Vasoconstriction
The mechanical and thermal effects of focused ultrasound can induce vasoconstriction, the reduction of blood vessel diameter, either temporarily or permanently1,2.
Clinically, this could be used to treat vascular malformations or to block the downstream flow of blood in order to deprive tumors of nutrients3,4.
When exposed to ultrasonic pulses of very short durations, blood vessels have been shown to constrict, though the mechanism is not well known. In preclinical studies, this vasoconstriction slowly reduced over a period of up to two weeks after the vessels had been affected by ultrasound. This temporary vasoconstriction occurs with minimal thermal effects, indicating that the mechanical activity of the ultrasound is most likely responsible for inducing the physiological change1.
Alternatively, by utilizing the thermal effects of focused ultrasound, it has been proposed that superficial venous insufficiency – a disorder caused by valvular incompetence in the venous system – could be treated by shrinking the intermediate fibers, namely collagen, in the endothelial lining. In one preclinical study, focused ultrasound was used to cause vasoconstriction in the great saphenous vein, correcting the insufficiency2.
[1] Hynynen K, Chung AH, Colucci V, Jolesz FA. Potential adverse effects of high-intensity focused ultrasound exposure on blood vessels in vivo. Ultrasound Med. Biol. 1996;22:193–201.
[2] Pichardo S, Milleret R, Curiel L, Pichot O, Chapelon J-Y. In vitro experimental study on the treatment of superficial venous insufficiency with high-intensity focused ultrasound. Ultrasound Med. Biol. 2006;32:883–91.
[3] Goertz DE. An overview of the influence of therapeutic ultrasound exposures on the vasculature: High intensity ultrasound and microbubble-mediated bioeffects. Int. J. Hyperthermia. 2015;31:134–44.
[4] Goertz DE, Karshafian R, Hynynen K. Antivascular effects of pulsed low intensity ultrasound and microbubbles in mouse tumors. IEEE Ultrason. Symp. 2008 IUS 2008. 2008. p. 670–3.
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