Published Online
on August 11, 2003

A more recent version of this article appeared on September 2, 2003

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Submitted on February 6, 2003
Revised on June 4, 2003
Accepted on June 6, 2003

Seasonal Variation of Fibrinogen in Dipper and Nondipper Hypertensive Patients

Ramón C. Hermida PhD^*, Carlos Calvo MD, PhD, Diana E. Ayala MD, PhD, José E. López MD, PhD, José R. Fernández PhD, Artemio Mojón PhD, María J. Domínguez MD, and Manuel Covelo MD

From the Bioengineering and Chronobiology Laboratories (R.C.H., D.E.A., J.R.F., A.M.), University of Vigo, Campus Universitario, Vigo, Spain; and Hypertension and Vascular Risk Unit (C.C., J.E.L., M.J.D., M.C.), Hospital Clínico Universitario, Santiago de Compostela, Spain.

^* To whom correspondence should be addressed. E-mail: rhermida{at}tsc.uvigo.es.

Background--A seasonal variation with higher values in winter has been previously reported in plasma fibrinogen, a recognized marker of the potential risk of myocardial infarction and stroke. The lack of nocturnal decline in blood pressure has also been associated with an increase in cardiovascular events. Accordingly, we have compared the yearly variation of plasma fibrinogen in dipper and nondipper hypertensive patients.

Methods and Results--We studied 1006 stage 1 to 2 hypertensive patients (482 men and 524 women, 53.0±13.4 years of age). Blood pressure was measured every 20 minutes during the day and every 30 minutes at night for 48 consecutive hours. Physical activity was simultaneously evaluated at 1-minute intervals with a wrist actigraph. A blood sample was collected on the same day before starting blood pressure monitoring. The circannual variation of fibrinogen was established for all patients as well as for subgroups of dippers and nondippers (n=513; nocturnal blood pressure decline <10%) by multiple-component analysis. For the whole group of patients, fibrinogen was characterized by a highly significant seasonal variation (P<0.001) with a mean value of 318 mg/dL, double circannual amplitude (extent of predictable change along the year) of 40 mg/dL, and time of peak value in February. Throughout the year, the nondippers showed higher plasma fibrinogen levels than did the dippers (P<0.001).

Conclusions--The elevated plasma fibrinogen levels in nondipper patients appear to be directly related to their increased risk in vascular events, which are more prominent during the late winter months.

Key words: fibrinogen • blood pressure • seasons

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