Contactless monitoring of the blood-flow changes in upper limbs.

Vasomotor reactivity, which is important to estimate neurogenic regulation of blood vessels in patients with different pathologies, is still assessed by occlusion plethysmography using sensors contacting the limbs. Recently we proposed a contactless approach for measuring blood flow changes during venous occlusion using imaging photoplethysmography [Kamshilin et al., Sci. Rep.7, 4642017]. In this work, the response of the vascular system on the occlusion was studied simultaneously by contact air-plethysmography system and remote optical system under illumination by incoherent polarized green light. A high correlation (r > 0.93) between the waveforms measured by both system was observed. Moreover, we found that the response of the optical system on the venous occlusion is uniform at the whole area of the forearm. The new optical technique is more convenient for assessment of the blood flow dynamics because it can be used for measurements in any part of the body. Method of imaging photoplethysmography is very promising for use in equipment intended for evaluation of neurogenic mechanisms of regulation of vascular blood flow.

Alterations of blood pulsations parameters in carotid basin due to body position change.

The velocity of the pulse wave (PWV) propagating through the vascular tree is an essential parameter for diagnostic the state of the cardiovascular system especially when it is measured in the pool of carotid arteries. In this research, we showed for the first time that the time of the blood-pressure-wave propagation from the heart to the face is a function of the body position. Significant asymmetry and asynchronicity of blood pulsations in the facial area were found in a recumbent position. Parameters of blood pulsations were measured by an advanced camera-based photoplethysmography system in 73 apparently healthy subjects. Most likely, observed changes of the blood-pulsation parameters are caused by variations of the arterial blood pressure due to hydrostatic pressure changes, and secondary reaction of blood vessels in response to these variations. Demonstrated feasibility of PWV measurements in the pool of carotid arteries provides considerable advantages over other technologies. Moreover, possibilities of the method to estimate physiological regulation of the peripheral blood flow (particularly, as a response to the gravitational changes) have been demonstrated. The proposed concept allows development of non-invasive medical equipment capable of solving a wide range of scientific and practical problems related to vascular physiology.

Estimation of light penetration depth in turbid media using laser speckles.

We present novel experimental method for estimation of the light penetration depth (LPD) in turbid media based on the analysis of the speckle pattern structure. Under the certain illumination conditions this structure is strongly dependent on the penetration depth. Presented theoretical model based on the Bragg diffraction from the thick holograms allows LPD estimation if only one parameter of the material, namely refractive index, of the material is known. Feasibility of the method was checked experimentally. Experimental results obtained for variety of the materials are in good agreement with the theoretical assumptions. It was shown that qualitative LPD comparison does not require knowledge of the material properties.

Fast noncontact measurements of tablet dye concentration.

A non-contact, non-destructive technique for estimating the dye concentration of a tablet is presented. These measurements are performed by an optoelectronic system capable for fast acquisition of two-dimensional distribution of reflection spectra with high spatial resolution by using a subspace vector model of surface reflection. Vector components representing compressed spectral data are used directly (without reconstruction of the reflection spectra) for discrimination of tablets with small dye-concentration difference. Analysis of the data obtained after tablet illumination by 7 mutually orthogonal spectral functions allows us to find a single optimal spectral function which is enough for estimating the dye concentration. Using the optimal spectral function, either the mean concentration of riboflavin or distribution of the concentration over the tablet surface can be evaluated with high rate which ensures application of the technique for online quality control of each tablet.

Accuracy of measuring systems using dynamic speckles.

Diffraction-limited accuracy is estimated for measuring systems exploiting dynamic speckles. Statistical properties of the signal in the systems with spatial filtering are used to evaluate the signal frequency with precision sufficient to achieve the diffraction-limited accuracy. The results of the analysis allow for designing an optimal measuring system in which components are matched with each other to provide the highest accuracy. Experiments carried out with a range sensor using spatially filtered dynamic speckles are in good agreement with theory.