What are the two arteries used for blood pressure measurements?

It’s no secret: high blood pressure is currently the most reliable and strongest modifiable risk factor known to medicine for cardiovascular disease. In fact, evidence suggests that we can prevent up to 80 percent of cardiovascular disease by making healthy lifestyle choices, including following a nutritious diet, getting sufficient exercise, avoiding drug and tobacco use, maintaining a healthy body weight, and using alcohol in moderation.

When it comes to measuring blood pressure, there are basically two approaches, and they are not equally accurate or diagnostic. The two methods in question are brachial blood pressure (BP) and central (aortic) blood pressure (cBP).

Brachial blood pressure does not give you the full picture

Brachial blood pressure measurement is by far the more common way blood pressure is currently taken. Simply, the pressure is measured on the brachial artery, which is palpable on the front (anterior) of the elbow, in the middle of the tendon of the biceps, typically using a blood pressure cuff. 

When arterial blood pressure is measured using a blood pressure cuff, the systolic and diastolic values represent the pressure within the brachial artery on the arm. This pressure differs from the pressure found in the aorta. That’s because as the aortic pressure pulse (the difference between the systolic and diastolic pressures) travels down the aorta into other arteries (which distribute the blood to other parts of the body), characteristic changes occur in both the systolic and diastolic pressures, as well as in the mean pressure.

More specifically, the systolic pressure rises and the diastolic pressure falls while the pulse pressure increases. This occurs because of reflective waves when the blood branches off into the other arteries and because of increased blood vessel stiffness as the pressure pulse moves away from the aorta into the other arteries.

The importance of measuring central (aortic) blood pressure and arterial stiffness

Central blood pressure is the pressure found in the ascending aorta, which is just outside the left ventricle. This is the blood pressure that the target organs—kidneys, heart, brain, and arteries—are exposed to. Therefore, this is the blood pressure information that is most important for physicians and patients to have in order to determine the possibility of end organ damage and other complications associated with elevated blood pressure.

Central blood pressure can be taken in several ways. One is to use a tonometer, a small wand-like instrument that is placed on the skin over the brachial artery. The wand takes the pulse and peripheral blood pressure values together, and the central blood pressure is calculated using a formula. Another approach is to use a regular blood pressure cuff that is attached to a specialized device like AtCor Medical’s XCEL SphygmoCor that takes the pulse waveform and provides central blood pressure measurements.

Along with taking central blood pressure, it is also important to determine the degree of arterial stiffness. If you’re thinking “atherosclerosis” or “hardening of the arteries,” you’re in the ballpark. Arterial stiffness is a byproduct of aging and is the amount of stiffness or rigidness of the arterial walls. It is mainly determined by components of the arterial wall, such as elastin, collagen, and vascular smooth muscle tone, among others.

An accurate assessment of the integrity of the arterial wall could help physicians better predict a patient’s cardiovascular risk. Stiffening of the arteries damages the capillaries that nourish your organs, which means organ damage is very possible. The damage could manifest in various ways: stroke, dementia, kidney failure, a heart attack, or other disorders.(1,2)

The easiest way to measure arterial stiffness is measuring pulse pressure, and that information can also be ascertained when taking central blood pressure, not brachial blood pressure. That’s why more and more doctors need to adopt the practice of taking central blood pressure and accessing arterial stiffness in their patients, especially those at risk for cardiovascular disease. In fact, increased arterial stiffness is an accurate predictor of future cardiovascular events as well as all-cause mortality, independent of traditional risk factors for cardiovascular disease.3,4

Focus on central systolic blood pressure

One of the best tools physicians can use to effectively evaluate patients with hypertension to determine their risk of target-organ damage is to assess central systolic blood pressure, which differs from conventionally measured brachial systolic blood pressure.(5)

It’s important to point out that even among people who have similar brachial systolic blood pressures, there can be significant differences in central systolic values. Another factor to consider is that use of blood pressure medication can have an impact on brachial and central systolic blood pressures differently – which is an important factor for physicians to know before prescribing treatment. (6-9)

It also appears that central blood pressure and how it fluctuates in the presence of hypertensive medication is more strongly associated with end-organ damage than is brachial blood pressure. (10)

Therefore, as suggested by the findings of a randomized trial, it would seem that an accurate estimation of central blood pressure would help doctors improve how they manage their patients with high blood pressure.(11)

After all, if you want to know what is actually going on at the heart and other key organs, isn’t it fundamental to actually measure the blood pressure directly at those organs and not the arm?

References

1. Thorin-Trescases N, Thorin E. Lifelong cyclic mechanical strain promotes large elastic artery stiffening: increased pulse pressure and old age-related organ failure. Canadian Journal of Cardiology 2016; 32(5): 624-33

2. Safar ME et al. Pulse pressure, arterial stiffness, and end-organ damage. Current Hypertension Reports 2012 Aug; 14(4): 339-44

3. Vlachopoulos C et al. Prediction of cardiovascular events and all-cause mortality with central haemodynamics: a systematic review and meta-analysis. European Heart Journal 2010; 31: 1865–71.

