A separable rapid-action coupling serves for connecting fluid lines includes a tubular plug-in part with a circumferential holding rib, a coupling housing with a cylindrical receptacle cavity for the plug-in part and a separate holding element. The airfoil includes a base, a tip, a pressure side wall, a suction side wall, and a cavity disposed therebetween. The apparatus comprises a memory, an interrupt unit and a logic circuit. The change in the second physiological property values for the first cycle signal between a pair of successive data points and the change in the second physiological property values for the second cycle signal between the same pair of successive data points are determined and averaged to produce an average change amount for the successive data points.