Comparison of brachial artery pressure and derived central pressure in the measurement of abdominal aortic aneurysm distensibility

Objective. AAA distensibility (Ep, beta) may predict growth and risk of rupture, However, distensibility measurements based on brachial rather than central pressure may be inaccurate. Our aim was to compare AAA distensibility using non-invasive brachial and derived central aortic pressure.

Design: brachial and central pressures were measured prospectively by automated sphygmomanometry (Omron) and pulse wave analysis (SphygmoCor) respectively. AAA distensibility was calculated using brachial (Ep(b), beta (b)) and central (Ep(c), beta (c)) pressures by ultrasonic echo-tracking (Diamove), Twenty-eight patients (18 males) were selected on a first come basis from a larger study of AAA patients. There were no exclusion criteria, so 54% had cardiac dysfunction (MI, angina) and 14% were hypertensive (BP > 140/90 mmHg).

Results: median (IQR) age was 74 (70-77) years, median AAA (IQR) diameter was 44 (40-51) min. Central and brachial systolic pressures were significantly different, [140 (121-153) vs 144 (130-164) mmHg respectively, p less than or equal to0.01]. Central and brachial diastolic pressures were not significantly different [76 (72-86) vs 76 (71-86) mmHg respectively, p=0.5]. Ey(c) (3.0, [2.2-4.9]) and beta (c) (22.2 [15.5-33.2]) were significantly lower than Ep(b) (3.6, [2.4-5.1] 10(5)Nm(-2)) and beta (b) (24.7 [17.1-33.0] a.u., all p <0.001. Brachial and central derived distensibility remained significantly different after adjusting for age and diameter (p<0.001).

Conclusion: the use of brachial pressure leads to a small, systematic overestimate of Ep (18%) and <beta> (11%) independent of age and AAA diameter. This systematic error will not bias follow-up of changes in distensibility.