3. BIS levels of 35 will be targeted (low frequency EEG activity). A propofol infusion will be titrated by the investigators to the designated BIS target according to randomization. Clinical personnel will not be blinded to the study, and if patient has clinically significant change in hemodynamic parameters study will be interrupted. Each BIS target level will be kept as constant as possible for at least one hour; thereafter, lower esophageal pressures will be recorded for 15 minutes using high resolution esophageal manometry. Studies will be done in supine position [Most ICU patients are now kept head-up.], and the manometric assembly will be positioned to record from the hypopharynx to the stomach with 4-6 of the sensors positioned in the stomach.