Ambulatory intra-arterial blood pressure in normal subjects.

It has been suggested that ambulatory blood pressure monitoring is superior to casual cuff methods in predicting cardiovascular events, but lack of reference data from a normal population seriously limits this method's clinical applicability. We therefore performed 24-hour intra-arterial ambulatory blood pressure (BP) monitoring in 50 normal volunteers (cuff BP less than 140/90 mm Hg) whose ages ranged from 18 to 74 years. There were 30 men and 20 women in the study, but there was no significant difference between the sexes with respect to age, cuff BP, or body mass index. A diurnal variation in BP was observed, qualitatively similar to that seen in hypertensive individuals, including a prewaking BP rise. Mean daytime intra-arterial pressures differed little between the sexes (124/74 mm Hg for women and 127/76 mm Hg for men, p = NS), but was lower at night in women than in men (96/52 versus 102/59 mm Hg, respectively; p less than 0.02 for diastolic pressure). Based on this group of subjects, we defined the upper limit of normal daytime BP in both men and women as 150/90 mm Hg and the upper limit of mean nighttime BP as 130/80 mm Hg for men and 115/65 mm Hg for women. The lower nighttime pressures in women compared with their male counterparts with similar daytime pressures may explain why women appear to tolerate similar levels of BP better than men.