Cardiac reserve measurements derived from ejection fractions can be used for patient-specific clinical monitoring

Abstract

Introduction: American Heart Association guide-lines using volume ejection fractions derived from ventricular volumes can be improved by cardiac reserve determination. Cardiac reserve is determined from serial readily available pressure ejection fractions. Methods: Pressure ejection, EF(P) is defined as EF(P) = SBP - DBP) / SBP, where SBP and DBP are systolic and diastolic blood pressures, respectively. Inefficient systems fail below minimal EF(P)min. They also fail above maximal EF(P)max, where the system has no longer sufficient reserves and is incapable of compensating for an increased demand. However, the system could still satisfy the lesser demand and survive. Cardiac reserve, EF(P)res, defined as EF(P)res = EF(P)max - EF, quantitatively measures the reserves available to satisfy demand and ultimately sustain life. Increases in cardiac reserve, with time or intervention suggest improvement, I, while decreases in cardiac reserve suggest deterioration, D. Changes in EF(P)res, caused by Enalapril injection in 67 randomly selected ICU patients were determined by chart evaluation at times immediately prior to and 30 min after injection for the entire group and for the three subgroups with low reserves, high reserves, and a transitional range. Results were compared with the American Heart Association guidelines on Enalapril treatment. Results: For the entire group and for the transitional subgroup Enalapril had no significant effect on EF(P)res. Enalapril injection resulted in an increase in EF(P)res in all patients in the subgroup with low reserves and in a decrease in all patients with large reserves. Results are consistent with American Heart Association guidelines for Enalapril use in patients with low ejection fractions. Discussion: Ejection fraction contains useful but not readily apparent diagnostic information. Referencing ejection fractions to the endpoint of maximal efficiency permits patientspecific serial determination of improvement or deterioration, suggesting cardiac reserve measurements as an ideal patient management tool useful in establishing guidelines for clinical decision making. © 2009 Springer-Verlag.