruction is a frequently performed and effective method to improve the subjective nasal breathing symptoms and the quality of life of patients.⁶ However, data on how conditions, such as obstructive sleep apnoea (OSA) and asthma may be impacted, are more limited.

The objective of this review is to perform a focused literature search to identify the existing data on how nasal anatomical abnormalities impact respiratory conditions, such as OSA and underlying cardiopulmonary functions. In addition, we will briefly review the available data on the association between nasal anatomical abnormalities and asthma. We hope that this knowledge could serve as a valuable resource for clinicians in making informed decisions regarding patient management. It may also facilitate discussions with patients and their families, offering insights into expected clinical outcomes. Lastly, this review will help to determine the areas in need of further research.

Methods

Search strategy

A scoping review was performed via a literature search using the PubMed electronic database and limited to the English literature from inception to December 2023. Search terms and keywords related to nasal anatomical abnormalities and respiratory conditions, such as nasal obstruction, deviated nasal septum, turbinate hypertrophy, asthma, cough, obstructive sleep apnea, respiratory and pulmonary, were included in multiple combinations, for example (sinus[MeSH Major Topic]) OR (nasal[MeSH Major Topic])) AND (deviated nasal septum OR DNS) AND (respiratory OR cardiopulmonary OR pulmonary OR asthma OR cough OR OSA OR obstructive sleep apnea); (Deviated nasal septum[MeSH Major Topic] OR DNS[MeSH Major Topic]) OR turbinate[MeSH Major Topic]) AND (cough OR obstructive sleep apnea OR OSA OR asthma OR respiratory OR cough OR CPAP).

Articles deemed to meet the inclusion criteria were included in the full-text review. Reference lists for reviewed articles were also reviewed for additional articles for inclusion.

Study evaluation

Screening of full-text articles was performed by the authors. Exclusion criteria include (1) case reports, (2) lack of relevant outcomes or unclear outcomes, (3) outcomes related to patients with inflammatory disease (chronic rhinosinusitis, rhinitis, aspirin-exacerbated respiratory disease, etc.), (4) not written in English and (5) participants <18 years old.

Narrative synthesis

Postoperative outcomes in males and females were reviewed and categorized by two independent reviewers, with the senior author weighing in for the final approval. The reported interventions and their results are summarized in the Results section.

Results

Nasal anatomy and obstructive sleep apnoea

The role of nasal anatomical variations in OSA is unclear, with mixed results published in the literature (Table 1).^7–29 Numerous epidemiological studies indicate that there is a higher percentage of OSA among patients with nasal obstruction compared with those without. Among 60 patients, Michalska et al. found that 52.5% of patients with OSA had nasal obstruction compared with none of those without and that DNS was the most common cause of nasal obstruction.²¹ A study by Magliulo et al. identified a group of 50 patients with OSA and evaluated them for nasal obstruction via clinical evaluation or rhinomanometry. Seventy per cent of these patients demonstrated some form of nasal obstruction.²⁰ Most convincingly, Yeom et al. conducted a retrospective cohort study of 11,238 patients diagnosed with a DNS and 22,476 control patients.²⁸ This study found that the overall hazard ratio for OSA in the DNS group was 4.39 (95% confidence interval [CI]: 3.56–5.42) compared with controls, and the hazard ratio for OSA after septoplasty was 0.71 (95% CI: 0.54–0.94). Conversely, a cross-sectional study of 100 patients by Leitzen et al. did not find a correlation between nasal anatomical abnormalities and the presence or severity of OSA among the included patients.¹⁷ A study by Miljeteig et al. found no difference in OSA severity between 683 patients divided into three groups based on the severity of nasal resistance.²²

