Abstract
Study Objectives:
Drug-induced sleep endoscopy with positive airway pressure evaluates the collapsibility of the upper airway. It is currently unknown whether body position affects this assessment. We sought to determine whether the collapsibility of the airway may change with head of bed elevation.
Methods:
A prospective, consecutive cohort study was performed by 2 sleep surgeons at a tertiary care center. Inclusion criteria included adults 18 years of age and older with obstructive sleep apnea who were intolerant to continuous positive airway pressure therapy. Patients underwent drug-induced sleep endoscopy with positive airway pressure to evaluate them for alternative treatment options. Patients were evaluated in supine position with the head of bed both level and elevated to 30°. The airway was evaluated using the standardized VOTE scoring system in both positions.
Results:
The 61 patients included in the study were predominantly male (70.5%), middle-aged (51.2 years), and obese (body mass index, 30.2 kg/m2) with moderate-to-severe obstructive sleep apnea (apnea-hypopnea index, 34.1 events/h). The cohort consisted of predominantly positional obstructive sleep apnea (mean supine apnea-hypopnea index 48.7 events/h, nonsupine apnea-hypopnea index 20.8 events/h). All 4 sites of the upper airway demonstrated a significant decrease in airway opening pressures with the head of bed elevated compared to level (P < .01 for all sites). There was no significant difference in VOTE scoring between level and upright positions.
Conclusions:
Patients with the head of bed elevated to 30° have a significantly lower degree of airway collapsibility compared to patients in the level position but no significant change in VOTE scoring was observed.
Citation:
Owen GS, Talati VM, Zhang Y, LoSavio PS, Hutz MJ. The effect of head of bed elevation on upper airway collapsibility during drug-induced sleep endoscopy. J Clin Sleep Med. 2024;20(1):93–99.
Keywords: DISE-PAP, drug-induced sleep endoscopy, positive airway pressure, sleep apnea, bed positioning, VOTE criteria
BRIEF SUMMARY
Current Knowledge/Study Rational: When evaluating patients for upper airway surgery, drug-induced sleep endoscopy with positive airway pressure is a novel diagnostic technique that allows for both the qualitative and quantitative evaluation of upper airway collapsibility. It is unclear what effect changes in body position, in particular head of bed elevation, will have on upper airway collapsibility or collapse patterns.
Study Impact: The severity of upper airway collapsibility was significantly lower with the head of bed elevated as compared to the level position, but collapse patterns were generally unchanged. As drug-induced sleep endoscopy with positive airway pressure becomes more frequently incorporated into clinical practice, the patient’s bed position should be considered because this may alter airway opening pressure.
INTRODUCTION
Obstructive sleep apnea (OSA) is a common clinical condition characterized by recurrent episodes of upper airway collapse during sleep, resulting in decreased airflow and hypoxemia.1 The pathophysiology of these events is multifactorial, including anatomic abnormalities, decreased muscle tone, neuromuscular responsiveness, arousal threshold, and positional dependence.2 Treatment of OSA traditionally involves the use of continuous positive airway pressure, although compliance with this treatment is often suboptimal.3 Alternative treatments include weight loss, positional therapy, oral appliances, and upper airway surgery. Changes in body position, such as head of bed (HOB) elevation, have also been shown to improve severity of OSA by decreasing upper airway collapsibility and increasing upper airway patency.4
When evaluating patients for upper airway surgery, drug-induced sleep endoscopy (DISE) is often utilized as a diagnostic tool for the qualitative evaluation of upper airway collapse. It is performed in a variety of clinical settings from the operating room to bronchoscopy suite and in various body positions. The VOTE classification system is a standardized approach commonly utilized to assess sites of obstruction of the upper airway during DISE.5 Previous studies have focused on the effect of body position and head rotation using DISE, with evidence that lateral positioning and head rotation improve upper airway patency compared to supine.6–10 These findings, as well as the demonstrated benefit of HOB elevation, are consistent with the notion that gravity influences the degree of upper airway collapsibility.11
DISE with positive airway pressure (DISE-PAP) is a novel technique that incorporates both the qualitative visualization of upper airway collapse patterns (VOTE classification) and the quantitative measurement of upper airway collapsibility (pharyngeal opening pressures).12,13 DISE-PAP has been examined for a potential role in improving patient selection for hypoglossal nerve stimulator implantation in the treatment of OSA.14 Although many studies have compared outcomes in DISE between supine, lateral, and head rotation, no study has examined the effect of HOB elevation, particularly in the setting of DISE-PAP. Understanding the effect of changes in HOB elevation during diagnostic studies such as DISE-PAP is crucial to accurately determining the need for possible surgical intervention in patients with OSA as well as to better understand upper airway physiology in varying positions, particularly as DISE-PAP becomes increasingly utilized within the sleep surgery community.12
In this study we aimed to determine the effect of HOB elevation on upper airway collapsibility during DISE-PAP. We hypothesized that HOB elevation would lead to a decrease in upper airway collapsibility but not significantly affect collapse patterns compared to level positioning.
