This paper reviews the history and current state of the art of fiber optic sensors as applied to biochemical measurements in living systems. Techniques for measuring blood oxygen saturation, pH, PCO₂, glucose, and other chemicals found in body fluids are described. The potential advantages of the optical techniques are discussed and some commercial as well as research activities are described.

Fibre optic laser Doppler anemometry (FOLDA) is a useful technique for in vitro studies but has yet to be used successfully for the measurement of intravascular velocity in man. Some reasons for this are: 1. The difficulty of locating the position of the fibre within the vessel. 2. Lack of knowledge of the precise velocity profile across the vessel. 3. The effects of flow perturbation at the tip of the probe. These problems have been assessed using a FOLDA system developed in our laboratory. Three dimensional velocity profiles of blood flowing in arteries with and without stenoses have been plotted at different rates of flow. The results show that the parabolic profile of fully developed laminar flow is flattened in an arterial stenosis and the degree of flattening increases as flow increases. This means the relationship of the flow and velocity is nonlinear. Any use of FOLDA to assess vessel dimension must take this into account. The position of the fibre in the vessel can only be adequately controlled in in-vitro studies. The region of measurement is only 50 μm diameter and must be at the position of the peak velocity to enable quantitative measurement. Thus the technique is useful in humans only when there is a flat velocity profile such as in the coronary sinus. The relationship between coronary sinus flow and FOLDA velocity is linear in experimental animals. The current FOLDA system has a limited range of projection into the blood stream. The velocity is not linearly related to blood flow when the direction of flow is the same as the projected light, probably due to flow perturbation at the fibre tip. This means that a probe introduced into a coronary artey would not measure linear flow however a probe introduced against the flow could be used to assess the severity of peripheral arterial stenoses. To measure flow across a stenoses before and after angioplasty is possible but requires a method of obtaining an average spatial velocity before it is practicable.

Optical fiber thermometers are of extreme interest for very localized and e.m. immune measurements in several medical procedures,such as cancer treatment by R.F. or microwave hyperthermia technique,or blood flow and cardiac output measurements by thermodilution techniques.Operational principle and technical data of an original sensor based on the light intensity modulation induced by a thermosensitive liquid cladding,applied on the distal end of a 200 μm core silica-plastic fiber,are reported.Performance characteristics of this ther-mometer are also reported.

Fiber optics, optrodes, and fluorescence spectroscopy have been combined to form the new technology of remote fiber fluorimetry (RFF). Both in-vivo and in-vitro clinical measurements can be made by using this technique. The optrode, a fiber termination with preselected chemical or physical properties, is attached to the distal end of the optical fiber so that specific, in-situ measurements can be made. RFF systems for pH, blood pressure, oxygen, and carbon dioxide are being completed, and other optrodes are in the development stages.

In this study we present a new laser Doppler velocimeter (LDV) with an optical fiber to measure blood flow velocities accurately. After fundamental experiments to evaluate the accuracy and performances of this LDV in the blood velocimetry, blood flow velocity profiles in coronary arteries were evaluated in mongrel dogs. It was shown that this LDV is a feasible and useful to measure the dynamic blood flow velocity in coronary arteries. Finally, our LDV was remodeled to a catheter type for clinical application.

The application of a double fiberoptic device for measurements of arterial and coronary venous dye dilution curves facilitates the determination of coronary mean transit times even under clinical conditions. Since the dye, indocyanine green, is an intravascular tracer, the calculation of tissue blood flow would be possible if the intracoronary blood volume per unit of muscular weight is known. This study was therefore designed to investigate the physiologic range and the influence of coronary vasodilation and different hemodynamic conditions on the amount of myocardial blood volume. All experiments were carried out on anaesthetized close chest mongrel dogs in heart catheterization technic. Myocardial preload, afterload and inotropism and coronary vascular tone were varied by induction of hypo-, normo- and hypervolemia as well as by intravenous application of catecholamines, 13-blocking agents and vasodilating drugs. The determination of coronary blood volume was based on arterial and coronary venous kinetics of the intravascular tracer indocyanine green and the freely diffusible tracers helium and argon. Simultaneous measurements of the dye and the inert gases were obtained by a double fiberoptic system and a twin mass spectrometer, respectively. The intravascular and the tissue mean transit times as well as the coronary blood volume per unit of tissue weight were computed from the impulse response functions obtained by numerical deconvolution of the arterial and coronary venous indicator dilution curves. In contrast to reports of other authors coronary blood volume did not increase to a major extend during coronary vasodilation or elevated afterload. These new results suggest that the variation of coronary blood volume described in the literature is mainly due to methodological errors resulting from monoexponential extrapolation and distortion of the dye signal by the sampling catheter. These systematic errors, which, in particular, lead to an overestimation of coronary blood volume during high values of coronary flow are avoided by the described fiberoptic device and the deconvolution technic.

