The Impact of Anatomic Manipulations on Pharyngeal Collapse

Abstract

Obstructive sleep apnea (OSA) is a common disease with important neurocognitive and cardiovascular sequelae. Existing therapies are unsatisfactory, leading investigators to seek alternative forms of anatomic manipulation to influence pharyngeal mechanics. We have developed a two-dimensional computational model of the normal human upper airway based on signal averaging of MRI. Using the finite element method, we can perform various anatomic perturbations on the structure in order to assess the impact of these manipulations on pharyngeal mechanics and collapse. By design, the normal sleeping upper airway model collapses at −13 cm H 2 O. This closing pressure becomes more negative (ie, less collapsible) when we perform mandibular advancement (−21 cm H 2 O), palatal resection (−18 cm H 2 O), or palatal stiffening (−17 cm H 2 O). Where clinical data are available in the literature, the results of our model correspond reasonably well. Furthermore, our model provides information regarding the site of obstruction and provides hypotheses for clinical studies that can be undertaken in the future (eg, combination therapies). We believe that, in the future, finite element modeling will provide a useful tool to help advance our understanding of OSA and its response to various therapies. Keywords breathing; computational model; lung; MRI; obstructive sleep apnea; pharyngeal collapse Obstructive sleep apnea (OSA) is an important disorder due to both its high prevalence and its well-established sequelae. 1,2 Although effective therapies exist for sleep apnea, [3][4][5][6] investigators continue to seek alternative methods to manipulate pharyngeal mechanics/ anatomy with the ultimate goal of improving currently available therapeutic modalities. [3][4][5][6][7][8] Various different methods of manipulating pharyngeal mechanics have been used to treat snoring in individuals with largely normal upper airway anatomy and to treat sleep apnea in those with a compromised pharyngeal lumen. These methods include weight loss, oral appliances, and upper airway surgery. 9-11 However, these techniques have also been problematic due to variable efficacy and minimal ability to predict therapeutic response. A number of investigators have attempted to determine which patients are most likely to respond to treatment, but without great success. [12][13][14][15][16] We believe that improvements in our Our group has been involved in the development of a computational model to better understand the behavior of the human upper airway. 17 We have used finite element analysis, which is a mathematical technique to quantitatively analyze the behavior of a given mechanical structure. We have previously published our two-dimensional model that uses anatomically correct structure from MRI of normal human subjects. 17 With this model, we have used the critical closing pressure (Pcrit) as our outcome measure to assess the collapsibility of the upper airway. 18 Using finite element analysis, we sought to determine the impact of mandibular advancement, pa...

Speech function of the oropharyngeal isthmus: a modelling study

“…Berry et al (1999) reports muscle forces around 0.3N, supporting our estimate of forces less than 1N. In previous models lacking embedded muscles, the material of the soft palate has been modeled as a linear elastic material with Young’s modulus E = 25,000 Pa (Wang et al 2012; Liu et al 2007; Huang et al 2005). We also use a linear elastic model, but take a slightly softer E = 15,000 Pa, bearing in mind that the embedded muscles in our model will cause soft palate tissue to stiffen with activation (see, e.g., Cui et al 2008).…”

Simulation of the upper airways in patients with obstructive sleep apnea and nasal obstruction: A novel finite element method

“…Previous modelling of the upper airways varies in complexity of geometry and material modelling. Two‐dimensional models investigate the pharyngeal mechanisms in the mid‐sagittal plane, however, they do not consider the influence of the lateral walls (Berry et al 1999, Huang et al 2007). Three‐dimensional models demonstrated that material modelling influences the response of the soft tissues when loads were applied (Pelteret et al 2014, Zhao et al 2013) but they are costly and are frequently based on single‐patient CT or MRI data.…”

“…The computed displacements resulting from supine to upright position presented in Table are compared to this value in order to have a guide on what material parameter set is most representative. Negative intraluminal pressure during inspiration narrows the airway and might lead to airway collapse . As the displacement of the soft palate is governed by air pressure with minimal influence of shear forces, the load on the soft palate during inspiration was modelled as a uniformly distributed negative pressure.…”

“…Previous modelling of the upper airways varies in complexity of geometry and material modelling. Two-dimensional models investigate the pharyngeal mechanisms in the mid-sagittal plane, however, they do not consider the influence of the lateral walls 27…”

Upper airway imaging in obstructive sleep apnea

“…Given these limitations, as well as the conflicting data generated by clinical studies in predicting response to therapies, Huang et al [38,39 ] developed a finite element computer model of the upper airway to explore the effect of palatal resection, mandibular advancement and palatal stiffening [39 ]. This model was derived from signal averaged sagittal MRI scans of individuals with a normal upper airway.…”