PubMed Health⌕ Search

Biomedical subjects

V S Letokhov

Publications and source records attributed to V S Letokhov.

15 recordsLinked to original sources
PubMed1993

Studies of acoustical and shock waves in the pulsed laser ablation of biotissue.

Quantitative studies are conducted into the absolute pressure values of the acoustical and shock waves generated and propagating in a biotissue under pulsed (tau p = 50 ns) UV (lambda = 308 nm) laser irradiation (below and above the ablation threshold). Powerful (several hundreds of bars in pressure) high-frequency (f approximately 10(7) Hz) acoustic compression and rarefaction pulses are found to be generated in the biotissue. The amplitudes and profiles of the acoustic pulses developing in atherosclerotic human aorta tissues and an aqueous CuCl2 solution under laser irradiation are investigated as a function of the laser pulse energy fluence. The results obtained point to the absence of the cold spallation of the objects of study by rarefaction waves. Based on experimental data, the rise rates, pressure gradients, and propagation velocities of shock waves in the biotissue are calculated. The experimental data are found to agree well with the theoretical estimates.

Acoustics↗
PubMed1991

Comparison of the effects of visible femtosecond laser pulses and continuous wave laser radiation of low average intensity on the clonogenicity of Escherichia coli.

To evaluate the contribution of local pulsed heating of light-absorbing microregions to biochemical activity, irradiation of Escherichia coli was carried out using femtosecond laser pulses (lambda = 620 nm, tau p = 3 x 10(-13) S, fp = 0.5 Hz, Ep = 1.1 x 10(-3) J cm-2, Iav = 5.5 x 10(-4) W cm-2, Ip = 10(9) W cm-2) and continuous wave (CW) laser radiation (lambda = 632.8 nm, I = 1.3 W cm-2). The irradiation dose required to produce a similar biological effect (a 160%-190% increase in the clonogenic activity of the irradiated cells compared with the non-irradiated controls) is a factor of about 10(3) lower for pulsed radiation than for CW radiation (3.3 X 10(-1) and 7.8 X 10(2) J cm-2 respectively). The minimum size of the microregions transiently heated on irradiation with femtosecond laser pulses is estimated to be about 10 A, which corresponds to the size of the chromophores of hypothetical primary photoacceptors--respiratory chain components.

Escherichia coli↗
PubMed1989

Laser ablation of atherosclerotic blood vessel tissue under various irradiation conditions.

A quantitative analysis is presented of the destruction of normal wall and atherosclerotic plaque areas of blood vessels by laser radiation. Threshold laser radiant exposure values were measured experimentally in vitro, along with the ablation efficiency for various laser wavelengths and irradiation conditions. Correlations were found between the ablation efficiency and fluence thresholds on the one hand and the optical properties of the blood vessel tissues on the other. Fibrous plaque was demonstrated to be selectively destroyed by the second-harmonic output from a pulsed Nd:YAG laser at lambda = 532 nm.

Aorta, Thoracic↗
PubMedDate not supplied

Laser biology and medicine.

The substantial repertoire of laser radiation--its coherence, range of intensity and frequency, controlability of focal area and of beam length--has been comprehensively explored in the contexts of micro- and macro-diagnostics of cells, biochemical kinetics, therapy and surgery.

Arteriosclerosis↗
PubMedDate not supplied

[Is the coherence of low-intensity laser light essential for its effect on biological objects?].

Low-intensity laser light coherence is considered in relation to biological objects under normal physiological conditions. Estimations show that the excitation rate (the rate of coherent states generation) of typical biomolecules in visible range (sigma abs = 10(-17) cm2, I = 10(-3) W/cm2) is 10(12)-10(13) times lower than that of their phase relaxation. It means that the role of coherent interaction processes is negligible. This conclusion is confirmed by the experimental results obtained with living cells of different types.

Animals↗
PubMedDate not supplied

[Comparison of the action of powerful pulses of ultrashort UV on the DNA replication and transcription functions in proliferating and resting HeLa cells].

It was established that the response of proliferating and resting HeLa cells to irradiation with single powerful UV-pulses (lambda = 266 nm, the pulse duration 3.10(-11) sec) is different. In the proliferating cells, the rate of DNA synthesis is markedly changed (accelerated or retarded) while the rate of RNA synthesis changes slightly. In the resting cells, RNA synthesis is stimulated while DNA synthesis remains at the control level. In all cases, the processes observed depend upon the intensity and the number of pulses.

Cell Division↗
PubMedDate not supplied

[Picosecond flash photolysis of Halobacterium halobium bacteriorhodopsin at room and low temperatures].

The primary stage of photoexcitation of bacteriorhodopsin from Halobacterium halobium upon the action of ultrashort (tau equal to 25 ps) laser impulse of 530 nm wavelength and of energy 2.5.10(-3) J has been studied. The primary photoproduct with a maximum of 630 nm is shown to occur in the differential spectrum in a time less than 25 ps both at room temperature (+20 degrees C) and at a low temperature (-150 degrees C).

Bacteriorhodopsins↗
PubMedDate not supplied

[Effect of pulse laser UV-radiation on proliferating and resting HeLa tumor cells].

Low-intensity pulse-periodic UV-radiation (lambda = 271.2 nm) within a definite repetition frequency interval (about 10 kHz and 22 kHz) and doses ranging from 0.1 to 10 J/m2 has a selective action on resting HeLa cells. In the same conditions, continuous UV-radiation (lambda = 270 nm) as well as powerful single picosecond pulses (lambda = 266 nm) do not affect the resting cells. The response of proliferating and resting cells to these types of irradiation in different.

Cell Division↗