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  Differential Measurement of Pain Perception

The Anesthesiology Section of the newly reorganized Pain Branch was to be an expanded program in the evaluation of drugs for dental anesthesia and analgesia. Edward Driscoll had cut back on his experimental work as he took on new administrative responsibilities in the Dental Institute, but he continued to be an advocate for pain research at NIDR, and for effective alternatives to general anesthesia during oral surgery.

To staff the Anesthesiology Section, Dubner and Driscoll looked for people with expertise in psychology, pharmacology, and neurology, as well as dentistry, and with the skills and background to refine the complex methodologies of clinical trials to evaluate analgesics.

Some Issues in Analgesic Clinical Trials
  • Differentiation of changes in sensory perception of pain from changes due to cognitive or affective factors
  • Relationship of activity of analgesic drugs to internal pain activation/modulation mechanisms
  • Variations in patient response to drugs

Clinical trials of analgesics presented special problems both because so little was understood about pain mechanisms and because evaluators had to rely on the subjective report of patients, whose sensory perceptions were often affected by their cognitive and affective, or emotional, responses. [This is the reason why many analgesic trials use the crossover method, so that the test drugs are evaluated in the same patient, each serving "as his own control".]

Richard Gracely, as a psychology graduate student at Brown University, began work on a verbal pain measurement tool that would differentiate the patient's sensory perception of pain intensity from his affective experience of the pain's "unpleasant" quality.

In 1975, Gracely joined the NAB and completed his dissertation work on the Differential Descriptor Scale . This scale can be used to demonstrate, for example, that the narcotic fentanyl decreases the perception of pain intensity, independent of its effects on affective quality; while the tranquilizing drug diazepam decreases the patient's sense of distress, independent of perceived changes in the intensity. Gracely went on to develop several innovative word scales for pain measurement, with collaborators including Patricia McGrath and Donna Kwilocz .

Awaiting Description

Differential Descriptor Scale.
Gracely's work is based on the idea that "You can't just do magnitude measures of pain and really get a lot of meaning out of it unless you anchor the judgment some way....Every word response is an anchor to a subjective level". 8

His research is characterized by the use of multiple internal controls to test the validity of the assessor (the patient); the validity of the internal relationships of the ranking terms; and the sensitivity of the scale to changes under analgesia or other environmental influences. In the initial set of studies, volunteer subjects selected words from two randomly organized lists to describe two different types of noxious stimuli (electrical shock and cold press or); their verbal rankings were further assessed against their analog responses (handgrip and line length) to stimuli. This "cross-modality matching" was a cross-check of both the subjects and the method.

Cross-modality matching of verbal descriptiors against noxious stimuli. From Richard Gracely, Ronald Budner, Patricia McGrath, and Marc Heft New methods of pain measurement and their application to control. International Dental Journal v. 28 (1978): 55, 59.

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8 Oral history interview with Richard Gracely, 1998-99. Tapes and transcript to be deposited in the NIH History Office and the John C. Liebeskind History of Pain Collection, UCLA.

Photograph of Rick Gracely at the computer
Rick Gracely at the computer
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