METHODS
Study population
This was a prospective cohort study of consecutive patients undergoing sleep surgery evaluation by 2 experienced sleep surgeons in a continuous positive airway pressure–alternatives clinic at a tertiary care center in the United States between December 2021 and June 2022. Inclusion criteria were patients age of 18 years and older, apnea-hypopnea index (AHI) greater than 5 events/h as demonstrated on either a home sleep apnea test or an in-laboratory polysomnogram, and intolerance to continuous positive airway pressure. Patients underwent DISE-PAP to assess the utility of continuous positive airway pressure alternative interventions. This study was approved by the Rush University Medical Center Institutional Review Board (no. 17060204).
Study design
Demographic factors were collected including age, sex, and body mass index. The following values from either a home sleep study or polysomnogram were collected: supine AHI, nonsupine AHI, AHI with 3% oxygen desaturation (if available), AHI with 4% oxygen desaturation (if available), and oxygen saturation nadir. Patients underwent DISE-PAP as initially described by Seay et al and previously reported by the senior author.12,14 An initial cohort of patients underwent DISE-PAP with HOB level. The HOB was then elevated to 30° and a repeat baseline evaluation as well as PAP ramp was performed with patient maintaining supine position. The neck was maintained in a neutral position throughout. A second cohort of patients underwent evaluation in reverse order (the HOB was elevated to 30° with the patient supine and then the procedure was repeated with the HOB at 0°). This served as an internal control to account for possible variability in depth of sedation during the procedure that may affect degree of airway collapsibility. Patterns of obstruction were assessed qualitatively using the VOTE classification.5 Quantitative measures of obstruction were assessed using pharyngeal opening pressures at the following sites: palatal opening pressure, lateral wall opening pressure, tongue base opening pressure, and epiglottic opening pressure.
Statistical analysis
Categorical data are presented as percentage frequencies, with continuous data presented as mean ± standard deviation. Categorical data were analyzed using chi-squared test or the Fisher exact test, as appropriate. Continuous data were analyzed by 2-sample t test or Mann–Whitney U test, as appropriate. Differences in opening pressures between level and upright positions were compared using the Wilcoxon signed-rank test. Spearman’s correlation coefficients were adopted to examine the association between pressure differences and age, body mass index, and differences between supine AHI and nonsupine AHI and overall AHI (categorized via 3% or 4% hypopnea criteria). Bowker’s test of symmetry or McNemar’s test was used to compare the collapse pattern between the level VOTE criteria and the upright VOTE criteria. The 95% confidence limit of the kappa coefficient was used to compare the difference between the level–upright cohort and upright–level cohort. Two-tailed tests were utilized. Additional subgroup analysis was performed to compare pharyngeal opening pressures and VOTE criteria between the positional and nonpositional OSA cohorts. Opening pressures were compared using Mann–Whitney U test and VOTE criteria was compared using Fisher’s exact test. Statistical significance was defined as P < .05, and analyses were performed with SAS v9.4 (SAS Institute, Cary, North Carolina).
RESULTS
A total of 61 patients were consecutively enrolled: 41 patients in the initial level–upright cohort (HOB 30°) and 20 patients in the subsequent upright–level cohort. The study population was predominantly male (70.5%), with a mean age of 51.2 years, an average body mass index of 30.2 kg/m2, and with moderate-to-severe OSA (AHI 34.1 events/h) (Table 1). Of note, the cohort consisted of predominantly positional OSA (mean supine AHI 48.7 events/h, mean nonsupine AHI 20.8 events/h). In subgroup analysis, no significant differences in pharyngeal opening pressures (Table 2) or VOTE scoring (Table S1 (33.4KB, pdf) in the supplemental material) were observed between the positional and nonpositional OSA cohorts. The duration of the procedure was on average 16.6 minutes.
