hypertension: resting time of 25 min before measuring blood pressure

 I came across a 2017 study finding that having patients relax 3-5 minutes prior to checking their blood pressure in the office was pretty inadequate: only ½ of the patients had their blood pressure stabilize in 5 minutes and it took 25 minutes for 90% of the patients' BP to stabilize (see htn bp measure after 25min rest Nature2017 in dropbox, or DOI:10.1038/s41598-017-12775-9) 

 

Details: 

-- 199 outpatients from a vascular clinic had their blood pressures assessed by automatic BP monitors every minute during 11 consecutive minutes (though they had “parameter estimates” of blood pressure for 25 minutes after the initial reading) 

-- mean age 67, 75 Kg, BMI 27, 89% men, 38% smokers 

-- hypertension 57%, dyspnea 22%, dyslipidemia 51%, MI 14% 

-- meds: ACE-i 43%, diuretics 30%, beta blockers 32%, antiplatelet drugs 46%, lipid-lowering drugs 53% 

-- 51% were assessed in the reclining position, and 49% in the sitting position 

 

Results: 

-- there was a clear decreasing trend for systolic blood pressure (SBP) over time, with a smaller but steady decline in diastolic blood pressure, while the heart rate remained unchanged during the observation period 

-- the decrease in SBP was not much different between those who were not on medications, those who were on non-antihypertensive medications, and those on antihypertensive medications 

 

 

This graph shows the evolution of systolic blood pressure resting times stratified by treatments: the middle graph depicts those who received treatments other than hypertensive drugs, the right graph showed patients receiving hypertensive treatment with at least one drug from the class of diuretics, beta blockers, or ACE-i. This graph does indicate a substantial proportion of patients who would have been considered hypertensive at the 3 to 5 minute mark but not later

 

-- Time to reach stable blood pressure: 50% of the population was stabilized within 5 mmHg after resting 5 minutes

-- up to 25 minutes would needed to ensure stable BP in 90% of the population

    -- if a variability of 10 mmHg were accepted (vs 5 mmHg in the above analysis), the resting time would fall to 15 minutes

 

-- Proportion of the population considered to be hypertensive:

    -- the predicted proportion of subjects diagnosed as hypertensive fell 50% when averaging measurements at times 3 to 5 minutes, decreasing to 44% two minutes later, and down to 33% at 25 to 27 minutes

 

 

This graph shows the proportion of subjects diagnosed as hypertensive depending on the time of SBP measurement, with mathematical modeling to extend the time to 25 minutes

 

-- Overall the baseline systolic blood pressure was 25% higher on average than the estimate of the plateaued blood pressure, with large inter-individual variability in the speed of decrease

-- No impact on the decreasing blood pressure by testing position (lying or sitting) or heart rate during the blood pressure measurement

 

Commentary: 

-- there are pretty clear-cut guidelines for how to take blood pressure from many different organizations, typically suggesting that patients rest quietly for 3 to 5 minutes before blood pressure measurement (eg the American Heart Association, the European Society of Cardiology, the European Society of Hypertension, etc.), but there really are limited data on the physiologic basis for this recommendation 

-- In general, it is rare for patients to go through the full set of recommendations using the optimal office-based technique for measuring blood pressure. A study of medical students found that only 11 of 159 students had the patient rest for 5 minutes in a chair before the measurement, and only one completed the full set of 11 recommendations (see http://gmodestmedblogs.blogspot.com/2017/09/the-most-important-hypertension-blog.html ), all suggesting that the students' clinical role models did not do what the medical students were taught to be proper technique

-- this study adds further substance to the primary recommendations to assess hypertension through ambulatory blood pressure monitoring (ABPM) or home-based blood pressure monitoring (HBPM), with the following points: 

    -- several studies have found that about 30% of “hypertensive” patients as determined in the clinic setting were not hypertensive by ambulatory blood pressure monitoring; this reflects the fact that the vast majority (about 80%) of those diagnosed as being hypertensive are in the “mild” category by ABPM

        -- i should emphasize that the arguments really do rest in those with mild hypertension; there is, or course, the imperative to treat clinic-based readings that are very high (no clear guidance here, but probably on the order of SBP>150-60 mmHg, especially if the BP is taken with a long resting period)

    -- in 2011, the National Institute for Health and Care Excellence (NICE, in the UK) did a quite systematic review finding that ABPM had the best clinical correlation with clinical outcomes and should be the primary tool to assess blood pressure control, with HBPM measurement as an acceptable alternative (see Htn nice recs 2011 in dropbox, or see their Clinical Guideline 127 from August 2011)

