Comparison of brachial and central blood pressures using an oscillometric device with 2 or 6 metre tubing lengths for assessment of central pressure during MRI exam

Abstract

Objective: Magnetic resonance imaging (MRI) offers the possibility to measure local and regional indices of aortic function. However calculations of these indices usually require blood pressure (BP) values. Up to now, because of its easier availability, brachial BP was used instead of local aortic pressure. The SphygmoCor Xcel system (AtCor Medical, Australia) estimates aortic pressure non-invasively. It consists in a MRI compatible brachial cuff connected via a hose to a recording unit and computer. The aim of this study was to compare brachial and central BP values given by SphgymoCor Xcel with the standard 2 meters hose and a 6 meters hose more suitable for central BP assessment during MRI. Design and method: After 5 min rest supine, BP was measured simultaneously on both arms with one 2m SphgymoCor Xcel and one 6m SphgymoCor Xcel. Arms were randomly assigned. Tubing were then interchanged (cuffs unchanged) and recordings repeated. Results: 38 patients were studied (63% men). Seven (18%) were treated for hypertension, 2 (5%) for diabetes and 3 (11%) for dyslipidaemia. Median age was 36.8 years (28.5-58.4). Brachial systolic (bSBP2), diastolic (bDBP2) and central systolic BP (cSBP2) with the standard 2m hose varied from 95 to 158, from 57 to 96 and from 85 to 145 mmHg respectively. The difference between left and right arm was 3.1±7.8 (mean±SD, p = 0.02), 1.1±5.3 (p = 0.2) and 2.5±7.2 mmHg (p = 0.04) for bSBP2, bDBP2 and cSBP2 respectively. Values obtained on left and right sides were then averaged. There was no difference between bSBP, bDBP and cSBP obtained with the 2 and 6m tubing (-1.2±3.0 mmHg, p = 0.02, -0,7±2,6 mmHg, p = 0.07 and 0.2±2,4 mmHg p = 0.56, respectively). Augmented pressure (AP) and augmentation index (Aix) with 2m and 6m tubing were statistically different (2.7±4.0 mmHg, p < 0.001 and 5.3±7.6 %, p < 0.001, respectively). Conclusions: Brachial and central BP recorded with SphygmoCor Xcel and a 6m hose are in agreement with measurements done with the standard 2m hose. Assessing central BP during MRI exam is hence feasible. Other parameters (AP and Aix) based on higher frequency content are however less reliable.