Once we’ve established that you’re breathing and you have a pulse, your blood pressure is a crucial vital sign. Even when you’re feeling well, that number can determine if you’re at risk for a stroke, heart attack, heart and kidney failure, vision loss, foot or toe amputations or the other dire consequences of blood vessel damage.
Getting the most accurate measurement is important.
If your real pressure is actually lower than what you measure, you might be over treated – and suffer side effects from too much medication. If you’re relying on incorrectly low BP readings, you’ll be lulled into a false sense of security while high blood pressure is silently damaging the vessels and organs of your body.
Here are six common ways to get the wrong number.
Position & posture
The ideal position for measuring your blood pressure is sitting with your back supported and your feet resting comfortably on the floor. If you cross your legs or clench your teeth, your blood pressure will go up. The arm on which the blood pressure cuff is attached should be supported at the level of the heart. If your arm is hanging down, the reading will be higher. If you are contracting muscles, your pressure will go up. Your arm should be supported by the healthcare provider, a table or an armrest.
The setting
White coat syndrome is when your blood pressure is higher when a doctor or nurse is measuring it. Even healthcare providers can have white coat syndrome, but hopefully their own pressures don’t go up when they look in the mirror.
If I suspect white coat syndrome, I ask my patients to measure their blood pressure at home and at work with a reliable blood pressure machine. I sometimes lend out a calibrated machine from my office. You can find a list of machines tested and approved by Hypertension Canada on the website at hypertension.ca. I often ask a patient to close his eyes and imagine that he is in his living room, but if he imagines his wife squeezing his arm and telling him to take out the trash, his pressure will be even higher.
How you breathe
You’ll get a higher reading if you hold your breath, if you are straining and when you’re talking. I politely ask my patients to stop talking and remember to breathe.
Exertion or exercise
When we exercise, the heart is working harder and both blood pressure and heart rate increase. Once we’re back to a normal resting heart rate, blood pressure is usually lower for the hour or so after exercise. The long-term effect of regular moderate physical activity, such as walking or cycling, is better blood pressure control.
If you measure your blood pressure just after running up the stairs, your reading will be higher, but after five minutes, it should be back to your usual resting level. If it isn’t, you may be deconditioned. Ask your doctor to guide you in finding an appropriate level of physical activity.
Equipment
A cuff too small for your upper arm will give a falsely high reading. A cuff too large will underestimate your pressure. Most cuffs have markings to indicate the correct fit.
If you are relying on an inaccurate or unreliable machine at home, you could be under or over treating your blood pressure. This is especially important if you have a very slow or an irregular pulse rate. If the cuff deflates too quickly, it will not pick up the moment when the pressure in your artery matches the pressure in the cuff. You may get a falsely low reading.
Most pharmacies calibrate their blood pressure machines, but the cuff will not fit every individual and after a thousand people use a machine, it may need recalibration. I frequently see patients bringing in impossibly high and low blood pressure numbers.
When I re-check their pressures and find them normal, I ask them to use the drug store machine as a random number generator for the next 6/49 draw.
Technique
Many patients have an auscultatory gap. In this case, the systolic pressure (the top number in the BP reading) is much higher than expected. When the doctor or nurse is listening over the arm as the cuff deflates, the pulse is heard, disappears and reappears before finally disappearing again at the diastolic pressure (the lower number).
If the cuff is not inflated high enough, the true systolic blood pressure is missed and mistaken for the reappearance of the pulse at a lower pressure.
With very high blood pressure, most machines will miss the top number and give a falsely reassuring reading. This can also happen in the doctor’s office if the cuff is not inflated high enough.
A lot of people re-check their blood pressure right after getting a high reading. They’ll repeat this until they get a number they like better, but with successive readings, they will get falsely low readings due to congestion of the veins in the arm. This muffles the volume of the pulse and results in an incorrect measurement. It’s better to fully deflate the cuff, take your arm out and wait at least a minute before taking another reading. Because your blood pressure has a tremendous impact on your future wellbeing, you need the most accurate measurements.
Davidicus Wong is a family physician and his Healthwise columns appear regularly in the Vancouver Courier. For more on achieving your positive potential in health, see his website atdavidicuswong.wordpress.com.
