Effects of inter-arm differences of brachial systolic blood pressure on the derivation of aortic systolic pressure

Background: Inter-arm differences in brachial systolic blood pressure (SBP) should not theoretically translate to differences in calculated aortic SBP, there being only a single value of aortic blood pressure (BP) at any time. Methods: This study assessed seated brachial and derived aortic SBP in 79 subjects (36±16 years, 40 male) using oscillometric brachial BP measurement and cuff volumetric displacement waveform recording. Measurements were taken simultaneously in left and right arm using identical SphygmoCor XCEL units (AtCor Medical, Sydney). Measurements were taken four times in each subject, swapping BP devices between arms. Results: Brachial SBP was significantly higher in 11 subjects (average difference 5.4±0.7 mmHg) and in 18 subjects for aortic SBP (average difference 3.1±0.6 mmHg). Across all subjects, absolute inter-arm brachial difference in SBP, irrespective of direction, was 3.2±0.3 mmHg (p<0.001) and inter-arm aortic SBP difference 2.1±0.3 mmHg (p<0.001). Inter-arm SBP differences for brachial and aortic sites were correlated (r2=0.74, p<0.001). Arm dominance accounted for 1.1±0.5 mmHg of inter-arm brachial SBP difference (p=0.032) but did not account for inter-arm aortic SBP difference (p=0.163). Average left arm SBP was not different to average right arm SBP for the whole cohort for brachial (p=0.083) or aortic (p=0.789) measurement. Conclusions: The inter-arm absolute difference in brachial SBP translates to a significant but small (2.1 mmHg) difference in derived aortic SBP. Further studies are required to establish if this artefactual difference in derived aortic SBP is predominantly due to arm dominance or other factors associated with left/right difference in vascular properties.