This is the largest study examining individuals who have not responded to OSA surgical treatment. The findings suggest that multiple mechanisms may contribute to nonresponse, including contributions from various upper airway structures (velum, oropharyngeal lateral walls, tongue, and epiglottis) and mouth opening that also narrows the pharyngeal lumen.
Similar to those without previous OSA surgery,19, 20, 28, 29
a diversity of factors may contribute to residual upper airway obstruction in surgical nonresponders. Differences between nonresponders and those without previous surgery (from previous studies) were that in the former, a higher proportion demonstrated contributions from the oropharyngeal lateral walls, tongue, and epiglottis and that a lower proportion had a contribution from the velum. As the subjects in the current study all had previous tonsillectomy and palate surgery, at a minimum, it is not surprising that residual contributions from the velum and tonsils would be less common.
The diversity of patterns of obstruction during DISE seen in this study is reassuring, as it may reflect the multifactorial nature of upper airway obstruction in OSA. The accuracy of propofol unconscious sedation (as in DISE) as a representation of natural sleep depends on multiple factors, including upper airway muscle tone, neuromuscular reflexes, and lung volumes--as well as outcomes of surgical treatment directed by DISE findings. During propofol unconscious sedation, normals have demonstrated decreases in genioglossus tone to 10% of maximum awake activity,30, 31
which is one-half to one-third of the level in normals at sleep onset32
but greater than during REM sleep in normals and subjects with OSA.33
While unconscious sedation under propofol may not a perfect simulation of natural sleep, with identical effects on upper airway collapsibility, pharyngeal dilator muscle activity appears to lie somewhere between NREM and REM sleep. There have been no comparisons of lung volumes or upper airway neuromuscular reflex activity between propofol sedation and natural sleep.
The five previous studies examining site of obstruction in nonresponders to pharyngeal OSA surgery include one incorporating a combination of drug-induced sleep endoscopy and pharyngeal manometry,11
two utilizing lateral cephalometry,10, 12
and two with airway pressure monitoring.13, 14
Woodson and Wooten examined 11 nonresponders and attempted to determine the primary region of collapse (palatal vs. hypopharyngeal) with two evaluation techniques.11
Manometry demonstrated palatal and hypopharyngeal obstruction, respectively, in 8 (73%) and 3 (27%) of all subjects. The proportion demonstrating primarily palatal obstruction (vs. hypopharyngeal obstruction) included 5/6 with previous uvulopalatopharyngoplasty alone, 0/2 with transpalatal advancement pharyngoplasty alone,34
and 3/3 with previous uvulopalatopharyngoplasty and hypopharyngeal surgery. Three patients with primarily palate obstruction on manometry also demonstrated hypopharyngeal obstruction during DISE, suggesting residual hypopharyngeal obstruction in 6/11 (55%). Riley et al. found a decreased posterior airway space and increased mandibular plane to hyoid distance on lateral cephalometry in a sample of 9 nonresponders to soft palate surgery,10
while Yao et al. compared preoperative and postoperative lateral cephalograms after combined palatal and hypopharyngeal surgery and showed that, in contrast to responders, nonresponders did not increase their posterior airway space, posterior uvular space (distance from the uvula to the posterior pharygneal wall), and mandibular plane to hyoid distance.12
With airway pressure monitoring, Metes et al. examined 8 nonresponders to uvulopalatopharyngoplasty and showed residual palatal (vs. hypopharyngeal) obstruction in 6/8 (75%), with the primary region of obstruction unchanged, based on a similar preoperative evaluation.13
In a study of 22 nonresponders after uvulopalatopharyngoplasty with airway pressure monitoring, Farmer and Giudici found a primary site of obstruction in the palatal region for 4/15 (27%) and in the hypopharyngeal region in 11/15 (73%).
Residual palatal obstruction, even after soft palate surgery (uvulopalatopharyngoplasty. uvulopalatal flap, or palatal implants) was common, consistent with previous studies. The inability of these soft palate procedures to resolve palatal obstruction has led to the development of a number of palate-directed procedures, including transpalatal advancement pharyngoplasty, lateral pharyngoplasty,35
expansion sphincter pharyngoplasty,36
Additional research can examine whether the latter group of procedures may be more effective in treating palatal obstruction and, possibly, a contribution from the oropharyngeal lateral walls.
Hypopharyngeal obstruction during DISE was nearly universal in this study, whether due to a contribution of the oropharyngeal lateral walls, tongue, or epiglottis. Hypopharyngeal obstruction was present even in subjects with previous hypopharyngeal procedures, suggesting that these procedures may not provide sufficient improvement in airway dimensions and/or that they treat structures that are not playing a specific role in hypopharyngeal obstruction for the individual subject. For example, genioglossus advancement and tongue radiofrequency are both directed primarily at the tongue and may not address the oropharyngeal lateral walls.
No subjects with previous hyoid suspension demonstrated an epiglottic contribution to upper airway obstruction during DISE. The epiglottis has multiple soft tissue attachments, but one of interest for OSA surgery may be the relationship to the hyoid bone via the hyoepiglottic ligament. Hyoid suspension may treat the epiglottis more specifically than other hypopharyngeal procedures due to anterior displacement and stabilization of the hyoid bone and, indirectly, the hyoepiglottic ligament. Additional studies may be able to determine this more systematically and consider which hyoid suspension technique, whether to the thyroid cartilage39
or inferior border of the mandible,40
is preferred. Other procedures such as supraglottoplasty or partial epiglottidectomy41, 42
may also be particularly beneficial in these cases.
One-third of all subjects in this study demonstrated substantial mouth opening during unconscious sedation with propofol, with apparent adverse effects on pharyngeal dimensions related to the velum, oropharyngeal lateral walls, and tongue base. This finding agrees with previous research showing that greater degrees of mouth opening during sleep are associated with poorer outcomes after primary palate surgery.43
It is unclear whether mouth opening during sleep occurs due to nasal or pharyngeal obstruction or whether it can reverse with adequate treatment of obstruction (at least apparent adequate treatment without mouth opening). The implications for surgical treatment as well as non-invasive treatments such as chin straps are not entirely clear, and future investigations, ideally with larger sample sizes, is needed.
The importance of characterizing the patterns of obstruction, whether in primary or secondary treatment, lies in the association between treatment selection and outcomes. While previous studies have shown associations between DISE findings and outcomes for uvulopalatopharyngoplasty and mandibular repositioning appliances, future research—ideally with large, prospective cohorts—will enable an examination of hypopharyngeal surgery outcomes and the potential association between DISE findings related to hypopharyngeal obstruction (especially in the specific structures that may contribute to obstruction) and individual hypopharyngeal procedures.
In addition to those outlined above, this study has other limitations. Although it is the largest study of its kind, larger and more-detailed investigations will be useful. The subgroups were differentiated according to previous surgical treatment, but there are other differences including age, gender, race/ethnicity among subjects that cannot be examined in detail with a study of this size. Primary surgery was performed by multiple surgeons in multiple institutions, and therefore the procedures (i.e., palate surgery) are not standardized. As the subjects did not undergo DISE prior to primary surgery, there is no comparison of preoperative and postoperative findings to evaluate changes.