[Basic principles of physics in optical imaging of the human eye]. / Základní fyzikální principy optického zobrazování v lidském oku.

Creation of a real picture of the observed object on the retina by optical system of the eye is the primary physical condition of the visual perception. Absorption of the light energy initiates the sequence of further physicochemical, biochemical and psychophysiological events partially taking place already in the retina but mostly in the higher cerebral and spinal centres. So the visual perception and its final evaluation is the result of a complicated complex of processes where the optical imaging itself plays the role of the starting factor. In the publication particularly the physical substance of the optical imaging on refraction surfaces between media with different refraction index has been accentuated. The laws of reflection and refraction and their origin are derived in the terms of the physical (Maxwell equations) and geometrical (Fermat principle, principle of the mutual independence of light beams) optics. In the adequate extent the development and structure of the eye and the whole visual complex, the bases of the quantification of the visual perception and contemporary opinions on mechanisms of the colour vision (trichromatic theory) have been described. The publication is completed by a mathematical appendix explaining some relations usually absent in the biomedical literature.

[Biophysical principals in radiotherapy of malignant tumors]. / Biofyzikální základy radioterapie zhoubných nádoru.

The successfulness of tumour radiotherapy depends before all on achieving the maximal effect of radiation on the tumour with contemporary minimalization of the injury of normal tissues in its vicinity. Such selectivity of radiation action may be realized by utilization of physical (kind and energy of radiation, irradiation conditions) as well as biological (modification of radiation effects) factors. The aim of this publication is to give a survey of fundamental biophysical and radiobiological principles conditioning the differential action of ionizing radiation on tumorous and normal cell populations from the standpoint of the relevancy of experimental radiobiology (radiation effect on the proliferative capacity of the tumorous and normal tissue) to radiotherapy. More accent than customary in medical literature is put on the physical interactions of radiations in matter and dosimetry as well as microdosimetry of radiation. The importance of microdosimetry will perhaps increase in future in connection with the therapeutic usage of non-conventional kinds of radiation (neutrons, heavy charged particles, pi-mezons). Basic biophysical machanisms of radiation action on cells and cell populations are described and explained in terms of quantum radiobiology (single- and multihit theory, target theory, stochastics of radiation injury development, etc.) as well as the main principles of modification of radiation effects (oxygen effect, radiosensitizers, fractionation of the dose). A brief interpretation of the Strandquist model of isoeffect curves for the fractionated irradiation is presented enabling to relate mutually the total absorbed dose to the total irradiation time and the number of fractions.

[Screening for venous thrombosis and pulmonary embolisms in patients with stroke using an adaptive classifier]. / Vyhledávání zilní trombózy a plicní embolie u nemocných s cévní príhodou mozkovou pomocí adaptivního klasifikátoru.

The use of adaptive linear neuron is referred to in recognizing veinous thromboses and lung embolism in a total of 88 acute palsies. As the input signs, the accessible clinical and laboratory data were used. Both training and adaptation of neuron have been performed in a part of total [35 patients], and 53 patients were submitted to the classification of patients with unknown distribution. In classified group with present complications, the screened diseases have been recognized in 16/20 patients. In 29 from 33 patients without thromboembolic states, the distribution by classificator appeared as correct one. The level of correct resolution was as high as 88% in all.

Use of the adaptive classifier for determination of LD50 in the acute radiation disease.

In experiments on female Wistar rats a new method for the determination of LD50 is demonstrated and compared with the classical probit method using the same experimental animals. The method is applicable for the computation of LD50 and analogical quantities in man, too. The method is based on the application of an adaptive logical circuit (ADALINE) trained for the dichotomous prognostic classification of irradiated individuals quod vitam according to a set of clinical and laboratory indicators registered on the third day after irradiation. After the training procedure has been finished, the classifier makes possible an individual prognosis of survival or death. The analogue output signal according to which the classification is performed changes continually from negative to positive values and exhibits S-shaped relation to the radiation dose. Its zero value corresponds to the position of LD50 on the abscissa. For the construction of the searched function, i.e. for the optimum approximation of experimentally obtained values of the output signal, the method of the changeable polyhedron was applied belonging to the optimalization numerical methods used in the regulation technics. The computed value of LD50 was 7.80 Gy in rats very closely corresponding with the value 7.61 Gy determined by means of the classical probit method.

