Haemodynamic responses and changes of haemostatic risk factors in cold-adapted humans

Epidemiological studies have shown an increase in acute myocardial infarcti ons or deaths due to myocardial infarction in colder weather; the mechanism s most likely involve increased blood levels of haemostatic risk factors, a nd increases in arterial blood pressure and heart rate. We studied the rela tionship between cold adaptation, haemostatic risk factors and haemodynamic variables. Cold adaptation was obtained by a programme of immersion of the whole body up to the neck in a water-filled bath, the temperature of which was gradually decreased from 22 degrees C to 14 degrees C, time of exposur e being increased from 5 to 20 min over a period of 90 days. We studied 428 patients (44% men) and measured blood levels of fibrinogen, plasminogen ac tivator inhibitor 1 (PAI-1), tissue plasminogen activator antigen (t-PA), p lasma viscosity, von Willebrand factor, D-dimer and platelet count, both at baseline and after 90 days of daily immersion. There were significant redu ctions in von Willebrand factor (-3%; p<0.001), and plasma viscosity (-3.0 s; p<0.001), and a mild but significant increase in PAI-1 (+ 0.3 IU/ml; p=0 .02). The pressure rate product (systolic blood pressure x heart rate) was also significantly lower after cold adaptation (-310; p=0.004). Cold adapta tion, compared with exposure to cold weather, induces different haemodynami c responses and changes of blood levels of haemostatic risk factors.