CHARACTERISTICS OF LEFT-VENTRICULAR ISOVOLUMIC PRESSURE WAVES IN ISOLATED DOG HEARTS

The peak pressure which a chamber would develop in isovolumic contract ion at end-diastolic distention (peak source pressure) is an expressio n of contractile vigor and a determinant of systolic performance. One can predict source pressure of an ejecting beat by fitting its isovolu mic phases with a model isovolumic-wave function. Characteristics of t he left-ventricular isovolumic pressure wave (amplitude, duration, sha pe) were studied in isolated, perfused, artificially loaded dog hearts , where strictly isovolumic conditions could be obtained over a wide r ange of cavity volumes at constant heart rate and approximately consta nt contractile state. The characterization involved two steps: (1) beg inning and ending points were identified by a transition-locating algo rithm, and (2) Fourier analysis was performed on points in between. Th e amplitude of the isovolumic pressure wave increased with cavity volu me as expected, the duration of contraction increased with cavity volu me, and the shape of the wave (normalized Fourier coefficients) depend ed slightly on the cavity volume. Duration of contraction declined sli ghtly with increasing heart rate, but the shape of the isovolumic pres sure wave was independent of heart rate. The mean shape was similar to that found in dog hearts subjected to one-beat aortic-root clamping i n vivo - the wave being less sharply peaked than a cosine wave and til ted to the left because relaxation was slower than contraction. When e jecting beats were produced with a Windkessel model, ejecting-beat dur ation declined linearly with increasing ejection fraction. This relati on could be used to predict the duration of the isovolumic beat corres ponding to the duration of an ejecting beat. Source pressure could the n be predicted by fitting a model isovolumic wave of predicted duratio n to the isovolumic contraction phase of the ejecting beat. In 270 com parisons, the ratio of predicted peak source pressure to observed peak source pressure was 1.04 +/- 0.10 (SD). This method provides a reason ably accurate prediction of an important determinant of systolic perfo rmance.