Does anyone know of research documenting large heart-rate decrease during episodes of psychological dissociation? 

Several trauma therapists have employed some of Stephen Porges' polyvagal suppositions to support how their therapies might work. A critical aspect of their argument is that trauma patients' dissociative responses will coincide with massive increases in cardiac vagal tone. This must produce large DECREASES in heart rate (since that is the effect of increased vagal tone upon the heart). I have perused the scientific literature searching for any evidence of this but so far failed to find anything (there appears a little evidence for very small heart rate decreases, but nothing that would account for dramatic increases in vagal tone upon the heart and no evidence that they are vagally mediated, so far as I can tell). Can anyone lead me to other litrrature that would support those claims? Thanks in advance for any help.