| While trained sonographers can reliably diagnose arterial injury using imaging ultrasound in the hospital, a portable ultrasound device with an automated algorithm to detect major bleeding would be useful for medics in the field. We characterized normal blood flow in the upper extremities with an image-based flow model and evaluated its ability to detect vascular abnormalities by looking for flows that deviate from the model. The power-law model states that blood flow q is proportional to the vessel diameter d taken to a power k, q α dk, where k is defined by the bifurcation pattern: d0k = d1k + d2k (0 = parent vessel, 1 & 2 = children vessels). To adapt this law for the upper extremities, ultrasound was performed on the brachial, ulnar, and radial arteries of 28 healthy volunteers to measure diameters and flows during rest and exercise (2.7 watts, 30 lb grip). The best-fit k for the brachial bifurcation was found to be invariant between rest and exercise and was determined to be 2.75. A k=2.75 power-law was found to adequately predict normal flow splits in children vessels: (q1, q2). The correlation between predicted and measured normal blood flows was R2=0.96. In injury, the flow split deviates from the normal split by a Δq amount of flow: (q1 ± Δq, q2 ± Δq). Flow split deviation (FSD) quantified Δq as a percent of total flow: FSD = 100% * Δq /(q1+q2). Computational 3D blood flow simulations of the brachial bifurcation with different size punctures in the children vessels confirmed that larger punctures produced larger FSDs. Moreover, FSDs were evaluated to determine whether hemodynamic alterations that occur due to surgically placed wrist arteriovenous fistulas (AVFs) can be detected in dialysis patients. Dramatic increases in FSDs easily differentiated between the arms before (4.3±1.9%) and right after (40.9±12.5%) AVF placement. Normal arm blood flow, regardless of physiologic state, can be well characterized and predicted with a k=2.75 power-law. The strategy of identifying perturbations of flow at bifurcations may provide a rapid automated method for localizing active bleeding with ultrasound. |