Abstract:
Although medium sized, muscular vessels normally respond to sympathetic stimulation
by reducing compliance, it is unclear whether the large brachial artery is similarly
affected by sympathetic stimulation induced via lower-body negative pressure (LBNP).
Similarly, the impact of flow-mediated dilation (FMD) on brachial artery compliance and
distensibility remains unresolved, hi addition, before such measures can be used as
prognostic tools, it is important to investigate the reliability and repeatability of both
techniques. Using a randomized order design, the effects of LBNP and FMD on the
mechanical properties of the brachial artery were examined in nine healthy male subjects
(mean age 24y). Non-invasive Doppler ultrasound and a Finometer were used to measure
simultaneously the variation in systolic and diastolic diameter, and brachial blood
pressure, respectively. These values were used to calculate compliance and distensibility
values at baseline, and during both LBNP and FMD. The within-day and between-day
repeatability of arterial diameter, compliance, distensibility, and FMD measures were
assessed using the error coefficient and intra-class correlation coefficient (ICC). While
heart rate (P<0.01) and peripheral resistance increased during LBNP (P<0.05), forearm
blood flow and pulse pressure decreased (P<0.01). hi terms of mechanical properties,
vessel diameters decreased (P<0.05), but both compliance and distensibility were not
changed. On the other hand, FMD resulted in a significant increase in diameter
(P<0.001), with no change in compliance or distensibility. hi summary, LBNP and FMD
do not appear to alter brachial artery compliance or distensibility in young, healthy males.
Whereas measures ofFMD were not found to be repeatable between days, the ICC
indicated that compliance and distensibility were repeatable only within-day.
