Cuff BP More Variable Than Intra-Arterial Measures

Using a cuff to assess blood pressure (BP) produces results that are less consistent than those of intra-arterial assessment. The overestimation of diastolic BP and the underestimation of systolic BP often seen with the arm-cuff technique support the need to improve measuring devices, say investigators.

“Researchers have long suspected problems with the accuracy of cuff-measured blood pressure, but as far as we know this is the first comprehensive analysis on the extent of the issue,” senior investigator James Sharman, MD (University of Tasmania, Hobart, Australia), told TCTMD.

Sharman and colleagues conducted three participant-level meta-analyses of studies from the 1950s to 2016 that measured intra-arterial aortic BP, intra-arterial brachial BP, and cuff BP. The analyses included 74 studies with 3,073 participants.

The first meta-analysis examined the level of intra-arterial BP agreement between the aorta and brachial artery. Intra-arterial brachial systolic BP was 8.0 mm Hg higher than aortic values (P < 0.0001) and intra-arterial brachial diastolic BP was 1.0 mm Hg lower than aortic values (P = 0.038).

The second and third meta-analyses looked at whether cuff BP measurement was accurate for either intra-arterial brachial BP (meta-analysis 2) or intra-arterial aortic BP (meta-analysis 3). Cuff measurement significantly underestimated intra-arterial brachial systolic BP and pulse pressure (P < 0.0001 for both). The mean absolute difference for systolic BP was 7.9 mm Hg. In addition, cuff measurement significantly overestimated intra-arterial brachial diastolic BP (P < 0.0001).

Only a small mean difference was found between brachial cuff BP and intra-arterial aortic systolic BP. The researchers noted that this was due to a balance between the number of studies reporting overestimation and the number reporting underestimation by cuff measurement. There was poor agreement between the two measures, with a mean absolute difference of 8.0 mm Hg. Additionally, brachial cuff measurement significantly overestimated intra-arterial aortic diastolic BP resulting in an underestimate of intra-arterial aortic pulse pressure. 

Consequences of Inaccuracy

According to the study, an inaccuracy in BP measurement of 5 mm Hg is estimated to misclassify the BP of about 50 million people each year in the United States.

“On the one hand, if the true level of blood pressure is underestimated by the cuff measurement method, then the level of cardiovascular risk from blood pressure is under appreciated. Thus, an opportunity may be missed to reduce an individual’s risk of future cardiovascular events by intervening with appropriate lifestyle advice and/or medication to lower blood pressure,” Sharman said. “On the other hand, if the true level of blood pressure is overestimated by the cuff measurement method, then this ‘overdiagnosis’ of hypertension could lead to unnecessary prescription of blood pressure lowering drugs.”

The variability of cuff measurement adversely influenced the classification of BP, with a particularly high discordance in the BP range for prehypertension (pre-HTN) and stage 1 hypertension (HTN).  Concordance between BP classification using the Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure cuff BP (normal, pre-HTN, and HTN stages 1 and 2) compared with intra-arterial brachial BP was 60%, 50%, 53%, and 80%. Using intra-arterial aortic BP, it was 79%, 57%, 52%, and 76%, respectively.

“These data suggest that the arm-cuff measurement might not be the optimal method for the evaluation of hypertension and that noninvasive technologies for central BP estimation may improve the evaluation and management of hypertension and thereby the cardiovascular prevention,” George Stergiou, MD (National and Kapodistrian University of Athens, Greece), the chairman of the European Society of Hypertension Working Group of Blood Pressure Monitoring and Cardiovascular Variability, told TCTMD.

Although the most accurate method for BP measurement involves using an intra-arterial catheter, Stergiou noted, this method is too invasive to be applied in routine clinical practice.

“Recent advances in technology provided devices that estimate central BP using cuff-based noninvasive methodologies, and cuffless devices are also being developed,” Stergiou said. “Such measurements may be more accurate that the conventional BP monitors in predicting the risk associated with elevated BP, yet they require proper clinical validation.”

The inaccuracies identified in this study affect most cuff BP devices, said Sharman. Other new and improved BP measurement methods are also in development, but most are still based on a cuff measurement technique. Meaning that, for the time being, there is no definitive solution, he said.

“In the meantime, the best options are out-of-office measurement of 24-hour ambulatory BP and home BP monitoring, as well as automated in-clinic BP,” Sharman said. “These methods use the same cuff methods but many BP measures are recorded over time, which may reduce error margin. Indeed, there is good evidence that these methods give a better appreciation of the BP level compared with doctor measured BP using a cuff in the clinic.”

An editorial written by Stergiou along with Anastasios Kollias, MD, PhD, and Athanase D. Protogerou MD, PhD (National and Kapodistrian University of Athens), notes: “From the scientific and the physiological point of view, the invasive intra-arterial BP measurements are the meaningful and relevant ones. In contrast, the science of clinical medicine and hypertension (BP as a vital sign or a marker for hypertension disease, respectively) applied for half a century in billions of people around the world has been inevitably based on noninvasive arm-cuff BP measurements.”

Despite these uncertainties over BP measurement, “hypertension management in clinical practice has been a great success story in medicine,” the editorialists say. What might constitute better testing, and whether it could lead to improved prevention of CV disease, are “21st century questions” that should be addressed by today’s scientific community, they add.