Zafiris, Eudoxia2025-09-192025-09-192025-09-192025-09-09https://hdl.handle.net/10012/22482The internal carotid artery (ICA) and external carotid artery (ECA) facilitate perfusion to the intracranial and extracranial regions, respectively. Under current dogma, the ICA is tightly regulated to ensure stable cerebral perfusion, while the ECA remains more pressure-passive, compensating for fluctuations in blood flow to the brain by redirecting blood flow to protect the cerebrovascular network during physiological stressors. While previous research has attempted to influence ECA flow through indirect stimuli such as facial cooling and exercise, direct experimental manipulation of ECA flow has rarely been tested. It remains unclear how ICA and ECA branches reallocate flow in response to changing demands in the facial vasculature. The purpose of this research is to determine whether the ECA can directly control carotid flow redistribution via jaw clenching by increased facial flow resistance and a post-exercise hyperemic response. 26 healthy adults (24±4 years; 15 female) performed isometric (25% maximum voluntary jaw clench (MVJC); 60 sec) and dynamic (50% duty cycle 3 seconds ON/OFF, for 60 sec at 75% MVJC) jaw clenching exercises. Additionally, a facial cooling mask was placed on each participants face to elicit a non-metabolic vasoconstrictor response. Blood velocity in the CCA, ECA and ICA was measured with conventional Doppler ultrasound before, during, and post clenching periods, and before and during facial cooling. Transcranial Doppler ultrasound continuously recorded middle cerebral artery velocity (MCAv), and vector flow imaging (VFI) was used to scan the carotid bifurcation before and post jaw clenching to determine changes in blood flow patterns. During both isometric and dynamic jaw clenching protocols, CCA and ECA blood flow increased from baseline, during, and post clenching, accompanied by a decrease in the pulsatility index (PI) (p < 0.05), indicating that jaw clenching actively increases extracranial blood flow via the ECA. In contrast, no changes were observed in ICA blood flow and PI throughout isometric jaw clenching, however, during dynamic jaw clenching, blood flow increased during the post clench phase compared to the ON phase (p < 0.05) and the PI decreased throughout (p < 0.05). MCAv increased during dynamic clenching (p < 0.05). The resistance index decreased during clenching and rebounded post clench for both jaw clenching conditions (p < 0.05), suggesting that intracranial responses depend on the clenching modality. VFI revealed that isometric jaw clenching increased flow and uniformity at the carotid bifurcation, reflecting laminar redistribution between the ECA and ICA. These findings provide novel evidence that jaw clenching can modulate carotid hemodynamics at both extracranial and intracranial levels and reshape local flow patterns at the carotid bifurcation. This has potential implications for understanding vascular contributions to temporomandibular disorders and the broader cerebrovascular impact of chronic jaw muscle activity.enMaster Thesis