The Impact of Preload Alteration on the Myocardial Performance Index through Implementing Positive End Expiratory Pressure

Load independent methods should be used for the assessment of ventricular function. Debate still exists regarding whether tissue Doppler imaging (TDI) indices are influenced by preload. Here, we evaluated the effect of positive end expiratory pressure (PEEP) related preload reduction on both conventional pulsed Doppler (PD) and TDI myocardial performance index (MPI). Thirty-eight mechanically ventilated patients of 3 months to 12 years old (mean ± SD age of 30 ± 11months) without overt heart disease were enrolled. Doppler mitral inflow velocities, isovolumetric contraction and relaxation times and aortic ejection time in addition to TDI peak systolic, early and late diastolic velocities from the basal segment of left ventricular lateral wall were determined for each patient before and after applying high PEEP (10 cmH₂O).PD-MPI was load dependent (0.61 ± 0.22 vs. 0.78 ± 0.25, P = 0.002). However, TDI-MPI did not significantly change after the use of high PEEP declining the left ventricular volume loading (0.78 ± 0.21 vs. 0.84 ± 0.22, P = 0.23). Hence, regarding various interfering pathophysiologic factors particularly preload reduction, it seems that TDI-MPI would be a more reliable index for the assessment of ventricular function.