Aj. Peixoto et al., EFFECTS OF ACTUAL VERSUS ARBITRARY AWAKE AND SLEEP TIMES ON ANALYSES OF 24-H BLOOD-PRESSURE, American journal of hypertension, 8(7), 1995, pp. 676-680
Investigators conducting hypertension trials with ambulatory blood pre
ssure (BP) monitoring have been analyzing study results using arbitrar
y times for day (wakefulness) and night (sleep). We prospectively eval
uated the impact of using arbitrary times instead of patient reported
awake and sleep times on mean 24-h, awake, and sleep BP, BP loads, and
the awake-sleep BP difference in 50 subjects. Daytimes and nighttimes
were derived from popular, arbitrary times reported in the literature
. Compared to actual awake and sleep periods, arbitrary day and night
division caused no significant differences in the mean awake and sleep
BPs. However, limits of agreement for BP values derived for the actua
l and arbitrary times of wakefulness and sleep were substantial especi
ally during sleep (awake systolic BP, -4 to 7 mm Hg; awake diastolic B
P, -2 to 4 mm Hg; sleep systolic BP, -12 to 7 mm Hg; and sleep diastol
ic BP -7 to 4 mm Hg). Sleep BP loads (proportion of BPs >120/80 mm Hg)
were altered by greater than 10% in 20% to 30% of the subjects, depen
ding on choice of time schedule. These data demonstrate that the calcu
lation of BP and BP load during sleep may be altered by use of arbitra
ry, rather than actual, times of wakefulness and sleep in 24-h studies
of ambulatory BP.