Quantitative Measurement of Pain *

Abstract

Clinical pain is generally measured by means of either the patient's subjective or involuntary responses. However, such measures are both imprecise and qualitative. Consequently, laboratory-induced pain has been used extensively in order to develop quantitative measures of pain. Historically, experimental human pain methods have had a controversial background, but recently improved methodology and more sophisticated techniques have established laboratory pain-induction methods as useful and valid instruments for human pain evaluations. While there are innumerable ways of inflicting pain experimentally, only a limited number of pain induction methods have been used extensively and appear to be of value. It is useful to classify these into various categories in terms of the nature of the physical noxious stimulus, such as electrical, mechanical, thermal, and chemical methods. Cutaneous electrical stimulation is probably the most widespread method. Ischemia is a good example of a chemical technique; the pressure algometer of a mechanical method; and the cold pressor and radiant heat methods of thermal techniques. Both the electrical and the cold pressor methods have been found valid instruments for human analgesic assays. The ischemic, radiant heat and pressure algometer techniques appear to be more equivocal in theii application to analgesic evaluations in man. The electrical stimulation technique, although the most widely used, suffers from the disadvantage that it produces a characteristic and unique sensation almost invariably identified as “electrical” stimulation. Usually, patients and individuals experiencing this electrical stimulation prefer not to use the label “pain” but describe it as discomfort or cramping.