Blood Pressure Basics and Beyond

Q: Blood pressure is such a routine measure that the nuances often are taken for granted. What aspects of blood pressure measurement are important for the health and fitness professional?

A:The measurement of blood pressure (BP) is one of the most commonly performed health-related assessments, and with good reason. BP is an independent risk factor for cardiovascular disease (¹³), and the relationship between BP and cardiovascular health is continuous across a broad blood pressure range (¹⁰). For example, the risk of cardiovascular disease in later adulthood has been found to double for each 20-mmHg increase in systolic blood pressure (SBP) greater than 115 mmHg (up to 185 mmHg) and for each 10-mmHg increase in diastolic blood pressure (DBP) greater than 75 mmHg (up to 115 mmHg) (¹⁰). Thus, regular and accurate assessment of BP is crucial.

BP is defined as the force of the blood against the walls of the blood vessels created by the pumping action of the heart (³). Two values are reported: SBP, which is the highest pressure in the arteries when the heart is contracting (systole) and DBP, which is the lowest pressure in the arteries when the heart is relaxing (diastole). BP is measured in units of mmHg (millimeters of mercury).

The direct measurement of BP using an intra-arterial catheter is not practical in most circumstances (⁹). Instead, a relatively cost-efficient and simple indirect way to measure BP involves using a cuff with an inflatable bladder and sphygmomanometer to measure pressure. A stethoscope is used to listen to the blood moving through the vessel; various sounds associated with changes in blood movement are referred to as Korotkoff sounds (Table 1) (³). The indirect method requires the cuff to be placed around the upper arm (Figure 1), and then the bladder of the cuff is inflated to block blood flow temporarily through the brachial artery. As pressure is reduced in the cuff, blood is able to pass through the artery at the highest pressure point (SBP) and then returns to smooth flow once the cuff pressure drops below the lowest pressure point (DBP). Thus, SBP is recorded as the point when the first Korotkoff sounds are heard, and the DBP is determined at the point of disappearance of the sounds.

Can you identify the 10 errors in this picture of resting BP measurement? See page 9 for the answer.

TABLE 1: Korotkoff Sounds (³)

Figure 1: Resting BP.

Consistent methods should be used when assessing resting BP. The following procedures should be followed (¹):

• Pretest behaviors: the client should avoid smoking cigarettes or consuming caffeine for at least 30 minutes prior; the client should be seated quietly for at least 5 minutes before BP is measured.
• Body position: the client should be seated in a chair with back support, feet on the floor, and the arm supported at heart level.
• Cuff selection: the bladder of the cuff should encircle at least 80% of upper-arm circumference.
• Cuff location: the cuff should be placed snugly around the upper arm at heart level and should allow for the stethoscope head to be placed below the bottom edge of the cuff over the brachial artery (note: either side of the stethoscope can be used; both the bell and diaphragm side have been found to be equally effective); the cuff should be placed so that the bladder is centered over the brachial artery.
• Cuff pressure: the pressure should be inflated to 20 mmHg more than the first sound and then released at a rate of approximately 2 to 5 mmHg per second.

Attention to these procedures will help ensure that BP measures are accurate and consistent. Typically, BP is recorded to the nearest 2 mmHg (i.e., nearest even number) (¹³). An average of two measurements should be recorded, with the two measures taken at least 1 minute apart (¹³).

The normal resting BP for adults is a SBP of less than 120 mmHg and a DBP of less than 80 mmHg (¹). Prehypertension is defined as a SBP between 120 and 139 mmHg or a DBP between 80 and 89 mmHg (¹). Stage 1 hypertension is considered for a SBP between 140 and 159 mmHg or a DBP between 90 and 99 mmHg; stage 2 includes a SBP of 160 mmHg or higher or a DBP of 100 mmHg or higher (¹). Lifestyle modifications including physical activity, weight management, and nutritional considerations (e.g., sodium reduction, moderation of alcohol consumption, and a healthy eating pattern), are key for helping to manage BP (^6,7). For insights on the potential benefits of lifestyle factors on BP, see Lifestyle Modifications Can Make a Difference (Box 1).

BOX 1:

Lifestyle Modifications Can Make a Difference

Although medications often are warranted in the treatment of hypertension, lifestyle modifications can have a positive impact. Maintaining normal body weight, defined as a body mass index of 18.5 to 24.9 kg/m², is recommended; a weight loss of 10 kg can reduce SBP by 5 to 20 mmHg (⁶). Physical activity, including at least 30 minutes per day on most days of the week, has been found to provide a 4- to 9-mmHg reduction in SBP (⁶). With regard to nutrition, consuming a diet rich in fruits, vegetables, and low-fat dairy while reducing intake of saturated fat and total fat (i.e., the DASH diet (Dietary Approaches to Stop Hypertension)) promotes an SBP reduction of 8 to 14 mmHg (⁶). Limiting alcohol consumption (<2 drinks per day inmost men and 1 drink per day in women and lighter-weight individuals) is associated with a 2- to 4-mmHg reduction in SBP (⁶). In addition, keeping sodium intake to less than 2,400 mg/day is recommended for a potential SBP reduction of 2 to 8 mmHg (and note that lowering sodium intake down to 1,500 mg/day is associated with even greater BP reductions) (⁷).

Unlike the specific values used to define hypertension, hypotension does not have numerical standards and typically is not a problem unless an individual is experiencing symptoms of chronically low BP (e.g., dizziness, fatigue, nausea, among others) (⁴). If symptoms are present, consulting with a health care provider is recommended to determine if there is an underlying cause (⁴). Although the focus often is on elevated BP, unusually low BP readings also should be evaluated (¹).

