Changes in esophageal pressure transmission during determination of lung compliance.

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Abstract
In the determination of the static pressure-volume curve of the lungs by means of pressure registration in the esophagus, the values of the esophageal pressure and thus the pattern of the pressure-volume curve may be influenced by the technique used to inflate or deflate the lungs. During slow stepwise deflation of the lungs of dogs, we observed an increase in the transpulmonary esophageal pressure, which was not noted in the simultaneously registered intrapleural pressure values. This increase was particularly pronounced when the deflation was preceded by a stepwise inflation or an inflation with expired air. During prolonged apnea, similar changes of the esophageal pressure were observed. They appeared to be the result of a decrease in the elastance of the esophagus during the period of apnea. The influence of apnea on eosphageal pressure and elastance was minimized when, prior to the apnea, the dog was ventilated with O2. The changes in esophageal pressure observed during slow deflation and prolonged apnea are probably the result of a hypoxic phenomenon affecting the pressure transmission in the esophagus.