Reduction of lung parenchyma compliance as a factor in the genesis of pleural effusion in neoplasms.

It is well known that bronchial obstruction causes an increase in negative pressure in the pleural cavity and is considered to be one of the factors giving rise to pleural fluid. We suggest that a reduction in the compliance of the lung parenchyma, whatever its cause (apart from bronchial obstruction), may also lead to an increase in negative pressure in the pleural cavity and may contribute, together with the other known factors, as an additional mechanism in the appearance of pleural fluid. We believe that this factor is valid in neoplastic pleurisy and may also apply in pleurisy, and possibly in other pathological conditions. The presence of pleural effusion may be better interpreted if we bear this factor in mind. We arrived at this view principally through the study of simple chest X-rays of normal subjects and of patients, mainly cancer patients.