Numerous studies looked at the impact of topical medical interventions designed to alleviate nasal obstruction on OSA. A study by Clarenbach et al. designed a randomized controlled trial of 12 patients with OSA with nasal obstruction who were given either oxymetazoline or a placebo for 1 week. Following treatment, there was no significant difference in the apnoea–hypopnoea index (AHI) between the experimental and placebo groups (29.3 ± 32.5 versus 33.2 ± 32.8).^8,22 Kerr et al. similarly looked at 10 patients with OSA and found no change in AHI with the application of oxymetazoline and nasal dilators compared with placebo.¹³ A systematic review and meta-analysis of five studies by Nguyen et al. did not find a significant decrease in AHI among patients using topically applied nasal decongestants.²⁵

Prospective trials have been performed to further elucidate the role of nasal surgery alone in OSA. Koutsourelakis et al. randomly assigned 49 patients with OSA with symptomatic DNS to either septoplasty or sham surgery and then repeated polysomnography (PSG). Of the 27 patients who underwent septoplasty, only 4 patients showed a statistically significant improvement in AHI with one patient demonstrating complete response (AHI <5). No patients from the sham group had improvement.¹⁶ Kim et al. conducted a study of 21 patients with nasal obstruction with pre- and postoperative PSG. They found a statistically significant reduction in respiratory disturbance index (RDI) (39 to 29, p<0.01), AHI (19 to 16, p<0.02) and oxygen saturation index (OSI) (48 to 32, p<0.01) following septoplasty with or without inferior turbinectomy.¹⁴ Similarly, Park et al. found a statistically significant reduction in AHI (23.96 ± 14.9 to 12.2 ± 6.4, p<0.05) and RDI (28.8 ± 14.4 to 17.1 ± 7.5, p<0.05) in 25 patients with OSA with DNS treated with septoplasty and/or turbinoplasty.²⁶ Studies by Moxness et al., Kim et al. and Hisamatsu et al. also found a statistically significant reduction in AHI among other PSG parameters in patients who underwent surgery to correct nasal obstruction, as summarized in Table 1.^10,15,23

In contrast, four meta-analyses have been conducted, which look at the role of nasal surgery in OSA, published in 2011 (Li et al.), 2015 (Ishii et al.), 2017 (Wu et al.) and 2022 (Schoustra et al.).^12,18,27,29 Li et al. included 11 prospective trials and found no statistically significant decrease in mean AHI (35.2 ± 22.6 to 33.5 ± 23.8, p=0.69) after nasal surgery.¹⁸ However, patient-reported outcomes measured via the Epworth Sleepiness Scale (ESS) significantly decreased from 10.6 ± 3.9 to 7.1 ± 3.7 (p<0.001) following isolated nasal surgery. Ishii et al. included 10 studies and similarly found no significant decrease in AHI. They did report a significant decrease in ESS by 3.53 points (95% CI: 0.64–6.23) and RDI by 11.06 points (95% CI: 5.92–16.19).¹² Wu et al. included 18 trials and noted a statistically significant improvement in AHI with a weighted mean difference (WMD) of 4.15 fewer events per hour following nasal surgery. As with the other studies, they also noted a significant reduction in ESS with a WMD of -4.08.²⁹ Schoustra et al. included 21 studies and found a statistically significant improvement in AHI with a WMD of 4.08 and a significant improvement in ESS with a WMD of 4.01 following nasal surgery alone.²⁷

Lastly, the impact of nasal surgery on continuous positive airway pressure (CPAP) tolerance and effectiveness has been studied. A 2015 meta-analysis by Camacho et al. included 11 studies and found that isolated nasal surgery converted 89% (57 of 64 patients) of non-CPAP users to CPAP-tolerant users and improved objective CPAP use hours from 3.0 ± 3.1 h per night to 5.5 ± 2.0 h per night.⁷

