The association between morning blood pressure and subclinical target organ damage in the normotensive population

Objective: To investigate whether isolatedly elevated morning blood pressure (BP) is associated with subclinical target organ damage in normotensive individuals. Methods: In all, 287 normotensive individuals were included in this cross-sectional study. Each participant underwent anthropometric measurements, serum biochemistry evaluation, 24-h ambulatory BP monitoring, echocardiography, and carotid ultrasonography. The morning BP and morning surge were defined as: the average BP within 2 h after waking up, and the difference between the mean systolic BP (SBP) within 2 h after waking up and the mean SBP during the hour that included the lowest BP reading during sleep, respectively. Results: The prevalence of elevated morning BP was 37.3%. Individuals with elevated morning BP had higher left ventricular mass index and morning surge, and also mean 24-h, daytime, and night-time SBP and diastolic BP, BP variability (all P < 0.05). Left ventricular mass index was correlated with 24-h, daytime, night-time, and morning SBP, and morning surge (Pearson's correlation coefficients: 0.271, 0.262, 0.215, 0.368, and 0.415, respectively; all P < 0.05); and standard deviations of 24-h, daytime, and night-time SBP (Pearson's correlation coefficient: 0.303, 0.234, and 0.309, respectively), and coefficient of variations of 24-h and night-time SBP (Pearson's correlation coefficients: 0.253 and 0.271, respectively). Morning surge had the strongest correlation with left ventricular mass index in multiple regression analysis. Only daytime and morning SBP could discriminate elevated morning surge (≥35 mmHg), with an area under the curve of 0.744 and 0.864, respectively (both P < 0.01), and an optimal threshold of 121.5 mmHg for morning SBP. Conclusion: Our findings suggest that isolated elevation of morning BP in normotensive individuals is associated with left ventricular hypertrophy. Home monitoring of morning BP may be suitable for detecting abnormal morning surge.