
==== Front
BMC Pulm Med
BMC Pulm Med
BMC Pulmonary Medicine
1471-2466
BioMed Central London

39261802
3278
10.1186/s12890-024-03278-1
Research
Effects of sitting, supine, and prone postures on nasal patency in individuals with obstructive sleep apnea syndrome
Yang Pei-Rung 12
Tsai Yao-Te yaote1215@gmail.com

347
Tsai Hsin-Yi 3
Chang Geng-He genghechang@gmail.com

34567
1 https://ror.org/02verss31 grid.413801.f 0000 0001 0711 0593 Department of Traditional Chinese Medicine, Chang Gung Memorial Hospital, Chiayi, Taiwan
2 grid.145695.a 0000 0004 1798 0922 School of Traditional Chinese Medicine, College of Medicine, Chang Gung University, Taoyuan, Taiwan
3 https://ror.org/02verss31 grid.413801.f 0000 0001 0711 0593 Department of Otolaryngology – Head and Neck Surgery, Chang Gung Memorial Hospital, Chiayi, Taiwan
4 grid.145695.a 0000 0004 1798 0922 Faculty of Medicine, College of Medicine, Chang Gung University, Taoyuan, Taiwan
5 grid.145695.a 0000 0004 1798 0922 Graduate Institute of Clinical Medical Sciences, College of Medicine, Chang Gung University, Taoyuan, Taiwan
6 https://ror.org/02verss31 grid.413801.f 0000 0001 0711 0593 Head and Neck Infection Treatment Center, Chang Gung Memorial Hospital, Chiayi, Taiwan
7 No.6, W. Sec., Jiapu Rd., Chiayi County 613, Puzih City, Taiwan
11 9 2024
11 9 2024
2024
24 44529 9 2023
6 9 2024
© The Author(s) 2024
2024
https://creativecommons.org/licenses/by-nc-nd/4.0/ Open Access This article is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, which permits any non-commercial use, sharing, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if you modified the licensed material. You do not have permission under this licence to share adapted material derived from this article or parts of it. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by-nc-nd/4.0/.
Background

Studies have found that in healthy individuals without nasal disease, changes in posture cause an increase in nasal resistance, especially in the prone posture. Many patients with obstructive sleep apnea syndrome (OSAS) sleep in a prone posture, but no studies have examined the effect of this change in posture on nasal resistance in patients with OSAS. Therefore, we conducted this study to investigate this posture-related physical phenomenon in individuals with OSAS.

Methods

We evaluated the nasal patency of 29 patients diagnosed with OSAS using the visual analog scale (VAS), acoustic rhinometry, and video-endoscopy in the sitting, supine, and prone postures.

Results

In the OSAS group, both supine and prone postures significantly influenced subjective nasal blockage and led to a notable reduction in the minimal cross-sectional area (mCSA) as determined by acoustic rhinometry, compared to the sitting posture. The prone posture exhibited a more pronounced effect than the supine posture. Endoscopic evaluations further revealed increased hypertrophy of the inferior turbinate in the supine posture for the right nasal passage and the prone posture for the left. However, no significant differences were observed between the prone and supine postures.

Conclusion

In OSAS patients, nasal resistance significantly increased in supine and prone postures compared to sitting, with the prone posture showing a greater effect. Clinicians should consider a patient’s habitual sleep posture and the effects of postural changes when assessing OSAS severity and devising treatment plans.

Level of Evidence

4.

Keywords

Nasal patency
Nasal obstruction
Supine
Prone
Posture
Position
Sleep
OSAS
Chang Gung Memorial Hospital, Chia-Yi Branchissue-copyright-statement© BioMed Central Ltd., part of Springer Nature 2024
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pmcIntroduction

Obstructive sleep apnea syndrome (OSAS) is a prevalent condition marked by recurrent upper airway obstructions and apneas during sleep, resulting in fragmented sleep and decreased blood oxygen levels [1]. Typical manifestations of untreated OSAS encompass excessive daytime drowsiness, fatigue, and cognitive impairments [2]. Additionally, it’s associated with comorbidities such as cardiovascular diseases, metabolic syndrome, respiratory issues, and extensive damage to various organ systems [3]. Nasal patency during sleep is pivotal in the progression and management of OSAS [4]. OSAS patients have been shown to have upper airway obstruction caused by the collapse of one or more pharyngeal structures and often aggravated by sleeping in the supine posture [5].

