Ambulatory blood pressure phenotypes and the risk for hypertension

Abstract

Ambulatory blood pressure (BP) monitoring provides valuable information on a person's BP phenotype. Abnormal ambulatory BP phenotypes include white-coat hypertension, masked hypertension, nocturnal nondipping, nocturnal hypertension, and high BP variability. Compared to people with sustained normotension (normal BP in the clinic and on ambulatory BP monitoring), the limited research available suggests that the risk of developing sustained hypertension (abnormal BP in the clinic and on ambulatory BP monitoring) over 5 to 10 years is approximately two to three times greater for people with white-coat or masked hypertension. More limited data suggest that nondipping might predate hypertension, and no studies, to our knowledge, have examined whether nocturnal hypertension or high ambulatory BP variability predict hypertension. Ambulatory BP monitoring may be useful in identifying people at increased risk of developing sustained hypertension, but the clinical utility for such use would need to be further examined.

Figure 1

Ambulatory Blood Pressure Phenotypes Based on Pairing Office and Ambulatory Measurements

Figure 2. A 24-Hour Ambulatory Blood Pressure Monitoring Graph

The 24-hour period of monitoring is divided primarily into awake (often called “daytime”) and sleep (often called “nocturnal”) periods (shaded section in above graph). Sometimes, to improve tolerability of wearing the monitor, readings are taken at less frequent intervals during the sleep period. A diary is often used as the basis by which to define sleep time, although some studies use a specified period (e.g., midnight to 6am) to denote sleep time. Based on the time periods, a person’s awake (or daytime) BP average can be calculated, as can their sleep (or nocturnal) average. Shown above is the graph of a person whose awake average (based on 31 measurements) was 128/81 (±14/11) mm Hg and sleep average (based on 7 measurements) was 108/64 (±13/11) mm Hg. The nocturnal systolic dip is calculated as (128-108)/128, which is approximately 16%. The lowest line on the graph shows heart rate.