Mechanism of decreased left ventricular stroke volume during inspiration in man

Radionuclide ventriculography was performed in 15 healthy subjects during quiet breathing and during inspiration against a 24 cm H₂O threshold load with a respiratory gating technique. Inspiratory threshold loading caused an inspiratory decrease in ejection fraction from 64% to 59% (p < .001). Stroke counts proportional to stroke volume decreased by 9.6% (p < .02) due to an increase in end-systolic counts of 15.9% (p < .05). End-diastolic counts decreased in four subjects and increased in three subjects, but the mean counts did not change signicantly. These findings suggest that negative pleural pressure causes an impediment to left ventricular ejection comparable to an increase in arterial pressure. Respiratory gating of radionuclide ventriculography during loaded breathing is suggested as a controlled stress on the ventricle for diagnostic purposes.