Several studies have indicated that elevated nasal resistance is linked to heightened OSAS severity [6]. The interaction between sleep postures and nasal patency has also been explored in various research [7, 8]. Evidence suggests that the minimal cross-sectional area (mCSA) of nasal passages diminishes, and nasal airway resistance escalates when transitioning from sitting to supine in healthy individuals and OSA patients [9]. Many individuals prefer sleeping in the prone posture, and our recent findings corroborate that both supine and prone postures intensify nasal obstruction relative to the sitting posture based on subjective and objective evaluations [8]. Notably, the prone posture exhibited a more pronounced impact on nasal patency than the supine posture in healthy subjects [8]. However, there’s a paucity of studies examining the influence of the prone posture on nasal patency in OSAS patients. Consequently, using subjective and objective assessments, the aim of this study is to investigate the effects of different body postures (sitting, supine, and prone) on nasal patency in individuals with OSAS, with a focus on analyzing the impact of the prone posture on nasal patency in OSAS patients.

Materials and methods

Participants with OSAS

We identified patients with OSAS who were hospitalized and scheduled for surgery the next day at the Otorhinolaryngology Department in Chiayi Chang Gung Memorial Hospital, with procedures possibly including septoplasty, inferior turbinoplasty, uvulopalatopharyngoplasty (UPPP), lingual tonsillectomy. A total of 29 patients diagnosed with OSAS, confirmed by an apnea-hypopnea index (AHI) of five or higher post-polysomnography (PSG) examination (SOMNOmedics GmbH, Randersacker, Germany and Advanced Brain Monitoring, Carlsbad CA, USA), were enrolled in the study. Informed consent was obtained from all participants before any testing procedures were conducted. The age group for inclusion was individuals aged 18 years and older. Exclusion criteria included: age below 18; pronounced nasal septal deviation (NSD); prior sinonasal surgeries such as inferior turbinoplasty, septomeatoplasty, endoscopic sinus surgery, nasal tumor resection, or endoscopic skull base surgery; a medical history of nasal cavity, sinus, or nasopharynx malignancy; endoscopic findings of nasal polyps or sinusitis; current smoking habits; and recent upper respiratory tract infections (within the past month). Those on rhinitis-related medications, like corticosteroid nasal sprays, oral or intranasal antihistamines, or oral corticosteroids, were asked to discontinue their use for at least two weeks before joining the study.

This study adhered to the principles outlined in the Declaration of Helsinki and received approval from the Chang Gung Memorial Hospital, Chia-Yi Branch, Taiwan, under the reference number 201801720B0C501.

Process of studying various postures

Participants underwent subjective and objective nasal resistance evaluations in a dedicated space adjacent to the ENT outpatient clinic. Each participant was accompanied by a research assistant who assisted throughout the testing process. Evaluations were conducted in three distinct postures: sitting, supine, and prone. The sequence of these postures was randomized for each participant through a drawing of lots. Before testing in each posture, subjects maintained that posture for 15 min (Fig. 1). In every posture, participants completed the VAS questionnaire to gauge subjective nasal congestion, underwent acoustic rhinometry to measure nasal mCSA objectively, and had video-endoscopy to record turbinate hypertrophy levels. A single examiner assessed all 60 participants, both with and without OSAS. All subjects were tested in a controlled environment with a humidity of 50–60% and a temperature of 25–26 °C.

Fig. 1 Flowchart of the postural examinations. The order of postures to be tested was determined by lottery (a random approach), including sitting (1a and 1b), supine (2a and 2b), and supine (3a and 3b) postures, and then subjective and objective assessments were performed at each posture. The subjects were required to remain in each posture for 15 min before being tested. The test included a visual analog scale to assess the subjective sensation of nasal congestion, and objective measurements by acoustic rhinometry and video-endoscopy

Assessments of nasal patency

Subjective measurements

The primary outcome of this study focused on the subjective evaluation of nasal obstruction in sitting, supine, and prone postures. We employed the VAS scale to gauge the extent of subjective nasal obstruction, with scores spanning from 0 (indicating no obstruction) to 100 points (representing the most severe obstruction).

