the time from emergency call to arrival of the vehicle or ambulance crew at the patient's side as an indicator of duration of collapse before intervention by ambulance crew might underestimate collapse intervals this study did not calculate collapse time collapse duration before application of interventions conventional therapies for cardiac arrest seem to have minimum effect after long collapse intervals long intervals in the intervention group might conceal the effect of these interventions assessment of the effect after mechanical CPR might throw light an the relative usefulness of this mode of resuscitation