Computer-aided characterization and optimization of the Thumper compression waveform in closed-chest CPR

Optimization of blood flow and blood pressure is critical for a positive outcome of cardiopulmonary resuscitation (CPR). The use of models can facilitate the analysis of different methods of performing CPR. Programming with SPICE software, the authors modified a hardware model electrically equivalent to the human cardiovascular system into a software model to analyze and predict the hemodynamic output parameters of different compression waveform inputs used in thoracic pump CPR. Thumper waveforms produced with the computer model predicted the same decaying frequency response as those found in other studies with humans and a recording manikin in which the generated pressures decreased with increased compression rates from 60 to 140 cycles/min. Using a square-wave input having a flat frequency response, the model predicted a constant diastolic pressure and a steady increase in systolic pressure from 94 to 109 mmHg while increasing compression rate from 60 to 140 cycles/min at a constant 50% duty cycle. Blood flows predicted with the use of a square-wave compression input were greater than the flows predicted with the use of a Thumper waveform, and increased with an increase in compression rate. The model also predicted increased mean systolic pressure when the duty cycle increased from 20% to 80% while diastolic pressure decreased slightly. Although mean systolic pressure increased with increased duty cycle, the model predicted a decrease in coronary flow at the higher duty cycles of all compression waveforms. Increases of 75% to 100% in systolic pressure and blood flow were produced when increases in chest compression force and the rapidity of the rise time, termed "spike-impulse" CPR, were simulated.