Abstract
Facial blood flow, which typically exhibits distinctive oscillation at a frequency of around 0.1 Hz, has been extensively studied. Although this oscillation may include important information about blood flow regulation, its origin remains unknown. The spatial phase distribution of the oscillation is thus desirable. Therefore, we visualized facial blood volume oscillation at a frequency of around 0.1 Hz using a digital camera imaging method with an improved approximation equation, which enabled precise analysis over a large area. We observed a slow spatial movement of the 0.1-Hz oscillation. The oscillation phase was not synchronized, but instead moved slowly. The phase velocity varies with person, measurement location, and time. An average phase velocity of 3.8 mm/s was obtained for several subjects. The results are consistent with previous studies; however, the conventional explanation that the blood flow at a certain point oscillates independently of adjacent areas should be corrected. If the primary origin of the movement is myogenic activity, the movement may ascend along a blood vessel toward the upstream. Otherwise, the oscillation and its propagation can be considered to be related to Mayer waves. By determining the mechanism, some questions regarding Mayer waves can be answered. The direction of the wave (upstream or downstream) provides important information.
Highlights
For 20 subjects, three cycle lengths based on Laser Doppler flowmetry (LDF), Visible light spectroscopy (VLS), and digital camera imaging (DCI) could be derived
The values obtained from DCI are lower than those obtained from LDF and VLS, and their slope is below one, but the correlations are still high
In terms of measurement parameters, in the applied DCI, the derived value is associated with blood volume, whereas in LDF, which was frequently used in previous studies, the derived value is blood flow
Summary
Facial blood flow typically exhibits distinctive oscillation at a frequency of around 0.1 Hz (Lossius and Eriksen, 1995; Sasano et al, 1999; Perlitz et al, 2004; Bari et al, 2005; Nelson et al, 2006). This oscillation may reflect the conditions of circulation, its origin is unknown (Ticcinelli et al, 2015). The oscillation is related to cardiovascular activity (Perlitz et al, 2004), which cannot be explained without involvement of the heart.
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