ObjectivesTo examine the mechanism of cardiac assist with systolic jet ventilation, specifically effects on loading conditions and left ventricular pressure-volume function. Both systolic and diastolic jet ventilation were compared in the absence and presence of heart failure.DesignProspective, two-factor, repeated-measures study.SettingAnimal laboratory.SubjectsTen anesthetized, closed-chest dogs.InterventionsThe measurement protocol consisted of two phases: a) apnea, randomized jet ventilation (systole- and diastole-synchronized); b) postjet ventilation apnea, before and after heart failure, induced with a propranolol-imipramine-plasma expansion treatment.Measurements and Main ResultsSystolic or diastolic jet ventilation was associated with mean airway pressures of approximate 7 mm Hg and intrapleural pressures of approximate 3 mm Hg in both heart conditions. In normal hearts, jet ventilation (either mode) decreased transmural left ventricular end-diastolic pressure by 40% to 60% (p less than .05), left ventricular end-diastolic volume 25 plus minus 8%, and stroke volume by 28% to 30%. Heart failure was associated with decreases (41 plus minus 6%) in end-systolic pressure-volume function (i.e., pressure change/volume change or elastance), transmural left ventricular end-systolic pressure (22 plus minus 3%), and stroke volume (16 plus minus 4%), and increased transmural left ventricular end-diastolic pressure (139 plus minus 6%). Application of jet ventilation (either mode) during heart failure did not affect stroke volume but significantly (p less than .05) attenuated transmural left ventricular end-diastolic pressure by 30% to 40%, left ventricular end-diastolic volumes by 33 plus minus 9%, and transmural left ventricular end-systolic pressure by 11% to 19% (p less than .05). After jet ventilation, left ventricular elastance was decreased 36 plus minus 8% in normal hearts and 35 plus minus 11% in failing hearts. Stroke volume, however, returned to baseline levels because of increases in transmural left ventricular end-diastolic pressure in both heart conditions, and also in failing hearts, because transmural left ventricular end-systolic pressure remained decreased approximate 30% (p less than .05).ConclusionsJet ventilation did not decrease stroke volume in failing hearts because of the afterload-reducing benefit (decreased transmural left ventricular end-systolic pressure) of increased intrapleural pressure in dilated ventricles. Moreover, jet ventilation did not have positive effects on myocardial function and had negative effects on left ventricular elastance in the postjet ventilation period in both normal and failing hearts. Cardiac assist by jet ventilation was not cycle specific, suggesting no selective benefit of jet ventilation over conventional positive-pressure ventilation during heart failure. These studies demonstrate a negative inotropy associated with jet ventilation that, during heart failure, may compromise the general benefit of positive-pressure-mediated increases in intrapleural pressure.(Crit Care Med 1996; 24:647-657)