    -- in 2015 the US Preventive Services Task Force followed suit and gave a Grade A recommendation to "screen for high blood pressure; obtain measurements outside of the clinical setting for diagnostic confirmation” (my emphasis), see http://gmodestmedblogs.blogspot.com/2015/01/uspstf-recs-on-ambulatory-blood.html; this blog references studies showing that clinical cardiovascular outcomes were much more predictable by assessing ABPM than clinic-based blood pressures (and a few studies finding NO association between clinic-based measurements with clinical outcomes)

    -- the more recent AHA guidelines in 2019 emphasized checking ABPM and HBPM over clinic-based blood pressures, noting that “substantial data have demonstrated that BP measured by ABPM has a stronger association with hypertension-related target-organ damage and clinical cardiovascular outcomes compared with office-based BP measurements” and then littering their guidelines with many repeated recommendations to get ABPM or HBPM (see http://gmodestmedblogs.blogspot.com/2019/03/new-aha-blood-pressure-measurement.html )

    -- another study found that home bp monitoring improves BP control http://gmodestmedblogs.blogspot.com/2018/03/home-bp-monitoring.html 

 

-- the current study found that it was projected to take 25 minutes for 90% of the population to develop a stable systolic blood pressure, defined as within a 5 mmHg swing

-- there were some of the participants who rapidly developed a stable blood pressure and others taking significantly more time, though there was a lot of individual variability

-- and, these findings run contrary to the recommendations by the leading international cardiology/hypertension societies

Limitations: 

-- all these patients came from a vascular clinic and had a higher risk of cardiovascular disease than the general population, limiting generalizability 

-- though this study was from five years ago, it is rather striking how few of the patients were on lipid-lowering drugs or antiplatelet meds, given their being in the vascular clinic

-- the assumption in this study is that the plateaued, resting blood pressure is the one that predicts cardiovascular events. this assumption is borne-out by the several older studies on white coat hypertension suggesting small clinical effects, and the fact that ABPM and HBPM are much more predictive of clinical events. But there are also several studies, and a systematic review/meta-analysis, finding that there does seem to be a significant cardiovascular association with white-coat hypertension (see htn whitecoat systematic review AIM2019 in dropbox or doi:10.7326/M19-0223), which raises a few isssues:

    -- is there an important difference in the quantity of stress-related events in a person's day? is the outcome different in those with an occasional BP increase (eg one office visit/month) vs lots of stress-related events (lots of stress at home, in their neighborhood,as well as the clinic)?

    -- and, the definition of white-coat hypertension is simply that the BP is higher in a clinic visit than at rest when it is normal (most studies consider the cutpoint of normal as BP <135/85, which is a bit higher than the cutpoint of the newest AHA recommendations). so maybe the "BP at rest" in those with very stressful lives is just a rare moment of no stress??

    -- if the issue is the amount of stress in the day, one would think that the ABPM would on average be higher in those folks with lots of stress, which might actually support the findings of the ABPM studies and the more recent recommendations to mostly ignore mild clinic-based BP readings and use ABPM or HBPM

-- the extrapolation from the 11-minute BP values to the 25-minute evaluation was mathematical, based on half-life measurements (eg, assuming that a 50% decrease in the numbers of patients who did not have stabilized blood pressure in the measured 11 minutes would extend similarly to the next 11 minutes). this might not be true....

so, the real reason i bring up this article is to add fuel to the fire that clinic-based blood pressure measurements in the mild hypertension range should not prompt clinical action in general, with a few points:

-- ABPM is really doable. machine cost is pretty low (and the test is billable), and it is pretty easy to use

-- those patients who cannot sleep with their BP cuff inflating a couple of times/hour do get pretty useful information from just the daytime recording

-- home BP monitoring is acceptable as an alternative, though i would suggest that the patient bring in their BP cuff and have them measure their own BP in the office, while an office person observes their technique and checks simultaneous readings from a certified office machine

    -- and several health insurers/plans do cover the cost of accurate BP cuffs

    -- and it allows more reliable blood pressure readings for decision-making when we do telemedicine

-- though there is clearly more white-coat hypertension (ie, normal out-of-office blood pressures) in those with mild hypertension, i have actually found some pretty huge outliers here: patients with SBP in the 160-180 range on coming to the health center, with my repeat measurements being in the 130 range after the patient waits in a quiet, dimly lit room for 5 minutes (while i write their notes, orders, etc in my office; or perhaps check another patient briefly). this does not happen often, but is also not so rare..... But, i do pretty often see a 20-30 mmHg drop from when patients are brought into the vital signs room pre-visit to my clinical rooms (with the 5+ minute waiting time quietly)

geoff

 

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