Objective measurements

We employed acoustic rhinometry and video-endoscopy to objectively evaluate nasal patency in subjects across all three postures. These results represent the secondary outcomes of this study. During acoustic rhinometry assessments, the examiner ensures the probe is closely aligned with the nasal passage to reduce errors from air leakage. The mCSA data from both nasal passages were combined to analyze resistance variations among the three postures.

Furthermore, we employed video-endoscopy to directly monitor variations in turbinate hypertrophy across different postures, utilizing a method previously validated in studies [8, 10, 11]. Measurements were conducted using a fixed rigid endoscope, marked 1.7 cm from its tip (Fig. 2A). The examiner consistently inserted the endoscope into each subject’s nasal passage to this depth, capturing nasal images with a video system (Fig. 2B). Within the image, a horizontal line was drawn at the broadest section of the inferior turbinate. The ratio of the width of the inferior turbinate (a) to the entire nasal passage width (b) served as an indicator of turbinate hypertrophy (Fig. 2C). Subsequently, hypertrophy variations across the three postures were compared.

Fig. 2 Video-endoscopy. We used a rigid endoscope connected to an imaging system to record the degree of swelling of the inferior turbinate mucosa in the subject at various postures. The same endoscope was marked 1.7 cm behind the anterior end (A); then the endoscope was photographed 1.7 cm behind the nostrils (B); and a horizontal line was drawn according to the most hypertrophied area of the inferior turbinate in the image (C). The width of the inferior turbinate (a) was divided by the width of the nasal cavity (b) to represent the degree of inferior turbinate hypertrophy and was expressed as a percentage

Statistical analysis

The gender distribution in the sociodemographic profiles of patients with OSAS was evaluated using Pearson’s chi-squared test. Age, body mass index (BMI), VAS scores for nasal blockage, and mCSA values are expressed as mean ± standard deviation and were assessed using the unpaired Student’s t-test. The bar and dot graphs depict VAS scores, mCSA, and endoscopy findings across the three postures. Comparisons between these postures were made using the paired Student’s t-test. Data analysis was conducted using SPSS version 18.0. Statistical significance thresholds were defined as * p < 0.05; ** p < 0.01; *** p < 0.001.

Results

Study population

In this study, we examined 29 participants with OSAS (4 females and 25 males, average age 39.93 ± 11.02 years), and the average BMI was 28.47 ± 3.95 for the OSAS group. The mCSA, as measured by acoustic rhinometry, showed values of 1.14 ± 0.35 cm2 when seated for OSAS (Table 1). Among these 29 subjects with OSAS, fourthree (10.3%) had mild OSAS (AHI ≥ 5 and < 15 times/hour), five (16.7%) had moderate OSAS (AHI ≥ 15 and < 30), and 21 (70.0%) had severe OSAS (AHI ≥ 30), thus most of the subjects were patients with severe OSAS. Of these 29 OSA patients, 29 underwent inferior turbinoplasty, 24 underwent septoplasty, 18 underwent UPPP, and 5 underwent lingual tonsillectomy.

Subjective assessment: primary outcome

We utilized VAS scores to evaluate subjective nasal blockage in OSAS participants across various postures. In OSAS patients, the supine posture notably exacerbated nasal blockage compared to the sitting posture (VAS scores: 30.69 ± 30.46.

vs. 22.76 ± 26.58, p = 0.041), reflecting a 1.35-fold increase in the average score. Similarly, the prone posture led to a more pronounced nasal blockage than the sitting posture (VAS scores: 41.38 ± 35.73 vs. 22.76 ± 26.58, p < 0.001), with an average score amplification of 1.82 times. Importantly, the nasal blockage in the prone posture was more significant than in the supine posture (VAS scores: 41.38 ± 35.73 vs. 30.69 ± 30.46, p = 0.016) (Fig. 3).

