Hemodynamic monitoring in the human temporalis muscle using near-infrared spectroscopy

Objective. Altered temporal muscle perfusion is implicated in several painful disorders afflicting orofacial and head regions, including temporomandibular joint dysfunctions, bruxism, and headache. Knowledge about the regulation of blood supply to the temporalis muscle is limited, due to methodological difficulties. The study aimed to test the feasibility of near-infrared spectroscopy (NIRS) monitoring of the human temporal muscle. Approach. Twenty-four healthy subjects were monitored with a 2-channel NIRS: a muscle probe placed over the temporal muscle and a brain probe placed on the forehead. A series of teeth clenching at 25, 50, and 75% of maximum voluntary contraction for 20 s and hyperventilation for 90 s at 20 mmHg of end-tidal CO2 were performed, to elicit hemodynamic changes in muscle and brain, respectively. Main results. In twenty responsive subjects, NIRS signals from both probes were consistently different during both tasks. The absolute change in tissue oxygenation index (Delta TOI) as detected by muscle and brain probes was -9.40 +/- 12.28 and 0.29 +/- 1.54% during teeth clenching (p < 0.01) at 50% maximum voluntary contraction, while -1.03 +/- 2.70 and -5.11 +/- 3.81% during hyperventilation (p < 0.01), respectively. Significance. Distinct response patterns were observed from the temporal muscle and prefrontal cortex which proves that this technique is adequate to monitor tissue oxygenation and hemodynamic changes in human temporal muscle. Noninvasive and reliable monitoring of hemodynamics in this muscle will help to extend basic and clinical investigations about the peculiar control of blood flow in head muscles.