 The investigators hypothesis is that upper airway collapsibility Pcrit in patients with obstructive sleep apnea OSA can be measured using equipment found in the clinical sleep laboratory and these Pcrit measurements obtained using clinical sleep laboratory equipment is comparable to those obtained using research equipment. OSA is a common disease characterized by repetitive collapse of the upper airway during sleep, leading to hypoxemia and arousals, and which has important neurocognitive and cardiovascular consequences. The single most important factor in the development of OSA is upper airway collapsibility: those with a more collapsible upper airway tend to have OSA while those with a stiffer upper airway do not. The gold standard treatment for OSA is continuous positive airway pressure CPAP, which acts by stenting open the collapsible airway. Upper airway collapsibility can be measured during sleep by changing the CPAP level and assessing the change in inspiratory flow through the upper airway. Although technically feasible, these measurements are typically only undertaken in research laboratories with specialized equipment. The purpose of this study is to measure upper airway collapsibility using clinically available i.e. equipment found in a clinical sleep laboratory equipment only. If successful, upper airway collapsibility could be routinely measured in clinical practice, which could help inform treatment decisions and help individualize therapy for OSA. 