Comparison of Esophageal Manometry and CT Scan Measurements

In the clinical setting, Pes is a surrogate for pleural pressure, while SP is measured by means of chest CT scan images. The SP highly approximates the vertical pleural pressure gradient both in normal lungs and injured lungs in lean subjects. It is known that in the healthy obese patient the Pes is higher than that in normal lean patients, but there is no information about the relationship between high Pes with the SP in subjects with morbid obesity. The investigators hypothesized that factors other than superimposed pressure determine the high Pes in subjects with morbid obesity. Hence, Pes should be high despite the low SP found in healthy obese individuals. The investigators will test this hypothesis in a prospective observational cohort study. In 12 subjects (6 with body mass index \> 40kg/m2, and 6 with body mass index \< 30kg/m2 ) with scheduled chest CT scan for clinical purposes: 1. The Pes will be measured during spontaneous breathing (baseline values at end-expiration and variations during tidal breathing). To achieve this purpose, an esophageal balloon (AVEATM Ventilator Esophageal Pressure Monitoring Tube Set, 8 FR, CareFusion, Yorba Linda, CA, USA) will be inserted after administration of local anesthesia (lidocaine spray 2%). 2. The SP will be determined by lung computed tomography imaging and the pleural pressure will be calculated in non-dependent lung regions as the difference between Pes and SP. For this purpose, an additional low-dose CT scan at the end-expiration will be taken after the scheduled CT scan. During the research procedure, the Pes during the whole respiratory cycle, the CT image at the end-expiration, demographics, past and current medical history will be recorded. There will be no follow-up phase in this study.