Understanding Blood Flow During Blood Pressure Measurements

Today, over a billion people suffer from hypertension worldwide, and 7.5 million die from hypertension each year. Monitoring blood pressure (BP) is crucial to diagnosing and treating hypertension and can also help detect other health problems in early stages. BP cuffs are seen as the gold standard for BP monitoring, and their use is common in both clinical and self-testing settings. These BP cuffs come in multiple sizes, and the size needed depends on a person's mid-upper arm circumference. However, it is uncommon for arms to be measured to apply a properly sized BP cuff. Once a BP cuff is applied to an arm, it is inflated to occlude the brachial artery and stop flow. As the cuff deflates, the person measuring BP listens for the rushing sound of flow in the artery. Pressure at which the flow returns is the systolic BP. As the cuff continues to deflate, the flow will eventually return to laminar, and the rushing sound will cease. The pressure when it does is called the diastolic BP. BP measurements are taken as systolic/diastolic. While under and over cuffing are known to affect BP measurements, their effect on arterial blood flow is not fully understood . Understanding how degree of occlusion of the brachial artery (the main artery under the cuff) influences blood flow velocity and pressure during measurements using under and oversized cuffs is imperative for improving measurement accuracy in both the clinical and home setting. This study investigates the flow velocity and pressure of blood inside the brachial artery at different levels of occlusion with under, over, and properly sized cuffs when pressure is applied to the exterior of the arm. Using particle image velocimetry, velocity profiles are characterized inside a physical model arm, which matches the compressive modulus of a standard arm, with varying occlusion levels to determine the different level of turbulent flow. The data collected from the model arm will be then compared to computational fluid dynamics data that will be collected from a digital version of the system. It is anticipated that information gathered from this research will inform designs of a more accurate and universal BP cuff.