4. Ben-Shlomo Y et al. Aortic pulse wave velocity improves cardiovascular event prediction: an individual participant meta-analysis of prospective observational data from 17,635 subjects. Journal of the American College of Cardiology 2014; 63: 636–46.

5. Herbert A et al. Establishing reference values for central blood pressure and its amplification in a general healthy population and according to cardiovascular risk factors. European Heart Journal 2014; 35: 3122–33.

6. Pucci G et al. Effects of β-blockers with and without vasodilating properties on central blood pressure: systematic review and meta-analysis of randomized trials in hypertension. Hypertension 2016; 67: 316–24.

7. Williams B et al. Differential impact of blood pressure-lowering drugs on central aortic pressure and clinical outcomes: principal results of the Conduit Artery Function Evaluation (CAFE) study. Circulation 2006; 113: 1213–25.

8. Boutouyrie P et al. Amlodipine-valsartan combination decreases central systolic blood pressure more effectively than the amlodipine-atenolol combination: the EXPLOR study. Hypertension 2010; 55: 1314–22.

9. Asmar RG et al. Improvement in blood pressure, arterial stiffness and wave reflections with a very-low-dose perindopril/ indapamide combination in hypertensive patient: a comparison with atenolol. Hypertension 2001; 38: 922–26.

10. Kollias A et al. Association of central versus brachial blood pressure with target-organ damage: systematic review and meta-analysis. Hypertension 2016; 67: 183–90.

11. Sharman JE et al. Randomized trial of guiding hypertension management using central aortic blood pressure compared with best-practice care: principal findings of the BP GUIDE study. Hypertension 2013; 62: 1138–45.

When you visit your health care provider, a blood pressure measurement is one of the most important routine tests you’ll have.

Blood pressure is the force exerted by your blood against your arteries. As your heart pumps, it forces blood out through arteries that carry the blood throughout your body. The arteries keep tapering off in size until they become tiny vessels, called capillaries. At the capillary level, oxygen and nutrients are released from your blood and delivered to the organs.

Types of Blood Pressure

There are two types of blood pressure: Systolic blood pressure refers to the pressure inside your arteries when your heart is pumping; diastolic pressure is the pressure inside your arteries when your heart is resting between beats.

When your arteries are healthy and dilated, blood flows easily and your heart doesn't have to work too hard. But when your arteries are too narrow or stiff, blood pressure rises, the heart gets overworked, and arteries can become damaged.

Measuring Blood Pressure

Blood pressure is measured with an instrument called a sphygmomanometer. First, a cuff is placed around your arm and inflated with a pump until the circulation is cut off. A small valve slowly deflates the cuff, and the doctor measuring blood pressure uses a stethoscope, placed over your arm, to listen for the sound of blood pulsing through the arteries. That first sound of rushing blood refers to the systolic blood pressure; once the sound fades, the second number indicates the diastolic pressure, the blood pressure of your heart at rest.

Blood pressure is measured in millimeters of mercury (mm Hg) and recorded with the systolic number first, followed by the diastolic number. For example, a normal blood pressure would be recorded as something under 120/80 mm Hg.

Blood pressure readings can be affected by factors like:

• Smoking
• Coffee or other caffeinated drinks
• A full bladder
• Recent physical activity

Blood pressure is also affected by your emotional state and the time of day. Since so many factors can affect blood pressure readings, you should have your blood pressure taken several times to get an accurate measurement.

What Is Normal Blood Pressure?

Experts consider normal blood pressure to be less than 120/80 mm Hg. Based on population data, about 42 percent of American adults have normal blood pressure. At one point, blood pressure at or above 120/80 and less than 140/90 was considered normal to high; these numbers are now considered pre-hypertensive. Blood pressure consistently at or above 140/90 is considered high blood pressure or hypertension.

Blood pressure normally rises as you age and grow. Normal blood pressure readings for children are lower than for adults, while blood pressure measurements for adults and older teenagers are similar.

Blood pressure can also be too low, a condition called hypotension. Hypotension refers to blood pressure lower than 90/60. Symptoms of hypotension include dizziness, fainting, and sometimes shock.

Checking Blood Pressure at Home

Many people can learn to check their blood pressure at home. You can buy blood pressure kits that use the cuffs or electronic digital technology at your pharmacy, a medical supply store, or an online retailer.

Since high blood pressure can exist without any symptoms, it is important to know your numbers. High blood pressure can cause stroke, heart attack, heart failure, and kidney failure.

Getting your blood pressure checked is quick, painless, and one of the most important things you can do to better your health.