Contribution to some radiobiological aspects of the investigation of radiosensitizers of hypoxic cells. Part IV: Radiosensitizing effect of metronidazole evaluated on the level of postirradiation changes of bone marrow cellularity in rats protected by induced hypoxia of lower body half.

Radiosensitizing effect of metronidazole (Entizol, Polfa, Poland) was tested on an experimental model of ischaemized bone marrow. The changes of bone marrow cellularity were recorded after whole body irradiation of rats protected with abdomen compression during irradiation. With an increasing dose of irradiation proportional and significant decrease of nuclear elements in bone marrow occurred the third day after irradiation. Metronidazole administered to unprotected rats (without compression) did not show any effect. The abdomen compression led to a pronounced radioprotection but metronidazole administration reduced this effect significantly. Ischaemization of the lower half of rat body produced on the level of bone marrow cellularity the protection corresponding to DRF (dose reduction factor) = 1.96 the third day after irradiation. DRF value decreased to 1.52 by metronidazole application which corresponds to ER (enhancement ratio) = 1.29.

Contribution to some radiobiological aspects of the investigation of chemical radiosensitizers of hypoxic cells. Part V: Metronidazole--dependence of its radiosensitizing effect on the dose, time interval of administration and hypoxia degree of the bone marrow evaluated according to the changes of its cellularity in rats.

In the experiments on female rats of Wistar strain the effect of metronidazole (Entizol - Polfa) was studied administrated in aqueous solution with a gastric pipette into the stomach. Dependence was analyzed on the dose of metronidazole, on the time interval of administration before irradiation and on the degree of hypoxia of bone marrow during irradiation induced in the lower part of the body and graded by the abdomen compression with an inflatable rubber cuff with overpressure 4, 6.7, 13.3 and 20 kPa. The effect of whole body irradiation (60Co source) was evaluated according to the changes of bone marrow cellularity (BMC) the third day after irradiation. The sensitizing effect of metronidazole increases rapidly up to dose of 30 mg/kg with rising dose of the drug, then at higher doses only slowly. With prolonging interval of the application of 600 mg/kg body weight the sensibilization increases and reaches the peak after 1-2 hours, then it gradually decreases till the complete disappearance after 10-15 hours. In both cases irradiation was carried out at abdomen compression corresponding to 20 kPa of overpressure in the rubber cuff. The induced hypoxia of bone marrow demonstrated a significant, protective effect, corresponding to the degree of abdomen compression which was reduced by metronidazole administration in the dose of 600 mg/kg. The reduction represents one half to one third of the protective value and is proportional to the degree of induced bone marrow hypoxia during irradiation.

Radioprotective and hemodynamic effects of WR-2721 and cystamine in rats: time course studies.

In experiments on rats radioprotective dose of WR-2721 (200 mg/kg) and cystamine (50 mg/kg) exhibited significant protective effects against radiation death during the first hour after their i. m. administration. Gamma rays were delivered with the dose rate of 0.35-0.31 Gy/min in gradually increased doses for the calculation of LD values and relative efficacy of the whole body irradiation. WR-2721 afforded protection with the highest dose reduction factor (DRF) of 1.51, while the best DRF value after cystamine was 1.36. No protection was found when the interval between injection of both protectors and the beginning of irradiation was longer than 60 min. WR-2721 as well as cystamine induced in pentobarbital anesthetized rats significant depression of cardiac output, hypotension and bradycardia immediately after their i. m. injections. The signs of depression of the hemodynamics persisted throughout the 4-hour observation period. Our results indicate that the hemodynamic effects of WR-2721 and of cystamine are not important for their radioprotective actions in rats.