[upbeat intro music]
[Dr. Handy] Hi, welcome to Harrison's Podclass where we discuss important concepts in internal medicine. I'm Cathy Handy. [Dr. Wiener] And I'm Charlie Wiener, and we're coming to you from the Johns Hopkins School of Medicine. Welcome to episode 69, a 65-year-old with an elevated blood pressure. So a 65-year-old man comes into the clinic for a routine visit. He last saw you about four years ago and did not have any medical problems and was not on any prescription medications.
Before you were even able to see him, the medical assistant in your office calls you because his blood pressure is 194/106. - Now Cathy, before you interrupt me, - [Dr. Handy chuckles] [Dr. Wiener] --I'm going to go right to the question because it's going to frame the discussion here. - Okay? - [Dr. Handy] Okay. [Dr. Handy] So the question asks, which of the following statements regarding blood pressure measurements is true?
Option A. systolic blood pressure increases and diastolic blood pressure decreases when measured in more distal arteries. Option B. systolic leg blood pressures are generally as much as 20 mmHg lower than arm systolic blood pressures. Option C. the difference in blood pressure measured in both arms should be less than 20 mmHg.
Option D. the concept of white coat hypertension, that is blood pressure measured in the office or in a hospital setting being significantly higher than in non-clinical settings has been shown to be a myth. And Option E. is using a blood pressure cuff which is too small will result in a marked underestimation of the true blood pressure. [Dr. Handy] Okay, so this is a good topic. As clinicians, we spend a lot of time focusing on the abnormality and what can be causing the abnormality.
So for example, in this case, going through the differential diagnosis of hypertension which is, I think initially what I was inclined to do before I let you finish with the question, but it's important for us to remember that all tests have limitations and when performing tests we must remain cognizant not only of the test characteristics but also think about the test methodology.
And this is really a great example of making sure we're obtaining accurate data before we make any therapeutic conclusions. [Dr. Wiener] Okay. So saying that in addition to understanding things like sensitivity, specificity, positive predictive value, we also must know that we're making accurate measurements before we draw any conclusions.
[Dr. Handy] Exactly. And for example, there was a recent report in the New England Journal of Medicine, demonstrating that in Black patients, pulse oximetry is notably less accurate compared to arterial blood gas. And they found that Black patients had nearly three times the frequency of occult hypoxemia defined as an arterial oxygen saturation less than 88% that was not detected by pulse oximetry compared to white patients. [Dr. Wiener] So true.
We often make such important conclusions from the vital signs but we seldom think about the validity of the measurements. In this case we're talking about blood pressure measurement. What are your thoughts in this case? [Dr. Handy] All right, let's go back to the basics. So first let's go through how to manually check blood pressure because that is what you would do here once you brought the patient back to the exam room.
So the length and the width of the blood pressure cuff/bladder should be 80% and 40% of the arm circumference respectively. So a common source of error in practice is to use an inappropriately small cuff that would result in a marked overestimation of the true blood pressure, or an inappropriately large cuff that would result in an underestimation of the true blood pressure.
The cuff should be inflated to 30 mmHg above the expected systolic pressure, and then the pressure release rate should be about 2-3 mmHg per second. And systolic and diastolic blood pressures are defined by the first and the fifth Korotkoff sounds respectively. And blood pressure is best assessed at the brachial artery level, though it can be measured at the radial, popliteal or even the pedal pulse level.
[Dr. Wiener] Okay. So that makes option E. wrong, a small blood pressure cuff will result in an overestimation not an underestimation of true blood pressure. You mentioned the other arteries. Are there differences based on where you measure? [Dr. Handy] Yeah and just going through the answers, so option A. is true and it's the correct answer. So in general, systolic pressure increases and diastolic pressure decreases when measured in more distal arteries.
[Dr. Wiener] Okay. Well, then why don't you go through the other answer choices and why they're incorrect? [Dr. Handy] Okay. Blood pressure should be measured in both arms and the difference should be less than 10 mmHg. A blood pressure differential that exceeds this threshold may be associated with atherosclerotic or inflammatory subclavian artery disease, supravalvular aortic stenosis or aortic coarctation, or aortic dissection.
Option B. talks about the difference between the arm and the leg pressures. So systolic blood pressures are usually as much as 20 mmHg higher, not lower as the question mentioned, than systolic arm pressures. And greater leg and arm pressure differences are seen in patients with chronic severe aortic regurgitation as well as patients with extensive and calcified lower extremity peripheral artery disease.
The ankle-brachial index or ABI should be about 1.0-1.4 and that's lower pressure in the dorsalis pedis or posterior tibial artery divided by the higher of the two brachial artery pressures. And abnormalities in the ABI are a powerful predictor of long term cardiovascular mortality. [Dr. Wiener] Great. What about the myth of white coat hypertension?
[Dr. Handy] So we do need to acknowledge that even when properly done, the blood pressure measured in an office or hospital setting may not accurately reflect the pressure in other venues. White coat hypertension is defined by at least three separate clinic-based measurements above the threshold for hypertension and at least two non-clinic-based measurements below the threshold for hypertension in the absence of any evidence of target organ damage.
Individuals with white coat hypertension may not benefit from drug therapy, usually lifestyle modifications and cardiovascular disease risk reduction should be recommended though for these patients. [Dr. Wiener] And what threshold do you have for considering whether or not patients are even hypertensive to begin with? [Dr. Handy] From an epidemiologic perspective, there's no obvious level of blood pressure that defines hypertension.
In adults there's a continuous incremental risk of cardiovascular disease, stroke and renal disease across levels of both systolic and diastolic blood pressure. The Multiple Risk Factor Intervention Trial, or MRFIT as it's more commonly called which included over 350,000 male participants, demonstrated a continuous and graded influence of both systolic and diastolic blood pressure on coronary heart disease mortality extending down to systolic blood pressures of 120 mmHg.
Similarly, results of a meta-analysis involving almost a million patients indicated that ischemic heart disease mortality, stroke mortality and mortality from other vascular causes are directly related to the height of the blood pressure beginning at 115/75, without evidence of a threshold. Cardiovascular disease risk doubles for every 20 mmHg increase in systolic and 10 mmHg increase in diastolic pressure.
And among older individuals, systolic blood pressure and pulse pressure are more powerful predictors of cardiovascular disease than is diastolic blood pressure. [Dr. Wiener] Wow. You said that there is a gradation of risk related to blood pressure. As a result of that, haven't the recommendations changed recently on what is the ideal or the optimal blood pressure? [Dr. Handy] Yeah, so some traditionally acceptable blood pressures are likely not healthy.
The most recent guidelines define stage one hypertension as systolic blood pressure between 130 and 139 mmHg and diastolic between 80 and 89, and stage two hypertension would be at or above 140/90. [Dr. Wiener] Great. So the teaching points here are that blood pressure measurements can vary based on technique, and it's important to have the appropriate size cuff, consider where you're measuring the blood pressure and also consider out of office-based measurements in the untreated patient.
Also, current recommendations for the goals of treatment for blood pressure and the staging of blood pressure have been changed and require review. [Dr. Handy] And for more information you can read about this in Harrison's chapter on hypertensive vascular disease and physical examination of the cardiovascular system.
And the article that I mentioned on pulse oximetry is from December 17th, 2020 in New England Journal of Medicine by Michael Sjoding et al. [outro music] [Mr. Shanahan] This is Jim Shanahan, publisher at McGraw Hill. Harrison's Podclass is brought to you by McGraw Hill's Access Medicine, the online medical resource that delivers the latest trusted content from the best minds in medicine. Go to accessmedicine.com to learn more.