Recommendations for Blood Pressure Measurement in Humans: An AHA Scientific Statement from the Council on High Blood Pressure Research Professional and Public Education Subcommittee

Abstract

Ten years have passed since the last version of the American Heart Association (AHA) blood pressure (BP) measurement recommendations,1 during which time there have been major changes in the ways in which BP is measured in clinical practice and research; hence this document represents a major revision of previous versions.2 BP determination continues to be one of the most important measurements in clinical medicine, and still one of the most inaccurately performed. The gold standard for clinical BP measurement has always been readings taken by a trained health care provider using a mercury sphygmomanometer and the Korotkoff sound technique. There is increasing evidence, however, that this procedure may lead to the misclassification of large numbers of individuals as hypertensive, and fail to diagnose other individuals whose BP may be normal in the clinic setting but elevated at other times. There are three reasons for this: 1) inaccuracies in the methods, some of which are avoidable; 2) the inherent variability of BP; and 3) the tendency for BP to increase in the presence of a physician (the so-called “white coat effect“). Numerous surveys have shown that physicians and other health care providers rarely follow established guidelines for BP measurement, but when they do, the readings they get correlate more closely with more objective measures of BP than the usual clinic readings. It is generally agreed that conventional clinic readings, when made correctly, are a surrogate marker for a patient's true BP, which is conceived as the average level over prolonged periods of time, and which is thought to be the most important component of BP in determining its adverse effects. Usual clinic readings give a poor estimate of this, not only because of poor technique, but also because they typically consist only of one or two individual measurements, and the beat-to-beat BP variability is such that a small number of readings may only give a crude estimate of the average level. The recognition of these limitations of traditional clinic readings has led to two parallel developments: first, increasing use of measurements out of the clinic, which avoids the unrepresentative nature of the clinic setting and also allows for an increased number of readings; and second, the increased use of automated devices, which are being used both in and out of the office setting. This decreased reliance on traditional readings has been accelerated by the fact that mercury is being banned in many countries, although there is still uncertainty as to what will replace it. Several dimensions of BP are associated with an increased risk of vascular disease. Clinic-based measurements that predict vascular disease include systolic and diastolic BP as well as mean arterial pressure and pulse pressure. Several studies have attempted to tease apart the relative importance of these measurements.3,4 Despite evolving interest in pulse pressure, the best available evidence still supports the use of systolic and diastolic BPs to classify individuals. As adults age, systolic BP tends to rise and diastolic BP tends to fall. When the average systolic BP is ≥140 and diastolic BP is <90 the patient is classified as having ISH. The increased pulse pressure (systolic − diastolic) and systolic pressure predict risk and determine treatment.5 In older children and young adults, more often males, the combination of rapid growth in height and very elastic arteries accentuates the normal amplification of the pressure wave between the aorta and brachial artery, resulting in a high systolic pressure in the brachial artery, but normal diastolic and mean pressures. The aortic systolic pressure is normal, however. This can be suspected from pulse wave analysis.6 More commonly in some younger adults, IDH is defined as systolic BP <140 and diastolic BP ≥90. Although diastolic pressure is generally believed to be the best predictor of risk in patients under the age of 50, some prospective studies of isolated diastolic hypertension have indicated that the prognosis may be benign.7 This topic remains controversial. WCH is commonly defined as a persistently elevated average office BP of >140/90 and an average awake ambulatory reading of <135/85 mm Hg, and occurs in about 15%–20% of people with stage 1 hypertension.8 Patients with WCH may progress to sustained hypertension and need to be followed carefully with office and out-of-office measurements of BP. Treatment with antihypertensive drugs may lower the office BP but does not change the ambulatory measurements.9 Somewhat less frequent than WCH, but more problematic to detect, is the converse condition—normal BP in the office and elevated BPs elsewhere, e.g., at work or at home. There is some evidence that such patients have more target organ damage and are at higher risk than subjects who are normotensive all the time.10 In a small number of elderly patients, the peripheral muscular arteries become very rigid, such that the cuff has to be at a higher pressure to compress them. The brachial or radial artery may be palpated distal to the fully inflated cuff in these instances (positive Osler's sign). When suspected, an intra-arterial radial artery BP can be obtained for verification. Osler's maneuver is not a reliable screen for pseudohypertension. Orthostatic hypotension is