Fig. 3 Visual analog scale. In patients with obstructive sleep apnea syndrome (OSAS), the subjective assessment of nasal blockage in the sitting, supine, and prone postures was conducted using the visual analog scale (VAS) with scores ranging from 0 to 100 points

Objective assessments: secondary outcomes

Acoustic rhinometry

Using acoustic rhinometry, we measured the individual mCSAs for both nasal passages in OSAS participants and subsequently summed them for analysis. The data revealed that both the supine and prone postures significantly decreased the mCSA relative to the sitting posture. The values were 1.05 ± 0.35 in supine vs. 1.14 ± 0.35 in sitting (p = 0.032) and 0.90 ± 0.32 in prone vs. 1.14 ± 0.35 in sitting (p < 0.001) (Fig. 4). When comparing the prone and supine postures, the OSAS group exhibited a statistically significant difference: 0.90 ± 0.32 in prone vs. 1.05 ± 0.35 in supine (p = 0.035).

Fig. 4 Acoustic rhinometry. Patients with OSAS underwent acoustic rhinometry to objectively evaluate nasal cavity patency in the sitting, supine, and prone postures. The minimal cross-sectional area (mCSA) detected in each subject’s nasal passage was summed, and the differences in mCSA between the three postures were compared

Endoscopy

Our findings indicated a pronounced hypertrophy of the inferior turbinate in the supine posture relative to the sitting posture for OSAS subjects. This hypertrophy was statistically significant in the right nasal passage for OSAS participants (degree of inferior turbinate hypertrophy of the right nasal passage in OSAS: 69.90 ± 13.62% in supine vs. 64.14 ± 14.81% in sitting, p = 0.021). When comparing the prone to the sitting posture, there was a significant increase in inferior turbinate hypertrophy in the left nasal passage for the OSAS group (degree of inferior turbinate hypertrophy of the left nasal passage in OSAS: 65.97 ± 15.70% in prone vs. 58.60 ± 15.94% in sitting, p = 0.014). (Fig. 5)

Fig. 5 Endoscopic assessment. Patients with OSAS underwent video-endoscopy on both sides of the nasal cavity in the sitting, supine, and prone postures. The results are expressed as a percentage calculated by dividing the width of the inferior turbinate by that of the nasal cavity, and the results are presented separately for each side of the nose

Table 1 Characteristics of the study population

Variable	OSAS (n = 29)	
Sex		
Women	4	
Men	25	
Age (years)	39.93 ± 11.02	
BMI (kg/m2)	28.47 ± 3.95	
VAS (0−100) when seated		
Nasal blockage	22.76 ± 26.58	
mCSA (cm2) when seated	1.14 ± 0.35	
AHI (times/hour)		
≥ 5 and < 15	6.50 ± 0.30 (3/29)	
≥ 15 and < 30	21.70 ± 3.65 (5/30)	
≥ 30	67.22 ± 26.55 (21/30)	
Abbreviations: OSAS, obstructive sleep apnea syndrome; BMI, body mass index; VAS, visual analog scale; mCSA, minimal cross-sectional area; AHI, Apnea-Hypopnea Index

#mean ± standard deviation

Discussion

This study first explores the relationship between the prone posture and nasal patency in OSAS patients. A central observation was the escalation of nasal resistance when transitioning from a seated to a supine posture, with the resistance being even more pronounced in the prone posture, as evidenced by both subjective and objective measures. Our endoscopic evaluations further highlighted increased hypertrophy at the head of the inferior turbinate in both supine and prone postures. These insights underscore the significant influence of body positioning on nasal patency in OSAS patients.

In addition, of the 29 OSAS subjects in our present study, the vast majority (70%) were severe (AHI ≥ 30); thus, the results of this study are more representative of the physiological characteristics of OSAS patients.

Some studies have found that in normal physiological responses, the nasal resistance of healthy individuals increases when changing from a sitting to a supine posture [8, 10, 12]. Some studies have shown that the pressure in the internal jugular vein increases when a person changes from sitting to lying [13]. The inferior turbinate has many venous plexuses in its lamina propria. Therefore, it has been hypothesized that the increase in nasal resistance when a person is lying down may be due to the increase in venous hydrostatic pressure, which leads to swelling of the mucous membrane of the inferior turbinate, increasing nasal resistance [14]. However, there is no direct evidence to support this hypothesis. According to our study, direct endoscopic observation showed that the hypertrophy of the inferior turbinate increased significantly when changing from a sitting to a supine posture, and the increase was even more pronounced when changing to a prone posture. This result indirectly supports the hypothesis that the increase in venous hydrostatic pressure due to changes in posture, coupled with the effect of gravity, increases resistance due to swelling of the nasal mucosa.