Table 1.
Demographic characteristics and sleep study results.
| Total (n = 61) | |
|---|---|
| Age (years) | 51.20 (14.79) |
| BMI (kg/m2) | 30.19 (3.62) |
| Sex | |
| Male | 43 (70.49%) |
| Female | 18 (29.51%) |
| Sleep study type | |
| Home sleep test | 28 (46.67%) |
| Polysomnography | 32 (53.33%) |
| Supine AHI | 48.74 (26.73, 47) |
| Nonsupine AHI | 20.77 (20.12, 43) |
| Difference between supine AHI and nonsupine AHI | 27.64 (22.86, 41) |
| AHI (3%) | 34.06 (22.38, 38) |
| AHI (4%) | 30.85 (23.38, 40) |
| O2 nadir (%) | 80.82 (8.14, 60) |
Discrete variables are reported as number (percent) and continuous variables are reported as mean (standard deviation, number [if varied from cohort]). AHI = apnea-hypopnea index, BMI = body mass index.
Table 2.
Comparison of pharyngeal opening pressures in level and upright position in the positional and nonpositional OSA cohort.
| Positional OSA | Nonpositional OSA | P | |
|---|---|---|---|
| Number (%)* | 29 (47.5%) | 14 (23.0%) | |
| Opening pressure difference | |||
| Pharyngeal | 1.18 | 1.08 | .73 |
| Lateral wall | 1.17 | 1.00 | .84 |
| Tongue base | 1.37 | 0.60 | .18 |
| Epiglottis | 1.20 | 0.33 | .21 |
There were 18 patients for whom supine apnea-hypopnea index (AHI) was not available in either supine, nonsupine, or both positions. OSA = obstructive sleep apnea.
The difference in pharyngeal opening pressure between level and upright position was significant for all 4 sites, with upright positioning exhibiting lower pharyngeal opening pressures on average compared to level (Table 3 and Figure 1). The difference between level and upright body position in palatal opening pressure (0.97 vs 1.94, P = .02) and tongue base opening pressure (0.63 vs 2.00, P = .02; Table 3) was significant when comparing the 2 cohorts, level–upright and upright–level. When analyzing collapse patterns between level and upright body positions (HOB 30°) utilizing the VOTE criteria, we noted no significant difference overall or between the 2 cohorts (Table 4). There was no significant difference in airway opening pressure between males and females (Table S2 (33.4KB, pdf) ).
Table 3.
Differences in pharyngeal opening pressure between level and upright positions and by cohorts.
| Site | Total Difference Between Positions | P | Level–Upright Cohort Difference | Upright–Level Cohort Difference | P |
|---|---|---|---|---|---|
| Palatal | 1.27 (1.63) | <.01 | 0.97 (1.48) | 1.94 (1.82) | .02 |
| Lateral wall | 1.13 (1.19) | <.01 | 0.93 (1.11) | 1.64 (1.29) | .09 |
| Tongue base | 1.02 (1.58) | <.01 | 0.63 (1.00) | 2.00 (2.30) | .02 |
| Epiglottic | 0.88 (1.73) | <.01 | 0.57 (1.19) | 1.62 (2.50) | .13 |
Values reported as mean (standard deviation); positive means indicate level values were greater than upright values on average. All units are mm H2O.
Figure 1. Differences in pharyngeal opening pressure by site between level and head of bed elevated positions.
EOP = epiglottic opening pressure, LOP = lateral wall opening pressure, POP = palatal opening pressure, TOP = tongue base opening pressure.
Table 4.
