Which of the following statements are true?

B. Positive intrapleural pressures as high as 40 cm. H 2O and negative pressures as low as -40 cm. H 2O are possible.

D. All pleural effusions are of clinical significance and should be investigated. 

DISCUSSION: The pleural spaces extend into the neck as well as retrosternally and into the costophrenic sinuses. This should be kept in mind when performing procedures such as subclavian and jugular puncture, to avoid pneumothorax. Markedly elevated intrapleural pressures are obtained with the Valsalva maneuver, and extreme negative pressures can be produced with forced inspiratory effort against a closed glottis. Because of the many microvilli present on the mesothelial cells that line the pleural cavity, a liter or more of fluid is easily secreted or absorbed within a 24-hour period. Most pleural effusions are caused by infection, tumor, or congestive heart failure and should be investigated to determine the proper course of management.