Heart rate and blood pressure will probably work in case of extreme pain/high level of pain. I am recovering from a 2 hours and half+ surgery on my ankle which was badly damaged: the surgery did require 2 experienced surgeons. The day post surgery my pain level was shooting to the roof even if I had a pain pump, the pain level was extreme -turn out that the pain pump was busted and was not working. At one time I decided to check my blood pressure and monitor my heart beat during a cycle of pain and yes it was definitely noticeable on the blood pressure, but slightly less on heart beat.