I concur with Alena, i think it could possibly be arousal, whether you notice it or not, there are things your body can control that you may try to stop it from doing, but you can only control so much with your mind, and men and women are alike in a state of arousal that all blood rushes to the genital area where.. well, for a guy it’s quite obvious, but for a girl it isn’t visible to the eye (can be, only in coloration though) so..
i’m not sure about the blood pressure thing, i don’t know anything about that stuff but it doesn’t make sense to me what would intensify something to where it would take/slow the bloodflow to the fingers, unless there is something going on between arousal and blood pressure.