Evaluation of the operating internal resistance, inductance, and capacitance of intact damped sine wave defibrillators.

A method is developed for determing actual values of circuit elements in a damped sine wave (Lown waveform) defibrillator solely from measurements of the output, using two or more power resistors and a storage oscilloscope. If a defibrillator containing capacitance C, inductance L, and internal resistance RI, is discharged into increasing 5- to 100-ohm resistive loads R, it is shown for underdamped output waveforms that â = RI/2L + R/2L and ĉ = CRI + CR, where â = pi[t2tan(pit1/t2)], ĉ = 2â/[â2 + (pi/t2)2], t1 = time from onset to peak, and t2 = time from onset to first zero crossing of the output waveform on the oscilloscope trace. Linear plots of â vs R are constructed for seven defibrillators, and values of RI and L computed as intercept/slope and 1/(2 slope) respectively. C is given by the slope of a linear plot of ĉ vs R. Delivered energy is accurately predicted as stored energy X R/(RI + R).