Geng-He Chang, MD1,2,3, Cheng-Ming Hsu, MD, PhD1,2,3, Ethan I. Huang, MD, PhD1, Hsin-Yi Tsai, MS1, Yun-Ting Wang, MD1, Ming-Shao Tsai, MD1,2,3, Pey-Jium Chang, PhD2, and Yao-Te Tsai, MD1,2,3
Ear, Nose & Throat Journal2023, Vol. 102(7) 460–466© The Author(s) 2021Article reuse guidelines:sagepub.com/journals-permissionsDOI: 10.1177/01455613211015437journals.sagepub.com/home/ear
Objectives: Supine position reduces nasal patency compared with that in the sitting position; however, data on the effects of prone position on nasal patency is lacking. Methods: We assessed the nasal patency of 30 healthy individuals without upper respiratory tract disorders by using visual analog scale (VAS) score and acoustic rhinometry in 7 positions: sitting; frontal, right, and left supine; and frontal, right, and left prone. Results: According to the VAS scores, compared with that in the sitting position, both the supine and prone positions significantly increased subjective nasal obstruction (P < .001). The prone position had a more significant effect than did the supine position (P = .017). The results of minimal cross-sectional area measured through acoustic rhinometry demonstrated that both the supine and prone positions reduced the nasal patency significantly, but without significant differences between the effects of prone and supine positions (P = .794). Conclusion: This is the first study to elucidate that the prone position can significantly reduce the nasal patency in healthy individuals through subjective and objective assessments. Level of Evidence: IV
Keywords
nasal obstruction, nasal resistance, prone position, supine position
Nasal patency is influenced by various factors, including the periodic alterations of the nasal cycle, demographic variables, nasal mucosal reaction to venous changes, medication, nasal structural abnormality, and sinonasal diseases, such as rhinitis, sinusitis, and nasal polyps.1 Through acoustic rhinometry, studies have indicated that the supine position decreases nasal patency in healthy individuals compared with that in the sitting position,2-6 possibly because an enlarged turbinate passive increases the hydrostatic pressure of the intranasal venous system.7 Several respiratory diseases, such as obstructive sleep apnea (OSA),7 asthma,8 and allergic rhinitis,5 have been investigated to examine the effects of sleeping in the supine position on nasal patency. Some people used to sleep in the prone position, but research on the effect of prone position on nasal patency is lacking. Therefore, we evaluated the association between different positions (sitting, supine, and prone) and nasal patency through subjective and objective measurements involving healthy individuals. The current findings may represent a cornerstone for subsequent studies discussing the effects of sleeping in the prone position in patients with various respiratory diseases.
We used subjective and objective assessments through health examinations to recruit healthy volunteers for our investigation of the effects of different positions, particularly the prone position, on nasal patency. First, we used the visual analog scale (VAS), ranging from 1 to 10, to measure the principal symptoms of rhinitis in our potential participants9,10 including nasal blockage, rhinorrhea, itchy nose, and sneezing. We included only the individuals with a VAS score of <5 for each symptom. We also used nasoendoscopy and the modified Lund-Kennedy endoscopic scoring system to assess the nasal cavity11,12 and included only the individuals with a score of zero. In addition, blood testing was used to exclude patients with allergic rhinitis; only the individuals with immunoglobulin (Ig) E levels < 120 kU/L and Phadiatop scores < 0.35 PAL/L were included. We excluded individuals who were aged <18 years; were pregnant; were active smokers; had a history of allergic rhinitis, sinusitis, nasal trauma, or nasal surgery; had psychological problems; had acute upper or lower respiratory tract infections within 2 weeks before recruitment; and used systemic corticosteroids within 4 weeks before recruitment.
All patients were recruited from the department of otorhinolaryngology in Chiayi Chang Gung Memorial Hospital. The methods of consent and study protocol were approved by the Institutional Review Board of Chang Gung Memorial Hospital (201801720B0C501).
