Hypoxia and altered platelet behavior influence von Willebrand factor multimeric composition in secondary pulmonary hypertension.

In pulmonary hypertension (PH), defective plasma von Willebrand factor (vWF) lacking the larger multimers with increased concentration of low-molecular-weight fractions (LMW) has been reported, although the mechanisms involved are not completely known. Altered platelet behavior may be involved in this alteration; this hypothesis was investigated in 10 patients with PH associated with chronic hypoxemia and erythrocytosis (age 13 to 51 years, mean pulmonary artery pressure 38 to 98 mmHg). The possible influence of the hematocrit (Hct) and decreased oxygen saturation (SpO2) on vWF abnormalities was examined. Patients were evaluated before and after therapeutic hemodilution. vWF alterations were quantified using the ratio of LMW/total multimers (densitometric analysis of luminographs after Western blotting). Platelet count and activation state (plasma levels of beta-thromboglobulin, enzyme-linked immunosorbent assay), the Hct and SpO2 were also assessed before and after hemodilution. Platelet activation and consumption were suggested by increased plasma beta-thromboglobulin (p=0.0444) with decreased platelet count (p<0.001). Altered vWF LMW/total ratio correlated significantly with decreased platelet count (p=0.0066) and low SpO2 (p=0.0088). The effects of both variables were independent and additive (p=0.0031, multiple regression). Hemodilution was followed by an increase in platelet count (p=0.0013) associated with improvement of LMW/total ratio (p=0.0079). Residual vWF alterations were associated with persistent hypoxemia and residual platelet activation (plasma beta-thromboglobulin still increased). These data suggest a common mechanism for platelet and vWF abnormalities in these chronically hypoxic PH patients. Hypoxia itself may play a role, possibly inducing endothelial release of unprocessed (LMW) vWF molecules.