Blood Pressure Measurement (Arm Cuff Method)

Relevant Social Security Medical Listings

  • Listing 4.02 Chronic Heart Failure (Adults)
  • Listing 4.04 Ischemic Heart Disease (Adults)
  • Listing 6.02 Chronic Kidney Disease (Adults)
  • Listing 9.06 Hyperfunction of the Adrenal Cortex (Adults)

Type

Objective/Blood Pressure (Arm)

Purpose

  • Diagnose high blood pressure (HBP).
  • Monitor response to treatment of high blood pressure (hypertension).
  • Monitor blood pressure (BP) as part of vital signs during illness, trauma, surgical procedures, etc.

Technique

The arm should be kept at the level of the heart during measurement of blood pressure, whether measurements are taken lying, sitting, or standing. If the arm is lower than the heart, an erroneously high pressure will be recorded; if higher than the heart, the pressure will be erroneously low. If the patient is lying flat or standing, the arm is approximately at heart level; adjustment of arm height may be necessary in the sitting position. Manual measurement is described below. Patient’s blood pressure is typically taken with a patient in a fairly cold examining room, sitting on an examining table with arms hanging down at his or her side. However, BP should be measured with the patient sitting in a chair that has a back and arms for support of the patient’s arms. The patient should sit quietly for at least 5 minutes prior to measurement. The blood pressure cuff should be directly on the patient’s skin; many medical personnel will attempt to take pressure readings through a patient’s shirt—even sweater—and erroneously state that “…it doesn’t matter” if asked about it by the patient.

Studies have shown that as many as 73% of health care workers incorrectly measure B.P. with the patient’s arms in the wrong position. As noted above, the arm should be at the level of the heart, but there is an additional consideration: the arm should be slightly flexed, rather than at a right angle at the elbow or in a straight position (extended). When the elbow is at a right angle to the body, both systolic and diastolic readings are about 10% lower than with the arm extended in the same direction as the body. When the arm is extended parallel to the body, whether sitting, supine, or standing, pressures taken in that position can lead to nearly double the number of hypertension diagnoses.

Blood pressure is measured by an instrument called a sphygmomanometer. A cloth cuff is wrapped around the arm about one inch above the elbow, which should be at the level of the heart. The blood pressure cuff must not be too large or too small for the patient’s arm.[1] For example, use of a regular-sized cuff on an obese arm will provide a falsely elevated blood pressure reading, while too large a cuff on a small arm will cause a falsely low reading.

Blood Pressure Cuff Sizes Needed (centimeters)
Arm Circumference Bladder Dimensions Cuff Size
22 to 26 12 x 22 Small adult arm
27 to 34 16 x 30 Adult arm
35 to 44 16 x 36 Large adult arm
45 to 52 14 x 42 Adult thigh

The cuff has an inner, rubber bladder that can be inflated by squeezing a rubber bulb. The cuff is inflated sufficiently to produce enough pressure to stop blood flow through the arm’s brachial artery, as determined by disappearance of the radial artery pulse in the patient’s wrist and then increased another 30 mm Hg. Failure to determine disappearance of the radial pulse can lead to a falsely high diastolic or falsely low systolic pressure reading.[2]

The stethoscope diaphragm should be lightly placed just below the lower edge of the cuff and positioned over the brachial artery on the inner surface of the arm; the diaphragm should not touch or be placed under the blood pressure cuff. Air is slowly released from the cuff by turning a small valve attached to the rubber bulb. The air should be released at a rate of 2 to 3 mm Hg per second; if released too slowly or too rapidly, the reading will not be accurate. The point when the first (Phase I) sounds can be heard is the systolic pressure; the cuff pressure is just low enough to let blood run under it during the heart’s contraction (systole).

As the cuff is progressively deflated, Phase II sounds appear with a swishing quality. Phase III sounds are maximum intensity. In Phase IV, the heart sounds become fainter and more muffled. Phase V represents the point of disappearance of the last faintest sounds and represents the diastolic pressure.[3]

The pressures are read from a gauge on the cuff, or are connected to a more accurate mercury manometer. The physician or nurse taking the reading should position their view level with the gauge or mercury manometer; if their view is at an angle, the reading will be incorrect. Measuring BP though a shirt sleeve is incorrect technique, since a crumpled shirt under the cuff interferes with pressure distribution from the cuff. At least 2 minutes should elapse before a repeat reading is made using the same arm.

High quality automated electronic sphygmomanometers of the type used in hospitals can provide accurate BP readings if the right size cuff is properly applied with the patient’s arm in correct position.