Subjective assessment. The primary outcome of this study was determined through the results of subjective assessments of nasal blockage after various postural changes. For evaluation, we used a VAS ranging from 0 to 10 points.10
Objective measurements. Studies on the relationship of nasal patency with positions have mostly used minimal crosssectional areas (mCSA) measured through acoustic rhinometry and aggregated the recorded data of bilateral nasal cavities for analysis.7,13 In this study, we measured the mCSAs of the nasal cavities on both sides for our participants in each position and analyzed the total and individual data of both nasal cavities for objective evaluation.
To explore the effect of the various positions on the nasal patency, 7 positions were tested here (1) sitting, (2) frontal supine, (3) left supine, (4) right supine, (5) frontal prone, (6) right prone, and (7) left prone (Figure 1). On assuming a position, the participant maintained it for 15 minutes before undergoing testing including VAS, for measuring the degree of subjective nasal blockage, and acoustic rhinometry, for measuring mCSAs. The acoustic rhinometry was performed by the same examiner (H. Y. Tsai), and the examination required no more than 5 minutes to complete for each position. The entire procedure was performed in an examination room with 50% to 60% humidity and at 25 to 26° C.
We used the degree of difference in subjective nasal blockage measured using VAS as the primary outcome of this study and statistically compared the scores measured in the aforementioned 7 positions. The objective assessments were set as the secondary outcomes. We present data as means with standard deviations (SD) and applied the paired Student’s t test for continuous variables. All analyses were performed on SPSS (version 18.0) and the level of statistical significance was set at P < .05.
The data of a total of 87 individuals who fulfilled the screening criteria were processed; of them, only 30 individuals (19 women and 11 men; mean age: 31.13 ± 7.28 years; mean body mass index: 22.77 ± 3.20 kg/m2) were enrolled. All included participants were serologically negative for allergic rhinitis (total IgE level: 40.39 ± 24.87 KU/L; Phadiatop scores: 0.17 ± 0.10 PAL/L). Visual analog scale scores were used to classify the 4 types of rhinitis-related symptoms in our participants as follows: nasal blockage, 0.83 ± 1.18; rhinorrhea, 0.57 ± 1.17; sneezing, 0.43 ± 0.94; and itchy nose, 0.80 ± 1.30 (Table 1).
Table 2 indicates the differences in the degrees of nasal blockage measured on VAS in various positions. Numbers 1 to 7 individually represent the various positions as labeled in Figure 1. First, compared with that in the sitting position, the degree of nasal blockage significantly increased in the supine position (mean VAS [95% confidence interval (CI)]: 1.80 ± 1.85 [1.14-2.46] vs 0.77 ± 1.17 [0.35-1.18], P<.001) and in the prone position (mean VAS [95% CI]: 2.47 ± 2.47 [1.58-3.35] vs 0.77 ± 1.17 [0.35-1.18], P < .001). Furthermore, compared with that in the supine position, the degree of nasal blockage significantly increased in the prone position (mean VAS [95% CI]: 2.47 ± 2.47 [1.58-3.35] vs 1.80 ± 1.85 [1.14-2.46], P = .017).
We also compared the differences in the degrees of nasal blockage in the prone and supine positions on the left and right sides. The results indicated that for both the sides, the degree of nasal blockage was significantly higher in the prone positions than in the supine position (left side, mean VAS [95% CI]: 2.67 ± 2.31 [1.84-3.49] vs 1.67 ± 1.63 [1.08-2.25], P < .001; right side, mean VAS [95% CI]: 2.83 ± 2.63 [1.89-3.77] vs 1.80 ± 1.81 [1.15-2.45], P < .001).
Table 3 presents the differences in the sums of bilateral mCSAs between the 7 positions. The results demonstrated that compared with that in the sitting position, both frontal supine and prone positions significantly reduced the objective nasal patency (supine vs sitting, mean sum of bilateral mCSAs: 0.89 ± 0.30 vs 1.00 ± 0.23 cm2, P = .002; and prone vs sitting, mean sum of bilateral mCSAs: 0.87 ± 0.32 vs 1.00 ± 0.23 cm2, P = .009).
