Study objectives: BP normally drops (or "dips") by approximately 10% at nighttime; however, in a number of illnesses there is an increased amount of "nondipping" of nocturnal BP. This study examined whether nondipping in older African Americans and older white subjects is related to the presence of sleep-disordered breathing (SDB) and hypertension.
Design: Prospective study with a convenience sample.
Setting: All data were collected in the subjects' homes.
Participants: Seventy self-defined African Americans with complaints of snoring or excessive daytime sleepiness, and 70 age-matched and gender-matched white subjects.
Measurements and results: Sleep was recorded for 2 nights, with 1 night of oximetry. BP was recorded on a separate 24-h period. African Americans had higher dipping ratios than white subjects even after accounting for covariates such as respiratory disturbance index (RDI), oxygen desaturation index (ODI), body mass index, and average 24-h mean arterial pressure (p = 0.025). Higher values of RDI (R(2) = 0.0686, p = 0.021) and ODI (R(2) = 0.042, p < 0.03) were correlated with higher dipping ratios in both African Americans and white subjects. However, there was a three-way interaction such that higher RDIs were correlated primarily with nondipping in African Americans receiving antihypertensive medication (R(2) = 0.0373, p = 0.022).
Conclusions: These results demonstrated that African Americans tend to be "nondippers," while white subjects tended to be "dippers." This nondipping was not a result of weight, gender, or of having SDB. The analyses also confirmed that, in both races, the dipping ratio was greatest in those with SDB and hypertension. The third hypothesis, that RDI would be greatest in the nondipping hypertensive subjects, was true only for the African Americans.