An Investigation Into the Improvement of Obstructive Sleep Apnea Therapy

Abstract

The upper airway (UA) patency is a critical element of the breathing cycle. Narrowing of the UA causes breathing difficulties that may cause sudden death. Repeated closure of the UA, and subsequent physiological consequences during sleep, lead to what is called “obstructive sleep apnea” (OSA) syndrome. OSA occurs because of the excessive relaxation in the UA soft tissue. Continuous positive air pressure (CPAP) is the gold standard treatment for OSA. Generally, high pressures of CPAP are needed to be effective in treating OSA. However, this high pressure has many negative side effects, such as dryness of the upper airway, nose soreness, and irritation of the throat. Furthermore, a prospective observational study has shown that CPAP treatment resulted in a significant reduction in intima-media thickness (IMT) of the carotid artery, which may increase the risk of cerebrovascular events or stroke. Reducing CPAP pressure and the AHI is one of the main goals of this research. To reduce CPAP pressure, superimposed pressure oscillations were used in recent studies and the results were promising. Pressure oscillations is a pressurised air pulse with certain frequencies that can trigger the augmentation of the UA muscles to contract, which leads to fewer OSA events. This is a two-fold thesis. First, it focuses on the clinical trials to reinforce previous findings and obtain statistical assurance. The second objective of this research is to develop a mathematical model to simulate the UA collapse and observe UA modulation due to pressure oscillations. The clinical trials were conducted at Fisher & Paykel Healthcare. In total, 19 participants were recruited along with 14 previous participants recruited in Switzerland. Each trial lasted two nights and consisted of patients monitored using a polysomnography (PSG) during sleep. A reduced pressure of CPAP (70% titration pressure) without a humidifier was applied on the first night, and this trial was considered to be the reference point. The same reduced value of CPAP pressure combined with the PO was used on the second night. A random allocation of the order of testing was done. The main two endpoints analysed on completion of the trials were the number of arousals (AHI) and UA dryness. This work enhances the efficacy of CPAP therapy among OSA patients as well as reducing its running cost. The developed computer modelling predicted the apnea hypopnea (AHI) index using MRI images of OSA patients’ upper airways, and by calculating the lateral pharyngeal wall thickness, it can be used for future estimations of the apnea hypopnea index to achieve UA opening at lower CPAP titration pressure with superimposed pressure oscillations.