[The maximum volume of urinary calculi to be disintegrated by ESWL]

In our investigations to develop microexplosion lithotripsy (MEL), the detonation theory, which was proposed in industrial blasting, was proved to be tenable also in MEL with tiny explosives of a few mg. According to the theory, the peak pressure of shock wave generated by blasting was analyzed relating to the volume of calculi.

472 cases of renal urinary calculi to be disintegrated by ESWL were examined.

For the successful disintegration, the maximum length of calculi, which was employed conventionally, was a good predictor as for those less than 15 mm (disintegrated in 95%) and those more than 25 mm (disintegrated in 8%). However, the maximum length could not predict the successful result in calculi with intermediate maximum length between 15 and 25 mm. For this intermediate range of the maximum length, the volume of calculi was a very good indicator to show whether the integration was possible or not, because the large majority (90%) of calculi less than 6 cm3 was treated successfully, while none of calculi more than 6 cm3 was disintegrated. According to the theory, the peak pressure of shock wave generated by blasting, which was required to disintegrate a calculated of 6 cm3, was calculated as 80 MPa.

Since it is believed that the peak pressure generated by usual ESWL machines is between 80 and 120 MPa at the focussing point, the conclusion in this report that the maximum volume of calculi disintegrated by ESWL might be 6 cm3 was thought to be fairly reasonable.