An apparatus for quantifying a users expiratory and inspiratory airflow includes an air tube adapted to be sealed over at least one of the nose or mouth of a user, a pressure sensor configured to be selectively fluidly connected with one of the air tube or an ambient environment external to the air tube, a valve assembly arranged between the air tube and the pressure sensor to switch between a measuring configuration in which the pressure sensor is fluidly connected with the air tube while fluid connection with the ambient environment is excluded, and a reference configuration in which the pressure sensor is fluidly connected with the ambient environment while fluid connection with the air-tube is excluded, and a data processing unit arranged to communicate with the pressure sensor and the valve assembly. The data processing unit is configured to provide instructions to the valve assembly to switch between the measuring and the reference configurations. The data processing unit is further configured to determine an absolute zero of expiratory and inspiratory airflow based on signals from the pressure sensor obtained while the valve assembly is in the reference configuration and to measure at least one of expiratory and inspiratory airflow while the valve assembly is in the measuring configuration. The processing unit is further configured to determine at least one of expiratory airflow limitation or inspiratory airflow limitation relative to the absolute zero airflow.
