Evaluation of blood flow and electromyographic activity in the perioral muscles

Although the electromyographic (EMG) activity of the perioral muscles, including the orbicularis oris and mentalis muscles, has been described in individuals with lip incompetence during lip sealing, blood flow through these muscles remains to be elucidated. The purpose of this study was to examine the blood flow associated with EMG activity in the perioral muscles using laser speckle imaging in individuals with lip incompetence.

Blood flow and EMG activity of the superior and inferior orbicularis oris and mentalis muscles were measured with the lips in contact (C condition) and apart (O condition) in lip incompetence (experimental) and control subjects (n = 15 in each group; mean age: 29.5 years). The change ratios of blood flow and EMG activity in the C condition versus O condition (C/O ratios) were calculated and plotted in a scattergram. The Mann-Whitney U-test, Wilcoxon signed-rank test, discriminant analysis using the Mahalanobis generalized distance, and Spearman correlation were used for statistical analysis.

In the experimental group, blood flow and EMG activity in all muscles were significantly greater in the C condition than in the O condition. The plots of C/O ratios in the experimental group showed a distinct and wide distribution and were significantly different than those in the control group. In both groups, a significant positive correlation was observed between blood flow and EMG activity in the mentalis muscle.

The present findings suggest that observing blood flow in the mentalis muscle is an effective and easily performed method of evaluating lip incompetence.