The Ups & Downs of Blood Pressure
Dr. Paul Whelton
We took this question to Paul Whelton, clinical professor and Show Chwan Health System Endowed Chair in Global Public Health at Tulane University in New Orleans. Whelton is the chair of the committee that wrote the new Guideline for the Prevention, Detection, Evaluation and Management of High Blood Pressure in Adults, A Report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines, published in November.
“People should be concerned if they’re not seeing fluctuations because that means they’re probably dead,” Whelton said. “If you’re alive, your blood pressure is going to fluctuate, it’s supposed to — you know, fight or flight.”
So, our blood pressures do move around quite a bit and there are a lot of things that we know will predictably lead to higher or lower pressures.
Of course, that fluctuation can be problem when you are trying to diagnose or treat high blood pressure (HBP) because it presents something of a moving target. But after decades of measuring BP, doctors know many of the factors that lead to higher and lower measurements.
“There are systematic or predictable sources of change in blood pressure, and we try to control for those when we are measuring pressure,” Whelton said. “Then there are also random or unpredictable sources of change, and we can control for those, too.”
Starting with the obvious, BP measurement needs to be done correctly. “It’s really, really, really important if we’re calculating a person’s cardiovascular risk and making decisions about treatment that may be lifelong, to make sure that we’re doing a good job to get the measurement right. Clinicians, nurses or pharmacists — anyone taking these readings — owe it to the patient to take the time to get the measurement right. Sadly, despite what’s been in recommendation after recommendation from AHA and others, we still have a lot of sloppy measurements being done, and there’s no excuse for it.”
Second obvious point, once is not enough. “One blood pressure reading is not an appropriate way to diagnose hypertension,” Whelton said. If BP fluctuates, and we all better hope it does, the way to compensate for that variation is to take an average of at least two readings at least one minute apart. “Averaging within the visit is very valuable, but averaging across visits is even more important. We usually like to space those visits out by about a week. For practical purposes, averaging two or three readings is enough to deal with most of the random error — two or more measures on two or more occasions, and you’re golden in terms of minimizing random error.”
In addition to random error, there is systematic error. This relates to things that doctors know influence the level of blood pressure. “Because these errors are predictable, we try to control for them,” Whelton said.
Because BP rises with activity, the first recommendation to reduce systematic error is that there should be a wait period. “In our guideline, we recommend five minutes of quiet rest before the measurement is taken,” he said. In addition, patients should empty their bladder beforehand.
The second recommendation regards the person’s posture and arm position. “It’s important that they be in a chair with a solid back, their feet on the ground, their arm supported, and the cuff really should be at the level of the heart,” he said. The patient’s arm should be bare, and he or she should not be lying down.
The third thing is that the person not be engaged in other activities — not talking, texting or searching for restaurants on their cellphone. “The person who’s taking the blood pressure, whether a clinician or a technician, should not engage them in conversation during the rest period or measurement either,” he said.
Fourth, you need to have the proper cuff size. “That’s almost foolproof these days because all cuffs are marked so that you just look at the markings on the cuff,” he said. In other words, one size does not fit all — a child’s cuff on an adult will not give an accurate reading.
Out-of-Office Monitoring: ABPM vs HBPM
There are two types of out-of-office BP monitoring — ambulatory BP monitoring (ABPM) and home BP monitoring (HBPM).
ABPM is used to obtain out-of-office BP readings at set intervals, usually over a period of 24 hours. ABPM is often used to supplement BP readings obtained in office settings. Patients wear a recording monitor (usually hanging from their belt during daytime recordings) attached to a cuff that records and stores BP measurements. “The monitors are usually programmed to obtain readings every 15 to 30 minutes throughout the day and every 15 minutes to 1 hour during the night,” Whelton said. The measurements are conducted while individuals go about their normal daily activities. The record of the readings is downloaded by the clinician and helps confirm an office-based diagnosis of hypertension or guide therapy.
HBPM is also used to obtain a record of out-of-office BP readings. In this method, the BP readings are taken by a patient at different times during the day. “It is generally agreed that ABPM is better than HBPM, but the latter is cheaper and more feasible, practical and acceptable to patients,” Whelton said. Both ABPM and HBPM provide BP estimates based on multiple measurements.
Individuals who are going to do home blood pressure measurements need to know how to obtain accurate measurements; they need to be instructed on how to use the device, which is simple and straightforward; and they need to be using a device that is clinically validated. Look for information on the packaging of the device that says it has been clinically validated for accuracy.
“There are poor-quality devices produced for commercial purposes, but there are many that are well-validated as well,” Whelton said. “Well-validated devices don’t have to be expensive. Many devices will actually record and store the BP readings. If the device doesn’t record them, then write them down and bring that written record to your appointment. That’s a good opportunity for discussion with your clinician.” The American Heart Association’s Check. Change. Control BP Tracker is a convenient way to record BP readings. It’s free, convenient and confidential.
Does time of day matter when measuring BP?
Whelton says there is no general agreement on when to take your BP, but as far as keeping track of it, you should take it at the same point in your day, e.g., upon rising or at bedtime. As for taking it before or after taking medication, follow your doctor’s preference. “It’s very common for clinicians to advise that the patient measure their blood pressure just before taking their antihypertensive medication or to wait for an hour or two after,” he said. “But that’s something where it would be a good idea to have a discussion with the clinician. The most important thing is to be consistent.”
White-coat and masked hypertension
White-coat hypertension describes the phenomenon where people have apparent high BP in the office but out of the office their pressures are much lower. “Most studies have suggested that this subset of people don’t seem to have a very high risk of complications from high blood pressure,” Whelton said. “They seem to have a risk pattern that is more consistent with lower pressures. So, the assumption is that they’re probably reacting to the white coat. That’s the circumstance in which we doctors say, ‘It would be really smart to get out-of-office pressures, preferably ambulatory blood pressure monitoring, but on a practical level, if you’re not going to be able to do that or choose not to do it, at least good home blood pressure monitoring.’ Certainly, we don’t want to start lifelong drug treatment in someone who has white coat rather than sustained hypertension, but we do encourage all of the appropriate lifestyle changes and will want to monitor them. Some of those people will go on to develop sustained hypertension over time.”
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Masked hypertension is the mirror opposite of the white-coat effect. “It is more sinister and disturbing,” he said. “This group appears to have normal pressure in the office, but when we measure their pressures out of the office, they have high pressures. They have a risk profile that is very much like traditional, sustained office hypertension. These people need treatment, especially if they have some indication of target organ damage, like left ventricular hypertrophy. These conditions are quite common, as much as 10 percent or 30 percent, depending on the particular group.”
“When you do these ambulatory blood pressure monitorings, we see that most people’s blood pressure goes down at nighttime,” Whelton said. “We call it dipping. There are some people who don’t seem to dip; we call them ‘non-dippers.’ That’s more common in African-Americans, but we don’t know why.”
Other things people do affect their measurements. “Caffeine and smoking will certainly have an impact,” Whelton said. “Both have a short-term impact of raising blood pressure. Likewise, drinking alcohol immediately prior to a blood pressure measurement can result in a higher blood pressure. As a consequence, we recommend no smoking or drinking during that rest period. There are also many meds and over-the-counter drugs that can result in an increase in blood pressure.”
As for common heart medications like antiplatelets, anticoagulants and statins, Eric MacLaughlin, professor and chair in the Department of Pharmacy Practice at Texas Tech University Health Sciences Center in Amarillo, and a member of guideline committee, indicates that they do not cause BP to increase.