The pressure measured in the intervertebral discs is a response to the loads acting on the spine. External loads, such as the reaction forces resulting from locomotion, manual handling and collisions are probably the most relevant in studying spine trauma. However, the physiological functions such as breathing and hearth rate also participate in subtle variations of intradiscal pressure that can be observed only in vivo at resting. Present work is an effort to measure the effect of breathing on intradiscal pressure of an anesthetized sheep.
We report on the use of a frequency-reflectometry domain technique for referencing optical intensity sensors located
between two fibre Bragg gratings. The experiment combines the concept of frequency modulated continuous wave with
the spectrally selective mirror properties of fibre Bragg gratings to interrogate with referencing properties intensity based
sensors. Multiplexing two of these sensors using this technique in a parallel topology system was also experimentally
demonstrated. Due to the use of different fibre lengths (delay lines), signals from the fibre Bragg gratings located at
different positions in an array are separated in the frequency-domain.