Previous studies have shown that intramyocardial blood volume does not vary to a major extent even during extreme variation of hemodynamics and coronary vascular tone. Based on a constant intramyocardial blood volume it is therefore possible to calculate tissue blood flow from the mean transit time of an intravascular tracer. The purpose of this study was to develop a clinically applicable method for measurement of coronary blood flow. The new method was based on indocyanine green, a dye which is bound to albumin and intravasally detectable by means of a fiberoptic catheter device. One fiberoptic catheter was placed in the aortic root and another in the coronary sinus. After central venous dye injection the resulting arterial and coronary venous dye dilution curves were processed on-line by a micro-computer. The mean transit time as well as myocardial blood flow were calculated from the step response function of the deconvoluted arterial and coronary venous signals. Reference flow was determined with an extracorporeal electromagnetic flowprobe within a coronary sinus bypass system. 38 steady states with coronary blood flow ranging from 49 - 333 ml/min*100g were analysed in 5 dogs. Mean transit times varied from 2.9 to 16.6 sec. An average intracoronary blood volume of 13.9 -7 1.8 m1/100g was calculated. The correlation between flow determined by the dye dilution technique and flow measured with the reference method was 0.98. According to these results determination of coronary blood flow with a double fiberoptic system and indocyanine green should be possible even under clinical conditions. Furthermore, the arterial and coronary venous oxygen saturation can be monitored continuously by the fiberoptic catheters. Therefore, additional information about the performance of the heart such as myocardial oxygen consumption and myocardial efficiency is available with the same equipment.

A new product for the direct visualization of cardiovascular and peripherial arterial systems has been investigated and developed using a miniature 1.0 mm diameter fiber optic system. The article presents documentation of the major design parameters that should be considered in angioscope instrument development. The instrument described incorporates a concentric image system/outer shaft design for truer imaging, a working diameter of 1.5 mm, affording visualization to approximately 80% of the coronary arteries, a depth of field experimentally honed to 2mm - 25mm, and a system resolution of over 60 L/mm within the typical inspection range.

We have previously described a fiberoptic angioscope for diagnostic use in the right heart and pulmonary arteries. The instrument has a 4 mm 0.D., a proximal flexion control lever, and a 0.8 mm inner channel used to inflate a polyurethane balloon attached to the distal end of the instrument. A conventional xenon light source provides illumination. The instrument is inserted through a right jugular venotomy and passed into the right heart and pulmonary arteries using direct vision and fluoroscopic guidance. The procedure has been performed in 4 patients with pulmonary hypertension suspected to be caused by chronic pulmonary emboli. Chronic emboli were found in two patients and central (resectable) emboli could be distinguished from peripheral ones. The third patient had normal pulmonary arterial intima and a final diagnosis of primary pulmonary hypertension was made. The fourth patient had extrinsic compression of pulmonary arteries by enlarged mediastinal nodes secondary to fibrosing mediastinitis. No complications occurred. We conclude that angioscopy appears to be useful in the diagnostic evaluation of patients with suspected chronic obstruction of the pulmonary arteries.

Our experience with angioscopy is presented elsewhere.^1,2 Rather than review our laboratory and clinical data, we intend this discussion to serve as an exhortation toward the refinement of angioscopic technology. The following empirical observations and practical considerations are aimed at identifying the major weaknesses of, and providing direction for the future course of technical research in, the field of angioscopy.

