Photoplethysmography is an important optical method in healthcare and contains a wealth of information about physiological dynamics. For a quantitative assessment of vascular tone indices, an effective and modern method of analyzing the relief of the photoplethysmogram within the pulse cycle is required. A new method for detecting singular points of the contour of photoplethysmograms is proposed, based on the model of a multilayer perceptron neural network (MLPNN). The successful work of the network of the method for finding the systolic peak, dicrotic notch and diastolic peak has been demonstrated. It is shown that the average relative error does not exceed 5 percent. The proposed method can be used in computer monitoring systems for vascular tone.
The paper presents the results of a harmonic analysis of the indicators of photoplethysmograms of the human index finger, which characterize the pulse blood filling and tone of large diameter arteries (blood distribution vessels), as well as indicators of the tone of small diameter arteries. Fourier analysis of periodic changes in the tone of regional arteries of various diameters was carried out with natural breathing, in a test with deep breathing (hyperventilation), with the voluntary breathing at three fixed frequencies (0.2Hz, 0.1Hz; 0.05Hz). The tests were performed under spirographic control. The advantage of the spectral analysis of photoplethysmographic indicators over the traditional harmonic analysis of PPG in studies of the relationship between changes in the tone of regional arteries of various diameters on the one hand, and the depth and frequency of breathing of the subject on the other hand is shown. Spectral analysis of photoplethysmographic indicators is more effective in observing the dynamics of transient changes in the tone of regional arteries in people with neurocirculatory disorders of blood circulation regulation.
Long-term continuous registration of photoplethysmograms allows observing periodic fluctuations of regional vascular tone, which is important for non-invasive functional diagnostics of a number of diseases of the vascular system. But the relief of the photoplethysmogram within the pulse cycle in some functional states is poorly expressed, which significantly reduces the possibility of a quantitative assessment of the indicators of vascular tone. We propose a new algorithm for detecting special points of the contour of photoplethysmograms, based on the discovered relationship between the position of these special points and the duration of the pulse cycle. The efficiency of the new algorithm in cases where there is no diastolic rise has been demonstrated. It is shown that the average relative error does not exceed 5%. The proposed algorithm can be used in computer monitoring systems for vascular tone.
In this paper, the propagation of nanosecond laser pulses in various media with reverse saturable absorption is studied by numerical methods. Numerical simulation of the propagation of nanosecond laser pulses in a three-level medium with reverse saturable absorption was carried out using the classical transport equation for the case of incoherent nonlinear interaction of radiation with the medium described by the proposed three-level model. The degree of pulse deformation in such media is estimated. It is shown that with an increase in intensity, the pulse begins to deform, the pulse front shortens, the trailing edge becomes longer, the asymmetry coefficient increases. An additional maximum begins to form during a trailing edge with a further increase in intensity. As the additional maximum increases, the asymmetry coefficient monotonously decreases to negative values.
The propagation of short light pulses in a three-level medium with reverse saturable absorption taking into account relaxation is considered. It is shown that in such a medium soliton-like pulses of constant duration can propagate. The areas in the five-dimensional parameter space in which such pulses can exist are determined by numerical methods. The parameters of the problem are the characteristics of the medium – the relaxation time, the ratio of the absorption cross sections of the first excited and ground states and the initial transmittance, as well as the characteristics of the pulse – the duration and intensity.
The most promising method for the quantitative determination of cardiovascular tone indicators and of cerebral hemodynamics indicators is the method of impedance plethysmography. The accurate determination of these indicators requires the correct identification of the characteristic points in the thoracic impedance plethysmogram and the cranial impedance plethysmogram respectively. An algorithm for automatic analysis of these plethysmogram is presented. The algorithm is based on the hard temporal relationships between the phases of the cardiac cycle and the characteristic points of the plethysmogram. The proposed algorithm does not require estimation of initial data and selection of processing parameters. Use of the method on healthy subjects showed a very low detection error of characteristic points.
The propagation of nanosecond laser pulses in solutions of large-scale carbon nanostructures has been theoretically and numerically investigated in this paper. The three-level ladder-type scheme was used to study the medium with RSA. Numerical simulation of the propagation of nanosecond laser pulses in RSA media was carried out using the classical transport equation for incoherent nonlinear interaction of radiation with the medium described by the proposed three-level model. It is shown that for sufficiently small relaxation times of the medium and high intensity of, a splitting of the transmitted pulse by two is possible.
Photoinduced nonlinear absorption of new carbon nanoparticles – astralenes and two types of carbon nanoclusters was investigated. The nonlinear absorption of aqueous suspensions of astralenes and solutions of carbon nanoclusters was studied by the method of z-scanning with Nd3+ -glass laser (wavelength λ = 1064 nm) in Q-switching regimes. A numerical model of the propagation of the laser pulse in a medium with reverse saturable absorption was created. Relaxation time of the first exited state and the ratio of absorption cross-sections of the first exited and ground states for the researched types of carbon nanoparticles were determined by the numerical simulation.
Significant deviation of light pulse group velocity from the speed of light с due to the anomalous dispersion of a medium (so-called “slow” and “fast” light phenomena) may be caused by several mechanisms. One of these mechanisms is reverse saturable absorption. This work presents experimental research of the propagation of high-power ultrashort laser pulses through the aqueous solution of the carbon nanostructures. Our experimental results demonstrate a “fast light” behavior of pulses transmitted through the aqueous solution of carbon nanostructures. Results of our numerical simulation are in good agreement with the experimental results and confirm that the observed phenomenon is due to reverse saturable absorption. The group velocity of nanosecond high-power laser pulses is negative and achieves value to –c/275.
This paper presents a theoretical approach to describe the effect of fast light. The propagation of the light pulses in the large-sized carbon nanostructures was investigated. Dependence of the group velocity on the pulse energy and the ratio of the absorption cross-sections of the medium was investigated. It is shown that the group velocity decreases if the duration and energy of the incident pulse on the medium with the reverse saturable absorption increase.
A model of the laser pulse propagation through a medium with a special mechanism of optical limiting - the effect of the reverse saturated absorption - was proposed. It is shown that the propagation through three-level medium with reverse saturable absorption leads to decrease duration and transformation of the profile of the pulse. Analytical expressions for the maximum intensity shift and change of duration of the laser pulse were obtained.
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