Abstract 071: An Attenuated Nocturnal Dip in Systemic Vascular Resistance is Associated With Increased Left Ventricular Mass

Abstract

Introduction: Previous work from our laboratory has demonstrated that the nocturnal “dip” in blood pressure (BP) is due primarily to a decrease in systemic vascular resistance (SVR), and that nondipping is associated with a blunted nighttime reduction in SVR. In this analysis, we examined the hypothesis that a blunted nocturnal SVR fall is associated with increased LV mass. Methods: 24-hour ambulatory hemodynamics were assessed in a biracial sample of 116 men and women with elevated clinic BP (130-159/80-99 mmHg). Ambulatory BP monitoring was coupled with synchronized measurements of cardiac output by ambulatory impedance cardiography. Values for SVR were derived for each ambulatory BP measurement. Left ventricular (LV) mass was measured by echocardiography and indexed by height 2.7 to adjust for differences in body size. Multivariable regression models were used to examine the relationships between LV mass index and demographic characteristics, anthropomorphic variables, daytime ambulatory systolic BP, and dipping of SVR and systolic BP. Results: The study cohort averaged 45.3 ± 8.3 years of age; 42% (49 of 116) of the subjects were female and 47% (54 of 116) were African American. The mean body mass index (BMI) was 28.3 ± 3.8 kg/m 2 . The mean daytime ambulatory systolic BP was 137 ± 11 mmHg; the systolic BP dip averaged 13 ± 5%, and the nocturnal fall in SVR averaged 13 ± 15%. In a model that included age, sex, race, BMI, and daytime systolic BP, daytime systolic BP was significantly associated with LV mass index (b=0.33, p=0.0004). The SVR percent dip, (b=-0.21, p=0.02) but not the percent dip in systolic BP (b=-0.15, p=0.11), was an independent predictor LV mass index when added to this model. Conclusions: A blunted nocturnal dip in SVR is associated with increased LV mass index, independent of daytime systolic BP. This finding suggests that an attenuated nighttime fall in SVR may contribute to left ventricular hypertrophy.