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 to improve assessment of local vascular function. Methods: Ultrasound was used to assess blood flow and diameters at the left brachial artery of twenty healthy adults [55% F, 27.9 y (5.2), 24.2 (2.8) kg/m2]. Blood pressure of both arms was measured simultaneously. Experimental (left) arm blood pressure 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 (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 (n2p = 0.75, p < 0.001) in the experimental arm when it was ABOVE (∆-4.4 mmHg) and BELOW (∆10.4 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: pulse wave velocity (blood flow method), compliance coefficient, beta-stiffness, distensibility coefficient, pulse wave velocity (Bramwell-Hill method), and pulse wave velocity (beta-stiffness index method). Conclusions: All single-point measures assessed are pressure-dependent. The pulse wave velocity (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

Effects of pressure-dependent segmental arterial compliance and postural changes on pulse wave transmission in an arterial model of the human upper limb

With increasing interest in the effect of postural changes on arterial blood pressure and vascular properties, it is important to understand effects of pressure-dependent arterial compliance. This study investigates effects of pressure-dependent compliance on pulse wave velocity (PWVar), pressure wave shape, and transmission characteristics in an arterial model of the human arm from heart to radial artery from supine to standing. Estimated central pressure waveform was used as the input for the model, calculated using a validated transfer function (SphygmoCor, AtCor Medical) from recorded radial pulses in 10 healthy male subjects (53.87.9 years) during 0, 30, 60 and 90 degree head-up tilt. A 5-segment linear model was optimized using estimated central and recorded radial arterial pulse; each segment represented by an equivalent inductance, resistance and capacitance (compliance (C)) Pressure-dependent compliance (C(P)aebP was added to develop a nonlinear model, and the radial pulse calculated. Comparison of the radial pulse calculated by the linear and nonlinear models showed no statistical difference in systolic, diastolic, mean, and pulse pressure in any position of tilt. However, waveform shape was increasingly divergent at higher angles of tilt (RMS error 2.31.2 mmHg supine, 6.53.0 mmHg standing) a s was PWVar (0% increase from supine to standing in the linear model, 16.7% increase in nonlinear model). Fourier analysis demonstrated peak amplitude of transmission being at higher frequencies and phase delay being lower in the nonlinear model relative to the linear model. Pressure-dependent arterial compliance, whilst having no effect on peak values of pressure, has significant effects on waveform shape and transmission speed, especially with a more upright position.4 page(s