A medical measuring device (2), as well as to a ventilator (1), as well as to a method for operating a medical measuring device (2) or a ventilator are provided. The medical measuring device (1) includes a sensor system (14) and measuring, signal processing and calculating device (21), to detect an inspiratory measured variable, which represents an indicator for the transport of breathing gases into the lungs of a patient (80), and an expiratory measured variable, which represents an indicator for the transport of breathing gases out of the lungs of a patient (80), and to determine an indicator for a ventilation-related shifting of secretion from the expiratory measured variable and the inspiratory measured variable.