An optical sensor includes photoemitter and photodetector elements at multiple spacings for the purpose of measuring the bulk absorptivity of an area immediately surrounding and including a hemodialysis access site, and the absorptivity of the tissue itself. A sensing circuit is coupled to the sensor plates 32 to measure the capacitances of the sensor plates. Loose ends of respective strength members fold back over opposite ends of the inner crimp tube to join strength members of each cable to a common structure. The inner layer 2 can be broken away from the outer layer 3 to form a partition wall or walls 8 that divide the inner space 9 of the tubular body into compartments.