defined as a reduction of systolic BP of at least 20 mm Hg or 10 mm Hg in diastolic BP within 3 minutes of quiet standing.11 If chronic, the decrease in BP may be part of pure autonomic failure, multiple system atrophy, and other dysautonomias. These patients may not only have profound hypotension on standing, but also severe hypertension when supine during the night. The auscultatory method has been the mainstay of clinical BP measurement for as long as BP has been measured; this is gradually being supplanted by other techniques that are more suited to automated measurement. It is surprising that nearly 100 years after it was first discovered, and the subsequent recognition of its limited accuracy, the Korotkoff technique for measuring BP has continued to be used without any substantial improvement. The brachial artery is occluded by a cuff placed around the upper arm and inflated to above systolic pressure. As it is gradually deflated pulsatile blood flow is reestablished and accompanied by sounds that can be detected by a stethoscope held over the brachial artery just below the cuff. The onset of phase I of the Korotkoff sounds (tapping sounds corresponding to the appearance of a palpable pulse) corresponds to systolic pressure, but tends to underestimate the systolic pressure recorded by direct intra-arterial measurement.12 The disappearance of sounds (phase V) corresponds to diastolic pressure, but tends to occur before diastolic pressure determined by direct intraarterial measurement.12 The fifth phase should be used, except in situations in which the disappearance of sounds cannot reliably be determined because sounds are audible even after complete deflation of the cuff, for example, in pregnant women, in which case the fourth phase (muffling) may be used.13 In older patients with a wide pulse pressure, the Korotkoff sounds may become inaudible between systolic and diastolic pressure and reappear as cuff deflation is continued. This phenomenon is known as the auscultatory gap. In some cases this may occur because of fluctuations of intraarterial pressure, and is most likely to occur in subjects with target organ damage.14 Mercury Sphygmomanometers. The design of mercury sphygmomanometers has changed little over the past 50 years, except that modern versions are less likely to spill mercury if dropped. There is less to go wrong with mercury sphygmomanometers than with other devices, and there is negligible difference in the accuracy of different brands. However, many devices in everyday use are defective. The random zero sphygmomanometer was designed to eliminate observer bias, but is no longer available. Aneroid Sphygmomanometers. In these devices, the pressure is registered by a mechanical system of metal bellows that expands as the cuff pressure increases and a series of levers that register the pressure on a circular scale. This type of system may not maintain its stability over time. They therefore require calibrating at regular intervals. Recent developments in the design of aneroid devices may make them less susceptible to damage when dropped. Hybrid Sphygmomanometers. Devices have been developed which combine features of both electronic and auscultatory devices, and are referred to as “hybrid” sphygmomanometers. The mercury column is replaced by an electronic pressure gauge, such as are used in oscillometric devices, and BP is taken using the auscultatory technique.15 The hybrid sphygmomanometer has the potential to become a replacement for mercury. When the oscillations of pressure in a sphygmomanometer cuff are recorded during gradual deflation, the point of maximal oscillation corresponds to the mean intra-arterial pressure. The oscillations begin above systolic BP and continue below diastolic BP, so that systolic and diastolic BPs can only be estimated indirectly according to some empirically derived algorithm. One advantage of the method is that no transducer needs to be placed over the brachial artery, so placement of the cuff is not critical. However, in older people with wide pulse pressures, the mean arterial pressure may be significantly underestimated.16 The oscillometric technique has been used successfully in ambulatory BP monitors and home monitors. The standard location for BP measurement is the upper arm, but wrist monitors may be useful in very obese patients if the monitor is held at heart level. Finger monitors are not recommended. It is recommended that only those devices that have passed standardized validation tests should be used in practice, and oscillometric monitors should be validated on each patient before the readings are accepted.17 With non-automatic devices, such as mercury and aneroid monitors, it is recommended that the accuracy of the pressure registration mechanism be checked. Accurate auscultatory office BP measurement is the bedrock of the diagnosis and treatment of hypertension; however, it is becoming increasingly clear that, as it is used in everyday practice, there are major shortcomings. A number of factors related to the subject can cause significant deviations in measured BP. These include room temperature, exercise, alcohol or nicotine consumption, positioning of the arm, muscle tension, bladder distension, talking, and background noise. The patient should be asked to remove all clothing that covers the location of cuff placement. The individual should be comfortably seated, with the legs uncrossed, and the back and arm supported, such that the middle of the cuff on the upper arm is at the