A comparison of ambulatory blood pressure patterns across populations.

Background: Black individuals are characterized by a blunted nocturnal decline (i.e. dipping) in blood pressure compared with whites. The resulting increase in cardiovascular load has been hypothesized to contribute to ethnic differences in hypertension and its sequelae.

Objective: To examine data from two different locations and determine factors related to ethnic differences in ambulatory blood pressure pattern.

Methods: Ambulatory blood pressure recordings were performed on 300 youths from Memphis, Tennessee and 195 youths from Augusta, Georgia, USA. Stepwise regressions were performed to determine the factors associated with daytime and night-time blood pressure and the nocturnal decline in blood pressure. The factors examined were recording location, ethnicity, gender, age, height, weight and genetic predisposition.

Results: Significant factors in the model for the nocturnal decline in systolic blood pressure included location (R(2) = 0.031, P < 0.001), followed by ethnicity (R(2) change = 0.015, P < 0.006) and height (R(2) change = 0.009,P < 0.03). Significant factors in the model for the nocturnal decline in diastolic blood pressure included location ( R(2) = 0.176, P < 0.001), followed by ethnicity ( R(2) change = 0.016, P < 0.002) and height (R(2) change = 0.02, P < 0.001). The nocturnal decline was greater in the Augusta subjects because of higher daytime systolic (P < 0.002) and diastolic (P < 0.001) blood pressure. Weight contributed significantly to the models for resting blood pressure and daytime blood pressure. Gender was the only variable that contributed to the model for resting systolic blood pressure.

Conclusions: Both genetic and environmental factors contribute to individual differences in ambulatory blood pressure patterns. Much of the variance of ambulatory blood pressure levels and patterns remains, however, unexplained.