Relation between perceived blood loss and vasovagal symptoms in blood donors

This study examined whether a belief of significant blood loss may be associated with vasovagal symptoms, irrespective of actual blood loss. Individual differences in vasovagal symptoms among blood donors who had an equivalent amount of blood withdrawn were significantly associated with their rating of perceived blood loss.

The anticipation or belief of blood loss, and perhaps more remotely associated ideas, may trigger processes similar to those induced by actual hemorrhage though further research is required to address other possibilities such as the inflation of ratings by vasovagal symptoms.