Collapse pattern comparison between level and upright using VOTE criteria.
| Site | Level Mean Score | Upright Mean Score | P | Kappa Coefficient | 95% CI |
|---|---|---|---|---|---|
| V | .99 | 0.83 | 0.71–0.97 | ||
| AP (n = 23) | 1.83 | 1.70 | |||
| CCC (n = 17) | 2.00 | 1.94 | |||
| Unsp. (n = 5) | 2.00 | 1.80 | |||
| O (n = 40) | 1.25 | 1.20 | .57 | 0.92 | 0.80–1.00 |
| T (n = 45) | 1.67 | 1.62 | .16 | 0.90 | 0.77–1.00 |
| E (n = 42) | 1.67 | 1.67 | >.99 | 0.79 | 0.59–0.98 |
P values, assessing for a statistically significant difference in VOTE score between level and upright positions, were based on results of Bowker’s test of symmetry or McNemar’s test. Kappa coefficient indicates the degree of agreement between the level and upright positions. AP = anteroposterior, CCC = complete concentric collapse, CI, confidence interval, E = epiglottis, O = oropharyngeal lateral wall, T = tongue, Unsp. = unspecified direction of collapse, V = velum.
When comparing surgeons, surgeon A performed 26 procedures in the level–upright cohort and surgeon B performed all other procedures. There was no significant difference in pharyngeal opening pressure for level or upright position between surgeons (Table 5 and Figure 2).
Table 5.
Pharyngeal opening pressure differences between level and upright by surgeon.
| Site | Surgeon A (P.L.) | Surgeon B (M.H.) | P |
|---|---|---|---|
| Palatal | 1.00 (1.61) | 1.48 (1.65) | .14 |
| Lateral wall | 0.87 (0.99) | 1.30 (1.29) | .33 |
| Tongue base | 0.63 (0.97) | 1.56 (2.06) | .12 |
| Epiglottic | 0.64 (1.29) | 1.22 (2.21) | .45 |
Values reported as mean (standard deviation). All units are mm H2O.
Figure 2. Comparison of pharyngeal opening pressure differences by surgeon.
EOP = epiglottic opening pressure, LOP = lateral wall opening pressure, POP = palatal opening pressure, TOP = tongue base opening pressure.
DISCUSSION
This study was the first to evaluate both the qualitative and quantitative collapsibility of the upper airway in different HOB positions using DISE-PAP. Patients with the HOB elevated had significantly lower upper airway collapsibility at all 4 anatomic sites studied compared to level patients. In terms of collapse patterns, no significant difference was noted between HOB positions when compared using the VOTE criteria. This suggests that elevating the HOB may reduce the collapsibility of the airway uniformly across anatomic sites, while the specific mechanisms remain unclear. A difference in pharyngeal opening pressures between the level–upright and upright–level cohorts was noted, which may be related to increased airway collapsibility as depth of anesthesia increases.15 Alternative hypotheses include central events occurring during propofol distribution that affect this analysis. Given the cohort demonstrated predominantly positional OSA, subgroup analysis was performed comparing pharyngeal opening pressure differences between level and upright position in patients with positional and nonpositional OSA. Overall, there was no significant difference in pharyngeal opening pressures between these 2 cohorts when comparing the 2 positions. However, there was a significant point estimate difference in pharyngeal opening pressures between the cohorts at the base of tongue and epiglottis, although it did not reach statistical significance. This may be attributable to the limited sample size in the subgroup analysis and further study is required to explore these findings.
Previous studies have examined the effect of changes in body and head position on upper airway collapsibility in OSA.7–10 Similarly, the effects of HOB elevation on airway collapsibility and OSA are well-documented. On computed tomography imaging, HOB elevation to 44° has been shown to increase the upper airway volume by 17.5%,16 and an HOB elevation of 7.5° has been shown to reduce the severity of OSA by 31.8% in mild-to-moderate cases.4 A greater reduction in AHI has been demonstrated when the angle was increased to 60°; however, this position may be less tolerable for patients.17 In the present study we used 30° for HOB elevation because a previous study demonstrated improvement in the critical closing pressure of the airway at 30° compared to level, in addition to the feasibility of obtaining this in the operating room while still maintaining a degree of patient comfort.18 The mechanisms accounting for improvement in airway volume and OSA are thought to be due to gravity, but specific mechanisms remain unclear. If gravity were the sole mechanism, then the palate and tongue base should be more affected because they are in the same plane as the change in vertical movement due to HOB elevation. An alternative mechanism could be changes in end-expiratory lung volume with elevation of the HOB, because this has been shown to correlate inversely with upper airway passive critical closing pressure.19,20 Other proposed mechanisms include preventing rostral fluid shifts, change in upper airway shape, and decreased muscle compensation, although further research is needed.21–23
This is also the first study to evaluate changes in upper airway collapse patterns with changes in HOB elevation. Yalamanchili et al found differences in VOTE scoring criteria based on supine vs lateral body positioning consistent with gravitational factors.10 However, we did not observe a significant difference in VOTE scoring between the 2 body positions. Although 30° was sufficient to observe changes in pharyngeal opening pressures, we suspect this degree of elevation was not sufficient to induce significant changes in qualitative observation. Perhaps increasing the angle of elevation to 60° or 90° would prompt a more significant change in VOTE scoring. It is unclear whether changing the degree of elevation to this magnitude to see changes in VOTE scoring would significantly change management, because quantitative opening pressure changes are already seen at 30°.