level of the right atrium (the midpoint of the sternum). At the initial visit, BP should be measured in both arms. The patient should be instructed to relax as much as possible, and not to talk during the measurement procedure; ideally 5 minutes should elapse before the first reading is taken. It is recommended that, if available, a properly maintained mercury sphygmomanometer be used for routine office measurements. There is a role for other types of devices, both as a substitute for the traditional mercury readings (e.g., aneroid and hybrid sphygmomanometers), and as supplements to them (e.g., oscillometric automatic devices). Mercury sphygmomanometers are necessary for evaluating the accuracy of any type of non-mercury device. A common source of error is “miscuffing,” where the use of a cuff that inadequately encircles the arm gives a falsely high reading. The “ideal” cuff should have a bladder length that is 80%, and a width that is at least 40% of arm circumference (a length-to-width ratio of 2:1). The recommended cuff sizes are: • For arm circumference of 22–26 cm, the cuff should be “small adult” size—12 × 22 cm. • For arm circumference of 27–34 cm, the cuff should be “adult” size—16 × 30 cm. • For arm circumference of 35–44 cm, the cuff should be “large adult” size—16 × 36 cm. • For arm circumference of 45–52 cm, the cuff should be “adult thigh” size—16 × 42 cm. BP measurement is most commonly made in either the sitting or supine position, but the two positions give different measurements. When measurements are taken in the supine position the arm should be supported with a pillow. Diastolic pressure measured while sitting is higher than when measured supine (by about 5 mm Hg). When the arm position is meticulously adjusted so that the cuff is at the level of the right atrium in both positions, the systolic pressure is about 8 mm Hg higher in the supine than the upright position.18 If the back is not supported (as when the patient is seated on an examination table rather than a chair) the diastolic pressure may be 6 mm Hg higher. Crossing the legs may raise systolic pressure by 2–8 mm Hg.19 The position of the arm is also important when seated measurements are taken: if the upper arm is below the level of the right atrium (when the arm is hanging down while in the sitting position) the readings will be too high. Similarly, if the arm is above the heart level, the readings will be too low. These differences can be attributed to the effects of hydrostatic pressure and may be 2 mm Hg for every inch above or below the heart level.20 BP should be checked in both arms at the first examination. This may be helpful in detecting of the aorta and upper arterial When there is a the arm with the higher pressure should be used for placement be by of the cuff for the arm The observer first the brachial artery in the and the of the bladder of the cuff so that it is over the arterial over the patient's upper The should not be such that it has a above the cuff, and the lower of the cuff should be above the the observer the patient should talk during the measurement. The Korotkoff sounds are best using the of the stethoscope over in the The cuff should be inflated to at least 30 mm Hg above the point at which the radial pulse and deflated at a of mm Hg pulse when the heart is very • The patient should be seated comfortably with the back supported and the upper arm without The legs should not be • The arm should be supported at heart level, and the bladder of the cuff should at least of the arm • The mercury column should be deflated at and the first and last audible sounds taken as systolic and diastolic pressure. The column should be to the 2 mm • the patient the observer should talk during the measurement. The observer is the most component of BP measurement, and • properly trained in the techniques of BP measurement. • an and properly maintained device. • subject such as and nicotine that BP measurements. • the subject • the cuff and position it • the measurement using the auscultatory or automated oscillometric method and the error is a major of the auscultatory is the most common of BP It is recommended that the observer should the BP to the 2 mm potential should be for and to out the and with that and accuracy in measurement are in and The of should include an of of the different types of observer bias, technique. of all health care is recommended. The of multiple BP is much than a office reading. One advantage of auscultatory readings with readings taken by an automated is the to a number of readings. When a series of readings is the first is typically the a of two readings should be taken at of at least 1 and the average used to the patient's BP. If there is more than a 5 mm Hg difference between the first and readings, or readings should be obtained and the average of these multiple readings is oscillometric BP devices are increasingly used in office BP measurement, as well as for home and ambulatory When they are used in the the readings are typically lower than readings taken by a physician or The potential of automated measurement in the office are the of observer the coat and increasing the number of readings. The are the error inherent in the oscillometric and the fact that are BP devices may also the to and of health care in which is necessary to observer use still patient for or nicotine of the cuff and patient positioning if BPs are to be Devices are available that can a series of readings and average them. In patients not in the BP recorded