STUDIES ON THE FRAGMENTATION PERFORMANCE

OF DIFFERENTLY APPLIED SHOCK WAVES ON

ARTIFICIAL STONES AND NATURAL GALLSTONES

From the Faculty of Medicine

of Christian-Albrechts University of Kiel

Inaugural dissertation

for

the degree of Doctor

of the Faculty of Medicine

of Christian-Albrechts University of Kiel

Submitted by

Oliver Theodor Zöphel

from Ahaus

Kiel 1996

SUMMARY

The purpose of this study was to improve the still unsatisfactory results of clinical gallstone lithotripsy.

The main focus of the investigations was on comparing the fragmentation performance of shock waves on artificial and natural gallstones using different patterns of application. Another part of this study was devoted to comparing a piezoelectric and an electromagnetic shock wave source and to analysing the exact mechanisms of stone fragmentation.

The following experimental procedure was chosen for this purpose: placed in a meshwork model, the stones were exposed to the shock waves until all the fragments had fallen through the meshes onto the base. The fragment debris was then analysed according to size and weight.

The results presented provide important data for clinical practice:

It was demonstrated with artificial stones and gallstones that the quality of fragmentation, i.e. the finest possible comminution of the stones, is markedly improved if the stones are treated with high energy levels from the beginning of the comminution process (application pattern A). The application pattern of stepwise increasing the shock wave pressures employed in clinical practice proved less effective (application pattern B).

With application pattern A at the highest energy level (9), for example, the artificial stones were broken down into fragments with a diameter < 1.0 mm and dust to an extent of 83.6 % ± 1.0 of their weight. Using energy levels 1 – 9 (application pattern B), only 74.4 % ± 1.1 was achieved. A comparison of energy levels 5 and 7 with energy levels 1 – 5 and 1 – 7 also revealed distinct differences between application patterns A and B. With application pattern A and energy level 9, the gallstones were broken down into fragments with a size of < 1.0 mm and dust to an extent of 80.3 % ± 3.2. With energy levels 1 – 9, the corresponding value was only 72.3 ± 5.3. As with the artificial stones, better results were also achieved in this case with energy levels 5 and 7 than with levels 1 – 5 and 1 – 7.

On the other hand, clear-cut differences in the disintegration mechanism of artificial and natural stones were revealed by fragment analyses and scanning electron micrograph enlargements.

Finally, it was demonstrated that the electromagnetic principle provides a higher fragmentation quality than the piezoelectric principle:

With the electromagnetic generator, for example, the artificial stones were already fragmented almost completely to an extent of 78.2 % ± 1.8 using a focal pressure of about 360 bar. In contrast, the piezoelectric generator was only able to reduce the stones to fragments < 1.0 mm to an extent of 54.5 % ± 1.7 of their weight using a focal pressure of about 400 bar. However, this value improved to 81.8 ± 0.3 on using the maximum pressure of about 1,600 bar.

The electromagnetic device however already achieved a fragmentation quality of 83.6 % ± 1.0 using a maximum pressure of about 620 bar.

The results demonstrate beyond doubt that maximal shock wave pressures should be used during the treatment of patients with gallstones and kidney stones. The development of lithotriptors in which the pressures are optimally matched to the shock wave propagation could contribute especially to patients suffering from gallstones benefiting from this gentle therapeutic modality with its low rate of side effects.