Nighttime vagal cardiac control and plasma fibrinogen levels in a population of working men and women.
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.
von Känel
Roland
R
Department of General Internal Medicine, Bern University Hospital, Inselspital, Bern, Switzerland. roland.vonkaenel@insel.ch
Thayer
Julian F
JF
Fischer
Joachim E
JE
D000293:Adolescent; D000328:Adult; D015415:Biomarkers / Q000097:blood; D002940:Circadian Rhythm; D015716:Electrocardiography, Ambulatory / Q000379:methods / Q000706:statistics & numerical data*; D004651:Employment; D005260:Female; D005340:Fibrinogen / Q000378:metabolism*; D005858:Germany; D006339:Heart Rate; D006801:Humans; D008019:Life Style; D008297:Male; D008875:Middle Aged; D017678:Sex Distribution; D014630:Vagus Nerve / Q000503:physiopathology*; D055815:Young Adult
D015415:Biomarkers; D005340:Fibrinogen