Are we measuring blood pressure the wrong way?

You probably know that mild elevations of blood pressure increase your risk of strokes and heart attacks. But measuring blood pressure accurately is not as easy as you would think.

There are many variables that can influence blood pressure readings. The most common way to measure blood pressure is with the arm cuff that most doctors use. But is there a more accurate way?

Researchers at Cornell University in New York have been studying the measurement of central aortic blood pressure as opposed to brachial blood pressure. Brachial blood pressure refers to the brachial artery in the arm. Measuring the brachial blood pressure uses a pressure cuff around the upper arm. This is how just about every doctor’s office and hospital measures blood pressure.

But central aortic blood pressure is different.

Central aortic pressure refers to the pressure in the aorta as it comes off the heart. In the past, in order to measure central pressure, your doctor had to place a catheter into the aorta. But now, new technology makes it easy to measure central aortic pressure. All your doctor needs is a device that looks like a blood pressure cuff. He attaches it to your wrist and connects it to a computer. It takes less than five minutes.

Central systolic pressure readings are often very different from the brachial pressure readings. This is because of pulse waves.

As the blood comes out of the heart and pulses down an artery, it will eventually hit an area where the artery splits. When it hits this area, some of the blood will bounce back in the opposite direction, creating an opposing pulse wave. This opposing wave influences the pressure in the artery.

And since the aorta and the brachial artery have different anatomies, the reflecting pulse waves are also going to be different. This causes the pressures to be different.

The other factor is the stiffness of the arteries. As we age, our arteries stiffen and develop more plaque. This will cause the rebounding pulse wave to have an even greater impact.

Why Is the Aortic Pressure More Accurate?

The aorta is closer to the heart and the brain. So the researchers believed that the pressure in this area would better represent the load imposed on the coronary and cerebral arteries than the brachial pressure does. If this is true, the central aortic pressure would be a much better indicator of heart attack and stroke risk than the traditional brachial pressure.

And that's just what they found.

They studied a population consisting of 3,520 Native Americans. They used ultrasound technology to determine how thick their carotid arteries were, and how much plaque they had.

The researchers measured the central aortic pressure with the new wrist cuff. And they measured the brachial pressure using the standard blood pressure cuff. Then they looked to see which pressure readings were more accurate at predicting a stroke or a heart attack.

They found that the central aortic pressure was able to predict cardiovascular events more strongly than brachial pressure. They also found that the central pressure correlated about 15% better with carotid artery thickness and plaque formation than did the brachial pressure.

What You Should Do

Whatever method you use, be sure to take the measurement accurately.

Many people are on blood pressure medication that don’t need to be simply because their blood pressure was not accurately measured. I’ve written in the past about the most accurate way to measure brachial arm pressure.

It’s important to remember that your blood pressure is not a static number. The body raises and lowers the blood pressure depending on the circumstances it finds itself in. When we are more in a sympathetic “Fight or Flight” mode, the body requires a higher head of pressure. When we are more in a parasympathetic mode, a lower pressure is required.

High blood pressure is not defined by having readings that are occasionally high any more than having low blood pressure is defined by having readings that are low. High blood pressure is defined by having elevated readings all the time. This will create damage to your arteries over time.

Here Is How I Tell My Patients to Check Their Blood Pressure

(1) Buy an automated arm blood pressure monitor. If your arm is much larger than average, you will also need to buy an extra-large cuff. A cuff that is too small can give a falsely elevated reading.

(2) Before taking your measurement, be sure that you are seated quietly for at least a minute with your arm resting on a table at the level of your heart.

(3) Do it before you have any caffeine, and before exercise.

(4) After the first measurement, wait 15 seconds and take a second measurement. If they are essentially the same, record that reading. If they are different, measure your pressure a third time. Record the lowest reading as your blood pressure.

(5) Do this twice a day, usually before breakfast and again just before dinner, for about two weeks.  Throw out any numbers that are unusually high or unusually low. These are called outliers and only represent isolated readings. Average the remaining numbers out, and that is your blood pressure. If that number is greater than 140/90, you should initiate some form of treatment.

One more thing. As we get older and our arteries stiffen, we need a higher head of pressure to circulate the blood adequately. So, the older you are, higher blood pressure readings both brachial and central are necessary.