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

Abstract

Objectives: Successful hemodialysis requires reliable vascular access that can deliver adequate blood flow. An arteriovenous fistula is preferred for access because of its longevity and low frequency of complications, but up to 60% of arteriovenous fistulas created surgically are never suitable for hemodialysis because of nonmaturation (insufficient vascular dilatation). Decreased arterial elasticity may impair dilatation, thereby affecting fistula maturation. This study evaluated the feasibility of brachial artery elasticity measurement in patients with chronic kidney disease obtained during routine pre-operative mapping ultrasound (US) imaging before hemodialysis access placement and compared the measurements to those obtained in healthy volunteers.

Methods: Brachial artery functional US studies were collected from 75 patients undergoing routine preoperative mapping for hemodialysis access and 50 healthy volunteers. Vascular strain was calculated from the change in intima-media thickness between end systole and end diastole, and vascular stress was estimated from the pulse pressure. Assuming a linear elastic medium, the elastic modulus was estimated as the ratio of vascular stress to strain.

Results: Elastic modulus measurements were significantly higher in patients than in volunteers (130 versus 100 kPa; P = .01). With combined volunteer and patient data, there was a significant correlation between elasticity and systolic blood pressure (R2 = 0.23; P < .001). Elasticity was correlated with age in volunteers but not in patients (R2 = 0.14; P = .017; R2 < .001; P = .829, respectively).

Conclusions: This analysis of clinical arterial vessel biomechanics shows that a noninvasive US measurement can detect elastic modulus differences between patients with chronic kidney disease and healthy individuals. Future studies will correlate the elastic modulus with histologic characteristics and eventual arteriovenous fistula maturation, which may provide supplemental information on arterial biomechanical properties as a useful addition to current predictors of fistula success.

Figure 1

As the cardiac cycle moves from peak systolic pressure to peak diastolic pressure, the intima-media thickness (IMT) changes. This change allows calculation of strain. Blood pressure acting perpendicularly on the vessel wall allows stress estimation. The estimated elastic modulus is measured by application of stress and the subsequent strain resulting from the applied force.

Figure 2

Arterial Health prototype software used in intima-media thickness (IMT) measurement changes. Postscan US images are used to measure the intima-media thickness of the brachial artery at end systole (largest diameter) and end diastole (smallest diameter) for elastic modulus assessment. The image shown here is in end diastole.

Figure 3

A, Comparison of blood pressure measurements between patients with chronic kidney disease (CKD) and healthy volunteers. B, With all participants combined, the correlation between the elastic modulus and systolic blood pressure was significant (R² = 0.14; P < .001). C, Comparison of elastic modulus values for the patients and volunteers plotted in ascending order. The patients overall had an increased elastic modulus compared to the volunteers. As the elastic modulus increases for both groups, variability also increases.

Figure 4

Stratification of the results into 3 groups (low, medium, and high elastic modulus values) gives further insight into the differences in vessel biomechanics between the patients with chronic kidney disease (CKD) and healthy volunteers. With additional information, a range could be set that will help predict fistula maturation.