Nasal anatomy and cardiopulmonary function

Adenotonsillar hypertrophy as a source of chronic upper airway obstruction in children has been known to impact cardiopulmonary function.³⁰ Nasal resistance comprises approximately one-half of the total airway resistance during nasal breathing.³¹ Nasal anatomical factors, such as DNS, turbinate hypertrophy and internal/external nasal valve collapse, can limit nasal airflow and increase nasal resistance. Through our literature search, we identified 16 articles that discussed how this nasal obstruction may contribute to abnormalities of the cardiopulmonary system.^32–39 Eight studies examining DNS and pulmonary arterial pressure (PAP) found that patients with DNS have increased PAP over control populations, including when controlled for OSA.^32–37,40 Nine studies tested pre- and post-septoplasty PAP values, and all nine found a statistically significant postoperative decrease in PAP (Table 2).^30,32–45 Six studies also reported an improvement in specific echocardiogram parameters, including a statistically significant reduction in the E/e’ ratio, a marker of diastolic dysfunction when elevated, statistically significant improvement in right ventricular systolic myocardial function and tricuspid annular plane systolic excursion as summarized in Table 2.^{32,33,36–39} Recent studies evaluated N-terminal pro-b-type natriuretic peptide (NT-proBNP), an inactive hormone that has been reported to provide information on cardiovascular disease and has shown to have a prognostic value in chronic heart failure, and found that it was elevated in those with septal deviation compared with controls.^39,41 After surgical correction of the DNS, NT-proBNP levels were significantly reduced.³⁹

Other studies examined the impact DNS may have on pulmonary function more directly. Five studies examined the effects DNS has on pulmonary function tests (PFTs).^40,42,43,45 Of these, three found a significant increase in forced vital capacity and forced expiratory volume in 1 s in patients with postoperative septoplasty.^40,42,43 These findings of improved PFT outcomes were also seen with a reduction in inferior turbinates.⁴⁵ One study found a significant increase in tracheobronchial resistance among patients with DNS and a significant reduction in resistance following surgery.⁴⁴ This particular study did not find any functional residual capacity differences between the DNS population and control patients (Table 2). When extrapolating the above-mentioned findings to asthma, there is a more limited conclusion. Ahn et al. conducted a review of 8,865 patients and found that 44.8% of patients had DNS. They found no association between DNS and any general health problems apart from asthma.⁴⁶ A retrospective database study by You et al. examined 29,853 patients divided into those with and without DNS. They found that the hazard ratio for asthma in the DNS group was 2.43 (95% CI: 2.31–2.56) and the hazard ratio for asthma after septoplasty was 0.83 (95% CI: 0.75–0.93).⁴⁷ Interestingly, Jura-Szoltys et al. investigated the impact of performing a turbinate reduction using argon plasma coagulation on 47 patients and found that this technique decreased the prevalence of patients with insufficient bronchial asthma control from 79 to 4% with a significant reduction in nasal resistance (Table 3).⁴⁸

Discussion

Inflammatory diseases of the upper and lower airways are known to impact one another. The unified airway theory is a concept that has been examined over the past 20–30 years and suggests that the nasal passages, paranasal sinuses, middle ear and lungs all exist as one functional unit. What is less clearly understood is the relationship between anatomical variations or abnormalities of the upper airway and the subsequent impact on the respiratory system as a whole. This review sought to identify the existing literature that investigates this question and to offer insight into clinically impactful interventions that may aid in patient care.

OSA is a multilevel disease with obstruction occurring most commonly at the velum but also at the level of the epiglottis, tongue base and oropharynx.⁴⁹ Each of these sites is a target for surgical correction, which has been shown to relieve obstruction and improve AHI and symptoms in the patient.⁵⁰ This review suggests that anatomical obstruction in the nasal cavity may provide another source of obstruction in certain patients. This correlation becomes less clear when looking at isolated nasal surgery for the treatment of OSA, which is best highlighted by the four meta-analyses discussed earlier.^7,12,27,29 While some of the literature cited reports statistically significant results, the clinical significance is less clear. The success of surgical interventions for OSA is traditionally defined as a >50% postoperative reduction in AHI and an AHI <20.⁵¹ It is unlikely that a modest decrease in AHI as described in these studies meets such criteria. Notably, however, all four of the meta-analyses report a significant decrease in ESS scores, which suggests that patients are attaining a noticeable, subjective improvement in their sleep quality, as the minimal clinically important difference for the ESS is estimated to be a change of 2–3 points.⁵² While this change is positive, patient-reported outcome measures such as ESS are susceptible to placebo and bias, particularly in retrospective studies that do not include a control arm.