This study is not without limitations. First, this study lacked the ability to have a blinded reviewer evaluate the pharyngeal opening pressure due to a lack of video integration to identify when the PAP ramp began. Thus, we were unable to perform interrater reliability analysis for both opening pressures and VOTE criteria. We have incorporated this ability into our clinical practice for future studies. However, a recent study by Yu et al demonstrated that pharyngeal opening pressure differences can be observed visually with similar accuracy to objective opening pressure measurements with strong interrater reliability.24 Second, differences in opening pressures between the level–upright and upright–level cohorts were statistically significant in only 2 of the 4 anatomic sites, as reported in Table 2, but all 4 sites showed substantial differences. This study may have lacked the statistical power to demonstrate statistical significance between these 2 cohorts, but these differences may be further explored in future studies. Additionally, although we theorize that depth of sedation may influence our results based on differences in level–upright and upright–level cohorts, we did not utilize monitoring to determine depth of sedation such as bispectral index monitoring in this study.25 This was not available at our institution at the time of this study but has been obtained for use in future studies. Finally, our patient population consisted of predominantly positional OSA, despite our consecutive sampling. Because the patients remained in supine position for the duration of the study, whether their sleep apnea was positional in nature was unlikely to affect our primary outcomes. This was supported by additional subgroup analysis demonstrating no significant difference in outcomes between positional and nonpositional OSA.
A major strength of this study was the use of consecutive prospective sampling, which is a commonly used form of nonprobability sampling and limits sampling bias.26 This study also included cohorts that were evaluated in level and then upright as well as upright then level positions. This was to ensure that depth of sedation or the timing of the procedure did not affect collapsibility, given the lack of sedation monitoring as described above. The difference in palatal opening pressure and tongue base opening pressure observed between the cohorts warrants further investigation, but given that both groups exhibited a significant decrease in palatal opening pressure and tongue base opening pressure between level and upright positions, it did not significantly affect the overall outcome. Finally, a standardized DISE-PAP protocol was developed and utilized by 2 experienced sleep surgeons.
As the frequency of DISE-PAP procedures increases both nationally and internationally, investigators are finding that the procedure may have utility in multiple areas, including its use as a predictor of persistent pharyngeal obstruction during PAP therapy and in identifying patients who may have improved outcomes with hypoglossal nerve stimulation.14,27 This study depicted the importance of HOB elevation on the degree of upper airway collapsibility. It also demonstrated that HOB elevation to 30° did not significantly affect VOTE scoring during DISE. Further evaluation of how pharyngeal opening pressures during DISE-PAP affect surgical decision-making and outcomes is needed.
DISCLOSURE STATEMENT
All authors have seen and approved the manuscript. Work for this study was performed at Rush University Medical Center. Findings of this manuscript were reported at the International Surgical Sleep Society Annual Meeting 2022 (Philadelphia, Pennsylvania, Sept. 8, 2022) and the American Academy of Otolaryngology Annual Meeting 2022 (Philadelphia, Pennsylvania, Sept. 10–14, 2022). The authors report no conflicts of interest.
ABBREVIATIONS
- AHI
apnea-hypopnea index
- DISE
drug-induced sleep endoscopy
- DISE-PAP
drug-induced sleep endoscopy with positive airway pressure
- HOB
head of bed
- OSA
obstructive sleep apnea
- PAP
positive airway pressure
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