When it is best to take your blood pressure, and the latest about salt
When is it best to take your blood pressure?
Many physicians recommend taking blood pressure in the evening just before retiring. In part, this may be due to the belief that nighttime blood pressures are more predictive of future complications and events. In searching for answers on different web sites, recommendations vary considerably. So when is best?
Blood pressure elevations should not be neglected
Uncontrolled high blood pressure may lead to heart attacks, strokes, kidney disease, heart failure, ad abnormal rhythms of the heart, including sudden death, and blindness. The further bad news is that over 91% of Americans will develop hypertension in their lifetime, and now about one in three of us have high blood pressure of one type or another. Even worse, nearly one-third who have it are unaware they do. There are also many misconceptions about blood pressure, some of which are addressed on the American Heart Association site.
Blood pressure generally goes down during sleep, and rises upon awakening. Physical and mental activity and other stimuli raise blood pressure normally—it goes up to provide additional blood flow for activities and is regulated by a complex set of reflexes and hormonal adjustments. The early morning rise in blood pressure does add some risk for a heart attack or stroke at that time. Some people have blood pressures that do not drop by the time they go to bed, and surge excessively in the early morning—they are the ones who have greater risk of premature death.
How to Take Blood Pressures
Measurement of blood arterial pressure is done with an inflatable rubber cuff, standardized for medium-sized arms, and a gauge. The standard mercury column has largely been replaced by other devices, because of the danger of column breakage and accidental mercury poisoning. For larger arms, a larger cuff must be used, lest the pressure read will be falsely high. For smaller arms a smaller cuff is necessary. Failure to do this may result in a falsely low blood pressure reading. For the same reasons, a blood pressure cuff to take a reading in the thigh must be larger. Measurement of the blood pressure from a cuff at the wrist is not recommended, although recording pressure directly from a catheter in an artery at the wrist does reflect the pressure accurately.
In taking blood pressure, a doctor or nurse inflates the cuff, which momentarily interrupts the blood flow in the (brachial) artery deep in the elbow area, then listens on top with a stethoscope for the appearance, change in character, and disappearance of sound produced by the surging pulse. Unfortunately, many blood pressures are taking incorrectly. And the automatic blood pressures are certainly not infallible–they are just machines. Since major changes in medication are usually based upon just this one reading, an error can cause the doctor to make major, inappropriate adjustments to prescription drugs.
AHA Guidelines call for the patient to be sitting still, quietly, in a chair at least 5 min before the blood pressure is measured, with the arm supported at the level of the heart, not have caffeine, alcohol, or smoke for at least ½ hour beforehand, and have the proper size cuff placed on the skin, not over an irregular piece of clothing. There should be no conversation, no talking on a cell phone, or TV. The area under the cuff should be at least 1” above any bony part of the elbow, firmly seated on soft tissue. The cuff material should be firmly layered flat, with the final Velcro grip uniform, so that when the cuff is inflated there are no layers that inflate alone, trapping air in a particular area, so that the cuff “bubbles up” in pockets. After inflation, there should be no irregularly distributed lumps and bumps of air, nor material, in the cuff. Cuffs should be deflated at a rate of 2-4 mmHg per heartbeat. A paper in the AMA News last year called for improvement in blood pressure-taking, since the numbers are frequently the only basis for important changes in treatment. Although the diagnosis of hypertension depends upon high measurements on two to three separate occasions, even a single elevated reading has predictive value. A single high reading should not be interpreted as a clean bill of health, even if two are normal afterwards. Most of the time, patients tend to “explain away” elevations, and underestimate the seriousness of the problem.
Home blood pressure monitoring is also a useful addition to office visits. While both aneroid and electronic monitors for home use are available, the electronic ones, with both automatic inflation and deflation, are preferred. Wrist and fingertip models are less accurate. Ask your doctor for recommendations, and pre-fit the cuff to your arm size before purchasing. Then compare the machine’s readings to those in your doctor’s office immediately, and at less-than-yearly intervals. Pressures may be taken immediately after arising, 3-5 hours after that, then 2 in the evening. All should be recorded methodically. Once a pattern is established, your physician will suggest the best times to monitor treatment. This will depend upon your lifestyle, exercise, and which type of medication you are taking. Most medications do not last 24 hours, and this works for most people because their blood pressure falls in the evening. A new tool available for following blood pressure is accessible at www.healthvault.com, or at americanheart.org/BloodPressureManagementCenter.
In the May, 2008 issue of Hypertension, The American Heart Association (AHA) and the American Society for Hypertension (ASH) jointly issued a seminal Call To Action On Use For Home Blood Pressure Monitoring, with the full content of the article available as well.