Interpretation

Hypertension is usually defined in adults as 140/90 or higher pressure on repeated readings. The first number is the systolic pressure and represents the arm’s arterial pressure during contraction of the heart. The second number is the diastolic pressure and is a lower value that represents blood pressure between heart beats. No single measurement is diagnostic; at least several readings over a period of days should be performed for accurate interpretation. Anger, anxiety, excitement, drugs, cold, and pain can cause transiently elevated readings; consequently, readings taken under these conditions should not be considered representative of the patient’s usual blood pressure. White coat hypertension is the phrase used to describe patients with elevated pressures in a doctor’s office while more normal at home and is a fairly common occurrence. This has led some authorities to recommend home BP measurements be used for treatment decisions. This recommendation assumes that the home pressures are accurate. However, patients are even more susceptible to making BP measurement errors than professional medical personnel and home equipment may not be calibrated, or even accurate if calibrated. There is an inverse effect to white coat hypertension known as masked hypertension. In these patients, blood pressure is abnormal at home but normal when measured in a doctor’s office. It has been reported that masked hypertension may occur in as many as 9% of patients.

Talking on the part of the patient during measurement can elevate systolic and diastolic pressures by as much as 17 and 13 mm Hg respectively, while ingestion of alcohol within 3 hours of measurement has been reported to increase systolic and diastolic pressures 7 and 8 mm Hg respectively. Caffeine may elevate pressures by several mm Hg, particularly in those not used to caffeine intake—effect is thought to be minimal in individuals used to drinking caffeinated beverages. Failure to provide support for the arm can result in an error of at least 2 mm Hg (systolic and diastolic pressures), and perhaps more. Systolic and diastolic pressures may both be increased 8 mm Hg for every 10 cm the arm is below heart level, and decreased 8 mm Hg for every 10 cm above heart level. It has been reported that use of a cuff that is too small can result in a systolic pressure that is 8 mm Hg lower than the actual pressure, and 8 mm Hg too high for the diastolic pressure. However, most medical sources state that too small a cuff will result in erroneously high readings and too large a cuff will result in readings that are too low, without making a possible distinction between systolic and diastolic pressures. It is clear that even everyday activities can result in significant elevations of blood pressure from their prior levels. For example, walking, dressing, attending meetings, commuting, and talking on the telephone have been reported to increase systolic pressure by 10-20 mm/g Hg systolic and with a somewhat lesser increase in diastolic pressure. Psychological stresses, such as performing mental arithmetic, can result in significant increases in blood pressure. Also, various sources report a significant difference between blood pressure in the left and right arms in about 8-30% of patients. It is widely agreed that, on at least initial evaluation of a patient, blood pressure should be measured in both arms—though rarely done in practice by most doctors and nurses.

The pulse pressure is the difference between systolic and diastolic pressures, and relatively little research has been done regarding the clinical implications of this value. In isolated systolic hypertension[4] over a period of 5 years in elderly patients (> age 60), an increase of the pulse pressure by 10 mm Hg has been found to be associated with a 32% increased risk of heart failure and a 24% increase in stroke risk, even after adjusting for other risk factors and the risk associated with the systolic hypertension itself. Understandably, increased mortality is also implied by these numbers. After controlling for diastolic blood pressure and other risk factors, the 5-year risk of heart failure and stroke is somewhat lower at 23% and 19%, respectively. Although increased risk based on pulse pressure is not seen in normals or in patients being treated for coronary artery disease, there are many people being treated for hypertension alone and attempts to decrease the pulse pressure would appear to be worthwhile although largely disregarded by the medical profession. There is evidence that blood pressures measured continuously during ambulatory monitoring are more reliable in assessing pulse pressure than BP readings taken in a physician’s office.

More recently, pulse pressure has been identified as a much stronger predictor of the development of atrial fibrillation (AF) than systolic or diastolic blood pressure, or average blood pressure. In one study, it was found that over a 20-year period, the incidence of AF was only 5.6% for those with a pulse pressure of 40 mm Hg or less, but increased to 23.3% for those with pulse pressure higher than 61 mm Hg. In addition to other risk factors and after adjusting for gender and age, the risk of developing AF is 34% higher for a 20 mm Hg increase in pulse pressure. The theory is that the greater stiffness of the aorta and other great arteries causes a greater workload on the heart and inability of the heart to fully relax. Intracardiac filling pressures, including atrial pressures, increase. The result is fibrotic atrial damage that is known to increase risk for AF.

The National Heart, Lung and Blood Institute of the National Institutes of Health (NHLBI, NIH) issued guidelines in 2003. The new blood pressure definitions are:

  • Normal less than 120/less than 80 mm Hg;
  • Prehypertension, 120-139/80-89 mm Hg;
  • Stage 1 hypertension, 140-159/90-99 mm Hg;
  • Stage 2 hypertension, at or greater than 160/at or greater than 100 mm Hg.

