Abstract
A thin-wall No. 6-7 French cardiac catheter is filled with optical fibers. The center fibers are gathered in one branch to carry the input light, and the surrounding fibers are gathered into a second branch. A thin (20-30μ) metalized glass diaphragm is mounted approximately 200 au from the tip of the fiber bundle. The diaphragm deflects in response to pressure, and varies the intensity of reflected light into the second branch of the catheter. The fiber bundle tip-to-diaphragm distance is critical, and must be adjusted to provide linear reflectance over the physiological ranges of pressure expected. The system is stabilized by providing a constant current source for the illuminating lamp, and a compensating bridge circuit. The lamp intensity is monitored by a second photodetector, and used in the bridge circuit to compensate for light fluctuations.
The time response of the pressure transducer to a step input is shown in Fig. 8.The upper trace shows the response from a conventional Statham pressure transducer, and the lower trace shows the response from the optical pressure transducer. The response from the optical transducer is observed sooner with a shorter rise time, indicating superior frequency and phase-shift response. Linearity is 1.5 %, from 0 to 300 mmHg, with a sensitivity of 200 millivolts per 300 mmHg. The excellent frequency response inherent in the glass membrane indicates that intracardiac sounds can also be obtained simultaneously with pressure measurements.
