The central aim of this research project is to determine how the ever-growing problem of obesity in the western world contributes to the pathophysiology of obstructive sleep apnea (OSA). To complete this aim, the investigators will determine the impact of obesity on the mechanisms underlying OSA. This will be achieved by making physiological measurements of 4 physiological traits known to cause OSA as well as the patients sleep apnea severity, before and after weight-loss surgery (i.e. bariatric surgery).