No significant differences, however, were observed between the frontal supine and prone positions (supine vs prone, mean sum of bilateral mCSAs: 0.89 ± 0.30 vs 0.87 ± 0.32 cm2, P = .794). In addition, no such significant difference was noted between the supine and prone positions on the left or right side (left supine vs prone, mean sum of bilateral mCSAs: 0.83 ± 0.26 vs 0.84 ± 0.32 cm2, P = .892; right supine vs right prone, mean sum of bilateral mCSAs: 0.82 ± 0.37 vs 0.81 ± 0.27 cm2, P = .791).
Figure 2A-D demonstrates the individual mCSA of the left and right nasal cavity in various positions. Regardless of the left or right nasal cavity, the results remained consistent. Compared with that in the sitting position, the mCSAs significantly decreased in the frontal, left, and right supine positions; the related P values were respectively .005, <.001, and P <.001 for the right nasal cavity and .043, .036, and .044 for the left nasal cavity. Similarly, that in the sitting position, the mCSAs significantly decreased in the frontal, left, and right prone positions; the related P values were respectively .027, .001, and .014 for the right nasal cavity and .013, .021, and .002 for the left nasal cavity.
This is the first study to investigate the association between prone position and nasal patency. By using subjective and objective measurements, we observed that the prone position was associated with decreased nasal potency in relatively healthy individuals. These findings may provide substantial rationale for further research on the impact of sleep position in patients with breathing disorders, such as OSA, rhinitis, and sinusitis. In addition, studies have reported that preterm infants have a higher developing sudden infant death syndrome (SIDS) risk than do full-term infants. Multiple hypotheses have been proposed to explain the association between the prone sleep position and increased risk of unexpected death.14,15 Several physiological features when sleeping in the prone position have been identified, and the decreased nasal patency when in the prone position is suspected to be a cause.14,16-19 However, no further research was performed to investigate the relationship between the nasal patency and prone position. On the basis of the current results, the role of prone position in patients with SIDS is also an important topic that warrants further research.
Most studies have used the sum of bilateral nasal cavity mCSAs to investigate the relationship between postural change and nasal patency. Roithmann et al4 demonstrated that the supine posture significantly lowered nasal patency than the sitting position by comparing the mCSA in patients with and without allergic rhinitis (mean sum of bilateral nasal cavity mCSAs: 1.00 ± 0.23 vs 0.99 ± 0.24 cm2, P = .004). Hellgren et al7 observed that the nasal patency did not decrease significantly in patients with OSA when changing position from the sitting to supine position; however, the comparative group in their study demonstrated positive results (mean sum of bilateral nasal cavity mCSAs: 1.06 ± 0.18 vs 0.94 ± 0.21 cm2, P = .01). In our study, the mCSA results obtained in the sitting and supine positions were similar to those in the aforementioned two studies mentioned earlier, suggesting that our methods and results for measuring the objective nasal patency in healthy participants were consistent with those of previous studies. Here, the results on the association between the prone position and nasal patency demonstrated exceptional credibility.
Studies have indicated that the supine position could cause decreased nasal patency,2-7,20 which may be partially explained by the increased venous pressure of the nasal mucosa in cases of an enlarged nasal turbinate when in the supine position compared with that in the sitting position.6,7 Extending from these studies, we postulated that the prone position might lead to higher hydrostatic pressure on the venous system and cause a more enlarged turbinate due to additional gravitational effect, particularly in the nasal valve area, than in the supine and sitting positions. The nasal valve area is the most narrow part in the nasal cavity21; therefore, exacerbated nasal valve congestion may significantly decrease the nasal patency further.
