Out-of-focus shockwaves: a new tissue-protecting therapy?

It seems that vasoconstriction induced by 12 Kv shock waves reduces kidney lesions caused by subsequent application of 24 Kv shock waves. The lowest shock wave voltage to induce this protective effect is not known yet and may be lower than the common energy setting of commercial lithotripters. Because of this we propose the application of shock waves as a tissue protecting method.

Preliminary pressure measurements were performed on an experimental unmodified HM3 lithotripter (at 12 and 24 Kv), using a 20 ns rise time needle hydrophone connected to a 100 MHz digital oscilloscope. Ten pressure records were obtained at different aging of the spark plug. A new spark plug was used for each voltage. Pressure measurement were also performed on a Tripter compact lithotripter at 6 positions along the focal axis, starting at F2 and moving away from the reflector, using maximum voltage and capacitance (22 Kv, HI-2). The position on the focal axis of the Tripter Compact with the same pressure as measured at 12 Kv on the HM3 at F2 was chosen as the prophylactic treatment spot (PTS). In vivo pressure measurement were done on the Tripter Compact placing the needle hydrophone inside the lower pole of the right kidney of an anesthetized healthy 25 kg female pig. Measurements were done at the same positions mentioned above, without moving the hydrophone, inside the pig. For both in vitro and in vivo measurements, the radiopaque hydrophone was aligned with the focal axis, using the fluoroscopy system of the lithotripter.

The mean positive pressure peak at the second focus of the HM3 lithotripter was 64 and 153 mV at 12 Kv, respectively. Coefficients of variations were 0.28 and 0.13. No significant pressure differences were detected below 700 and 2220 discharges with the HM3 and the Tripter compact, respectively. The difference peak amplitudes are all significant (p<0.01 in a one tailed test) with the exception of F2 and F2+1 Ohm.

Prophylactic administrations of out-of-focus shock waves may reduce tissue damage during SWL. Experiments in vivo are underway in order to prove this hypothesis.