**5. Conclusions**

The novel wearable sensors implementing the measuring principles of laser Doppler and dynamic light scattering techniques for blood perfusion monitoring significantly extend the capabilities of researchers and practical clinicians in terms of monitoring parameters of skin blood perfusion. The analysis of signals recorded by the wearable LDF devices can be effectively realized using machine learning algorithms. Nevertheless, practical applications of the sensors for medical diagnostics require taking into account a considerable number of details. Some of the factors greatly influencing the patterns of the blood perfusion behavior are the posture and body position. In this study, we demonstrate what kind of relative changes can be expected in average perfusion and blood flow oscillations during postural changes being measured on skin of the limbs and on the brow of forehead. We show the importance of taking into account the position of the body in space during the monitoring of physiological parameters interrelated with blood perfusion. Presented findings of the amplitude–frequency analysis of LDF signals measured in different body

positions confirm the early promise of the measurement technique for the orthostatic test and diagnostic procedures based on it, and more specifically, for the use of this particular type of wearable device together with the physiological tests. The results obtained can be of particular interest for the development of new protocols for the study of microcirculation, including those related to daily monitoring. The vast majority of modern fitness trackers use the method of photoplethysmography to record physiological parameters. In this and previous works, we have shown that the LDF method can also be of significant interest for wearable applications, opening up new opportunities for the diagnostics of the microcirculation and cardiovascular systems.
