Technical Modifications of the Dornier HM3: Preliminary Results from a Single Center
The low-pressure generator works with reduced pressures in the second focus. At a generator voltage of 18 kV, a focus pressure of 600 bars is generated, compared to the old standard generator with 900 bars. This decreased focal pressure reduces the pain perception of the patient while maintaining an equally-effective stone disintegration.
The theoretical background for the introduction of a modified semiellipsoid reflector was to modify the shock-wave generation and propagation unit in such a way that most of the painful shock-wave elements would be eliminated. The diameter of the semi-ellipsoid was increased to 17.2 cm (standard HM3, 15.6 cm) and the geometric dimensions changed. These alterations lead to a more accurate focussing with reduction of the focal area which increased the energy in the second focus by 10–20% while using the same generator voltage. Because of the increased diameter, the area of shock-wave entry on the skin was diminished. This results in a considerably reduced pain perception during shock-wave release.
The twin-pulse technique represents a modification of the triggering unit. Synchronized with the R-wave of the ECG, two impulses are released at a constant interval of 70 msec. In order to avoid interference with atrial or ventricular conduction, the first impulse is released 30–40 msec after recognition of the ‘R’ wave.
KeywordsRenal Colic Generator Voltage Ventricular Conduction Focal Pressure Infundibulum Stenosis
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