The maximal rate of pressure rise in the right ventricle of isolated canine hearts in isovolumic and auxotonic systole under various hemodynamic and inotropic conditions.

The influence of changes in pre- and afterload, heart frequency and inotropic state on the difference between right ventricular dP/dtmax measured isovolumically and auxotonically has been investigated in canine heart-lung preparations. Isovolumic systoles were obtained by occluding the pulmonary artery during diastole by balloon inflation. The mean difference between isovolumic and auxotonic dP/dtmax is 40 mm Hg/sec (15 to 80 mm Hg/sec) - i.e. about 10% of the value measured auxotonically. Neither hemodynamic (pre- and afterload changes) nor inotropic changes influence this difference. Heart rate increase from 140 to 200/min also has no effect. This corresponds with the unchanged time interval between pulmonary valve opening and right ventricular dP/dtmax under all these conditions. Only heart rates below 100/min seem to enhance the difference between isovolumic and auxotonic dP/dtmax. Since the difference is not altered at various inotropic states, the result of this study leads to the conclusion that the relative changes in contractility could be slightly overestimated by using the auxotonic dP/dtmax for inotropic assessment. Practically, this inexactitude is within the error range of the method. Therefore, the use of dP/dtmax measured auxotonically does not introduce a marked disadvantage related to isovolumic dP/dtmax for assessment of relative inotropic changes of the right ventricle in isolated hearts.