Sonography of pleural space in healthy individuals

This research was performed to detect physiologic pleural fluid by chest ultrasonography, to assess the frequency of this finding, and to check the status of pleural space, searching for possible individual variations of the amounts of pleural fluid.

In the baseline study, chest ultrasonography of both pleural spaces was performed in a group of 106 healthy volunteers, searching for pleural fluid, first in the lateral decubitus position and then leaning on the elbow. An anechoic fluid layer at least 2-mm thick was taken as a positive result. The follow-up study was repeated on each subject after 2-4 months.

In the baseline study, a 2-mm-thick pleural fluid layer was found in 28 of 106 (26%) volunteers, both sided in 17 of 28 (61%), and unilaterally in 11 of 28 (39%). The follow-up study, showed a fluid layer in 24 of 106 (23%) volunteers, on both sides in 14 of 24 (58%), and unilaterally in 10 of 24 (42%). In the first study, the mean fluid layer thickness in the decubitus examination position was 2.9 mm (SD, 0.4 mm) and in elbow examination position 2.8 mm (SD, 0.4 mm). On follow-up study, the mean fluid layer thickness in both examination positions was the same, 3.1 mm (SD, 0.6 mm). Taking into consideration baseline and follow-up studies, the fluid was observed in 32 subjects, and 21 (66%) of them showed pleural fluid twice. Their mean fluid layer (3.1 mm) was significantly larger than the group of subjects with only one positive result (2.5 mm), with p values of <.01 for the baseline and <.05 for the follow-up study.

In experimental conditions, small amounts of pleural fluid can be detected by chest sonography in healthy individuals. Our research suggests that there are individuals with sonographically permanently less ("dry pleural space") or more ("wet pleural space") physiologic pleural fluid.