A pleural manometry catheter comprises two tubes and a pressure transducer. The first tube provides a first flow path from the pleural cavity to the pressure transducer. The second tube provides a second flow path from the pleural cavity such that fluid can be drained from the pleural cavity. The pressure transducer comprises a processor for processing, continuously, the real-time fluctuations in the pressure of the second flow path and therefore the pleural cavity as fluid is aspirated from it via the first tube.