Nighttime Vagal Cardiac Control and Plasma Fibrinogen Levels in a Population of Working Men and Women

Roland von Kaenel, M.D., ∗ Julian F. Thayer, Ph.D.,†‡ and Joachim E. Fischer, M.D., M.Sc.‡

From the Department of General Internal Medicine, Bern University Hospital, Inselspital, and University of Bern, Bern, Switzerland; †Department of Psychology, Ohio State University, Columbus, OH; and Department of Public Health, Social and Preventive Medicine, Mannheim Medical Faculty, University of Heidelberg, Mannheim, Germany

Background: Elevated plasma fibrinogen levels have prospectively been associated with an increased risk of coronary artery disease in different populations. Plasma fibrinogen is a measure of systemic inflammation crucially involved in atherosclerosis. The vagus nerve curtails inflammation via a cholinergic antiinflammatory pathway. We hypothesized that lower vagal control of the heart relates to higher plasma fibrinogen levels.

Methods: Study participants were 559 employees (age 17–63 years; 89% men) of an airplane manufacturing plant in southern Germany. All subjects underwent medical examination, blood sampling, and 24-hour ambulatory heart rate recording while kept on their work routine. The root mean square of successive differences in RR intervals during the night period (nighttime RMSSD) was computed as the heart rate variability index of vagal function.

Results: After controlling for demographic, lifestyle, and medical factors, nighttime RMSSD explained 1.7% (P = 0.001), 0.8% (P = 0.033), and 7.8% (P = 0.007), respectively, of the variance in fibrinogen levels in all subjects, men, and women. Nighttime RMSSD and fibrinogen levels were stronger correlated in women than in men. In all workers, men, and women, respectively, there was a mean ± SEM increase of 0.41 ± 0.13 mg/dL, 0.28 ± 0.13 mg/dL, and 1.16 ± 0.41 mg/dL fibrinogen for each millisecond decrease in nighttime RMSSD.

Conclusions: Reduced vagal outflow to the heart correlated with elevated plasma fibrinogen levels independent of the established cardiovascular risk factors. This relationship seemed comparably stronger in women than men. Such an autonomic mechanism might contribute to the atherosclerotic process and its thrombotic complications.

Ann Noninvasive Electrocardiol 2009;14(2):176–184