According to the American Heart Association, healthy blood pressure is less than 120/80. Elevated blood pressure is a systolic reading from 120-129 and a diastolic reading less than 80. Stage 1 hypertension is when blood pressure ranges from 130-139 systolic or 80- 89 diastolic (1). Hypertension increases the risk of heart attack and stroke and contributes to about 700,000 deaths per year in the US. Forty eight percent of US adults have hypertension, defined as a systolic blood pressure greater than 130 mmHg or a diastolic blood pressure greater than 80 mmHg or are taking medication for hypertension. About 1 in 4 adults with hypertension have their hypertension under control (2). Measuring blood pressure over a 24 hour period reveals multiple clinically significant facets of blood pressure that are underappreciated and infrequently detected, such as elevated nocturnal blood pressure, masked hypertension, and masked hypotension.
AMBULATORY BLOOD PRESSURE MONITORING
Ambulatory blood pressure monitoring (ABPM) refers to the continuous measurement of blood pressure over a 24 hour period including periods when a person is awake and asleep. This method of frequent measurements over a 24 hour period provides a high degree of accuracy and specific insights into health outcomes impacted by blood pressure. Cardiovascular complications are more closely associated with ambulatory blood pressure measurements versus their office blood pressure measurements (3).
CIRCADIAN VARIATION OF BLOOD PRESSURE
Blood pressure typically follows a circadian variation, and is lower at night and higher during the day. About 20% of patients with hypertension lack the normal decrease in nighttime BP. People with non-dipping blood pressure, higher blood pressure at night, have a 27% higher risk of cardiovascular events including heart attacks and strokes (4). Non-dipping blood pressure has also been linked to vascular dementia and all-cause mortality (5).
Masked hypertension refers to normal clinic blood pressure and elevated blood pressure outside of clinic (daytime blood pressure, nocturnal blood pressure, or 24 hour ABPM). Twenty four hour ambulatory blood pressure monitoring can accurately detect elevated nocturnal and 24 hour blood pressure and is the gold standard for diagnosing masked hypertension. In individuals with normal office blood pressure, ABPM data showed masked hypertension in 15% – 60% of patients across three studies (6,7). Masked hypertension is clinically significant because it is associated with an increased risk of kidney dysfunction, stroke, and heart attack (9,10).
Masked hypotension refers to systolic blood pressure <100 and/or diastolic blood pressure< 60 with 24-hour ABPM or nighttime ABPM <90 and/or 50 mmHg, and normal office blood pressure with systolic >110 and diastolic >60.
About 15% of elderly patients treated for hypertension have masked hypotension (11). This can lead to a variety of adverse clinical effects including falls, cognitive decline, and increased mortality (12,13). Similar to masked hypotension, ABPM is the most accurate tool to identify masked hypotension. Masked hypotension may be clinically significant in other populations including women, but at present, the clunkiness and cost of ABPM devices have limited our data on continuous blood pressure monitoring.
24-HOUR ABP and MORTALITY
A recent ambulatory blood pressure study of about 60000 patients with a median follow-up of about 10 years showed that 24 hour ambulatory blood pressure versus clinic blood pressure has a tighter correlation to all-cause mortality and cardiovascular mortality. Nighttime blood pressure was the best predictor of cardiovascular events and all-cause mortality. Masked Hypertension also conferred an increased risk of cardiovascular mortality (14).
NEW APPROACHES TO BLOOD PRESSURE MONITORING
The Aktiaa bracelet is a wearable device available in Europe that can accurately estimate blood pressure in the most common body positions of daily life (15). The device uses optical sensors to measure the amount of light that is absorbed or reflected by blood vessels in living tissue. In a one month validation trial, simultaneous blood pressure measures with the Aktiaa Bracelet and double-blinded auscultation by two trained observers were compared. The mean and standard deviation of the differences between Aktiia Bracelet estimates and the reference were 0.5 ± 7.8 for systolic blood pressure and 0.4 ± 6.9 for diastolic blood pressure (16).
Often the questions we ask in clinical medicine are bounded by our current diagnostic tools. For example, before the advent of continuous glucose monitors our studies focused on average glucose (hemoglobin A1C) and clinical outcomes. With the ubiquity of wearable glucose monitors, we can consider the relationship between surges in glucose and insulin and our energy levels, cognitive performance, and inflammatory markers. Continuous blood pressure monitoring elevates its own set of significant clinical information by rendering previously invisible nocturnal hypertension, masked hypertension, and masked hypotension visible.
Bradford Rabin MD is a concierge medicine doctor caring for patients in the San Francisco Bay Area including Palo Alto, Menlo Park, Los Altos, Portola Valley, Hillsborough, and Woodside.
1 New ACC/AHA High Blood Pressure Guidelines Lower Definition of Hypertension
2 Facts About Hypertension
3 Ambulatory Blood Pressure Monitoring to Diagnose and Manage Hypertension
4 Prognostic Effect of the Nocturnal Blood Pressure Fall in Hypertensive Patients: The Ambulatory Blood Pressure Collaboration in Patients With Hypertension (ABC-H) Meta-Analysis
5 Night-time blood pressure patterns and target organ damage: a review
6 Prevalence of Masked Hypertension in Untreated and Treated Patients With Office Blood Pressure Below 130/80 mm Hg
7 Unmasking masked hypertension: prevalence, clinical implications, diagnostic correlates and future directions
8 Masked Hypertension and Cardiovascular Disease Events in a Prospective Cohort of Blacks
9 Prognostic value of white-coat and masked hypertension diagnosed by ambulatory monitoring in initially untreated subjects: an updated meta-analysis
10 Masked Hypertension
11 Magnitude of Hypotension Based on Office and Ambulatory Blood Pressure Monitoring: Results From a Cohort of 5066 Treated Hypertensive Patients Aged 80 Years and Older
12 Low blood pressure levels for fall injuries in older adults: the Health, Aging and Body Composition Study
13 Diastolic Blood Pressure and Mortality in the Elderly With Cardiovascular Disease
14 Relationship Between Cinic and Ambulatory Blood Pressure and Mortality: an Observational Cohort Study in 59124 patients
15 Validation of the optical Aktiia bracelet in different body positions for the persistent monitoring of blood pressure
16 Blood pressure from the optical Aktiia Bracelet: a 1-month validation study using an extended ISO81060-2 protocol adapted for a cuffless wrist device