Three types of hypertension are especially important to recognize: white coat hypertension, masked hypertension, and nocturnal hypertension. Suspicion of these entities and assessing the effects of treatment are indications for ambulatory blood pressure monitoring.

■ White coat hypertension (isolated clinic hypertension): White coat hypertension is defined as blood pressure ≥140/90 in medical settings and mean awake ambulatory readings <135/85. This phenomenon, reported in up to 20% of patients with elevated office blood pressure, is important to identify since it carries normal to slightly increased cardiovascular risk and does not require treatment. It is attributed to a conditioned anxiety response. Poor measurement technique, including rounding of measurements to zero, the presence of a physician or nurse, and even the prior diagnosis of hypertension can also substantially alter office readings. Replacing manual office measurements with an automated device that makes several readings with the patient seated alone in a quiet room has been shown to reduce the "white coat effect."

■ Masked hypertension: Masked hypertension, defined as office blood pressure <140/90, but an elevated daytime blood pressure of >135/85 on home or ambulatory testing, is more serious. Untreated adults with masked hypertension, an estimated 10% to 30% of the general population, have increased risk of cardiovascular disease and end-organ damage.

■ Nocturnal hypertension: Physiologic blood pressure "dipping" occurs in most patients at night as they shift from wakefulness to sleep. A nocturnal fall of <10% of daytime values is associated with poor cardiovascular outcomes and can only be identified on 24-hour ambulatory blood pressure monitoring. Two other patterns have poor cardiovascular outcomes, a nocturnal rising pattern and a marked nocturnal fall of >20% of daytime values.

责任编辑：admin