Christena Wood and Dr. Kenneth L. Knight, Health and Human Performance
Research Question
Is an electric hot pad as effective as a hydrocollator pack in heating tissue?
Significance
Since the advent of the hydrocollator heat pack, a sand filled canvas bag that is heated in a hot water bath, in the 1950s, the use of the traditional electrical hot pad has diminished. Treatment using heat has been confined to hospitals, physical therapy clinics, athletic training rooms, and other such venues that can afford the expensive hydrocollator heating units. There is a common belief that the electric hot pad is not as effective as a hydrocollator pack, even though before this study, a direct comparison study had not been done. If a home heat treatment, such as could be provided with an electric heat pad, is as effective as the more expensive hydrocollator pack, treatments could be given at home thus decreasing medical costs.
Therapeutic effects of heat include decreases in pain and spasm [2,3,5,7] and increases in blood flow [2,5,7] Increased blood flow can lead to local improved tissue nutrition, improved wound healing, decreased susceptibility to infection, and facilitated soft tissue repair [2,3,5,7]. Wet heating is thought to be more effective than a similar level of dry heating in increasing tissue temperatures [1]. Comparison studies between hydrocollator heat packs and dry air heat have been done to test this theory [4], but not between hydrocollator packs and electrical heat pads.
As decreased pain and full return to normal activity are the primary goals in treatment, the correct application of heat is necessary to facilitate the shortest recovery period. This study focused on whether an electric hot pad was as beneficial as a hydrocollator pack in increasing tissue temperatures. This research is valuable to those who treat or rehabilitate a variety of injuries, illnesses, and diseases as it will provide insight into the most effective method of treatment. It is also of interest to those who want to provide quality, inexpensive home treatments.
Design and Setting
Twenty-four college age subjects volunteered to be in this study. (12 males, age = 23.4 ± 3.5 years; mass = 192.9 ± 42.9 lbs.; height = 71.5 ± 3.8 in. and 12 females, age = 22.8 ± 2.6 years; mass = 146.5 ± 19.8 lbs.; height = 67.3 ± 3.2 in.) Each subject reported to the Modalities Lab (123 RB) in the Human Performance Research Center on three separate days. At the first visit, each participant was screened for any medical risks, and/or contraindications to heat therapy.
Admitted subjects were informed of the risks and benefits of the study and signed an Institutional Review Board approved informed consent. Height, weight, age, and calf skin fold were also measured at this time. From the calf skinfold, the needed depth of the intramuscular thermocouple to be 2 cm in the muscle was determined. The intramuscular and four skin interface thermocouples were then placed in the subject. After 5 minutes of baseline monitoring, the assigned heating modality, according to a Balanced Latin Square, was then applied for 20 minutes. An additional 10 minutes of monitoring continued after the heat was removed. Surface and intramuscular temperatures were measured with type-T thermocouples interfaced with a 16- channel Isothermex unit and a personal computer. Tissue temperatures were recorded every 30 seconds.
Results
Results showed no gender differences, so the data was combined. There was no difference between conditions for skin (~31ºC) and muscle (~36ºC) temperatures before heat application. After 20 minutes of application, the electric heat over a wet towel, electrical, and hydrocollator pack resulted in temperature increase of ~5.6ºC, ~9.4ºC, and ~10ºC, respectively, and intramuscular temperature increases of ~.02ºC, ~.7ºC, and ~.95ºC, respectively. At the end of the 20 minute application, the electrical hot pad was gradually continuing to increase skin and muscle temperature whereas the hydrocollator heat pack had peaked and was decreasing.
Conclusions
Even though these two heat treatments were different at 20 minutes, the difference was only .6 of a degree. It is probable that if a few more minutes were added to the treatment, the electrical heat would be as warm as the hydrocollator pack. Electrical hot pads are less expensive than hydrocollator units, do not require rewarming between uses, and are tolerated better than hydrocollator packs. Electric heat pads appear to be a viable alternative to hydrocollator packs for heat applications in excess of 20 minutes.
References
- Abramson, DI, Tuck, S, Lee, SW, Richardson, G. Comparison of wet and dry heat in raising temperature of tissues. Arch Phys Med Rehabil. 1967; 48:654-661.
- Behrens, BJ, Bell, GW. The effects of therapeutic modalities on blood flow in the human calf. J Orthop Sports Phys Ther. 1991; 13:23-27.
- Bracciano, AG. Physical Agent Modalities: Theory and Application for the Occupational Therapist. (2000). Thorofare, N.J.: Slack, Inc.
- Erdman, WJ, Stoner, EK. Comparative heating effects of moist air and hydrocollator hot packs. Arch Phys Med Rehabil. 1956; 37:71-74
- Halverson, GA. Therapeutic heat and cold for athletic injuries. Physician and Sports Med. 1990; 18:87-94.
- Lehman, JF, Silverman, DR, Baum, BA, Kirk, NL. Temperature distributions in the human thigh, produced by infrared, hot pack, and microwave applications. Arch Phys Med Rehabil. 1966; 47:291-299.
- Smith, KL. The effects of a hot pack treatment on muscle tissue temperature. Thesis (M.S.): Brigham Young University (1994).