A method using body surface potential maps for assessment of myocardium lesions with changed repolarization is presented and suitable mapping system is introduced. Differences between normal and altered QRST integral maps together with torso volume conductor model were used to determine the equivalent dipole representing the lesion. Performance of the method was studied on simulated data. Changed repolarization was modeled by shortening of myocyte action potentials in regions typical for stenosis of the main coronary arteries. The equivalent dipole estimated the positions of small lesions with a mean error of 9±4 mm (17±14 mm for larger transmural lesions). The subepicardial or subendocardial character of the lesions was reflected in the dipole orientation. Tests of the method on patients after myocardial infarction that underwent coronary intervention on a single coronary vessel showed that in 7 of 8 successfully treated patients the dipole position matched well with the treated vessel. A small dipole moment in another patient indicated unsuccessful treatment. The method was implemented in a new 128-channel mapping system. Its active electrodes, battery powered measuring unit and optical computer interface help to minimize noise in ECG and guarantee patient´s safety. The results suggest that the method and mapping system offer useful tools for noninvasive identification of local repolarization changes in the myocardium., M. Tyšler, P. Kneppo, M. Turzová, J. Švehlíková, S. Karas, E. Hebláková, K. Hána, S. Filipová., and Obsahuje bibliografii
b1_We previously demonstrated in rats that noninvasive delayed limb ischemic preconditioning (LIPC) induced by three cycles of 5-min occlusion and 5-min reperfusion of the left hind limb per day for three days confers the sa me cardioprotective effect as local ischemic preconditioning of the heart, but the mechanism has not been studied in depth. The aim of this project was to test the hypothesis that delayed LIPC enhances myocardial antioxidative ability during ischemia-reperfusion by a mitochondrial KATP channel (mito KATP)-dependent mechanism. Rats were randomized to five gr oups: ischemia-reperfusion (IR)- control group, myocardial ischemic preconditioning (MIPC) group, LIPC group, IR-5HD group and LIPC-5HD group. The MIPC group underwent local ischemic precondi tioning induced by three cycles of 5-min occlusion and 5-min reperfusion of the left anterior descending coronary arteries. The LIPC and LIPC-5HD groups underwent LIPC induced by three cycles of 5-min occlusion and 5-min reperfusion of the left hind limb using a modified blood pressure aerocyst per day for three days. All rats were subjected to myocardial ischemia-reperfu sion injury. The IR-5HD and LIPC-5HD groups received the mito KATP channel blocker 5-hydroxydecanoate Na (5-HD) before and during the myocardial ischemia-reperfusion injury. Compar ed with the IR-control group, both the LIPC and MIPC groups showed an amelioration of ventricular arrhythmia, reduced my ocardial infarct size, increased activities of total superoxide dismutase, manganese-superoxide dismutase (Mn-SOD) and glutathione peroxidase, increased expression of Mn-SOD mRNA and decreased xanthine oxidase activity and malondialdehyde concentration. These beneficial effects of LIPC were prevented by 5-HD. In conclusion , delayed LIPC offers similar cardioprotecti on as local IPC., b2_These results support the hypothesis that the activation of mito K ATP channels enhances myocardial antioxidat ive ability during ischemia- reperfusion, thereby contributing, at least in part, to the anti- arrhythmic and anti-infarct effects of delayed LIPC., Y.-N. Wu ... [et al.]., and Obsahuje bibliografii a bibliografické odkazy
The spectral analysis technique was applied for noninvasive assessment of heart-rate baroreflex sensitivity (BRS). The coherence between fluctuation of blood pressure and heart rate at 0.1 Hz and at respiratory frequency is high. This fact enables the assessment of BRS by means of calculating the modulus (or gain) of the transfer function between variations in blood pressure and heart rate. The noninvasive continuous blood pressure registration according to Peňáz was used. During voluntarily controlled breathing intervals, the amplitude of 0.1 Hz and respiratory peaks in the spectra of heart rate and blood pressure changed markedly. Nevertheless, the average sensitivity of the baroreflex (modulus) changed insignificantly. This result indicated that the stability of BRS can be advantageous for the use of BRS in clinical practice. The difference between the modulus at 0.1 Hz and at the breathing rate indicates that baroreflex is only one of the factors causing respiratory arrhythmia. We also compared the determination of BRS by spectral analysis with the following alternative method: both lower extremities were occluded for 5 minutes. The release of pressure in the occluding cuffs decreased blood pressure which was followed by a baroreceptor-mediated increase of heart rate. Both methods correlated, but more detailed analysis revealed the role of the low pressure receptors in BRS determined by spectral analysis.
