elevated mRAP leading to elevated central
and systemic venous pressures can contribute to pleural
fluid formation. First, elevated venous pressures can
mechanically impede parietal pleural lymphatic drainage.
This was shown in a study of sheep [3] in which
elevations of superior vena cava (SVC) pressures greater
than 15mmHg led to decreased lymphatic drainage and
pleural effusions. Second, increased venous pressures can
cause increased hydrostatic pressure in bronchial and
chest wall veins leading to transudation of fluid into
the pleural space. In a study in dogs, balloon obstruction
of the SVC and IVC led to formation of pleural effusions
by this mechanism [4]. Interestingly, it also led to pericardial
effusions suggesting that the elevated mRAP
directly induced the pericardial effusions, which may
have been the reason why pericardial effusions were seen
in the study