Inter-arm differences in measured brachial systolic blood pressure translate to false differences in calculated central aortic blood pressure

Background: Inter-arm differences in brachial systolic blood pressure (SBP) may be real and cardiovascular risk predictive or measurement artefact. If real, measurement from either arm should result in similar calculated central, aortic SBP, there being only one aortic SBP at any time. If artefactual, differences may correlate with inter-arm asymmetry in factors influencing brachial SBP assessment, such as arm geometry. Aims: To ascertain whether inter-arm differences in brachial SBP translate to differences in aortic SBP and to determine whether these inter-arm differences are correlated with arm geometry. Methods: Brachial SBP was measured simultaneously in both arms 4 times (alternating blood pressure devices for each measurement) in 79 people (aged 18–71 years; 40 male). Each measurement included brachial volumetric displacement waveform recording, from which central, aortic SBP was calculated (SphygmoCor XCEL). Arm volume covered by the cuff was measured using a perometer and an indication of arm muscle mass asymmetry was measured using a maximal hand grip strength test with appropriate position of the arm. Results: Brachial SBP was significantly higher in one arm compared to the other in 11 subjects (average difference across those 11 subjects: 5.4±0.7 mmHg). Aortic SBP was higher when calculated from one arm than when calculated from the other in 18 subjects (average difference across those 18 subjects: 3.1±0.6 mmHg). Across the cohort, average brachial SBP inter-arm difference was 4.1±2.5 mmHg. Aortic SBP as calculated from each arm exhibited a difference of 3.1±2.0 mmHg, and was highly correlated with inter-arm difference in brachial SBP (R2 =0.67, P<0.0001). Dominant/non-dominant difference in SBP was not correlated with inter-arm difference in brachial volume or grip strength. However, inter-arm brachial SBP difference was positively associated with BMI and dominance in the right arm (i.e., more prevalent in right handed people) and negatively associated with age and absolute brachial systolic pressure. Conclusion: Calculation of aortic SBP from both arms simultaneously leads to a false “difference” in aortic pressure as measured from each arm. This was highly associated with the inter-arm brachial SBP difference. The brachial SBP inter-arm difference was negatively associated with traditional cardiovascular risk factors such as age and SBP magnitude, but was not associated with asymmetry in arm strength or volume.