Understanding upper airway dynamic characteristics in OSA patients under invasive and non-invasive treatment
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Obstructive sleep apnea (OSA), a common upper airway (UA) respiratory sleep disorder, is considered one of the most threatening diseases to quality of life worldwide. OSA occurs due to obstruction in the UA region, and is characterized by repeated collapse and/or obstruction of the pharyngeal airway during sleep. UA collapse occurs when the airway muscle forces are less than those generated from the airway negative pressures during respiration. The collapse may occur at the nasopharynx, oropharynx, or hypopharynx; but it is more likely to occur at the rear of the uvula (during expiration) and rear of the tongue (during inspiration). OSA can lead to hypertension, cardiovascular disease, stroke, low sexual drive in males, atherosclerosis, and increased rate of sudden death. Treatment of this ailment can be achieved invasively and non-invasively. Bariatric surgery is one of the invasive treatment modalities that has been used for many years for weight reduction and consequently alleviate OSA symptoms in morbid obese patients, but no biomechanical assessment for the UA characteristics and OSA symptoms before and after the surgery has been yet conducted. For many years, continuous positive airway pressure (CPAP) has been proven to be the golden and the first line non-invasive treatment for patients with moderate to severe OSA, mainly due to its non-invasive nature. There are many side effects of CPAP including dry nose, nasal congestion (itching or rhinorrhea), and it has been reported that due to its high operating pressure, stroke symptoms were recorded for cardiovascular disease patients. Respiratory devices that use pressure oscillations (PO) have been proven to have better respiratory outcomes in both animal and human models. PO have resulted in increasing both the activity and the stiffness of the UA muscles in both anesthetized and tracheotomised sleeping dogs, which in turn increased the UA patency and reduced its collapsibility. It has been reported that in sleeping humans, muscles in the UA increase their activity in response to high-frequency-low-amplitude pressure oscillations applied through the nasal airway. This electromyographic response was observed in both normal subjects and patients with OSA. From these results, it is clear that the PO can change the activity of the UA muscles, and consequently affect the surface tension, the airway compliance, and the airway collapsibility. Our hypothesis is that the PO superimposed on CPAP will reduce the required mean pressure to keep the airway open during sleep, and will reduce the risk of high pressure using the conventional CPAP. Therefore, this research aims to investigate the biomechanical changes and/or improvements in the UA characteristics before and after the invasive bariatric surgery in morbid obese OSA patients; and with the non-invasive CPAP superimposed with the PO, specifically we attempt to improve understanding of the effects of the PO on the UA respiratory system, which will lead to a more controlled method of delivering the PO in respiratory devices by determining the frequencies and amplitudes that optimise the breathing variables. Moreover, it will keep the airway open in OSA patients at a much lower CPAP than currently used, which will in turn increase the patient’s comfort. Bariatric surgery resulted in completely resolving OSA symptoms in morbid obese middle aged patients diagnosed with moderate to severe OSA. Also the use of the PO succeeded in keeping the airway open with no sign of collapse at much lower pressure distributions than the obtained values when using the conventional CPAP alone to prevent the occurrence of the apneic events.