The pressure-dependency of local measures of arterial stiffness.

Abstract

To determine which ultrasound-based, single-point arterial stiffness estimate is least dependent on blood pressure (BP) to improve assessment of local vascular function. Ultrasound was used to assess blood flow and diameters at the left brachial artery of 20 healthy adults [55% female, 27.9 years (5.2), 24.2 (2.8) kg/m]. BP of both arms was measured simultaneously. Experimental (left) arm BP was then systematically manipulated by adjusting its position ABOVE (+30°) and BELOW (-30°) heart level in a randomized order following measurement at heart level (0°). The control (right) arm remained at heart level. Six stiffness measurements were calculated: compliance, distensibility, beta-stiffness, and three estimates of pulse wave velocity (PWV) (Bramwell Hill, blood flow, and beta-stiffness). We considered the measurement technique with the least significant change across positions to be the least pressure-dependent. There was a large effect change in mean arterial pressure (np = 0.75, P < 0.001) in the experimental arm when it was ABOVE (Δ-4.4 mmHg) and BELOW (Δ10.4 mmHg) heart level. There was a main effect (P < 0.05) of arm position on all arterial stiffness measures. From least to most pressure-dependent, the arterial stiffness measurements were: PWV (blood flow method), compliance coefficient, beta-stiffness, distensibility coefficient, PWV (Bramwell-Hill method), and PWV (beta-stiffness index method). All single-point measures assessed are pressure-dependent. The PWV (blood flow method) may be the least pressure-dependent single-point measure, and may be the most suitable single-point measure to assess local vascular function.