Improving the utility of the nocturnal hypertension definition by using absolute sleep blood pressure rather than the "dipping" proportion.

A lthough the diagnosis of hypertension is usually based on blood pressure (BP) values measured in the clinic during daytime hours, increasing evidence suggests that nocturnal BP has an important relation to target organ disease and even prognosis.1–4 In most patients with hypertension, BP decreases by 10% to 30% at night compared with daytime values; patients with a blunted nighttime decrease in BP have been termed “nondippers” in the hypertension literature for nearly 15 years. It is estimated that nearly 30% of patients with essential systemic hypertension fall into this nondipper category. Despite this history, the use of the nondipper and “dipper” classifications to describe the circadian variation of BP in patients with hypertension has been controversial. Many studies have shown that classifying nondippers by an arbitrary threshold of a 10% decrease in BP at night compared with daytime BP had poor reproducibility.5–7 An alternative to this dipper/nondipper classification would be to use an absolute threshold for defining nocturnal hypertension. Based on a growing database from epidemiologic and target organ surveillance studies, a consensus panel from the American Society of Hypertension Ad Hoc Committee previously defined nocturnal hypertension as a nighttime BP of 125/80 mm Hg.8 The reproducibility of nocturnal hypertension has not been formally studied, but an absolute value could be more appealing for both clinical purposes and evaluating the effects of antihypertensive therapy. To assess the validity of the hypothesis that an absolute nocturnal BP value improves the definition and utility of nocturnal BP, we conducted 2 analyses. The first analysis compared the reproducibility of proportional decreases (i.e., 5% and 10%) in nighttime BP relative to daytime BP, with the reproducibility of an absolute value of nighttime BP recognized as hypertensive ( 125/80 mm Hg).8 The second analysis assessed the effects of placebo and treatment with an angiotensin II receptor blocker on nocturnal BP according to baseline nocturnal BP values. ANALYSIS OF DEFINITION REPRODUCIBILITY Using an ambulatory BP database (courtesy of Joan Kempthorne-Rawson, biostatistician, Boehringer Ingelheim Pharmaceuticals, Ridgefield, Connecticut), data were extracted from high-quality 24-hour BP recordings on 2 separate occasions, 4 to 8 weeks apart, during the placebo run-in phase of different trials (129 patients). Patients were included in these studies if they had systemic hypertension, with mean clinic BPs of 140/95 and 200/114 mm Hg. The proportion of patients whose nocturnal BP status remained the same during the 2 separate ambulatory BP readings was calculated according to the following definitions of nocturnal BP: (1) 5% nondippers were patients who demonstrated a 5% decrease in nighttime BP relative to daytime BP; (2) 10% nondippers were patients who demonstrated a 10% decrease in nighttime BP relative to daytime BP; and (3) patients with nocturnal hypertension were those with a mean nighttime BP of 125/80 mm Hg.8 Nocturnal BP status was determined separately for both systolic and diastolic BP. A statistic for agreement between the 2 ambulatory BP measurements was calculated for each definition of nocturnal hypertension.