Lung function measurement arrangement

A measurement arrangement (2) for measuring carbon dioxide partial pressure of exhaled air from a person (4), the arrangement comprises a calculation unit (8), a carbon dioxide analyser device (10), and a gas conduit assembly (12). The gas conduit assembly (12) comprises a gas conduit (14) configured to lead air flow to and from a person during inhalation and exhalation of the person (4). The gas conduit assembly (12) is provided with a connection member structured to connect said carbon dioxide analyser device (10) to said gas conduit (14) such that said carbon dioxide analyser device (10) is enabled to measure the carbon dioxide partial pressure of the exhaled air, and to determine the end expiratory carbon dioxide partial pressure of each breath in dependence of the measured carbon dioxide partial pressure, and of the respiratory rate. A perturbation volume member (15) is provided, defining a predetermined known perturbation volume, and configured to be selectively connected and disconnected to the person such that both inspiratory and expiratory air flows can pass either through said perturbation volume member (15) or not, thereby introducing a variation of the determined end-tidal carbon dioxide. The perturbation volume member being either said gas conduit (14), or a being a perturbation space conduit (18) which is configured to be connected to and disconnected from said gas conduit (14). The calculation unit (8) is configured to calculate the effective pulmonary blood flow (EPBF) and the effective lung volume (ELV) based upon these induced variations of the determined end-tidal carbon dioxide partial pressure, the known perturbation volume, and the respiratory rate.