Myocardial performance index during rapidly changing loading conditions: impact of different tidal ventilation.

BACKGROUND AND OBJECTIVES: The myocardial performance index is a non-geometric, heart rate-independent echocardiography-derived index of left ventricular performance combining systolic and diastolic function. There is an ongoing debate whether the myocardial performance index is affected by preload or not. Moreover, a systematic evaluation of the effect of changing tidal volume ventilation on the myocardial performance index is still lacking. The aim of our study was to assess whether acute changes in preload and/or different depth of tidal volume ventilation affect the myocardial performance index.

METHODS: In all, 14 anesthetized pigs (35 +/- 2 kg) were studied during changing tidal volumes (VT 5, 10 and 15 mL kg(-1)) at baseline, after removal of 500 cm(3) of blood (haemorrhage) and after retransfusion of shed blood plus additional 500 cm(3) 6% hydroxyethyl starch (fluid loading). Echocardiographic measurements at each experimental stage included myocardial performance index, left ventricular end-diastolic area and fractional area change. Central venous pressure, pulmonary capillary wedge pressure, cardiac output and stroke volume index were obtained by a pulmonary artery catheter. Global end-diastolic volume was obtained by transpulmonary thermodilution.

RESULTS: Comparing different loading conditions, we found significant changes in cardiac output, stroke volume index, central venous pressure, pulmonary capillary wedge pressure, global end diastolic volume and left ventricular end-diastolic area, indicating clinically relevant changes in preload. In the haemorrhage group, there was a significant reduction in the myocardial performance index (P < 0.05) independent of tidal volume applied and this was reversed after fluid loading. However, myocardial performance index was significantly impaired (P < 0.05) by high tidal volume ventilation (15 mL kg(-1)), while tidal volumes of 5 and 10 mL kg(-1) had no effect.

CONCLUSIONS: The myocardial performance index is largely dependent on changes in preload. Moreover, high tidal volume ventilation significantly impaired the myocardial performance index.