Predictors of interindividual variation in ambulatory blood pressure and their time or activity dependence

The objectives of this study were to determine whether total interindividua l variation in blood pressure (BP) differs between inactive and active hour s of the day, to identify predictors of interindividual variation in BP, an d to assess whether variation associated with any of these identified predi ctors is greater (or less) during inactive hours than during active hours o f the day. We obtained ambulatory BP recordings over 20 consecutive hours ( 12 active, out of bed [daytime]; and 8 inactive, in bed [nighttime]) in a s ample of 240 unrelated, non-Hispanic white adults (138 men; 102 women). We estimated total interindividual variation in BP, and the percentage of inte rindividual variation associated with measures of age and body size, metabo lic traits, catecholamines, erythrocyte cation transport, and renal functio n. We used linear regression to assess changes in the hourly estimates of t otal interindividual variation and in variation attributable to each set of predictor traits over the 20 h. In both men and women, total interindividual variation in systolic BP was s ignificantly greater (not less) during inactive hours than during active ho urs. In addition, in women, total interindividual variation in diastolic BP was as great during inactive hours as during active hours. Each set of tra its considered predicted a statistically significant percentage of interind ividual variation in BP, None of the sets of traits predicted a greater per centage of interindividual variation during the inactive hours than during the active hours. Measures of age and body size, catecholamines, cation tra nsport and renal function traits predicted significantly less interindividu al variation during inactive hours than during active hours of the day, That total interindividual variation in BP is as great or greater during in active hours than during active hours of the day emphasizes the potential f or differences in nighttime BP to contribute to the development of cardiova scular disease. In as much as the predictors of interindividual variation i n BF differ between the daytime and nighttime, the causes of variation duri ng these two times may also differ. (C) 2000 American Journal of Hypertensi on, Ltd.