• Katie McLellan, Jerrold S Petrofsky, Gurinder Bains, Grenith Zimmerman, Michelle Prowse, and Scott Lee.
• Department of Physical Therapy, School of Allied Health Professions, Loma Linda University, Loma Linda, CA 92350, United States.
• Med Eng Phys. 2009 Mar 1; 31 (2): 165-72.

AbstractThe Pennes model predicts the ability of the skin to dissipate heat as a function of conductive heat transfer and blood flow. Conductive heat exchange may be affected by skin moisture and subcutaneous fat thickness, factors not considered by Pennes. In the present investigation, we sought to expand the Pennes model by examining subcutaneous fat and skin moisture as factors of heat dissipation and their effects on heat exchange and blood flow. Subjects who were older (O) (mean age 64.2+/-5.9 years, n=15), had diabetes (D) (mean age 62+/-5.9 years, mean duration 13.2+/-9.1 years, n=15), and were younger (Y) (mean age 25.7+/-2.9 years, n=15) participated. Thermisters were placed in an iron heat probe and on the skin to measure the change in skin temperature to create a thermal change index to demonstrate the ability of the skin to dissipate heat. The lower back had the thickest subcutaneous fat layer for all subjects, which contributed to higher skin temperatures than the foot and hand in response to local and global heat. There was a significant inverse correlation between skin moisture and skin temperature after 5s of heat application (r=-0.73, p<0.001) with O and D having significantly less skin moisture than Y (p<0.05). O and D had significantly increased skin temperatures in response to local heat, as compared to Y, in all global temperatures (p<0.05). Thus, the Pennes model may need to be adjusted to take into consideration aging, diabetes, skin moisture, and subcutaneous fat thickness.

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