Objective evaluation of pain using experimental heat stimulation

Abstract

Background & goal of the study. International Association for the Study of Pain defines pain as an unpleasant sensory and emotional experience which leads to the concept that pain is subjective. Everyone must agree that doctors have to treat patients’ pain if they say that they feel severe pain. However, doctors sometimes encounter problems due to lack of objective evaluation methods of pain. For example, even after the doctor has administered full strength of the medicine for the specific patient for the pain he/she is experiencing, the patient at times still remain unsatisfied. This is because patients are not always able to tell that the medicine has already taken effect. To evaluate patients’ pain correctly, objective evaluation methods should be developed. The goal of the study is to develop a way to evaluate the sharp, momentary pain objectively using electroencephalogram (EEG). Methods. After signing the written informed consent, 20 healthy volunteers attended the study. Five different thermal stimuli (selected from 40, 42, 44, 46, 48, 50°C stimulus based on individual heat pain tolerance data) were applied randomly using PATHWAY (Medoc Co Ltd., Israel). Participants’ subjective evaluation of pain was done using Visual Analog Scale (VAS). Moreover, participants were randomly subjected to 20 pairs of the above mentioned stimuli. The relative rating scale of subjective pain for each thermal stimulus was used as subjective evaluation. Rating were based on the subjective declaration of ("–3 : The former is very painful" "0 : Neither can you say" "+3 : the latter is very painful"), the pairing comparison method of Chefe Method used for scale. Results. In the thermal stimulation, half of the participants showed over 0.6 of R2 value which means correlation coefficient between relative pain scale and amplitude extracted from EEG data. Discrimination rates between maximum stimulation and middle stimulation was 80%, middle stimulation and minimum stimulation also 80% based on subjective evaluation and fluctuation of amplitude data. Discussion. A close relationship between the stimulation intensity and EEG data is clarified. Objective discrimination of pain can be developed using EEG, and in particul ar, it must be useful for patients who cannot describe the amount of pain they are experiencing properly.