Note the new term “prehypertension” invented by the NHLBI. The problem with this word is that it is derived from the statistical properties of large populations showing an increase in stroke risk as BP increases. Increasing risk is not surprising, but does not imply that there are functional limitations in “prehypertension” or that any individual with a BP in the “prehypertension” range will suffer progressive elevation in BP. It is not at all certain that the new NHLBI hypertension guidelines will have any practical benefit to clinical medicine. Use of the word “prehypertension” is misleading and of questionable practical significance. The NHLBI guidelines for the diagnosis of hypertension are prepared by the Joint National Committee on the Prevention, Detection, and Treatment of High Blood Pressure (JNC). The 2003 guidelines are sometimes referred to as JNC 7.

In 2005, the Writing Group of the American Society of Hypertension (WG-ASH) recommended a new way to approach the diagnosis of hypertension, one which recognizes the importance of taking into account the clinical condition of the individual patient in the diagnosis of hypertension itself. This is a subtle but important departure from conventional definitions, which assign the same numerical thresholds for various stages of hypertension without consideration of organ damage or risk factors—although the importance of such adverse conditions is not disregarded in treatment of hypertension, they are not conventionally a part of the diagnosis of hypertension itself.

The WG-ASH recommendations are not, however, unreasonable or without precedent. For example, it has long been known that the diagnosis of glaucoma cannot rationally rely solely on pressure inside the eye (intraocular pressure, IOP). Some individuals have no eye damage with pressures much higher than the majority of people, while other individuals have glaucomatous eye damage with pressure that would be normal for most other people. Thus, the proposed WG-ASH definitions recognize hypertension appropriately as a multi-faceted cardiovascular disorder rather than only an arterial pressure abnormality. Risk factors, such as diabetes or hyperlipidemia, lead to organ damage (e.g., eyes, heart, kidneys) which then have overt clinical consequences like blindness or heart or kidney failure. In other words, an increase in blood pressure in the presence of diabetes mellitus with early kidney disease is more serious than in a person without diabetes, and the same blood pressure numbers might be considered hypertension in a diabetic and normal in a non-diabetic. The WG-ASH is a potentially important advance in the clinical concept of hypertensive cardiovascular disease, and would emphasize the importance of individualized medical judgment over cookbook assignment of patients who are actually different to the same diagnostic category.

Comparison of JNC-7 and 2005 WG-ASH Hypertension Categories
JNC 7 WG-ASH Systolic BP (mm Hg) Diastolic BP (mm Hg)
Normal Normal < 120 and < 80
Prehypertension Hypertension 129-139 or 80-90
Stage 1 <130 and <85
130-139 or 85-95
Hypertension
Stage 1 Stage 1 or 140-159 or 90-99
Stage 2 Stage 2 <=160 or >=100
Stage 3 160-179 or 100-109
WG-ASH 2005 Definition and Classification of Hypertension
Classification Blood Pressure Elevations Cardiovascular Disease Cardiovascular Risk Factors Early Disease Markers Target Organ Disease
Normal Normal or rare or None None or few None None
Hypertension
Stage 1 Occasional or intermittent or Early Several Usually present None
Stage 2 Sustained or Progressive Many Overtly present Early signs present
Stage 3 Marked and Sustained or Advanced Many Overtly present and progressive Overtly present with or without cardiovascular disease events

Comments

There is probably no more frequently performed medical test than determination of blood pressure using a cuff, and no test that is performed more incorrectly or more carelessly by doctors and nurses when done manually.

Sometimes blood pressure is measured in the thigh, using the same general technique with a much larger cuff and listening over the popliteal artery behind the knee rather than the brachial artery in the arm. However, when blood pressure in the legs must be known it is usually measured with Doppler ultrasound. Systolic pressures in the legs are higher than in the arms. In hospitals, it is sometimes necessary to insert intra-arterial lines to monitor blood pressure and extremely accurate values can be recorded. Elderly individuals in particular may have falsely elevated blood pressures when measured by conventional means—a condition known as pseudohypertension. Pseudohypertension results from abnormal stiffening of arterial walls associated with age and arteriosclerosis. In some of these individuals, the examining doctors can actually feel hardened arteries roll under their fingertips.

Footnotes

  1. The cuff should be 20% wider than the diameter of the arm, or have a width of at least 40% of arm circumference. Cuff length should be at least 80% of arm circumference.
  2. If the radial pulse is not obliterated with inflation of the cuff, the true systolic pressure cannot be measured since cuff pressure is not raised high enough to measure it. In some patients an auscultatory gap appears, which means a gap in the usual sequence of heart sounds in which they cannot be heard (auscultated). When the auscultatory gap starts, the disappearance of sounds can be mistaken for too high a diastolic pressure; or when they reappear at the end of the auscultatory gap, they can be mistaken for a too low systolic blood pressure.
  3. Some authorities recommend reading the diastolic pressure with onset of muffling (Phase IV). Some physicians or nurses record both the Phase IV and Phase V sounds as different diastolic pressures; most do not. A usual BP reading might be a systolic pressure and a diastolic pressure such as 134/75, while a double diastolic pressure record might look like 134/75/65. The sounds heard while measuring the blood pressure are called Korotkoff sounds.