Relationship between mouth and esophageal pressures in different body postures

Static voluntary efforts, both inspiratory and expiratory (executed with the glottis open against a closed airway) are commonly utilized for the evaluation of correct esophageal balloon positioning for indirect pleural pressure measurement. Agreement between delta Pm (change in mouth pressure) and delta Pes (change in esophageal pressure) indicates the valid indirect determination of pleural pressure. Measurements of delta Pes are more commonly made with the thorax in the upright position, and some investigators have reservations about determinations carried out in the supine position. In the present investigation, the airway shutter occlusion test as well as Müller's maneuver were applied to patients sitting in a plethysmographic box to determine the validity of delta Pes in several body positions. Measurements were made on 8 patients sitting with the thorax in the vertical (90 degrees) position and at angles of 45 degrees, 0 degree and -10 degrees. Thoracic gas volume was also determined at each angle studied. The esophageal balloon was shown to need frequent repositioning when body position was changed. With proper care, valid delta Pes measurements could be made in all positions studied. A plot of the delta Pes/delta POm ratio showed values closer to one for the "occlusion test" than for Müller's maneuver. Phase differences between delta Pes and delta Pm were very small in different body positions. Cardiac artifacts in esophageal measurements were more pronounced in the horizontal and -10 degrees positions. The "occlusion test" is particularly useful for clinical application because it does not require patient cooperation and is a very simple technique for evaluating correct esophageal catheter placement.