Abstract 13192: The Influence of Posture and Steps on Daytime Ambulatory Blood Pressure

Abstract

Introduction: Ambulatory blood pressure (BP) monitoring (ABPM) provides data beyond clinic BP. Yet, free-living activity prior to measurements may add variability and obscure clinical interpretation. The influence of posture and ambulation on ABPM is unclear. Hypothesis: Posture and ambulation will partially explain variability in daytime ABPM. Methods: This study used baseline data from RESET BP (NCT03307343), a randomized clinical trial testing a sedentary behavior reduction intervention among inactive desk workers with elevated, unmedicated BP. ABPM was measured 2 x per self-reported waking hour over 24 hours with a SunTech Medical ® Oscar 2 TM ambulatory BP monitor. Upright posture and step count were concurrently captured with an activPAL TM thigh-worn accelerometer. Upright time and steps were summed for the 1-, 5-, 10-, and 15-minute intervals prior to each ABPM measurement. Percentage of BP variability explained (R 2 ) by upright time, steps, and both was calculated within-subject using linear regression. Additional models considered quadratic terms for upright time and steps. Results: Participants (n=256) were 59% female, with mean±SD age of 45.2±11.6 years, resting systolic BP (SBP) of 130±10 and diastolic BP (DBP) of 84±7, and provided 32.5±3.9 daytime ABPM measurements. Upright time and steps were directly associated with BP. Upright time and steps explained the most variability (highest R 2 ) using the 1-minute interval prior to ABPM measurement; R 2 gradually declined with increasing interval length. From 1-minute prior, upright time explained 12% of the variability in SBP and 10% of DBP, on average. Adding an upright time quadratic term increased R 2 (SBP: 16%; DBP: 13%). Steps in the minute prior explained 12% and 7% of the variability in SBP and DBP, respectively, and increased to 16% and 11% with the addition of a quadratic term. A final model including upright time, steps, and quadratic terms explained 25% and 20% of the variability in SBP and DBP, respectively. Conclusions: Posture and steps, especially in the minute prior, explained a substantial amount of individual variability in ABPM. These findings advance our understanding of BP variability and may have implications for the quantification and interpretation of daytime ABPM data.