M. Preeti Sivasankar

Objectives Systemic dehydration decreases total body blood volume; however, hemodynamic alterations at the level of local organs, such as the larynx, remain unclear. Here we sought to quantify superior thyroid artery (STA) blood flow after dehydration and rehydration using in vivo magnetic resonance angiography (MRA) and ultrasound imaging in a rat model. Methods Male Sprague–Dawley rats ( N = 17) were included in this prospective, repeated measures design. Rats first underwent MRA to determine baseline STA cross‐sectional area, followed by high‐frequency in vivo ultrasound imaging to measure STA blood velocity at baseline. Next, rats were systemically dehydrated (water withholding), followed by rehydration (water ad‐lib). Ultrasound imaging was repeated immediately after dehydration and following rehydration. The STA blood velocity and STA cross‐sectional area were used to compute STA blood flow. Three rats served as temporal controls for ultrasound imaging. To determine if the challenges to hydration status affected the STA cross‐sectional area, four rats underwent only MRA at baseline, dehydration, and rehydration. Results Systemic dehydration resulted in 10.5% average body weight loss. Rehydration resulted in average body weight gain of 10.9%. Statistically significant reductions were observed in STA mean blood flow rate after dehydration. Rehydration reversed these changes to pre‐dehydration levels. No significant differences were observed in STA cross‐sectional area with dehydration or rehydration. Conclusion Systemic dehydration decreased blood flow in the superior thyroid artery. Rehydration restored blood flow in the STA. Change in hydration status did not alter the STA cross‐sectional area. These preliminary findings demonstrate the feasibility of using ultrasound and MRA to quantify hemodynamic changes and visualize laryngeal blood vessels. Level of Evidence NA Laryngoscope , 134:779–785, 2024