ORIGINAL ARTICLE

Changes in muscle temperature induced by 434 MHz microwave hyperthermia

Noriko Ichinoseki-Sekine¹, Hisashi Naito², Norio Saga², Yuji Ogura¹, Minoru Shiraishi³, Arrigo Giombini⁴, Valentina Giovannini⁵, Shizuo Katamoto²

¹ Institute of Health and Sports Science & Medicine, Juntendo University, Inba, Japan
² Graduate School of Health and Sports Science, Juntendo University, Inba, Japan
³ Division of Sports Medicine, Jikei University School of Medicine, Minatoku, Japan
⁴ National Institute of Sports Medicine-Physiotherapy and Rehabilitation Unit, Rome, Italy
⁵ Research and Development Department, Restek Medical Device, Rome, Italy

Correspondence to:
Dr N Ichinoseki-Sekine
Institute of Health and Sports Science & Medicine, Juntendo University, 1-1 Hiragagakuendai, Inba, Chiba 270-1695, Japan; noriko.sekine{at}sakura.juntendo.ac.jp

Objective: To investigate the changes in temperature of human muscle during microwave hyperthermia.

Methods: Skin surface and muscle temperatures were measured in 11 healthy adult men (mean (SD) age 24.3 (2.2) years; height 174.2 (6.1) cm; weight 70.0 (5.3) kg) during a 30 min exposure of the thigh to 434 MHz microwave hyperthermia. Skin temperature was maintained at the pilot temperature of 40°C, and the temperature of the water in the bolus was 38°C. The peak power output was set at 60 W and controlled automatically to maintain the pilot temperature. The temperature was measured in the vastus lateralis muscle at an average muscle depth of 2.0 (0.2) cm, using a 23 G Teflon-shielded thermocouple. Biopsy specimens were obtained for light microscopy from three subjects. A muscle-equivalent phantom was used to evaluate the vertical heating pattern.

Results: Both skin and muscle temperatures increased from baseline, and muscle temperature was higher than skin temperature (skin temperature 39.2 (0.5)°C, temperature rise 5.0 (1.5)°C; muscle temperature 43.7 (0.8)°C, temperature rise 8.9 (1.4)°C). At the end of the hyperthermia treatment, muscle temperature decreased to 39.8 (0.9)°C, but was still 4.8 (1.5)°C higher than the baseline. No signs of muscle damage were observed on the basis of the blood creatine kinase activity and histological sections.

Conclusions: The results show that the 434 MHz microwave hyperthermia treatment increased and maintained muscle temperature locally by 6.3–11.4°C without muscle damage. These findings suggest that the microwave hyperthermia system provides effective and safe treatment.

Abbreviations: CK, creatine kinase; HSP, heat shock protein

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