The origin of loud claps during endovenous laser treatments

Optoacoustic and ultrasound methods have shown that the loud "claps" perceived by patients and medical staff during endovenous laser ablation (EVLA) are caused by volumetric blood boiling when large vapor-gas bubbles appear and collapse under the action of laser radiation, which is well absorbed in water. Acoustic effects when using lasers in the near infrared range (1.94, 1.47, and 0.97 μm) were studied in an experiment with non-deaerated water, as well as in EVLA. The nature of these acoustic signals was investigated using high-speed video recording. It turned out that the amplitude of the emerging acoustic pulses in the case of surface boiling, which prevails when using lasers with a wavelength of 0.97 μm, is two orders of magnitude smaller than in the case of volumetric boiling (1.94 and 1.47 μm). The reasons for the decrease in sound effects in this case are associated with numerous microbubbles at the tip of the laser fiber. The results obtained may be useful for further understanding of the mechanisms of EVLA.