Rate of Morning Increase in Blood Pressure Is Elevated in Hypertensives

Abstract

We applied a new logistic curve fitting procedure to ambulatory blood pressure (ABP) recordings to determine whether the rate of increase in systolic (SBP), mean (MBP) and diastolic blood pressure (DBP) and heart rate (HR) in the morning is related to the level of BP in subjects. The rate of transition in the morning and evening period was determined using a six-parameter double-logistic equation applied to 528 ABP recordings from a cardiovascular risk assessment clinic. Based on daytime BP (MBP, SBP, or DBP), the upper quartile (UQ, n = 132) and lower quartile (LQ) were compared. Subjects in the UQ of daytime MBP were hypertensive and showed greater day-night differences compared to normotensive subjects in the LQ (29 +/- 1 mm Hg for MBP compared to 20 +/- 1 mm Hg). The rate of morning increase in SBP and DBP was 42% and 30% greater in UQ subjects compared to the LQ subjects (P < .05). The rates of evening decrease in all BPs were 69% to 84% greater in the subjects in the UQ. Similar results were obtained if subjects were divided according to daytime SBP or DBP. The rate of morning increase in MBP was correlated with daytime BP, but not night-time or 24 h MBP. The rate of morning increase in BP is greater in those subjects with the highest daytime BP. The exaggerated rate of morning increase in BP in this group, which were all hypertensive, may also be important for greater cardiovascular risk.