The Implications of Blood Pressure Measurement Methods on Treatment Targets for Blood Pressure
Over the past 45 years, a number of clinical outcome trials have evaluated the effects of blood pressure (BP) reduction on cardiovascular outcomes.1 Most recently, SPRINT (Systolic Blood Pressure Intervention Trial) randomly assigned 9361 persons with a systolic blood pressure (SBP) of ≥130 mm Hg and increased cardiovascular risk to a SBP target <120 mm Hg versus <140 mm Hg. Although the results of SPRINT provide evidence that the goal SBP should be closer to 120 than 140 mm Hg, the methods of BP measurement were notably different between this trial and many others. More important, the methodology for measuring BP in SPRINT is not what is used in most clinical practices, and this difference has significant clinical implications.
Most cardiovascular outcome trials, to date, have used either ausculatory or automatic oscillometric methods of seated BP measurement performed shortly after the patient’s arrival for a visit, with similar methods currently used in most clinical practices. The SPRINT methodology is not in widespread use clinically; BP was measured after the participant sat quietly alone for 5 minutes, after which study personnel returned to the room to measure BP 3 times at 1-minute intervals with all 3 values averaged.
BP recorded in research studies using the standard BP measurement guidelines, which mandate a rest period before measurement (with or without automated office BP), is on average 10/7 mm Hg lower than BP measured in routine clinical practice.2 Even when patients take their own BP using an automated sphygmomanometer while alone in an examining room, the mean SBP is still ≈5 mm Hg higher than the corresponding awake ambulatory or home BP.3 Thus, SBP as measured in recent randomized trials, including SPRINT, is likely ≈5 to 10 mm Hg lower than that measured with traditional office BP measurement methodology. Consequently, targeting the SBP <120 mm Hg without using similar BP measurement methods as in the trials may increase the risk of serious adverse events by systematically overshooting the trial-based BP targets and potentially leading to hypotensive complications. Thus, applying the SPRINT intensive BP targets based on usual office measurements would correspond to a SBP target range of 125 to 135 mm Hg to be similar to the level of BP control targeted and achieved in the SPRINT intensive BP group.
Another method of BP measurement has been proposed using a specific method termed automated office BP (AOBP). Similar to the SPRINT method, the AOBP measurement assesses BP after the patient has rested for 5 minutes, but adding to that a fully automated sequence of 5 readings over a 5-minute period, all with the patient resting quietly alone.4 The AOBP method of BP measurement corresponds more closely with mean daytime BP (using ambulatory-awake monitoring) than with manual (ausculatory) or automated oscillometric office BP measurement and has been shown to diagnose masked hypertension as well as 24-hour ambulatory monitoring.5 The AOBP approach minimizes white coat hypertension and yields up to a 10 mm Hg lower result for SBP than single automated/oscillometric BP measurement most commonly done in the real-world clinic setting.2,3
Almost all AOBP research has involved the patient resting alone in an examining room, most commonly for a 5-minute period, which is often impractical in a busy clinical setting. A recent study examined whether it would be possible to obtain valid AOBP readings with the patient resting quietly in a waiting room. AOBP readings using a BpTRU device (VSM MedTech Ltd) recorded with the patient resting quietly in the waiting room were obtained in patients referred for ambulatory BP monitoring. The relationship between the waiting-room–acquired AOBP measurements and the awake ambulatory blood pressure (mm Hg) were examined in 422 patients.2 The awake ambulatory blood pressure was similar to the mean AOBP measurement recorded in the waiting room, with both values being significantly lower than a single office BP measurement taken by a nurse. Therefore, it seems plausible that even in a busy clinical practice with little time to spare, AOBP measurement could be incorporated before engagement with the healthcare professional.
For AOBP methodology to be incorporated into clinical practice, one needs to consider the following points. First, using a fully automated patient rest time of 5 minutes followed by 1-minute cycling for repeat BP measures, all with the patient alone, decreases the likelihood of the patient being disturbed. A second consideration is the cost of the AOBP devices, which range from $400 to $700 US dollars. Although most of the research to date using AOBP methods has been performed with a BpTRU device, which is among the most expensive, other models are as good and more reasonably priced. For example, the Omron 907 (Omron Healthcare), which has been extensively used in clinical trials such as ONTARGET (Ongoing Telmisartan Alone and in Combination With Ramipril Global End Point Trial), ACCORD (Action to Control Cardiovascular Risk in Diabetes), and SPRINT, is less expensive. Similar to the BpTRU device, Omron and many other oscillometric BP monitors can be programmed to take 3 consecutive measurements after 5- to 10-minute delays. Last, when patient-activated, nonautomated devices are used, readings are only ≈5/5 mm Hg higher than those with AOBP method, and this might represent a practical compromise.
Thus, these protocolized approaches to BP measurement suggest that the current practice of office BP measurement in most of the world overestimates BP levels, and attempting to attain lower levels achieved in trials such as SPRINT where BP was properly measured may be associated with a higher risk for adverse events, which were observed in SPRINT, ACCORD, and ONTARGET associated with hypotension. Thus, improving the accuracy of office BP measurement such as using AOBP is the goal, but it may be impractical in some settings; hence, if standard office BP measurement is used without a resting period and without automatic cycling of measurements with clinic personnel out of the room, the goal SBP ranges for those meeting risk profiles similar to clinical trials should be adjusted 5 to 10 mm Hg higher than the trials.
The opinions in this article are not necessarily those of the editors or of the American Heart Association.
Circulation is available at http://circ.ahajournals.org.
- © 2016 American Heart Association, Inc.