Depressed autonomic nervous system function in African Americans and individuals of lower social class: a potential mechanism of race- and class-related disparities in health outcomes.

BACKGROUND: Both race and social class influence cardiovascular outcomes, through mechanisms not yet fully understood. Minority race and lower social class are sources of chronic stress, which can alter autonomic nervous system function. Heart rate variability (HRV), a measure of autonomic function, is also an important predictor of cardiovascular outcomes.
METHODS: To determine whether minority race/ethnicity and lower social class are associated with depressed HRV, we prospectively collected data on sociodemographic, clinical, psychological, and behavioral factors by survey in 360 outpatients undergoing ambulatory electrocardiographic monitoring. Heart rate variability (24-hour) was measured by frequency domain analysis.
RESULTS: In unadjusted analysis, African Americans had lower HRV than whites, and individuals of lower social class as measured by education, occupation, and income had lower HRV than those of higher class. In multivariable analysis, both race and social class were independent predictors of ultralow frequency power after controlling for clinical and psychological factors. African Americans were 3.45 (95% CI 1.74-6.98, P = .0004) times as likely as whites to have depressed HRV (ultralow frequency power, lowest tertile), and non-college graduates 2.94 (95% CI, 1.71-5.14, P = .0001) times as likely as college graduates to have depressed HRV.
CONCLUSIONS: Heart rate variability is lower in African Americans and individuals of lower social class, independent of the effects of measured clinical, psychological, or behavioral factors. This suggests that the adverse effects of minority race and lower social class on cardiovascular outcomes may be mediated by dysregulation of autonomic function.