Abstract: Apparatus for examining pulmonary function parameters of a patient comprises a rebreathing system (1-6) adapted to be connected with the patient and including a variable-volume reservoir (1), a carbon dioxide absorber (19) in an inhalation conduit (3) and valve means (24) for selectively switching the carbon dioxide absorber (19) on and off. A carbon dioxide meter (25) is controllable to selectively measure the carbon dioxide content of respiratory gas being exhaled and of exhaled respiratory gas collected in the reservoir (1). Volume monitoring devices (17,18) monitory the volume variations of the reservoir (1). A computing unit (30) computes the pulmonary blood flow and other pulmonary function parameters using carbon dioxide concentration parameters measured by the carbon dioxide meter (25) and ventilatory rate parameters are measured by the monitoring devices (17,18).