Hematoporphyrin derivative (HpD) photodynamic therapy (PDT) is presently being used to diagnose and treat a variety of tumors in various organs. A number of fiber optics systems have been developed to detect HpD fluorescence for diagnosis and to photodynamically activate it for treatment. Use of single multimode optical fibers with various distal tips have allowed HpD-PDT to be done throughout the human body by interstitial and endoscopic techniques.

Photodynamic therapy (PDT) of diseased tissues with hematoporphyrin derivative (HPD) within the cardiovascular system could be performed with a light-emitting antra-arterial optical fiber. However, the penetration of light at 631 nm through oxygenated whole blood first needs to be studied. In vitro studies were, therefore, performed to measure the transmission of 631 nm light, generated by an argon-ion pumped dye laser, through whole blood and serial dilutions of whole blood with the relatively translucent blood substitute Fluosol-DA. The results indicate that whole blood attenuates 631 nm light far greater than tissues, where HPD-PDT is currently applied, and that a 2 mm thickness of whole blood at a normal hematocrit may prevent a photodynamic tissue reaction when a conventional light dose is applied. Preliminary observations in rabbits treated in vivo with hematoporphyrin and 631 nm light via an intra-aortic optical fiber, with and without Fluosol-DA hemodilution, confirm these results. Hemodilution of whole blood with translucent liquids will enhance photodynamic tissue reactions and may be a necessary adjunct when this therapy is applied within the cardiovascular system.

In eight human formalin preserved cardiac specimens, various cardiac and vascular obstructions were relieved by argon laser irradiation. Interatrial communication was also produced by a transar'rial approach in a live dog. In-vivo fresh canine cardiac tissues required power density of at feast 80, 90, and 110 watts/cm² for vaporization of myocardial, vascular and valvular tissues respectively. The fiber tip to tissue distance (effective irradiation distance) for effective vaporization was less than I mm for vascular and valvular tissues and less than 4 mm for myocardium. Light microscopy showed four zones of histological damage common to all tissues - central crater surrounded by layers of charring, vacuolization and coagulation necorsis. Myocardium showed additionally a layer of normal appearing muscle cells (skip area) surrounded by a peripheral coagulation halo. Laser irradiation effects on valvular tissue showed the most lateral extension of coagulation necrosis. It is concluded that palliation and treatment of certain congenital heart defects by laser irradiation is anatomi-cally feasible and may be safe for in vivo application when low power output and short exposure time are used from a very short irradiation distance.

Carbon dioxide laser energy was used for the dissolution of atheromatous plaques. Delivery system was based on a AgCl:AgBr fiber which was inserted in a loose teflon tube. The system was used to vaporize human plaques in vitro as well as blocked human arteries which were transplanted in dogs. Preliminary results indicate that a system based on a CO₂ laser and an infrared transmitting fiber may be useful in cardiology.

Because of the difficulty of laser treatment of superficial telangiectasia in man, a mini vascular fiberoptics probe has been developed for these vessels. Controls have included sclerotherapy, intravascular-galvanic current probes and direct impacts from 0.2 mm argon fiberoptics probes.

In a medical CO₂ laser system for clinical use, it is necessary to develop the new type laser beam guide. As this one technique, a light guide by metal-polymer hollow tube was developed with aluminum foil and polymer. An aluminum foil and thin polymer were used as light beam reflector and the spacer between aluminum foils. The laser beam is propagated in a space bounded with the aluminum foils and polymer spacers. Namely,beam propagation medium is the air,therefore,this guide tube is non-toxic for CO₂ laser beam propagation. The present experimental results she that the CO₂ laser beam transmission rate exceeds 80% per meter, emitted power was obtained about 25W at lm guide length and any accidents were not happen under condition that the continuous transmission in an hour.

The feasibility study of a new type of hollow-core waveguide for CO2 laser radiation guidance is described. This kind of fiber has an air core surrounded by an oxide-glass cladding which for Ary10.6 μm exibis a complex refractive index with real part <1. Curves of the measured reflectivity and real and immaginary part of the refractive index for glass samples with different PbO percentage are shown, along with attenuation measurements performed on fiber drawn from such glasses.