Beat-to-beat change in "myocardial performance index" related to load.
BACKGROUND
This study was designed to assess the relationship of the "myocardial performance index" (MPI) to the beat-by-beat change in pre-load with static or unchanged contractile status.


METHODS
Eight anesthetized juvenile pigs were studied using direct measurement of the left ventricular pressure and volume. Transient inflation of a vena cava balloon catheter produced controlled pre-load alterations. Consecutive beats were analyzed, grouped for first, second, third, etc. during the pre-load alteration, and evaluated for the change in MPI during the same contractile status with a controlled pre-load alteration. Two pharmacologic inotropic interventions were also included to generate several myocardial conditions in each animal.


RESULTS
MPI demonstrated a strong linear relationship to the pre-load and after-load. MPI increased progressively during decreasing end-diastolic volume, mostly related to changes in ejection time. MPI was observed at the same level for three different myocardial function conditions (all eight animals), with a different relationship between MPI and pre-load noted for each observation.


CONCLUSIONS
MPI is strongly load dependent, and can vary widely in value for the same contractile status if the load is varied. The use of this index in critically ill patients should be limited in this respect. Further work is needed to establish the relationship of MPI to load and contractile status.
Haney
M F
MF
Anesthesia and Intensive Care Medicine, University Hospital of Umeå, S-901 85 Umeå, Sweden. michael.haney@anestesi.umu.se
A'Roch
R
R
Johansson
G
G
Poelaert
J
J
Biber
B
B
D000818:Animals; D001794:Blood Pressure / Q000502:physiology; D004837:Epinephrine / Q000494:pharmacology; D007530:Isoflurane / Q000494:pharmacology; D009200:Myocardial Contraction / Q000187:drug effects* / Q000502:physiology; D009204:Myocardial Revascularization / Q000379:methods; D013318:Stroke Volume; D013552:Swine; D014662:Vasoconstrictor Agents / Q000494:pharmacology
D014662:Vasoconstrictor Agents; D007530:Isoflurane; D004837:Epinephrine