A comparative analysis of the cardiopulmonary effects of intermittent positive pressure breathing (IPPB) and extrathoracic assisted breathing (ETAB) has been performed in closed-chest anesthetized animals subjected to sublethal acute hemorrhage. Equal inspiratory times and rates were maintained at high tidal volumes with a prolonged inspiratory phase. Significant suppression of cardiac output occurred in all trials, with slightly less suppression accompanying ETAB. Respiratory phase analysis of central venous and pulmonary arterial pressures suggests that impedance to transpulmonary blood flow occurred with IPPB primarily during inspiration and with ETAB during expiration, although of lesser degree. The greater interference of IPPB with cardiac output was largely due to its detrimental phase being twice as long as that of ETAB.
Cook TI, Trimble C, Smith DE, Rehman I, Trummer MJ. Intermittent Positive Pressure and Extrathoracic Assisted Breathing in HypovolemiaComparative Hemodynamic Effects. Arch Surg. 1971;102(6):586-588. doi:10.1001/archsurg.1971.01350060050014