Although the treatment in the intensive care unit has improved in recent years enabling greater surgical engagements and improving patients survival rate, no adequate monitoring is available in imminent severe pathological cases. Otherwise such kind of monitoring is necessary for early or prophylactic treatment in order to avoid or reduce the severity of the disease and protect the patient from sepsis or multiple organ failure. In these cases the common monitoring is limited, because clinical physiological and laboratory parameters indicate either the situation of macro-circulation or late disturbances of microcirculation, which arise previously on sub-cellular level. Optical sensor systems enable to reveal early variations in local capillary flow. The correlation between clinical parameters and changes in condition of oxygenation as a function of capillary flow disturbances is meaningful for the further treatment. The target should be to develop a predictive parameter, which is useful for detection and follow-up of changes in circulation.
Isolated mitochondria were used to investigate quantitative oxygen uptake rate during oxidative phosphorylation. At the PO2 of 70 mmHg the reaction was initiated. During the initial part of oxidative phosphorylation the turnover rate increased. The recorded PO2 slope decayed linearly over time from 60 to about 10 mmHg, which is correlated to a constant oxygen uptake rate. Below 10 mmHg the PO2 deviated from linearity indicating a decreasing O2 uptake of mitochondria. No change in redox state of respiratory enzymes was observed. At very low PO2 values the scattering of mitochondria decreased and finally at total anoxia a very fast drop of backscattered light intensity and a total reduction of cytochrome was observed.
Local intra capillary HbO2 was monitored in beating hearts of 14 patients undergoing coronary bypass surgery. The spectra were measured in the epicardium of the left ventricle, supplied by the left coronary artery (LAD). All selected patients suffered form stenosis or occlusion of two to three vessels. The patients suffered from severe angina and showed hypokinesia in the angiography. Micro-light guide fibers with a diameter of 75micrometers were used for monitoring before and after bypass surgery. These light guides were connected to the Erlanger Micro Light guide Spectro Photometer EMPHO for registration. Local measurements were performed in the epicardium of the left ventricle in 25 areas 2.25cm2 each. Integrated gradient fields were plotted for each of the 14 patients before and after bypass surgery. The mean values of HbO2 in the respective areas were calculated and evaluated against the local value distribution.
In pharmacology many optical sensors are applied for investigations in vitro and in reduced systems. Due to a lack of sensors for optical imaging of functional structures in capillaries as well as in subcellular spaces the drug-tissue interaction in organs could not be monitored systematically. However, recent developments opened the door of this microcosm of life in its smallest entities. This will enable a better understanding of the questions of area and quality of drug action in tissue.
Questions about development of hypo-kinetic zones in myocardium of patients suffering from severe coronary heart disease are discussed controversially among heart surgeons. We established a model for isolated and hemoglobin free perfusion of rat heart in which sufficient flow was established within all capillaries and thus existence of ischemic capillaries could be excluded. A definite diagnosis of tissue anoxia is only possible by optical measurements of the oxidation and the reduction (redox state) of the cytochrome oxidase of intact myocytes. Therefore, we used an EMPHO for this kind of measurements. Intracellular oxygenation of myoglobin oxygenation (MbO2) and redox state of cytochrome aa3, b and c were recorded in the outer wall of working, hypo-kinetic and a-kinetic myocardium. As a result of our investigations we were able to prove that by lowering at the venous end of capillaries tissue pO2 and myoglobin oxygenation stepwise below 5 mmHg and 50% of saturation respectively, a continuous decrease of myocardial contractility could be achieved.
In a recent optical study two dimensional intensity patterns of light irradiated into suspensions of mitochondria were investigated. We designed our experimental model in such a way that the concentration of scattering particles was similar to concentrations found in tissues of humans and mammals. Earlier measurements performed in isolated and hemoglobin-free perfused rat liver and heart revealed that tissue spectra were strongly altered by light scattering when functional states of the two organs e.g. tissue oxygenation were changed. Based upon Mie's theory as well as our observations in perfused organs we concluded that an important factor able to induce sizeable changes in light scattering under physiological or pathophysiological conditions could be alterations in size of subcellular particles. The classical Mie theory which yields for single multipole scattering shows an increase in forward and backward scattering as a function of particle radius. E.g. when particle size is increased from a radius of 0.1 to 2 micrometers forward scattering is augmented by a factor of 273,000 while backward scattering attains a value of 13,900. Measurements of angular light distribution obtained in mitochondrial suspensions revealed first evidence that multiple multipole scattering increases backward scattering while forward scattering becomes diminished when particle size is enlarged.
