Effect of time of day on intraindividual variability in ambulatory blood pressure

• Published in: American journal of hypertension 2000-11, Vol.13 (11), p.1203-1209
• Main Authors: Schwartz, Gary L, Turner, Stephen T, Moore, Jason H, Sing, Charles F
• Format: Article
• Language: English
• Subjects: Adult; Ambulatory blood pressure; Biological and medical sciences; Blood Pressure - physiology; Blood Pressure Monitoring, Ambulatory; blood pressure variability; Cardiology. Vascular system; Circadian Rhythm - physiology; clinical studies; Coronary heart disease; Female; Heart; Humans; Male; Medical sciences; Middle Aged; Predictive Value of Tests; Reference Values; Sex Factors; Time Factors
• ISSN: 0895-7061; 1879-1905; 1941-7225
• DOI: 10.1016/S0895-7061(00)01198-5

The aim of this study was to determine whether intraindividual blood pressure (BP) variability, measured by noninvasive ambulatory monitoring, differs between the active (daytime) and inactive (nighttime) periods of the day. We obtained ambulatory BP recordings in 143 healthy adults (95 men, 48 women) from Rochester, Minnesota. Readings were obtained every 10 min for a 24-h period. We calculated the standard deviation of each individual's BP readings about the means for the active period and for the inactive period as measures of intraindividual BP variability. In men, mean within-individual standard deviations for both systolic (SBP) and diastolic blood pressure (DBP) were significantly greater during the inactive period than during the active period (for SBP: 10.3 ± 2.1 v 11.9 ± 2.7, P < .0001; for DBP: 8.8 ± 2.0 v 9.7 ± 2.5, P = .0027). In women, the mean within-individual standard deviation for SBP did not differ significantly between the active and inactive periods (9.7 ± 2.2 v 10.3 ± 2.4, P = 0.225) but for DBP was significantly greater during the inactive period than during the active period (8.1 ± 2.0 v 9.2 ± 2.3, P = .020). Statistically significant predictors of intraindividual BP variability included measures of age and body size, metabolic traits, neuroendocrine traits, erythrocyte cation traits, and renal function traits. This study demonstrates that intraindividual BP variability, as measured by noninvasive ambulatory monitoring, is as great or greater during the inactive period as during the active period of the day.