The presence of office staff when blood pressures are taken may raise it, commonly known as “white coat” hypertension. For this and other reasons, it is sometimes useful to monitor blood pressures over a period of time outside the office. To clarify or solidify the diagnosis, ambulatory blood pressure monitoring (ABPM) may be requested. A device is worn for 1-2 days, and includes a cuff which automatically inflates at 15 min intervals while awake and every 30 min at night. Readings are stored, and later transferred to a computer in a doctor’s office. A diary of eating, sleeping, physical activity, emotions, and drugs taken should accompany the recording for best interpretation. Ambulatory monitoring is used to exclude the white coat effect, or help decide whether treatment is adequate. Although not routine, it has been called the “gold standard” of diagnosis and treatment, and should be done more often. In medicine, generally when measurements are not taken, or less reliable ones are used, the true severity of the condition is unrecognized. When ambulatory BPs are used, a study in the American Journal of Medicine, Dec 2008, showed only 15% of patients being treated had acceptable pressures throughout the day. Only about 40% of patients taking medications for hypertension have their blood pressures under control, using office and/or home blood pressure readings.
Using ambulatory monitoring, the normal 24-hour blood pressure pattern has been identified as follows:
- BP rises upon awakening, peaks around midmorning, perhaps 10 AM, and decreases throughout the day into the night to reach a trough early the next morning, perhaps 3AM.
- From that point it rises slowly, but the rate that it rises increases upon awakening, perhaps 6AM, as physical activity begins.
Dipping–that’s what blood pressure does…
Traditionally it has been believed that raised night-time readings, or failure to “dip” at night, typically about 10%, may predict cardiovascular complications. But a paper in the journal Lancet (October 6, 2007;370(9594):1219-1229) questioned this conventional view. The authors found that while night time blood pressures were better at predicting premature death. The daytime readings were also good at predicting all cardiovascular events—but not in patients taking antihypertensive drugs. Since most such medications are taken in the morning, by nightfall their effects wane, and blood pressure rises. In any case, when readings are higher at night than in the day, there is a higher risk of death from all causes. The authors concluded that blood pressures should be taken throughout the day.
High blood pressure is classified in stages, as indicated in this table.
A word about salt. Although the debate about whether salt should be restricted for healthy people continues, there is no question that for populations, and as a public health measure, salt intake is much too high, and restriction lowers blood pressures. In fact, excessive salt intake is responsible for about 17-30% of all high blood pressure worldwide. The ill effects of excessive salt intake in relation to the needs of the human body, which are extremely small, is not just blood pressure elevation. Salt intake drives up the incidence of cardiovascular disease, in part because blood pressure elevations amplify and accelerate atherosclerosis or coronary artery disease. A recent paper in the British Medical Journal found that just an extra 5 grams of salt, about one teaspoon, raises rates of stroke by 23% and all cardiovascular disease by 17%. Another study published in the New England Journal of Medicine confirmed the report, calculating that lowering dietary salt by 3g/day would lower new cases of heart disease by about 90,000/year, stroke by 49,000/yr, heart attacks by 76,500/yr and deaths from any cause by 68,000/yr. This amounts to between $10-24 billion in health care costs annually, equivalent to 293,000 human life-years! An accompanying editorial called lowering dietary salt intake compelling, inexpensive, and highly effective. Even just 1g less of salt would produce substantial public health improvements.
In addition, recently a careful and scholarly review of all the evidence concerning salt prompted the American Heart Association to revise recommendations for salt intake in setting 2020 goals for heart health promotion and reduction of heart disease. Now the current recommendation is a daily intake of less than 1,500 milligrams of sodium (=3.8g of salt), down from a prior recommendation of 2,300mg of sodium (5.8g of salt). Some of our current fast food and not-so-fast meals easily contain more than this in one sitting. Adhering to this amount is definitely a worthwhile challenge, but a must for anyone with high blood pressure. Much of the lack of blood pressure control that patients and physicians face is actually due to unrecognized excess salt intake. The most frequent trigger for hospital admissions in people with heart failure is due to a sudden increase in salt consumption.
Unfortunately, salt is “hidden” in almost all foods we all commonly consume. Yet another reason to prepare foods yourself at home, favor a diet high in fresh vegetables and fruits, and avoid processed, pickled, and canned foods.
Conclusion
A sensible approach, at the outset, is to take your blood pressure at different times during the day, depending upon your schedule. If you work, take a reading in the morning, an hour after you return home, and later in the evening. It should be done at the same time each day, at the same point in your routine. If you are taking medication for your blood pressure twice a day, you may want to take it just before your evening dose, to see how long the first dose kept your blood pressure down. If you have symptoms, then take your blood pressure right away when you have them. Out of interest, a spot check or two at the moment you awaken might be of interest. Your doctor will want to know this initial pattern, to better advise when the next readings should be taken, and perhaps begin or adjust the medication dose and/or timing. And, please, read labels on every food you pick up at the supermarket before you buy it, keeping in mind the 1500 mg/day ceiling.