Portal-systemic shunting is an important circulatory abnormality in patients with liver cirrhosis. Glyceryl trinitrate (GTN) that is normally subject to first pass elimination, may exhibit higher bioavailability in these patients. This study compares the pharmacodynamic effects of GTN after peroral and sublingual administration for noninvasive assessment of shunting. Six control subjects and 15 patients with cirrhosis were studied after oral and sublingual application of 0.5 mg of GTN. Liver cirrhosis was complicated by portal hypertension in 7 of the patients and 4 patients had surgically implanted portocaval anastomosis. Digital plethysmography, which is highly sensitive and is essentially noninvasive in nature, was used to assess and compare the pharmacodynamic effects of GTN. The following values of the ratio of areas under the pharmacodynamic effects/time curve were obtained: 0.08±0.06 in healthy subjects, 0.52±0.21 in patients with uncomplicated cirrhosis, 0.99±0.34 in patients with portal hypertension and 1.24±0.43 in patients with portal-systemic shunts. We conclude that increased bioavailability of GTN reflects portal-systemic shunting and might be used providing that the pharmacodynamic data reflect both pharmacokinetic variability and the pharmacokinetic-pharmacodynamic interrelations., O. Slanař, J. Aubrecht, F. Perlík., and Obsahuje bibliografii
The pathophysiology of microcirculation is intensively investigated to understand disease development at the microscopic level. Orthogonal polarization spectral (OPS) imaging and its successor sidestream dark-field (SDF) imaging are relatively new noninvasive optical techniques allowing direct visualization of microcirculation in both clinical and experimental studies. The goal of this experimental study was to describe basic microcirculatory parameters of skeletal muscle and ileal serous surface microcirculation in the rat using SDF imaging and to standardize the technical aspects of the protocol. Interindividual variability in functional capillary density (FCD) and small vessels (<25 μm in diameter) proportion was determined in anesthetized rats on the surface of quadriceps femoris (m. rectus femoris and m. vastus medialis) and serous surface of ileum. Special custom made flexible arm was used to fix the SDF probe minimizing the pressure movement artifacts. Clear high contrast images were analyzed off-line. The mean FCD obtained from the surface of skeletal muscle and ileal serous surface was 219 (213-225 cm/cm2) and 290 (282-298 cm/cm2) respectively. There was no statistically significant difference between rats in mean values of FCD obtained from the muscle (P = 0.273) in contrast to ileal serous surface, where such difference was statistically significant (P = 0.036). No statistically significant differences in small vessels percentage was detected on either the muscle surface (P = 0.739) or on ileal serous surface (P = 0.659). Our study has shown that interindividual variability of basic microcirculatory parameters in rat skeletal muscle and ileum is acceptable when using SDF imaging technique according to a highly standardized protocol and with appropriate fixation device. SDF imaging represents promising technology for experimental and clinical studies., Z. Turek, V. Černý, R. Pařízková., and Obsahuje bibliografii a bibliografické odkazy
A study of energetic femtosecond laser pulses interaction with multicomponent glasses was performed. The nonlinear interaction was analysed by registration of spectral broadening, caused mainly by selfphase modulation effect. The source of the pulses was a femtosecond Cr:Forsterite laser system working at wavelength of 1240 nm and providing gigawatt peak power pulses. Using various multicomponent glasses linear dependency between the measured spectral broadening and nonlinear refractive index n2 values, determined previously by Z-scan method, was identified. Moreover, correction of broadening values for real interaction intensity was performed considering the reflection and absorption losses in the glass samples, resulting in significant increase of the