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Friday, January 20, 2012

Who Knows What Their Blood Pressure Is?



     Everyone knows that blood pressure is one of the most important variables in health. Uncontrolled blood pressure leads over many years to strokes, heart attacks, peripheral vascular disease, aneurysms, and heart failure. 
     Most people know that the recommended level of blood pressure is to have the upper number (systolic pressure) be less than 140 mm Hg, and to have the lower number (diastolic pressure) less than 90 mm Hg.  The systolic number is the level of pressure achieved in the arteries when the heart contracts, and the diastolic number is the level of pressure in the arteries when the heart relaxes in between beats. Of these two numbers the upper systolic pressure number is the more important.
     So, what's your blood pressure? How would one know? Most people know (if they can remember it) their blood pressure from a visit to the doctor's office. But is the number you get from the doctor's office the correct number? A large number of new studies suggests that it is not. 
     First, there is the factor of "white coat hypertension," which by now most of my patients seem to know about; this is when your blood pressure is transiently elevated because one may feel somewhat nervous or anxious about going to the doctor. Pain is another factor that will elevate the blood pressure in a doctor's office. 
     A second factor is that in the busy flow of doctors' office practice, the correct technique for measurement may not be employed. According to the experts, the proper way of measuring blood pressure is to check it after at least 5 minutes of quiet sitting waiting for the doctor. In most practices, the nurse checks it as soon as or right before leading a patient into the exam room, which is not optimal. Usual practice, however, is for the doctor to re-measure any high readings after 5 minutes has passed. If the patient has been waiting for 45 minutes to an hour for the doctor, however, the blood pressure may be elevated just due to aggravation.
     The expert recommendations also call for the blood pressure to be taken while the patient is sitting upright in a chair with his/her back supported and the feet flat on the floor. Checking the patients' blood pressure while they are sitting on the exam table with their backs unsupported and their feet dangling in the air is not consistent with these standards, but it is, in fact, the most common way blood pressure is measured in the office. 
     Other problems that occur in doctors' office are the use of an incorrect cuff size (cuffs that are too small tend to elevated the pressure readings) due to an inexperienced staff person. Also, the blood pressure devices themselves can get banged up, dropped, or just old and no longer give accurate readings.
     For all of these reasons and some others a single blood pressure measurement in a doctor's office is simply not a reliable indicator of the true blood pressure.  A new study in the Annals of Internal Medicine* concludes that: "Physicians who want to have 80% or more certainty that they are correctly classifying patients' BP control should use the average of several measurements. Hypertension quality metrics based on a single clinic measurement potentially misclassify a large proportion of patients." The data from this study show clearly that patients could not be classified as having BP that was in or out of control with 80% certainty on the basis of a single clinic systolic blood pressure measurement anywhere in the range from 120 mm Hg to 157 mm Hg. The investigators recommend obtaining an average of several measurements and feel that the optimal number of readings to average is 5 to 6.
     Based on several other studies it now appears that the optimal way to measure and manage patients' blood pressure is for the patients to monitor their blood pressure at home with the increasingly accurate and inexpensive automatic measuring devices that are now available. This is actually better than using the numbers obtained in the doctor's office, even if the doctor does go through the trouble to average 5-6 readings. (Most don't!)
     I advise patients not to be obsessive about it. (This tends to raise your blood pressure.) There is no point in checking it several times a day; nor is there any need really to check it more than twice a week. I tell most patients that once a week is fine. Ideal management calls for patients to bring into their doctor a list or log of at least 5-6 recent measurements so that a reliable average blood pressure may be obtained. In the near future, I expect that the makers of the blood pressure devices will computerize and memorize hundreds of measurements so that a continuous average is reported automatically. Until then we'll just have to obtain an average the old fashioned way--add up all the numbers and divide by the number of readings. The improvement that should come soon to doctors' offices is that electronic medical record system will begin to automatically calculate the average of multiple physician readings.
     It is certainly clear to me in my practice that blood pressures vary quite erratically for many patients, and I only make my decisions on blood pressure medication adjustment based on an average blood pressure. I recommend that all patients who have been told that they have high blood pressure get themselves a home blood pressure measuring device (now available for less than $50). If they can bring in at least 5-6 readings from home every 4 months we will really be able to do a great job of managing hypertension.

* References: (Powers BJ et al, "Measuring blood pressure for decision making and quality reporting: Where and how many measures?" 2011; 154: 781-788; editorial by Appel LJ et al., "Improving the measurement of flood pressure: Is it time for regulated standards?" 154: 836-7) 

1 comment:

  1. Blood pressure monitors can save your life, giving you a warning sign that your pressure is heading toward the sky. In addition, they can save you time and convenience because you don't always have to go to your doctor to get a blood pressure reading. Ambulatory blood pressure monitors perform while you work, play, or sleep, giving an accurate reading of your pressure throughout the day.

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