KEYWORDS: Prostate, Tissues, Laser coagulation, Temperature metrology, Waveguides, In vivo imaging, In vitro testing, Laser irradiation, Laser therapeutics, Nd:YAG lasers
We report on the new technique of interstitial laser coagulation of the prostate (ILCP) in the treatment of benign prostatic hyperplasia (BPH). Basic experiments by use of a Nd:YAG laser in combination with a newly designed fiber tip homogeneously distributing the laser irradiation have been performed in potato, muscle, liver, and surgically removed human BPH-tissue to determine the volume of coagulation. The coagulation zone surrounding the probe was well defined and homogeneous. The size was dependent on laser power and irradiation time. Carbonization was never present except in darker tissues irradiated with high energy. Volume and time resolved measurements correlated well with the size of coagulation. 10 W and 5 minutes, for example, resulted in a coagulation zone of 17 X 15 mm. Comparable results have been seen in in-vivo experiments in surgically exposed canine prostates. Specimen for macroscopic and microscopic examination were taken immediately after treatment and after 5 and 35 days. The well demarked coagulation necrosis of the early stage resulted in cystic degeneration and fibrosis in the later stages. This was combined with shrinkage and reduction in volume. The urothelium of the urethra, the external sphincter and the rectum showed no damage. Until now, 15 patients suffering from obstructive symptoms due to BPH have been treated with interstitial laser coagulation. The probes were inserted from the perineum into the center of each lateral lobe of the prostate by transrectal ultrasound guidance, while the median lobe was treated by urethroscopic guidance, while the median lobe was treated by urethroscopic control. Dependent on the size of the prostate irradiation, time was 5 to 10 minutes per lobe at a power setting of 5 to 10 W.
In order to determine the interaction between laser light and biological tissues quantitatively the physical parameters of the biological objects have to be related to the parameters of the laser light. The degree and extent of the effect depend on the one hand on the properties of the tissue which are determined by the structure water content and blood circulation and on the other hand on the geometry of the laser beam and the wavelength. Depending on the duration of the laser irradiation on tissue and on the laser irradiance in surface or volume interaction three types of tissue interactions can be distinguished: photochemical effects photothermal effects and photoionizing effects. With extremely long interaction times and low power densities photo chemical transformation occurs by absorption of light with no primary heating of the tissue. With decreasing interaction time and higher power density the transition to photothermally induced effects begins. The early and main surgical applications for lasers are based on the conversion of laser light into heat. This thermal effect is broadly applied in surgery for tissue removal and tissue coagulation with the sealing of vessels and lymphatics as well as for tissue7weldig. When exceeding a power density of 10 W/cm nonlinear effects result. The high irradiance generates strong electric fields which lead to a dissociation or ionization of the material involved. Thus laser light is converted into kinetic energy. From
The laser has established a strong position in the field of tumor
surgery. The endoscopic modalities of tumor coagulation in particular
have been developed so far, that in some cases even tumors in anatomically difficult locations or inoperable tumors can be coagulated
interstitially. The Nd:YAG laser is well suited to this technique due
to its good coagulation properties and the transmissiblity through
flexible fibers. Application systems such as the bare fiber, the diffuse emitting
fiber, the frosted sapphire tip and a newly developed circumferentially emitting fiber, the so-called ITT light guide, differ widely
with respect to beam characteristics, power density at the fibertissue transition, maximum laser power, geometrical dimension,
flexibility, adhesive properties and compatibility with MRI diagnostics and MRI therapy control. In vitro experiments as well as first
results from animal trials and clinical experiments prove that the
Nd:YAG laser and the new ITT light guide provide a simple and
reliable technique for interstitial thermo therapy.
For the laser-induced shockwave lithotripsy the electromagnetic
energy of a laser light pulse is converted intracorporally into the
acoustic energy of a shock wave. The lithotriptor is based on a
specially developed, Q-switched Nd:YAG laser whose high power light
pulses (70 mJ, 25 ns) are coupled into a flexible quartz fiber of
600 pim core diameter.
Using focussing elements energy densities higher than 6 1O J m2
can be achieved resulting in an optical breakdown in water followed
by a shock wave.
As a result of different absorption mechanisms the breakdown threshold
can be decreased by placing a metallic target into the laser
beam. The different shockwave formations of such optomechanical
transducers have been measured. First clinical applications have been
performed.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.