Obesity is currently one of the most serious public health problems. The prevalence of this condition has grown in an accentuated fashion in recent decades, even in developing countries, leading to a global epidemic. Over 1.6 billion adults worldwide are overweight, among which 400 million are obese. The World Health Organisation predicts that 10% of the global population will be obese by 2015 . As poverty has been undergoing a process of eradication, obesity has become a more frequent and more serious problem than malnutrition [2, 3]. In adults, overweight is characterised by a body mass index (BMI) between 25 kg/m2 and 29.9 kg/m2 and obesity is defined beginning at 30 kg/m2 .
When excess weight reaches very high values (BMI ≥ 40 kg/m2), obesity is considered a severe dysfunction due to the association with diseases that are either caused or aggravated by this condition, corresponding to grade III obesity, which is also denominated morbid obesity . The most frequent comorbidities are systemic arterial hypertension [5, 6], type II diabetes mellitus , obstructive sleep apnoea , degenerative joint disease , dyslipidemia, coronary disease [10, 11], respiratory dysfunction  and psychosocial problems .
Obesity is the most important risk factor for obstructive sleep apnoea (OSA), especially with fat build-up in the upper portion of the abdomen and the neck region. At least 60 to 70% of patients with OSA are obese . Moreover, the incidence among patients with Grade III obesity is 12-fold to 30-fold greater than that in the general population [15, 16]. OSA is characterised by recurrent episodes of partial or complete obstruction of the upper airway during sleep in the presence of ventilatory effort, with a consequent drop in oxyhemoglobin saturation, generating negative intrathoracic pressure and arousals . The gold standard for the diagnosis of OSA is basal nocturnal polysomnography (PSG), which is the simultaneous recording of physiological parameters during a night of sleep, involving the analysis of sleep stages, breathing pattern, cardiovascular function and body movements [18, 19].
The association between obesity and respiratory sleep disorders was first described in 1918 by William Osler, who was reminded of a Charles Dickens' characters nicknamed "John, the fat boy", a plethoric snorer and terribly sleepy . The treatment of obesity in these patients has since become a priority . Common diseases such as obesity and hypertension should not be analysed without considering respiratory sleep disorder as a possible causal factor. In recent years, the prevalence of such disorders has grown, affecting 40% of the general population [22, 23].
The aim of the treatment of obesity is to improve both health and quality of life through enough of a reduction in body weight to eliminate or improve comorbidities and promote psychological wellbeing . Medical management of obesity is routinely the first line of treatment prescribed by physicians and lay persons alike. Medical therapy often involves a combination of calorie restriction, behaviour modification, increased exercise and pharmacotherapy. Behaviour modification in the treatment regimen may help slow the tendency toward weight regain, but does not prevent it entirely. Unfortunately, the medical treatment of morbid obesity provides minimal sustained weight loss in the majority of patients [25, 26]. The fact that morbid obesity remains largely refractory to dietary and medication therapy makes bariatric surgery a viable option .
Patients with a BMI of greater than 40 Kg/m2 or 35 to 39.9 Kg/m2 and associated to comorbidities are candidates for bariatric surgery. The most often employed surgical methods are divided into three groups: restrictive, malabsorptive and mixed [28, 29]. The most common techniques are Fobi-Capella surgery and Scopinaro's biliopancreatic diversion, which are mixed techniques .
This study will sleep study, respiratory mechanics, chemosensitive response and quality of life in morbidly obese patients undergoing bariatric surgery.
Aims and hypotheses
The aims of this study are to assess the evolution of pulmonary function through spirometry, ventilatory mechanics and breathing tests as well as sleep study parameters and quality of life in subjects suffering from morbid obesity undergoing bariatric surgery and determine a possible correlation between weight loss and these physiological variables. We hypothesise that the weight loss induced by surgical intervention reduces the impact of this disease on sleep quality, cardiovascular consequences and quality of life as well as financial expenditures on treatment.