Signal Processing for Evaluation of Capillary Blood Flow Regulation upon Exposure to Simulated Microgravity

In this study we demonstrate about the variation in capillary blood flow on very short exposure to simulated microgravity condition employing NASA’s well-established terrestrial analogues for spaceflight, head down tilt bed rest position (HDTBR). Blood flow oscillation was measured through laser Doppler flowmetry method. The aim of this study was to evaluate the regulatory mechanism of blood microcirculation in the prefrontal cortex region (forehead). For the improvement of quantitative analysis of blood flow signals of LDF wavelet analysis was performed. The proposed algorithm consists of two phases where first blood flow was measured through LDF sensors. The second phase consists of transformation of signals through wavelet technique to extract the features of signals. LDF sensors were placed on the forehead and the protocol was used to record three body positions on the tilt table in the following sequence: (a) supine body position; (b) head down tilt at − 20° (− 20°, Trendelenburg position); (c) recovery to normal supine position. Skin blood perfusion was recorded for 10 min in each body position, followed by the amplitude-frequency analysis of the registered signals using wavelet decomposition. After wavelet analysis of the blood flow signals various frequency bands were distinguished. The results identified a statistically significant changes in microcirculation parameters of the average level of skin blood perfusion and oscillations of amplitudes of different frequency-dependent regions. We here have for the first time utilised discrete wavelet transformation technique to evaluate the LDF signals alterations occurring due to − 20° HDTBR body position as analogue for simulated microgravity.