by a physician or is typically higher than the average level, and this difference is commonly referred to as the “white coat also typically higher than and it is recommended that physician BPs should not be used in the routine of the The standard monitor for home use is an oscillometric that pressure from the brachial of validated monitors is or has over ambulatory which are that it is and a for BP over long periods of time There is some evidence that it both and BP readings not to the Devices that have or of the readings are therefore recommended. When readings are the patient should not have in any such as or that is likely to the BP, and should be in a for minutes with the upper arm at heart level. readings should be taken in by at least one It is helpful to get readings both in the and the BPs are lower than clinic in most The recommended upper of normal for home and ambulatory BP is mm Hg, which is to a clinic pressure of mm As with office BP, a lower home BP is for patients, pregnant women, and patients with One that has held back the use of in clinical practice has been the of prospective studies have that home BP than conventional clinic Devices are available that have the to readings in and them the to a and to the health care They have the potential to patient and hence BP is a fully automated technique in which BP is recorded over an of time, typically It has been by for in patients with suspected coat The standard a cuff, a small monitor to a and a the monitor to the cuff. devices use an oscillometric technique. of validated monitors is a BP is measured every minutes over a both awake and on a The number of readings between 50 and BP are in the monitor and The can be a that mean by and and BP, both for systolic and diastolic BP. The most common used in are of BP, that mean and The monitors are by a trained who should be in BP measurement The cuff is to the upper arm, and a series of readings taken with a mercury sphygmomanometer to that the is readings 5 mm Hg of the mercury It is important to the patient to the arm still by while the is a reading. It may be helpful to the patient to a of when to and in the The most common of is to an usual level of BP the clinic and individuals with potential of include the of individuals with a (e.g., in patients with hypertension but little target organ suspected autonomic and patients in there is a large between clinic and home measurements. The normal for and average are shown Several prospective studies have that the average level of risk of than clinic In to mean of may predict The of interest are WCH and BP. WCH is a in which clinic BP is in the but is normal or low. with WCH are at lower risk for BP related in to individuals with sustained both and one can who not the normal in BP. BP by or more from BP. with a BP reduction from to to be at increased risk of with those with a normal evidence that the BP may be the best predictor of patients are more likely to have isolated systolic and pseudohypertension. BP should be measured while seated, two or more at each visit, and the readings BP should also be taken in the position as the elderly may have can be helpful when changes in of antihypertensive BP with of can some such as and A longer and cuff is for of the brachial artery in the obese patient with a very large upper The error of the pressure when measuring with a cuff that is too small for an obese arm can be and can lead to misclassification of an individual as and to and BP is most measured in children by with a standard mercury The cuff should have a bladder width that is at least 40% of the upper arm and of the circumference of the For a cuff of × 8 is for 6 × and for older × cm. A standard cuff, a large cuff, and a cuff for BP measurement and for use in children or with very large arms should also be available. The techniques for BP measurement are the as in BP measurements in a or be on before a as having individual BP at high tends to decrease on subsequent measurement. a more of an BP level is an average of multiple BP measurements taken for or to this for generally well children be situations in which the is or has elevated BP. who elevated BP on measurement should also have the BP measured in the as a screen for of the the BP in the a cuff or an cuff should be placed on the and the BP measured by over the If the systolic BP measured in the is more than 10 mm Hg lower than the systolic BP measured in the arm and peripheral are studies for should be performed. There continues to be an increase in the use of automated devices to BP in These devices are to and are becoming for BP measurement when mercury sphygmomanometers are not available. The of the BP measurement in children of the age, and in children and is defined as systolic diastolic BP that is to or than the of the BP are available that the systolic and diastolic BP level at the according to age, and These should be to determine if the BP measurements are normal or also coat but the role of ambulatory BP is less clear in The of elevated BP during is one of the major of and measurement of BP is Mercury continues to be the recommended method for BP measurement during BP should be obtained in the seated position, but the position is a during The Korotkoff sound should be used for diastolic pressure, but when sounds are audible with the cuff deflated Korotkoff should be It is that to mercury devices may be necessary in the and a small number of automated BP have been validated for use in may be useful in evaluating BP changes during