776 BLOOD PRESSURE MEASUREMENT DEVICE, NUMBER AND TIMING OF VISITS, AND INTRA-INDIVIDUAL STANDARD DEVIATION OF BLOOD PRESSURE

Abstract

Background: Visit-to-visit variability (VVV) of blood pressure (BP) has been associated with the incidence of cardiovascular disease. However, the effects of the number and timing of visits and BP measurement device (manual or automated) on VVV of BP have not been investigated thoroughly. Design and methods: We examined the influence of the number and timing of visits and BP measurement device on VVV using data from the placebo arm of the Trial of Preventing Hypertension (TROPHY) (n = 225, 18 follow-up visits) and a simulation study (n = 200, 100 follow-up visits). VVV was assessed using the intra-individual standard deviation (SD) of systolic BP. Results: The intra-individual SD increased with number of visits used to calculate VVV in both the TROPHY population and the simulated data (Figure). Using the mean of 3 manual measurements per visit from consecutive visits (median time between visits = 3 months) in TROPHY, the average SD was 5.6 mmHg from 3 visits, 6.8 mmHg from 7 visits, and 7.7 mmHg from 18 visits. When the 7 visits were spread out across 4 years (median time between visits = 8 months), the average SD was higher (7.5 mmHg). The SD was higher when using a single BP measurement per visit and with automated versus manual devices.Conclusions: The number and timing of visits and BP measurement device influence the intra-individual SD of BP and need to be considered when designing, interpreting and comparing studies of VVV of BP.