Noninvasive Low-Frequency Ultrasound Energy Causes Vasodilation in Humans
Kiyoshi Iida, MD,
Huai Luo, MD,
Kohsuke Hagisawa, MD,
Takashi Akima, MD,
Prediman K. Shah, MD, FACC,
Tasneem Z. Naqvi, MD, FACC and
Robert J. Siegel, MD, FACC*
Division of Cardiology, Department of Medicine, Cedars-Sinai Medical Center, Los Angeles, California

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Figure 1 The ultrasound transducer was put on the upper arm covering the brachial artery. The transducer-radiating area is about 60 cm2 and the surface was coupled to the skin with ultrasound transmission gel.
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Figure 2 Percentage brachial artery diameter changes before and immediately after ultrasound (US) exposure in different time durations. There is significant vasodilation after 2, 3, and 5 min of ultrasound exposure compared with the baseline values. Images of the brachial artery were digitized and measured using the Vericis Echo Review application (Camtronics Medical Systems, Hartland, Wisconsin). The R-wave of the electrocardiogram was used to time the measurements of vascular diameter. *p < 0.01; p < 0.001; mean ± SEM (%), n = 10.
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Figure 3 A representative case of B-mode ultrasound image on brachial artery at baseline (left) and after 5 min ultrasound exposure (right). Brachial artery diameter was measured off-line after the procedure by the Vericis Echo Review application (Camtronics Medical Systems, Hartland, Wisconsin) using a semiautomatic quantitative analysis system (3.938 mm at baseline and 4.567 mm after ultrasound exposure). *p < 0.001, mean ± SEM (mm), n = 20.
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Figure 4 The brachial artery diameter before and after 5 min of low-frequency ultrasound (US) exposure. On the vertical axis is brachial artery diameter; on the horizontal axis is the time after ultrasound exposure (immediately, 3 min, and 5 min after ultrasound). Percentages were expressed as relative changes from baseline ([diameter change/baseline diameter] x 100). *p < 0.001; mean ± SEM (mm), n = 20.
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Figure 5 The correlation between brachial artery %UMD and %FMD. UMD = ultrasound-mediated vasodilation; FMD = flow-mediated vasodilation.
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