Zhou Y et al, 2012: Characteristics of the secondary bubble cluster produced by an electrohydraulic shock wave lithotripter
Zhou Y, Qin J, Zhong P
School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore
This study investigated the characteristics of the secondary bubble cluster produced by an electrohydraulic lithotripter using high-speed imaging and passive cavitation detection techniques. The results showed that (i) the discrepancy of the collapse time between near a flat rigid boundary and in a free field of the secondary bubble cluster was not as significant as that by the primary one; (ii) the secondary bubble clusters were small but in a high bubble density and nonuniform in distribution, and they did not expand and aggregate significantly near a rigid boundary; and (iii) the corresponding bubble collapse was weaker with few microjet formation and bubble rebound. By applying a strong suction flow near the electrode tip, the production of the secondary shock wave (SW) and induced bubble cluster could be disturbed significantly, but without influence on the primary ones. Consequently, stone fragmentation efficiency was reduced from 41.2 ± 7.1% to 32.2 ± 3.5% after 250 shocks (p < 0.05). Altogether, these observations suggest that the secondary bubble cluster produced by an electrohydraulic lithotripter may contribute to its ability for effective stone fragmentation.
Copyright Â© 2012 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.
Ultrasound Med Biol. 2012 Apr;38(4):601-10. doi: 10.1016/j.ultrasmedbio.2011.12.022
PMID: 22390990 [PubMed - in process]. FREE ARTICLE
From a physical point of view the paper of Zhou, Qin and Zhong is very interesting since it investigates for the first time a unique detail of electrohydraulically (EH) generated shock waves, the characteristics of secondary bubble clusters (SBC) produced by the Dornier HM3 lithotripter. The in vitro generation of a SBC is a unique feature of an EH shock wave lithotripter and is checked for its potential effect on stone fragmentation. According to Zhou et al. SBC are claimed to enhance stone fragmentation in vitro and cause "the performance difference between electrohydraulic and electromagnetic, piezoelectric lithotripters", (meaning "superior performance of the HM3 vs. all other lithotripsy devices")
We cannot follow this conclusion since at least one electromagnetic (EM) device has proven at least equally effective or even slightly superior.
Up to our best knowledge, there is only one single studyi comparing the in vitro fragmentation efficiency of different shock wave lithotripters (including HM3) with respect to different types of urinary calculi. This study does not support the above conclusion. Performance studies in vivo provide an ambivalent picture and show better and less good results for all investigated devices (including HM3) mostly dependent on the treatment strategies, skills and care of the operator. Coupling e.g. is a critical point requiring special care in most of to dates "dry" machines compared to the open bathtub of the HM3. These and other handling differences are of major importance for successful stone fragmentationii iii and are deemed to outweigh minor differences of shock wave fields as investigated by Zhou et al..
No question, the nice laboratory experiments shin some additional light on previously neglected details of EH generated shock wave fields.
The impact thereof on in vitro and in vivo lithotripsy, however, is questionable (see above), and mostly academic since the HM3 is out of production for more than a decade.
i Teichman J, Portis A, Cecconi P, Bub W, Endicott R, Denes B, Pearl M, Clayman R: In vitro comparison of shock wave lithotripsy machines, The Journal of Urology Vol. 164, 1259-1264, October 2000
ii Tiselius HG, Chaussy CG: Aspects on how extracorporeal shockwave lithotripsy should be carried out in order to be maximally effective. Urol Res. 2012 Jun 27. [Epub ahead of print]
iii Bohris C, Roosen A, Dickmann M, Hocaoglu Y, Sandner S, Bader M, Stief CG, Walther S.Monitoring the coupling of the lithotripter therapy head with skin during routine shock wave lithotripsy with a surveillance camera. J Urol. 2012 Jan;187(1):157-63. Epub 2011 Nov 17.