Background and Objective: All internal defibrillators and some external def
ibrillators use biphasic waveforms. The study analysed the discharged wavef
orm pulses of two manual and two semi-automated biphasic external defibrill
ators. Methods and Results: The defibrillators were discharged into resisti
ve loads of 25, 50 and 100 Ohm simulating the patient's transthoracic imped
ance. The tested biphasic defibrillators differed in initial current as wel
l as initial voltage, varying from 10.9 to 73.3 A and from 482.8 to 2140.0
V, respectively. The energies of the manual defibrillators set at 100, 150
and 200 J deviated by up to + 19.1 or - 28.9% from the selected energy. Imp
edance-normalised delivered energy varied from 1.0 to 12.5 J/Ohm. Delivered
energy, shock duration and charge flow were examined with respect to the t
otal pulse, its splitting into positive and negative phases and their imped
ance dependence. For three defibrillators pulse duration increased with the
resistive load, whereas one defibrillator always required 9.9 ms. All test
ed defibrillators showed a higher charge flow in the positive phase. Defibr
illator capacitance varied between approximately 200 and 100 muF and intern
al resistance varied from 2.0 to 7.6 Ohm. Defibrillator waveform tilt range
d from - 13.1 to 61.4%. Conclusions: The tested defibrillators showed remar
kable differences in their waveform. design and their varying dependence on
transthoracic impedance. (C) 2001 Elsevier Science Ireland Ltd. All rights
reserved.