The pursuit of accurate blood pressure measurement: A 35‐year travail

Appropriately, cardiovascular disease has recently been dubbed “the largest epidemic known to mankind, and hypertension is the major contributory risk. ”1 The number of adults around the globe living with hypertension has nearly doubled since 1975, from 594 million to 1.1 billion in 2015.2 A recent systematic analysis that assessed 67 risk factors of disease in 21 regions around the world from 1990 to 2010 showed increased blood pressure (BP) to remain the leading risk factor for death and disability globally.3 When we talk of hypertension, or high BP, it is often forgotten that we are referring to a physiological phenomenon, namely normotension, that can become a pathological entity (ie, a disease) when BP exceeds a certain level, and that the transformation from normality to abnormality is exclusively dependent on a measurement. Although the severity of hypertension may be influenced by associated risk factors, such as family history, lifestyle, and the presence of associated illnesses, such as diabetes mellitus, the diagnosis and all subsequent therapeutic decisions are dependent on being able to measure BP accurately. Put another way, the empirical aphorism of H. James Harrington: “If you can’t measure something, you can’t understand it; if you can’t understand it, you can’t control it; if you can’t control it, you can’t improve it,”4 has been ignored, not only by clinical practitioners but also by scientific researchers. To diagnose and treat hypertension, it is necessary to have a device capable of measuring at least two levels of BP accurately, namely systolic and diastolic pressures. Devices may be developed further to measure BP in patients with varying characteristics, such as children, obese and pregnant persons, and in certain circumstances, such as during exercise, and over time, such as with ambulatory BP monitoring. However, whatever the circumstances or conditions of measurement, the sine qua non for all forms of measurement is that the device must be accurate. It is worth emphasizing that although evolving technology can offer the means to measure complex functions of cardiovascular physiology, the basic phenotype remains the BP, and all other methodologies of measurement become meaningless unless BP is measured accurately. This has been stated with similar emphasis in the recently published Lancet Commission on hypertension: “In hypertension, blood pressure is an almost ideal biomarker. Blood pressure is causally related to the development of the condition, defines the condition, predicts the outcome, is the target of therapeutic interventions, and serves as a surrogate marker to assess the benefit of therapies. Therefore, the role that other biomarkers could have in hypertension requires careful thought. ”5 The “pursuit of accuracy” for BPmeasuring devices has a long legacy. In 1918, Dr Faught made a despairing statement: “At the present time the market is flooded with instruments of all descriptions for estimating bloodpressure, so that it is important that the prospective purchaser should be able to separate the good from the bad. ”6 However, serious efforts to distinguish the “good from the bad,” so that patients would not be disadvantaged by inaccurate measurement only began in the 1980s when efforts to standardize the validation of BP monitors were made.