Effects of spontaneous respiration on right and left ventricular function: evaluation by respiratory and ECG gated radionuclide ventriculography.

To clarify the mechanism of inspiratory reduction of left ventricular (LV) stroke volume (SV) during spontaneous respiration, we measured right and left ventricular volume changes from expiration to inspiration using radionuclide ventriculography with respiratory gating technique. In this method, scintigraphic data were acquired in a list mode with ECG R wave triggers and respiratory volume curve derived from respiratory flowmeter. Cardiac cycles occurring during the second halves of inspiratory and expiratory phases were separately selected and used to produce multigated images for the respective phases. Twelve patients with normal LV ejection fraction (EF) (greater than 50%) and right ventricular (RV) EF (greater than 40%) and without pulmonary diseases were studied. LV end-diastolic volume (EDV) decreased during inspiration in all subjects (by 11 +/- 5%), whereas LV end-systolic volume (ESV) was insignificantly changed. Accordingly, LVSV decreased during inspiration in all subjects (by 17 +/- 7%). LVEF decreased from 64 +/- 6% during expiration to 60 +/- 6% during inspiration (p less than 0.001). In contrast to the left ventricle, RVEDV and RVSV increased during inspiration by 13 +/- 11% and 22 +/- 18%, respectively. RVESV did not change significantly. RVEF increased from 48 +/- 6% during expiration to 52 +/- 5% during inspiration (p less than 0.05). These results indicate that inspiratory reduction of LVSV during spontaneous respiration is due to a decrease in LVEDV which may be derived from an increase in RVEDV during inspiration through the mechanism of ventricular interdependence.