Assessment of Diaphragm Function and Pleural Pressures during Thoracentesis

Abstract Purpose This prospective observational study reports on diaphragm excursion, velocity of diaphragm contraction, and changes in pleural pressure that occur with thoracentesis. Methods Twenty-eight patients with pleural effusion underwent therapeutic thoracentesis. Diaphragm excursion and velocity of diaphragm contraction were measured with M-mode ultrasonography of the affected hemidiaphragm. Pleural pressure was measured at each aliquot of 250cc of fluid removal. Fluid removal was continued until no more fluid could be withdrawn, unless there was evidence of non-expandable lung defined as a pleural elastance greater > 14.5 cmH20/L and/or ipsilateral anterior chest discomfort. Results Twenty-three patients had expandable lung while five patients had non-expandable lung. Velocity of diaphragm contraction increased from 1.5±0.4 cm/sec (mean± S.D.) to 2.8 ± 0.4 cm/sec (mean ± S.D.) pre- and post-thoracentesis respectively (P Conclusions The velocity of diaphragm contraction and diaphragm excursion increased in association with fluid removal with thoracentesis in patients with expandable lung, while it did not significantly change in patients with non-expandable lung. This may derive from improvement in loading conditions of the diaphragm in patients with expandable lung related to its preload and length-tension characteristics.