Fiber-optic catheters

Invasive continuous hepatic function monitoring by the fluorescence procedure was also evaluated in rabbits [148]. In this study, a commercial catheter equipped with fiber optic technology for mixed venous oxygen saturation measurements (SVO2) was modified to emit light at 780 nm and detect fluorescence at 840 nm. The catheter was placed into the right jugular vein and advanced... 

Thus, in critically ill patients where catheters are conventionally inserted for diagnostic or therapeutic interventions, incorporation of the appropriate fiber optics to commercial catheters would enable the monitoring of hepatic function continuously and simultaneously with other medical interventions. Previous studies by the absorption method also found a close correlation between invasive and noninvasive ICG plasma elimination kinetics [157,160]. 

For samples of weaker absorbance the use of fiber optics might be required to achieve a sufficiently high number of reflections. Also, using a fiber optics catheter may permit in vivo measurements. 

Figure 15.1 The fiber optic oximetry catheter. (From Sperinde J M and Seneli K M 1987 The Oximetrix Opticath oximetry system theory and development Continuous Measurement of Blood Oxygen Saturation in the High Risk Patient vol 2, ed P J Fahey (Chicago Abbott Laboratories) pp 59-75 with permission.)...

Tanaka and Benedek (1974), in a novel and important study, have measured the velocity of blood flow in the femoral vein of rabbit by detecting (in the heterodyne mode) the Doppler shift of laser light introduced into the vein by means of a fiber optic catheter. The light is scattered from the moving erythrocytes in the blood. It is important to recognize that the blood-flow velocity is not uniform across a vein but varies from zero near the vein wall to a maximum in the center. Thus the spectrum observed should be an average over the distribution of velocities of the illuminated erythrocytes, approximately... 

Solid state lasers have become ubiquitous in our society. Pulsed YAG Nd lasers are used for welding of metals and plastics. Among the applications are medical apparatus catheters where the weld size must be very small fiber optics communication systems and hermetic sealing of integrated circuit packages. 

Figure 17-13. Fiber-optic invasive catheter for measuring oxygen in vivo [114].

Figure 18- Fiber-optic catheter for invasive absorbance measurement and associated instrumentation. From [50].

A concept of the fiber-optic-based absorbance sensor is shown in Figure 18-8. Again, the fiber is threaded in a standard catheter, thus allowing its insertion into tissue or body fluids. A piece of aluminium foil is attached to the end of the inner needle (which contains the optical fiber). Fluids can be drawn into the sample irradiation cavity by aspiration, the volume between foils and Hber being Hlled through the hole shown. Typical pathlengths (twice the distance from the Hber tip to the foil) are O.S-4.3 mm. 

Manuccia,T. and Eden, J. (1985) Infrared optical measurement of blood gas concentrations and fiber optic catheter ... 

Since the original discovery of this phenomenon over 50 years ago, there has been progressive development in instrumentation to measure oxygen saturation along three different paths bench-top oximeters for clinical laboratories, fiber optic catheters for invasive intravascular monitoring, and transcutaneous sensors, which are noninvasive devices placed against the skin. 

FIGURE 6.5 Principle of a three-fiber optical catheter for SvOj/HCT measurement. (Taken from Bornzin G.A., Mendelson Y., Moran B.L. et al. 1987. Proc. 9th Ann. Conf. Eng. Med. Bio. Soc. pp. 807-809. With permission.)... 

FIGURE 6.7 Structural diagram of an integrated fiber optic blood gas catheter. (Taken from Otto S. Wolfbeis, Viher Optic Chemical Sensors and Biosensors, Vol. 2, CRC Press, Boca Raton, FL, 1990.)... 

Optical sensors have been used in many ways to detect physiological variables both in vitro and in vivo. The most frequent biomedical application involves the use of fiber optics within an interluminal catheter or tissue probe with some sort of optical indicator at or near its distal tip. This indicator communicates with body fluids or tissues through a membrane permeable to the analyte but not the indicator so the latter remains in the sensor. The intensity of the light produced or modulated by the indicator is determined by optoelectronic systems back at the proximal end of the catheter or probe. Such devices have many applications in clinical medicine but are particularly important in critical care medicine. 

Typical fiber-optic chemical sensors for in vivo monitoring are constructed from optical fibers that are connected to an external compact unit containing the light source and the detector, as shown in Fig. 18. The optical fiber s distal end is inserted into the patient through a catheter. 

Sensors incorporating glass or plastic optical fibers have demonstrated several advantages over electrosensors for biomedical applications. These sensors involve no electrical connections and hence are safe from that standpoint the leads are quite small and flexible they can be incorporated in catheters for multiple sensing where required, they can be implanted for relatively long periods. The fibers are considerably less than 1 millimeter in diameter. Where designed for simplicity, they often can be considered disposable. 

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