Abstract
[Purpose] To clarify the relationship between head position and blood flow in masseter muscles, masseter hemodynamic change caused by head inclination was investigated.
[Methods] Sixteen healthy subjects participated in this study. Blood flow in masseter muscles was measured by using a three-wavelength near-infrared spectroscope, and the angle of head inclination was measured by using a head inclination measuring device. The subjects were instructed to incline their head forward or laterally at angles of 10, 20 and 30 degrees, and total hemoglobin volume (Hb) and oxygen saturation level (StO2) during head inclination were measured. In addition, blood flow in masseter muscle before and after maximum voluntary contraction was measured and compared with that during head inclination.
[Results] The percentage of changes in Hb during forward and lateral inclinations of the head were significantly larger than those during rest. Moreover, Hb change during head inclination of 30 degrees was about half of the maximum change after maximum voluntary contraction. On the other hand, the percentage of change StO2 change during head forward inclination of 30 degrees was significantly larger than that during rest and was about 40% of the maximum change after maximum voluntary contraction. The percentage of change in StO2 change during head lateral inclination was not significantly larger than that during rest.
[Conclusions] The results suggest that blood flow in masseter muscles is changed by head inclination. Therefore, head posture must be kept constant during blood flow measurements of masseter muscles.
