Abstract: A coupling for selectively connecting a plurality of conduits running to a common connection point, for controlling flows for medical purposes, includes a coupling element having one or more passages which, by rotation and/or displacement of the coupling element, are connectable to selected conduits for selective connection of the selected conduits at the same time as other conduits running to the connection point are closed by the coupling element so as to determine a flow path. The coupling element may be formed by a cannula, or alternatively may be formed by a coupling cone or element maneuverable by a cannula. In a restriction device for a conduit for carrying a fluid, especially for medical purposes, a first tube is connected to a channel extended through an elastic body. The body is surrounded by a stiff sleeve.