Hemodynamic signal changes during saliva and water swallowing: a near-infrared spectroscopy study

Here, we compared the hemodynamic response observed during swallowing of water or saliva using near-infrared spectroscopy (NIRS). Sixteen healthy adults swallowed water or saliva in a randomized order. Relative concentration changes in oxygenated and deoxygenated hemoglobin during swallowing were assessed. Both swallowing tasks led to the strongest NIRS signal change over the bilateral inferior frontal gyrus. Water swallowing led to a stronger activation over the right hemisphere while the activation focus for saliva swallowing was stronger left lateralized. The NIRS time course also differed between both swallowing tasks especially at the beginning of the tasks, which might be a sign of differences in task effort. Our results show that NIRS is a sensitive measure to reveal differences in the topographical distribution and time course of the hemodynamic response between distinct swallowing tasks and might be therefore an adequate diagnostic and therapy tool for swallowing difficulties.