Ultrasound measurement of brachial artery elasticity prior to hemodialysis access placement: a pilot study.

In the United States, chronic kidney disease affects 26 million adults.1 Chronic kidney disease is a progressive disease that takes months or years to develop, with diabetes and high blood pressure the most common causes. Patients with end-stage renal disease need life-sustaining dialysis or renal transplantation. They are frequently treated with regular hemodialysis to remove toxins and fluid. Reliable vascular access is critical for adequate hemodialysis and must provide high blood flow (≈400–500 mL/min) to the dialysis circuit.2 Among the 3 types of vascular access (arteriovenous fistula, synthetic graft, and catheter), the arteriovenous fistula is preferred because of its longevity and low frequency of complications. An arteriovenous fistula is placed surgically by creating a direct anastomosis between a native artery and vein and is the preferred method for reliable vascular access.3 However, the feeding artery of a successful arteriovenous fistula first needs to dilate to supply the estimated 500 mL/min necessary for a mature arteriovenous fistula.4,5 For the arteriovenous fistula draining vein to withstand arterial pressure and to accommodate greater blood flow, it also needs to enlarge and mature before use.6 When these necessities are met to yield a mature arteriovenous fistula, advantages of a fistula compared to other vascular access options include lower infection rates and a lower incidence of thrombosis.4 Preoperative vascular ultrasound (US) mapping is routinely used to assess the upper extremity arteries and veins, identifying suitable conduits for arteriovenous fistula creation.7,8 To optimize fistula maturation, minimum vascular diameter criteria aid in selection of vessels that are likely to support successful fistula maturation, and veins with stenosis or thrombosis are excluded. Although preoperative vascular mapping has had positive impact on increasing fistula placement, it has not decreased the fistula nonmaturation rate.4,7,9 With institutions recording 20% to 60% of fistulas failing to mature,9–13 other potential etiologies for arteriovenous fistula nonmaturation need to be investigated. There are currently some known technical causes of fistula nonmaturation that contribute to this failure rate, such as thrombosis, anatomic lesions, accessory veins, early vascular stenosis, and poor venous outflow.13 Although these circumstances can occur, they do not explain all of the failures, and the remaining reasons for arteriovenous fistula failure remain unknown. This disappointing observation suggests the existence of functional vascular parameters that may impair fistula maturation despite vessel selection by adequate structural measurement. Evaluation of the vessel diameter alone provided by preoperative vascular mapping is not sufficient to determine vascular properties such as distensibility and capacity. Thus, for example, a heavily calcified inflow artery may not be able to dilate sufficiently to supply a mature arteriovenous fistula.4,5,14 Elasticity has been shown to identify abnormalities within biological tissues, and imaging these elastic properties has become a pivotal point of many research efforts.15,16 Tissue characterization can estimate elastic properties of tissue, which is known to change with disease. The high temporal resolution of US and its ability to image small changes in vessel motion have proven useful for visualizing abnormalities in the vascular system.17–21 Stress is naturally applied to the arterial vessels by the cardiovascular pulsations from each individual.16,22–24 For a given stress field, one can attain high strain for lower moduli due to collagen fibers engaging to maintain the wall shape.25,26 Basic theory from engineering mechanics points us to the conclusion that the stiffer the material, the less deformation will occur under an applied stress. Ultrasound can be used to track vessel wall motion and overall vessel deformation.27 Thus, US-based noninvasive elasticity measurements may be a useful addition to current predictors, yielding supplemental information on the biomechanical properties of arteries. The ability to adapt algorithms to image data currently being collected clinically helps minimize cost and learning curves associated with adopting new imaging technology. The long-term goal of this research is to investigate the use of US and image processing to noninvasively measure the elasticity of human brachial arteries in patients with chronic kidney disease. This investigation presents the results of a pilot study to assess the feasibility of this approach.