We individually analyzed the acoustic rhinometry results of the left and right nasal cavities in various positions to investigate the gravity impact on lateral position (Figure 2A-D). We observed that in the supine position and when lying on the right side, the right nasal cavity was on the ground side, in the direction of gravity, and had a smaller mCSA (0.38 ± 0.18 cm2) than that in the frontal supine position (0.42 ± 0.19 cm2). In the frontal prone position, the effect was slightly reduced (0.41 ± 0.19 cm2) possibly because the venous blood was evenly distributed in the nasal cavities on both sides. However, the right prone position caused the lowest mCSA (0.37 ± 0.16 cm2), presumably because the prone position itself resulted in increased venous blood in the nasal mucosa, and the right nasal cavity was in the direction of gravity (ground side) in this position, leading to more venous blood in the right side nasal cavity. Synergizing the effects of the 2 factors mentioned earlier caused the lowest nasal patency. The results of the prone and supine positions of the left nasal cavity on the front and left side were conceivably similar to the results of the right nasal cavity. Based on these observations, we suggested that gravity effects may play an important role in the influence of position change on the nasal patency, which warrants further investigation.
Our study had some limitations. First, structural factors, such as nasal septal deviation (NSD), might influence the effect of position-related reduction in nasal patency. In order to reduce this potential bias, we performed the flexible nasopharyngoscopy to all patients and observed that 12 cases had no obvious NSD but 10 and 8 cases demonstrated mild left NSD and mild right NSD, respectively. Computed tomography of head and neck may be useful to evaluate the degree of NSD and its effect on the nasal patency in different positions. Second, based on the analysis of the changes in bilateral nasal mCSAs in various positions, we indirectly inferred the possible causes but lacked direct observational comparison. Future studies should apply nasoendoscopy for recording and compare the changes in nasal turbinate under various positions so as to verify our inference. Third, although the succession of positional changes was identical for each participant and all tests were completed in the same examination room with constant atmosphere settings, bias in the mCSA might result from acclimatization to the sequence of postural changes. Therefore, further prospective studies with varied successions of positions are required to validate the results of our study. Another potential bias was slight variation in the angle between the acoustic rhinometer tube and the nasal floor in different positions. To mitigate this bias, the tests of acoustic rhinometry were performed by the same investigator to ensure that the tip of the rhinometer tube was properly fit on the nostril in each position. Finally, we performed the testing when the participants were awake, and thus, it may not completely represent the change of nasal patency during sleep. Further prospective clinical trials were required to validate our findings during sleep.
The results of this study suggest that prone position may reduce the nasal patency and the effect is more obvious than in the supine position as per subjective aspects. In addition, the prone position may result in an increased venous pressure via the gravity effect, particularly in the nasal valve area, leading to the decreased nasal patency. Further studies are required to explore the influence of prone position on nasal patency in patients with breathing disorders during sleep.
The study was financially supported by the Chiayi branch of Chang Gung Memorial Hospital in Taiwan with grant numbers of CMRPG6J0202.
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: The study was financially supported by the Chiayi branch of Chang Gung Memorial Hospital in Taiwan with grant numbers of CMRPG6J0202.
ORCID iDs
Geng-He Chang https://orcid.org/0000-0001-5939-9747
Cheng-Ming Hsu https://orcid.org/0000-0003-3792-3784
Ethan I. Huang https://orcid.org/0000-0002-2789-189X
Yun-Ting Wang https://orcid.org/0000-0001-6190-4351
Ming-Shao Tsai https://orcid.org/0000-0002-9314-5940
Yao-Te Tsai https://orcid.org/0000-0002-2313-0890
1 Department of Otolaryngology–Head and Neck Surgery, Chang Gung Memorial Hospital, Chiayi
2 Graduate Institute of Clinical Medical Sciences, College of Medicine, Chang Gung University, Taoyuan
3 Faculty of Medicine, College of Medicine, Chang Gung University, Taoyuan
Received: March 07, 2021; revised: April 10, 2021; accepted: April 16, 2021
Corresponding Author:
Yao-Te Tsai, MD, Department of Otolaryngology Head and Neck Surgery, Chang Gung Memorial Hospital, Chiayi, No.6, W. Sec., Jiapu Rd, Puzi City, Chiayi 613.
Email: yaote1215@gmail.com
