Giordano Venzi

Laser lithotripsy with the Ho :YAG laser : fragmentation process revealed by time-resolved imaging

Improvements of endoscopic techniques have renewed the interest of urologists in laser lithotripsy in recent years. Laser energy can be easily transmitted through flexible fibers thereby enabling different surgical procedures such as cutting, coagulating and lithotripsy. The Ho:YAG laser offers multiple medical applications in Urology, among them stone fragmentation. However, the present knowledge of its fragmentation mechanism is incomplete. The objective was therefore to analyze the fragmentation process and to discuss the clinical implications related to the underlying fragmentation mechanism. The stone fragmentation process during Ho:YAG laser lithotripsy was observed by time resolved flash video imaging. Possible acoustic transient occurrence was simultaneously monitored with a PVDF-needle hydrophone. Fragmentation was performed on artificial and cystine kidney stones in water. We observed that though the fragmentation process is accompanied with the formation of a cavitation bubble, cavitation has only a minimal effect on stone fragmentation. Fragment ejection is mainly due to direct laser stone heating leading to vaporization of organic stone constituents and interstitial water. The minimal effect of the cavitation bubble is confirmed by acoustic transients measurements, which reveal weak pressure transients. Stone fragmentation with the Holmium laser is the result of vaporization of interstitial (stone) water and organic stone constituents. It is not due to the acoustic effects of a cavitation bubble or plasma formation. The fragmentation process is strongly related with heat production thereby harboring the risk of undesired thermal damage. Therefore, a solid comprehension of the fragmentation process is needed when using the different clinically available laser types of lithotripsy.

Bulbomembranous anastomotic urethroplasty for strictures of the proximal bulbar urethra unassociated with pelvic trauma

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Urethral stricture vaporization with the KTP laser provides evidence for a favorable impact of laser surgery on wound healing

The objective of this study was to evaluate and compare the safety and efficacy of the KTP 532 laser to direct vision internal urethrotomy (DVIU) in the management of urethral strictures. A total of 32 patients were randomized prospectively in this study, 14 DVIU and 18 KTP 532 laser. Patients were evaluated postoperatively with flowmetry and in the case of recurrence with cystourethrography at 3, 12, 24 weeks. With the KTP 532 laser complete symptomatic and uredynamic success was achieved in 15 (83%) patients at 12 and 24 weeks. Success rate was lower in the DVIU group with 9 (64%) patients at 12 weeks and 8 (57%) patients at 24 weeks. Mean preoperative peak-flow was improved from 6 cc/s to 20 cc/s at 3, 12 and 24 weeks with the KTP laser. With DVIU mean preoperative peak-flow was improved from 5.5 cc/s to 20 cc/s at 3 weeks followed by a steady decrease to 13 cc/s at 12 weeks and to 12 cc/s 24 weeks. No complication was observed in either group of patients. Our results confirm that stricture vaporization with the KTP 532 laser is a safe and efficient procedure. The better results after laser surgery make it also a valuable alternative in the endoscopic treatment of urethral strictures. These findings suggest a favorable influence of laser surgery on wound healing with less wound contraction and scarring. The lack of contraction of laser wounds might be related to the absence and the lack of organization of myofibroblasts in laser induced lesions.

Wound repair in rat urinary bladder following electrocautery or holmium laser incision

Woundhealing is a complex phenomenon which varies according the type of tissue but is also depending from the type of tissue injury. Electrocautery mainly induces coagulation necrosis while thermal damages induced by the Holmium laser primarily lead to tissue vaporization which may induce less tissue injury. The aim of this study was to evaluate the healing process of the Holmium laser induced lesions compared to electrocautery induced lesions in urothelial tissue by assessing the inflammatory response and myofibroblast behavior in sequential healing phases. A surgical wound was created in the urinary rat bladder of 32 rats either by electrocautery or by laser (N=16). The inflammatory response, the total lesion depth and the myofibroblast activity during woundhealing was then analyzed on a qualitative basis on days 0/2/4/8. The overall inflammatory response was comparable in both groups up to days two and four. However, at day eight less cellular inflammatory reaction and less myofibroblast activity was found in the specimen of lesions created by the Holmium laser. These results suggest that wound repair may be a less invasive process after Holmium laser than electrocautery.