While AHI may not be demonstrably impacted by nasal obstruction, ventilatory burden, a novel metric, may be affected. This is a recently described measure that more accurately predicts long-term sequelae of OSA, such as all-cause or cardiovascular disease mortality, when compared with AHI.⁵³ Ventilatory burden is a breath-by-breath measure of inspiratory flow rate, which is independent of physiological consequences such as hypoxia similar to AHI. These findings suggest that OSA may have many components that are relevant to long-term OSA outcomes that are not accurately captured by AHI, such as decreased inspiratory nasal flow. Patients with OSA have reduced peak nasal inspiratory flow and increased nasal resistance compared with healthy controls.^11,24 Other studies have noted that decreased inspiratory flow is associated with particular sites of pharyngeal, tongue and epiglottic obstruction among patients with OSA and that reduction in nasal airway resistance also decreases resistance at the palatopharyngeal cavity.^9,19 A potential mechanism would be that improvement in inspiratory flow may improve the total ventilatory burden while reducing respiratory effort-related arousals that do not meet the criteria for apnoea or hypopnoea but still result in improved sleep quality and ESS.

Furthermore, though nasal surgery alone is not likely to provide a clinically significant improvement in a patient’s AHI, it has been shown to provide benefits to CPAP tolerance. Increased CPAP tolerance following nasal surgery continues to be supported by literature published since the findings noted by Camacho et al. and others.^29,54,55 Kempfle et al. found that both septoplasty and rhinoplasty are cost-effective methods to improve CPAP tolerance when compared with non-surgical management.⁵⁶

This review highlights the relationship between nasal anatomical obstruction and cardiopulmonary function, with numerous studies demonstrating an improvement in PFTs and PAP following surgical correction of nasal obstruction. While the studies cited are either of small sample size or population-based observational studies, their results do demonstrate the need for a mechanistic explanation of their findings. It has been suggested that long-term nasal obstruction as evident through septal deviation, for example, could increase nasal resistance creating reduced lung ventilation, resulting in hypoxia, hypercapnia, pulmonary vasoconstriction and increased intrathoracic pressure, causing increased pulmonary arterial pressure.³² This mechanism has been described in children with adenotonsillar hypertrophy impacting cardiopulmonary function.^30,57 However, more studies will need to be performed to fully investigate this phenomenon and the mechanism behind these findings in adults with nasal anatomical abnormalities. In addition, one hypothesis is that relieving the nasal obstruction allows the nasal cavity to more effectively protect the lower airway. Physiologically, the nasal cavity acts as the primary entry point for inhaled air, providing a physical barrier from the distal airway.^1,58 An inability to protect the distal airway may lead to insufficiently warmed or humidified air or inflammatory agents entering into the lungs, causing bronchoconstriction and consequently decreased pulmonary performance.⁵⁹

The impact of anatomical abnormalities in the nasal airway and its role in respiratory conditions remain largely understudied with data of varying quality. While the above-mentioned studies provide valuable insight into the benefits of nasal surgery for OSA and cardiopulmonary function, future areas of research should focus on producing high-quality studies that demonstrate the interplay between nasal anatomy and respiratory conditions. These studies should work to further elucidate the mechanisms by which the nasal airway impacts the distal airway.

Conclusion

This review highlights the relationship between nasal anatomy and respiratory pathology. While there are mixed data on the impact of nasal obstruction on OSA, surgical correction of that obstruction leads to a clear improvement in patient quality of life, CPAP tolerance and subjective sleep quality. Limited data suggest that nasal obstruction may play a significant role in the pathology of the distal airway and a negative impact on pulmonary and ultimately cardiac function. A comprehensive evaluation of the nasal airway is warranted in patients presenting with numerous respiratory conditions, including OSA, pulmonary hypertension and asthma.