Airway and Airflow Characteristics In OSAS

Transcription

1 Airway and Airflow Characteristics In OSAS 16 th Annual Advances in Diagnostics and Treatment of Sleep Apnea and Snoring February 12-13, 2010 San Francisco, CA Nelson B. Powell M.D., D.D.S. Adjunct Clinical Professor Departments of Otolaryngology Head and Neck Surgery and Sleep Disorders and Research Department of Psychiatry Stanford University School of Medicine

2 Two Dimensional Anatomical Airway Nasal Adenoids Palate Tonsils Pharyngeal Wall Tongue Base

3 Imaging in OSAS Pharyngeal Airway Imaging 2-Dimensional (e.g. X-Ray Ceph) 3-Dimensional Computed Tomography (CT) Magnetic Resonance Imaging (MRI) Computational Fluid Dynamics (CFD) Pharyngeal Airflow Imaging 3-Dimensional Computational Fluid Dynamics (CFD)

4 Imaging in OSAS Two Dimensional Cephalometrics Riley R, Guilleminault C, Herran J, Powell N. Cephalometric Analysis & Flow-Volume Loops in OSA Patients 1983 Sleep 6(4):

5 2-D X-Ray Imaging Single Arch for Mild SDB Severe skeletal facial deformity and mild OSAS Pre-Op Post-Op 54 year old female

6 Imaging in OSAS Computed Tomography (CT) Magnetic Resonance Imaging (MRI) Used often for research of the OSAS airway CT and MRI provide three dimensional imaging CT is rigid MRI may evaluate compliance Schwab R, et al. Using MRI imaging found that tongue and lateral walls independently increased the risk of sleep apnea. Am J Respir Crit Care Med 2003

7 only pre treatment findings 3D-CT Imaging For anatomical airway evaluation in severe OSAS Note: obstruction at palate and occlusal plane C-Dental Menlo Park, CA And Dolphin software Pre Treatment

8 49 year old male, severe OSAS obstructed at palate and occlusal plane 3D-CT Image

9 MR 3D-CT Minimum axial area 220mm 2 note palate length size and length of uvula

10 Pre-op 3D-CT Imaging 54 year old female mild OSAS Post-op Sagittal osteotomy (SSRO) C-Dental X-Ray, INC. Menlo Park, CA and Dolphin

11 Surgical treatment 52 year old male Previously OSAS RDI 56 L sat 83% After 18 years, 40 lbs gained, RDI 39, with EDS Not tolerant of CPAP or weight loss Partial recurrence of OSAS requiring Revision Bi-Max Outcomes RDI < 10 L sat >90% EDS resolved

12 3D-CT Imaging Applications in OSAS Treatment Trial with CPAP Pre Post 37 year old male with moderate OSAS

13 Computational Fluid Dynamics (CFD) Analysis of the Pharyngeal Airway and Airflow Reconstructed 3D models from Computed Tomography(CT) Nelson Powell Christian Guilleminault Stanford University Goutham Mylavarapu Shanmugam Murugappan Mihai Mihaescu Ephraim Gutmark University of Cincinnati

14 3D Modeling Airflow in OSAS Computational Fluid Dynamics (CFD) Construct 3-dimensional geometry of the airway Captures airflow patterns (inspiration/expiration) Models airway and airflow dynamics Method to assess changes in pharyngeal airflow using 3 metrics: axial velocity, static airway wall pressure, wall shear stress Simulation model can be rigid (CT) or compliant (MRI)

15 Objectives Reconstruct three dimensional anatomically accurate upper airway models from pre & post treatment CT axial scans Simulate expiratory and inspiratory flows at a peak flow rate of 5,10,15,20,30 L/min Compare flow dynamics pre & post treatment Compare the change in flow dynamics between inspiration and expiration

16 Process Outline

17 Contours of: pressure, shear stress and velocity Color Bars represent magnitude of either pressure, velocity or shear stress Red = high value Blue = smallest value Positive values represent expansion of airway walls Negative values represent compression Three axis of Cartesian coordinates

18 Pre Treatment CFD results - Inspiration Hard palate level Retro palatal region *OPJ Epiglottis tip Even during inspiration, maximum axial velocity and minimum wall pressure were observed in the proximity of retro palatal constriction. However, flow appears to be less spread laterally in the airway during inspiration than in expiration.*opj =oral pharyngeal junction

19 Post Treatment CFD results - Inspiration Hard palate level Retro palatal region *OPJ Retro glossal region Site of minimum cross-section is in the retroglossal region of the airway. Maximum Axial velocity and minimum wall pressure are observed in the downstream of the constriction at the level of epiglottis tip during expiration * OPJ= oral phryngeal junction

20 Axial Velocity comparison (mid sagittal plane) - Inspiration Pre Treatment Post Treatment Max 6.8m/s Max 2.69 m/s Maximum velocity reduced by almost 2.5-fold in magnitude. Also, the flow distribution is different with lower velocities in the region downstream of the epiglottis in post treatment compared to pre treatment during inspiration

21 Wall static pressure comparison - Inspiration Pre Post Resistance is defined as the ratio of pressure drop with flow rate. Pre resistance is nearly 7.7 times more than post resistance.

22 Wall shear stress comparison - Inspiration Max 1.69 Pa Pre Post Max 0.372Pa Maximum wall shear stress reduced almost 4.5-fold from pre to post treatment

23 Computational Fluid Dynamics Unsteady- Large Eddy Simulation (LES) Axial Velocity (m/sec) Inspiratory 30 Liters/Min Pre treatment Post treatment

24 Computational Fluid Dynamics Unsteady- Large Eddy Simulation (LES) Wall Shear Stress (Pascal) Inspiratory 30 Liters/Min Pre treatment Post treatment

25 Conclusion for CFD Volume of airway pre to post treatment increased 2-fold At a peak flow rate of 15 L/min, a 9-fold reduction in pressure drop across the airway during expiration and 7.7 fold reduction during inspiration were observed between pre and post treatment Maximum wall shear stress reduced 6 fold Maximum velocity also reduced by 2.5 fold during inspiration between pre and post treatment Pre treatment showed significant turbulent airflow compared to the post treatment where laminar flow was now predominant Additional studies are required to assess the importance of airflow and airway changes in OSAS