Non-invasive measurements of arterial structure and function: repeatability, interrelationships and trial sample size

1. Repeatability of measurements of arterial compliance and flow-mediated d ilation of the brachial artery has been infrequently reported, despite incr easing use in interventional and risk-factor modification studies. Furtherm ore, little is known about the interrelationships of the various indices. T he purposes of this study were to determine the repeatability and interrela tionships of a range of arterial indices. 2. Fifty healthy volunteers, 20 men and 30 women, aged 20-70 (mean 46.5) ye ars, were studied on two occasions, using an identical protocol, at a mean interval of 2.5 weeks. Tonometry, ultrasound and Doppler technique were use d to measure the following: carotid wall intimamedia thickness (IMT), total systemic artery compliance (SAC), arterial pulse wave velocity [PWV aorto- femoral (A-F), and femoral-dorsalis pedis (F-D)], carotid distensibility co efficient (DC) and carotid augmentation index (AI). Brachial flow-mediated dilation was measured in 30 subjects with analysis of diameter change for 4 min post ischaemia. 3. There were no systematic differences over the observed range of measurem ents for any of the reported parameters. Coefficients of variation were as follows: IMT 2.8%, SAC 9.2%, PWV(A-F) 3.2%, PWV(F-D) 5.0%, DC 10.0%, AI 1.3 %. Brachial flow-mediated dilation curves were not different between visits ; changes were maximum 60-s post ischaemia. All indices of arterial complia nce were significantly correlated with age. The three different indices of central arterial compliance [SAC, PWV(A-F) and AI] were significantly corre lated with carotid intima-media thickness. 4. Under controlled, experimental conditions there was good repeatability o f measurements of indices between sessions of both intrinsic and functional arterial mechanical properties (central and carotid arterial compliance, i ntima-media thickness and brachial flow-mediated dilation). Sample size tab les for clinical trials using these indices are presented.