Beyond office sphygmomanometry: Ways to better assess blood pressure
ABSTRACTTo diagnose and manage hypertension optimally, we may need to do more than measure the patient’s blood pressure in the office using traditional sphygmomanometry. A variety of devices—some already available, validated, and reimbursable, some still in development—provide more information and give us a better picture of the patient’s true hypertensive status, degree of blood pressure control, and risk of end-organ damage.
KEY POINTS
- Traditional office blood pressure measurements have diagnostic limitations, since they are only snapshots of a very dynamic variable.
- Ambulatory 24-hour blood pressure monitoring is a useful and proven tool and can reveal nocturnal hypertension, a possible new marker of risk.
- Automatic devices can be used in the clinician’s office to minimize the “white coat effect” and measure blood pressure accurately.
- Pulse-wave analysis provides physiologic data on central blood pressure and arterial stiffness. This information may help in the early identification and management of patients at risk for end-organ damage.
Hypertension is difficult to diagnose, and its treatment is difficult to monitor optimally on the basis of traditional office blood pressure measurements. To better protect our patients from the effects of undiagnosed or poorly controlled hypertension, we need to consider other options, such as ambulatory 24-hour blood pressure monitoring, automated measurement in the office, measurement in the patient’s home, and devices that analyze the peripheral pulse wave to estimate the central blood pressure and other indices of arterial stiffness.
MANUAL OFFICE MEASUREMENT HAS INHERENT LIMITATIONS
Office blood pressure measurements do provide enormous information about cardiovascular risk and the risk of death, as shown in epidemiologic studies. A meta-analysis1 of 61 prospective observational studies that included more than 1 million patients showed that office blood pressure levels clearly correlate with increased risk of death from cardiovascular disease and stroke.
But blood pressure is a dynamic measure with inherent minute-to-minute variability, and measurement will not be accurate if the correct technique is not followed. Traditional office sphygmomanometry is a snapshot and does not accurately reflect a patient’s blood pressure in the real world and in real time.
Recently, unique patterns of blood pressure have been identified that may not be detected in the physician’s office. It is clear from several clinical trials that some patients’ blood pressure is transiently elevated in the first few minutes during office measurements (the “white coat effect”). In addition, when office measurements are compared with out-of-office measurements, several patterns of hypertension emerge that have prognostic value. These patterns are white coat hypertension, masked hypertension, nocturnal hypertension, and failure of the blood pressure to dip during sleep.
WHITE COAT EFFECT
The white coat effect is described as a transient elevation in office blood pressure caused by an alerting reaction when the pressure is measured by a physician or a nurse. It may last for several minutes. The magnitude of blood pressure elevation has been noted to be higher when measured by a physician than when measured by a nurse. Multiple blood pressure measurements taken over 5 to 10 minutes help eliminate the white coat effect. In a recent study,2 36% of patients with hypertension demonstrated the white coat effect.
In a study by Mancia et al,3 46 patients underwent intra-arterial blood pressure monitoring for 2 days, during which time a physician or a nurse would check their blood pressure repeatedly over 10 minutes. This study found that most patients demonstrated the white coat effect: the blood pressure was higher in the first few measurements, but came down after 5 minutes. The white coat effect was as much as 22.6 ± 1.8 mm Hg when blood pressure was measured by a physician and was lower when measured by a nurse.
WHITE COAT HYPERTENSION
In contrast to the white coat effect, which is transient, white coat hypertension is defined as persistent elevation of office blood pressure measurements with normal blood pressure levels when measured outside the physician’s office. Depending on the population sampled, the prevalence of white coat hypertension ranges from 12% to 20%, but this is understandably difficult or almost impossible to detect with traditional office blood pressure measurements alone.4–7
MASKED HYPERTENSION
Patients with normal blood pressure in the physician’s office but high blood pressure during daily life were found to have a higher risk of cardiovascular events. This condition is called masked hypertension.8 For clinicians, the danger lies in underestimating the patient’s risk of cardiovascular events and, thus, undertreating the hypertension. Preliminary data on masked hypertension show that the rates of end-organ damage and cardiovascular events are slightly higher in patients with masked hypertension than in patients with sustained hypertension.
NOCTURNAL HYPERTENSION
Elevated nighttime blood pressure (>125/75 mm Hg) is considered nocturnal hypertension and is generally considered a subgroup of masked hypertension.9
In the African American Study of Kidney Disease and Hypertension (AASK),10,11 although most patients achieved their blood pressure goal during the trial, they were noted to have relentless progression of renal disease. On ambulatory 24-hour blood pressure monitoring during the cohort phase of the study,10 a high prevalence of elevated nighttime blood pressure (66%) was found. Further analysis showed that the elevated nighttime blood pressure was associated with worse hypertension-related end-organ damage. It is still unclear if lowering nighttime blood pressure improves clinical outcomes in this high-risk population.
