Choi MJ, Lee JY, Park EJ.
Ultrason Sonochem. 2022 Feb;83:105927. doi: 10.1016/j.ultsonch.2022.105927 FREE ARTICLE
Abstract
The shock wave used in extracorporeal shock wave lithotripsy (ESWL) induces strong cavitation and generates a large amount of free radicals (FR). In order to evaluate the harmfulness of FR in the ESWL, information on the incidence and persist time of FR caused by shock waves is required. FR markers can estimate the amount of FR generated, but not how long the FRs will survive. The OH* FR generated by the ESWL shock wave reacts with luminol and emits blue light, which is called sonochemical luminescence (SCL) phenomenon. In this study, FR generation and persist time were measured by recording SCL phenomenon with a sensitive photomultiplier tube (PMT) that responds in nanoseconds. As a result of measurement with the PMT, when the electromagnetic shock wave used in clinical practice was irradiated to the luminol solution, the amount of light emitted per unit time reached its maximum value within a very short time (< ∼600us) and then exponentially decreased for a long time (∼several hundred ms). The measured FR persist time reaches a maximum of 1000 ms. As the output setting of the shock wave generator increases, the minimum or average FR persist time increases, but the maximum value does not show a high correlation with the output setting. The amount of generated FR shows a very high correlation with the shock wave setting, and when the setting is changed from low to high, it increases very sensitively, rapidly and non-linearly. In order to reduce the risk of FR in patient treatment using lithotripsy, the output setting of the shock wave should be minimized, and the interval between the shock wave pulses should be sufficiently larger than the FR persist time. Therefore, it is recommended to avoid increasing the output setting and setting the shock wave irradiation frequency below 1 Hz to shorten the treatment time in clinical practice. For the purpose of formulating these recommendations, additional studies on the generation and persist time of FR depending on the shock wave generation method and set conditions in living tissue or similar environment are required in the future.
Comment Hans-Göran Tiselius
The flavour of SWL is that the method is non-invasive and associated with few negative side effects. Accumulated experience has shown that a low frequency of shockwave generation apparently leads both to improved stone disintegration and reduced occurrence of tissue injuries. The latter factor is of particular interest when treating patients with stones in the kidney. There is, however, no global consensus in this regard and high frequency administration of shockwaves commonly is used to keep the treatment time short.
In this perspective it is of interest to learn from this experimental study how shockwaves affect formation of free radicals and for how long period free radicals remain after one or multiple shockwaves.
It is necessary to understand that free radicals are generated by collapse of cavitation bubbles.
In this experimental study the authors used a Korean lithotripter with properties like that of Storz Modulith. The occurrence and disappearance of free radicals was measured in vitro in a solution of luminol by a sonochemical luminescence reaction. The interested reader should carefully read this manuscript, but the essential information is as follows:
1. The peak shockwave pressure occurred 169 s after shockwave induction and was associated with formation of a large number of cavitation bubbles.
2. The shockwave power was varied between settings 1 and 9, where the highest power corresponded to 20 kV.
3. The collapse of generated cavitation bubbles resulted in formation of free radicals (OH* free radicals) measured with the method briefly described.
4. Although most cavitation bubbles collapsed early, others resulted in large bubbles remaining in the solution for up to 600 s.
5. It was noted that free radicals might persist in the solution for up to 1000 ms (1 sec). The recorded interval was 75-1000 ms.
It is of note that the formation and survival of free radicals may be different in biological tissues. That question needs to be further explored but based on the experimental data in this report it seems relevant to treat patients with stones in the kidney with shockwave frequencies not exceeding 60 per minute (1Hz).
Hans-Göran Tiselius