Statistical Base Value of 24-Hour Blood Pressure Distribution in Patients With Essential Hypertension

Abstract

Abstract— The purpose of this study was to calculate statistically the minimum (base) blood pressure (BP) of nighttime (sleep-time) BP values obtained by ambulatory BP monitoring (ABPM) and to investigate its clinical significance. Twenty-four-hour recording of ECG with ABPM was performed directly (n=89) or indirectly (n=117) in 206 patients with essential hypertension. A telemeter was used for the direct method and a multi-biomedical recorder (TM2425) was used for indirect measurement. First, minimum heart rate (HR 0 =60/RR 0 ) was determined from sleep-time ECG. The mean product of sleep-time diastolic BP (DBP) and pulse interval (RR) was divided by RR 0 to obtain DBP 0 [DBP 0 =(DBP×RR)s/RR 0 ]. The correlation between systolic BP (SBP) and DBP was used to determine SBP 0 corresponding to DBP 0 . Statistical base mean BP (MBP 0 ) was calculated from these values, and its reproducibility and relation to hypertension severity were investigated. MBP 0 values were similar to true base values of sleep-time MBP obtained by the direct method (mean±SD difference, 2.0±4.2 mm Hg). Direct MBP 0 criteria predicted hypertension severity (mild, moderate, or severe target organ damage) more accurately (predictive accuracy, 89%) than daytime MBP criteria (53%, P <0.01). Almost the same results were obtained using indirect MBP 0 criteria. Day-to-day indirect MBP 0 variation (mean absolute difference) was smaller (2.4±1.8 mm Hg) than day-to-day daytime and nighttime MBP variation (6.3±5.3 and 5.4±3.4 mm Hg, respectively; n=61, P <0.01), and the correlation coefficient between day-to-day variations of daytime MBP and physical activity (measured by an acceleration sensor) was 0.38 ( P <0.05). In conclusion, statistical base BP was almost equal to true base (minimum) BP of sleep-time BP distribution. It was closely related to the severity of hypertensive organ damage, was highly reproducible, and is considered likely to serve stochastically and physiologically as a representative BP value in an individual subject.