Presented at the 2013 AAPM Annual Meeting « Back

Characteristics of Thermal Analgesia in Human Subjects

Charles Chabal, MD, chabal@talariainc.com¹, Peter J. Dunbar, MB ChB MBA², Susan A. Stoner, PhD³, (1) Evergreen Medical Center, Kirkland, Washington, (2) University of Washington, Seattle, Washington, (3) Talaria, Inc., Seattle, Washington

Introduction: Physical modalities such as heat and cold are often used to relieve pain. However, little is known about how these methods work. This study examined the analgesic properties of physical measures, specifically thermal analgesia in humans. It was hoped that the results could offer methods to better systematically evaluate physical analgesia and lead to more effective drug-free therapies. Methods: A computer-driven test device was created that controlled the area heated, rate of temperature rise, characteristics of the heat wave, and max/minimum temperatures. Outcomes scales were based on standardized measures used in environmental sciences. After IRB approval, 23 subjects participated in the study that examined several fundamental questions. Does the size of area heated, the absolute temperature, and the characteristics of the heat wave affect analgesic preferences? Results: Subjects preferred a 1x1-inch heated area. Smaller areas could not be detected and larger areas (2x6) did not produce greater analgesia. The preferred temperature was 44.6°C (range42-48°C, SD±1.4°C) and showed a bell-shaped distribution. Comfort and "liking" increased until 45.5°C then declined. Rapid temperature increases were unpleasant but slower rates were very pleasant. Subjects could detect as little as 0.5°C variation in temperature. Conclusions: This study produced a standardized methodology to evaluate physical analgesics and tested thermal analgesia. The results demonstrated some surprising findings related to the area of body heated, the preferred analgesic temperatures and characteristics of the heat wave. It is hoped that these methods can be applied to other physical analgesics and lead to more effective drug-free therapeutic options. References: 1) Nadler SF, Steiner DJ, Petty SR, Erasala GN, Hengehold DA, Weingand KW. Overnight use of continuous low-level heatwrap therapy for relief of low back pain. Arch Phys Med Rehabil. 2003 Mar;84(3):335-42. 2) Lewis SE, Holmes PS, Woby SR, Hindle J, Fowler NE. Short-term effect of superficial heat treatment on paraspinal muscle activity, stature recovery, and psychological factors in patients with chronic low back pain. Arch Phys Med Rehabil. 2012. 3) French SD, Cameron M, Walker BF, Reggars JW, Esterman AJ. A Cochrane review of superficial heat or cold for low back pain. Spine (Phila Pa 1976). 2006 Apr 20; 31(9):998-1006.

Funding: NIH 2R44CA099305-02

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