**6.3 Cardiology**

Flow-directed thermodilution catheters with conventional thermistor and thermocouple devices were commercially available for many years to monitor heart efficiency. However, as these sensors are electrically active they are not appropriate for use in a number of medical applications, especially in high magnetic fields associated with NMR machines. In a study, Rao et al (1997) and coworkers in UK used a catheter with FBG temperature sensor in place of thermocouple in a test rig set up to simulate blood flow in the heart with a peristaltic pump to simulate the heart pump. The results were found to be in good agreement with the electrical sensor with smoother temperature profile.

In 2005, Deniz Gurkan et al had proposed FBG sensor to monitor heartbeat using sound pressure for possible application in ballistocardiography (BCG). For a proof-of-concept demonstration, an FBG sensor was glued to vibrating membrane of a subwoofer of a speaker set. Using recordings of various heartbeat sounds, spectral changes were monitored and analyzed to extract all relevant information. They predicted that in a real life scenario, the FBG would be placed on the patient's body in the same way as a stethoscope to detect any abnormalities in the heart muscle more efficiently. FBG for blood pressure monitoring had been reported by Brakel et al (2004) where they had proposed FBG Fabry-Perot interferometer (FBGI) as a sensor configuration to detect strain resulting from blood pressure applied to the walls of an artery situated near the patient's skin. In an investigation they demonstrated an optical blood pressure manometer that not only measured accurate systolic and diastolic blood pressures once it was calibrated, but also provided a continuous pressure waveform quite comparable with conventional Sphygmomanometer pulse wave velocity system readings.

FBG sensors, being small and light, have particular advantages for use in endoscopic applications and offer the possibility of being used in conjunction with MRI scanning, thus opening up an opportunity for performing surgery with continual scanning. FBGs can be mounted on the tip of an intra-aortic catheter that serves as a laser-ablation delivery probe for the treatment of atrial fibrillation. The FBGs can give real-time, objective measure of tip-to-tissue contact force during the catheter ablation procedure. Force control is essential for delivering appropriate laser ablation pulses needed to produce lesions that are induced in the heart walls. If the contact force is too great, the catheter tip may perforate the heart wall and if it is too light, the procedure may be ineffective. Such force-sensing catheters with accompanying system have undergone extensive pre-clinical and clinical validation in the United States & Europe and are currently undergoing precertification trials5.
