A Comparison of Human Muscle Temperature Increases During 3-MHz Continuous and Pulsed Ultrasound With Equivalent Temporal Average Intensities

Joseph A. Gallo, David O. Draper, Lori Thein Brody, Gilbert W. Fellingham

DOI: 10.2519/jospt.2004.1363

Study Design: A repeated-measure crossover design was used. The independent variable was the type of ultrasound (pulsed or continuous) and the dependent variable was intramuscular temperature. Objective: To compare changes in intramuscular temperature resulting from the use of pulsed ultrasound versus continuous ultrasound with an equivalent spatial average temporal average (SATA) intensity. Background: There is a lack of research on the heat-generating capabilities of pulsed ultrasound within human muscle. Methods and Measures: The subjects were 16 healthy volunteers (mean age ± SD, 21.3 ± 2.5 years). Each subject was treated with pulsed ultrasound (3 MHz, 1.0 W/cm ₂, 50% duty cycle, for 10 minutes) and continuous ultrasound (3 MHz, 0.5 W/cm ₂, for 10 minutes) during a single testing session. Tissue temperature returned to baseline and stabilized between treatments and treatment order was randomized. Tissue temperature was measured every 30 seconds using a 26-gauge needle microprobe inserted at a depth of 2 cm in the left medial gastrocnemius muscle. Data were analyzed using a linear mixed model. Results: Treatment with continuous ultrasound produced a mean (±SD) temperature increase of 2.8°C ± 0.8°C above baseline. Treatment with pulsed ultrasound produced a mean (±SD) temperature increase of 2.8°C ± 0.7°C above baseline. Statistical analysis revealed no significant differences in either the extent or rate of temperature increases between the 2 modes of ultrasound application. Conclusion: Pulsed ultrasound (3 MHz, 1.0 W/cm ₂, 50% duty cycle, for 10 minutes) produces similar intramuscular temperature increases as continuous ultrasound (3 MHz, 0.5 W/cm₂, for 10 minutes) at a 2-cm depth in the human gastrocnemius. Spatial average temporal average intensity is an important consideration when selecting pulsed ultrasound parameters intended to deliver nonthermal effects.

J Orthop Sports Phys Ther. 2004;34(7):395-401. doi:10.2519/jospt.2004.1363 

Key Words: heat, physical agents, spatial average temporal average intensity

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