The present invention relates to a measuring device, insertable into a living body. The device includes an elongated flexible member in the form of a thick-walled hollow tube with a proximal end and a distal end. The tube defines a central lumen with an inner wall. The lumen may contain a core and an insulating material provided between the core and the inner wall. The core may be made of an electrically conductive material and may be of essentially constant diameter over its entire length. Alternatively, the lumen may contain at least two electrical leads. An electrical sensor is attached to the distal end of the elongated flexible member and is electrically connected to the core.
