Alternative Methods and Improvements to Current Delivery of Continuous Positive Airway Pressure for Treating Obstructive Sleep Apnea

  • Author / Creator
    Duong, Kelvin
  • For adults, the standard treatment for obstructive sleep apnea (OSA) is the delivery of continuous positive airway pressure (CPAP) through nasal/facial masks. For children, CPAP therapy is used if adenotonsillectomy is not a viable option or if OSA persists after surgery. By acting as a pneumatic stent, CPAP can prevent the collapse of the upper airways, thus restoring breathing and sleep. Though effective, tight-fitting CPAP masks can be uncomfortable to patients, contributing to adherence concerns. Recently, several groups have been investigating alternative methods of treatment to improve adherence to CPAP. One method is the delivery of CPAP through customized nasal/facial masks. Another method is generating positive airway pressures using nasal high flow (NHF) therapy. Both methods seek to improve comfort of OSA treatments, and therefore potentially increase adherence. This thesis aims to add greater insight into alternatives and improvements to current OSA treatments.
    The feasibility of delivering CPAP through customized nasal masks were demonstrated by assessing mask leakage and comfort and comparing them to commercially available CPAP nasal masks. Customized masks, fabricated using 3D facial scanning and modern additive manufacturing process, were assessed against three different sizes of commercial masks (petite, small/medium, and large) from the same supplier in a cross-over study involving six healthy adult volunteers. Mask leakage and comfort were evaluated for varying CPAP levels (4 cmH2O. 8 cmH2O, and 12 cmH2O) and mask tightness (loose – 100 g, appropriate – 350 g, and tight – 600 g). Leak was measured in real time using an inline low-resistance Pitot tube flow sensor, and each mask was ranked for comfort by the subjects.
    As expected, mask leak rates varied directly with CPAP level and inversely with mask tightness. The petite mask yielded the highest mask leaks and was ranked least comfortable by all subjects. Relative mask leaks and comfort rankings for the other commercial and customized masks varied between individuals. Three participants found their customized masks to be most comfortable, whereas the other three participants found a commercial sized mask most comfortable. The mask leak rates between each participants’ customized masks were comparable to the leak rates of their preferred commercial sized masks. At an appropriate fit, fit typically tightened to for night use, the customized nasal masks were able to deliver target CPAP levels in all six participants without triggering any alarms on the CPAP machine. This demonstrates the feasibility of using customized nasal masks as an alternative to commercial manufactured ones.
    With a focus on children, NHF therapy was investigated as an alternative treatment option to CPAP. Positive airway pressures and gas washout were compared between the two therapies in 10 nasal airway replicas, built based on computed tomography scans of children aged 4 to 8 years. NHF was tested at a single flow rate of 20 L/min, and CPAP was tested at two CPAP levels, 5 and 10 cmH2O. NHF was delivered with three different high flow nasal cannula models provided by the same manufacturer, and CPAP was delivered with a sealed mask. A lung simulator was used to establish tidal breathing in each replica, and airway pressure at the trachea was recorded over time. For gas washout measurement, end tidal carbon dioxide (EtCO2) was measured at the trachea with a capnograph, while carbon dioxide was being injected at the lung simulator. Changes in EtCO2 compared to baseline values (no intervention) were assessed.
    NHF therapy generated positive end-expiratory pressures (PEEP) ranging from 3.5 to 5.4 cmH2O across the three nasal cannulas, similar to a PEEP of 4.9 cmH2O generated by CPAP at a setting 5 cmH2O. Variation in tracheal pressure was higher between airway replicas for NHF compared to CPAP. EtCO2 decreased from baseline during administration NHF, whereas it increased during CPAP. No statistical difference in tracheal pressure nor EtCO2 was found between the three high flow nasal cannulas. This demonstrates that NHF therapy can generate positive airway pressures similar to lower end CPAP settings used in children, with the added benefit of gas washout.
    Both customized nasal masks and NHF therapy through nasal cannulas are feasible alternative methods to current CPAP treatments. Both methods may potentially improve comfort and increase adherence, and they may provide a treatment option to those who are CPAP-intolerant or have craniofacial abnormalities.

  • Subjects / Keywords
  • Graduation date
    Fall 2021
  • Type of Item
  • Degree
    Master of Science
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.