Autonomic tone and C-reactive protein: A prospective population-based study

Objectives: To examine the cross-sectional and longitudinal relationships between cardiac autonomic tone and serum CRP and to investigate potential causal links between these measures. Methods: A population-based sample of 188 home-dwelling, middle-aged and older adults (104 women, mean age 59 years) from Cook County, IL, participated in this prospective cohort study. High-frequency heart rate variability (HF) and pre-ejection period (PEP) served as markers of cardiac parasympathetic and sympathetic tone, respectively. Cardiac autonomic balance (CAB) was defined as the arithmetic difference between normalized values of HF and PEP. Multivariate regression and autoregressive cross-lagged panel analyses were used to investigate cross-sectional and longitudinal relationships, respectively. High-sensitivity enzyme immunoassay measured serum CRP. Results: After removing three cases with CRP values suggesting acute inflammation, the mean CRP value was 1.43 mg/L (range 0.02-7.96 mg/L, SD = 1.55). In models that adjusted for gender, age, race/ethnicity, education, body mass index, smoking, exercise, systolic blood pressure and health conditions including diabetes and hypertension, HF (B = -0.15, SE = 0.04, P < 0.01) and CAB (B = -0.14, SE = 0.04, P < 0.01) were significantly associated with natural log (ln) CRP. In longitudinal analysis, higher CRP levels in any one year predicted greater increases in HF in the subsequent year. Interpretation: The inverse relationship between HF and CRP in cross-sectional analysis is consistent with previous studies, while the longitudinal results suggest that cardiac parasympathetic tone may increase over time as a result of higher circulating CRP.