Abstract: The present invention relates to a medical device, in particular to a blood treatment apparatus, having a control and processing unit, having at least one structure-borne sound emitter and having at least one structure-borne sound sensor, each configured for coupling to coupling points of a medical tubing kit which can be coupled to the medical device, wherein the filling level of a bubble chamber arranged in the tubing kit can be determined at the tubing kit via the control and processing unit based on the measurement of the structure-borne sound.