A method and apparatus for determining cardiac output in conjunction with flow through an extracorporeal circuit, wherein flow through an arterial line of the extracorporeal circuit is temporarily reversed and an indicator is passed through the cardiopulmonary circuit. The first part is an elongate strip having upper and lower faces, opposite sides, and opposite first and second ends, with elongate grooves extending along the opposite sides. A housing is also provided with a recess defined by sidewalls and an opening for receiving the head portion of the bone fastener. This tensioning and retaining mechanism also comprises a tensioning nut threaded onto the thread so as to, in use, brace against the suspension bracket to urge the tubular rod carrier in the direction of the rod bearing surface so as to apply tension to the rod. The center bowl includes an angled tab arm over its top. The common interface device further comprises switching means for selectively connecting, by switching combinations, the first line termination, the second line termination and auxiliary sources of broadband or narrowband transmission modes.