Assessing Pain in a Noninvasive Manner by Measuring Changes in the Microcirculation

ABSTRACT The quantitative determination of the level of pain is one of the most challenging clinical problems. This article proposes a method for quantitative assessment of both acute and chronic levels of pain, based on the analysis of hemodynamic patterns measured using a non-invasive sensor. Hemodynamic characteristics were taken from the finger using a sensor measuring the dynamic scattering of light from the skin surface. Changes in hemodynamic parameters in patients with chronic pain were studied. One group of patients with chronic back pain required epidural injection for pain relief. The second group of patients had a Spinal Cord Stimulator implant which was switched off one hour before arriving at the clinic. Optical signals were collected before and after pain relief, either by epidural injection or by turning on the stimulator. Both groups reported their pain level using a standard numerical rating scale. Processing of the results showed that the changes in measured hemodynamic parameters corresponded in most cases to the changes in pain reported by patients following medical intervention. The results suggest that this new non-invasive measurement of pain can be used both for physiological studies and for monitoring various categories of patients suffering from pain.