The pressure-dependency of local measures of arterial stiffness

OBJECTIVE: To determine which ultrasound-based, single-point arterial stiffness estimate is least dependent on blood pressure (BP) to improve assessment of local vascular function. METHODS: 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. RESULTS: 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). CONCLUSION: 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.