linear approximation correlation. The results express reasonable correspondence with experimental Z-scan method values in the case of samples with lower nonlinear refractive index. Using an appropriate reference sample with known n2, the presented method has potential to estimate the nonlinear refractive index of arbitrary new sample. and Interakcia energetických femtosekundových laserových impulzov s viaczložkovými sklami bola študovaná. Nelineárna interakcia bola analyzovaná na základe registrácie rozšírenia spektra, ktorá bola zapríčinená hlavne javom samomodulácie fázy. Zdrojom impulzov bol femtosekundový Cr:Forsteritový laserový systém generujúci impulzy na vlnovej dĺžke 1240 nm s gigawattovými špičkovými výkonmi. Pomocou rozličných viaczložkových skiel bola identifikovaná lineárna závislosť medzi rozšírením spektra a nelineárnym indexom lomu n2, získaným z predošlých meraní metódou Z-scan. Okrem toho korekcia na reálnu interakčnú intenzitu bola prevedená, do ktorej boli zahrnuté odrazové a absorpčné straty vzoriek, vedúca k značnému zlepšeniu lineárity študovanej závislosti. Výsledky vykazujú rozumnú koreláciu s hodnotami získanými experimentálnou metódou Z-scan pri vzorkách s menším nelineárnym indexom lomu. Použitím vhodnej referenčnej vzorky so známym n2 predkladaná metóda može byť využitá na približné určenie nelineárneho indexu lomu ľubovoľnej novej vzorky.
In this paper, the problem of nonlinear viscoelastic rectangular thin plate subjected to tangential follower force is examined. The nonlinear strain-displacement relation is used to express non-linearity. After obtaining the equilibrium equation of the system in Laplace domain and performing the Laplace inverse transformation, the nonlinear differential equation of plate constituted by Kelvin-Voigt model and subjected to tangential follower force in time domain is obtained. Multi-scales method is firstly used to solve the governing equation, and the influence of the initial amplitude on the nonlinear frequency ratio is studied. Secondly, the differential quadrature method (DQM) is employed to confirm the obtained results. and Obsahuje seznam literatury
An analytical solution for nonlinear vibration of an initially stressed beam with elastic end restraints resting on two-parameter foundation is obtained. The mode functions for linear vibration of a beam with elastic end restraints resting on a linear elastic foundation are obtained first and used to solve the nonlinear vibration equation recalling elliptic integrals. The results obtained from the present solution are compared against those obtained from finite element method and found in close agreement. The effects of elastic support stiffnesses at the beam ends, foundation stiffness, initial axial load and vibration amplitude on the natural frequency are studied. and Obsahuje seznam literatury
We examined the capacity for nonshivering thermogenesis in four rodent species residing in the Ordos Plateau of Inner Mongolia. Nonshivering thermogenesis (NST, maximum NST minus resting metabolic rate) was determined for northern three-toed jerboas (Dipus sagitta), midday gerbils (Meriones meridianus), desert hamsters (Phodopus roborovskii), and striped hamsters (Cricetulus barabensis) in spring (May), summer (July, and autumn (OCtober) captured in the Kubuqi desert in 1997. NST was induced by norepinephrine (NE) and measured by using the closed-circuit respirometer at 27 °C. Our results showed significant increases from summer to autumn in NST for the four species. NST capacities were 0.52±0.27 ml O2/g0.73.h (n = 7) in summer and 2.49±1.29 (n = 6) in autumn for jerboas, 1.61±0.74 (n = 6) in summer and 3.26±1.35 (n = 5) in autumn for gerbils, 3.62±0.75 (n = 5) in summer and 9.71±2.81 (n = 6) in autumn for desert hamsters, and 6.81±3.02 (n = 8) in summer and 11.23±2.77 (n = 8) in autumn for striped hamsters. These results suggest that small mammals living in the inland arid region on Ordos Plateau adapt to their extreme environment physiologically by adjusting their thermogenic capacities to cope with the dramatic seasonal temperature fluctuations.