Direct measurement of respiratory pleural pressure changes in normal man

Using a specially designed needle system, pressures were recorded directly from the pleural space in seated normal men. Respiratory pressure changes (ΔP) measured simultaneously from different pleural sites and the esophagus are not the same but become so after a large pneumothorax is produced. Since esophageal ΔP is little affected by a pneumothorax of 2–300 ml, it is suggested that, in the absence of pneumothorax, esophageal ΔP represents a better measure of the over-all elastic behavior of the lung than any local pleural ΔP. In the absence of pneumothorax, ΔP is less in the upper than in the lower chest. This may be an expression of a gradient either of distribution of ventilation or of elastic forces opposing expansion of the lung. In three of four subjects, end expiratory pressure was more positive in the low chest than in the high chest. Acute central vascular engorgement (pressure suit inflation) caused similar changes in esophageal and intrapleural ΔP. These observations confirm the previously observed decrease in lung compliance during acute central vascular engorgement and provide evidence of local differences in respiratory pleural pressure change in man.