19 July 2019 Blog Post: Blood Pressure Measurements

When it comes to blood pressure measurements, patients often ask me, “Which one matters? The top one or the bottom one?”
 
One thing that Medicine is exceptional at doing is replacing simple terms with complex ones. Blood pressure measurement is no exception. The ‘top one’ is termed ‘systolic’ blood pressure and represents the amount of pressure in your arteries during the contraction of your heart muscle. The ‘bottom one’ is termed ‘diastolic’ blood pressure and represents the pressure when your heart muscle is relaxed between beats.
 
Studies have gone back and forth about which one ‘matters’ (i.e. is more predictive of bad outcomes) more. Generally studies have shown a greater predictive value of the systolic blood pressure. However, the increased use of non-invasive or electronic blood pressure units (NIBP) may lead to inaccuracy. In 2013, a group of ICU researchers where they compared blood pressure from an invasive arterial line to NIBP readings, they determined that the NIBP significantly overestimated the systolic blood pressure when compared to the arterial line.
 
A study published today in the New England Journal of Medicine shows that both matter, although systolic blood pressure (the top number) exerted a greater effect. The investigators looked at composite outcome of myocardial infarction (heart attack), ischemic stroke, or hemorrhagic stroke over a period of 8 years. Data from 1.3 million (!) adults was used in the analysis.
 
Recently revised guidelines with two different thresholds (≥140/90 mm Hg and ≥130/80 mm Hg) for treating hypertension. So now we know, both the top number and the bottom number matter.

Effect of Systolic and Diastolic Blood Pressure on Cardiovascular Outcomes

Alexander C. Flint, M.D., Carol Conell, Ph.D., Xiushui Ren, M.D., Nader M. Banki, M.D., Sheila L. Chan, M.D., Vivek A. Rao, M.D., 
Ronald B. Melles, M.D., and Deepak L. Bhatt, M.D., M.P.H.

Abstract

Background:

The relationship between outpatient systolic and diastolic blood pressure and cardiovascular outcomes remains unclear and has been complicated by recently revised guidelines with two different thresholds (≥140/90 mm Hg and ≥130/80 mm Hg) for treating hypertension.

 

Methods:

Using data from 1.3 million adults in a general outpatient population, we performed a multivariable Cox survival analysis to determine the effect of the burden of systolic and diastolic hypertension on a composite outcome of myocardial infarction, ischemic stroke, or hemorrhagic stroke over a period of 8 years. The analysis controlled for demographic characteristics and coexisting conditions.

 

Results:

The burdens of systolic and diastolic hypertension each independently predicted adverse outcomes. In survival models, a continuous burden of systolic hypertension (≥140 mm Hg; hazard ratio per unit increase in z score, 1.18; 95% confidence interval [CI], 1.17 to 1.18) and diastolic hypertension (≥90 mm Hg; hazard ratio per unit increase in z score, 1.06; 95% CI, 1.06 to 1.07) independently predicted the composite outcome. Similar results were observed with the lower threshold of hypertension (≥130/80 mm Hg) and with systolic and diastolic blood pressures used as predictors without hypertension thresholds. A J-curve relation between diastolic blood pressure and outcomes was seen that was explained at least in part by age and other covariates and by a higher effect of systolic hypertension among persons in the lowest quartile of diastolic blood pressure.

 

Conclusions:

Although systolic blood-pressure elevation had a greater effect on outcomes, both systolic and diastolic hypertension independently influenced the risk of adverse cardiovascular events, regardless of the definition of hypertension (≥140/90 mm Hg or ≥130/80 mm Hg). (Funded by the Kaiser Permanente Northern California Community Benefit Program.)

𝗦𝗶𝗴𝗻 𝗨𝗽 𝗳𝗼𝗿 𝗢𝘂𝗿 𝗡𝗲𝘄𝘀𝗹𝗲𝘁𝘁𝗲𝗿

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