Doppler Ultrasound Assessment of Effects on Renal Resistance of Blood Flow in Human Aortorenal Systems

The renal arterial resistive index (RI) is a sonographic index of intrarenal arteries defined as (peak systolic velocity - end-diastolic velocity) / peak systolic velocity.  It assesses the ratio of the upstroke of the systolic wave in the renal artery to the end-diastolic flow rate.  The normal range is 0.50-0.70. Elevated values are associated with poorer prognosis in various renal disorders and renal transplants. We recently built up a pulsatile flow loop, mimicking the blood flow in the human circulatory system, to measure the in vitro RI using a portable ultrasound system (Philips CX50) in 3-D printed aortorenal artery systems anatomically extracted from patient’s CT images. We Preliminary study is to assess the effects of aortic pulsatility, heart rate, and renal arterial stenosis on renal RI via parameterization. It is found that RI is inversely proportional to heart rate but proportional to aortic pulsatility, meaning either increased heart rate or reduced aortic pulsatility can prevent elevated RI.  Meanwhile, reduction of the renal arterial lumen, a medical condition called stenosis, will elevate RI. These results agree with numerical simulation and medical observation.