The measurement of BP in children and adolescents is similar to the procedures in adults with some considerations, including the following (^11,14):

• Correct cuff selection is typically made by using the largest cuff that still provides room for correct positioning of the stethoscope head below the cuff.
• BP is classified by percentiles for age, sex, and height, as follows:
• ○ Normal: SBP and DBP are less than the 90th percentile.
• ○ Prehypertension: SBP or DBP greater than the 90th percentile to less than the 95th percentile or BP greater than 120/80 mmHg to less than the 95th percentile
• ○ Stage 1 hypertension: SBP and/or DBP greater than the 95th percentile to less than the 99th percentile plus 5 mmHg
• ○ Stage 2 hypertension: SBP and/or DBP greater than the 99th percentile plus 5 mmHg

A pocket guide (including tables for percentiles for boys and girls) can be found at bp_child_pocket.pdf (¹¹), and for more detailed information related to BP in children, see The Fourth Report on the Diagnosis, Evaluation, and Treatment of High Blood Pressure in Children and Adolescents (¹⁴).

In addition to the assessment of BP at rest, health and fitness professionals often measure BP responses to exercise. For appropriate comparison, in such situations, resting BP should be obtained in the exercise position (e.g., standing position for a treadmill test) (¹). Normal responses to increases in workload include (¹)

• Increase in SBP
• No change or a slight decrease in DBP

SBP increases linearly with increases in workload — approximately 10 mmHg per MET (MET is a metabolic equivalent, equal to 3.5 mL/kg/min) (³). An abnormal response would be considered if SBP drops by 10 mmHg or more or if SBP does not increase along with increases in workload (¹). Concerns associated with this type of exertional hypotension include myocardial ischemia, left ventricular dysfunction, and an increased risk of a future cardiac event (¹). Excessive increases in BP also are a concern; exercise testing termination criteria include an SBP greater than 250 mmHg or a DBP exceeding 115 mmHg (¹). Various medications may impact BP at rest and during exercise (e.g., beta-blockers lower BP) (¹); this underscores the importance of a complete healthy history, including awareness of all medications, to anticipate any potential impact on BP.

Accurately assessing BP during exercise can be a challenge because of client movement, physical location on exercise equipment, and general noise associated with the testing environment. Some considerations when assessing BP during exercise include the following:

• Support the client's arm rather than allowing the client to grasp the treadmill rails or bike handlebars (¹).
• Hold the client's arm in a relatively straight position; do not allow the client to flex at the elbow (¹).
• Maintain appropriate physical orientation to the client; for example, consider using a step stool when assessing BP for a client engaging in treadmill walking on a grade.
• Control the movement of tubing; avoid allowing tubing to rub against one another or to make contact with the stethoscope head because both of these situations can introduce noise artifact and impair one's ability to hear the Korotkoff sounds.

Attention to one's orientation to the client as well as the equipment are key factors in taking BP during exercise (Figure 2). The accurate assessment of exercise BP is vital given the inclusion of abnormal BP responses in exercise testing termination criteria (see Exercise Termination Criteria Related to BP).

Figure 2: Exercise BP.

Although BP measurement seems to be a simple measurement, various factors can impact one's accuracy. Table 2 includes some issues associated with BP measurement along with tips on minimizing the impact of those issues (^1–3,8,9,12). In addition, the location of the BP assessment as well as the person taking the measurement can have an impact. White coat hypertension refers to situations where an individual has an increased resting BP when in the clinic or doctor's office (¹²). The impact of physician-measured BP has been found to be as much as 30 mmHg higher than similar measures at home (¹²). White coat hypertension differs from true hypertension in that the BP is normal when outside of the clinical setting; this is considered to be a low-risk condition compared with sustained hypertension (¹²).

TABLE 2: Issues Associated With Blood Pressure Measurement (^1–3,8,9,12)

In light of concerns with white coat effects, some clients may use home BP monitoring (i.e., when an individual measures BP outside of the clinical setting). Self-measured BP monitoring has been found to improve adherence and health outcomes for hypertensive individuals (⁵). The American Medical Association (AMA) recommends that the following features be considered when recommending a device for self-monitoring (⁵):

• Check if the device is certified (e.g., Association for the Advancement of Medical Instrumentation, British Hypertension Society, European Society of Hypertension).
• The device should use the upper arm rather than the wrist.

BOX 2:

Exercise Termination Criteria Related to BP

Among a number of other criteria, BP responses to exercise may warrant exercise testing termination. General indications for stopping a nondiagnostic exercise test (assuming no direct physician involvement or monitoring of electrocardiogram result) include (¹):

• A drop in SBP of 10mmHg or more with an increase in work rate or if the SBP decreases below the value obtained in the same position before testing
• An excessive rise in BP: systolic pressure is greater than 250 mmHg and/or diastolic pressure is greater than 115 mmHg.

In addition, other practical features include ease of use, visual commands, clear readouts, storage of readings, calculation of averages, ability to transmit information to other devices or apps, and, of course, cost (⁵). For more detailed information, see the link to the AMA in the Web Resources found at the end of this article.

SUMMARY

BP measures are routinely performed and, to ensure correct values are reported, attention must be given to the methods used. Specific techniques, including selection of an appropriately sized cuff along with correct positioning of the client in relation to the equipment, are foundational to providing accurate measures at rest and during exercise. Health and fitness professionals need to be aware of normal versus hypertensive BP readings at rest and also be aware of normal versus abnormal BP changes with exercise.

Acknowledgment

The author thanks the Kinesiology Department students at Missouri State University for their assistance with the BP demonstration photos.