However, when it was used to treat low-back pain, fentanyl caused a significantly larger decrease in VAS affective responses (dropping by 65%) than sensory ones (a decline of 51%).
These data don't show that the two components, sensory and affective, are independent. In fact, it would be difficult to imagine that the emotional component of the pain experience is unrelated to the sensory intensity of the pain. The findings do suggest, however, that analgesic treatments, whether they be pharmacological, surgical, or psychological, might alter sensation and affect differentially. A tranquilizer, for example, could reduce the emotional reaction to discomfort while leaving the intensity of the sensation unchanged ( Gracely, McGrath, & Dubner, 1978). An assessment tool that focused only on intensity would mistakenly conclude that the patient's condition was unimproved.
As noted earlier, pain patients are faced with a disease or injury that has both sensory and emotional consequences. Price, Harkins, and Baker examined whether
Affective VAS ratings of clinical pain will be higher in patients whose pain is likely to be associated with a serious threat to health or life in comparison to patients whose pain is likely to be less threatening... for comparable levels of pain sensation intensity. ( 1987)
Their results indicate that affective VAS ratings were, as expected, generally greater than sensory ratings for patients suffering from back pain, the burning causalgia pain that follows nerve injury, and cancer pain. Those suffering from the dental myofascial pain dysfunction (MPD) syndrome had no difference between the two ratings. Women undergoing labor, which is an acute pain with a very positive outcome, rated the emotional component as significantly less intense than the sensory. The steep increase in affective response to experimentally induced pain in volunteer subjects, compared with the sensory response, was not replicated.
Pain assessment is a complex but rewarding area of research. Rigorous psychophysical procedures ( Chapman et al., 1985; Gracely, 1989; Rollman, 1989) can be utilized to assist in diagnosis and to evaluate treatment. The last 25 years have seen an explosive interest in pain research and treatment, in the establishment of international research societies and journals, in the proliferation of pain clinics, and in the understanding of the physiological and psychological factors that contribute to the experience of pain and to its alleviation. There is no cause for complacency about the status of pain control, but there is much cause for hope.
Algom D., Raphaeli N., & Cohen-Raz L. ( 1986). "Integration of noxious stimulation across separate somatosensory communications systems: A functional theory of pain". Journal of Experimental Psychology: Human Perception and Performance, 12, 92-102.