Blood Pressure for Dummies.

05/07/11

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Doctor Aaronson is the OTHER oracle of Omaha

Doctor Aaronson, Omaha, Nebraska's OTHER Oracle. Dr. Michael Aaronson is a kidney physician specializing in Nephrology and hypertension.




 The “J Curve“: Low blood pressure is associated with increased death. High blood pressure is associated with increased death. Optimal blood pressure is associated with less death. The curve on the graph looks like a “J” hence the name.

Kidney consultants are experts at blood pressure management. Hypertension comprises 10% of the American Board of Internal Medicine Board Examination in Nephrology. (Source: Maintenance of Certification Examination Blueprint in Nephrology). Although understanding high blood pressure can be complex, I can help simplify. Providers who correctly manage the condition can help increase your lifespan. Providers who incorrectly manage the condition may hasten your death.

My charge today is to clarify key hypertension concepts. I plan to present pearls and take home points that will keep you and your loved ones who suffer from high blood pressure happy and healthy.

Let’s start with a key concept called the hypertension “J Curve” (see figure above). What we mean when we say J Curve is that there appears to be a perfect pressure range at which blood pressure does not contribute to the risk of cardiovascular disease including heart disease and stroke. This preferred range is located at the bottom of the “J.” It turns out that blood pressure that is too high or too low may lead to death (mortality). However, too high is more risky than too low, hence the J shape of the curve on the graph.




When I zig zagged all over America teaching hypertension management to primary care providers, the paradigm was “lower is better.” If you are not experiencing symptoms, the lower your blood pressure the safer you should be from disease. You could call this a slash “/” curve if you will. We basically taught that “any blood pressure load is bad.” It turns out that this thinking is incorrect because blood pressure can indeed get too low and create risk for the individual.

Consider a patient suffering from infectious septic shock, hospitalized in the Alegent intensive care unit in Omaha, Nebraska. If this patient presents with a low enough blood pressure, the patient might get a blood pressure raising medication (a pressor) to raise the blood pressure and treat the shock! Blood pressure can be too low.

Therefore the teaching that “every 20/10 decrease in blood pressure decreases the risk of death from hypertension by 50%” needs to be taken in the context of the individual patient and that patient’s comorbid conditions.

Moving on to the next point: correctly interpreting blood pressure requires one’s taking into account both the top number (the systolic bp) and the bottom number (the diastolic bp) separately and together. Clinicians consider the systolic blood pressure as more important in some situations and the diastolic blood pressure as more important in others. One key determinant of risk is your age.

    The diastolic pressure is considered more important in patients younger than 50 years old.
    The systolic pressure is considered more important in patients 50 years of age and older.

As people age, their blood vessels can stiffen. In this setting the heart pumps the blood through the body with the following result: the systolic pressure is higher and the diastolic blood pressureis lower because the arteries are less elastic than they once were.

In the past, researchers focused on diastolic blood pressure. As the American population ages, more people have isolated systolic hypertension (high top number and low to normal bottom number). Therefore, the geriatric population should focus on systolic blood pressure so that they do not have a stroke while at the same time trying to keep the diastolic blood pressure around 70.

Key point: the heart gets its oxygen requirement from the diastolic component of blood pressure. A diastolic blood pressure that is too low (bottom number less than 70) puts the patient at risk for depriving the coronary arteries of the oxygen it needs because of poor perfusion to the vessels. This untoward effect may lead to angina (chest pain) and quite possibly a heart attack.

So if we overtreat the systolic blood pressure so that a patient has “perfect” systolic blood pressure (115 mm Hg), we may put the patient at unnecessary risk. How do we do that? Both the systolic and diastolic blood pressure decrease when blood pressure medication is prescribed to patients. If the said patient’s diastolic blood pressure decreases to 40, and the patient has heart disease, that patient is at risk for a heart attack from a lack of perfusion pressure to the coronary arteries.

Moreover, recent studies suggest that a blood pressure benefit can be seen below a certain blood pressure, but no additional benefit is seen below that threshold value. In the setting of over-treatment, you may want to ask your doctor to taper down your anti-hypertensive medication. An example of lower blood pressure medicine requirements include a patient’s losing a lot of weight causing a natural decrease in her blood pressure.

So I would rather see a patient with a blood pressure of 115/40 raised to 135/60 by decreasing or stopping one of the prescribed bp medications. This approach would enable the diastolic blood pressure to increase closer to a target of 70. An added benefit: the patient would decrease some of the monies spent on medication with this approach.

I frequently use the concept of pulse pressure (systolic blood pressure minus diastolic blood pressure) to glean further information to help treat the patients I serve. A wide pulse pressure is a risk factor for heart disease. I worry about a patient with a blood pressure of 160/60 more than 150/70 because of the pulse pressure differential: 160-60=100 versus 150-70=80. The patient with the higher pulse pressure has stiffer vessels and is at more risk.

In conclusion, when evaluating blood pressure numbers and goal rate attainment, we need to keep the above concepts in mind, treating the patient and not the statistics. If you are getting treated for hypertension, consider the risks versus the benefits of the therapy. Ask your doctor what your ideal blood pressure range should be. If you have concerns about your blood pressure, consider asking Alegent Nephrology to help manage it. We are happy to help.











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