Possible errors using esophageal balloon in determination of pressure-volume characteristics of the lung and thoracic cage

The static pressure-volume curves of the lung, thoracic cage and total respiratory system were studied in the sitting, supine, prone and knee-elbow position in four subjects. The lung and thoracic-cage pressures were measured with the aid of an esophageal balloon and recorded on a water manometer. The analysis of these various components suggests that in the supine position the esophageal balloon is compressed by the mediastinal content, giving rise to an artifact in the recording of the lung pressure. If this artifact is taken into consideration, it would appear that the effect of posture on the compliance of the lung is negligible. Lung pressures calculated for various lung volumes during active breathing are compared with static values recorded on a water manometer.