Interarm difference in blood pressure

Posted by jchoules

19 June 2017

Dr Chris

Dr Chris Clark writes: The difference in blood pressure between arms sometimes found in the surgery has been a longstanding research interest of mine. After joining the Mid Devon Medical Practice we were able to start studying it and demonstrated the first association of an interarm blood pressure difference with poorer survival outcomes in 2002. The subject has stayed with me ever since and each study throws as many questions as answers. We can look back over the 15 years and identify some areas of increased certainty and others still in need of research.

We now know that, where systolic blood pressure differs between arms by at least 5mmHg, there is likely to be a survival difference in unselected populations. One goal of our current international collaboration, INTERPRESS, is to address what might be the lower limit of an interarm difference that is associated with differences in survival.
We know that interarm differences are associated with peripheral artery disease, with cerebrovascular disease and in diabetes with both retinopathy and nephropathy.

A common criticism is that the interarm difference is not always reproducible on repeated measures. We do know that the method of measurement is important; if a blood pressure is measured sequentially there is likely to be a three-fold over-estimation of the presence of an interarm difference compared with measuring both arms simultaneously. We know that the white coat effect contributes to this overestimation as well so a repeated simultaneous method of assessment is the only way forward for further research.

We do not know the cause of an interarm difference. It is unlikely to be due simply to narrowing of one large artery in one arm. The competing hypothesis, which is gaining favour, is that arterial stiffness can be unevenly distributed between arms, particularly early in the course of hypertension, so we see differences for that reason. This could account for variability in interarm differences since stiffness has both static and dynamic components. We do lack robust imaging studies to show us the arteries in people with and without interarm difference and this is one area of research for us going forward.

I recently summarised evidence around interarm difference in an article entitled “Do we know enough yet” and it’s clear that whilst we know a lot there is plenty more to learn. Emerging areas of interest include the association of interarm difference with development of cognitive impairment, delineating the causes of and contributing factors to interarm difference, and describing how interarm difference relates to absolute blood pressures and prediction of cardiovascular risk. These are all goals which we are working towards in our INTERPRESS collaboration and we look forward to presenting findings from this project in 2018.

Dr Chris Clark @chrisellesclark
June 2017

CEC is supported by an NIHR Clinical Lectureship award; INTERPRESS is supported by the NIHR Research for Patient Benefit programme, grant no: PB-PG-0215-36009.