Past studies have shown that the degree of nasal congestion affects the severity of OSAS [15, 16], and that effective treatment of nasal congestion improves the severity of OSAS [17]. According to the present study’s findings, in patients with OSAS, the change in posture, whether supine or prone, causes an increase in nasal resistance. When assessing the nasal congestion of a patient in the clinic, apart from asking the patient about the degree of subjective nasal congestion, we will use a rhinoscopy or endoscope to observe the degree of swelling of the mucous membranes of the turbinate in the nose. However, patients are usually asked to sit in a sitting posture for the examination, but when these OSAS patients are supine or prone, the changes in the swelling of the nasal mucosa and the degree of increase in nasal resistance are more important examinations that need to be evaluated by the clinician to obtain more comprehensive information, which is conducive to the improvement of the effectiveness of the treatment of OSAS. In addition, when treating patients with OSAS, whether medication or surgery can be used to reduce the effect of the increase in nasal obstruction caused by this change in posture, and to what extent it can help in the treatment of OSAS, is an important topic that deserves to be explored in subsequent studies.

Our study has several advantages. Firstly, 70% of the OSAS subjects in our study were patients with severe OSAS, therefore, the results of this study are more representative of the physiological phenomenon of such patients. Second, in addition to the subjective questionnaire and objective acoustic rhinometry test, endoscopy was used to directly observe and compare the changes in the nasal mucosa, providing a more intuitive and objective assessment. However, there were some limitations: patients with significant NSD were excluded during the screening process to minimize the effect of NSD on the study results, but we used rhinoscopy for the direct assessment and did not use computed tomography to measure the degree of NSD for objective adjudgments. In addition, all subjects were assessed by the same examiner to minimize errors. However, when measuring nasal resistance, especially in the prone posture, slight air leakage may occur when the acoustic rhinometry transducer is attached to the nostrils, which may cause some bias in the experimental results.

Conclusion

The present study found that supine and prone postures caused a significant increase in nasal resistance compared to sitting in patients with OSAS, and the increase in nasal resistance was greater in the prone than in the supine posture. Therefore, when assessing the severity of OSAS and planning treatment, clinicians need to evaluate the patient’s sleep habitual posture and the impact of changes in posture on the patient, to obtain more comprehensive information and plan a more appropriate treatment.

List of abbreviations.

AHI	apnea-hypopnea index	
BMI	body mass index	
CPAP	continue positive airway pressure	
mCSA	minimal cross-sectional area	
NSD	nasal septal deviation	
OSAS	obstructive sleep apnea syndrome	
PSG	post-polysomnography	
SIDS	sudden infant death syndrome	
VAS	visual analog scale	

Acknowledgements

The study was financially supported by the Chiayi branch of Chang Gung Memorial Hospital in Taiwan with the grant number: CMRPG6J0202.

Author contributions

Conceptualization, Investigation, Writing-Original Draft Preparation: P-R Y; Data, Interpretation, Study Execution, Critically Reviewed the Article: Y-T T; Data Acquisition, Data Analysis, Software: H-Y T; Study Conception, Study Design, Data Interpretation, Writing-Review & Editing, Supervision: G-H C. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by Chang Gung Memorial Hospital, Chia-Yi Branch.

Grant number: CMRPG6J0202.

Data availability

If detailed data are required, they can contact the correspondence of the study, Geng-He Chang (Email address: genghechang@gmail.com ).

Declarations

Ethics approval and consent to participate

The study was performed in accordance with the principles of the Declaration of Helsinki and was approved by the Institutional Review Board of Chang Gung Memorial Hospital, Chia-Yi Branch, Taiwan (No. 201801720B0C501). The informed consent has been obtained from patients and/or parents and/or legal guardian.

Consent for publication

All patients and/or parents and/or legal guardian agreed that the text, figures, tables, and data in this paper can be published in your journal.

Competing interests

The authors declare no competing interests.

List of Abbreviations

AHI apnea-hypopnea index

BMI body mass index

CPAP continue positive airway pressure

mCSA minimal cross-sectional area

NSD nasal septal deviation

OSAS obstructive sleep apnea syndrome

PSG post-polysomnography

SIDS sudden infant death syndrome

VAS visual analog scale

Publisher’s note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
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